Contrasting Water Availability Research Articles

Dissecting and modelling the comparative adaptation to water limitation of sorghum and maize: role of transpiration efficiency, transpiration rate and height

Abstract Maize is considered less drought-tolerant than sorghum, but sorghum is commonly grown as a short triple dwarf (3dwarf) type, so difference in plant height confounds the species comparison. The objectives of this study were to experimentally determine effects of species and plant height differences on transpiration efficiency (TE) and transpiration rate per unit green leaf area (TGLA) and use findings to explain input parameters in a simulation study on the comparative adaptation of 3dwarf sorghum and maize in environments with contrasting water availability. Maize, tall double dwarf (2dwarf) and short 3dwarf sorghum genotypes were grown in two lysimeter experiments in 2011 in SE Queensland, Australia. Each plant was harvested after anthesis and total transpiration, shoot and root dry mass were measured to estimate TE. Daily TGLA was used to compare transpiration rates. Species and height had limited effect on TE, but significantly affected TGLA. This was associated with differences in biomass allocation. The similar TE but higher TGLA in maize compared with 3dwarf sorghum meant it potentially produces more biomass, consistent with published differences in biomass accumulation and radiation use efficiency (RUE). The simulation study, which used similar TE for maize and 3dwarf sorghum, but captured differences in TGLA through differences in RUE, predicted crossover interactions for grain yield between species and total water use. The greater TGLA of maize decreased grain yield in water-limited environments, but increased yields in well-watered situations. Results highlight that similarity in TE and differences in TGLA can influence comparative adaptation to water limitation.

Stover biogas potential of corn crops grown under contrasting water availability and nitrogen supply

Corn stover is a biogas feedstock capable of enhancing agriculture bioenergy potential. Although the influence of growing conditions on biogas yield of corn stover has been reported, the joint effects of water and nitrogen on biogas production potential have not been addressed. A two year experiment (Exp. 1 and Exp. 2) was conducted in Balcarce, Argentina to assess nitrogen supply effects on stover composition and potential methane yield of corn crops grown under contrasting water regimes. Treatments were a combination of two nitrogen fertilization doses (0 and 120 kg ha−1) and two water regimes (irrigated and rainfed). Biomass composition (mass closure procedure) was determined, a BMP test was carried out and first-order kinetic parameters were obtained. Interactive effects of nitrogen and water on stover composition were found. BMP tests showed that the biogas production rate (k) decreased upon irrigation while its response to nitrogen depended on water availability. Nitrogen supply decreased specific biogas potential (Bmax) independently of water availability. Methane yield increased with nitrogen fertilization under irrigation, while it decreased under rainfed conditions. The observed water and nitrogen supply interactive effects on stover yield, methane yield and biomass conversion efficiency highlights the importance of considering the joint effects of multiple factors when trying to assess the effects of the environment on biomass quality for bioenergy purposes.

Comprehensive analysis of the isomiRome in the vegetative organs of the conifer Pinus pinaster under contrasting water availability.

An increasing number of microRNAs (miRNAs) and miRNA-related sequences produced during miRNA biogenesis, comprising the isomiRome, have been recently highlighted in different species as critical mediators of environmental stress responses. Conifers have some of the largest known genomes but an extensive characterization of the isomiRome from any conifer species has been lacking. We provide here a comprehensive overview of the Pinus pinaster isomiRome expressed in roots, stem and needles under well-watered and drought conditions. From the 13,441 unique small RNA sequences identified, 2,980 were annotated as canonical miRNAs or miRNA* and the remaining were classified as isomiRNA or miRNA-like sequences. A survey of their expression patterns highlighted roots as the most responsive organ under drought, where specific sequences of which a 24-nt novel miRNA stood out, were strongly down-regulated. Given the putative roles of the miRNA-targeted transcripts validated specifically in root tissues, some of the miRNAs, conserved and novel, are shortlisted as potential regulators of drought response. These results provide a valuable resource for comparative studies between gymnosperms and angiosperms. Furthermore, it evidences high transferability of the isomiRome between pine species being a useful basis for further molecular regulation and physiological studies, and especially those focused on adaptation to drought conditions.

