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Increasing heatwaves are threatening forest ecosystems globally. Leaf thermal regulation and tolerance are important for plant survival during heatwaves, though the interaction between these processes and water availability is unclear. Genotypes of the widely distributed foundation tree species Populus fremontii were studied in a controlled common garden during a record summer heatwave-where air temperature exceeded 48 °C. When water was not limiting, all genotypes cooled leaves 2 to 5 °C below air temperatures. Homeothermic cooling was disrupted for weeks following a 72-h reduction in soil water, resulting in leaf temperatures rising 3 °C above air temperature and 1.3 °C above leaf thresholds for physiological damage, despite the water stress having little effect on leaf water potentials. Tradeoffs between leaf thermal safety and hydraulic safety emerged but, regardless of water use strategy, all genotypes experienced significant leaf mortality following water stress. Genotypes from warmer climates showed greater leaf cooling and less leaf mortality after water stress in comparison with genotypes from cooler climates. These results illustrate how brief soil water limitation disrupts leaf thermal regulation and potentially compromises plant survival during extreme heatwaves, thus providing insight into future scenarios in which ecosystems will be challenged with extreme heat and unreliable soil water access.

Very little is known about potential benefits of using AM inoculation as a tool to alleviate drought stress of trees grown under nursery conditions. There is some evidence that benefits of mycorrhiza on gas exchange parameters and growth of trees are proportionally greater when trees are subjected to drought stress. We hypothesized that inoculation with mycorrhiza would increase growth, nutrition, stem water potential and gas exchange of containerized almond (Prunus dulcis (Mill.) D.A. Webb) when young trees are grown under low water availability. In the spring of 2015 and 2016, forty containerized almond trees (Nonpareil scion grafted on Hansen 536, a peach/almond hybrid rootstock) were either inoculated or not with a commercially available arbuscular mycorrhizal inoculum and kept well-watered for 60 days in 2015 and 54 days in 2016, after which half of the plants were exposed to gradually reduced water availability over 38 days in 2015 and 61 days in 2016. Measurements included growth metrics, stem water potential, stomatal density, leaf NPK concentration, light saturated photosynthesis, and parameters calculated from CO2 response curves (Vcmax, J, TPU, Rd, gm, and stomatal limitation).The low-water treatment decreased stem water potential and reduced trunk diameter growth, light saturated photosynthesis (A), stomatal conductance (gs), Vcmax, J, TPU, gm, specific root length, leaf N and K concentration and total leaf N, P, and K content. Inoculation decreased root mass, increased leaf mass fraction, and decreased root mass fraction in 2015, but not in 2016. Neither stem water potential nor gas exchange were significantly altered by inoculation. Inoculation decreased leaf stomatal density, and slightly elevated leaf N and P concentrations in the low water treatments, although not consistently across years. Contrary to expectations we did not find substantially greater benefits from mycorrhizal inoculation in young drought stressed almond trees and conclude that the potential for mycorrhizal inoculant to alleviate drought stress in containerized trees is minimal.

Environmental variation commonly drives functional trait diversity within species, among species, and across communities. Climate and shared evolutionary history can both influence trait–environment relationships. We studied variation in plant functional traits among closely related Costus species occurring across environmental gradients, the extent to which this variation occurs within single species, and how that variation may be influenced by shared evolutionary history. We measured leaf, aboveground stem, rhizome, and fine root traits of 17 species of Costus in eight sites in Costa Rica and Panama, which varied in elevation, temperature, and precipitation. We then assessed the relationships among traits and environmental variables and estimated the phylogenetic signal of the traits. We observed significant relationships between functional traits and climate. Stomatal conductance decreased, but stem density and rhizome dry matter content increased with decreasing mean annual temperature and precipitation seasonality in both cross-species and single-species analyses. This suggests that herbaceous species have a similar trade-off between plant hydraulic efficiency and safety as found in woody plants. Mean annual temperature was a stronger driver of trait variation than mean annual precipitation. We also found phylogenetic signal in leaf and stem structural traits (i.e., closely related species are more similar than distantly related species), but not in physiological or belowground traits. Our results demonstrate significant trait variation within and among species of Costus, a widespread understory and herbaceous genus in the tropics, which is driven by both climate and shared evolutionary history.

