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Simple Summary: "Rhizobia" are alpha- and beta-proteobacteria with the ability to associate in symbiosis with legumes, establishing complex root structures (nodules) where the process of biological N2-fixation takes place. The knowledge of these bacteria which efficiently associate with particular legumes is a key aspect in understanding the origin, diversification, practical use, and improvement of the symbiotic systems. In this work, we present the phenotypic and genomic characteristics of a collection of bacterial isolates of the genera Sinorhizobium, present in soils of northwest Argentina and able to associate with plants of the Desmanthus virgatus complex. Results showed an important genetic diversity among the local isolates (including different species), heterogeneous profiles of tolerance to abiotic stresses, and an outstanding capacity to support plant growth in the absence of fixed nitrogen. Upon the genomic and phylogenetic analyses of selected isolates, evidence of the horizontal gene transfer of nodulation (nod) genes was obtained, accounting for current genomic constitution of the local symbionts of Desmanthus. Desmanthus spp. are legumes with the ability to associate with diverse α-proteobacteria—a microsymbiont—in order to establish nitrogen-fixing root nodules. A previous investigation from our laboratory revealed that the main bacteria associated with Desmanthus paspalaceus in symbiosis in central Argentina (Province of Santa Fe) were quite diverse and belonged to the genera Rhizobium and Mesorhizobium. To achieve a more extensive view of the local microsymbionts associated with Desmanthus spp., we sampled three different sites in Jujuy and Salta, in northwest Argentina. Matrix-assisted Laser-Desorption-Ionization Time-of-Flight mass spectrometry (MALDI-TOF) typing, 16S-rDNA analysis, and genome sequencing demonstrated that the dominant root-nodule microsymbionts belonged to the genus Sinorhizobium, with some sequenced genomes related to Sinorhizobium mexicanum, Sinorhizobium chiapanecum, and Sinorhizobium psoraleae. An analysis of nodA and nodC markers indicated that, in some of the isolates, horizontal gene transfer appeared to be responsible for the lack of congruence between the phylogenies of the chromosome and of the symbiotic region. These results revealed diverse evolutionary strategies for reaching the current Desmanthus-microsymbiont diversity. What is remarkable beside their observed genetic diversity is that the tolerance profiles of these isolates to abiotic stresses (temperature, salt concentration, pH) were quite coincident with the separation of the sinorhizobia according to place of origin, suggesting possible ecoedaphic adaptations. This observation, together with the higher aerial dry-weight matter that some isolates generated in Desmanthus virgatus cv. Marc when compared to the biomass generated by the commercial strain Sinorhizobium terangae CB3126, distinguish the collected sinorhizobia as constituting valuable germplasm for evaluation in local fields to select for more efficient symbiotic pairs. [ABSTRACT FROM AUTHOR]

Climate change will increase heat and drought stress in many dryland areas, which could reduce soil nutrient availability for plants and aggravate nutrient limitation of primary productivity. Any negative impacts of climate change on foliar nutrient contents would be expected to negatively affect the photosynthetic capacity, water use efficiency and overall fitness of dryland vegetation.We conducted a 4‐year manipulative experiment using open top chambers and rainout shelters to assess the impacts of warming (~2°C, W), rainfall reduction (~30%, RR) and their combination (W + RR) on the nutrient status and ecophysiological performance of six native shrub species of contrasting phylogeny in a semi‐arid ecosystem. Leaf nutrient status and gas exchange were assessed yearly, whereas biomass production and survival were measured at the end of the study.Warming (W and W + RR) advanced shoot growth phenology and reduced foliar macro‐ (N, P, K) and micronutrient (Cu, Fe, Zn) concentrations (by 8%–18% and 14%–56% respectively), net photosynthetic rate (32%), above‐ground biomass production (28%–39%) and survival (23%–46%). Decreased photosynthesis and growth in W and W + RR plants were primarily linked to enhanced nutritional constraints on carbon fixation. Poor leaf nutrient status in W and W + RR plants partly decoupled carbon assimilation from water flux and led to drastic reductions in water use efficiency (WUEi; ~41%) across species. The RR treatment moderately decreased foliar macro‐ and micronutrients (6%–17%, except for Zn) and biomass production (22%). The interactive impacts of warming and rainfall reduction (W + RR treatment) on plant performance were generally smaller than expected from additive single‐factor effects.Synthesis. Large decreases in plant nutrient pool size and productivity combined with increased mortality during hotter droughts will reduce vegetation cover and nutrient retention capacity, thereby disrupting biogeochemical processes and accelerating dryland degradation with impending climate change. Increased macro‐ and micronutrient co‐limitation of photosynthesis with forecasted climate change conditions may offset any gains in WUEi and productivity derived from anthropogenic CO2 elevation, thereby increasing dryland vegetation vulnerability to drought stress in a warmer and drier climate. The generalized reduction in leaf nutrient contents with warming compromises plant nutritional quality for herbivores, with potential cascading negative effects across trophic levels. [ABSTRACT FROM AUTHOR]

Abstract: Warmer and drier conditions associated with ongoing climate change will increase abiotic stress for plants and mycorrhizal fungi in drylands world‐wide, thereby potentially reducing vegetation cover and productivity and increasing the risk of land degradation and desertification. Rhizosphere–microbial interactions and feedbacks are critical processes that could either mitigate or aggravate the vulnerability of dryland vegetation to forecasted climate change. We conducted a 4‐year manipulative study in a semi‐arid shrubland in the Iberian Peninsula to assess the effects of warming (c. 2.5°C; W), rainfall reduction (c. 30%; RR) and their combination (W+RR) on the performance of native shrubs (Helianthemum squamatum) and their associated mycorrhizal fungi. Warming (W and W+RR) decreased the net photosynthetic rates of H. squamatum shrubs by c. 31% despite concurrent increases in stomatal conductance (c. 33%), leading to sharp decreases (c. 50%) in water use efficiency. Warming also advanced growth phenology, decreased leaf nitrogen and phosphorus contents per unit area, reduced shoot biomass production by c. 36% and decreased survival during a dry year in both W and W+RR plants. Plants under RR showed more moderate decreases (c. 10%–20%) in photosynthesis, stomatal conductance and shoot growth. Warming, RR and W+RR altered ectomycorrhizal fungal (EMF) community structure and drastically reduced the relative abundance of EMF sequences obtained by high‐throughput sequencing, a response associated with decreases in the leaf nitrogen, phosphorus and dry matter contents of their host plants. In contrast to EMF, the community structure and relative sequence abundances of other non‐mycorrhizal fungal guilds were not significantly affected by the climate manipulation treatments. Synthesis. Our findings highlight the vulnerability of both native plants and their symbiotic mycorrhizal fungi to climate warming and drying in semi‐arid shrublands, and point to the importance of a deeper understanding of plant–soil feedbacks to predict dryland vegetation responses to forecasted aridification. The interdependent responses of plants and ectomycorrhizal fungi to warming and rainfall reduction may lead to a detrimental feedback loop on vegetation productivity and nutrient pool size, which could amplify the adverse impacts of forecasted climate change on ecosystem functioning in EMF‐dominated drylands. [ABSTRACT FROM AUTHOR]

