Search

Background and aims: The frequent occurrence of extreme rainfall events results in soils experiencing drying–rewetting (DRW) cycles. Such rewetting can lead to a surge in soil CO2 emissions; however, the main regulatory factors involved in this priming effect are unclear. Methods: In this study, we conducted a meta-analysis using data extracted from 43 published papers, to determine the direct regulatory factors involved in the priming effect of soil CO2. Results: The results indicated that the priming effect of rewetting on soil CO2 emissions was influenced by ecosystem type, soil properties, climatic factors, and the number of DRW cycles. The priming effect was the highest in cropland but the lowest in grassland when taking flux values observed before rewetting as the control group. It was also greater in acidic soils (pH < 6.5) and soils with a high clay fraction (clay ≥ 30%) than in other soils. The effect size (lnRR) of soil CO2 emissions was exponentially related to the mean annual precipitation (MAP), and decreased with increases in MAP. In DRW experiments, the priming effect of the first rewetting on soil CO2 emissions was the largest, an effect that gradually decreased with the number of DRW cycles, before disappearing completely. Most importantly, soil moisture influenced the peak time and the pulse time of the priming effect: the greater the change in soil moisture, the longer the peak time duration; the higher the maximum soil moisture content after rewetting, the longer the pulse time duration; and the lower the initial soil moisture content, the bigger the priming effect. Conclusion: Generally, physical mechanisms, especially soil moisture, directly regulate the CO2 priming effect during DRW cycles. Thus, this study provides a theoretical basis for assessing and predicting the impact of future precipitation changes on soil carbon cycling. Future studies should also carefully monitor any changes in soil microorganisms in response to changes in soil moisture during DRW cycles, because these appear to be significantly involved in CO2 release from soils. [ABSTRACT FROM AUTHOR]

Rice ( I Oryza sativa i L.) is the world's second most important cereal crop and a staple food for approximately 50% of the global population. In their study on C allocation, Zang et al. ([16]) observed no immediate effects on C allocation following C assimilation but found that all administered C remained below ground. Tracking the photosynthesized carbon input into soil organic carbon pools in a rice soil fertilized with nitrogen. [Extracted from the article]

Background and aims: Soil acidification is known to be one of the constraints of tree growth; however, it is unclear how it affects tree growth at photosynthesis level (i.e., through affecting stomatal conductance vs. carboxylation rate) during the growth of trees. This paper studied the effects of soil acidification on Pinus densiflora foliar chemistry and tree ring C isotope ratio (C/C, expressed as δC) and their relationship with tree growth. Methods: Tree growth (diameter, annual growth ring area, and root biomass), soil chemistry (pH, mineral N, and exchangeable Ca and Al), foliage chemistry (N, Ca/Al, and δC), and tree ring δC in P. densiflora stands along a soil pH gradient (from 4.38 to 4.83, n = 9) in southern Korea were investigated. Results: Overall, trees with relatively poor growth under more acidic soil conditions (low pH and Ca/Al) had lower values of foliar N concentration and δC and tree ring δC, suggesting that restricted N uptake under more acidic soil conditions caused N limitation for photosynthesis, leading to poor tree growth. In addition, relationships between mean annual area increment and carbon isotope discrimination of tree rings at five-yr intervals from 1968 to 2007 revealed that the impact of soil acidification on tree growth became severer during the last 15 yrs as negative correlations between them became significant after 1993. Conclusions: Reduced N uptake under acidic soil conditions resulted in lower radial growth of P. densiflora via non-stomatal limitation of photosynthesis. [ABSTRACT FROM AUTHOR]

Subsurface acidity is a major factor limiting crop yield in some agricultural soils. The surface application of lime has limited effect on the subsurface acidity due to the slow downward movement, while deep incorporation of lime is costly. This paper tested the concept of biologically ameliorating subsurface acidity in a highly acidic soil through the net uptake of anions by plant roots . Nitrogen was supplied to the top soil (0–10 cm) as Ca(NO3)2 at rates equivalent to 30–240 kg N ha−1. Four water levels were imposed (40, 60, 80 and 100% of field capacity). Aluminium-tolerant wheat was grown for 58 days. The high N and high water treatments stimulated root growth below 15 cm, which in turn increased N capture, resulting in a greater excess anion uptake over cations and thus alkalisation of subsurface soil layers. This study suggests that it is feasible to exploit the process of nitrate uptake by an aluminium-tolerant wheat genotype to increase pH in acidic subsoil. [ABSTRACT FROM AUTHOR]

Aims: Elucidating the mechanisms of understory vegetation response to forest management practices is critical to the impact of soil nutrient cycling. However, as common management practices, how thinning leading to the restoration of understory vegetation affects soil biochemical properties and microbial-mediated belowground processes and their main drivers remains unclear. Methods: We investigated the differences of 16 S rRNA, nifH gene abundance, diversity and composition of vegetation restoration using a 5-year in situ experiment including Pinus massoniana-dominated forests (CK), virgin Cunninghamia lanceolata plantations (CF) and C. lanceolata plantations that have undergone a cycle of cutting and replanting (CS) in southern China. Results: We found that understory vegetation restoration improved some soil physicochemical properties (e.g., AP) and enzyme activity. The abundance of nifH were higher in CF than in CK or CS. As a result of vegetation restoration, α-diversity of soil diazotrophic communities significantly increased in CF. These communities were clustered into different groups based on the forest type. The number of potential keystone species of diazotrophs was highest in CF, including several beneficial taxa (e.g., Paraburkholderia and Pelomonas). Most of the bacterial functional groups related to soil nitrogen cycling were also significantly elevated in CF, such as nitrogen fixers. Partial least squares path modelling (PLS-PM) further showed that soil diazotrophic communities were clearly shaped by soil nutrient content. Conclusions: Overall, these results highlight the effects of vegetation restoration on soil diazotrophic communities and clarify the contributions of potential for improving edaphic conditions in areas of southern China with acidic red soils. [ABSTRACT FROM AUTHOR]

Background: Zinc (Zn) enrichment in cereal grains is a promising method to relieve human Zn malnutrition. Many factors influence grain Zn accumulation, but the role of rhizosphere microbes in soil environment and crop Zn uptake remain unknown. Methods: This study examined the relationships between rhizosphere microbes, rhizosphere soil nutrients, vegetal and grain Zn concentrations in six wheat (Triticum aestivum L.) cultivars with contrasting grain Zn concentrations grown in Zn-deficient soil. Results: Roots and spikes Zn concentrations at anthesis were positively correlated with grain Zn concentrations. Root Zn concentration was negatively correlated with rhizosphere soil available phosphorus (AP) and Zn (AZn). Spike Zn concentration was positively correlated with rhizosphere ammonium-N. The bacterial community assembly was more profoundly dominated by stochastic processes in the rhizosphere of high-Zn cultivars. Specifically enriched microbes were found within 144 amplicon sequence variants (ASVs) affiliated with 15 phyla in the rhizosphere of the high-Zn cultivars at anthesis. Enriched microbes significantly correlated with AZn were only identified in the rhizosphere of high-Zn cultivars, where g_Olivibacter and o_Microtrichales had the function of decomposing organic matter, potentially facilitating the formation of organic acids and dissolving soil Zn. The AP-related enriched microbes g_Lysobacter, g_Crossiella, and g_TM7a in the rhizosphere of high-Zn cultivars were significantly negatively correlated with AP, indicating their role in decreasing the AP. Conclusion: This study implied that the rhizospheric microbes in the high-Zn cultivars had the potential function of increasing soil Zn availability and decreasing soil P availability, as an important microbial strategy for wheat grain Zn biofortification. [ABSTRACT FROM AUTHOR]

Background and Aims: Suitable N source supply is critical to improve plant growth and N uptake, but the importance of nitrate (NO3−) for rice (Oryza sativa L.) and microbiota is often neglected in acidic paddy soils where ammonium (NH4+) is dominant. This study aimed to explore the differential effects of NH4+ and NO3− on rice growth, fertilizer nitrogen recovery efficiency (FNRE), and rhizosphere bacterial community in acid soil. Methods: Two rice varieties, Kasalath (Al-sensitive indica) and Koshihikari (Al-tolerant japonica), were exposed to different N sources with or without lime in an acid soil. Results: Liming and NO3− application solely improved the growth and FNRE of the Al-sensitive rice, namely, by increasing soil pH and alleviating Al toxicity. Compared with liming and rice variety, N source had a more pronounced influence on rhizobacterial community composition. Of the two sources, NO3− had a stronger effect on the rhizobacterial community than NH4+. Remarkably, rice plants fed with NH4+ specifically recruited Desulfosporosinus and Desulfitobacterium associated with ferric NH4+ oxidation in the rhizosphere, whereas those exposed to NO3− recruited Alicyclobacillus with NO3−-reducing iron oxidation ability. Three keystone taxa were identified in a rhizobacterial co-occurrence network analysis: Alicyclobacillus, which was positively associated with rice growth and FNRE, and Acidobacteriales and WPS-2, both with negative associations. Conclusion: Compared with NH4+, NO3− enhances the growth and FNRE of Al-sensitive rice and exerts dominant effects on the rhizobacterial community, which indicates the importance of NO3− for rice and has instructive implications for N management in acid soil. [ABSTRACT FROM AUTHOR]