Summary: A long‐standing debate looks at whether air or soil dryness is more limiting to vegetation water use and productivity. The answer has large implications for future ecosystem functioning, as atmospheric dryness is predicted to increase globally while changes in soil moisture are predicted to be far more variable. Here, I review the complexities that contribute to this debate, including the strong coupling between atmospheric and soil dryness, and the widespread heterogeneity in vegetation hydraulic traits, acclimations, and adaptations to water stress. I discuss solutions to improve understanding and modeling of vegetation sensitivity to dryness, including how different types of observational data can be used together to gain insight into vegetation response to water stress across spatial and temporal scales. [ABSTRACT FROM AUTHOR]

Summary: Carbon isotope discrimination (∆) in leaf biomass (∆BL) and tree rings (∆TR) provides important proxies for plant responses to climate change, specifically in terms of intrinsic water‐use efficiency (iWUE). However, the nonphotosynthetic 12C/13C fractionation in plant tissues has rarely been quantified and its influence on iWUE estimation remains uncertain.We derived a comprehensive, ∆ based iWUE model (iWUEcom) which includes nonphotosynthetic fractionations (d) and characterized tissue‐specific d‐values based on global compilations of data of ∆BL, ∆TR and real‐time ∆ in leaf photosynthesis (∆online). iWUEcom was further validated with independent datasets.∆BL was larger than ∆online by 2.53‰, while ∆BL and ∆TR showed a mean offset of 2.76‰, indicating that ∆TR is quantitatively very similar to ∆online. Applying the tissue‐specific d‐values (dBL = 2.5‰, dTR = 0‰), iWUE estimated from ∆BL aligned well with those estimated from ∆TR or gas exchange. ∆BL and ∆TR showed a consistent iWUE trend with an average CO2 sensitivity of 0.15 ppm ppm−1 during 1975–2015.Accounting for nonphotosynthetic fractionations improves the estimation of iWUE based on isotope records in leaf biomass and tree rings, which is ultimate for inferring changes in carbon and water cycles under historical and future climate. [ABSTRACT FROM AUTHOR]

Summary During periods of stomatal closure, such as drought, plant leaves continue to lose water at a rate determined by the minimum leaf conductance, gmin. Although gmin varies with temperature, less is known about what drives this variation, including how the pathways of water loss (cuticle or stomata) vary with temperature. We used gas exchange and bench drying methods to measure gmin and cuticular conductance, gcw, across a wide temperature range (20–50°C) in 11 broadleaf species. Vapour pressure deficit (VPD) covaried with temperature from 0.83 to 10.7 kPa. The dominant pathway of water loss for gmin shifted from stomatal transpiration towards cuticular transpiration as temperature increased. Leaf traits had variable, temperature‐dependent relationships with gmin and gcw, with trait–conductance relationships being generally stronger at higher temperatures. Cuticular thickness varied inversely with high‐temperature gcw. Simulation results showed that gcw may impact photosynthetic capacity estimates, particularly in species with low stomatal conductance. The pathways of water loss in leaves during times of stomatal closure depend strongly on temperature. This effect may have large implications for landscape‐scale water balance modelling and improving gas exchange measurements. We propose variation in VPD as a potential contributing factor in gmin and gcw variation among studies. [ABSTRACT FROM AUTHOR]

