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Purpose: The increase in frequency of freeze–thaw episodes with the diminution of snow cover protection due to climate change compromises the winter survival of alfalfa (Medicago sativa L.). Symbiosis with cold-tolerant rhizobial strains can improve the ability of alfalfa to survive and grow under stressful conditions. Methods: Six strains of Sinorhizobium (Ensifer) meliloti were tested in combination with two alfalfa populations bred to differ in their levels of freezing tolerance. Plants of each different combination were grown for eight weeks in a growth chamber before being exposed to temperatures promoting their acclimation to cold. Plants were then exposed to a freezing stress (-11ºC) and regrown for three weeks. Shoot, root and nodule biomass were measured before cold acclimation and three weeks after the freezing stress. Results: After freezing stress, the alfalfa population A-TF7 had shoot and root biomasses that were respectively 19% and 15% larger than cultivar A-TF0. Alfalfa plants inoculated with strain NRG34 showed both a larger shoot biomass and a higher nodule dry weight than plants inoculated with any other strains. Assessment of freezing damages on nodules showed that plants inoculated with NRG34 had the largest proportion of undamaged nodules or of nodules with a regeneration zone. Conclusion: This study shows for the first time a relationship between nodule and shoot regrowth after a freezing stress, the latter being linked with the proportion of nodules showing less freezing damage. Our results demonstrated that both the choice of alfalfa populations and S. meliloti strains adapted to stress are complementary to increasing alfalfa persistence. [ABSTRACT FROM AUTHOR]

Background and Aims: The intercropping has great advantages in production gain, resources use and soil quality improvement. However, the effects of perennial forage legumes intercropped with annual grain crop on soil alkali-salinity was not well revealed. This study aimed to propose a spring wheat (Triticum aestivum L.)/alfalfa (Medicago sativa L.) intercropping and reveal whether this cropping system could ameliorate soil salinity. Methods: A two-year field experiment was conducted under 3 cropping systems at 3 irrigation amounts in the inland arid area of northwestern China. The cropping systems were sole spring wheat cropping (W), 12 rows spring wheat/4 rows alfalfa intercropping (W12A4) and 8 rows spring wheat/4 rows alfalfa intercropping (W8A4), and irrigation amounts included 450 (full irrigation amount, If), 360 (moderate irrigation amount, Im) and 180 mm (low irrigation amount, Il). Results: The intercropping system, especially W8A4, could more decrease soil salinity, pH and topsoil bulk density, and increase soil water content, topsoil porosity, and Ca2+ and Mg2+ contents, compared to W. Soil electrical conductivity was positively correlated with topsoil bulk density and negatively correlated with topsoil porosity, which were enhanced by intercropping and irrigation. There was weak correlation between soil electrical conductivity and soil water content. W12A4 and W8A4 led to reduction in contents of Na+, K+, Cl−, and SO42−, while Ca2+ and Mg2+ accumulated in the soil. Conclusion: Intercropped alfalfa and spring wheat could reduce soil salinity, improve soil structure and ions balance. It was recommended that W8A4 with 360 mm irrigation could be extensively used in the arid area of northwestern China, gaining grain and forage production, and helping reduce salt accumulation. [ABSTRACT FROM AUTHOR]

Chickpea (Cicer arietinum) is known to secrete organic anions. We investigated its effectiveness in obtaining P over a range of pH values. Methods: We grew two cultivars of chickpea, supplied with either ammonium or nitrate nitrogen, at 10 levels of applied P, and at four initial pH values. We measured plant weight, P concentration in the tops, and rhizosphere pH. We compared the results with those previously obtained for lucerne (Medicago sativa), mustard (Brassica campestris) and rice (Oryza sativa). Results: Above an initial pHCaCl2, of about 5, rhizosphere pH decreased; below this value it increased. The changes in pH were proportional to the amounts of P applied. They were greatest at high levels of applied P. Best growth occurred when the initial pHCaCl2 was 5.9 and when the rhizosphere pHCaCl2 was close to 5. Plots of growth against plant shoot P concentration showed little effect of low pH suggesting that aluminium toxicity was only of minor importance. Nevertheless, plant weight was severely depressed by low pH. Conclusions: The mechanism of P uptake for chickpea seems to differ from that for lucerne, mustard and rice. The way that the charge on the phosphate ions is balanced seems to depend on the soil pH. Further, uptake is much more markedly depressed by at low pH. [ABSTRACT FROM AUTHOR]

Background and aims: The abandonment of alfalfa fields is increasing in a semi-arid region. To determine the change of soil physicochemical properties and plant diversity in abandoned alfalfa fields for a long-term is essential for vegetation restoration. This study surveyed alfalfa fields of different planting ages in 2003 (1–30 years), 2014 (12–41 years), and 2022 (20–49 years) to explore the change in various indicators using a space-for-time method. Results: The results suggested that abandoned alfalfa fields converted into natural grasslands after 15 years, where the abundances of Gramineae and Asteraceae (59.1–84.0%) increased, whereas those of legumes decreased (16.5–9.4%). As the plant composition changed, the soil water content (SWC) decreased by 19.0% 1–15 years after abandonment, but increased by 54.5% 15–49 years after abandonment. The plant diversity (Margalef, Pielou, Simpson, and Shannon–Wiener indices), and soil organic carbon (SOC), and total nitrogen (TN) contents increased by 0.5% to 51.5% with the number of years alfalfa planting. Furthermore, the plant composition significantly affected the SWC through the soil physicochemical characteristics and plant diversity. Conclusions: This study demonstrated that the longest time of alfalfa planting was 15 years. Furthermore, the plant composition changed from alfalfa to local grasses due to the natural succession of abandoned alfalfa fields, with increases in SWC, SOC, TN, and plant diversity in the semi-arid region. [ABSTRACT FROM AUTHOR]

Background: Salt stress seriously impacts the plantation and productivity of global alfalfa (Medicago sativa). Previously, we genetically defined the M. sativa DROUGHT-INDUCED UNKNOWN PROTEIN 1 (MsDIUP1) as a drought tolerance gene of alfalfa. However, whether it is associated with salt tolerance needs to be explored. Results: In this study, we re-classified MsDIUP1 as a putative novel late embryogenesis abundant protein, and found its promoter activity was strongly induced by salt and ABA treatment. Heterologous overexpression of MsDIUP1 in Arabidopsis led to enhanced salt tolerance and ABA insensitivity, with a higher fresh weight, lateral root number, primary root length, and survival rate compared to the wild-type (WT) plants. Similarly, homologous overexpression of MsDIUP1 also enhanced the salt tolerance of alfalfa over-expression (OE) plants, accompanied by reduced oxidative damage, higher K+/Na+ ratio, increased osmoprotectant accumulation, and improved photosynthetic capacity relative to the WT plants. In reverse, disruption of MsDIUP1 expression caused a salt-hypersensitive phenotype of alfalfa RNA interference (RNAi) plants, with higher oxidative damage, less osmoprotectant accumulation, and lower photosynthetic pigment content than that of the WT. These physiological discoveries were in accordance with differential transcript profiles of the relevant genes associated with stress signaling, antioxidant defense, and osmotic adjustment in the salt-treated alfalfa WT, OE, and RNAi lines. Furthermore, we found that alfalfa OE plants showed no apparent alteration in their forage quality compared with the WT plants. Conclusions: Overall, these results reveal that MsDIUP1 improves plant salt tolerance via regulating stress signaling, antioxidant defense, ion homeostasis, osmotic adjustment, and photosynthesis. [ABSTRACT FROM AUTHOR]

Background and Aims: Wet processed alfalfa-based products can provide high-quality concentrated protein, also contain nutrients and phytochemicals. Agronomic fortification can increase selenium (Se) incorporation into green biomass. For this reason, the aim was to investigate how different forms of Se are incorporated into the green biomass of multiple-harvest alfalfa and how they affect the chemical quality of the processed product candidates. Methods: In this research, alfalfa was enriched with three forms of selenium at different concentrations [selenate (Se(VI)); selenite (Se(IV)); and red elemental Se (Se0)]. The fortified green biomass was fractionated into leaf protein concentrate (LPC), fiber and phytoserum, and changes in selenium content and speciation, protein and phytochemical composition were determined. Results: Total Se content in alfalfa fractions drastically reduced within the four consecutive harvests, particularly for Se(VI) and Se(IV) forms, and significantly varied according to the Se treatments. Selenomethionine (SeMet) was the predominant organic Se species in LPC (35.7–246.0 µg g −1 DW) and fiber (9.0- 47.7 µg g −1 DW) fractions. Se-fortification induced considerable changes in the crude protein of LPC, which varied between 29—45 (m/m)%. Phytochemical composition markedly varied among Se-treatments. Besides several flavonoids, aglycones and glycosyl derivatives, apigenin glucuronide, and apigenin were the most abundant with a concentration up to 170.85 µg g −1 DW. Medicagenic acid concentration was below 1.86 µg g −1 DW in LPC. Conclusions: Se-enhanced alfalfa green biomass could provide functional products, such as LPC, for human and animal consumption with enhanced nutritional value, including Se, protein, and phytochemical contents. [ABSTRACT FROM AUTHOR]

Purpose: Alfalfa is one of the most valuable forage crops in temperate climate zones. Ensifer meliloti, the endosymbiont of alfalfa, contains all the denitrification genes but the capacity of alfalfa root nodules to produce nitrous oxide (N2O) is not known. In this work, N2O emissions as well as the influence of bacteroidal denitrification on nodulation competitiveness and N2O release from alfalfa nodules has been investigated. Methods: Medicago sativa cv. Victoria plants were inoculated with E. meliloti 1021, a periplasmic nitrate reductase (Nap) defective mutant, a Nap overexpressing strain and a nitrous oxide reductase defective mutant. Plants were grown in the presence of different nitrate and copper treatments and subjected to flooding during one week before harvesting. N2O production by the nodules was analysed by using gas chromatography. Methyl viologen-dependent nitrate reductase (MV+-NR), nitrite reductase (MV+-NIR) and nitrous oxide reductase (N2OR) enzymatic activities were measured in isolated bacteroids. Results: Alfalfa root nodules produce N2O in response to nitrate and flooding. Overexpression of Nap improved nodulation competitiveness and induced N2O emissions from nodules. Copper is required for an effective symbiosis as well as triggered a reduction of N2O production due to the induction of the N2OR and a reduction of NIR activities in the bacteroids. Conclusion: Alfalfa root nodules emit N2O. Nap is involved in nodulation competitiveness and in N2O emissions by the nodules. Bacteroidal N2OR and NIR activities are modulated by Cu and may be considered as effective targets for the mitigation strategies of N2O emissions derived from alfalfa crops. [ABSTRACT FROM AUTHOR]