Foliar traits of sessile oak (Quercus petraea Liebl) seedlings are largely determined by site properties rather than seed origin.

Due to climate change, sessile oak (Quercus petraea) seedlings experience an increasing risk of drought during regeneration of forest stands by management practices. The present study was aimed at elucidating the potential of sessile oak seedlings originating from sites with different aridity and nitrogen (N) supply to acclimate to contrasting water availability. For this purpose, a free-air cross-exchange experiment was conducted between a dry and a humid forest stand with high and low soil N contents, respectively, during two consecutive years differing in aridity before harvest. Almost all structural and physiological foliar traits analyzed did not differ consistently between seed origins during both years, when cultivated at the same site. As an exception, the arid provenance upregulated foliar ascorbate contents under drought, whereas the humid provenance accumulated the phenolic antioxidants vescalagin and castalagin (VC) under favorable weather conditions and consumed VC upon drought. Apparently, differences in long-term aridity at the forest sites resulted in only few genetically fixed differences in foliar traits between the provenances. However, structural and physiological traits strongly responded to soil N contents and weather conditions before harvest. Foliar N contents and their partitioning were mostly determined by the differences in soil N availability at the sites, but still were modulated by weather conditions before harvest. In the first year, differences in aridity before harvest resulted in differences between most foliar traits. In the second year, when weather conditions at both sites were considerably similar and more arid compared to the first year, differences in foliar traits were almost negligible. This pattern was observed irrespective of seed origin. These results support the view that leaves of sessile oak seedlings generally possess a high plasticity to cope with extreme differences in aridity by immediate acclimation responses that are even better developed in plants of arid origin.

Different Post-Sowing Nitrogen Management Approaches Required to Improve Nitrogen and Water Use Efficiency of Canola and Mustard.

Strategic use of nitrogen (N) may improve N use efficiency, but there is limited information on the influence of N supply at crucial growth stages on N accumulation, water use, and water use efficiency of canola and mustard. In this study, we hypothesize that genetic variation among canola and mustard can alter the response of timing and rate of post-sowing N application at targeted phenological growth stages by improving N and water use and their efficiencies. Field experiments were conducted in South Australia during two growing seasons with contrasting water availabilities. Two mustard and four canola cultivars, including two triazine tolerant (TT) and two non-TT cultivars were evaluated under different post-sowing N application strategies comprising three N rates and different timings of application. Mustard used more water than canola in the season with higher rainfall, but canola and mustard used similar amounts of water in the drier season. Nitrogen increased the water use efficiency (WUE) of canola and mustard cultivars. Nitrogen rate and timing did not influence the total water use of canola and mustard but influenced the partitioning of pre- and post-flowering water use. Even though, highest N uptake was observed in the treatment with continuous supply of N with 200 kg N ha−1 in five splits it did not influence the N efficiencies parameters which indicate that yield of canola and mustard are limited by N rate in these environments. In treatment with limited N supply, targeting N at the rosette stage improve N use efficiency of canola and mustard. However, the limited N uptake potential of mustard makes timing of N application the most important consideration whereas correct N rate should be main consideration for canola.

Sunflower growth and yield response to sewage sludge application under contrasting water availability conditions

Good knowledge of crop response to biosolids is necessary for optimizing their use as soil amendments. The present 2-yr study evaluated the impact of soil application of municipal sewage sludge on growth, dry matter translocation, achene and oil yield as well as on achene Fe, Cu, Zn and Mn content of field-grown sunflower (Helianthus annuus L.) under contrasting water availability in terms of seasonal rainfall. Treatments included three sewage sludge rates (9, 18, and 36 Mg dry weight ha−1 yr−1) compared with inorganic fertilizer (138 kg N plus 24 kg P ha−1 yr−1) and a non-amended control. Adding sewage sludge increased stem diameter, height, and early growth of sunflower plants compared with control. Dry matter at flowering was positively correlated with translocation of dry matter to achenes (r = 0.855**). However, high early dry matter was translated into enhanced achene yield only with adequate water availability along growth cycle, while water shortage resulted in fewer achenes and poor seed-filling. Sewage sludge application increased achene yield even under water shortage, suggesting a beneficial effect of sewage sludge on soil water status. Achene yield with added sewage sludge was similar to or greater than with the inorganic fertilizer. Sewage sludge decreased achene oil concentration and increased achene N concentration, compared with the non-amended control, without affecting Zn, Fe, Mn, and Cu content in achenes even at the high application rate of 18 Mg ha−1. Findings support that sewage sludge addition in soil at the rate of 9 Mg ha−1 was agronomically adequate and could replace inorganic fertilizer in sunflower production, irrespective of seasonal rainfall amount and distribution patterns.