Accounting for the dynamic responses of photosynthesis and photoprotection to naturally fluctuating irradiance can improve predictions of plant performance in the field, but the variation of these dynamics within crop canopies is poorly understood. We conducted a detailed study of dynamic and steady-state photosynthesis, photoprotection, leaf pigmentation, and stomatal anatomy in four leaf layers (100, 150, 200, and 250 cm from the floor) of a fully grown tomato (Solanum lycopersicum cv. Foundation) canopy in a greenhouse. We found that leaves at the top of the canopy exhibited higher photosynthetic capacity and slightly faster photosynthetic induction compared with lower-canopy leaves, accompanied by higher stomatal conductance and a faster activation of carboxylation and linear electron transport capacities. In upper-canopy leaves, non-photochemical quenching showed faster induction and relaxation after increases and decreases in irradiance, allowing for more effective photoprotection in these leaves. Despite these observed differences in transient responses between leaf layers, steady-state rather than dynamic photosynthesis traits were more influential for predicting photosynthesis under fluctuating irradiance. Also, a model analysis revealed that time-averaged photosynthesis under fluctuating irradiance could be accurately predicted by one set of Rubisco activation/deactivation parameters across all four leaf layers, thereby greatly simplifying future modelling efforts of whole-canopy photosynthesis. [ABSTRACT FROM AUTHOR]

Strawberry (Fragraria x ananassa) is a crop affected by various soil-borne fungal pathogens with mostly non-specific foliar symptoms and often requiring laboratory isolation for correct diagnosis. Moreover, these nonspecific foliar symptoms, appreciated by the human eye, appear after some time following infection by the pathogen. Early detection of plant diseases is one of the primary objectives in agriculture because it may contribute to identifying more tolerant cultivars in breeding programs and optimise pesticide use in agricultural production with earlier applications in emerging disease foci. New technologies, such as remote sensing and machine learning (ML) algorithms, have arisen as potential tools to improve the ability to detect and classify different crop diseases. The combined use of hyperspectral imagery and ML algorithms were investigated to detect and classify the physiological stress caused by early infections of Fusarium wilt in strawberry plants. Six ML models, namely artificial neural network, decision tree, K-nearest neighbour, support vector machine, multinomial logistic regression and Naïve Bayes were developed to estimate physiological stress associated with Fusarium wilt disease. The results showed that stomatal conductance (gs) and photosynthesis (A) declined even without visual symptoms of the disease. Among the six ML models evaluated, the artificial neural network model showed the highest classification performance with an overall accuracy of 81%, regardless of the physiological parameter utilized for model training. Moreover, the artificial neural network accurately predicted the absolute values of both physiological parameters (gs and A) based on the complete spectral signature from visually healthy foliar tissue, achieving coefficients of determination of 84% and 81%, respectively. Consequently, ML models utilizing physiological response data and hyperspectral imaging exhibited remarkable robustness, facilitating the estimation of Fusarium wilt severity in strawberry plants even without visual symptoms. [ABSTRACT FROM AUTHOR]

Summary: Analyses of leaf gas exchange rely on an Ohmic analogy that arrays single stomatal, internal air space, and mesophyll conductances in series. Such models underlie inferences of mesophyll conductance and the relative humidity of leaf airspaces, reported to fall as low as 80%. An unresolved question is whether such series models are biased with respect to real leaves, whose internal air spaces are chambered at various scales by vasculature.To test whether unsaturation could emerge from modeling artifacts, we compared series model estimates with true parameter values for a chambered leaf with varying distributions and magnitudes of leaf surface conductance ('patchiness').Distributions of surface conductance can create large biases in gas exchange calculations. Both apparent unsaturation and internal CO2 gradient inversion can be produced by the evolution of broader distributions of stomatal apertures consistent with a decrease in surface conductance, as might occur under increasing vapor pressure deficit.In gas exchange experiments, the behaviors of derived quantities defined by simple series models are highly sensitive to the true partitioning of flux and stomatal apertures across leaf surfaces. New methods are needed to disentangle model artifacts from real biological responses. [ABSTRACT FROM AUTHOR]

