Rainout Shelters Research Articles

Ekmeklik buğdayda (Triticum aestivum L.) 15N izotopu kullanılarak çiçeklenme sonrası kuraklığın azot mobilizasyonu ve gelişimine etkileri

Water and nitrogen shortage are one of the main limiting factors of crop productivity such as wheat and cereals. Increased variation and changes in climate conditions are expected to dominate yield potential of wheat. Nitrogen isotope technique widely used in recent years provides useful information about mobilization and nitrogen use efficiency under environmental constraints. This study aimed to determine the effects of drought conditions applied during different growing periods on nitrogen uptake by using stable 15N isotope, yield and quality properties and stomatal conductivity of bread wheat. Environmental variation was obtained by designing 4 artificial practices (irrigated condition, rainfed condition, early drought (flowering-harvest) and late drought (grain filling-harvest) by rainout shelter with covering progress about drought in different growing periods. Number of grains per spike, 1000 grain weight, single spike yield, spike numbers per square meter, plant height, grain yield, biomass yield, stomatal conductance, protein, ash content and stem δ15N (‰), flag leaf δ15N (‰), grain δ15N (‰) values were determined. The drought period from the beginning of flowering till harvest of plants had adverse impact on grain yield and yield components. The results clearly indicated the practices that may cause drought stress in the generative period should be avoided. In addition, nitrogen use efficiency of bread wheat was disrupted with the decrease in the amount and efficiency of plant water use during drought periods. The results also revealed that contribution of nitrogen to crop yield decreased due to less consumption of nitrogen in plant metabolic activities during drought periods. Based on the results additional water supply decreased δ15N content in mature grains from 13420 ‰ to 9278 ‰. Nitrogen applied in stem elongation period had greater contribution to grain δ15N content (15269 ‰) compared to tillering growth stage (8975 ‰). Nitrogenous fertilizer application time suggested not to be delayed to improve nitrogen contribution in metabolic activities and to prevent postponing the tillering and stem elongation periods. The application of nitrogen improved mobilization and efficiency of nitrogen contribution to different plant parts during generative development stages of bread wheat.

Pinpointing genomic loci for drought-induced proline and hydrogen peroxide accumulation in bread wheat under field conditions

BackgroundProline (Pro) and hydrogen peroxide (H2O2) play a critical role in plants during drought adaptation. Genetic mapping for drought-induced Pro and H2O2 production under field conditions is very limited in crop plants since their phenotyping with large populations is labor-intensive. A genome-wide association study (GWAS) of a diversity panel comprised of 184 bread wheat cultivars grown in natural field (control) and rain-out shelter (drought) environments was performed to identify candidate loci and genes regulating Pro and H2O2 accumulation induced by drought.ResultsThe GWAS identified top significant marker-trait associations (MTAs) on 1A and 2A chromosomes, respectively for Pro and H2O2 in response to drought. Similarly, MTAs for stress tolerance index (STI) of Pro and H2O2 were identified on 5B and 1B chromosomes, respectively. Total 143 significant MTAs were identified including 36 and 71 were linked to drought and 2 and 34 were linked to STI for Pro and H2O2, respectively. Next, linkage disequilibrium analysis revealed minor alleles of significant single-markers and haplotypes were associated with higher Pro and H2O2 accumulation under drought. Several putative candidate genes for Pro and H2O2 content encode proteins with kinase, transporter or protein-binding activities.ConclusionsThe identified genetic factors associated with Pro and H2O2 biosynthesis underlying drought adaptation lay a fundamental basis for functional studies and future marker-assisted breeding programs.