Whereas warming enhances plant nutrient status and photosynthesis in most terrestrial ecosystems, dryland vegetation is vulnerable to the likely increases in evapotranspiration and reductions in soil moisture caused by elevated temperatures. Any warming-induced declines in plant primary production and cover in drylands would increase erosion, land degradation, and desertification. We conducted a four-year manipulative experiment in a semi-arid Mediterranean ecosystem to evaluate the impacts of a ~2°C warming on the photosynthesis, transpiration, leaf nutrient status, chlorophyll content, isotopic composition, biomass growth, and postsummer survival of the native shrub Helianthemum squamatum. We predicted that warmed plants would show reduced photosynthetic activity and growth, primarily due to the greater stomatal limitation imposed by faster and more severe soil drying under warming. On average, warming reduced net photosynthetic rates by 36% across the study period. Despite this strong response, warming did not affect stomatal conductance and transpiration. The reduction of peak photosynthetic rates with warming was more pronounced in a drought year than in years with near-average rainfall (75% and 25-40% reductions relative to controls, respectively), with no indications of photosynthetic acclimation to warming through time. Warmed plants had lower leaf N and P contents, δ13C, and sparser and smaller leaves than control plants. Warming reduced shoot dry mass production by 31%. However, warmed plants were able to cope with large reductions in net photosynthesis, leaf area, and shoot biomass production without changes in postsummer survival rates. Our findings highlight the key role of nonstomatal factors (biochemical and/or nutritional) in reducing net carbon assimilation rates and growth under warming, which has important implications for projections of plant carbon balance under the warmer and drier climatic scenario predicted for drylands worldwide. Projected climate warming over the coming decades could reduce net primary production by about one-third in semi-arid gypsum shrublands dominated by H. squamatum. [ABSTRACT FROM AUTHOR]

The annual water status and phenological patterns of Rosmarinus officinalis plants in relation to irrigation were studied to improve the use of this species in gardening conditions. Rosmarinus officinalis seedlings were pot-grown for 4 months in the nursery. After this period, plants were transplanted to field conditions before three irrigation treatments were applied from Nov. 2000 to Dec. 2001 (control and deficit treatments: C, T-1 and T-2, respectively). The total amount of water applied by irrigation during the experimental period was 167 mm for control, 83.5 mm for T-1 (50% of the control), and 50 mm for T-2 (30% to the control). Two main periods of vegetative growth (beginning of spring and fall) were observed in all treatments. At the end of the experimental period, deficit irrigation had altered the morphology of the R. officinalis plants, reducing plant height and shoot growth. Maximum flowering intensity occurred at the beginning of fall for all irrigation treatments. Deficit irrigation treatments induced a more intense flowering density, although of lower longevity than control plants. The annual pattern of shoot water potential at predawn reflected the irrigation regimes, although less difference resulting from irrigation effect was detected in this parameter at midday. Plants under deficit irrigation showed a conservative strategy in the use of water, reducing stomatal conductance. This finding may be of use for the successful gardening of Rosmarinus officinalis plants in semiarid conditions. [ABSTRACT FROM AUTHOR]

This study tests the hypothesis that diffusional limitation of photosynthesis, rather than light, determines the distribution of photosynthetic capacity in olive leaves under drought conditions. The crowns of four olive trees growing in an orchard were divided into two sectors: one sector absorbed most of the radiation early in the morning (MS) while the other absorbed most in the afternoon (AS). When the peak of radiation absorption was higher in MS, air vapour pressure deficit (VPD) was not high enough to provoke stomatal closure. In contrast, peak radiation absorption in AS coincided with the daily peak in VPD. In addition, two soil water treatments were evaluated: irrigated trees (I) and non-irrigated trees (nI). The seasonal evolution of leaf water potential, leaf gas exchange and photosynthetic capacity were measured throughout the tree crowns in spring and summer. Results showed that stomatal conductance was reduced in nI trees in summer as a consequence of soil water stress, which limited their net assimilation rate. Olive leaves displayed isohydric behaviour and no important differences in the diurnal course of leaf water potentials among treatments and sectors were found. Seasonal diffusional limitation of photosynthesis was mainly increased in nI trees, especially as a result of stomatal limitation, although mesophyll conductance ( gm) was found to decrease in summer in both treatments and sectors. A positive relationship between leaf nitrogen content with both leaf photosynthetic capacity and the daily integrated quantum flux density was found in spring, but not in summer. The relationship between photosynthetic capacity and gm was curvilinear. Leaf temperature also affected to gm with an optimum temperature at 29 °C. AS showed larger biochemical limitation than MS in August in both treatments. All these suggest that both diffusional limitation and the effect of leaf temperature could be involved in the seasonal reduction of photosynthetic capacity of olive leaves. This work highlights the need for models of plant growth and ecosystem function to incorporate new parameters affecting the distribution of photosynthetic capacity in canopies. [ABSTRACT FROM AUTHOR]