Khattab et al. ([10]) revealed that Si and Se increased the expression of two TFs - DREB2A (dehydration-responsive element-binding protein) and NAC5 gene - and some drought-specific genes (e.g., I OsCMO i encoding rice choline monooxygenase and dehydrin I OsRAB16b i ). With urbanization, rapid industrialization, and uncontrolled anthropogenic activities, abiotic stresses have plagued the world - from more intense hurricanes to record-breaking temperatures, waterlogging, salinity, potentially toxic metals, mineral toxicity, and persistent droughts - threatening the stability of food-production systems. 2021; Cambridge University PressIn Press 7 Jiao L, Zhang L, Zhang Y, Wang R, Lu B, Liu X. Transcriptome analysis provides new insight into the distribution and transport of selenium and its associated metals in selenium-rich rice. Furthermore, the application of selenium (Se) fertilizers [selenite (SeO SB 3 sb SP 2- sp ), fermented Se, and potassium selenocyanoacetate (Se-AAF)] at 30 g ha SP -1 sp during different stages of rice growth significantly enhanced total biomass, yield, and total Se content (Yuan et al. [28]). [Extracted from the article]

Purpose: Aimed to identify the differences in ion accumulation and photosynthetic electron transport between Medicago truncatula and Medicago sativa during NaCl stress, and reveal their different physiological mechanism of salt resistance. Methods: The plants were cultivated in nutrient solutions with and without 300 mM NaCl. We then measured the plant growth, leaf ion contents, prompt and delayed chlorophyll a fluorescence (PF and DF), and modulated 820 nm reflection (MR/MRO) values of the leaves on the 0 d, 10 d, 20 d, 30 d, and 40 d of NaCl stress. Results: The lower dry weight reduction and leaf wilting were found in M. sativa compared with M. truncatula under NaCl stress, and M. sativa appeared to have lower leaf Na+/K+, Na+/Ca2+, Na+/Mg2+ ratios than M. truncatula. With the NaCl treatment, the PF intensity at P-step (FP) values in the prompt chlorophyll a fluorescence transient (OJIP) curves for both species decreased gradually as the duration of exposure increased. However, the FP value of M. truncatula suggested a faster decline than that of M. sativa. Compared with M. truncatula, the DF amplitude in M. sativa exhibited a decrease that was slower and lower in response to the NaCl treatments, NaCl stress also made the lowest points of the MR/MRO appear later in M. truncatula, but not in M. sativa. Conclusion: Our results indicated that M. sativa was more effective in inhibiting Na+ and Cl− accumulation and regulating nutrient ion balance in leaves than M. truncatula during NaCl stress. Moreover, M. sativa had a strong ability to maintain stable electron transport under NaCl stress, so it is suitable for cultivation in saline soil. [ABSTRACT FROM AUTHOR]

Background and aims: Maintaining sustainable high yield and soil fertility is the key to cultivate perennial alfalfa grassland. However, little is known about the effects of rhizosphere microbes on soil fertility and alfalfa yield in different planting years and regimes. Methods: We sampled 10 alfalfa fields to investigate the rhizosphere soil microbial community and yields in monoculture and rotation systems in different planting years. Results: The alfalfa yield in monoculture was significantly declined (P < 0.05) starting in 6 yr. Wheat-corn-alfalfa rotation generated higher (P < 0.05) soil fertility index and alfalfa yield than wheat-alfalfa rotation and 2 yr alfalfa monoculture. The alfalfa yield significantly (R2 = 0.583, P < 0.001) increased with soil fertility. Significant differences were observed for bacteria (RANOSIM = 0.955, P = 0.001) and fungal (RANOSIM = 0.889, P = 0.001) communities in different planting years and regimes. Different ecological processes dominated bacterial and fungal communities assembly. Blastococcus and Massilia were important biomarkers, which had a significant (P < 0.05) positive correlation with alfalfa yield. PLS-PM analysis identified that planting regimes had positive impacts on alfalfa yield through edaphic variables, microbial genera and fungal community composition. Conversely, planting years had negative effects on alfalfa yield by indirectly regulating fungal genera and community composition through fungal community assembly. Conclusions: This study could help improve our understanding of the role and importance of rhizosphere soil microbial changes in regulating farmland soil processes and crop productivity. [ABSTRACT FROM AUTHOR]

Background and Aims: Forage legumes fix atmospheric nitrogen through a mutualistic relationship with soil rhizobia bacteria. However, frequent defoliation stress from grazing and mowing can alter the source-sink relationship between above-ground and below-ground tissues, potentially impacting their nitrogen-fixing ability.In this study, we evaluated the effects of defoliation intensities on nodulation, root phenotypic traits, plant biomass, symbiotic nitrogen fixation, soil available nitrogen, soil enzyme activities, and soil microbial community structure of alfalfa (Medicago sativa L.) and red clover (Trifolium pretense L.). Two defoliation intensities were applied at flowering: mild (removing half of above-ground biomass) and severe (leaving only 2 cm stubble), along with non-defoliated controls.Mild defoliation positively affected final shoot biomass in both legumes but had negative effects on nodulation and non-symbiotic root traits, including root biomass. The symbiotic nitrogen fixation capacity was reduced in red clover under severe defoliation stress, whereas it was unaffected in alfalfa. Soil available nitrogen content was greater following severe defoliation in red clover compared to the mild and non-defoliation, but no changes were observed in alfalfa following defoliation. Severe defoliation significantly increased soil enzyme activities of β-1, 4-glucosidase, β-D-cellobiosidase, and phosphatase enzymes in both legumes. Defoliation had no significant effect on shifting soil bacterial diversity or taxonomic composition.Overall results suggest that defoliation intensity had a deleterious effect on root traits, a positive influence on C and P extracellular enzyme activities, but varied influence on the shoot growth, symbiotic nitrogen fixation, and soil available nitrogen based on the forage legume.Methods: Forage legumes fix atmospheric nitrogen through a mutualistic relationship with soil rhizobia bacteria. However, frequent defoliation stress from grazing and mowing can alter the source-sink relationship between above-ground and below-ground tissues, potentially impacting their nitrogen-fixing ability.In this study, we evaluated the effects of defoliation intensities on nodulation, root phenotypic traits, plant biomass, symbiotic nitrogen fixation, soil available nitrogen, soil enzyme activities, and soil microbial community structure of alfalfa (Medicago sativa L.) and red clover (Trifolium pretense L.). Two defoliation intensities were applied at flowering: mild (removing half of above-ground biomass) and severe (leaving only 2 cm stubble), along with non-defoliated controls.Mild defoliation positively affected final shoot biomass in both legumes but had negative effects on nodulation and non-symbiotic root traits, including root biomass. The symbiotic nitrogen fixation capacity was reduced in red clover under severe defoliation stress, whereas it was unaffected in alfalfa. Soil available nitrogen content was greater following severe defoliation in red clover compared to the mild and non-defoliation, but no changes were observed in alfalfa following defoliation. Severe defoliation significantly increased soil enzyme activities of β-1, 4-glucosidase, β-D-cellobiosidase, and phosphatase enzymes in both legumes. Defoliation had no significant effect on shifting soil bacterial diversity or taxonomic composition.Overall results suggest that defoliation intensity had a deleterious effect on root traits, a positive influence on C and P extracellular enzyme activities, but varied influence on the shoot growth, symbiotic nitrogen fixation, and soil available nitrogen based on the forage legume.Results: Forage legumes fix atmospheric nitrogen through a mutualistic relationship with soil rhizobia bacteria. However, frequent defoliation stress from grazing and mowing can alter the source-sink relationship between above-ground and below-ground tissues, potentially impacting their nitrogen-fixing ability.In this study, we evaluated the effects of defoliation intensities on nodulation, root phenotypic traits, plant biomass, symbiotic nitrogen fixation, soil available nitrogen, soil enzyme activities, and soil microbial community structure of alfalfa (Medicago sativa L.) and red clover (Trifolium pretense L.). Two defoliation intensities were applied at flowering: mild (removing half of above-ground biomass) and severe (leaving only 2 cm stubble), along with non-defoliated controls.Mild defoliation positively affected final shoot biomass in both legumes but had negative effects on nodulation and non-symbiotic root traits, including root biomass. The symbiotic nitrogen fixation capacity was reduced in red clover under severe defoliation stress, whereas it was unaffected in alfalfa. Soil available nitrogen content was greater following severe defoliation in red clover compared to the mild and non-defoliation, but no changes were observed in alfalfa following defoliation. Severe defoliation significantly increased soil enzyme activities of β-1, 4-glucosidase, β-D-cellobiosidase, and phosphatase enzymes in both legumes. Defoliation had no significant effect on shifting soil bacterial diversity or taxonomic composition.Overall results suggest that defoliation intensity had a deleterious effect on root traits, a positive influence on C and P extracellular enzyme activities, but varied influence on the shoot growth, symbiotic nitrogen fixation, and soil available nitrogen based on the forage legume.Conclusion: Forage legumes fix atmospheric nitrogen through a mutualistic relationship with soil rhizobia bacteria. However, frequent defoliation stress from grazing and mowing can alter the source-sink relationship between above-ground and below-ground tissues, potentially impacting their nitrogen-fixing ability.In this study, we evaluated the effects of defoliation intensities on nodulation, root phenotypic traits, plant biomass, symbiotic nitrogen fixation, soil available nitrogen, soil enzyme activities, and soil microbial community structure of alfalfa (Medicago sativa L.) and red clover (Trifolium pretense L.). Two defoliation intensities were applied at flowering: mild (removing half of above-ground biomass) and severe (leaving only 2 cm stubble), along with non-defoliated controls.Mild defoliation positively affected final shoot biomass in both legumes but had negative effects on nodulation and non-symbiotic root traits, including root biomass. The symbiotic nitrogen fixation capacity was reduced in red clover under severe defoliation stress, whereas it was unaffected in alfalfa. Soil available nitrogen content was greater following severe defoliation in red clover compared to the mild and non-defoliation, but no changes were observed in alfalfa following defoliation. Severe defoliation significantly increased soil enzyme activities of β-1, 4-glucosidase, β-D-cellobiosidase, and phosphatase enzymes in both legumes. Defoliation had no significant effect on shifting soil bacterial diversity or taxonomic composition.Overall results suggest that defoliation intensity had a deleterious effect on root traits, a positive influence on C and P extracellular enzyme activities, but varied influence on the shoot growth, symbiotic nitrogen fixation, and soil available nitrogen based on the forage legume. [ABSTRACT FROM AUTHOR]