Thermal tolerance and growth responses to in situ soil water reductions among alpine plants

ABSTRACT Background Changes to precipitation patterns and warming temperatures are predicted to reduce the water available to Australian alpine plants during the growing season. Soil water deficits are likely to co-occur with frost extremes that are common throughout the year and heatwaves which are increasing in severity with ongoing climate change. Aims We aimed to determine whether co-occurring reductions in soil moisture would affect the capacity of alpine plants to tolerate temperature extremes. Methods We used small rainout shelters to impose a drought treatment in situ in the alpine zone, which chronically reduced soil moisture in plots of alpine plant species including evergreen shrubs, graminoids and perennial forbs. We determined photosynthetic freezing tolerance and heat tolerance during the growing season across 2 years, and measured plant growth, in response to the drought treatment. Results Thermal tolerance was insensitive to chronically reduced soil moisture, and graminoids exhibited overall greater freezing and heat tolerance thresholds than other life forms. The drought treatment improved shrub growth, likely due to the amelioration of wind and the slightly warmer temperatures provided by the rainout shelters. Conclusion We conclude that Australian alpine plants maintain high tolerances to both high- and low-temperature extremes during the growing season and are relatively robust to combined temperature extremes and reductions in near-surface soil moisture that are likely to occur with ongoing climate warming.

Higher resistance and resilience of bacterial growth to drought in grasslands with historically lower precipitation

Climate change is expected to alter precipitation regimes, resulting in longer periods of drought and heavier precipitation events. Even though the direct effect of water availability on soil microbial processes is well documented, the influence of precipitation legacy on microbial resistance and resilience to drought remains unclear. Using soils from a natural mean annual precipitation (MAP) gradient (∼550–950 mm yr−1) equipped with long-term (>8 yr) rain-out shelters, we investigated how the history of precipitation influenced microbial ‘resistance’ (tolerance to drying) and ‘resilience’ (ability to recover growth rates following rewetting) to drought. We found that bacterial growth was more resistant and resilient to drought in sites with lower MAP. In contrast, the precipitation-reduction treatments had no detectable influence on microbial drought resistance or resilience. The microbial carbon-use efficiency immediately after rewetting was higher in soils from lower precipitation sites. In contrast, the steady-state microbial growth rates and respiration (under standardized moisture conditions) were consistent along the precipitation gradient. The variation in microbial drought resistance and resilience across the precipitation gradient was linked to the microbial community structure. Taken together, our results suggest that historical precipitation regimes – and the associated differences in exposure to drought – had selected for bacterial communities that were more resistant and resilient to drought.

Legacies of precipitation influence primary production in Panicum virgatum.

Precipitation is a key driver of primary production worldwide, but primary production does not always track year-to-year variation in precipitation linearly. Instead, plant responses to changes in precipitation may exhibit time lags, or legacies of past precipitation. Legacies can be driven by multiple mechanisms, including persistent changes in plant physiological and morphological traits and changes to the physical environment, such as plant access to soil water. We used three precipitation manipulation experiments in central Texas, USA to evaluate the magnitude, duration, and potential mechanisms driving precipitation legacies on aboveground primary production of the perennial C4 grass, Panicum virgatum. Specifically, we performed a rainout shelter study, where eight genotypes grew under different precipitation regimes; a transplant study, where plants that had previously grown in a rainout shelter under different precipitation regimes were moved to a common environment; and a mesocosm study, where the effect of swapping precipitation regime was examined with a single genotype. Across these experiments, plants previously grown under wet conditions generally performed better than expected when exposed to drought. Panicum virgatum exhibited stronger productivity legacies of past wet years on current-year responses to drought than of past dry years on current-year responses to wet conditions. Additionally, previous year tiller counts, a proxy for meristem availability, were important in determining legacy effects on aboveground production. As climate changes and precipitation extremes-both dry and wet-become more common, these results suggest that populations of P. virgatum may become less resilient.

Coarsened soil reduces drought resistance of fibrous-rooted species on degraded steppe