Summary: The experiment was carried out in a research field near Murcia, Spain, over a 3-week period between September 26 and October 16, 2000. Sixteen trees were used in the experiment, eight of which were placed under a rectangular shading net, while the other eight were maintained in the open air. Trees were irrigated once per day and, after October 5th, water was witheld from eight trees (four shaded and four unprotected for 5 days). The leaf stomatal conductance and the photosynthesis rates were higher in the shaded trees than in the exposed plants, probably because the leaf water potential was lower in the unshaded plants. This higher leaf conductance partially compensated for the effect of low radiation on transpiration, and the reduction of daily sap flow registered in shaded trees was only around 10–20%. The net also affected trunk diameter changes, with the shaded trees showing lower values of maximum daily shrinkage. Soil water deficit and high radiation had a similar effect on plant water parameters, lowering leaf water potential, leaf stomatal conductance, and the photosynthesis rate. The effects of both conditions were accumulative and so the exposed water-stressed plants showed the lowest values of total hydraulic resistance and water use efficiency, while the shaded well-irrigated trees registered the highest values for both parameters. For this reason, we think that net shading could be extended to apricot culture in many areas in which irrigation water is scarce and insolation is high. [Copyright &y& Elsevier]

Pesticides have been used extensively in agriculture to control pests and soil-borne diseases. Most of these pesticides can persist in soil in harmful concentrations due to their intrinsic characteristics and their interactions with soil. Soil solarization has been demonstrated to enhance pesticide degradation under field conditions. Recently, ozonation has been suggested as a feasible method for reducing the pesticide load in agricultural fields. However, the effects of ozonation in the soil microbial community have not been studied so far. Here, we evaluate the combined effects of solarization and ozonation on the microbial community of a Mediterranean soil. For this purpose, soil physico-chemical characteristics and enzyme activities and the biomass (through analysis of microbial fatty acids) and diversity (through 16S rRNA and ITS amplicon sequencing) of soil microbial communities were analyzed in a 50-day greenhouse experiment. The degradation of the pesticides was increased by 20%, 28%, and 33% in solarized soil (S), solarized soil with surface ozonation (SOS), and solarized soil with deep ozonation (SOD), respectively, in comparison to control (untreated) soil. Solarization and its combination with ozonation (SOS and SOD) increased the ammonium content as well as the electrical conductivity, while enzyme activities and soil microbial biomass were negatively affected. Despite the biocidal character of ozone, several microbial populations with demonstrated pesticide-degradation capacity showed increases in their relative abundance. Overall, the combination of solarization plus ozone did not exacerbate the effects of solarization on the soil chemistry and microbial communities, but did improve pesticide degradation. Unlabelled Image • Solarization combined with ozonation enhanced pesticide degradation in soil. • Solarization with surface-ozonation rose 300-times the NH 4 + content over the control. • Soil enzyme activities were negatively affected by soil solarization and ozonation. • Relative abundance of known pesticide-degrading microbes increases after ozonation. [ABSTRACT FROM AUTHOR]

The ratio between net photosynthetic rates and the foliar contents of essential plant macronutrients (N, P, K) is termed photosynthetic nutrient use efficiency (PNutUE). A universal trade-off exists whereby plants cannot maximize their PNutUE and their intrinsic water use efficiency (WUEi, carbon gain per unit water spent) simultaneously, because any increase in intercellular CO 2 concentration (c i) through a greater stomatal opening would increase PNutE but also enhances transpiration and therefore decreases WUEi. Rising temperatures associated with climate change can result in large decreases in WUEi in semiarid shrubs through photosynthetic machinery impairment and enhanced stomatal conductance and transpiration, but we know remarkably little about the influence of warming and drought on PNutUE and its interplay with WUEi in dryland vegetation. Using a 6-year (2011–2017) manipulative field experiment, we examined the effects of warming (2.5ºC, W), rainfall reduction (30%, RR), and their combination (W+RR) on the photosynthetic use efficiency of three essential nutrients (PNUE, PPUE and PKUE) and on WUEi in three shrub species growing at two semiarid shrublands for the years 2015–2017. Across species, warming (W and W+RR) reduced PNUE by 42.9%, PPUE by 43.8% and PKUE by 41.5% on average relative to shrubs growing under ambient temperatures, whereas RR did not significantly affect their PNutUE. These drastic reductions in PNutUE with warming were mainly driven by non-stomatal and largely non-nutritional decreases in net photosynthetic rates, which were almost halved in warmed shrubs. The photosynthetic use efficiencies of N, P and K were inversely related to foliar δ13C, a proxy for time integrated WUEi, in both ambient (control and RR) and warmed (W and W+RR) shrubs, but with significantly smaller slopes and intercepts for warmed shrubs. Thus, plants achieve a smaller gain in PNutUE for any given increase in stomatal conductance (and reduction in WUEi) under warmer climatic conditions. The strong negative impact of warming on PNutE, along with the warming-induced shift in the trade-off between PNutUE and WUEi, could be indicative of an increasing inability of native plants to cope with warmer conditions, with dire implications for dryland vegetation productivity and survival under climate change. • We assessed the effects of climate change on plant physiology and traits in dryland plants. • Warming strongly reduced the photosynthetic nutrient use efficiency (PNutUE) of N, P and K. • Reductions in PNutUE were due to non-stomatal and non-nutritional decreases in photosynthesis. • Warming altered the universal trade-off between water and nutrient use efficiency. • This could be indicative of an inability of dryland plants to cope with warmer conditions. [ABSTRACT FROM AUTHOR]

Background and Aims Water deficit is the most serious environmental factor limiting agricultural production. In this work, the tolerance to water stress (WS) of transgenic plum lines harbouring transgenes encoding cytosolic antioxidant enzymes was studied, with the aim of achieving the durable resistance of commercial plum trees. Methods The acclimatization process was successful for two transgenic lines: line C3-1, co-expressing superoxide dismutase (two copies) and ascorbate peroxidase (one copy) transgenes simultaneously; and line J8-1, harbouring four copies of the cytosolic ascorbate peroxidase gene (cytapx). Plant water relations, chlorophyll fluorescence and the levels of antioxidant enzymes were analysed in both lines submitted to moderate (7 d) and severe (15 d) WS conditions. Additionally, in line J8-1, showing the best response in terms of stress tolerance, a proteomic analysis and determination of the relative gene expression of two stress-responsive genes were carried out. Key Results Line J8-1 exhibited an enhanced stress tolerance that correlated with better photosynthetic performance and a tighter control of water-use efficiency. Furthermore, this WS tolerance also correlated with a higher enzymatic antioxidant capacity than wild-type (WT) and line C3-1 plum plants. On the other hand, line C3-1 displayed an intermediate phenotype between WT plants and line J8-1 in terms of WS tolerance. Under severe WS, the tolerance displayed by J8-1 plants could be due to an enhanced capacity to cope with drought-induced oxidative stress. Moreover, proteomic analysis revealed differences between WT and J8-1 plants, mainly in terms of the abundance of proteins related to carbohydrate metabolism, photosynthesis, antioxidant defences and protein fate. Conclusions The transformation of plum plants with cytapx has a profound effect at the physiological, biochemical, proteomic and genetic levels, enhancing WS tolerance. Although further experiments under field conditions will be required, it is proposed that J8-1 plants would be an interesting Prunus rootstock for coping with climate change. [ABSTRACT FROM AUTHOR]