Background and aims: Aluminum (Al) stress is a global problem that inhibits root growth and crop production in acidic soils. The inhibitive effect is greatly attributed to the reduction of cell wall elasticity. The present study aimed to investigate the function of a polygalacturonase gene MsPG4 in regulating cell wall extensibility and alfalfa resistance to Al stress. Methods: The transgenic alfalfa plants of overexpression (MsPG4-OE) and knockdown (MsPG4-RNAi) of MsPG4 were treated with or without 100 µM AlCl3. The methods of field emission scanning electron microscope, transmission electron microscope and atomic force microscopy were used in physiological and histological analysis. Results: The relative root elongation was higher in MsPG4-OE lines and lower in MsPG4-RNAi lines than wild type (WT) plants under Al stress. Al contents in root tips and cell wall decreased in MsPG4-OE lines but increased in MsPG4-RNAi lines, which positively related to their pectin contents. The contents of water soluble pectin (WSP) and chelator soluble pectin (CSP) decreased in MsPG4-OE lines and increased in MsPG4-RNAi lines in the absence or presence of Al compared to WT plants. Consequently, the dimensions of the two pectin's molecules reduced, the porosity and extensibility of cell wall increased in MsPG4-OE lines comparted to WT plants under Al stress. Conclusions: MsPG4 effectively increases the cell wall extensibility and Al resistance of alfalfa via hydrolysis of pectins in the cell wall. [ABSTRACT FROM AUTHOR]

Aims: Perennial crops with more extensive and deep root systems could access deep stored water and build resilience to water shortage. In the context of human nutrition, perennial grain crops are very interesting. However, it is still questionable whether they are effective in using subsoil water. We compared intermediate wheatgrass (Kernza®) Thinopyrum intermedium, a perennial grain crop, to alfalfa Medicago sativa, a forage crop, for subsoil root growth and water uptake. Alfalfa was chosen because of its deep root system and agronomical interest as a companion crop. Methods: Using TDR sensors, deuterium tracer labelling, minirhizotrons and the Hydrus-1D model we characterised the root distribution and water uptake patterns of these two perennial crops during two cropping seasons under field conditions down to 2.5 m soil depth. Results: Both crops grew roots down to 2.0 m depth that were active in water uptake but alfalfa was deeper rooted than intermediate wheatgrass. All experimental methods concluded that alfalfa used more water from below 1.0 m depth than intermediate wheatgrass. However, simulations predicted that intermediate wheatgrass used more than 20 mm of water after anthesis from below 1 m soil depth. Simulations confirmed the advantage of deep roots in accessing deep soil water under drought. Conclusions: In regions with high groundwater recharge, growing deep-rooted perennial crops have great potential to exploit deep soil water that is often left unused. However, the road to a profitable perennial grain crop is still long and breeding intermediate wheatgrass (Kernza®) cultivars for increased root growth at depth seems to be a worthy investment for the development of more drought tolerant cultivars. [ABSTRACT FROM AUTHOR]

Purpose: Studying the legume nodule microbiome is important for understanding the development and nutrition of the plants inhabited by the various microbes within and upon them. We analyzed the microbiomes of these underground organs from both an important crop plant (Medicago sativa) and a related legume (M. polymorpha) using metagenomic and culture-based techniques to identify the main cultivatable contributors to plant growth enhancement. Methods: Using high-throughput sequencing, culturing, and in planta techniques, we identified and analyzed a broad population of the bacterial taxa within Medicago nodules and the surrounding soil. Results: Fifty-one distinct bacterial strains were isolated and characterized from nodules of both Medicago species and their growth-promoting activities were studied. Sequencing of 16S rRNA gene amplicons showed that in addition to Ensifer, the dominant genus, a large number of Gram-positive bacteria belonging to the Firmicutes and Actinobacteria were also present. After performing ecological and plant growth-promoting trait analyses, selecting the most promising strains, and then performing in planta assays, we found that strains of Bacillus and Micromonospora among others could play important roles in supporting the growth, health, and productivity of the host plant. Conclusion: To our knowledge, the comparison of the biodiversity of the microbiota of undomesticated vs. cultivated Medicago roots and nodules is novel and shows the range of potential Plant Growth-Promoting Bacteria that could be used for plants of agricultural interest. These and other nodule-isolated microbes could also serve as inoculants with rhizobia with the goal of replacing synthetic fertilizers and pesticides for sustainable agriculture. [ABSTRACT FROM AUTHOR]

Aims: It is well established that mycorrhizal symbiosis can affect plant-plant interactions. On the other hand, how intraspecific plant interactions influence communities of arbuscular mycorrhizal fungi (AMF) is still very poorly understood. Methods: We applied 454 pyrosequencing to determine the responses of AMF communities to intraspecific shoot and root interactions using Medicago sativa L. as host plant. Results: We found that intraspecific plant interaction caused significant variation in the structure of the AMF community assessed from roots but not from soil. Intraspecific root system interaction resulted in significantly elevated AMF species richness, greater total mycorrhizal and arbuscular colonization, and a larger root:shoot ratio compared to plants experiencing intraspecific shoot interaction or no interaction. Intraspecific shoot interaction resulted in significantly depressed AMF species richness. Conclusions: Our results support two hypotheses. The first is that increased AMF species richness in plants experiencing intraspecific root interaction originates from competitive release provided by high root density. The second is that shoot interaction leads to reduced allocation to root systems, increasing the stringency with which host plants selectively reward the most cooperative fungi. Because intraspecific interactions among host plants can influence the structure of their AMF community, interactions among species in complex plant communities may influence AMF community structure in addition to a plant diversity effect. [ABSTRACT FROM AUTHOR]

Aims: Carboxylate release by roots has been considered a strategy for mobilisation and acquisition of phosphorus (P). However, recently, it was argued that carboxylate release may be a way to discharge surplus carbon produced under conditions that limit plant growth. Plant P status may not be the main factor driving carboxylate release by roots. Instead, plant nitrogen (N) status and/or N:P ratio of the soil or plant may play a more important role in enhancing carboxylate release. Methods: A greenhouse pot experiment was performed to grow alfalfa in a P-deficient soil, supplied with two rates of P (0 and 20 mg kg−1) in combination with four forms of nitrogen (N) at five rates (0, 25, 50, 75, and 100 mg kg−1), to explore the effects of P rate, N form, N rate, and their interactions on plant growth, P and N status, and carboxylate release, and to determine the factors driving carboxylate release. Results: Nitrogen addition weakened the positive effect of P addition on plant growth, and increased plant N and P concentrations; P addition increased plant P concentration, but weakened the effect of N addition on plant N concentration. The amount of tartrate increased dramatically with increasing N rate, which decreased shoot growth, depending on N form. At high P supply, tartrate exudation correlated negatively with shoot biomass. Conclusions: Nitrogen addition to P-deficient alfalfa decreased shoot growth and enhanced the release of tartrate, likely to discharge surplus carbon; and the effects varied with N form. [ABSTRACT FROM AUTHOR]

Purpose: Beneficial soil microbes, such as rhizobia, engage in facultative symbioses in the roots of leguminous host plants to exchange nitrogen for products of photosynthesis, and these symbioses can be altered by biotic and abiotic factors. Here, we investigated how soil nitrate supply and aboveground insect herbivory interact to influence biological nitrogen fixation in Medicago sativa (alfalfa or lucerne). Methods: Using field and greenhouse experiments, we quantified above- and belowground allocation of rhizobially fixed nitrogen using isotopic nitrogen ratios in plants with different combinations of herbivory and nitrate supplementation. We caged Empoasca fabae (potato leafhopper) on fixing and non-fixing cultivars of M. sativa and supplemented soils with varied nitrate concentrations. Results: We detected strong changes in legume above- and belowground allocation of fixed nitrogen in response to both herbivory and nitrate supply. Moderate nitrate soils, irrespective of herbivory, induced little to no fixed nitrogen allocation across both field and greenhouse experiments. In the field only, non-supplemented soil increased aboveground allocation of fixed nitrogen following herbivore damage but resulted in no changes belowground. In contrast, non-supplemented and high nitrate soils in the greenhouse increased above- and belowground fixed nitrogen allocation relative to moderate nitrate soils. Conclusion: Our results demonstrate herbivory drives distinct plant allocation strategies across soil nitrate levels, advancing our understanding of how rhizobia influence legumes both above- and belowground. Herbivory-induced changes in rhizobia-legume symbioses are likely widespread across both agricultural and natural ecosystems. [ABSTRACT FROM AUTHOR]