Grassland degradation is often accompanied by coarsened soil, which could change water and nutrient uptake by plant roots. Studying the effects of soil coarsening on species performance with different root systems under manipulated irrigation has important practical significance in grassland restoration under changing climate. We conducted a common garden experiment with three water treatments (control, drought stressed and water addition) and two soil texture (loamy soil which is fine and sandy soil which is coarse) under a rainout shelter to explore the effects of degradation on the growth and drought response of tap-rooted species and fibrous-rooted species. Three fibrous-rooted species (Setaira viridis, Cleistogenes squarrosa and Leymus chinensis) and three tap-rooted species (Medicago ruthenica, Artemisia frigida and Potentilla bifurca) were used in the study (P. bifurca failed to germinate). The results showed that three of the five selected species tended to have higher aboveground biomass, greater belowground biomass, larger height and longer root length in sandy soil than in loamy soil. For fibrous-rooted species, drought had negative influence on several plant traits in sandy soil, and had no influence on plant traits in loamy soil. For tap-rooted species, drought had negative influence on plant traits both in loamy soil and in sandy soil, and the influence was larger in loamy soil than in sandy soil. The results showed that loamy soil might provide a buffer against drought for fibrous-rooted species, but make tap-rooted species more sensitive to drought. Our results implied that degraded grasslands with coarsened soil might change community composition in the grassland, making tap-rooted species take the place of fibrous-rooted species. Thus, soil coarsening is an important factor in predicting drought resistance as well as composition of the community, and should be given more attention under future climate changes.

Microbial community response to drought depends on crop

Growing season drought can be devastating to crop yields. Soil microbial communities have the potential to buffer yield loss under drought through increasing plant drought tolerance and soil water retention. Microbial inoculation on agricultural fields has been shown to increase plant growth, but few studies have examined the impact of microbial inoculation on plant and soil microbial drought tolerance. We conducted a rainout shelter experiment and subsequent greenhouse experiment to explore 3 objectives. First, we evaluated the performance of a large rainout shelter design for studying drought in agricultural fields. Second, we tested how crop (corn vs. soybean) and microbial inoculation alter the response of soil microbial composition, diversity, and biomass to drought. Third, we tested whether field inoculation treatments and drought exposure altered microbial communities in ways that promote plant drought tolerance in future generations. In our field experiment, the effects of drought on soil bacterial composition depended on crop type, while drought decreased bacterial diversity in corn plots and drought decreased microbial biomass carbon in soybean plots. Microbial inoculation did not alter overall microbial community composition, plant growth, or drought tolerance despite our efforts to address common barriers to inoculation success. Still, a history of inoculation affected growth of future plant generations in the greenhouse. Our study demonstrates the importance of plant species in shaping microbial community responses to drought and the importance of legacy effects of microbial inoculation.

Soybean resilience to drought is supported by partial recovery of photosynthetic traits.

Climate change affects precipitation dynamics and the variability of drought frequency, intensity, timing, and duration. This represents a high risk in spring-sown grain legumes such as soybean. Yet, under European conditions, no evidence supports the potential recovery and resilience of drought-tolerant soybean cultivars after episodic drought, at different growth stages. A field experiment was conducted using a representative drought-tolerant cultivar of soybean (cv. Acardia), in 2020 and 2021, on sandy soils in Germany, applying four water regimes (irrigated, rainfed, early-drought, and late-drought stress). Drought stress was simulated by covering the plots during the event of rain with 6 × 6m rainout shelters, at the vegetative (V-stage) and flowering (Fl-stage) stages. Drought response was quantified on plant height, chlorophyll fluorescence ratio (ChlF ratio), chlorophyll content (Chlc), and leaf surface temperature (LST), at different intervals after simulating drought until pod filling. Grain yield and yield components were quantified at the end of the growing season. Compared to rainfed conditions, a drought at V-stage and Fl-stage reduced significantly plant height, ChlF ratio, and Chlc by 20%, 11%, and 7%, respectively, but increased LST by 21% during the recovery phase. There was no recovery from drought except for Chlc after V-stage in 2021, that significantly recovered by 40% at the end of the growing season, signifying a partial recovery of the photochemical apparatus. Especially, there was no recovery observed in LST, implying the inability of soybean to restore LST within the physiological functional range (Graphical abstract). Under rainfed conditions, the grain yield reached 2.9t ha-1 in 2020 and 5.2t ha-1 in 2021. However, the episodic drought reduced the yield at V-stage and Fl-stage, by 63% and 25% in 2020, and 21% and 36% in 2021, respectively. To conclude, the timing of drought was less relevant for soybean resilience; however, pre- and post-drought soil moisture, drought intensity, and drought duration were likely more important. A drought-tolerant soybean cultivar may partially be drought-resilient due to the recovery of photosynthetic traits, but not the leaf thermal traits. Overall, these findings will accelerate future efforts by plant breeders, aimed at improving soybean drought resilience.

