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Defining the metabolic strategies used by wheat to tolerate and recover from drought events will be important for ensuring yield stability in the future, but studies addressing this critical research topic are limited. To this end, the current study quantified the physiological, biochemical, and agronomic responses of a drought tolerant and drought sensitive cultivar to periods of water deficit and recovery. Drought stress caused a reversible decline in leaf water relations, membrane stability, and photosynthetic activity, leading to increased reactive oxygen species (ROS) generation, lipid peroxidation and membrane injury. Plants exhibited osmotic adjustment through the accumulation of soluble sugars, proline, and free amino acids and increased enzymatic and non-enzymatic antioxidant activities. After re-watering, leaf water potential, membrane stability, photosynthetic processes, ROS generation, anti-oxidative activities, lipid peroxidation, and osmotic potential completely recovered for moderately stressed plants and did not fully recover in severely stressed plants. Higher photosynthetic rates during drought and rapid recovery after re-watering produced less-pronounced yield declines in the tolerant cultivar than the sensitive cultivar. These results suggested that the plant's ability to maintain functions during drought and to rapidly recover after re-watering during vegetative periods are important for determining final productivity in wheat.

Respiratory carbon evolution by leaves under abiotic stress is implicated as a major limitation to crop productivity; however, respiration rates of fully expanded leaves are positively associated with plant growth rates. Given the substantial sensitivity of plant growth to drought, it was hypothesized that predawn respiration rates (RPD) would be (1) more sensitive to drought than photosynthetic processes and (2) highly predictive of water-induced yield variability in Gossypium hirsutum. Two studies (at Tifton and Camilla Georgia) addressed these hypotheses. At Tifton, drought was imposed beginning at the onset of flowering (first flower) and continuing for three weeks (peak bloom) followed by a recovery period, and predawn water potential (ΨPD), RPD, net photosynthesis (AN) and maximum quantum yield of photosystem II (Fv/Fm) were measured throughout the study period. At Camilla, plants were exposed to five different irrigation regimes throughout the growing season, and average ΨPD and RPD were determined between first flower and peak bloom for all treatments. For both sites, fiber yield was assessed at crop maturity. The relationships between ΨPD, RPD and yield were assessed via non-linear regression. It was concluded for field-grown G. hirsutum that (1) RPD is exceptionally sensitive to progressive drought (more so than AN or Fv/Fm) and (2) average RPD from first flower to peak bloom is highly predictive of water-induced yield variability., (Copyright © 2015 Elsevier GmbH. All rights reserved.)

Cotton is well adapted to dry areas, but progressive water deficits can lead to declines in net photosynthesis (A), ultimately reducing yield. However, the exact mechanism responsible for this decline in net photosynthesis (stomatal or non‐stomatal) is not fully understood under field conditions, partially due to limitations in the ability to collect critical data. To our knowledge, no other study has compared the drought responses of Pima and upland cotton using both CO2 response and chlorophyll fluorescence under field conditions. To this end, a field study was conducted to quantify the impact of progressive mild drought, as measured by midday stomatal conductance to water vapour (gs), on cotton leaf metabolism in Pima and upland cotton. Survey gas exchange and rapid photosynthetic CO2 response (RACiR) were conducted during flowering on the same leaf. The study observed decline in A as gs declined for both species. Correlation analysis indicated typical relationships with A and parameters associated with stomatal limitations such as decreased CO2 inside the leaf and at the site of carboxylation; however, it was found that while Pima exhibited a strong relationship between maximum electron transport rate (Jmax) and electron transport rate (ETR), upland cotton did not. Furthermore, when ETR is broken down into proportions contributing to net photosynthesis and photorespiration (ETRA, ETRP, respectively), we found that a greater proportion of ETR is being shuttled to the photorespiratory pathway in upland, relative to Pima as gs decreases. Our results fill critical knowledge gaps that can be useful for modellers and breeders when preparing for future climate change scenarios. [ABSTRACT FROM AUTHOR]