Aims: Low molecular weight soluble compounds in rhizosphere soils are important composition of soil organic carbon, which are mainly derived from root exudates and easily affected by biological and abiotic factors. Here, we investigated the effect of arbuscular mycorrhizal fungi (AMF, Funneliformis mosseae) on soluble sugars, flavonoids, and phenolic acids in the rhizosphere soil of black locust seedlings grown under elevated CO2 and Cd-contaminated soils. Results: F. mosseae decreased (p < 0.05) contents of mannose, glucose, galactose, arabinose, total flavonoids, quercetin, total phenolic acids, gallic acid, chlorogenic acid, p-hydroxybenzoic acid, and caffeic acid in rhizosphere soils under elevated CO2 + Cd; however, the concentration of p-coumaric acid increased (p < 0.05). Additionally, F. mosseae led to significant decreases in mannose, galactose, quercetin, gallic acid, chlorogenic acid, and p-hydroxybenzoic acid in roots under elevated CO2 + Cd; however, glucose content in roots increased (p < 0.05). Contents of small compounds in roots significantly affected low molecular weight soluble compounds in rhizosphere soils, and F. mosseae colonization rate and rhizosphere soil C, pH, and DTPA-Cd significantly influenced the accumulation of low molecular weight soluble compounds. Conclusions: F. mosseae colonization significantly decreased the accumulation of low molecular weight soluble compounds in the rhizosphere of black locust under elevated CO2 + Cd, leading to significant increases in pH and Cd content in rhizosphere soils, which could improve our understanding of the regulation of AMF on rhizosphere soil carbon pool and the migration of heavy metals under elevated CO2 scenarios. [ABSTRACT FROM AUTHOR]

Background and purpose: The fertility of anthropogenic soils developed from dumpsites used for arable fields is not well-studied. The study aimed to evaluate the fertility of anthropogenic soils from an abandoned dumpsite in Awotan, Nigeria, by measurable indicators and the bioaccessibility of elements of selected plant species. Methods: The study adopted multi-analytical approaches to determine the signatures of the soils and further parameterized the bioaccessibility of elements to plants. Results: The comparatively high content of Ca and Na in the anthropogenic soil contributed to the slightly alkaline soil reaction against the slightly acidic control. The high amount of organic matter is well-indicated by the enrichment of organic C and N in the anthropogenic soil. Waste deposition significantly contributed to the high accumulation of macronutrients (P, Ca, K, S) and micronutrients (Mn, Na, Fe) sufficient for maximum plant growth and yields, with an adequate C/N ratio supporting effective mineralization. The high cation exchange capacity of the anthropogenic soil contributed to cations binding. Indiscriminate waste deposition resulted in a high accumulation of potentially toxic elements (PTEs; Cu, Zn, As, Cd, Pb) above permissible limits in agricultural soils following WHO limits. Potential effects on lives are evident in the high PTEs accumulation in roots and leaves of Chromolaenaodorata, Saccopetalumtectonum, Passiflorafoetida, and Sennasiamea. These plant species exhibited various PTEs accumulation, especially for Cd and Pb. Conclusion: Although anthropogenic soils remained fertile, the bioaccessibility of PTEs by plants indicates potential threats to consumers of crops and herbs produced from such sites. [ABSTRACT FROM AUTHOR]

Aims: Nitrate content in crops might be affected by soil abiotic properties and endophytic and soil microbes. This study aimed to reveal the effects of spent mushroom substrate (SMS) and nitrification inhibitor dicyandiamide (DCD) and 3,4-dimethylpyrazole phosphate (DMPP) on the nitrate content of pepper fruit and to link the nitrate with soil abiotic properties and endophytic and soil bacterial communities. Methods: Our current study contained four different treatments: blank control (CK); sole SMS application (SAA); SMS + DCD (SDCD); and SMS + DMPP (SDMPP). The nitrate contents and bacterial communities in fruit, root and soil samples were quantified and linked. Results: Compared with the CK treatment, the nitrate contents of pepper fruit decreased by 43.2%, 66.8% and 64.4% in the SAA, SDCD and SDMPP treatments, respectively. The combined applications of SMS and nitrification inhibitors significantly enhanced the pH and bacterial community diversity of soil samples. The SMS applications significantly changed bacterial community structures in the soils and roots rather than in the fruit. The relative abundances of aerobic chemoheterotrophy function in the fruit samples were 0.28, 0.17, 0.10 and 0.15 for the CK, SAA, SDCD and SDMPP treatments, respectively. The relative abundances of Bacteroidetes and aerobic chemoheterotrophy were significantly and positively correlated with nitrate contents in the fruit. Conclusions: Apart from promoting fruit yield, the SMS and nitrification inhibitor applications could also decrease the health risk of crop nitrate accumulation via affecting the soil pH, ammonium content and endophytic bacterial community diversity, structures and functions in fruit samples. [ABSTRACT FROM AUTHOR]

Purpose: Nitrogen (N) and sulphur (S) are essential for plant growth and development. Cysteine (Cys) and methionine (Met) are N- and S-containing amino acids in soils. However, it is unclear whether plants possess a strong ability to utilise N- and S-containing amino acids from the plant physiology perspective, and whether they can access amino acids when facing rapid microbial decomposition in the soil. Methods: Wheat and oilseed rape were cultivated using a sterilised hydroponic solution in the laboratory and field conditions with 13C-, 14C-, 15N-, and 35S-labelled Cys and Met. Results: With sterilised hydroponic cultivation, wheat and oilseed rape possessed a greater ability for Cys and Met uptake than for SO42− uptake, but these compounds did not support plant growth at high concentrations. The uptake rate of Cys and Met in oilseed rape was almost 20-fold higher than that in wheat, while the transportation ratio was even higher, indicating that oilseed rape not only possesses a great ability for S-containing amino acid uptake but also metabolises and transports them to the shoot quickly. A short-term labelling uptake test (6 h) in the field showed that 0.6–2.2% of total added Cys and Met were utilised by wheat and oilseed rape in the intact form owing to fierce competition from soil microorganisms. Conclusions: Wheat and oilseed rape possess a great ability for Cys and Met uptake but can access limited amounts owing to rapid microbial decomposition in soil. [ABSTRACT FROM AUTHOR]

Background and aims: Liming is widely used to alleviate soil acidity worldwide. However, the vast majority of studies with liming are restricted to agricultural systems that incorporate lime into the soil, not considering its effects as surface applications. Although liming effects on soil fertility and crop yield are well understood, there are few studies that elucidate the role of soil improvements in the established crop physiology and the revenue in lime-amended soils, especially when cultivated in regions prone to agroclimatic risks. Here, we address the effects of surface liming, for three growing seasons (2017–2019) subsequent to the lime treatment (2016), on soil fertility, root growth, crop nutrition, photosynthetic pigment concentrations, gas exchange parameters and production costs of maize cultivated in a tropical region on an acidic soil with low water regime. Methods: The treatments consisted of four dolomitic lime doses applied to the soil surface as follows: i) control (untreated soil), ii) half the recommended dose (½ RD), iii) full recommended dose (1 RD) and iv) twice the recommended dose (2 RD). Results: Surface liming increased soil fertility, and higher doses provided better results. Ca2+ and Mg2+ concentrations increased at greater depths under higher lime doses, directly influencing maize root growth. Even under low water availability, also in the driest year of 2018, this liming induced improvement of growing conditions and increased growth was observed'. Maize grown under lime at 2 RD exhibited better nutrition, improved chlorophylls concentration, photosynthetic parameters and water use efficiency. As a result, both shoot growth and grain yield also increased. Net profit in the first growing season was higher in 1 RD, whereas in the two following growing seasons the application of 2 RD resulted in higher revenue. Conclusions: Increased water use efficiency, chlorophyll and photosynthesis were the main physiological traits regulating the growth and yield of maize plants in response to lime supply. Additionally, root development was favoured in the entire soil profile, mainly in deeper layers, after improvements on soil fertility by cascading effects of liming. These results were more prominent in 2RD lime-amended soil, which also resulted in greater net profit over the 3 years studied. [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]