The work was performed in order to know the effects of different doses of a mycorrhizal inoculant in liquid support in growth variables, water relations and efficiency in the use tomato plants nutrients. For its realization, tomato plants INCA 9 [1] were grown in pots and placed in a polycarbonate greenhouse. Three doses were studied (D1, D2 and D3) 75 (D1), 150 (D2) and 300 spores plant-1, applied in seeding through injection by irrigation system and a non-inoculated control. At 25 and 40 days after germination (DDG) evaluation of fungal variables, growth on dry biomass, leaf water potential and its components, stomatic conductance the concentration of foliar nutrients and efficiency use of these. The results showed that with any of the applied doses important benefits are achieved by symbiosis with increases of fungal variables, the content of dry biomass, water relations and the best efficiency in the use of nutrients. However, in general only with the application of the D1 dose, these benefits were obtained, resulting in this work the most appropriate and economic dose. [ABSTRACT FROM AUTHOR]

The soilborne pathogen Verticillium dahliae, causal agent of Verticillium wilt, has a worldwide distribution and many hosts of agronomic value. The worldwide spread of a highly virulent defoliating (D) pathotype has greatly increased the threat posed by V. dahliae in olive trees. For effective disease management, it is important to know if the D pathotype is spreading long distances from contaminated material, or if D pathotype isolates may have originated locally from native V. dahliae populations several times. We identified a double-stranded RNA mycovirus in an olive D pathotype isolate from Turkey. Sequencing and phylogenetic analysis clustered the virus with members of the family Partitiviridae. The virus was most similar to a partitivirus previously identified in a V. dahliae isolate from cotton in China (VdPV1), with sequence identities of 94% and 91% at the nucleotide level for RNA1 and RNA2, respectively. The virus therefore corresponded to a strain of the established species, and we designated it VdPV1-ol (VdPV1 from olive). The identification of the same viral species in these two fungal isolates from geographically distant origins provides evidence of their relationships, supporting the hypothesis of longdistance movement of V. dahliae isolates. [ABSTRACT FROM AUTHOR]

Variation in the stable carbon and oxygen isotope composition (δ13C, Δ18O) of co-occurring plant species may reflect the functional diversity of water use strategies present in natural plant communities., We investigated the patterns of water use among 10 coexisting plant species representing diverse taxonomic groups and life forms in semiarid southeast Spain by measuring their leaf δ13C and Δ18O, the oxygen isotope ratio of stem water and leaf gas exchange rates., Across species, Δ18O was tightly negatively correlated with stomatal conductance ( gs), whereas δ13C was positively correlated with intrinsic water use efficiency ( WUEi). Broad interspecific variation in Δ18O, δ13C and WUEi was largely determined by differences in gs, as indicated by a strong positive correlation between leaf δ13C and Δ18O across species, The 10 co-occurring species segregated along a continuous ecophysiological gradient defined by their leaf δ13C and Δ18O, thus revealing a wide spectrum of stomatal regulation intensity and contrasting water use strategies ranging from 'profligate/opportunistic' (high gs, low WUEi) to 'conservative' (low gs, high WUEi). Coexisting species maintained their relative isotopic rankings in 2 yr with contrasting rainfall, suggesting the existence of species-specific 'isotopic niches' that reflect ecophysiological niche segregation in dryland plant communities. [ABSTRACT FROM AUTHOR]

Abstract: Callistemon is an Australian species used as ornamental plant in Mediterranean regions. The objective of this research was to analyse the ability of Callistemon to overcome water deficit in terms of adjusting its physiology and morphology. Potted Callistemon laevis Anon plants were grown in controlled environment and subjected to drought stress by reducing irrigation water by 40% compared to the control (irrigated to container capacity). The drought stress produced the smallest plants throughout the experiment. After three months of drought, the leaf area, number of leaves and root volume decreased, while root/shoot ratio and root density increased. The higher root hydraulic resistance in stressed plants caused decreases in leaf and stem water potentials resulting in lower stomatal conductance and indicating that water flow through the roots is a factor that strongly influences shoot water relations. The water stress affected transpiration (63% reduction compared with the control). The consistent decrease in g s suggested an adaptative efficient stomatal control of transpiration by this species, resulting in a higher intrinsic water use efficiency (P n /g s ) in drought conditions, increasing as the experimental time progressed. This was accompanied by an improvement in water use efficiency of production to maintain the leaf water status. In addition, water stress induced an active osmotic adjustment and led to decreases in leaf tissue elasticity in order to maintain turgor. Therefore, the water deficit produced changes in plant water relations, gas exchange and growth in an adaptation process which could promote the faster establishment of this species in gardens or landscaping projects in Mediterranean conditions. [Copyright &y& Elsevier]

Silvicultural thinning usually improves the water status of remaining trees in water-limited forests. We evaluated the usefulness of a dual stable isotope approach ( δC, δO) for comparing the physiological performance of remaining trees between forest stands subjected to two different thinning intensities (moderate versus heavy) in a 60-year-old Pinus halepensis Mill. plantation in semiarid southeastern Spain. We measured bulk leaf δC and δO, foliar elemental concentrations, stem water content, stem water δO ( δO), tree ring widths and leaf gas exchange rates to assess the influence of forest stand density on tree performance. Remaining trees in low-density stands (heavily thinned) showed lower leaf δO, and higher stomatal conductance ( g), photosynthetic rate and radial growth than those in moderate-density stands (moderately thinned). By contrast, leaf δC, intrinsic water-use efficiency, foliar elemental concentrations and δO were unaffected by stand density. Lower foliar δO in heavily thinned stands reflected higher g of remaining trees due to decreased inter-tree competition for water, whereas higher photosynthetic rate was largely attributable to reduced stomatal limitation to CO uptake. The dual isotope approach provided insight into the early (12 months) effects of stand density manipulation on the physiological performance of remaining trees. [ABSTRACT FROM AUTHOR]