Aims: Here, we assess the differential impact of drought on root carbon metabolism in the widely cultivated alfalfa (Medicago sativa, Ms) and the model legume Medicago truncatula (Mt). Understanding how carbon allocation is regulated under drought stress conditions is a central issue to improving alfalfa productivity under future climate change scenarios. Methods: Alfalfa and Medicago truncatula were compared under water deficit conditions. Root carbon metabolism of the taproot and fibrous roots was analysed. M. truncatula drought tolerance variability was compared to that of alfalfa using six accessions of the Medicago Hapmap project. The prominent taproot is much less developed in M. truncatula than in alfalfa with the former exhibiting an extensive fibrous root system. Results: In both examined Medicago species the taproot contained the major pools of soluble protein, sucrose and pinitol, whereas the major pools of hexoses and carbon metabolism enzymes appeared to be in the fibrous roots. Under water-deficit conditions, the response of M. sativa strongly differed from that of M. truncatula at the root level. Conclusions: Water deficit conditions differentially modulate the root carbon metabolism of M. sativa and M. truncatula. Mt maintained a more active carbon metabolism in the fibRs, as sucrose, myo-inositol and pinitol accumulated to cope with the water deficit (WD). Conversely, the root system of Ms did not accumulate cyclitols and carbon metabolism was more severely affected under water deficit conditions. This differentially exerted control may determine the drought response of these two close relatives. [ABSTRACT FROM AUTHOR]

Purpose: Precrops exhibit vigorous deep root growth, especially when grown perennially. However, their contribution to accumulate essential nutrients derived from deeper soil layers in the topsoil has not been quantified. We determined the vertical distribution of phosphorous (P) and potassium (K) affected by contrasting root systems of 3 precrops and their effects on subsequently grown spring wheat. Methods: Three precrops (lucerne, chicory and tall fescue) were grown for 1, 2 and 3 years prior to spring wheat cultivation. We measured plant available soil P and K from 0 to 30 cm to 75–105 cm of soil depth after precropping. Root growth and crop performance of spring wheat as affected by precropping were measured in two repeated trials. Results: We observed maximum 22-fold higher root-length density (RLD; cm cm− 3) of taprooted chicory compared with fibrous-rooted tall fescue in the subsoil. There were significant increases in plant available K in the topsoil by 27 mg kg− 1 over the precrop duration between 1 and 3 years. Grain yield of subsequently grown spring wheat was significantly increased by 10 % and 14 % from 1 year to 3 year-treatments of lucerne and chicory, respectively. Similarly, significant increases in P uptake (7 % and 19 %) and K uptake (21 and 14 %) of spring wheat was noted for the same treatments. Conclusions: Our data suggest that there is potential for the yield of short-season cereals to be improved by increased soil nutrient bioavailability in the topsoil derived from deeper soil layers by the deep roots of perennial precrops. [ABSTRACT FROM AUTHOR]

Below-ground traits that explain: Geographic distribution of plants Phosphorus availability can partly explain the distribution of two native Australian plant species. Since its discovery in 1988, the plant-beneficial rhizobacterium I Pseudomonas simiae i WCS417 served as a model strain in numerous investigations on how free-living mutualists colonise the rhizosphere, modulate plant immunity, promote plant growth, and influence microbe-microbe interactions in the soil. This special issue of Plant and Soil contains selected papers from the Rhizosphere 5 conference "Shining light on the world beneath our feet" that was held in Saskatoon, Canada, from 7 to 11 July 2019. Therefore, rational P fertilisation should be considered for efficient Zn biofortification on Zn-deficient soils and phytoremediation of Zn-contaminated soils. [Extracted from the article]

Aims: Residues of antibiotics such as oxytetracycline (OTC) in soil can affect microbial compositions and activities, thus affecting soil P availability, and consequently plant P uptake and growth. Methods: A pot experiment was performed to grow alfalfa in a loess soil with different doses of P (0, 25, 50, and 100 mg kg−1) and OTC (0, 25, 50, and 100 mg kg−1). Plant dry mass, shoot and root P concentrations, bulk soil and rhizosheath pH, rhizosheath carboxylates, and bulk soil alkaline phosphatase activity were determined. Results: Shoot dry mass and root dry mass increased with increasing P dose, while shoot dry mass decreased with increasing OTC dose, especially at lower P doses (0 and 25 mg kg−1). Addition of OTC slightly reduced P concentrations in shoots and roots, but did not reduce plant P content consistently. Increasing OTC dose significantly reduced bulk soil alkaline phosphatase activity at 0P and strongly reduced rhizosheath tartrate amount at all P doses. Conclusions: The effects of OTC on plant growth and P uptake depended on both OTC and P doses in soil. High OTC dose had negative effects on shoot P uptake and growth, especially at lower P doses, while it had a positive effect on root growth at higher P doses. [ABSTRACT FROM AUTHOR]

Aims: Zinc (Zn) and phosphorus (P) often interact negatively with each other in soil-plant systems. We investigated the effects of P-Zn interaction on Zn and P accumulation and partitioning in alfalfa. Methods: Plants were grown in a calcareous soil supplied with different rates of Zn (0, 200, and 800 mg kg−1) and P (0, 20, and 80 mg kg−1). Plant dry mass, Zn and P concentrations in shoots and roots, bulk soil and rhizosheath pH, rhizosheath carboxylates, and DTPA-extractable Zn concentration in the bulk soil were determined. Results: Phosphorus-Zn interaction significantly affected DTPA-extractable Zn concentration, plant dry mass, accumulation of Zn and P, and partitioning of Zn in alfalfa, but did not affect rhizosheath pH or the amounts of rhizosheath carboxylates. Increasing P rate promoted plant growth at all soil Zn rates and might enhance the plants' capacity to cope with excessive Zn; it resulted in a lower rhizosheath pH, which likely contributed to greater Zn and P uptake. Zinc deficiency enhanced exudation of citrate, malonate and malate, while the release of tartrate was related with P deficiency. Conclusions: There are strong P-Zn interactions in calcareous soil-plant system, such interactions significantly affect Zn bioavailability, plant growth, accumulation of Zn and P, and partitioning of Zn in alfalfa. Rational P fertilization should be considered for efficient Zn biofortification on Zn-deficient soils and phytoremediation of Zn-contaminated soils. [ABSTRACT FROM AUTHOR]

Aims: Evaluate crop rotation diversity, perenniality, carbon (C) inputs, and C input quality as predictors of soil organic carbon (SOC) concentration and aggregate mean weight diameter (MWD). Methods: At a crop rotation trial in its 37th year in Ontario, Canada, species in rotations included corn (C, Zea mays L.), alfalfa (A, Medicago sativa L.), soybean (S, Glycine max (L.) Merr.), winter wheat (W, Triticum aestivum L.), and red clover (rc, Trifolium pratense L.). Rotations were: CC, CCAA, CCSS, CCSW, CCSWrc, AA. Soils (0–20 cm) were analyzed for aggregate MWD, aggregate C, and SOC concentrations. We estimated C inputs from historical yields and C input quality (C:N, lignin: N, or NMR-derived index) from structural plant tissues. C stabilization efficiency was estimated as the ratio of SOC stock per unit total or root C input. Results: Crop rotation diversity failed to increase SOC concentrations or aggregate MWD. Perennialized rotations (CCSWrc, CCAA, AA) maintained the numerically highest SOC concentrations, and root C input increased SOC concentration. Out of 12 statistical tests relating C input quality to C stabilization efficiency, only 3 indicated a positive effect and 6 tests indicated a negative effect. Conclusions: Including a perennial forage such as alfalfa and limiting soybean frequency promotes aggregate MWD and SOC concentration more so than optimizing crop rotation diversity. Quality of structural plant inputs does not explain differences in C stabilization efficiency, possibly due to overriding influence of living root inputs. [ABSTRACT FROM AUTHOR]

Aims: Many soil scientists think that soil phosphate availability is highest at near-neutral pH and decreases with decreasing pH. This belief does not appear to have ever been subjected to experimental test. Methods: In a pot trial, we measured response curves to phosphate at seven pH(CaCl2) values ranging from 3.99 to 7.26 using three plant species: mustard (Brassica campestris), lucerne – also known as alfalfa – (Medicago sativa) and rice (Oryza sativa). We used a form of the Mitscherlich equation that allowed us to estimate the phosphate contribution from the soil as well as the slope of the response curve and the maximum yield. Results: Plants grew best near pH 5.5 and worst at near-neutral pH. We think the large decrease in growth with increasing pH was caused by decreasing rate of P uptake by plants. There was a smaller decrease in growth as pH decreased below 5.5. We think this was caused by aluminium toxicity. Conclusions: The conventional belief that phosphate availability is greatest near neutral pH is wrong. [ABSTRACT FROM AUTHOR]

Aims: The potential of "biosaline agriculture" relies on easy-to-apply tools to select plant genotypes that are best adapted to saline conditions. We aimed to determine the effects of salinity-sodicity on the functional response of alfalfa varieties by evaluating instantaneous vs integrated plant-based measurements for the selection of alfalfa cultivars in biosaline agriculture. Methods: Functional responses of three alfalfa varieties were evaluated in a greenhouse study under different saline-sodic conditions. Physiological parameters included instantaneous (gas exchange and chlorophyll fluorescence) vs time-integrated (carbon isotope discrimination -∆13C- and nitrogen isotope composition -δ15N-; specific leaf weight and chlorophyll content) measurements. Results: From all assessed physiological traits, only δ15N was able to effectively discriminate among genotypes WL656HQ, PGI908S and SW8421S, and showed the highest correlation with biomass production at all experimental stages. On average, the δ15N increased by a factor of 3.3 as salinity increased from the non-saline control treatment (ECiw ~ 0.4 dS m−1) to the highest salinity level (ECiw ~ 10.0 dS m−1) indicating that biological N fixation was significantly limited by salinity. Specific leaf weight was also significantly correlated with dry matter although to a much lesser extent than was δ15N. Conclusions: δ15N was found to be the best proxy for assessing alfalfa varieties for their adaptation potential in saline conditions. This parameter was able to discriminate alfalfa's functional response within a narrow range of irrigation water salinity. δ15N was also capable of differentiating between alfalfa varieties classified as tolerant to salinity defined at a particular plant growth stage, making this an excellent tool for genotypic selection. [ABSTRACT FROM AUTHOR]