Purpose: Increasing the pH of acid soils is a well-recognized means of improving their fertility; however, the effects that plants impose on rhizosphere soils in response to this change are not well understood. This research sought to investigate changes in phosphorus (P) availability in the rhizosphere of blue lupin (Lupinus angustifolius) in response to an increase in pH. Methods: Blue lupin plants were grown in rhizoboxes using two contrasting acid soils at their native pH (5.3 and 4.7) and treated with lime to increase their pH to 6.3 in a replicated trial. Measurements of localized acid phosphomonoesterase activity and P flux were made next to lateral root segments using a combination of zymography and diffusive gradient in thin films (DGT). Rhizosphere and bulk soils were tested for pH, organic anions, exchangeable aluminium (Al), labile P and phosphomonoesterase activity. Root morphological traits, root and shoot yields and shoot nutrient concentrations were also recorded. Results: Profiles of DGT-P fluxes across lateral roots showed mobilization of P in the soil with the higher organic P content, and depletion in the other. The extent of acid phosphomonoesterase activity in the rhizosphere decreased with soil pH increase. Shoot P uptake was strongly correlated with fine root length and total organic anions in the rhizosphere. The proportion of thin roots decreased at pH 6.3 compared to the native pH, whereas that of thick roots increased. Conclusion: Soil pH increase to 6.3 using lime negatively affects the P acquisition by blue lupin due to the reduction of organic anion exudation, fine root length and the extent of acid phosphomonoesterase activity in the rhizosphere. [ABSTRACT FROM AUTHOR]

Aims: Aluminium toxicity in acidic soils adversely affects wheat growth. Foliar-applied magnesium (Mg) contributes to mitigating soil acidity stress in wheat, but the mechanisms are unknown. This study explored the mechanism of foliar-Mg mediated enhancement of wheat growth in acidic soil. Methods: Two contrasting near-isogenic wheat (Triticum aestivum L.) genotypes differing in Al resistance (Al-sensitive ES8 and Al-resistant ET8) were grown to the vegetative stage (Zadoks 24) in a reconstituted acidic soil (pH0.1 M CaCl2 4.0) profile with three rates of foliar Mg (0, 200 and 500 mg Mg L− 1 using MgSO4.7H2O). Magnesium was applied to the foliage twice [14 and 28 days after sowing (DAS)], and plant growth and root exuded carboxylates were measured up to 42 DAS. Results: Applying 200 mg Mg L− 1 to the foliage increased organic acid anion exudation from wheat roots by ~ 2-fold compared to 0 foliar Mg treated plants. The Al-resistant wheat genotype exuded 1.3-fold more malate and citrate from roots than the Al-sensitive genotype in the absence of foliar Mg. Malate exudation was delayed relative to citrate following foliar Mg application. The foliar-applied Mg increased shoot and root dry weight (by ~ 38 %), total root length (by ~ 33 %) and intrinsic water-use efficiency (by ~ 80 %) compared to plants treated with no Mg. Applying foliar Mg decreased soil acidity stress (as shown by a significant increase in chlorophyll fluorescence Fv/Fm ratio) in wheat compared to 0 foliar Mg. Conclusions: Increased malate and citrate exudation is the underlying mechanism of enhanced wheat growth following foliar Mg application under acidic soil conditions. [ABSTRACT FROM AUTHOR]

Discusses the mean cover, biometric and vitality parameters and mineral nutrient status of wood-sorrel (Oxalis acetosella L.) control and experimental plots of a mature Norway spruce stand on acid soil. Impact of Oxalis's presence on the control plot on leaf growth of the plant; Effects of dolomitic liming on Oxalis; Response shown by Oxalis in the presence of acid concentrations.

Background and aims: Mine tailings are challenging substrates for ecological restoration, as the establishment of diverse native plant communities can be constrained by a range of edaphic factors. Thus, the ability to restore native vegetation communities will depend upon developing a clear evidence-base as to what types of species and communities are likely sustainably reinstated on such altered substrates. As global tailings production and the cumulative footprint of tailings storage facilities continue to grow, understanding the effect of edaphic filters on community establishment is foundational for developing effective restoration solutions for tailings. Methods: We standardised growth rate estimates derived from nine root and shoot parameters for plants grown in magnetite tailings and natural topsoil, using crops (eight species) to characterise previously identified plant responses and native plants (40 species) to understand the impact of edaphic conditions on the species pool available for restoration. Results: The edaphic conditions of unweathered magnetite tailings select against the majority of native plant species and nutrient-acquisition guilds (approximately 75% of reference floristic biodiversity), with plant development on tailings compared with natural topsoil compromised in a number of variables in all but six species. Plant growth on tailings was limited by a lack of available nitrogen (N) and high alkalinity (pH >9), and seedling growth and development was positively associated with seed N concentration. Calcicole species and species from N2-fixing and cluster root-producing strategies performed better on tailings than calcifuge species and species without specialised nutrient-acquisition strategy or those reliant upon mycorrhizal associations. Conclusions: The return of plant communities native to highly weathered, acidic soils on magnetite tailings is likely unsuccessful, unless strategies to ameliorate substrate hostility through acidification of the soil profile and improving N availability are prioritised. [ABSTRACT FROM AUTHOR]

Aims: The purpose of this study was to clarify how the morphological traits of Chamaecyparis obtusa (Sieb. & Zucc.) Endl. roots vary with soil acid buffering capacity (ABC), i.e., along a gradient in soil acidification. We used an order-based root classification system instead of a diameter-based root classification system, as the former relates better to root function. Methods: We sampled 210 intact fine root systems up to the fourth order and measured the morphological traits of a total of 16,657 individual branch-order roots in three C. obtusa stands with high soil ABC and four stands with low soil ABC. Results: We found significant differences in the morphological traits of the first- to fourth-order roots between the soil ABCs. In the low-ABC soils, the fine root systems consisted of more and thinner roots than in the high-ABC soils. The diameter of the second-order roots was positively correlated with the soil pH and the concentration of base cations, but negatively with soil aluminum. Conclusion: Morphological traits of fine roots are sensitive indicators of soil acidification in C. obtusa forests. [ABSTRACT FROM AUTHOR]

Background and aims: Subsoil acidity with a high aluminium (Al3+) soil content inhibits root growth and proliferation of durum wheat (tetraploid AABB, Triticum turgidum) leading to poor nutrient and water uptake. This study evaluated the impact of Al3+-tolerantTaMATE1B allele on root and shoot traits of durum wheat grown in an acidic soil with a high Al3+concentration. Methods: Two durum wheat lines, Jandaroi–TaMATE1B with the TaMATE1B gene introgressed from Al3+-tolerant bread wheat and Jandaroi–null (a sister line lacking the Al3+-tolerant TaMATE1B allele), were grown in rhizoboxes in a glasshouse. We mapped root growth and proliferation over time and measured shoot traits and grain yield. Results: Introgression of the Al3+-tolerant TaMATE1B allele into durum wheat enabled root growth and proliferation below 0.25 m of the soil profile, where the soil pH was low (4.1, CaCl2 extract) with high Al3+ content (16.5 mg kg−1), and increased total root length and biomass at 42 days after sowing (DAS; Z33) by 38.3 and 22%, respectively, relative to the Jandaroi–null. Differences in root growth between the two lines were apparent from tillering stage (Z33) and by 50% anthesis (Z64), respectively. Jandaroi–TaMATE1B had 69.2% greater root biomass, 76.2% greater root length, 5.89% greater leaf area and 18% greater shoot biomass than Jandaroi–null at 50% anthesis (Z64). Time to anthesis and physiological maturity was delayed 6–7 days in Jandaroi–TaMATE1B, compared to Jandaroi–null. Jandaroi–TaMATE1B tended to have relatively greater, but not significantly different, shoot biomass, grain yield and yield components than Jandaroi–null. Conclusions: Introgression of the Al3+-tolerant TaMATE1B allele into durum wheat enabled root growth and proliferation down an acidic soil profile with a high Al3+ concentration. We assume that in the field where plants need to acquire water at depth differences in above-ground parameters would be amplified. [ABSTRACT FROM AUTHOR]

Background and aims: Although phosphorus (P) application is known to affect the zinc (Zn) nutrition of crops, the underlying mechanisms and effects of soil type are unclear.Methods: A greenhouse pot experiment was conducted with wheat, two soils (calcareous and acid), and nine P fertilizer rates (0, 50, 100, 200, 400, 1000, 2000, 3000, and 5000 mg P2O5 kg−1 soil).Results: The effects of P application on the Zn content of shoots and roots in wheat and on the levels of available Zn in soil differed on the two soils. The wheat dry weight on both soils was highest with 2000 mg P2O5 kg−1. Total Zn accumulation was reduced above 2000 mg P2O5 kg−1 on the acid soil and above 100 mg P2O5 kg−1 on the calcareous soil. Available soil Zn declined when the Bray-P concentration reached about 34 mg kg−1 in the acid soil and when the Olsen-P concentration exceeded 200 mg kg−1 in the calcareous soil. Shoot Zn concentrations were negatively related to available soil P on the two soils.Conclusion: The negative effects of increasing P application rates on Zn accumulation by wheat differed between the two soils. The effects showed no close relationship to available soil Zn. [ABSTRACT FROM AUTHOR]