Different root strategies of perennial native grasses under two contrasting water availability conditions: implications for their spatial distribution in desert dunes

The distribution pattern of perennial native grasses in the dune systems of the Monte desert might be determined by the ability of plant roots to acquire water under drought conditions in different topographical positions and soil substrates. This study examined differences in root traits of two species growing in sand dunes, Aristida mendocina and Panicum urvilleanum, and two species growing in interdune valleys, Pappophorum caespitosum and Leptochloa crinita, under different water availability conditions in a sand substrate. Grasses were grown in rhizotrons and the factorial design included species, irrigation treatments, days from sowing, and depth soil profile. Root length, total root length, number of root branches, length of root branches-to-number of root branches ratio (LB:NB), daily elongation rate (DER), root length density (RLD), root angles, aerial and root dry mass, and shoot-to-root ratio (S:R) were measured. The four species studied were affected by drought conditions causing a decrease in root growth and modifying root structure, partition of assimilates, root angles, and exploration of the soil profile. However, we found that species from sand dunes were less affected by drought and showed a deeper root exploration under drought conditions, mainly due to proliferation of longer and more lateral roots in the deepest soil layer. The different root traits and responses of the species under drought conditions would imply adaptations to the topographical position each species occupies and could explain their spatial distribution in desert dunes.

Changes in irradiance and vapour pressure deficit under drought induce distinct stomatal dynamics between glasshouse and field-grown poplars.

Recent research has shown that plant acclimation to diverse patterns of light intensity modifies the dynamics of their stomatal response. Therefore, whether plants are grown in controlled conditions or in the field may impact their stomatal dynamics. We analysed the stomatal dynamics of two Populus euramericana and two Populus nigra genotypes grown in the field under contrasting water availability. By comparing their stomatal dynamics with that of the same genotypes grown in a glasshouse, we were able to test whether differences between these growing conditions interacted with genotypic differences in affecting stomatal dynamics and responses to soil water deficit. We found that, despite higher stomatal density and smaller size, in the field stomatal dynamics were much slower than in the glasshouse. Overall, differences among genotypes and their response to soil water deficit were much less pronounced in the field compared with the glasshouse. These results indicate that stomatal dynamics are regulated by both genotype-specific and environmental factors. Moreover, having slower stomata may be advantageous under some conditions. While stomatal dynamics were linked with whole-plant transpiration per leaf area in both experiments, the contribution of stomatal morphology varies dependent on the environmental conditions.

Impacts of a partial rainfall exclusion in the field on growth and transpiration: consequences for leaf-level and whole-plant water-use efficiency compared to controlled conditions

• Water use efficiency (WUE), oftentimes estimated as transpiration efficiency (TE): the amount of biomass produced with regard to the water used, has not yet been used as a breeding trait to select poplar genotypes with simultaneously high productivity and conservation of water. Before its application as a selection target, evidence must be presented showing that WUE or its estimators remain constant with age and across environmental conditions.• We conducted a rainfall exclusion experiment in the field on two Populus euramericana (Moench.) and two Populus nigra (L.) genotypes, and assessed leaf-level (A/gs) and whole-plant WUE (DMT/WU as well as their components and related traits. Then, we aimed to compare these results with the same poplar genotypes grown in a glasshouse under contrasting water availability.• Despite a reduction of soil water content and whole-plant transpiration, growth was stimulated in the rainfall exclusion plot, likely as a result of an increased nitrogen assimilation. However, TE values between the glasshouse and the field were similar, and genotype ranking remained fairly constant for transpiration, carbon isotopic discrimination (∆, as a proxy for Wi) and TE. Moreover, even though the drivers of WUE in both experiments were different, increases of WUE measured as ∆ or TE was not associated with lower biomass production. Relatively good agreement was found between ∆ and TE in the field, absence of a similar correlation in the glasshouse is discussed.• These results suggest that ∆ may be a good proxy for TE, and could be used, both as a breeding target for genotype selection in glasshouses without impacting biomass production when planted in the field. However, reduced water availability modified the genotype ranking more significantly than between the field/glasshouse experiments, suggesting a diversity of poplar response to drought that should be considered in breeding strategies.