Simulating drought tolerance of peanut varieties by maintaining photosynthesis under water deficit

Over two-third of global peanuts are grown mainly in seasonally rainfed regions across arid and semi-arid zones where drought is a major yield limiting factor. Breeders are targeting drought adaptive traits by selecting high yielding genotypes under water-limited environments. Recently, several peanut varieties have been developed that exhibit drought tolerant characteristics. Crop models can be used to simulate the impact of these traits for different environments. The overall goal of this study was to develop an approach to simulate drought tolerant traits using the CROPGRO-Peanut model and assess the long-term yield response to these desired traits. Four peanut varieties and one advanced breeding line variety with varying degrees of drought tolerance response were grown under both field and rainout shelter conditions in 2019 and 2020. The trait of maintaining photosynthesis under water deficit was observed in the rainout shelter experiments and incorporated into the crop model as a new drought tolerance cultivar coefficient. The evaluation results with independent data showed that the modified model simulated peanut growth and yield under water-limited conditions reasonably well. The rainfed yield, seasonal evapotranspiration (ET), and grain water use efficiency (WUE) were simulated for both drought tolerant and baseline peanut varieties at two representative sites using weather data from 1998 to 2020. The drought tolerant mechanism of maintaining photosynthesis under water deficit was shown to be an advantageous trait for peanut varieties, which produced higher simulated rainfed yield with enhanced seasonal ET and grain WUE, especially for dry seasons. The simulated photosynthesis and yield were sensitive to values of the drought tolerant factor over an expected range of values. Further research is needed on other potential drought tolerant mechanisms, such as maintaining nitrogen fixation, pod harvest index and leaf growth under drought.

Variation in mid-south soybean genotypes for recovery of transpiration rate and leaf maintenance following severe water-deficit stress

Ninety-four percent of U.S. soybeans are produced under rainfed conditions with potential for intermittent late season droughts during reproductive stages. Therefore, the ability of a crop to recover effectively from drought is important for yield stability. In 2019 and 2020, two controlled environment and two field studies were conducted to screen nine soybean genotypes for transpiration rate (TR) recovery following water-deficit stress. In experiment 1, under a controlled environment, soybeans were grown in pots sealed to prevent evaporation. Soybeans gradually transpired until the endpoint of transpirable soil water before being re-watered. In experiment 2, soybeans were exposed to varying vapor pressure deficit (VPD) levels. In both experiments, TR was measured gravimetrically. In field studies, portable rainout shelters were used to exclude precipitation. In experiment 1 and the field studies, recovery irrigation was applied after a period of extreme water-deficit. Then, leaf wilting score (WS) was rated visually on a scale of zero to five. Stomatal conductance (g s ), pre- and post-recovery canopy temperature (CT), and stomatal density (SD) were measured under field conditions. Genotypic differences in soybean contributed to differentiated recovery from water-deficit in experiment 1 and field studies. In experiment 1, genotypes TN09–029, TN16–520R1, and Ellis had superior recovery from water-deficit based on WS while USG Allen and TN09–008 had the most rapid TR recovery; RIL #1360 and USG 7496XTS showed the least recovery. In experiment 2, seven genotypes expressed a limited-TR trait under high VPD. In the field studies, Ellis, USG Allen, and TN09–029 exhibited a more robust recovery based on WS and Ellis exhibited the highest post-recovery g s . TN09–029 and Ellis had the largest reduction in CT after recovery. The top five yielding genotypes all expressed desirable responses in several of the individual drought recovery traits, confirming the utility of these phenotypes. Ellis produced the highest yield at 3517 kg ha −1 , consistently expressed the early decrease in TR with delayed wilting when soil water-deficit developed, and had the highest g s post-recovery. Response and recovery to drought and high yield relative to other genotypes under the water-deficit conditions make Ellis and related lines good candidates in future efforts to breed for drought tolerance traits. • The ability of a crop to recover effectively from drought is important for yield stability. • Identifying variation in mid-south genotypes transpiration and leaf maintenance recovery from severe water-deficit stress. • Field studies confirmed the results found and reported in the controlled environment experiments. • The top yielding genotypes had early stomatal closure, lower stomatal density, and lower thermal rate following recovery.