Aim: A major limitation to plant growth in acid soils is the prevalence of toxic Al3+. Most genotypic variation for acid soil-tolerance in wheat is linked with the Al3+-activated efflux of malate anions from roots which is controlled by TaALMT1 on chromosome 4DL. Recent studies have also linked TaALMT1 with tolerance to high pH solutions and alkaline soils. This study tested the hypothesis that an Al3+-resistant allele of TaALMT1 also confers tolerance to alkaline conditions.Methods: The near-isogenic wheat lines, ET8 (Al3+-resistant) and ES8 (Al3+-sensitive), have different alleles of the TaALMT1 gene and contrasting resistance to Al3+ toxicity. Growth of these lines was compared in acid and alkaline soils with contrasting mineralogy and in a range of high pH hydroponic solutions of varying composition.Results: No consistent differences in root or shoot growth were detected between the lines in the alkaline soils or in the high pH hydroponic treatments. Malate efflux was detected from ET8 in acidic solution with Al3+ but no substantial malate efflux was detected at pH 9.0 treatment with added Na2SO4.Conclusion: The results are inconsistent with the hypothesis that the TaALMT1 gene confers an advantage to wheat on alkaline soils. [ABSTRACT FROM AUTHOR]

Aims: Panax notoginseng is normally cultivated in acidic red soil with high soluble Al, however, the distribution pattern of Al in P. notoginseng is unknown. The aim of this study is to investigate the Al distribution in different organs of P. notoginseng grown in different acid soil, in order to get a deeper insight into the Al tolerance mechanism in this species.Methods: P. notoginseng was sampled from different sites and subjected to Al determination. Al tolerance and accumulation were investigated by exposing the seedlings to different Al concentrations in hydroponic solution. The expression of pectin methylesterase genes was determined by quantitative RT-PCR.Results: The soil pH ranged from 4.68 to 6.13. The total Al concentration in soil was 76.7-168.5 g·kg−1 and active Al was 1.34-5.01 g·kg−1. Al concentration differed with organs of P. notoginseng, following the order: rootlet > rhizome > main root > leaf and stem. Furthermore, Al concentration in the cell wall, organelle and cytoplasmic supernatant of P. notoginseng was approximately 15:2:1 and most Al in the cell wall was bound to pectin component. Al treatment significantly increased the content of pectin and enhanced the expression of PME3, PME7, and PME40 of P. notoginseng root.Conclusions: P. notoginseng was able to grow under high active Al condition and accumulated high Al in its underground parts. The pectin component in the cell wall was the major binding site of Al of P. notoginseng root. [ABSTRACT FROM AUTHOR]

Background and aims: Acidic soil occupies 30% of the world's ice-free land, and exchangeable aluminum (Al) availability increases under these conditions, being toxic to many plant species. However, some plants accumulate Al without damage to their metabolism. Vochysia tucanorum is an Al-accumulating species endemic to the cerrado vegetation with acidic soils in South America. Here, we predict that it is a calcifuge species. Methods: We assessed macro and micronutrient concentrations as well as Al accumulation, plant height and root length of potted plants grown on acidic and calcareous soil for 60 days. A LC-MS-based metabolite fingerprinting of plants on both conditions was also performed. Results: Plants grown on acidic soil showed higher biomass and Al concentration in roots and shoots than those grown on calcareous soil. Despite the higher concentration of macronutrients on plants grown on calcareous soil, micronutrients concentration was similar between plants grown on these soils. Plants grown on the calcareous soil showed necrotic leaves. The metabolite fingerprinting indicated significant changes in the metabolism of phenolics and organic acids. Conclusions: Due to the high Al accumulation in plants grown on acidic soil, and their inability to survive in calcareous soil, we conclude that V. tucanorum is an Al-accumulating species with calcifuge behavior. [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: Acid soils constrain legume growth and biochars have been shown to address these constraints and enhance biological N fixation in glasshouse studies. A dissection of causal mechanisms from multiple crop field studies is lacking. Methods: In a sub-tropical field study, faba bean ( Vicia faba L.) was cultivated in rotation with corn ( Zea mays) following amendment of two contrasting biochars, compost and lime in a rhodic ferralsol. Key soil parameters and plant nutrient uptake were investigated alongside stable N isotope methodologies to elucidate the causal mechanisms for enhanced biological N fixation and crop productivity. Results: Biological N fixation was associated with plant Mo uptake, which was driven by reductions in soil acidity following lime and papermill (PM) biochar amendment. In contrast, crop yield was associated with plant P and B uptake, and amelioration of soil pH constraints. These were most effectively ameliorated by PM biochar as it addressed both pH constraints and low soil nutrient status. Conclusions: While liming resulted in the highest biological N fixation, biochars provided greater benefits to faba bean yield by addressing P nutrition and ameliorating Al toxicity. [ABSTRACT FROM AUTHOR]

Background and aims: Biochar has demonstrably improved crop yields in weathered and acidic soils, but studies in calcareous soils are particularly lacking, so biochar effects on plant growth was investigated under these conditions. Methods: Six biochars were obtained from different feedstocks and production technologies. Chemical characterization of fresh biochars included total and extractable nutrients, labile carbon, and Fourier transform infrared spectroscopy. Extractable nutrients were also evaluated in biochar-soil mixtures with a basic (pH >8.2) test soil. Bioassays with lettuce and ryegrass were carried out to relate biochar chemical properties to effects on plant biomass. Results: A sewage sludge slow pyrolysis char was stimulatory to plant growth, as was a slow pyrolysis pine wood char at an intermediate concentration, while gasification and fast-pyrolysis pine and poplar wood chars were strongly inhibitory, with reductions in biomass at realistic application rates of 5-19 t ha. Conclusions: Statistical comparison of plant responses with biochar composition led to the assessment that plant responses were most correlated with volatile matter content and total P content, whose availability was likely regulated by pH and Ca content. Potential effects of phytotoxins were considered, but these were seen to be much less probable than effects due to nutrient availability. [ABSTRACT FROM AUTHOR]

Background: Aluminum (Al) toxicity has limited the productivity and expansion of cereal crops on acid soils; however, a number of plant species or cultivars have developed different strategies for detoxifying aluminum both internally and externally. Scope: This review focuses on recent progress on molecular mechanisms of Al tolerance in gramineous plants. Conclusions: A common mechanism in all gramineous plants is the secretion of organic acid anions (citrate and malate) from the roots. Genes belonging to ALMT (for Aluminum-activated malate transporter) and MATE ( Multidrug and toxic compound extrusion) family involved in the secretion have been identified in several plant species; however, different plant species show different gene expression patterns including Al-induction, spatial and temporal expression, and tissue localization. Furthermore, the mechanisms regulating the gene expression also differ with plant species, which are achieved by increased tandem repeated element, increase of copy number, insertion of transposon, or alteration of cis-acting element. In addition to these common Al exclusion mechanisms, rice as a highly Al-tolerant species has developed a number of other mechanisms for detoxification of Al. A transcription factor for Al tolerance ART1 identified in rice regulates at least 30 genes implicated in internal and external detoxification of Al. These multiple genes may contribute to the high Al tolerance of rice. In the future, regulation mechanisms of Al-tolerance genes need to be further investigated. [ABSTRACT FROM AUTHOR]

Background and purpose: To date, very few studies have investigated the effects of litter decomposition on gross nitrogen (N) transformations and N retention in subtropical forest soils. In this study, six forest soils were taken from two contrasting forest types (broad-leaved vs. coniferous) in the humid subtropical zones of China to investigate the effects of litter decomposition on gross N transformations. Methods: A N tracing experiment was conducted to investigate the effects of litter decomposition (at a rate of 0.5 % w/w) on soil gross N transformations rates in broad-leaved and coniferous forests. Results: Litter decomposition enhanced gross N mineralization and NH immobilization rates by 45.9-79.0 % and 553-563 %, respectively. There was a shift from net N mineralization to net N immobilization in each of the forest soils, which was due to litter decomposition. In contrast, gross nitrification rates were unaffected by litter decomposition for each of the forest soils, while gross NO immobilization rates were stimulated significantly by litter decomposition in broad-leaved forest soils but not in coniferous forest soils. On average, 39.4 % of the total NO produced was immobilized into organic-N in broad-leaved forest soils due to litter decomposition. Therefore, the decrease in net nitrification rates caused by litter decomposition was attributed to increasing gross NO immobilization rates rather than decreasing gross nitrification rates. During 15 days of incubation, the decomposition of litter increased cumulative NO emissions by 55-76 % and 100-640 % in broad-leaved forest and coniferous forest soils, respectively, but there was no effect on the cumulative NO emissions for both forest soil types. Conclusions: The combined results suggest that the decomposition of litter stimulates NO emissions but reduces NH and NO accumulation in forest soils, and thus a delay in N availability for plant N uptake or leaching. [ABSTRACT FROM AUTHOR]