A field experiment to determine the effect of dry-season irrigation on vegetative and reproductive traits in the wet-deciduous tree Bonellia nervosa

AbstractSeasonally dry tropical forests (SDTFs) stand out by the diversity of phenological patterns used by plants to deal with dry periods. Although the predominant phenological pattern is dry deciduousness, in Mesoamerican SDTFs the heliophilous tree species Bonellia (formerly Jacquinia) nervosa displays an unusual inverted leaf phenology, producing and holding leaves through the dry season while becoming deciduous in the rainy season. Applying a dry season irrigation field experiment (no water, low watering, high watering), we studied the consequences of contrasting water availability from a phenological plasticity response perspective. Contrary to our expectations, our results show no effect of irrigation treatment on leaf phenology. In addition, mid-day twig water potential showed no significant differences across treatments, but reproductive phenological responses varied among treatments: canopy flowering per cent decreased gradually until the beginning of the wet season in all treatments; meanwhile canopy fruit per cent showed a significant decline under low irrigation. Finally, non-structural carbohydrate concentration (starch) was significantly higher in the high irrigation treatment. Our results showed that inverted leaf phenology remains unaffected regardless of supplemental water availability, and suggest a reallocation of non-structural carbohydrates to fruits and seeds in high-irrigation treatments. Given the current and expected increase in extreme drought events, investigations on the responses of trees of different phenologies, including those of inverted leafing such as Bonellia nervosa, are warranted.

Can native shrubs facilitate the establishment of trees under arid bioclimate? A case study from Tunisia

The scarcity of tree regeneration is a major concern for the long-term conservation of tree cover in the arid areas of Tunisia and the causes of this shortage are poorly understood. The objectives of the study, conducted in the National Park of Bou Hedma, were to examine the direction of interaction between the nurse shrub Retama raetam on the survival of the keystone tree species Acacia tortilis subsp. raddiana in the arid bioclimate of Tunisia.The survival of transplants of Acacia was monitored during two years in the presence/absence of Retama in two communities of contrasting water availability. We quantified the intensity of biotic interactions and their variation between the two communities and among three treatments (in areas without woody vegetation, among intact Retama shrubs, and among cropped Retama shrubs).Contrary to the predictions of established models of plant-plant interactions, the results always showed negative interactions (competition or allelopathy) between plants along the natural water stress gradient. Our study highlights the fact that nurse based ecological restoration should not be an automatic process, but must be tailored to the species and environment in question.

Climate and water availability impacts on early growth and growth efficiency of Eucalyptus genotypes: The importance of GxE interactions