The phenological stages of early-maturing peach trees were described using the traditional nomenclature of Baggiolini and according to the BBCH General Scale. The heat requirement of each stage was calculated as growing degree hours (GDH) and growing degree days (GDD). The annual growth pattern of trunk, shoot, and fruit was also studied. After dormancy breaking involving 225 chilling units, this early peach cultivar required ≈6244 GDH to reach full bloom and 27106 GDH before the fruit could be harvested. In the case of GDD, the heat requirements were 329 and 1246 for full bloom and fruit harvest, respectively. According to plant growth measurements, shoot growth lasted ≈7 months with a significant increase in the growth rate after fruit harvest reaching a maximum value in July. Trunk growth followed a similar annual pattern as that of the shoots but with its maximum rate occurring ≈30 days latter. Fruit growth, which lasted an average of 89 days from full bloom to harvesting, took place under mild climatic conditions (10 Feb. to 10 May) coinciding with only 30% of the total annual shoot length. This pattern of reproductive and vegetative growth pointed to the interest of redirecting regulated deficit irrigation practices in early-maturing cultivars toward postharvest water-saving strategies, but only to the extent that any limitation of shoot and trunk growth does not adversely affect the productivity of the following year. [ABSTRACT FROM AUTHOR]

Seedlings of Lycopersicon esculentum Mill. var. Amalia were grown in a growth chamber under a photoperiod of 16 h light at 25°C and 8 h dark at 20°C. Five different treatments were applied to 30-day-old plants: Control treatment (plants maintained in the normal growth conditions throughout the experimental time), heat acclimation (plants exposed to 35°C for 4 h in dark for 3 days), dark treatment (plants exposed to 25°C for 4 h in dark for 3 days), heat acclimation plus heat shock (plants that previously received the heat acclimation treatment were exposed to 45°C air temperature for 3 h in the light) and dark treatment plus heat shock (plants that previously received the dark treatment were exposed to 45°C air temperature for 3 h in the light). Only the heat acclimation treatment increased the thermotolerance of the photosynthesis apparatus when the heat shock (45°C) was imposed. In these plants, the CO2 assimilation rate was not affected by heat shock and there was a slight and non-significant reduction in maximum carboxylation velocity of Rubisco (Vcmax) and maximum electron transport rate contributing to Rubisco regeneration (Jmax). However, the plants exposed to dark treatment plus heat shock showed a significant reduction in the CO2 assimilation rate and also in the values of Vcmax and Jmax. Chlorophyll fluorescence measurements showed increased thermotolerance in heat-acclimated plants. The values of maximum chlorophyll fluorescence (Fm) were not modified by heat shock in these plants, while in the dark-treated plants that received the heat shock, the Fm values were reduced, which provoked a significant reduction in the efficiency of photosystem II. A slight rise in the total superoxide dismutase (SOD) activity was found in the plants that had been subjected to both heat acclimation and heat shock, and this SOD activity was significantly higher than that found in the plants subjected to dark treatment plus heat shock. The activity of Fe-SOD isoenzymes was most enhanced in heat-acclimated plants but was unaltered in the plants that received the dark treatment. Total CuZn-SOD activity was reduced in all treatments. Darkness had an inhibitory effect on the Mn-SOD isoenzyme activity, which was compensated by the effect of a rise in air temperature to 35°C. These results show that the heat tolerance of tomatoplants may be increased by the previous imposition of a moderately high temperature and could be related with the thermal stability in the photochemical reactions and a readjustment of Vcmax and Jmax. Some isoenzymes, such as the Fe-SODs, may also play a role in the development of heat-shock tolerance through heat acclimation. In fact, the pattern found for these isoenzymes in heat-acclimated Amalia plants was similar to that previously described in other heat-tolerant tomato genotypes. [ABSTRACT FROM AUTHOR]

BACKGROUND: Non‐conventional water sources and water‐saving techniques can be valuable in semi‐arid regions, although their long‐term effects on citrus quality are little known. This study evaluated the effects of irrigation with two sources, transfer water (TW) and reclaimed water (RW), combined with two irrigation strategies, full irrigation (FI) and regulated deficit irrigation (RDI), on fruit quality of mandarins and grapefruits during eight growth seasons. RESULTS: Reclaimed water irrigation in mandarin, without water restriction, influenced maturity index (MI) less than TW‐FI, because titratable acidity (TA) increased to a greater degree than soluble solid contents (SSC). Nevertheless, juice quality standards were satisfied. Regardless of the irrigation treatment (FI or RDI), a trend towards increasing fruit weight was also detected with RW. In grapefruit, its rootstock (Citrus macrophylla) enhanced salinity resilience with respect to the rootstock of mandarin ('Carrizo' citrange) and, hence, MI was not affected by RW. The RDI strategy, without saline stress (TW‐RDI), increased, to a similar degree, both SSC and TA in mandarin fruit, not affecting the MI. In grapefruit, the water stress of RDI did improve the MI due to the TA did not change and SSC increased significantly, the TA did not change. The combination of both strategies, RW‐RDI, decreased the MI only in some years because TA increased proportionally more than SSC in mandarin. CONCLUSIONS: The medium‐ and long‐term feasibility of using RW and RDI to irrigate citrus was demonstrated. However, they must be performed cautiously and with appropriate management to avoid damaging fruit quality as a result of phytotoxic elements. © 2019 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

The DESERT-prototype, a state-of-the-art compact combination of water treatment technologies based on filtration and solar-based renewable energy, was employed to reclaim water for agricultural irrigation. Water reclaimed through the DESERT-prototype (PW) from a secondary effluent of a wastewater treatment plant, as well as conventional irrigation water (CW) and the secondary effluent (SW) itself, were employed to cultivate baby romaine lettuces in a greenhouse in Murcia (Spain), by means of drip and sprinkler irrigation methods, thus establishing six treatments. Assessments of physicochemical and microbiological quality of irrigation water, as well as agronomic and microbiological quality of crops from all treatments, showed that results associated to PW complied in all cases with relevant standards and guidelines. In contrast, results linked to SW and CW presented certain non-compliance cases of water and crop microbiological quality. These assessments lead to conclude that the DESERT-prototype is an appropriate technology for safe water reclamation oriented to agricultural production, that can be complemented by a proper irrigation method in reaching safety targets. [ABSTRACT FROM AUTHOR]