Background: Aluminium (Al) toxicity and drought stress are two major constraints for crop production in the world, particularly in the tropics. The variation in rainfall distribution and longer dry spells in much of the tropics during the main growing period of crops are becoming increasingly important yield-limiting factors with the global climate change. As a result, crop genotypes that are tolerant of both drought and Al toxicity need to be developed. Scope: The present review mainly focuses on the interaction of Al and drought on root development, crop growth and yield on acid soils. It summarizes evidence from our own studies and other published/related work, and provides novel insights into the breeding for the adaptation to these combined abiotic stresses. The primary symptom of Al phytotoxicity is the inhibition of root growth. The impeded root system will restrict the roots for exploring the acid subsoil to absorb water and nutrients which is particularly important under condition of low soil moisture in the surface soil under drought. Whereas drought primarily affects shoot growth, effects of phytotoxic Al on shoot growth are mostly secondary effects that are induced by Al affecting root growth and function, while under drought stress root growth may even be promoted. Much progress has recently been made in the understanding of the physiology and molecular biology of the interaction between Al toxicity and drought stress in common bean ( Phaseolus vulgaris L.) in hydroponics and in an Al-toxic soil. Conclusions: Crops growing on acid soils yield less than their potential because of the poorly developed root system that limits nutrient and water uptake. Breeding for drought resistance must be combined with Al resistance, to assure that drought resistance is expressed adequately in crops grown on soils with acid Al-toxic subsoils. [ABSTRACT FROM AUTHOR]

Background and aims: Iron toxicity decreases rice ( Oryza sativa) grain yield especially in acid soils after flooding. Our aim was to establish a high-throughput screening technique using nutrient solution culture for identifying Fe-toxicity-tolerant genotypes. Methods: Varying levels of Fe, pH, and chelators in Yoshida nutrient solution culture were tested to maintain sufficient Fe concentration over time to optimize the severity of Fe toxicity stress for distinguishing between a tolerant (Azucena) and sensitive (IR64) genotype. The optimized solution was tested on 20 diverse genotypes in the greenhouse, with measurement of leaf bronzing scores and plant growth characteristics at the seedling stage. The same 20 genotypes were grown to maturity in a field with natural Fe toxicity stress, with measurement of seedling-stage leaf bronzing scores and grain yield to determine their inter-relationship. Results: Optimized nutrient solution conditions were 300 mg L Fe supplied as Fe at pH 4.0 with a 1:2 molar ratio of Fe:EDTA, which maintained sufficient Fe stress over 5 days. The highest correlation of nutrient solution phenotypic data with field grain yield was found with leaf bronzing scores at 4 weeks, with a Pearson r of 0.628 for simple association and a Spearman corrected r of 0.610 for rank association ( P < 0.01) using 20 diverse rice genotypes with proven Fe toxicity tolerance reaction. The Leaf bronzing scores at 4 weeks in nutrient culture solution were also found highly correlated with LBS under natural field stress after 8 weeks that had highest correlation with grain yield under stress. Conclusion: This culture solution-based standardized screening technique can be used in plant breeding programs as a high-throughput technique to identify genotypes tolerant to Fe toxicity. [ABSTRACT FROM AUTHOR]

Aims: The aim of this study was to compare the residual effects in soil and the influence on a flax crop ( Linum usitatissimum L.) of applying Zn from different commercial synthetic chelates. The chelates used were: Zn-EDDHSA (Zn-ethylenediamine-N,N'-bis(2-hydroxyphenylacetate), Zn-EDTA (Zn-ethylenediaminetetraacetate), Zn-HEDTA (Zn-N-2-hydroxyethyl-ethylenediaminetriacetate), Zn-EDTA-HEDTA and Zn-DTPA-HEDTA-EDTA (Zn-DTPA, Zn-diethylenetriaminepentaacetate). Methods: The experiment was conducted in a greenhouse using two different soils (Soil: a weakly acidic soil and Soil: a calcareous soil). Each treatment was administered, in a single application, to a previous flax crop at different Zn application rates. The yield and some of the flax crop quality parameters were determined in the present flax crop. Soil Zn behavior was then evaluated by single and sequential extraction. Results: In Soil, the Zn-HEDTA and Zn-EDDHSA fertilizers produced the highest plant parameters values (total Zn concentration, total uptake Zn), percentages of Zn utilization and values of the transfer factor, TF. In contrast, in Soil these fertilizers produced the lowest in-plant values, with this soil producing the highest yield, quality, percentage of utilization and TF associated with the application of Zn-DTPA-HEDTA-EDTA and Zn-EDTA fertilizers. However, the Zn-EDTA in Soil and Zn-DTPA-HEDTA-EDTA in Soil, were associated with the greatest amounts of bioavailable Zn in soil and also with the highest Zn concentrations associated with the sum of the most labile fractions (water soluble plus exchangeable fractions). Conclusions: The residual Zn produced by the different fertilizer treatments estimated using the DTPA, Mehlich-3- and LMWOAs methods- was available in sufficient quantities that it not be necessary to add any further Zn (which could have resulted in over-fertilization) for the subsequent crop to either of the soils. [ABSTRACT FROM AUTHOR]

Aims: The high concentrations of Mn, Fe and Al in acid soils during waterlogging impair root and shoot growth more severely in intolerant than tolerant wheat genotypes. This study aims to establish whether this difference in vegetative growth and survival during waterlogging (1) is verifiable across a range of tolerant/intolerant genotypes and acid soils, and (2) results in improved recovery after cessation of waterlogging and enhanced grain yield. Methods: Wheat genotypes contrasting in their tolerance to ion toxicities were grown in four acid soils until 63DAS and maturity, with a 42-day waterlogging treatment imposed at 21 DAS. Results: The shoot Al, Mn and Fe concentrations increased by up to 5-, 3- and 9-fold respectively due to waterlogging in various soils. Compared to the intolerant lines, Al-, Mn- and Fe-tolerant genotypes maintained a relatively lower increase in shoot concentrations of Al (79 vs. 117%), Mn (90 vs. 101%) and Fe (171 vs. 252%) and demonstrated better waterlogging tolerance at the vegetative stage expressed in relative root (38% vs. 25%) and shoot (62% vs. 52%) growth. After cessation of waterlogging and the continued growth to maturity, tolerant genotypes maintained a relatively lower plant concentration of Al, Mn and Fe, but produced a higher above-ground biomass (74% vs. 56%) and most importantly demonstrated improved waterlogging tolerance (a relative grain yield of 78% vs. 54%) compared to intolerant genotypes. Maturity following waterlogging stress was delayed less in tolerant than intolerant genotypes (114 vs. 124%, respectively), which would reduce the potential yield loss where post-anthesis coincides with drought. Conclusions: The results confirm the validity of a novel approach of enhancing waterlogging tolerance of wheat genotypes grown in acid soil via increased tolerance to ion toxicities. [ABSTRACT FROM AUTHOR]

Effects of soil pH on damping-off of sugar beet by R. solani (AG2-2) and soil suppressiveness against the disease were studied by comparing disease incidences in pasteurized versus non-pasteurized, infested soils. Soil pH was correlated neither to disease incidence in five soils ranging from pH 4.5 to 7.2 nor to indigenous disease suppressiveness, the difference in disease incidences between non-treated soil and its pasteurized counterpart. When an alkaline soil was acidified with HSO, disease suppression markedly declined, increasing disease incidence in the non-pasteurized soil. Inversely, disease suppression was enhanced when an acidic soil was neutralized by adding Ca(OH). Soil amendment with dried peanut plant residue suppressed the disease in two pasteurized, near-neutral soils, lowering the incidence to the levels in the non-pasteurized soils, but was less effective in two pasteurized, acidic soils. In vitro mycelial growth of the pathogen and seedling growth was optimal at pH 4.5-5.5 and 6.0-6.5, respectively, and declined as the pH became higher or lower. (Conclusions) These results suggest that the seedlings were inhibited more than the pathogen at low pH, and that indigenous disease suppressiveness through the activity of antagonistic soil microorganisms operates effectively in near-alkaline soils, but is weakened or nullified in acidic soils. [ABSTRACT FROM AUTHOR]