Increases in shrub height, biomass and canopy cover are key whole‐plant features of warming‐induced vegetation change in tundra. We investigated leaf functional traits underlying photosynthetic capacity of Arctic shrub species, particularly its main limiting processes such as mesophyll conductance. In this nutrient‐limited ecosystem, we expect leaf nitrogen concentration to be the main limiting factor for photosynthesis. We measured the net photosynthetic rate at saturated light (Asat) in three Salix species throughout a glacial valley in High‐Arctic tundra and used a causal approach to test relationships between leaf stomatal and mesophyll conductances (gsc, gm), carboxylation capacity (Vcmax), nitrogen and phosphorus concentration (Narea, Parea) and leaf mass ratio (LMA). Arctic Salix species showed no difference in Asat compared to a global data set, while being characterized by higher Narea, Parea and LMA. Vcmax, gsc and gm independently increased Asat, with Vcmax as its main limitation. We highlighted a nitrogen‐influenced pathway for increasing photosynthesis in the two prostrate mesic habitat species. In contrast, the erect wetland habitat Salix richardsonii mainly increased Asat with increasing gsc. Overall, our study revealed high photosynthetic capacities of Arctic Salix species but contrasting regulatory pathways that may influence shrub ability to respond to environmental changes in High Arctic tundra. Summary statement: The photosynthetic capacity and limitations in Arctic shrubs revealing contrasting adaptations among Salix species that may influence their ability to provide negative carbon feedback to the atmosphere in high‐Arctic tundra, despite their similar photosynthetic rate compared to a global data set. [ABSTRACT FROM AUTHOR]

The most prevalent light source for different plant species being cultivated under ex situ conditions is fluorescent lighting. Nevertheless, other light sources, such as light-emitting diodes (LEDs) in different colors, have shown to be more effective for such controlled conditions. In the present research, we have assessed the impact of variable light qualities on stevia (Stevia rebaudiana Bert.) seed germination and plant growth inside regulated environmental conditions. For this intent, red (RD), white (WH), blue (BL), and the different combinations of RD and BL LEDs were arranged in the plant factory system (PFS). Interestingly, it was found that the fresh weight (FW) and dry weight (DW) of leaves per plant (10.8 and 1.9 g) and FW and DW of roots per plant (2.7 and 0.4 g) measured to be maximum under RD:BL (1:1) exposure. The plants grown in PFS illuminated with RD:BL (8:2) LEDs showed maximum photosynthesis rate (8 μmol CO2/m2/s), chlorophyll a content (1.1 µg/ml), and stomata length and width in comparison to other LED exposures. Stomatal conductance and transpiration rate recorded maximum at 200 μmol/mol of CO2 concentration in plants raised under RD:BL (1:1) with 275 and 2.3 mmol H2O/m2/s, respectively. RuBisCO activity was recorded to be maximum under WH LED (0.17 µg/g). It was observed that a combination of RD and BL LEDs is more suitable for improved biomass, photosynthesis rate, chlorophyll contents, and stomatal conductance in the PFS than that of other individual light sources. The application of such biomass enhancement approach described in the present work might be advantageous for ameliorated steviol glycosides accumulation in stevia. [ABSTRACT FROM AUTHOR]

Water is the most important resource in plant growth and is a major limiting factor in sugarcane productivity worldwide. Improving water use efficiency (WUE) can increase sugarcane productivity relative to available water resources by increasing photosynthetic capacity relative to transpiration and stomatal conductance instead of decreasing stomatal conductance. Leaf carbon stable isotopic composition (δ13Cleaf) can serve as a proxy for intrinsic WUE (WUEi) because WUEi and δ13Cleaf are theoretically related through the link between intracellular and ambient CO2 concentrations (Ci/Ca) and leaf CO2 discrimination (Δ13Cleaf). In this study we surveyed 55 sugarcane genotypes for WUEi, leaf WUE (WUEleaf), Ci/Ca, and δ13Cleaf by gas exchange measurements and stable isotope analysis. We hypothesized that significant genotypic variation was found in WUEi, WUEleaf, and δ13Cleaf within the sugarcane population in Louisiana. We also hypothesized that both WUEi and δ13Cleaf and Δ13Cleaf and Ci/Ca were correlated and that δ13Cleaf could be used as a proxy for WUEi in sugarcane. Here WUEi and WUEleaf had a genetic effect and were controlled mostly by water loss (stomatal conductance or transpiration). WUEi, WUEleaf, Ci/Ca, and δ13Cleaf were correlated, but δ13Cleaf was not correlated with the component traits of WUEi (photosynthetic rate and stomatal conductance). δ13Cleaf shows promise as a proxy for WUEi to at least be able to select the tails of the distribution, but the relationship between WUEi and δ13Cleaf may not be sufficiently strong to select WUE at a finer scale. [ABSTRACT FROM AUTHOR]