Sequía experimental en plántulas en un claro y en el sotobosque de un bosque de niebla, Veracruz, México

Antecedentes y Objetivos: Se espera que las sequías inducidas por el cambio climático afecten al bosque de niebla. Como los rasgos funcionales son indicadores útiles del desempeño de especies vegetales, el objetivo de este trabajo fue determinar el efecto del ambiente lumínico y la sequía sobre área foliar (AF), área foliar específica (AFE), contenido de clorofila, grosor, dureza foliar, supervivencia y tasas de crecimiento relativo (TCR) de plántulas en sotobosque y claro. Métodos: En un bosque de niebla en Veracruz, México, se usaron exclusiones de lluvia para simular sequía en sotobosque y claro. Se midieron AF, AFE, contenido de clorofila, grosor, dureza, supervivencia y TCR en Eugenia capuli (especie de sotobosque tolerante a la sombra), Liquidambar styraciflua (especie del dosel de tolerancia intermedia) y Trema micranthum (árbol pionero colonizador de claros) en sotobosque-control y -sequía, y claro-control y -sequía. Resultados clave: El AF aumentó con sequía en E. capuli en claro y decreció para L. styraciflua en ambos ambientes lumínicos. El contenido de clorofila fue similar entre tratamientos de agua para E. capuli y L. styraciflua en sotobosque. El grosor y dureza foliares difirieron con sequía para E. capuli y L. styraciflua en claro. Los rasgos foliares de T. micranthum cambiaron solo en sotobosque. Eugenia capuli presentó la mayor y similar supervivencia entre tratamientos. Liquidambar styraciflua mostró una mayor supervivencia en claro-sequía, y T. micranthum en claro. Eugenia capuli tuvo la mayor TCR en sotobosque, mientras que T. micranthum en claro. Conclusiones: Los rasgos funcionales de plántulas de E. capuli y L. styraciflua respondieron a sequía moderada más en claro que en sotobosque. Los resultados sugieren que los rasgos funcionales de las especies intermedia y tolerante a la sombra tienden a cambiar menos bajo una sequía moderada, que los del árbol pionero si se mantiene el ambiente lumínico forestal.

Functional traits and their plasticity shift from tolerant to avoidant under extreme drought.

Under climate change, extreme droughts will limit water availability for plants. However, the species-specific responses make it difficult to draw general conclusions. We hypothesized that changes in species' abundance in response to extreme drought can be best explained by a set of water economic traits under ambient conditions in combination with the ability to adjust these traits towards higher drought resistance. We conducted a 4-year field experiment in temperate grasslands using rainout shelters with 30% and 50% rainfall reduction. We quantified the response as the change in species abundance between ambient conditions and the rainfall reduction. Abundance response to extreme drought was best explained by a combination of traits in ambient conditions and their functional adjustment, most likely reflecting plasticity. Smaller leaved species decreased less in abundance under drought. With increasing drought intensity, we observed a shift from drought tolerance, i.e., an increase in leaf dry matter content, to avoidance, i.e., a less negative turgor loss point (TLP) in ambient conditions and a constancy in TLP under drought. We stress the importance of using a multidimensional approach of variation in multiple traits and the importance of considering a range of drought intensities to improve predictions of species' response to climate change.