Drought appears at flowering and boll formation for cotton frequently. However, reports on the impact of carbon dynamics in the subtending leaf on boll biomass under periodic droughts are limited. To investigate this, experiments were carried out with two cultivars (drought‐tolerant: Dexiamian 1; drought‐sensitive: Yuzaomian 9110), three water levels [soil relative water content (SRWC): control (75 ± 5)%, moderate drought (60 ± 5)%, severe drought (45 ± 5)%] and five drought durations (10, 17, 24, 31 and 38 days). A 38‐day drought declined the net photosynthetic rate of subtending leaf, which could be collectively attributed to the reduction in carboxylation with reduced ribulose‐1,5‐bisphosphate carboxylase activity, and stomal limitation with decreased stomatal conductance, along with the damage of photosynthetic apparatus with depressed maximum and actual photochemical quantum yield, leading to lower starch content. A 38‐day drought also increased the activities of sucrose phosphate synthase (SPS), sucrose synthase (Susy) and expressions of genes (GhSPS1, GhSPS2, GhSusA and GhSusB) associated with these enzymes, causing the accumulation of sucrose content, finally resulting in lower boll biomass. Some of the above parameters fully recovered under more than 17‐day moderate drought or over 10‐day severe drought, but boll biomass still decreased after re‐watering. Under 10‐day moderate drought, all aforementioned indices and boll biomass were completely recovered within 7 days of re‐watering, and the recovery capacity of Yuzaomian 9110 was lower than that of Dexiamian 1. Therefore, rapid recovery of photosynthesis and decline in the subtending leaf sucrose content to pre‐stress levels are important factors in lessening the impacts of drought on boll biomass and are indicative of cultivar tolerance to short‐term moderate water deficit. [ABSTRACT FROM AUTHOR]

Previous studies have documented cotton boll weight reductions under drought, but the relative importance of the subtending leaf, bracts and capsule wall in driving drought-induced reductions in boll mass has received limited attention. To investigate the role of carbon metabolism in driving organ-specific differences in contribution to boll weight formation, under drought conditions. Controlled experiments were carried out under soil relative water content (SRWC) (75 ± 5)% (well-watered conditions, control), (60 ± 5)% (moderate drought) and (45 ± 5)% (severe drought) in 2018 and 2019 with two cultivars Yuzaomian 9110 and Dexiamian 1. Under severe drought, the decreases of photosynthetic rate (Pn) and carbon isotope composition (d13C) were observed in the subtending leaf, bract and capsule wall, suggesting that carbon assimilation of three organs was restricted and the limitation was most pronounced in the subtending leaf. Changes in the activities of sucrose phosphate synthase (SPS), sucrose synthase (SuSy), invertases as well as the reduction in expression of sucrose transporter (GhSUT1) led to variabilities in the sucrose content of three organs. Moreover, photosynthate distribution from subtending leaf to seeds plus fibers (the components of boll weight) was significantly restricted and the photosynthetic contribution rate of subtending leaf to boll weight was decreased, while contributions of bracts and capsule wall were increased by drought. This, in conjunction with the observed decreases in boll weight, indicated that the subtending leaf was the most sensitive photosynthetic organ to drought and was a dominant driver of boll weight loss under drought. Therefore, the subtending leaf governs boll weight loss under drought due to limitations in carbon assimilation, perturbations in sucrose metabolism and inhibition of sucrose transport. [ABSTRACT FROM AUTHOR]

The cotton (Gossypium hirsutum L.) crop is an indeterminate species that is most sensitive to drought stress during the flowering and boll‐formation stage of development. To evaluate the effect of water deficit on fibre quality and carbon metabolism at different fruiting branches (FB), multiple controlled experiments were conducted. The cotton cultivar Siza 3 was used under three soil relative water content (SRWC): control (CK, SRWC (75 ± 5) %), moderate drought stress (MDS, SRWC (60 ± 5) %) and severe drought stress (SDS, SRWC (45 ± 5) %) treatment, imposed at the beginning of the flowering of FB6–7. Fibre quality was significantly affected by drought level and fruiting branch location on the plant. Compared to the CK, under MDS and SDS, sucrose content and sucrose synthase (SuSy) activity decreased prior to 24 days post‐anthesis (DPA; the fibre elongation phase), which caused low fibre turgor pressure. This decreased the rate of fibre elongation and final fibre length. Moreover, from 24 to 38 DPA (during fibre thickening), low fibre sucrose content led to insufficient UDP‐glucose (UDPG; uridine diphosphate glucose) for cellulose synthesis. Furthermore, more of the existing UDPG was allocated to the synthesis of callose instead of cellulose, which resulted in lower cellulose accumulation and decreased fibre strength. The magnitude of the drought stress effect on fibre qualities, as well as the formation process, was strongly influenced by fruiting branch position, where differences were most pronounced for fruiting branches further away from the base of the plant. [ABSTRACT FROM AUTHOR]