The aim of our research was to discover the effects of the long-term irrigation with saline reclaimed (RW) and transfer (TW) water and different irrigation strategies: control (C) and regulated deficit irrigation (RDI) on yield and fruit quality of grapefruit at harvest and during cold storage. TW-RDI treatment decreased tree canopy (TC) and crop load, resulting in a 21% reduction of fruit yield. Regarding fruit quality, RW notably decreased peel thickness at harvest (about 8%); however, this difference was not remained during cold storage. Sugar/acid ratio was mainly increased by RDI, but also by RW, due to an important increase in soluble solid content (11% of average value for TW-RDI, RW-C and RW-RDI). In addition, RDI combined with RW, significantly increased the number of fruits in small category 5 at the end of cold storage. Finally, neither ratio yield/TC nor irrigation water productivity were affected by any irrigation treatments. [ABSTRACT FROM AUTHOR]

The aim was to assess the usefulness of spectral data to detect structural and physiological changes in Citrus crops under water and saline stress. Multispectral images were acquired from a fixed-wing Unmanned Aerial Vehicle (UAV) while concomitant measurements of gas exchange, plant water status, leaf structural traits and chlorophyll were taken in a commercial farm located in southeast Spain with two Citrus species, grapefruit and mandarin irrigated for eight years with saline reclaimed water (RW) combined with regulated deficit irrigation (RDI). Measurements at leaf scale and airborne flights were carried out twice a day, at 7 and 10 GMT. Irrigation with RW decreased gas exchange and leaf dry mass per unit area (LMA) on grapefruit. However, salinity from RW resulted in an increase in pressure potential (Ψ P ) on mandarin and allowed maintaining net photosynthesis (A) and stomatal conductance (g s ) when vapour pressure deficit increased. On both crops, leaf total chlorophyll (ChlT) concentrations were significantly reduced by RW. Moreover, RDI decreased A, g s and stem water potential (Ψ s ) on grapefruit, independently of water quality. Regarding spectral data, red wavelength (R) was significantly correlated with Chl T (p < 0.001), except when mandarin was subjected to stressful climatic conditions (at 10 GMT); since R was influenced, in addition to Chl T, by the plant water and gas exchange status. Near infrared (NIR) was a useful indicator of Ψ s , A and g s on both crops. The normalized difference vegetation index (NDVI) was clearly related to gas exchange in both species and to Ψ s only on mandarin. Finally, we combined data from both Citru s species and the best indicators were NIR and R. The novelty of this study was to show that diurnal changes in physiological and structural traits of Citrus irrigated with RW combined with RDI can be determined by multispectral images from UAVs. [ABSTRACT FROM AUTHOR]

Water scarcity and increasing water use in many socioeconomic sectors lead to an urgent need to improve irrigation management, especially in arid and semiarid areas, such as southeast Spain. For this reason, we studied, during 3 years, the possibility of scheduling regulated deficit irrigation (RDI) using maximum daily shrinkage (MDS) measurements on peach trees [ Prunus persica (L.) Batsch cv. 'Catherine'] in Murcia (Spain). Three irrigation treatments were established: a control treatment (C), irrigated above the estimated crop water requirements, and two treatments based on measurements of maximum daily trunk shrinkage signal intensity (MDS SI), namely a precision treatment (C) using a threshold value of MDS SI = 1 during all the period and a RDI treatment using MDS SI = 1 all the period except for stage II and post-harvest where MDS SI = 2. The low coefficients of variation for MDS SI indicated that this information was sufficient to adjust the irrigation schedule to maintain MDS SI close to the selected threshold values. Maintaining the MDS SI close to unity throughout the growing season allowed us to estimate peach water requirements (ET). The RDI treatment significantly reduced pruning weight, but no differences were found in terms of reproductive growth and yield. Moreover, RDI increased water productivity and fruit quality, since soluble solids content and maturity index were higher in the RDI treatment compared to C and C. This study demonstrated that irrigation scheduling in peach trees based exclusively on MDS SI was feasible without detrimental effects on yield and fruit quality. [ABSTRACT FROM AUTHOR]

The aim of this study was to evaluate the robustness of infra-red thermometry to estimate stomatal conductance (g s) in grapefruit trees. For this purpose, the ability of several thermal indices to determine g s was tested for different: (i) irrigation strategies: full irrigation (FI) and regulated deficit irrigation (RDI), (ii) water sources: transfer water (TW) -optimal for agricultural uses- and saline reclaimed water (RW) and (iii) phenological stages: flowering-sprouting (FS) and fruit growth (FG). During two growing seasons, measurements of g s and canopy temperature (T c) were taken in 14-year-old ´Star Ruby´ grapefruit trees (Citrus paradisi Macf.,). Air temperature (T a) was also recorded and then the derived thermal indices: T c -T a , and CWSI (crop water stress index) were calculated. Subsequently, thermal-g s correlations were established at different averaged thermal data intervals, and VPD (vapour pressure deficit) and PAR (photosynthetically active radiation) conditions. The results indicated that both, water quality and deficit irrigation, affected negatively g s and T c during FG. In addition, the highest r2 values in thermal indices-g s correlations were found when i) the thermal data was averaged 60 min before the g s measurement, ii) g s was measured over a wide range of VPD (between 0 and 3.5 kPa), and iii) PAR was 1200 µmol m−2 s−1. The ability of the thermal indices to estimate g s improved under RDI and RW conditions, when compared to the control treatment (TW-FI). Moreover, the thermal indices that more accurately estimated g s were T c -T a and CWSI in FS (P < 0.001), and the absolute values of T c in FG (P < 0.001). Overall, thermal indices obtained by infra-red sensors could be a useful tool to estimate g s in grapefruit trees. However, irrigation treatment, water quality, tree phenological stage and environmental conditions (VPD and PAR) must be considered when interpreting thermal indices-g s correlations. • Infra-red sensors allowed for estimating the stomatal conductance of grapefruit trees. • Environmental conditions affected the estimation of stomatal conductance. • Crop phenological stage affected thermal indices-stomatal conductance correlations. [ABSTRACT FROM AUTHOR]