Morpho-physiological Responses of Sorghum Cultivars to Drought Stress

The experiment was carried out to assess the following objectives: (i) To understand the effect of drought stress on plant height and leaf area in diverse sorghum genotypes. (ii) To study the alterations in chlorophyll index and yield components under drought stress. (iii) To correlate yield with all morpho-physiological traits to understand drought tolerance mechanism of sorghum. Screening experiment was carried out in Augmented design I during April 2022 to July 2022 at Rain Out Shelter (ROS), Department of Crop Physiology, Tamil Nadu Agricultural University, Coimbatore. 33 germplasms from Agricultural Research Station, Kovilpatti (ARS, Kovilpatti) and Indian Council of Agricultural Research- Indian Institute of Millet Research, Hyderabad (ICAR-IIMR, Hyderabad) were collected. Among 33, M35-1, K -12, CSV 27 and CSV 29-R were used as checks, where all the germplasms were cultivated with two treatments under field conditions; T1: (Control) well watered throughout life cycle, T2: Two weeks of drought stress (50%) at booting stage. Traits such as plant height and leaf area, were recorded before and after imposing drought. Chlorophyll index, ear head weight, ear head length, grain yield, total dry matter production, harvest index were recorded after imposing drought stress in control and drought stress. Under drought stress morpho-physiological and yield traits significantly reduced compared to control. There was a significant positive correlation of yield under stress with all the morpho-physiological traits. Among ICAR-IIMR sorghum germplasm collections screened for drought stress tolerance PEC 14, PEC 17, PEC31, PEC 34 EP 90 showed drought tolerance on par with the checks. Similarly, TKSV 1036, TKSV 1707, TKSV 1801, TKSV 1802 germplasms from ARS, Kovilpatti were tolerant to drought stress at booting stage.

The Higher Water Absorption Capacity of Small Root System Improved the Yield and Water Use Efficiency of Maize.

The root system in plants absorbs water and minerals. However, the relationship among root size, yield, and water use efficiency (WUE) is controversial. Two pot experiments were conducted to explore these relationships by using two maize varieties with contrasting root sizes and reducing the root–shoot ratio (R/S) through root pruning to eliminate genotypic effects. Maize plants were grown in an open rainout shelter under both water-sufficient and deficient conditions. Yield-related parameters, root hydraulic conductivity (Lpr), and WUE were determined. The results showed that the small root variety (XY) has a higher yield and WUE compared to large root variety (QL) under both soil moisture conditions, likely related to the higher Lpr of XY. XY also had a higher leaf water potential than QL under drought stress, indicating that small root system could provide enough water to the shoot. Further pot experiment showed that both small and large root pruning on QL (cut off about 1/5 roots, RP1; and cut off about 1/3 roots, RP2, respectively) improved WUE and Lpr, and the RP1 yield increased by 12.9% compared to the control under well-watered conditions. Root pruning decreased transpiration and increased photosynthesis. Thus, this study reveals that it is possible to increase water absorption, yield, and WUE by reducing R/S in modern maize varieties, which may be important for the future breeding of new cultivars suitable for arid regions.

Many paths to one goal: Identifying integrated rice root phenotypes for diverse drought environments.

Drought is a major source of yield loss in the production of rice (Oryza sativa L.), and cultivars that maintain yield under drought across environments and drought stress scenarios are urgently needed. Root phenotypes directly affect water interception and uptake, so plants with root systems optimized for water uptake under drought would likely exhibit reduced yield loss. Deeper nodal roots that have a low metabolic cost per length (i.e., cheaper roots) via smaller root diameter and/or more aerenchyma and that transport water efficiently through smaller diameter metaxylem vessels may be beneficial during drought. Subsets of the Rice Diversity Panel 1 and Azucena × IR64 recombinant inbred lines were grown in two greenhouse and two rainout shelter experiments under drought stress to assess their shoot, root anatomical, and root architectural phenotypes. Root traits and root trait plasticity in response to drought varied with genotype and environment. The best-performing groups in the rainout shelter experiments had less plasticity of living tissue area in nodal roots than the worst performing groups. Root traits under drought were partitioned into similar groups or clusters via the partitioning-around-medoids algorithm, and this revealed two favorable integrated root phenotypes common within and across environments. One favorable integrated phenotype exhibited many, deep nodal roots with larger root cross-sectional area and more aerenchyma, while the other favorable phenotype exhibited many, deep nodal roots with small root cross-sectional area and small metaxylem vessels. Deeper roots with high theoretical axial hydraulic conductance combined with reduced root metabolic cost contributed to greater shoot biomass under drought. These results reflect how some root anatomical and architectural phenes work in concert as integrated phenotypes to influence the performance of plant under drought stress. Multiple integrated root phenotypes are therefore recommended to be selected in breeding programs for improving rice yield across diverse environments and drought scenarios.