This study was aimed to identify genotypic differences in shoot growth rate and root architecture traits in response to water-deficit stress at early growth stages of wheat seedling, and to quantify relationships between genotypic variation in shoot physiological traits and root system architecture with a drought tolerance at several development stages. Eight bread wheat cultivars, namely Bam, Mahooti, Roshan, Tabbasi, Atrak, Falat, Shiraz and Qods, were grown in polyvinyl chloride tubes filled with soil in the greenhouse under well-watered and water-deficit stress conditions. Water stress elicited genotypic variation in root traits and shoot growth across cultivars. Drought stress decreased root architecture traits, with greater effects in drought-sensitive cultivars compared with those that were drought-tolerant. Branch root length was less influenced compared with seminal root length. We showed that cultivars Roshan and Bam were most tolerant to drought due to their shorter distance between the first branch root and the root tip, higher branch root length, longer seminal roots and higher stomatal conductance compared to the other cultivars. Positive relationship between root growth and shoot physiological responses was quantified upon drought stress, highlighting the role of leveraging more efficient root systems as a strategy to enhance resource uptake under water-deficit conditions. Thus, root growth responses can be used as a drought tolerance selection criterion at the seedling stage of employed genotypes. [ABSTRACT FROM AUTHOR]

Plants have developed many defensive mechanisms to maintain their metabolism and growth under stress that, albeit inadequate with increased soil salinization rates and climate change, deliberately affect plant growth, productivity, and quality. As an alternative, yet effective, economical, and sustainable choice of environmentally benign source, seaweeds are proving to be potential replacements for conventional plant protectants and biostimulants. Seaweed extracts from various families have known to exert ameliorating effect in plants affected by salt stress as a cumulative action of sequential bio array of compounds under diverse categories such as phytohormones (Auxin, cytokinin, and Gibberilic acid), polyamines (putrescine and spermidine), phenolics (Vanillic and gallic acid), protein (Taurine, phosphoserine), carbohydrates (Trehalose, sorbitol, and mannitol) and betaines (glycine and proline beatine, and glycine, aminobutyric acid). These compounds are sought to promote the production and accretion of ameliorative compounds such as osmolytes that activates the MAPK pathway, triggering various signal cascades activating several genes and miRNAs that promote Na+ compartmentalization, Cl− efflux, increase cytosolic Ca+, ion homeostasis, cell–organ integrity. An increased rate of antioxidant enzymes (peroxidase, superoxide dismutase, and ascorbate peroxidase) in rapidly scavenging reactive oxygen species is also observed. Consequently, there is an increase in chlorophyll activities promoting sugar allocation, water, and resource utilization efficiencies, thereby protecting and promoting plant growth and productivity in an eco-friendly yet effective manner. [ABSTRACT FROM AUTHOR]

Under light with a low proportion of far-red (FR) light, plants perceive themselves as growing in open places, which may lead them to increase leaf hydraulic conductance (Kleaf) to cope with the higher water demand associated with increased light intensities. We evaluated Kleaf of cucumber (Cucumis sativus L.) seedlings that had been acclimatized to light with different proportions of FR. Kleaf tended to increase with decreasing FR light. Kleaf and leaf vein length density were positively correlated, indicating that increased Kleaf caused by low FR light may have been caused by changes in leaf vein structure. To clarify whether acclimatization to low-FR light can improve tolerance to high evaporative demand, we evaluated changes in stomatal conductance (gs), quantum yield of photosystem II (ΦPSII), and leaf water potential (Ψleaf) when seedlings that had been acclimatized to light with FR light in the same proportion as sunlight (FR+) or light without FR light (FR−) were transferred to a high vapor-pressure deficit (VPD) condition. After transfer to high VPD, gs and Ψleaf of the seedlings decreased in all treatment groups, but the decrease was smaller in the FR− seedlings. After transfer to high VPD, ΦPSII decreased significantly in the FR+ seedlings, but not in the FR− seedlings. These findings suggest that the changes in stress tolerance induced by FR light may be partly mediated by changes in Kleaf. Our results also indicate a potential new technique for mitigating drought stress in horticultural crops by controlling FR light. [ABSTRACT FROM AUTHOR]