Indole-3-acetic acid (IAA) has been found to be involved in plant resistance to various types of environmental stress. Aluminum (Al) toxicity, as one of the most important environmental stress in acid soils, is coped by most plants through the efflux of organic acids via anion channel. This study aims to evaluate the effect of IAA on efflux of malic acid from wheat ( Triticum aestivum L.) under Al stress. Hydroponic experiments were performed by wheat ET8 (Al-tolerant). The efflux of malic acid was investigated under different treatments. Results showed that Al treatments increased the accumulation of endogenous IAA, but decreased the activity of IAA oxidase in a dose-dependent manner. A good correlation between all the data of malic acid efflux rate and endogenous IAA content was obtained (R = 0.9859**). IAA treatment alone had no effect on the efflux of malic acid. But compared to Al (50 μM) treatment, the efflux of malic acid increased significantly under the co-treatment of IAA (50 μM) and Al (50 μM). In split-root experiments, the root with half of it being treated with Al (CK/Al), the other part (CK) showed significantly higher malic acid efflux rate and endogenous IAA content in root apexes, compared with the root without such treatment (CK/CK). The Al-induced malic acid efflux decreased under the treatments of IAA transport inhibitor N-1-napthyl-phtalamic acid (NPA) (or 2,3,5-triiodobenzoic acid, TIBA). These above results suggested the possible involvement of IAA in the stimulation of malic acid efflux under Al stress. In addition, anion channel inhibitor treatment experiment showed that IAA (50 μM) relieved the inhibiting effect of 5 μM anthracene-9-carboxylic acid (A9C) (or niflumic acid, NIF) on malic acid efflux induced by Al (50 μM), compared to the co-treatment of Al (50 μM) and 5 μM anion channel inhibitor A9C (or NIF) it is thus speculated that the anion channel might have been activated when IAA was involved in malic acid efflux. This study showed that IAA was involved in aluminum-induced efflux of malic acid from wheat. [ABSTRACT FROM AUTHOR]

Perennial pasture species are important for sustainable pasture systems; yet some species display poor persistence on acid soils. This work investigated the effect of soil acidity on primary root length and root-hair and rhizosheath development of five perennial grass genotypes varying in acid-soil resistance. Plants were grown in three low-P acid soils that were limed (CaCO) to modify soil pH (0.01 M CaCl extractable) from <4.3 to >5.0 and Al concentrations from ≥ 16 to <4 mg kg (0.01 M CaCl extractable). Root morphology of tall wheatgrass ( Thinopyrum ponticum (Podp.) Z.-W. Liu & R.-C Wang), phalaris ( Phalaris aquatica L.), cocksfoot ( Dactylis glomerata L.) and weeping grass ( Microlaena stipoides Labill. R. Br.) was assessed after 20–25 days growth. The root length of tall wheatgrass and phalaris cv Sirosa was sensitive to acidity, with lateral root length more sensitive to acidity than seminal root length. Lime increased the root-hair length and density of both acid-soil sensitive and resistant genotypes (cocksfoot and an acid-resistant line of phalaris) and root-hair length was positively correlated to an increase in rhizosheath size per unit root length. Restricted root length and poor root-soil contact of acid-soil sensitive genotypes may explain their low yield and relatively poor persistence on acid soils. The improvement to root-hair and rhizosheath development of genotypes that are acid-soil resistant in terms of root length demonstrates the benefit of using resistant genotypes in conjunction with liming to manage acid soils. Weeping grass was exceptional in its ability to maintain root length, root-hair and rhizosheath development in acid soil. [ABSTRACT FROM AUTHOR]

Field experiments in calcareous and acidic field soils were conducted to study the effects of copper (Cu) and nickel (Ni) added to soils on maize growth and metal accumulation in maize plants. The results revealed that the critical concentrations of Cu added to soils that decreased maize grain yield by 10% (EC10) were 711 mg kg−1 for calcareous soil with a pH of 8.9, and 23 mg kg−1 for acidic soil with a pH of 5.3. The toxicity thresholds of EC10 did not differ significantly for Cu and Ni. A different pattern of Cu and Ni accumulation in maize plants was also found. The accumulation of Cu in above-ground parts of the plants increased initially as the concentrations of Cu added to soils increased, after which they decreased to a constant level. As the concentrations of Ni added to soils increased, the accumulation of Ni in stems and leaves increased linearly, but the accumulation of Ni in the grains was nonlinear. Additionally, the results revealed that Ni was transported to grains more easily than Cu. The results also showed that the concentrations of Cu and Ni in soil solutions as toxicity predictors and the critical concentrations of Cu and Ni in maize were all soil-dependent. [ABSTRACT FROM AUTHOR]

A greenhouse experiment was conducted on weakly acidic and calcareous soils to evaluate the relative efficiencies of three natural Zn chelates [Zn-aminelignosulphonate (Zn-AML), Zn-polyhydroxyphenylcarboxylate (Zn-PHP) and Zn-S,S-ethylenediaminedisuccinate (Zn-S,S-EDDS)] applied to a crop textile flax ( Linum ussitatisimum L.) at application rates of 0, 5 and 10 mg Zn kg−1. In the flax plant, the following parameters were determined: dry matter yield, soluble and total Zn concentrations in leaf and stem, chlorophyll, crude fibre, and tensile properties. For the different soil samples, the following parameters were determined: available Zn (DTPA-AB and Mehlich-3 extractable Zn), easily leachable Zn (BaCl2-extractable Zn), the distribution of Zn fractions, pH and redox potential. On the basis of the use of added Zn by flax, or Zn utilization, it would seem recommendable to apply Zn-S,S-EDDS at the low Zn rate in both soils. In contrast, adding the high Zn rate of this chelate to the weakly acidic soil produced an excessive Zn concentration in the plant, which caused a significant decrease in both dry matter yield and chlorophyll content. Furthermore, assessing available Zn with the DTPA-AB method proved the best way of estimating the level of excess Zn in flax plants. The soluble Zn concentration, which was established with 2-( N-morpholino)ethanesulfonic acid reagent (MES), of plant fresh and dry matter could be used as an alternative way of diagnosing the nutritional status of Zn in flax plants. In this experiment, the highest soil pHs were associated with the lowest redox potentials, which coincided with the smallest amounts of available Zn and water soluble Zn in soil, and the lowest levels of Zn uptake by flax plants. [ABSTRACT FROM AUTHOR]

Open-top chamber (OTC) climate change simulation was used to predict the potential effects of climate change on biogeochemistry, including: 1) soil decomposition of three litter types (trembling aspen ( Populus tremuloides Michx.), black spruce ( Picea mariana (Miller) BSP), and Sphagnum); 2) soil nutrient supply rates, and; 3) soil acidity. We assessed the effects of OTCs on these biogeochemical factors in the presence or absence of Sphagnum moss substrate at post-fire and logging sites, in the transitional mixedwood-boreal zone of northwestern Quebec. Higher air temperatures and cooler, drier soils created by the OTC treatment resulted in lower decomposition rates and a higher C:N ratio of aspen litter, and lower Ca concentrations of the Sphagnum litter after 14 months of incubation, as well as lower K concentrations of spruce litter after 24 month incubation. There were no effects of the OTC treatment on decomposition rates for Sphagnum and spruce litter. The nutrient supply rates of Ca and Mg were consistently lower in the OTCs. The supply rates of N were significantly higher in the control plots at the logging site than at any other combination of the OTC treatment and disturbance site. Soil pH was lower in the OTCs by the end of the growing seasons in 2006 and 2007. The results suggest that the impact of climatic changes, as simulated by the OTC treatment, on the soil system of mixedwood-boreal post-disturbance sites is likely to affect biogeochemical processes such as nutrient supply rates and the soil pH, but the effects on decomposition may be minimal. [ABSTRACT FROM AUTHOR]

The major limit to plant growth in acid soils is the presence of toxic aluminum (Al) cations, which limit growth by inhibiting root elongation. Aluminum tolerance in rye is controlled by (at least) four independent loci ( Alt1, Alt2, Alt3 and Alt4) located on chromosome arms 6RS, 3RS, 4RL and 7RS, respectively. In this work, we analyzed several F2 populations in which two different Alt loci were segregating. We constructed a map of chromosome 7R, which contains the Alt4 locus and microsatellite and PCR-markers ( B1, B4, B11, B26 and BCD1230). These markers were mapped to the S arm of 7R using wheat-rye addition lines. Our results show that all these markers are linked to the Alt4 locus already known to be on 7RS. In addition, the OPS14 705 RAPD marker was linked to the Alt3 locus using bulked segregant analysis. This RAPD marker was transformed into a SCAR ( ScOPS14 705) and was localized to arm 4RL using wheat-rye addition lines. Finally, this SCAR was linked to the Alt3 locus at a genetic distance of 23.4 cM. In light of the current findings, and taking into account the synteny relationships in cereals, we propose candidate Alt3 and Alt4 orthologues in other cereals. [ABSTRACT FROM AUTHOR]