Predicting Eucalyptus plantation productivity in the face of climate change is a key challenge for intensively managed forest plantations around the world. Forest industry tree improvement and advanced silvicultural programs are charged with maximizing forest production but face challenging selection choices where Eucalyptus genotypes may be sensitive to genetic × environment interactions (GxE). Our study investigated the importance of GXE interactions by measuring the early (establishment to 2.6 years old) cumulative growth response of 30 selected genotypes of Eucalyptus globulus, E. nitens, E. badjensis, E. smithii, E. nitens × globulus and E. camaldulensis × globulus hybrid seedlings established across contrasting water availability conditions (High vs Low Irrigation). We compared the same genotypes at a low vapor pressure deficit (VPD) and clayey soil (North site) and a high VPD sandy soil (South site) in order to evaluate the stability of these genotypes across environmental gradients and thus evaluate the importance of genetic versus environmental impacts on growth. Stand growth was evaluated at 2.6 years when leaf area index (LAI) reached canopy closure in order to estimate a growth efficiency relationship (GE) with current annual increment (CAI). As expected, irrigation increased cumulative growth and LAI for all taxas, except for E. smithii at the North site. Genotypes showed large significant differences of performance within and across sites under each irrigation treatment. However, a strong relationship between North and South cumulative volume at age 2.6 years was observed for irrigated genotypes but not for non-irrigated genotypes. This suggests that a large GxE interaction may be expected under low water resource availability conditions associated with strong effects in ranking change of evaluated taxas and genotypes. Comparing taxas with at least two genotypes or more in our experiment, GE increased under High Irrigation for all taxas across sites. However, E. nitens × globulus hybrids showed small differences between High vs Low Irrigation treatments GE relationships compared to E. nitens and E. globulus genotypes. Our results suggest the need for strategic allocation of genotypes to contrasting drought risk environments and the need to assess our understanding of how particular genotypes interact with water stress conditions.

Differences in isoprenoid-mediated energy dissipation pathways between coastal and interior Douglas-fir seedlings in response to drought.

Plants have evolved energy dissipation pathways to reduce photooxidative damage under drought when photosynthesis is hampered. Non-volatile and volatile isoprenoids are involved in non-photochemical quenching of excess light energy and scavenging of reactive oxygen species. A better understanding of trees' ability to cope with and withstand drought stress will contribute to mitigate the negative effects of prolonged drought periods expected under future climate conditions. Therefore we investigated if Douglas-fir (Pseudotsuga menziesii(Mirb.)) provenances from habitats with contrasting water availability reveal intraspecific variation in isoprenoid-mediated energy dissipation pathways. In a controlled drought experiment with 1-year-old seedlings of an interior and a coastal Douglas-fir provenance, we assessed the photosynthetic capacity, pool sizes of non-volatile isoprenoids associated with the photosynthetic apparatus, as well as pool sizes and emission of volatile isoprenoids. We observed variation in the amount and composition of non-volatile and volatile isoprenoids among provenances, which could be linked to variation in photosynthetic capacity under drought. The coastal provenance exhibited an enhanced biosynthesis and emission of volatile isoprenoids, which is likely sustained by generally higher assimilation rates under drought. In contrast, the interior provenance showed an enhanced photoprotection of the photosynthetic apparatus by generally higher amounts of non-volatile isoprenoids and increased amounts of xanthophyll cycle pigments under drought. Our results demonstrate that there is intraspecific variation in isoprenoid-mediated energy dissipation pathways among Douglas-fir provenances, which may be important traits when selecting provenances suitable to grow under future climate conditions.

Seasonal changes in water sources used by woody species in a tropical coastal dune forest

Our aim was to investigate the water sources used by woody species under contrasting water availability and the extent of water-sources-use differentiation among dominant woody species in a tropical coastal dune forest. We sampled 15 woody species in a Brazilian restinga forest and, through Bayesian isotope mixing models, we estimated the proportion of water sources used. We tested whether water-sources-use was (i) different between contrasting water availability conditions; (ii) dependent on growth form, plant size or crown illumination; and (iii) influenced by stand density, evenness or biomass. We found a seasonal variation in water-sources-use, but no vertical soil-water partitioning among woody species. In wetter periods, plants used mainly water from top-soil, as a shallow water table limited water uptake to top-soil layers recharged with rainwater. Contrastingly, during drier periods, with the absence of rain and a deeper water table, plants generally relied on deeper (50 cm) soil layers. Only under less-wet conditions, a greater evenness and density implied higher water-uptake depth heterogeneity among plants. However, changes in the main water-sources used by plants were neither evoked in more dense or diverse plots, nor induced by plant size. Our study shows that restinga species have dynamic shifts in water-uptake depth caused by seasonal water availability changes, influenced by the combined effect of insufficient moisture at shallow soil layers and water-table lowering in drier periods. These temporal shifts are common among species, implying that restinga woody community has a homogeneous strategy of water-resources acquisition. This study enhances our understanding of the effects that water variations can have on water-resource use in restinga forests.