The current study evaluated the possibility that growth‐limiting, early‐season drought stress sufficient to decrease net photosynthesis (AN) would be associated with declines in stomatal conductance (gs) and ATP content, regardless of stress level. Studies were conducted in greenhouse facilities in Athens and Tifton, GA, and imposed different early‐season drought durations to generate a range of early‐season water‐deficit stress conditions. The early‐season drought durations imposed decreased AN to values ranging from 20 to 60% of the levels observed in well‐watered plants. Where declines in AN were observed, gs and photosynthetic electron transport rate (ETR) declined substantially, indicating some level of metabolic and possibly diffusional limitation to photosynthesis. The ATP content was unaffected or actually increased in response to photosynthesis‐limiting drought in both years of the study, suggesting that ATP‐induced limitations to photosynthesis are minimal over a broad range of AN–limiting, early‐season drought stress conditions in cotton (Gossypium hirsutum L.). All drought durations limited leaf, stem, reproductive, and total dry matter production. Declines in dry matter under mild stress were primarily associated decreased leaf area production, whereas decreased AN was likely an important contributor under more severely stressed treatments. Photosynthetic declines under growth‐limiting, early‐season drought do not appear to be associated with reduced ATP production, as suggested in other plant species. [ABSTRACT FROM AUTHOR]

Abstract Drought is known to limit carbon assimilation in plants. However, it has been debated whether photosynthesis is primarily inhibited by stomatal or non-stomatal factors. This research assessed the underlying limitations to photosynthesis in peanuts (Arachis hypogaea L.) grown under progressive drought. Specifically, field-grown peanut plants were exposed to either well-watered or drought-stressed conditions during flowering. Measurements included survey measurements of gas exchange, chlorophyll fluorescence, PSII thermotolerance, pigment content, and rapid A-C i response (RACiR) assessments. Drought significantly decreased stomatal conductance with consequent declines in photosynthesis (A N), actual quantum yield of PSII, and electron transport rate (ETR). Pigment contents were variable and depended on stress severity. Stomatal closure on stressed plants resulted in higher leaf temperatures, but F v /F m and PSII thermotolerance were only slightly affected by drought. A strong, hyperbolic relationship was observed between stomatal conductance, A N , and ETR. However, when RACiR analysis was conducted, drought significantly decreased A N at C i values comparable to drought-stressed plants, indicating non-stomatal limitations to A N. The maximum rate of carboxylation and maximum electron transport rate were severely limited by drought, and chloroplast CO 2 concentration (C C) declined substantially under drought along with a comparable increase in partitioning of electron flow to photorespiration. Thus, while stomatal conductance may be a viable reference indicator of water deficit stress in peanut, we conclude that declines in A N were largely due to non-stomatal (diffusional and metabolic) limitations. Additionally, this is the first study to apply the rapid A-C i response method to peanut, with comparable results to traditional A-C i methods. [ABSTRACT FROM AUTHOR]

Novel yield component traits and fiber quality indices have been recently developed by breeders to screen for desirable cotton ( Gossypium hirsutum L.) lines, but assessing these components in response to water-induced yield variability has received little attention. We investigated the hypothesis that differential sensitivities of whole-crop and intra-boll yield components to drought will largely explain water-induced yield and fiber quality variation in cotton. To test this hypothesis, two cotton cultivars were grown in the field under five contrasting irrigation regimes during the 2013 and 2014 growing seasons near Camilla, GA. Measurements included predawn leaf water potential (Ψ PD ) throughout the growing season and extensive yield component and fiber quality assessments at the end of the season. Water-induced yield variability was primarily associated with Ψ PD at the flowering and boll development phase of crop growth. Boll density (bolls ha −1 ) was the dominant driver of drought-induced yield loss, but reduced boll mass and seed number per boll also contributed somewhat to yield loss. By comparison, increased drought severity decreased fiber density but increased individual fiber mass, producing a peak in total fiber weight per seed at a −0.7 MPa Ψ PD irrigation threshold and increasing lint percentage in stressed treatments. Thus, the negative impacts of drought on overall boll mass and seed number per boll are partially offset by increased dry matter partitioning toward fiber growth. Fiber length declined with increased drought severity, whereas fiber micronaire increased in the most severely stressed treatments. This indicates that increasing drought severity during flowering and boll development decreases the number of individual fibers per seed and their final length, but their thickness is increased. The end result is a decline in the overall fiber quality index (Q-score) under drought stress. [ABSTRACT FROM AUTHOR]