Pyruvate phosphate dikinase (PPDK) catalyses the phosphorylation of pyruvate (+ ATP + Pi) yielding phosphoenolpyruvate (+ AMP + PPi). PPDK levels are induced upon drought and salt stress and both cytosolic and plastidic isoforms are found in higher plants. Herein we investigate the role of this enzyme upon aluminum exposure. We generated transgenic tobacco plants expressing either a plastidic (PPDK) or a putative cytosolic (ΔPPDK) Mesembryanthemum crystallinum PPDK under the transcriptional control of the patatin B33 promoter and found that they can ameliorate Al stress. Enhanced root growth in the presence of Al was observed in transgenic lines, while that of wild-type (WT) seedlings was strongly inhibited. Al content in root tips of stressed plants was reduced in the transgenic lines compared with WT, as judged by Eriochrome cyanine R (ECR) staining and atomic absorption spectrometry. Moreover, all transformants excreted higher levels of citric acid cycle intermediates (citrate and malate) than the WT seedlings did. Interestingly, we found different behavior between the two sets of transformants, based on results of ECR root staining, organic acid exudation and Al accumulation. In general, lines harboring the PPDK construct were more tolerant to Al stress than those expressing the ΔPPDK construct. We conclude that the overexpression of PPDK can serve to protect roots against Al toxicity. Furthermore, we provide the first physiological evidence for a link between Al stress and PPDK in plants and postulate that such approach could be successful under certain edaphic conditions, namely acid soils. [ABSTRACT FROM AUTHOR]

Excess aluminum (Al) ions and phosphorus (P) deficiency are the key factors that limit plant growth in acid soils. Secretion of organic acids (OA) from roots has been proposed as an Al-resistance mechanism. Nonetheless, the correlation between Al resistance and this mechanism has not been tested beyond a very small number of Al-resistant and Al-sensitive genotypes. To elucidate the mechanisms responsible for plant adaptability to acid soils, we studied the secretion of OA from roots of Stylosanthes in response to high-Al and low-P stresses using six different genotypes. Relative root inhibition by 50 µM Al ranged from 25–71% and differed significantly among six Stylosanthes genotypes. Al treatment induced the secretion of citrate from the roots of Stylosanthes seedling in a dose- and time-dependent manner. Moreover, the secretion rate was significantly higher in the Al-resistant genotype. On the other hand, inhibition of Al-induced citrate secretion by phenylisothiocyanate or 9-anthracenecarboxylic acid resulted in an increase in Al content in Stylosanthes root apices. P deficiency also induced citrate secretion from Stylosanthes seedling roots. Furthermore, citrate secretion was much more robust with exposure to both excess-Al and P-deficiency stresses than under either stress alone. Unlike Al-induced citrate secretion, which was rapid, low-P-induced secretion was a slow process, with significant increases in secretion only becoming evident after 6 d of treatment with free phosphate. The lag between treatment with Al and citrate secretion was approximately 4 h. These results suggest that the secretion of citrate is a mechanism for resistance to both excess-Al and low-P stresses in Stylosanthes. [ABSTRACT FROM AUTHOR]

Mechanisms causing the calcifuge–calcicole behavior of lichens are largely unexplored. Studying the case examples of two closely related terricolous lichens, the calcifuge Cladonia furcata subsp. furcata and the calcicole C. rangiformis, we found that preference for acidic or calcareous soils in these lichens is related to iron and phosphate uptake as in vascular plants. In laboratory studies, the calcicole species was more efficient in the intracellular uptake of Fe3+ and phosphate at pH 8 than the calcifuge species. At pH 3, intracellular uptake of Fe2+ in the calcicole species significantly exceeded that in the calcifuge species suggesting that calcicole lichens suffer from toxicity symptoms by excess Fe2+ at acidic sites. Though these observations parallel findings from calcifuge and calcicole vascular plants, mechanisms leading to the different iron and phosphate uptake characteristics in the studied calcifuge and calcicole lichens may differ from those in vascular plants and should be the topic of future research. A role of the depside atranorin in facilitating iron uptake by reducing Fe3+ in the apoplast is hypothesized. [ABSTRACT FROM AUTHOR]

Al stress and ammonium–nitrogen nutrition often coexist in acidic soils due to their low pH and weak nitrification ability. Rice is the most Al-resistant species among small grain cereal crops and prefers NH4 + as its major inorganic nitrogen source. This study investigates the effects of NH4 + and NO3 − on Al toxicity and Al accumulation in rice, and thereby associates rice Al resistance with its NH4 + preference. Two rice subspecies, indica cv. Yangdao6 and japonica cv. Wuyunjing7, were used in this study. After treatment with or without Al under conditions of varying NH4 + and NO3 − supply, rice seedlings were harvested for the determination of root elongation, callose content, biomass, Al concentration and medium pH. The results indicated that Wuyunjing7 was more Al-resistant and NH4 +-preferring than Yangdao6. NH4 + alleviated Al toxicity in two cultivars compared with NO3 −. Both NH4 +-Al supply and pretreatment with NH4 + reduced Al accumulation in roots and root tips compared with NO3 −. NH4 + decreased but NO3 − increased the medium pH, and root tips accumulated more Al with a pH increase from 3.5 to 5.5. Increasing the NO3 − concentration enhanced Al accumulation in root tips but increasing the NH4 + concentration had the opposite effect. These results show NH4 + alleviates Al toxicity for rice and reduces Al accumulation in roots compared with NO3 −, possibly through medium pH changes and ionic competitive effects. Making use of the protective effect of NH4 +, in which the Al resistance increases, is advised for acidic soils, and the hypothesis that rice Al resistance is associated with the preferred utilization of NH4 + is suggested. [ABSTRACT FROM AUTHOR]

Simple compounds in soil such as organic acids, amino acids and monosaccharides are believed to be important in regulating many aspects of terrestrial ecosystem functioning (e.g. C cycling, nutrient acquisition). Understanding the fate and dynamics of these low molecular weight (MW) compounds is therefore essential for predicting ecosystem responses to disturbance. Our aim was to quantify the amounts of these compounds in two podzolic forest soil profiles (O, E, Bs and C horizons) and to quantify their contribution to total soil respiration. The total concentration of organic acids, amino acids and monosaccharides in soil solution comprised on average 15 ± 10% of the total dissolved organic C (DOC), with declining concentrations in the deeper soil layers. Dissolved organic N (DON) was the dominant form of N in soil solution and free amino acids contributed to 34% of this pool. The mineralization behaviour of glucose and galactose was described by parabolic (Michaelis–Menten) type kinetics with V max and K M values in the range of <1–250 μmol kg−1 h−1 and 15–1,100 μM, respectively. Assuming that (1) microbially mediated substrate turnover follows Michaelis–Menten kinetics, and (2) steady state soil solution concentrations, we calculated the rate of CO2 efflux attributable to the mineralisation of the three classes of low MW compounds. Our results indicated that in the O horizon, the turnover of these substrates could comprise ~100% of the basal, heterotrophic, soil respiration. In contrast, in the deeper mineral soil <20% of total soil respiration could be attributable to the mineralization of these compounds. Our compound-specific approach has identified the main substrates contributing to soil respiration in forest topsoils. However, our results also suggest that soil respiration in subsoils may be attributable to compounds other than organic acids, amino acids and monosaccharides. [ABSTRACT FROM AUTHOR]

Lespedeza bicolor ( Lespedeza bicolor Turcz. cv. Jiangxi) is a leguminous shrub that is well adapted to acid infertile soils. However, the mechanisms of aluminum resistance in this species have not been established. This study aimed to assess the possible resistance mechanisms of this plant to Al. An Al-sensitive species of Lespedeza, sericea lespedeza [ Lespedeza cuneata (Dum.-Cours.) G. Don cv. Zhejiang], was used as a reference. The roots of L. bicolor secreted both malate and citrate after exposure to Al, but roots of L. cuneata did not. The secretion of organic acids from L. bicolor was specific to Al; neither 15-day P starvation nor 50 μM lanthanum induced the secretion of these organic acid anions. Secretion of organic acid anions in L. bicolor was detected after 3–6 h exposure to Al, and the amount increased significantly after 6 h exposure, suggesting that this plant shows a pattern II-type organic acid secretion. This is supported by the finding that the secretion was significantly inhibited by a protein-synthesis inhibitor, cycloheximide. Two kinds of anion-channel inhibitors had different effects on Al-induced secretion of organic acids: 9-anthracene carboxylic acid completely inhibited secretion, phenylglyoxal had no effect. Root elongation in L. bicolor was more severely inhibited by Al in the presence of 9-anthracene carboxylic acid. All these results indicated that the secretion of malate and citrate is a specialized response to Al stress in L. bicolor roots, which might be one of the Al-resistance mechanisms in this species. [ABSTRACT FROM AUTHOR]