Exploring soybean management options for environments with contrasting water availability

AbstractSoybean is commonly cultivated under rainfed conditions being water availability the main constraint. We evaluated the performance of different managements under contrasting water availability to test possible trade‐offs among managements, and to determine physiological variables explaining these yield differences. Four treatments were designed through specific combinations of cultivar, row spacing and stand density. They were classified as stress tolerance or yield potential strategies and were evaluated under two contrasting water availability treatments. Treatments ranged from 349 to 954 mm total water availability. Water stress treatments yielded 72% and 59% of the well‐watered treatment each year, similar to frequent soybean water stress levels for our production region. Management treatments showed significant yield differences (p < 0.05), but the management × water availability interaction did not (p = 0.42). No management option helped reduce negative water stress effects. Highest yields were achieved using 0.25 m row spacing, a stand density of 60 pl per m2, and a high yield potential genotype. Yield variations were explained by differences in harvested seeds per unit area (R2 = 0.75; p < 0.001) and total N uptake at maturity (R2 = 0.93; p < 0.001) across environments. Because management strategies specifically tailored to cope with water shortages showed limited value, farmers need to target yield potential management options.

Narrow-sense heritability and PST estimates of DNA methylation in three Populus nigra L. populations under contrasting water availability

In a context of climate change and forest decline, a better understanding of the sources of tree flexibility involved in phenotypic plasticity and adaptation is needed. These last years, the role of epigenetics in the response to environmental variations has been established in several model plants at the genotype level but little is known at the level of natural populations grown in pedoclimatic sites. Here, we focused on three French natural populations of black poplar, a key pioneer tree from watersheds, planted in common garden and subjected to controlled variations of water availability. We estimated common genetic parameters such as narrow-sense heritability (h2), phenotypic differentiation index (PST), and the overall genetic differentiation index (FST) from genome-wide SNPs to evaluate the extent of epigenetic variations. Indeed, global DNA methylation levels from individuals exposed to drought or irrigated in a common garden were used. We found that the three populations were not distinguished by their levels of DNA methylation. However, a moderate drought was associated to a significant decrease in DNA methylation in the populations. Narrow-sense heritability and PST estimates of DNA methylation were similar to those found for biomass productivity. Heritability and PST were higher when trees were subjected to drought than in control condition. Negative genetic correlations between global DNA methylation and height or biomass were detected in drought condition only. Altogether, our data highlight that global DNA methylation acts as a genetic marker of natural population differentiation under drought stress in a pedoclimatic context.

Effect of insect herbivory on plant community dynamics under contrasting water availability levels

Abstract Plant diversity is impacted by multiple global change drivers but also by altered biotic interactions with antagonist and mutualist organisms that can potentially affect species coexistence. With a 2‐year, outdoor mesocosm experiment in realistic mesic grassland communities, we explored the role of insect herbivory in impacting plant community dynamics under contrasting levels of water availability simulating altered rainfall regimes. We selected a grasshopper species (Calliptamus italicus L.) feeding predominantly on forbs while avoiding grasses. High water availability reduced species coexistence, boosting productivity while decreasing individual plant survival. At the community level, herbivores were not able to promote species coexistence but asymmetrically influenced grasses and forbs, reducing forb biomass under high water availability. Herbivores shaped individual plant responses to both abiotic conditions and individual‐neighbours’ interactions. Herbivores influenced focal plant survival by altering the effect of neighbouring plants, mitigating the negative effect of high neighbour biomass at low water availability and exacerbating it at high level of water availability. Synthesis. Altered rainfall has the capacity to change the relative strength of plant–plant interactions and also to determine the effects of herbivores on grassland communities. The complexity of the interactions between plants and herbivores and the observed context dependence indicate the need to incorporate multiple biotic and abiotic drivers to fully understand the mechanisms underlying plant dynamics and species coexistence in a changing world.