Precise irrigation is essential in arid and semi-arid areas where water is scarce, such as the South-East of Spain. Therefore, finding a precise and reliable plant water status indicator, which could be automatically monitored, is of paramount importance. Maximum daily trunk shrinkage (MDS) showed some potential for irrigation scheduling. However, MDS records may be difficult to interpret and reference baselines could be useful for this interpretation. In the current study, measurements of midday stem water potential (Ψ s ) and MDS were taken over a 3-year period in peach trees [ Prunus persica (L.) Batsch cv. ‘Catherine’], in order to obtain reference baselines for irrigation scheduling. Plants were daily irrigated above their water requirements (∼120%) in order to obtain non-limiting soil water conditions. Climate parameters and MDS were recorded automatically, whereas midday stem water potential was assessed in the field every 3 days. The relationships between MDS and climate parameters such as ET 0 , daily maximum and midday air temperatures (T max and T mid , respectively), maximum and midday air vapour pressure deficit (VPD max and VPD mid , respectively) were determined. The results indicate that MDS records were better related to T mid and T max than to other meteorological variables. The relationship between MDS and Ψ s differed from year to year. However, these relationships varied greatly with the conditions of each year, tree phenological stage and crop load. Therefore, the growers must be aware of these factors when using MDS values for irrigation scheduling. [ABSTRACT FROM AUTHOR]

Irrigation techniques that reduce water applications are increasingly applied in areas with scarce water resources. In this study, the effect of two regulated deficit irrigation (RDI) strategies on peach [ Prunus persica (L.) Batsch cv. 'Catherine'] performance was studied over three growing seasons. The experimental site was located in Murcia (SE Spain), a Mediterranean region. Two RDI strategies (restricting water applications at stage II of fruit development and postharvest) based on stem water potential (Ψ) thresholds (−1.5 and −1.8 MPa during fruit growth and −1.5 and −2.0 MPa during postharvest) were compared to a fully irrigated control. Soil water content (θ), Ψ, gas exchange parameters, vegetative growth, crop load, yield and fruit quality were determined. RDI treatments showed significantly lower values of θ and Ψ than control trees when irrigation water was restricted, causing reductions in stomatal conductance and photosynthesis rates. Vegetative growth was reduced by RDI, as lower shoot lengths and pruning weights were observed under those treatments when compared to control. However, fruit size and yield were unaffected, and fruit quality was slightly improved by RDI. Water savings from 43 to 65 % were achieved depending on the year and the RDI strategy, and no negative carryover effect was detected during the study period. In conclusion, RDI strategies using Ψ thresholds for scheduling irrigation in mid-late maturing peach trees under Mediterranean conditions are viable options to save water without compromising yield and even improving fruit quality. [ABSTRACT FROM AUTHOR]

Highlights: [•] Irrigation exerted a great influence on the majority of the traits studied. [•] Sorbitol content affected by height (or location) of fruit in the crown. [•] Sucrose and fructose contents were affected by orientation. [•] Exposure to sunlight influenced soluble solid content. [•] Significant correlations were detected among fruit attributes. [ABSTRACT FROM AUTHOR]

Highlights: [•] A middle-late maturing peach cultivar was successfully implemented into QualiTree. [•] QualiTree was able to adequately simulate the effects of water stress on fruit growth. [•] Fructose, glucose and sorbitol contents in the fruit flesh were well simulated. [•] Water stress increased sugar contents in the fruit flesh. [ABSTRACT FROM AUTHOR]

Regulated deficit irrigation strategies are common practices in areas with low water availability. Thus, water stress, which can limit fruit growth, is imposed to the trees. Fruit thinning can be used to relieve this water stress in peach. In this paper, the ability of an existing fruit tree model (QualiTree) for describing the effects of water stress and fruit thinning on peach fruit and vegetative growth was assessed. The model was parameterized and calibrated for a very early-maturing peach cultivar ('Flordastar'). Important parameters were those expressing the effect of distance between organs on carbon exchange within the tree, the potential dry masses, and the relative growth rates of fruits and leafy shoots. Then, the model was tested in a wide range of water stress situations and three fruit thinning intensities: no thinning, commercial thinning, and heavy thinning. Fruit and vegetative growth simulations were consistent with observed data derived from 2006 field experiments. The variability over time of fruit and vegetative growth was well predicted. The model reproduced reductions in fruit growth observed in field experiments. It also reacted to simulated scenarios that combined water stress and thinning. Increasing thinning intensity reduced total fruit yield but increased fruit size at harvest, compensating the negative effects of water stress on fruit growth. These simulations broadened the predictive capabilities of the model and showed that it might be a useful tool in the design of innovative horticultural practices. [ABSTRACT FROM AUTHOR]

Abstract: Improving current approaches to quantify the transpiration of fruit trees is needed for water allocation purposes and to enhance the precision of water applications under full and deficit irrigation. Given that transpiration of tree crops is mainly modulated by canopy conductance (G c) and vapour pressure deficits, we developed a functional model of tree transpiration by quantifying an average daily G c based on radiation use efficiency and CO2 assimilation. For model calibration, an extensive experimental dataset of tree transpiration (E p) was collected in many of the main temperate fruit tree species, namely, apricot, apple, citrus, olive, peach, pistachio, and walnut, all under non-limiting water conditions, in different orchards in Spain and California (USA). In all species, E p was assessed by measuring sap flux with the Compensation Heat Pulse method for several months, and a transpiration coefficient (K t) was calculated as the ratio of measured E p to the reference evapotranspiration. For three deciduous species (apricot, peach and walnut) K t showed maximum values close to 1, a value which stayed more or less constant throughout the summer in peach and walnut. The maximum K t values were measured in pistachio (1.14) while they only reached 0.35 in olive and citrus trees. In the latter two species, K t varied seasonally between 0.2 and 0.6 depending on the weather. The average G c in July was high for apple, walnut, peach and pistachio (range 0.240–0.365molm−2 s−1) and low for olive and orange (range 0.074–0.100molm−2 s−1). The calibrated model outputs were compared against measured E p data, suggesting the satisfactory performance of a functional model for E p calculation that should improve the precision of current empirical approaches followed to compute fruit tree water requirements. [Copyright &y& Elsevier]