Aims: A field experiment was conducted to evaluate the effects of alley cropping systems on microbial activity and soil organic matter (SOM) pools. We hypothesized that enzyme activity and labile pools of SOM are early and sensitive indicators of changes induced by tree introduction in the cropping systems. Methods: Poplar-alfalfa and alder-gramineous (cereal or ryegrass) associations and their respective control systems (alfalfa and gramineous) were compared in terms of soil carbon (C), nitrogen (N) and water contents, SOM labile pools, NIRS-MIRS spectra and microbial enzyme activity in the topsoil (0–15 cm) for 4 years after tree planting. Results: After 1 year, tree introduction induced a decrease in soil water content, microbial biomass N and some enzyme activities under alfalfa system. After 4 years, tree introduction resulted in higher soil water contents in both systems (alfalfa and gramineous); higher microbial biomass N and lower C:N in alfalfa-poplar plots compared to control plots. MIRS-NIRS analyses showed a greatest differentiation in SOM quality between alfalfa-based systems. Conclusions: The effects of temperate agroforestry systems on SOC in the topsoil are relatively weak in the first years after tree introduction. Observed effects were more pronounced in the alfalfa-poplar system, probably due to higher tree growth. Further studies will provide insights into the longer-term effects of these systems on soil functioning. [ABSTRACT FROM AUTHOR]

Aims: Alfalfa is the most important forage legume but sensitive to aluminum (Al), which largely limits its growth in acid soils. To improve Al resistance in alfalfa, responses to Al toxicity were investigated for understanding of the mechanisms of Al resistance in alfalfa. Methods: Growth performance and Al resistance in forty-two cultivars was evaluated. Organic acids synthesis and exudation as well as the key genes in response to Al were investigated. Results: Alfalfa cultivars showed diversity in Al resistance. Compared to the sensitive cultivar 'Magnum 801', the Al resistant cultivar 'WL414' had higher relative root elongation in response to Al toxicity, with less accumulation of Al. Al activated citrate and malate exudation in alfalfa, with higher citrate exudation and concentration as well as higher levels of citrate synthase (CS) activity, MsCS, MsALMT1, and MsMATE22 transcripts in root apex in WL414 than in Magnum 801. Citrate exudation is the major mechanism in Al resistance in alfalfa. Conclusions: Alfalfa cultivars had diversity in Al resistance. Citrate synthesis and exudation plays a key role in Al resistance in alfalfa. Higher levels of citrate concentration and exudation are associated with Al resistance in Al resistant cultivar as compared with the sensitive cultivar. [ABSTRACT FROM AUTHOR]

Aims: To investigate the relative contributions of pH, organic anions concentration, and phosphatase activity to rhizosphere soil phosphorus availability and crop phosphorus uptake in polycultures. Methods: A field experiment was conducted for three consecutive years in a split-plot design with main plots treated with two phosphorus levels and subplots treated with maize and alfalfa grown alone or intercropped. Results: Intercropped maize and alfalfa had 0.35 and 0.24 units lower rhizosphere pH, 28% and 30% higher total organic anions (TOA) concentration, and 21% and 41% greater acid phosphatase activity than those in monoculture. These changes in root exudates induced significant increases in rhizosphere phosphorus concentration of intercropped maize and alfalfa by 21% and 41%, and pH and TOA had greatest contributions, respectively. Rhizosphere phosphorus mobilization facilitated phosphorus uptake of intercropped maize, but this facilitation was offset by phosphorus uptake reduction due to decreased crown root surface area. Lateral root volume enhancement accounted for phosphorus uptake improvement of intercropped alfalfa by 86.6%, while rhizosphere phosphorus mobilization only had a 0.2% contribution. Conclusions: Rhizosphere pH and organic anions exhibit greater contributions than acid phosphatase activity in enhancing rhizosphere phosphorus availability. However, root surface area of maize and lateral root volume of alfalfa unveil greater influences on crop phosphorus uptake than rhizosphere pH and organic anions. [ABSTRACT FROM AUTHOR]

Aims: Cereal can stimulate legume N fixation through competition for soil mineral N. In addition, organic acids in the rhizosphere can mobilize external nutrients, which may help nodulation. However, how much NO3− and NH4+ competition and organic acids in the rhizosphere of intercropped crops contribute to N fixation remains unclear and requires study. Methods: Field and greenhouse experiments were conducted to quantify effects of N competition and organic acids on N fixation in a maize/alfalfa intercropping system. Results: Intercropping increased nitrogen derived from the atmosphere (%Ndfa), nodules number, and leghemoglobin content by 43.66%, 85.53%, 141.05%, respectively, leading to significantly improved total N uptake and yield, compared to monoculture. The improved %Ndfa was not only due to the depletion of NO3−, but also significantly correlated with the decrease of NO3−/NH4+ ratio and the increase of citric acid in rhizosphere of alfalfa, which could mobilize soluble resources for N fixation under no N addition. Overall, 15.4%–21.5% of N fixed by alfalfa was transferred to associated maize, and the improved N fixation enhanced N transfer. Conclusions: Our findings provide a mechanism for how root interactions facilitate N fixation, highlighting the importance of NO3−/NH4+ ratio and citric acid in nutrient mobilization for N fixation. [ABSTRACT FROM AUTHOR]

Aims: Mycorrhizae and root exudates have been considered the two important pathways for nitrogen (N) transfer from legume to non-legume plants. The present study aimed to investigate contribution of the relative importance of arbuscular mycorrhizal fungi and root exudates in short-term N transfer. Methods: A field experiment was conducted to explore N transfer from alfalfa to maize under two different N application levels using 15N leaf labeling. Results: N transfer amount ranged from 7 to 10 mg N plant−1 from alfalfa to maize and significantly decreased (by 11%–22%) with N fertilizer application. Intercropping of 4 rows of maize and 6 rows of alfalfa with 30 cm intra-row spacing (IMA43) was the optimal intercropping mode, which increased N transfer, total N uptake and yield by 18%, 15% and 11%, respectively. The relative importance of arbuscular mycorrhizal fungi and root exudates on N transfer was dependent on soil N availability. Under no N addition, hyphal length density (HLD) of rhizosphere soil explained the largest significant amount (50%) of the variability in N transfer and crop yield. However, root exudates explained 77% of the variability in N transfer and crop yields with N fertilizer application. Conclusions: Our findings highlighted that N transfer is reliant more on arbuscular mycorrhizal fungi than root exudates in N-deficient soil, whereas root exudates play a more important role in N-fertilized soil. [ABSTRACT FROM AUTHOR]

Background and aims: This study investigated the detailed mechanism underlying the alleviation of osmotic stress by exogenous hydrogen (H2) in Medicago sativa. Methods: By using biochemical and molecular approaches, the experiments were performed with the analyses of biomass, relative water content (RWC), lipid peroxidation, abscisic acid (ABA) content, antioxidant activities, and related gene expression profiles. Results: H2 application stimulated ABA production, which was accompanied by the regulation of ABA biosynthesis and deactivation/activation genes. Elevated H2-induced ABA synthesis was sensitive to tungstate, an inhibitor of ABA synthesis. Meanwhile, H2-alleviated osmotic stress, which was supported by the increases in biomass and RWC, and the reduction of lipid peroxidation, was impaired by the inhibition of ABA synthesis. Consistently, tungstate blocked H2-induced antioxidant defense. Molecular evidence revealed that miR528 was down-regulated by H2, showing a negative correlation with its target gene POD2. When tungstate was added together, the decreased miR528 and increased POD2 transcripts were respectively blocked. Transcriptional factor genes involved in ABA signaling, including MYB102, MYC2, and ABF/AREB2, were differentially upregulated by H2, but further impaired by the co-incubation with tungstate. Conclusions: Collectively, our results suggested the possible role of ABA signaling in exogenous H2-mediated tolerance against osmotic stress in alfalfa. [ABSTRACT FROM AUTHOR]

Aims: To investigate whether legume-dominated cereal/legume intercropping could facilitate phosphorus acquisition and yield enhancement via changes in root morphology and distribution. Methods: A field experiment was conducted for two consecutive years in a split-plot design with main plots treated with two phosphorus levels and subplots treated with maize and alfalfa grown alone or intercropped. Results: In maize/alfalfa intercropping, alfalfa was 3.0–5.7 times more competitive than maize. Compared to monoculture, soil water balance of intercropped maize was significantly reduced by 115%, while that of alfalfa was dramatically enhanced by 469%. Thus, intercropped maize had pronouncedly reduced root growth by 17–36%, phosphorus uptake by 24%, and yield by 12%, but the associated alfalfa had significantly increased root growth by 26%–175%, phosphorus uptake by 208%, and yield by 137%, leading to significantly improved phosphorus uptake and yield of the composite population. Among root morphological and distribution traits, crown root surface area and lateral root volume were the best predictors of maize and alfalfa phosphorus uptake, respectively. Conclusions: Legume-dominated maize/alfalfa intercropping can significantly improve phosphorus acquisition and yield production through modifications in soil water balance and root morphology and distribution, and the system overyielding was performed via alfalfa rather than maize. [ABSTRACT FROM AUTHOR]

Aims: The detailed Se distribution in plants has been poorly described. This study was performed to determine the optimal dose of selenite for enhanced Medicago sativa growth and comprehensively explore the distribution characteristics of Se in this plant.Methods: Alfalfa pot experiments were conducted in a growth chamber. The plants were grown in sterilized quartz sand and treated with different selenite levels for 21 days to determine the effect of Se on growth. Plants exposed to 1 and 10 μM selenite were used to clarify the Se distribution in alfalfa.Results: Alfalfa growth was significantly stimulated (P < 0.05) under <5 μM Se. Three linear correlations were found between the applied Se doses and Se concentrations in alfalfa roots, stems, and leaves. The following patterns of Se concentrations were observed: root>leaf>stem in the organs; rhizodermis and cortex>stele in the tissues; and younger leaf >mature leaf>older leaf and marginal leaf>midrib>internal leaf in the leaves. In addition, Se concentration in the cytoplasm fraction was significantly higher than that in cell wall fraction at 1 μM selenite, and the opposite result was found at 10 μM selenite.Conclusions: Appropriate selenite addition (1 μM) benefited alfalfa. Se binding in the rhizodermis and cortex of the root caused relatively low transport efficiency of Se from the root to the shoot. Se redistributions may be a possible important factor affecting the transportation of Se in shoot and Se was transported along with the transpiration stream within a single leaf. Cell wall immobilization might be a major strategy to protect plant organs from potential Se toxicity. [ABSTRACT FROM AUTHOR]