Drought can substantially limit yield in cotton, and water loss in any crop is closely associated with plant growth, but studies addressing the effects of growth management on drought sensitivity are limited in cotton. We tested the hypothesis that aggressive plant growth management would decrease cotton sensitivity to drought during flowering and boll development. Cotton was grown at a field site near Tifton, GA during the 2021 and 2022 growing seasons. Treatments included mepiquat chloride (MC) strategies (aggressive and untreated) and two water availability treatments (well-watered and drought-stressed). At approximately 2 weeks after first flower, water was withheld from the drought-stressed treatment for a three-week period, and well-watered plots were kept irrigated using a regionally accepted water balance approach. Measurements throughout the season included heights, nodes, length of the fourth internode below the plant terminal, nodes above white flower (NAWF), and soil moisture. End-of-season measurements included lint yield, fiber quality, and yield component assessments. MC treatment significantly affected plant height, mainstem node number, 4th internode length, and cutout date. Soil moisture was significantly reduced during the drought stress period. Aggressive MC treated plots showed less drought-induced yield reduction than untreated in response to drought, but did not reach the same lint yield, boll density, or uniformity as well-watered, untreated plots. Aggressive MC treatment produced greater seed surface area, seed number boll-1, and boll mass. Aggressive MC management may prevent drought-induced yield reductions but penalize yield under well-watered conditions. Among the potential components driving yield, boll number per unit land area was the most important contributor. Our findings highlight the potential for aggressive MC management to mitigate drought risk, but future efforts should evaluate this possibility in a broader range of cultivars adapted for production in the southeastern United States and with the inclusion of a moderate MC treatment. • Aggressive mepiquat chloride treatment can mitigate drought risk but also penalize yield in a well-watered environment. • Aggressive mepiquat chloride treatment produced greater seed surface area, seed number boll-1, and boll mass. • Boll density was primarily associated with lint yield. • Only fiber uniformity and strength were impacted by aggressive mepiquat chloride treatment. [ABSTRACT FROM AUTHOR]

Temperature and drought are major abiotic limitations to crop productivity worldwide. While abiotic stress physiology research has focused primarily on fully expanded leaves, no studies have investigated photosynthetic tolerance to concurrent drought and high temperature during leaf ontogeny. To address this, Gossypium hirsutum plants were exposed to five irrigation treatments, and two different leaf stages were sampled on three dates during an abnormally dry summer. Early in the growing season, ontogenic PSII heat tolerance differences were observed. Photosystem II was more thermotolerant in young leaves than mature leaves. Later in the growing season, no decline in young leaf net photosynthesis (P N ) was observed as leaf temperature increased from 31 to 37 °C, as average midday leaf water potential (Ψ MD ) declined from −1.25 to −2.03 MPa. In contrast, mature leaf P N declined 66% under the same conditions. Stomatal conductance (g s ) accounted for 84–98% of variability in leaf temperature, and g s was strongly associated with Ψ MD in mature leaves but not in young leaves. We conclude that young leaves are more photosynthetically tolerant to heat and drought than mature leaves. Elucidating the mechanisms causing these ontogenic differences will likely help mitigate the negative impacts of abiotic stress in the future. [ABSTRACT FROM AUTHOR]

Although cotton is a drought-tolerant crop, irrigation is still needed to ensure productivity, even in the humid Southeastern United States. Irrigation must be carefully managed to limit unnecessary water use while ensuring maximum economic productivity. To better understand the costs and net returns of irrigation and cultivar selection, field experiments were conducted in 2016 and 2017 to compare cotton lint yield and fiber quality in dryland plots and plots irrigated using the University of Georgia checkbook method (UGA Checkbook) at a field site near Camilla, Georgia. Results showed cultivar differences in fiber quality parameters of micronaire and uniformity in 2016, but there was no cultivar difference in fiber quality in 2017. Cultivar differences were not observed in yield or net returns for both years. However, stoplight chart analysis of net returns indicated differences in cultivar selection for irrigated or dryland production. ST 6182 GLB2 would be a better option for a producer to minimize downside risk under dryland conditions, and PHY 333 WRF would be a better option under irrigated production. Results also indicated that broadly applying simplistic water balance approaches could decrease yield, water productivity, and net returns, especially in environments where rainfall is sufficient yet unpredictable. Overirrigation affected some fiber quality parameters but did not impact the overall market price for cotton. In 2016, irrigating according to the UGA Checkbook method negatively impacted yield and net returns. In 2017, irrigation did not affect yield but negatively impacted net returns. Average losses in net returns associated with excessive irrigation in these two wet years were $336 per hectare for net return over irrigation variable costs, and $645 per hectare for net return over irrigation total costs. Implementing robust, efficient irrigation strategies is necessary to achieve high cotton yields, reduce water usage, and improve economic returns. • The checkbook method resulted in over-irrigation in wet years and decrease yield. • Water-balance based irrigation reduced water productivity in wet years. • Reductions in water productivity were associated with declines in net returns. • In one of the two years studied, yield reductions were observed with irrigation. • Advanced irrigation approaches are needed to maximize water productivity and profitability. [ABSTRACT FROM AUTHOR]