Abstract: Regulated deficit irrigation (RDI) strategy using saline reclaimed water is becoming a frequent practice under semiarid Mediterranean climatic conditions in the southeastern region of Spain. There is a concern that the long-term use of this strategy will affect the production sustainability of the agricultural soils. This paper evaluates the field consequences of this strategy on the accumulation of salts within the plant root zone. Full and regulated deficit surface drip deficit irrigation was combined with fresh water (EC 1dSm−1) and saline (EC 3dSm−1) tertiary reclaimed water to irrigate adult mandarin trees over a 3-year period. The control treatment received 100% of the crop evapotranspiration “ETc” and the RDI treatment received 50% of ETc during the 2nd stage of fruit growth. Soil water content was monitored every other week within the soil wetted volume under the emitter. Gravimetric soil samples were collected from 3 depths and at 3 distances to the emitter, twice a year: at the end of irrigation season and at the conclusion of RDI period. Soluble salts, electrical conductivity and sodium adsorption ratio were determined in the saturated paste extract. The results show how the RDI strategy intensifies the development of salinity gradient away from the emitter even when using good quality water. The combination of RDI with saline reclaimed water produced transient saline-sodic conditions at the outer superficial limits of the wetted bulb under the emitter. The appearance of such adverse conditions is alarming and would threaten the sustainability of agricultural soils. Therefore soil water deficit should be avoided whenever saline reclaimed water is in use for irrigation. [Copyright &y& Elsevier]

ABSTRACT We investigated whether stand structure modulates the long-term physiological performance and growth of Pinus halepensis Mill. in a semiarid Mediterranean ecosystem. Tree radial growth and carbon and oxygen stable isotope composition of latewood ( δ13CLW and δ18OLW, respectively) from 1967 to 2007 were measured in P. halepensis trees from two sharply contrasting stand types: open woodlands with widely scattered trees versus dense afforested stands. In both stand types, tree radial growth, δ13CLW and δ18OLW were strongly correlated with annual rainfall, thus indicating that tree performance in this semiarid environment is largely determined by inter-annual changes in water availability. However, trees in dense afforested stands showed consistently higher δ18OLW and similar δ13CLW values compared with those in neighbouring open woodlands, indicating lower stomatal conductance and photosynthesis rates in the former, but little difference in water use efficiency between stand types. Trees in dense afforested stands were more water stressed and showed lower radial growth, overall suggesting greater vulnerability to drought and climate aridification compared with trees in open woodlands. In this semiarid ecosystem, the negative impacts of intense inter-tree competition for water on P. halepensis performance clearly outweigh potential benefits derived from enhanced infiltration and reduced run-off losses in dense afforested stands. [ABSTRACT FROM AUTHOR]

• B. yuanmingense P10 130 promotes the growth of the leguminous plant D. incanum. • ANIb and dDDH supported the classification P10 130 as a B. yuanmingense strain. • Diverse genes involved in plant growth promotion traits are present in its genome. Strain P10 130, an isolated Bradyrhizobium strain from Argentina which promotes the growth of the leguminous plant Desmodium incanum by different mechanisms was previously selected as the best candidate for D. incanum inoculation based on broader selective criteria. A close relationship between this strain and B. yuanmingense was determined by MALDI BioTyper identification and 16S rRNA gene phylogenetic analysis. This study aimed to analyse the genome sequence of B. yuanmingense P10 130 in order to deepen our knowledge regarding its plant growth-promoting traits and to establish its phylogenetic relationship with other species of Bradyrhizobium genus. The genome size of strain P10 130 was estimated to be 7.54 Mb that consisted of 65 contigs. Genome Average Nucleotide Identity (ANI) analysis revealed that B. yuanmingense CCBAU 10071 T was the closest strain to P10 130 with ca. 96% identity. Further analysis of the genome of B. yuanmingense P10 130 identified 20 nod/nol/NOE, 14 nif/ 18 fix , 5 nap/ 5 nor genes, which may be potentially involved in nodulation, nitrogen fixation, and denitrification process respectively. Genome sequence of B. yuanmingense P10 130 is a valuable source of information to continue the research of its potential industrial production as a biofertilizer of D. incanum. [ABSTRACT FROM AUTHOR]

Water is not always accessible for agriculture due to its scarcity. In order to successfully develop irrigation strategies that optimize water productivity characterization of the plant, the water status is necessary. We assessed the suitability of thermal indicators by infrared thermometry (IRT) to determine the water status of grapefruit in a commercial orchard with long term irrigation using saline reclaimed water (RW) and regulated deficit irrigation (RDI) in Southeastern Spain. The results showed that Tc-Ta differences were positive in a wide range of vapor pressure deficits (VPD), and the major Tc-Ta were found at 10.00 GMT, before and after the highest daily values of VPD and solar radiation, respectively, were reached. In addition, we evaluated the relationships between Tc-Ta and VPD to establish the Non-Water Stressed Baselines (NWSBs), which are necessary to accurately calculate the crop water stress index (CWSI). Two important findings were found, which include i) the best significant correlations (p < 0.005) found at 10.00 GMT and their slopes were positive, and ii) NWSBs showed a marked hourly and seasonal variation. The hourly shift was mainly explained by the variation in solar radiation since both the NWSB-slope and the NWSB-intercept were significantly correlated with a zenith solar angle (θZ) (p < 0.005). The intercept was greater when θZ was close to 0 (at midday) and the slope displayed a marked hysteresis throughout the day, increasing in the morning and decreasing in the afternoon. The NWSBs determination, according to the season improved most of their correlation coefficients. In addition, the relationship significance of Tc-Ta versus VPD was higher in the period where the intercept and Tc-Ta were low. CWSI was the thermal indicator that showed the highest level of agreement with the stem water potential of the different treatments even though Tc and Tc-Ta were also significantly correlated. We highlight the suitability of thermal indicators measured by IRT to determine the water status of grapefruits under saline (RW) and water stress (RDI) conditions. [ABSTRACT FROM AUTHOR]