Changes in Leaf and Shoot Water Statutes of Grapevines in Response to Contrasting Water Availability and Glycine Betaine Pulverization

Drought is one of the most widespread stress factors adversely affecting plant growth, crop yield and quality. In Subtropical region, on the face of global warming, temperature extremes aggravate the negative effects of drought. Increased resistance to stress has been achieved in several plants by exogenous application of various organic osmoprotectants. In this study, the role of glycine betaine (GB) as exogenous application, is aimed to investigate for increasing grapevine stress tolerance to drought. The grapevines of Alphonse Lavalléeʼ cultivar, grafted on the rootstock 41 B, were subjected to four different applications; (1) full irrigation (FI) as control (irrigation at field capacity level), (2) deficit irrigation (DI, 50% of FI), (3) DI plus 5000 ppm GB pulverization, and (4) DI plus 10000 ppm GB pulverization in a pot experiment under glasshouse condition. Leaf fresh weight of vines subjected to DI was 31.8% lower than those of FI vines. GB appeared to exert an influence on leaf water statute, slightly alleviating the leaf water loss resulting from water shortage. GB treatments, regardless of the concentration, slightly increased the fresh weight of the leaves (22.2% lower than FI). Investigations on leaf turgid weight and dry weight were also similar to those of fresh weight in that the highest and the lowest values were determined in FI and DI applications, respectively. Reduction in shoot water content in response to water deficit was closely related to the decrease in leaf water content.

Foliar application of selenium increases fertility and grain yield in bread wheat under contrasting water availability regimes

The study was conducted to assess whether selenium (Se) application modulates fertility to alter grain yield in bread wheat grown under different moisture regimes. Seeds of wheat cultivar Millat-2011 were sown in the plots using a randomized complete block design with three replicates per treatment. After germination, the plants were exposed to six moisture regimes, viz. no irrigation after germination, irrigation at boot stage, irrigations at boot and grain-filling stages, irrigations at crown root, boot and grain-filling stages, irrigations at crown root, boot, heading and grain-filling stages and irrigations at crown root, stem elongation, boot, heading and grain-filling stages. At the heading stage, foliar spray of sodium selenate (0, 2 and 4 mg Se L−1) was done. Withholding water at early growth stages significantly increased oxidative stress and decreased growth and grain yield. Irrespective of moisture regimes, foliar application of Se (2 mg L−1) decreased oxidative stress, modulated photosynthetic pigments and fertility and increased grain yield in wheat. The Se-mediated increase in grain yield was attributed to the increase in chlorophyll and ascorbic acid contents and fertility coupled with decrease of oxidative stress under different moisture regimes. The results could be helpful to manage wheat production in the semi-arid environments.

Sex determines xylem anatomy in a dioecious conifer: hydraulic consequences in a drier world.

Increased drought frequency and severity may reshape tree species distribution in arid environments. Dioecious tree species may be more sensitive to climate warming if sex-related vulnerability to drought occurs, since lower performance of one sex may drive differential stress tolerance, sex-related mortality rates and biased sex ratios. We explored the effect of sex and environment on branch hydraulic (hydraulic conductivity and vulnerability to embolism) and trunk anatomical traits in both sexes of the dioecious conifer Juniperus thurifera L. at two sites with contrasting water availability. Additionally, we tested for a trade-off between hydraulic safety (vulnerability to embolism) and efficiency (hydraulic conductivity). Vulnerability to embolism and hydraulic conductivity were unaffected by sex or site at branch level. In contrast, sex played a significant role in xylem anatomy. We found a trade-off between hydraulic safety and efficiency, with larger conductivities related to higher vulnerabilities to embolism. At the anatomical level, females' trunk showed xylem anatomical traits related to greater hydraulic efficiency (higher theoretical hydraulic conductivity) over safety (thinner tracheid walls, lower Mork's Index), whereas males' trunk anatomy followed a more conservative strategy, especially in the drier site. Reconciling the discrepancy between branch hydraulic function and trunk xylem anatomy would require a thorough and integrated understanding of the tree structure-function relationship at the whole-plant level. Nevertheless, lower construction costs and higher efficiency in females' xylem anatomy at trunk level might explain the previously observed higher growth rates in mesic habitats. However, prioritizing efficiency over safety in trunk construction might make females more sensitive to drought, endangering the species' persistence in a drier world.