Background and aims: Pseudomonas spp . have previously been isolated from lucerne nodules. The aims of this study were to: 1) investigate the microbiome within a lucerne nodule; and 2) assess the ability of two Pseudomonas spp. isolated from lucerne nodules to form nodules. Methods: The microbial community within 27 lucerne nodules, collected from plants inoculated with Sinorhizobium meliloti as a seed coat or peat slurry and an uninoculated control, was identified using 16S rRNA based Illumina sequencing. Lucerne seedlings were inoculated with the two Pseudomonas spp . strains. The plants were grown in sterile conditions for 6 weeks and nodulation was assessed. 16S rRNA, nodC, nodA and nifH genes were amplified. Results: Sinorhizobium was the dominant genus in nodules, comprising 90-99% of all sequences regardless of inoculation treatment. Overall, 9 other genera were identified, with each represented by <3% of the total sequences. Both Pseudomonas strains were able to form nodules with lucerne. From one of these strains, a nodC gene was detected. Conclusion: Lucerne nodules contained a diverse assemblage of bacterial species, some of which were capable of forming nodules in the absence of rhizobia. [ABSTRACT FROM AUTHOR]

Background and aims: Nitrogen balances are useful tools to increase our understanding of soil N processes and the efficiency of plants in taking up animal urine-N. This study aimed to investigate the effect of forage type on the fate of autumn-applied urine-N (700 kg N ha). Methods: In a 17-month lysimeter study the recoveries of N in herbage, leachate, nitrous oxide, and soil + roots (at the end of the trial) were determined for three forage types: perennial ryegrass-white clover (RGWC, Lolium perenne L. -Trifolium repens L.), Italian ryegrass (Italian RG, Lolium multiflorum Lam.), and lucerne ( Medicago sativa L.) under simulated autumn grazing. Results: We recovered 81.5-85.5% of the N applied in the urine. Italian RG had the greatest amount of urine-N recovered in the herbage (49.5%) and the least recovered in leachate (16.8%) making it the most efficient of the three forages for utilizing urine-N. For RGWC, herbage and leachate recoveries were 40.1% and 23.7% , respectively. Lucerne was the least efficient with recoveries of N in herbage and leachate equaling 18.4% and 52.5%, respectively. Conclusions: This study demonstrates that Italian ryegrass could offer benefits in reducing urine-N leaching losses through its ability to take up more urine-N over winter. [ABSTRACT FROM AUTHOR]

Aims and methods: Lucerne and Caucasian clover dry matter were measured in response to recommended lime and capital P inputs for six years in an acidic soil in the New Zealand high country. The initial three years of the field experiment indicated successful establishment and persistence of both legumes. Lucerne dry matter (DM) yield was up to 4 t/ha/yr in this period and higher than Caucasian clover yields. However, a lack of persistence of lucerne was apparent from this point forward compared with Caucasian clover which produced 7.7 t DM/ha in Year 6. An experiment using tubes of soil was used to investigate whether differences in root traits, nodulation and nodule occupancy were responsible for the differences observed in field persistence over time. Results: These showed that when rhizobia inoculant was added, the fine root length of Caucasian clover was unaffected (R = 0.14) by aluminium (Al) content of the soil. In contrast, fine root growth of lucerne was suppressed (R = 0.79) by the soil Al content. Nodulation of Caucasian clover was unaffected by soil pH or Al when the rhizobia inoculant was provided which suggests the viability of the commercial genotype ICC148 in this soil with a pH of 5.5 and Al ca. 7 mg/kg soil. For lucerne, the maximum nodulation score of 7.3 occurred with 2 t/ha of lime added (soil pH ca.6, Al ca. 0.3 mg/kg) plus inoculant. Conclusions: This suggests an Al toxic threshold of <1.0 mg Al/kg soil for effective lucerne nodulation. From the lucerne nodules, eight naturalized strains of Ensifer meliloti were identified. In contrast, only one R. leguminosarum strain was detected in the Caucasian clover nodules. The competition between those rhizobia genotypes may negatively affect the efficiency of biological nitrogen fixation in lucerne. Therefore, the lack of genetic diversity of R. leguminosarum bv. trifolii in New Zealand soils might be an advantage especially if the commercial strain is acid soil tolerant. [ABSTRACT FROM AUTHOR]

Background and aims: Phosphorus (P) deficiency is a major problem for alfalfa ( Medicago sativa) productivity on alkaline soils on the Loess Plateau, China. Our aim was to investigate growth, morphological and physiological responses of alfalfa to P supply in two alkaline soils when water supply is limited. Methods: A pot experiment was carried out to grow alfalfa in two alkaline soils supplied with different rates of P. Parameters of plant growth and root morphology, rhizosphere pH and carboxylates, and plant concentrations of mineral nutrients were measured. Results: Plant growth and nutrient uptake were enhanced by supplying P, but shoot growth was not further increased when P supply was >20 μg P g soil. Specific root length was only responsive to changes in soil P when P supply was low in the loessial soil. The rhizosphere carboxylate amount was significantly greater when no P was supplied than when P was supplied to the loessial soil. The rhizosphere pH was lower than the bulk soil pH, but did not vary with soil P. Conclusions: A P supply of 20 μg P g soil was optimal for alfalfa growth. The responses of specific root length and rhizosphere carboxylates depended on soil type. [ABSTRACT FROM AUTHOR]

Background and aims: Lucerne ( Medicago sativa L.) is often grown under water-limited production conditions due to its capacity to extract water from deep soil layers through an extensive taproot system. These soils often contain stones which cause the roots to become unevenly distributed due to displacement by rock fragments. To improve the estimation of water use by lucerne grown in stony soils, we investigated the temporal pattern of water supply and demand, and how this influences crop growth. Methods: Naturally occurring stones in the silt loam soil profile were used to reduce the plant available water capacity for three lucerne crops. The Monteith model was fitted against observed soil water to obtain estimates of the extraction rate constant ( kl, day) and extraction front velocity (EFV, mm day) of lucerne roots. Crop water demand was represented by transpiration losses driven by intercepted solar radiation based on the 'canopy conductance' approach. Results: The Monteith model described the pattern of water extraction for lucerne grown on stony soils. However, a single, constant kl and EFV were inappropriate for characterising water extraction. The main physiological responses to water stress were (i) a reduction in canopy conductance, (ii) a reduction in canopy expansion and (iii) the rearrangement of leaves into a more vertical position. Conclusion: This study validated frameworks to quantify lucerne water extraction and transpiration demand which can be used to improve the estimation of water use by lucerne crops. [ABSTRACT FROM AUTHOR]