Limited hydraulic recovery in seedlings of six tree species with contrasting leaf habits in subtropical China.

Subtropical tree species may experience severe drought stress due to variable rainfall under future climates. However, the capacity to restore hydraulic function post-drought might differ among co-occurring species with contrasting leaf habits (e.g., evergreen and deciduous) and have implications for future forest composition. Moreover, the links between hydraulic recovery and physiological and morphological traits related to water-carbon availability are still not well understood. Here, potted seedlings of six tree species (four evergreen and two deciduous) were grown outdoors under a rainout shelter. They grew under favorable water conditions until they were experimentally subjected to a soil water deficit leading to losses of ca. 50% of hydraulic conductivity, and then soils were re-watered to field capacity. Traits related to carbon and water relations were measured. There were differences in drought responses and recovery between species, but not as a function of evergreen or deciduous groups. Sapindus mukorossi exhibited the most rapid drought response, which was associated with a suite of physiological and morphological traits (larger plant size, the lowest hydraulic capacitance (Cbranch), higher minimum conductance (gmin) and lower HV (Huber value)). Upon re-watering, xylem water potential exhibited fast recovery in 1–3 days among species, while photosynthesis at saturating light (Asat) and stomatal conductance (gs) recovery lagged behind water potential recovery depending on species, with gs recovery being more delayed than Asat in most species. Furthermore, none of the six species exhibited significant hydraulic recovery during the 7 days re-watering period, indicating that xylem refilling was apparently limited; in addition, NSC availability had a minimal role in facilitating hydraulic recovery during this short-term period. Collectively, if water supply is limited by insignificant hydraulic recovery post-drought, the observed carbon assimilation recovery of seedlings may not be sustained over the longer term, potentially altering seedling regeneration and shifting forest species composition in subtropical China under climate change.

Determining the plant critical saturated water accumulation curve in maize

Water scarcity is one of the major factors limiting crop growth and productivity. Judicious water management reduces the application of irrigation water and increases grain yield, farm profits, and water use efficiency . The assessment of crop water status is the key to in-season irrigation scheduling . The plant diagnostic approach has the potential to assess the in-season crop water status for optimizing crop water use. For this purpose, a series of field and rainout shelter experiments with varying amounts of irrigation water (0–275 mm for field and 0–315 mm for rainout shelter experiments) and planting densities (6–8 ×10 4 plants ha −1 ) using seven maize cultivars were conducted from the 2017–2020 growing seasons in North China Plain to determine and validate the plant critical saturated water accumulation (SWA) curve during the vegetative growth period of maize. The result showed that the plant dry mass (DM) and the SWA ranged from 0.07 to 8.22 t ha −1 and 0.63–59.06 t ha −1 during the vegetative growth period of maize, respectively. The plant DM and SWA increased with the increase in irrigation amount. However, plant DM and plant SWA showed non-significant differences under non-water-limiting conditions. An allometric relationship between plant DM and plant SWA was used to develop the plant critical SWA curve (SWA = 8.26DM 0.89 , R 2 =0.98 ** ). A plant water diagnosis index (WDI) was then derived using the critical SWA curve to quantitatively assess the in-season water status of maize. The WDI increased with the increase of irrigation amount and ranged from 0.72 to 1.26 with a value of 1, indicating an optimum plant water status. The newly developed curve could diagnose and categorize the water-limiting and non-water-limiting plant water status and can be employed for precision irrigation management during maize cultivation.