Background: Climate change and the growing demand for agricultural water threaten global food security. Understanding water use characteristics of major crops from leaf to field scale is critical, particularly for identifying crop varieties with enhanced water-use efficiency (WUE) and stress tolerance. Traditional methods to assess WUE are either by gas exchange measurements at the leaf level or labor-intensive manual pot weighing at the whole-plant level, both of which have limited throughput. Results: Here, we developed a microcontroller-based low-cost system that integrates pot weighing, automated water supply, and real-time monitoring of plant water consumption via Wi-Fi. We validated the system using major crops (rice soybean, maize) under diverse stress conditions (salt, waterlogging, drought). Salt-tolerant rice maintained higher water consumption and growth under salinity than salt-sensitive rice. Waterlogged soybean exhibited reduced water use and growth. Long-term experiments revealed significant WUE differences between rice varieties and morphological adaptations represented by altered shoot-to-root ratios under constant drought conditions in maize. Conclusions: We demonstrate that the system can be used for varietal differences between major crops in their response to drought, waterlogging, and salinity stress. This system enables high-throughput, long-term evaluation of water use characteristics, facilitating the selection and development of water-saving and stress-tolerant crop varieties. [ABSTRACT FROM AUTHOR]

Summary: As temperature rises, net carbon uptake in tropical forests decreases, but the underlying mechanisms are not well understood. High temperatures can limit photosynthesis directly, for example by reducing biochemical capacity, or indirectly through rising vapor pressure deficit (VPD) causing stomatal closure.To explore the independent effects of temperature and VPD on photosynthesis we analyzed photosynthesis data from the upper canopies of two tropical forests in Panama with Generalized Additive Models.Stomatal conductance and photosynthesis consistently decreased with increasing VPD, and statistically accounting for VPD increased the optimum temperature of photosynthesis (Topt) of trees from a VPD‐confounded apparent Topt of c. 30–31°C to a VPD‐independent Topt of c. 33–36°C, while for lianas no VPD‐independent Topt was reached within the measured temperature range. Trees and lianas exhibited similar temperature and VPD responses in both forests, despite 1500 mm difference in mean annual rainfall.Over ecologically relevant temperature ranges, photosynthesis in tropical forests is largely limited by indirect effects of warming, through changes in VPD, not by direct warming effects of photosynthetic biochemistry. Failing to account for VPD when determining Topt misattributes the underlying causal mechanism and thereby hinders the advancement of mechanistic understanding of global warming effects on tropical forest carbon dynamics. See also the Commentary on this article by Gauthey & Gardner, 244: 1119–1121. [ABSTRACT FROM AUTHOR]

The article "Stomata: custodians of leaf gaseous exchange" published in the Journal of Experimental Botany discusses the role of stomata in regulating gaseous exchange in plants. Stomata, surrounded by guard cells, modulate CO2 uptake for photosynthesis while minimizing water loss. The article explores the impact of stomatal conductance on photosynthesis, water use efficiency, and plant performance, emphasizing the potential for crop improvement through enhanced photosynthesis and water use efficiency. It also delves into the manipulation of stomatal anatomical features to improve water use efficiency and plant resilience to climate-induced stresses. [Extracted from the article]