Background and aims: The interaction between apricot and alfalfa will increase land use efficiency and improve the production capacity of trees, and allow the exploration of the impact of apricot intercropping with alfalfa on physiological and root morphological characteristics.Four planting modes were set up: alfalfa monoculture, apricot monoculture, apricot intercropped with alfalfa with a 20 cm row spacing and apricot intercropped with alfalfa with a 30 cm row spacing. Through measurements of the plant height, soil and plant analyzer development value, root length density, root surface area, and crop yield, the above and belowground growth status of the crops under different planting modes was explored.In 2020 and 2021, in the horizontal direction, root length density was mainly concentrated at 60–90 cm. With the increase in the horizontal distance, root length density was mainly concentrated at 90–120 cm. In the vertical direction, root length density was mainly concentrated at 0–20 cm. In 2020, compared with the yield in the alfalfa treatment, the yield of intercropping alfalfa (30 cm) and (20 cm) decreased by 71.2% and 58.7%, respectively, and alfalfa differed significantly between apricot intercropped alfalfa (20 cm) and apricot intercropped alfalfa (30 cm). In 2021, the land equivalent ratios of apricot intercropped alfalfa (20 cm) and apricot intercropped alfalfa (30 cm) were 1.25 and 1.26, respectively.Indicating that both planting modes have land production advantages. Under the two row spacing intercropping modes, apricot intercropped alfalfa (20 cm) is more suitable for local planting.Methods: The interaction between apricot and alfalfa will increase land use efficiency and improve the production capacity of trees, and allow the exploration of the impact of apricot intercropping with alfalfa on physiological and root morphological characteristics.Four planting modes were set up: alfalfa monoculture, apricot monoculture, apricot intercropped with alfalfa with a 20 cm row spacing and apricot intercropped with alfalfa with a 30 cm row spacing. Through measurements of the plant height, soil and plant analyzer development value, root length density, root surface area, and crop yield, the above and belowground growth status of the crops under different planting modes was explored.In 2020 and 2021, in the horizontal direction, root length density was mainly concentrated at 60–90 cm. With the increase in the horizontal distance, root length density was mainly concentrated at 90–120 cm. In the vertical direction, root length density was mainly concentrated at 0–20 cm. In 2020, compared with the yield in the alfalfa treatment, the yield of intercropping alfalfa (30 cm) and (20 cm) decreased by 71.2% and 58.7%, respectively, and alfalfa differed significantly between apricot intercropped alfalfa (20 cm) and apricot intercropped alfalfa (30 cm). In 2021, the land equivalent ratios of apricot intercropped alfalfa (20 cm) and apricot intercropped alfalfa (30 cm) were 1.25 and 1.26, respectively.Indicating that both planting modes have land production advantages. Under the two row spacing intercropping modes, apricot intercropped alfalfa (20 cm) is more suitable for local planting.Results: The interaction between apricot and alfalfa will increase land use efficiency and improve the production capacity of trees, and allow the exploration of the impact of apricot intercropping with alfalfa on physiological and root morphological characteristics.Four planting modes were set up: alfalfa monoculture, apricot monoculture, apricot intercropped with alfalfa with a 20 cm row spacing and apricot intercropped with alfalfa with a 30 cm row spacing. Through measurements of the plant height, soil and plant analyzer development value, root length density, root surface area, and crop yield, the above and belowground growth status of the crops under different planting modes was explored.In 2020 and 2021, in the horizontal direction, root length density was mainly concentrated at 60–90 cm. With the increase in the horizontal distance, root length density was mainly concentrated at 90–120 cm. In the vertical direction, root length density was mainly concentrated at 0–20 cm. In 2020, compared with the yield in the alfalfa treatment, the yield of intercropping alfalfa (30 cm) and (20 cm) decreased by 71.2% and 58.7%, respectively, and alfalfa differed significantly between apricot intercropped alfalfa (20 cm) and apricot intercropped alfalfa (30 cm). In 2021, the land equivalent ratios of apricot intercropped alfalfa (20 cm) and apricot intercropped alfalfa (30 cm) were 1.25 and 1.26, respectively.Indicating that both planting modes have land production advantages. Under the two row spacing intercropping modes, apricot intercropped alfalfa (20 cm) is more suitable for local planting.Conclusion: The interaction between apricot and alfalfa will increase land use efficiency and improve the production capacity of trees, and allow the exploration of the impact of apricot intercropping with alfalfa on physiological and root morphological characteristics.Four planting modes were set up: alfalfa monoculture, apricot monoculture, apricot intercropped with alfalfa with a 20 cm row spacing and apricot intercropped with alfalfa with a 30 cm row spacing. Through measurements of the plant height, soil and plant analyzer development value, root length density, root surface area, and crop yield, the above and belowground growth status of the crops under different planting modes was explored.In 2020 and 2021, in the horizontal direction, root length density was mainly concentrated at 60–90 cm. With the increase in the horizontal distance, root length density was mainly concentrated at 90–120 cm. In the vertical direction, root length density was mainly concentrated at 0–20 cm. In 2020, compared with the yield in the alfalfa treatment, the yield of intercropping alfalfa (30 cm) and (20 cm) decreased by 71.2% and 58.7%, respectively, and alfalfa differed significantly between apricot intercropped alfalfa (20 cm) and apricot intercropped alfalfa (30 cm). In 2021, the land equivalent ratios of apricot intercropped alfalfa (20 cm) and apricot intercropped alfalfa (30 cm) were 1.25 and 1.26, respectively.Indicating that both planting modes have land production advantages. Under the two row spacing intercropping modes, apricot intercropped alfalfa (20 cm) is more suitable for local planting.Graphical abstract: The interaction between apricot and alfalfa will increase land use efficiency and improve the production capacity of trees, and allow the exploration of the impact of apricot intercropping with alfalfa on physiological and root morphological characteristics.Four planting modes were set up: alfalfa monoculture, apricot monoculture, apricot intercropped with alfalfa with a 20 cm row spacing and apricot intercropped with alfalfa with a 30 cm row spacing. Through measurements of the plant height, soil and plant analyzer development value, root length density, root surface area, and crop yield, the above and belowground growth status of the crops under different planting modes was explored.In 2020 and 2021, in the horizontal direction, root length density was mainly concentrated at 60–90 cm. With the increase in the horizontal distance, root length density was mainly concentrated at 90–120 cm. In the vertical direction, root length density was mainly concentrated at 0–20 cm. In 2020, compared with the yield in the alfalfa treatment, the yield of intercropping alfalfa (30 cm) and (20 cm) decreased by 71.2% and 58.7%, respectively, and alfalfa differed significantly between apricot intercropped alfalfa (20 cm) and apricot intercropped alfalfa (30 cm). In 2021, the land equivalent ratios of apricot intercropped alfalfa (20 cm) and apricot intercropped alfalfa (30 cm) were 1.25 and 1.26, respectively.Indicating that both planting modes have land production advantages. Under the two row spacing intercropping modes, apricot intercropped alfalfa (20 cm) is more suitable for local planting. [ABSTRACT FROM AUTHOR]

Aims: Soil salinity varies greatly in the plant rhizosphere. The effect of nonuniform salinity on the growth and physiology response of alfalfa plants was determined to improve understanding of salt stress tolerance mechanisms of alfalfa. Methods: Plant growth, predawn leaf water potential, water uptake, and tissue ionic content were studied in alfalfa plants grown hydroponically for 9 days using a split-root system, with uniform salinity or horizontally nonuniform salinity treatments (0/S, 75/S, and 150/S corresponding to 0, 75, and 150 mM NaCl on the low salt side, respectively). Results: Compared with uniform high salinity, 0/S and 75/S treatments significantly increased the alfalfa shoot dry mass and stem extension rate. Compensatory water uptake by low salt roots of 0/S and 75/S treatments was observed. However, decreased leaf Na concentration, increased leaf K/Na, and compensatory growth of roots on the low salt side were observed only following the 0/S treatment. Conclusions: Nonuniform salinity dose not enhance plant growth once a threshold NaCl concentration in low salinity growth medium has been reached. Compensation of water uptake from the low-salt root zone and regulation of K/Na homeostasis in low salt root play more important role than regulation of leaf ions in enhancing alfalfa growth under nonuniform salinity. [ABSTRACT FROM AUTHOR]

Background and Aims: Salt stress negatively affects alfalfa ( Medicago sativa L.) production and biological nitrogen fixation. We investigated whether rhizobium symbiosis has an effect on host plant tolerance to salt stress. Methods: We determined the survival rate, oxidative damage level, activities of antioxidant enzymes, and contents of osmotic solutes in the leaf and root of 4-month-old alfalfa with active nodules, inactive nodules or without nodules, and under short-term salt stress. Results: Alfalfa with active nodules showed higher survival rate. Higher survival rate was associated with reduced lipid peroxidation, higher activities of superoxide dismutase (SOD), catalase (CAT), peroxidase (POD), and ascorbate peroxidase (APX) as well as higher concentrations of reduced glutathione (GSH) and soluble sugar, especially in roots under salt stress. Variance analysis indicated nodulation affected the activities of SOD, CAT, POD, and APX along with concentrations of GSH, soluble sugar, and soluble protein. Inoculation also resulted in higher basal levels of superoxide anion radical (O·) without salt stress. Conclusions: Rhizobium symbiosis had a positive effect on alfalfa salt tolerance by improving the activity of antioxidant enzymes and osmotic adjustment capacity. [ABSTRACT FROM AUTHOR]

Aims: We hypothesised that a) species with greater acid soil tolerance have an increased capacity to utilise incipient rainfall; and b) liming increases the productivity and the ability of pasture species to utilise available water resources in the profile of an acid soil. Methods: A field experiment was established on a moderately acidic yellow Kandosol and monitored over 5 years. Five perennial pasture species including lucerne ( Medicago sativa L.), phalaris ( Phalaris aquatica L.), chicory ( Cichorium intybus L.), tall fescue ( Festuca arundinacea Schreb.) and cocksfoot ( Dactylis glomerata L.), were sown in monocultures with and without 2.9 t/ha lime. Results: Both lucerne and phalaris were more persistent than chicory, tall fescue and cocksfoot under severe drought, despite both being considered sensitive to soil acidity. Surface liming increased the soil water deficit by up to 27 mm at 0.75-1.65 m under perennial pastures compared to unlimed treatments, despite lime having no physical presence at that depth. Lime increased lucerne, phalaris and cocksfoot cumulative herbage biomass by 150, 30 and 20 %, respectively, but had no significant effect on chicory or tall fescue biomass. Conclusions: The two most acid-sensitive species, lucerne and phalaris, were more resilient under drought despite the acidic nature of the soil. We contend that species sensitive to acidity can be a valuable addition to pastures on acid soils. Lime used in conjunction with deep-rooted perennial species is likely to maximise the ability of pastures to utilise scarce available soil water reserves. [ABSTRACT FROM AUTHOR]

Aims: We tested the responses of soil respiration to irrigation, at different proportions of field capacity, in constructed grasslands in the Inner Mongolia Autonomous Region of northern China, and tried to identify the underlying physiological mechanisms. Methods: The experiment included a legume ( Medicago sativa) and a forage grass ( Elymus nutans) in sole-crops and a mixed sowing, with four water treatments: a control and three levels of irrigation (low, medium, and high) at three application times: during the regreening, elongation, and heading stages. Results: The soil respiration rate ( R) responded strongly to water addition. Irrigation increased the cumulative growing season R, which ranged from 257 g C m years to 500 g C m years for M. sativa, from 299 to 391 g C m years for E. nutans + M. sativa, and from 209 to 296 g C m years for E. nutans. Irrigation increased the cumulative R by 7 to 49 %. R of the grass-legume mixture was 1.2 to 1.4 times the corresponding values in the E. nutans plots. In addition to the effects of soil temperature and moisture content, R was explained by differences in the net photosynthetic rate and in microbial biomass. Water addition increased Q, which was strongly and positively correlated with the total C, C/N ratio, and cellulose content of the plants. Conclusions: R responded strongly to irrigation, although the response differed between the two species. The grass-legume mixtures showed increased R compared to values in the grass sole-crop. R appears to be determined by moisture and temperature, but also by the net photosynthetic rate and by microbial properties such as microbial biomass. [ABSTRACT FROM AUTHOR]