The decline of sugar maple ( Acer saccharum Marsh.) in forest of north-eastern North America is an important environmental issue. In this study, relationships between, soil, wood and foliar chemistry were assessed for 17 stands distributed within a large area of the Quebec sugar maple forest and that were growing on soils with a strong gradient of acidity and base saturation. There were many significant relationships between variables describing the acid-base status of the top-B soil (Ca and Mg concentrations, exchangeable acidity and base saturation) and Ca and Mn concentrations and Ca/Mn and Mg/Mn in tree tissues. Manganese was the element that showed the strongest inverse non-linear relationships with top-B soil base saturation with variance explanation of 71 and 65%, for wood and foliage, respectively. The 17 sites were divided in two groups according to their level of decline. The declining stands had significantly higher wood Mn and Mg concentrations and lower Ca/Mn ratios and significantly higher foliar Mn and lower Ca and Al concentrations. It was impossible to determine if these differences were a cause or a symptom of sugar maple health. However, the increase in Mn concentrations in tree tissues with increasing soil acidity, as well as the higher Mn concentrations in declining as compared to healthy stands suggest that Mn, as well as low Ca availability, could be an important contributing factor in the sugar maple decline. [ABSTRACT FROM AUTHOR]

Aluminum (Al) toxicity is a major constraint for wheat production in acidic soils. An Al resistance gene on chromosome 4DL that traces to Brazilian wheat has been extensively studied, and can provide partial protection from Al damage. To identify potentially new sources of Al resistance, 590 wheat accessions, including elite wheat breeding lines from the United States and other American and European countries, landraces and commercial cultivars from East Asia, and synthetic wheat lines from CIMMYT, Mexico, were screened for Al resistance by measuring relative root elongation in culture with a nutrient solution containing Al, and by staining Al-stressed root tips with hematoxylin. Eighty-eight wheat accessions demonstrated at least moderate resistance to Al toxicity. Those selected lines were subjected to analysis of microsatellite markers linked to an Al resistance gene on 4DL and a gene marker for the Al-activated malate transporter ( ALMT1) locus. Many of the selected Al-resistant accessions from East Asia did not have the Al-resistant marker alleles of ALMT1, although they showed Al resistance similar to the US Al-resistant cultivar, Atlas 66. Most of the cultivars derived from Jagger and Atlas 66 have the Al-resistant marker alleles of ALMT1. Cluster analysis separated the selected Al-resistant germplasm into two major clusters, labeled as Asian and American–European clusters. Potentially new germplasm of Al resistance different from those derived from Brazil were identified. Further investigation of Al resistance in those new germplasms may reveal alternative Al-resistance mechanisms in wheat. [ABSTRACT FROM AUTHOR]

Toxic aluminum (Al) ion is a major constraint to plant growth in acid soils. Aluminum tolerance in wheat ( Triticum aestivum L.) is strongly related to the Al-triggered efflux of malate from root apices. A role of the secreted malate has been postulated to be in chelating Al and thus excluding it from root apices (malate hypothesis), but the actual process has yet to be fully elucidated. We measured Al content and root growth during and after Al exposure using seedlings of near-isogenic lines [ET8 (Al tolerant) and ES8 (Al sensitive)] differing in the capacity to induce Al-triggered malate efflux. Aluminum doses that caused 50% root growth inhibition during 24-h exposure to Al in calcium (Ca) solution (0.5 mM CaCl2, pH 4.5) were 50 µM in ET8 and 5 µM in ES8. Under such conditions, the amount of Al accumulated in root apices was approximately 2-fold higher in ET8 than ES8. Al-treated seedlings were then transferred to the Al-free Ca solution for 24 h. Compared to control roots (no Al pretreatment), root regrowth of Al-treated roots was about 100% in ET8 and about 25% in ES8. The impaired regrowth in ES8 was observed even after 24-h exposure to 2.5 µM Al which had caused only 20% root growth inhibition. The addition of malate (100 µM) during exposure to 50 µM Al in ES8 enhanced root growth 1.6 times and regrowth in Al-free solution 7 times, resulting in similar root growth and regrowth as in ET8. Short-term Al treatments of ES8 for up to 5 h indicated that the Al-caused inhibition of root regrowth started after 1-h exposure to Al. The stimulating effect of malate on root regrowth was observed when malate was present during Al exposure, but not when roots previously exposed to Al were rinsed with malate, although Al accumulation in root apices was similar under these malate treatments. We conclude that the malate secreted from root apices under Al exposure is essential for the apices to commence regrowth in Al-free medium, the trait that is not related to the exclusion of Al from the apices. [ABSTRACT FROM AUTHOR]

An experiment was conducted from 1997 to 2000 on an acid soil in Cameroon to assess the effectiveness of cultivating acid tolerant maize ( Zea mays L .) cultivar and the use of organic and inorganic fertilizers as options for the management of soil acidity. The factors investigated were: phosphorus (0 and 60 kg ha−1), dolomitic lime (0 and 2 t ha−1), organic manure (no manure, 4 t ha−1 poultry manure, and 4 t ha−1 of leaves of Senna spectabilis), and maize cultivars (ATP-SR-Y – an acid soil-tolerant, and Tuxpeño sequia – an acid susceptible). On acid soil, maize grain yield of ATP-SR-Y was 61% higher than the grain yield of Tuxpeño sequia. Continuous maize cultivation on acid soil further increased soil acidity, which was manifested by a decrease in pH (0.23 unit), exchangeable Ca (31%) and Mg (36%) and by an increase in exchangeable Al (20%). Yearly application of 60 kg ha−1 of P for 3 years increased soil acidity through increases in exchangeable Al (8%) and H (16%) and a decrease in exchangeable Ca (30%), Mg (11%) and pH (0.07 unit). Lime application increased grain yield of the tolerant (82%) and susceptible (208%) cultivars. The grain yield increases were associated with a mean decrease of 43% in exchangeable Al, and 51% in H, a mean increase of 0.27 unit in pH, 5% in CEC, 154% in exchangeable Ca, and 481% in Mg contents of the soil. Poultry manure was more efficient than leaves of Senna producing 38% higher grain yield. This yield was associated with increases in pH, Ca, Mg and P, and a decrease in Al. The highest mean grain yields were obtained with lime added to poultry manure (4.70 t ha−1) or leaves of Senna (4.72 t ha−1). Grain yield increase was more related to the decrease in exchangeable Al ( r = −0.86 to −0.95, P<0.01) and increase in Ca ( r = 0.78–0.94, P<0.01), than to pH ( r = −0.57 (non-significant) to −0.58 ( P<0.05)). Exchangeable Al was the main factor determining pH ( r = −0.88 to −0.92, P<0.01). The yield advantage of the acid tolerant cultivar was evident even after correcting for soil acidity. Acid soil-tolerant cultivars are capable of bringing unproductive acid soils into cultivation on the short run. The integration of soil amendments together with acid soil-tolerant cultivar offers a sustainable and comprehensive strategy for the management of acid soils in the tropics. [ABSTRACT FROM AUTHOR]

Various extraction methods have been used to determine selenium (Se) concentrations in soils and plants in the second seleniferous regions of China. Our results show tea Se contents in the study area range from 1.009 to 2.6 mg/kg, which reveal that the tea areas in Ziyang County are in seleniferous regions. The four extraction methods evaluated in this study provide different information concerning soil and plant Se levels. The quality control/quality assurance program for this project indicated there is excellent agreement between total soil Se and extractable Se. For example, phosphate extractable Se results from the field investigation and greenhouse study were found to be highly correlated ( R 2 > 0.91) by linear regression analyses. Results from rye seedling experiments further show phosphate extractable Se has significant correlations with plant Se uptake and that a 0.1 M solution of KH2PO4 can be used as the extractant of soil available Se. In the acid soil, the Brassica campestris yield could be significantly reduced when the content of Se6+–Se ≥ 0.5 mg/kg, and the influence on the yield was not as obvious when the content of Se6+–Se reached up to 2.0 mg/kg. The uptake by Brassica campestris of Se6+–Se is higher than that of Se4+–Se. The main factors influencing the biological availability of soil Se, in order of their importance are CaCO3, the presence of silt grains, organic matter and the presence of clay grains. pH could affect KH2PO4 extractable Se through CaCO3. [ABSTRACT FROM AUTHOR]