Variabilities in symbiotic nitrogen fixation and carbon isotope discrimination among peanut (Arachis hypogaea L.) genotypes under drought stress

AbstractDrought stress is one of the major environmental factors limiting peanut (Arachis hypogea L.) productivity. Peanut response to drought varies depending on genotypic characteristics, crop growth stages, and environmental conditions. The objective of this study was to evaluate the effects of drought stress and rehydration on symbiotic nitrogen fixation and carbon isotope discrimination in peanut genotypes with varying drought tolerance. Experiments were conducted for 2 years in rainout shelters under three irrigation regimes: irrigated control, middle‐season drought with rehydration, and late‐season drought with rehydration. Reduction in percentages of shoot N derived from the atmosphere (%Ndfa) occurred under both drought treatments in both years; a greater reduction occurred under middle‐season drought than under late‐season drought. Middle‐season drought negatively affected carbon isotope discrimination in both years, although there were no significant differences under late‐season drought. Variabilities in %Ndfa and carbon isotope discrimination were found among different genotypes. Under middle‐season drought, both %Ndfa and carbon isotope discrimination were higher in drought‐tolerant lines than drought‐susceptible lines. The most drought‐tolerant lines had the highest N‐fixing capacity under both drought treatments. Additionally, there was a positive correlation between %Ndfa and carbon isotope discrimination under both drought treatments. In most genotypes, %Ndfa remained unchanged after rehydration; only a few genotypes showed a slight increase in %Ndfa after rehydration following both drought treatments. Our data suggested that symbiotic nitrogen fixation in many peanut genotypes was negatively affected by drought and may not recover from the damage caused by drought upon rehydration.

Tolerance to mid‐season drought in peanut can be achieved by high water use efficiency or high efficient use of water

AbstractPeanut (Arachis Hypogaea L) is an economic cash crop mainly planted in arid and semi‐arid regions where drought causes approximately 20% yield losses every year. It has been demonstrated that drought tolerance can be achieved by two different mechanisms in plants: either by saving water or by extracting more water from the soil (water spender genotypes). The objective of this research was to screen for these two mechanisms of drought tolerance in peanut. Plants were grown in rainout shelters under irrigated conditions until mid‐pod filling, then drought was induced using rain‐out shelters. Gas exchange parameters were measured regularly during the drought period and recovery. Genotypes PI 502120 and AU‐NPL 17 were classified as water spender genotypes as they showed high yield, Δ13C, photosynthesis, and stomatal conductance under drought. This is the first time that water spender genotypes have been identified in peanut. On the other hand, genotypes Line‐8 and AU16‐28 were classified as water savers as they showed equally high yields but with low Δ13C and stomatal conductance and moderate photosynthesis under drought stress. In this study, water spender genotypes did not show a yield advantage in comparison with water savers.

Improving water status prediction of winter wheat using multi-source data with machine learning

Water and nitrogen (N) are the most important factors limiting crop productivity. Effective monitoring of the water status of winter wheat under different N treatments is imperative for precision irrigation in improved crop management. Hyperspectral remote sensing is widely used for monitoring the crop water status. However, changes in canopy architecture during ontogeny lead to poor inversion of crop properties and limit the use of spectral indices. This study aimed to improve the water status prediction of winter wheat using multi-source data with machine learning (ML). Two multi-irrigation levels (0, 120, 240, 360 mm) and N rates (75, 225 kg N ha-1) experiments were conducted during the 2019–2021 wheat growing seasons under field conditions using a rainout shelter. Hyperspectral, soil, plant, and climate data were evaluated with two feature selection methods. Selected results were chosen as input variables for prediction models by using three ML algorithms. By constructing the normalized difference spectral index (NDSI), ratio spectral index (RSI), and difference spectral index (DSI), the DSI(2015, 2375), NDSI(2175, 2245), and RSI(720, 1200) showed the strongest correlation with canopy water content (CWC), plant water content (PWC), and canopy equivalent water thickness (CEWT), respectively. The best feature selection method and data were delivered by the Pearson correlation coefficient together with the soil, plant, and climate data. The best performing ML algorithm for CWC and PWC prediction was RF, while SVM was the best ML algorithm for CEWT prediction. The R2 of the optimal models ranged from 0.86 to 0.97. These models with multi-source data significantly improved the prediction accuracy of the water status and can thus assist in precision irrigation management of winter wheat.