Aim: To investigate how the chemical composition of native organic matter of two contrasting soils varies with inputs of biochar and fresh material (including plant roots) and how these underlying changes influence microbial community structure. Methods: Corn stover (CS) and CS-derived biochars produced at 350 °C and 550 °C were applied at a dose of 7.2 t C ha to two contrasting soils-an Alfisol and an Andisol. After 295 days of incubation, two undisturbed subsamples from each pot were taken: (i) in one, lucerne ( Medicago sativa L.) was seeded (plant study, P) and (ii) in the other, the incubation was continued without the plants (respiration study, R); all subsamples were incubated for an additional 215 days. Soils without amendments were used as controls. At the end of the incubation (510 days), their bacterial community profiles were characterised using ARISA and the molecular composition of soil organic matter (SOM) was investigated by pyrolysis-GC/MS. Results: There were significant interactions between soil type, study type (P or R) and organic amendment. Organic amendments influenced overall SOM composition with microbial community response being mainly influenced by soil type but also strongly affected by the presence or absence of plants. For a specific soil type, ≥ 40 % of total variation in bacterial community ordination could be explained by the molecular composition of SOM. Conclusions: The molecular composition of SOM is proposed as an important factor influencing the microbial response to organic amendments, including biochar. [ABSTRACT FROM AUTHOR]

Background and aims: The productivity of lucerne ( Medicago sativa L.) is limited by phosphorus (P) deficiency and drought on alkaline soils in northwest China. The aim of this study was to identify the morphological and physiological responses of roots to P- and moisture-limited conditions in an alkaline soil. Methods: A pot experiment compared the growth and root characteristics of an introduced (Arkaxiya) and a locally-selected (Longzhong) lucerne cultivar grown in alkaline soil, with an initial available soil P of 6.9 μg P g dry soil and a pH of 8.3, with four applied-P rates (0, 4.2, 8.4 and 16.8 μg P g dry soil) and three soil moisture treatments [maintained at 75-90 %, 45-55 % and 30-35 % of field capacity (FC)]. Results: At high soil P and high soil water content (SWC), high total root length contributed to high P uptake, high P-use efficiency, and greater plant growth in Arkaxiya compared to Longzhong. However at low SWC, Longzhong had a higher specific root length (thinner roots) and higher total root length than Arkaxiya. At low SWC greater biomass was allocated to roots, at low P-supply the specific root length increased, while the combination of low soil P and low SWC induced greater release of rhizosphere carboxylates. Conclusions: The results suggest that the introduced cultivar has traits that will benefit lucerne production in all but the driest and low-phosphate alkaline soils. [ABSTRACT FROM AUTHOR]

Aims: Differences in the ability to fix and transfer N have been shown between perennial legume species. However, the traits responsible for such variations are largely to be identified. This study aimed at comparing the dynamics of N transfer from alfalfa and white clover and test whether their differences resulted from difference in fixation, legume proportion, population dynamics or tissue composition. Methods: A three-year field experiment and a greenhouse experiment were carried out. Nitrogen fixation and transfer were assessed trough N dilution and difference methods. Results: Both experiments confirmed significant differences between legumes regarding N transfer capacity. Although alfalfa cumulated twice as much biomass and fixed nitrogen, it transferred smaller amounts of N (59 versus 147 kg N.ha over three years in the field) under a delayed dynamic. The amounts of nitrogen transferred were related to recent decreases in legume population density. Moreover, root tissue composition differed; white clover had a higher proportion of fine roots with a lower C/N and lignin content. This resulted in more rapid N release from the severed roots of clover. Conclusions: The traits controlling plant persistency, root material turnover and residue quality may better explain N transfer dynamics than overall legume production and fixation. [ABSTRACT FROM AUTHOR]

Aims: That legumes improve soil fertility is well established, however the extent that N fixed by legumes may increase trace gas emissions is poorly understood. Our aim was to determine if greater soil N in native prairies interseeded with alfalfa would increase trace gas emissions of nitrous oxide (NO) and methane (CH). Methods: A chronosequence study to investigate interseeded alfalfa on the fluxes of NO and CH was undertaken on three prairie sites. At each site, native grasslands interseeded with alfalfa for 38, 16 and 5 years, along with adjacent native grassland controls and native grasslands fertilized with a one-time addition of N fertilizer, were measured for NO and CH using static chambers. Results: Across interseeding years there were few significant differences between the three treatments (Native, Alfalfa, Fertilized). Despite increased soil N, the interseeded treatment released no more NO than native grasslands. Methane uptake was generally greatest on interseeded grasslands and least on fertilized grasslands. Conclusions: Our results suggest that while alfalfa can increase soil N and improve productivity, it did not increase trace gas production relative to native grasslands. This is a win-win situation for ranchers wishing to increase soil fertility and thus their overall productivity and forage quality without increasing trace gas emissions. [ABSTRACT FROM AUTHOR]

Background and aims: Quantification and characterization of dissolved organic matter (DOM) leached from leaf litter in the laboratory may well depend on the method used to leach the litter. However, we lack a comparative assessment of the available methods. Here, we test how: i) four commonly used methods to leach plant litter, ii) cutting of the litter, and iii) litter species affect the quantity and composition of dissolved organic carbon (DOC) and total dissolved nitrogen (TDN) leached using fourier transform mid-infrared spectroscopy (FTIR). Methods: We tested how soaking litter in water, dripping water over litter, and shaking litter in two different volumes of water affected leaching of both cut and whole leaves of alfalfa ( Medicago sativa), ash ( Fraxinus excelsior), big bluestem grass ( Andropogon gerardii), oak ( Quercus macrocarpa) and pine ( Pinus ponderosa) litter. We measured DOC and TDN on the leachate to quantify how much DOM was leached by each method. We used the DOC:TDN ratio and FTIR to analyze the composition of the DOM leached. Results: The leaching method and cutting had an impact on the amount of DOM leached from the litter. The amount of DOM leached was also affected by the litter species and its interaction with leaching method and cutting. FTIR analysis identified the same main functional groups of plant litter leachates across all of the litter species. Leaching method, cutting and litter type affected the concentration of the leachate and the resolution of the FTIR spectral data but not the relative contribution of the main functional groups. Conclusions: Methods of leaching should be chosen consistently with experimental objectives and type of litter examined. The leaching method, cutting of the litter and litter species should be taken into consideration when comparing data on DOM amounts obtained from different leaching methods but the leachate consists of similar functional group components across method, cutting and litter species. [ABSTRACT FROM AUTHOR]

Background and aims: Nutrient resorption from the senesced to the green leaves can help a plant re-use elements, thus improving adaptability and persistence. How the resorption of nitrogen (N), phosphorus (P) and potassium (K) varies among differently aged lucerne ( Medicago sativa) stands and how they correlate to their stoichiometry in the leaves and soil remain uncertain. This study aimed to analyze the resorption efficiencies (REs) of N, P and K and their possible correlations with stoichiometric ratios in the plant and soil. Methods: The concentrations of plant N, P and K and soil N, P, K and carbon (C) were measured under lucerne stands established in different years, and stoichiometric ratios and REs were calculated. The relationships of REs with stoichiometric ratios were analyzed. Results: The nitrogen resorption efficiency (NRE) was quite variable among the different stands and tended to rise and then drop with stand age, ranging from 4.6 to 33.7 % with an average of 16.2 %. The phosphorus resorption efficiency (PRE) tended to increase with stand age, ranging from 11.1 to 38.3 % with an average of 27.3 %. The potassium resorption efficiency (KRE) increased with stand age, ranging from 21.0 to 49.8 % with an average of 36.9 %. The KRE was generally highest, followed by the PRE, and the NRE was lowest. Leaf N:P and N:K generally decreased and then increased with stand age, while the K:P increased and then decreased. In the green leaves, total N concentration increased significantly with NRE and PRE, and total P concentration rose significantly with PRE, while in the senesced leaves, total N concentration decreased significantly with NRE and KRE. The N:P in the green leaves decreased significantly with PRE and the K:P in the senesced leaves dropped with NRE. Furthermore, the REs decreased with total soil nutrition status if there was any correlation. The REs increased significantly with soil ammonium N concentration, while the NRE decreased significantly with soil nitrate N concentration. In addition, soil available P concentration at most depths led to significant increases in NRE and KRE. However, the REs were rarely influenced by stoichiometric ratios of soil N, P, K and C. Conclusions: The NRE rose and then dropped, and the PRE and KRE both increased with stand age. Leaf N:P and N:K generally decreased and then increased with stand age, while K:P increased and then decreased. The concentrations of N, P and K increased in the green leaves and decreased in the senesced leaves with REs if there was any correlation. The REs decreased with total soil nutrition status if there was any correlation. However, the REs hardly changed with stoichiometric ratios in the leaves and soil under differently aged lucerne stands. There appear to be no correlations between REs and element stoichiometries. [ABSTRACT FROM AUTHOR]

Background and aims: Inoculation of legumes at sowing with rhizobia has arguably been one of the most cost-effective practices in modern agriculture. Critical aspects of inoculant quality are rhizobial counts at manufacture/registration and shelf (product) life. Methods: In order to re-evaluate the Australian standards for peat-based inoculants, we assessed numbers of rhizobia (rhizobial counts) and presence of contaminants in 1,234 individual packets of peat-based inoculants from 13 different inoculant groups that were either freshly manufactured or had been stored at 4 °C for up to 38 months to determine (a) rates of decline of rhizobial populations, and (b) effects of presence of contaminants on rhizobial populations. We also assessed effects of inoculant age on survival of the rhizobia during and immediately after inoculation of polyethylene beads. Results: Rhizobial populations in the peat inoculants at manufacture and decline rates varied substantially amongst the 13 inoculant groups. The most stable were Sinorhizobium, Bradyrhizobium and Mesorhizobium with Rhizobium, particularly R. leguminosarum bv. trifolii the least stable. The presence of contaminants at the 10 level of dilution, i.e. >log 6.7 g peat, reduced rhizobial numbers in the stored inoculants by an average of 37 %. Survival on beads following inoculation improved 2-3 fold with increasing age of inoculant. Conclusions: We concluded that the Australian standards for peat-based rhizobial inoculants should be reassessed to account for the large differences amongst the groups in counts at manufacture and survival rates during storage. Key recommendations are to increase expiry counts from log 8.0 to log 8.7 rhizobia g peat and to have four levels of inoculant shelf life ranging from 12 months to 3 years. [ABSTRACT FROM AUTHOR]