Environmental change requires more crop production per water use to meet the rising global food demands. However, improving crop intrinsic water use efficiency (iWUE) usually comes at the expense of carbon assimilation. Sorghum is a key crop in many vulnerable agricultural systems with higher tolerance to water stress (WS) than most widely planted crops. To investigate physiological controls on iWUE and its inheritance in sorghum, we screened 89 genotypes selected based on inherited haplotypes from an elite line or five exotics lines, containing a mix of geographical origins and dry versus milder climates, which included different aquaporin (AQP) alleles. We found significant variation among key highly heritable gas exchange and hydraulic traits, with some being significantly affected by variation in haplotypes among parental lines. Plants with a higher proportion of the non-stomatal component of iWUE still maintained iWUE under WS by maintaining photosynthetic capacity, independently of reduction in leaf hydraulic conductance. Haplotypes associated with two AQPs (SbPIP1.1 and SbTIP3.2) influenced iWUE and related traits. These findings expand the range of traits that bridge the trade-off between iWUE and productivity in C4 crops, and provide possible genetic regions that can be targeted for breeding. [ABSTRACT FROM AUTHOR]

In this study, we assessed 43 accessions of sorghum from 16 countries across three continents. Our objective was to identify stomatal and photosynthetic traits that could be exploited in breeding programmes to increase photosynthesis without increasing water use under dynamic light environments. Under field conditions, sorghum crops often have limited water availability and are exposed to rapidly fluctuating light intensities, which influences both photosynthesis and stomatal behaviour. Our results highlight a tight coupling between photosynthetic rate (A) and stomatal conductance (g s) even under dynamic light conditions that results in steady intrinsic water use efficiency (W i). This was mainly due to rapid stomatal responses, with the majority of sorghum accessions responding within ≤5 min. The maintenance of the ratio of the concentration of CO2 inside the leaf (C i) and the surrounding atmospheric concentration (C a) over a large range of accessions suggests high stomatal sensitivity to changes in C i, that could underlie the rapid g s responses and extremely close relationship between A and g s under both dynamic and steady-state conditions. Therefore, sorghum represents a prime candidate for uncovering the elusive mechanisms that coordinate A and g s, and such information could be used to design crops with high A without incurring significant water losses and eroding W i. [ABSTRACT FROM AUTHOR]

The ratio of net CO2 uptake (A net) and stomatal conductance (g s) is an intrinsic measurement of leaf water use efficiency (WUEi); however, its measurement can be challenging for large phenotypic screens. Measurements of the leaf carbon isotope composition (δ13Cleaf) may be a scalable tool to approximate WUEi for screening because it in part reflects the competing influences of A net and g s on the CO2 partial pressure (p CO2) inside the leaf over time. However, in C4 photosynthesis, the CO2-concentrating mechanism complicates the relationship between δ13Cleaf and WUEi. Despite this complicated relationship, several studies have shown genetic variation in δ13Cleaf across C4 plants. Yet there has not been a clear demonstration of if A net or g s are the causal mechanisms controlling WUEi and δ13Cleaf. Our approach was to characterize leaf photosynthetic traits of two Zea mays recombinant inbred lines (Z007E0067 and Z007E0150) which consistently differ for δ13Cleaf even though they have minimal confounding genetic differences. We demonstrate that these two genotypes contrasted in WUEi driven by differences in the speed of stomatal responses to changes in p CO2 and light that lead to unproductive leaf water loss. These findings provide support that differences in δ13Cleaf in closely related genotypes do reflect greater WUEi and further suggest that differences in stomatal kinetic response to changing environmental conditions is a key target to improve WUEi. [ABSTRACT FROM AUTHOR]

Stomata regulate CO2 and water vapor exchange between leaves and the atmosphere. Stomata are a target for engineering to improve crop intrinsic water use efficiency (iWUE). One example is by expressing genes that lower stomatal density (SD) and reduce stomatal conductance (g sw). However, the quantitative relationship between reduced SD, g sw, and the mechanisms underlying it is poorly understood. We addressed this knowledge gap using low-SD sugarcane (Saccharum spp. hybrid) as a case study alongside a meta-analysis of data from 10 species. Transgenic expression of EPIDERMAL PATTERNING FACTOR 2 from Sorghum bicolor (SbEPF2) in sugarcane reduced SD by 26–38% but did not affect g sw compared with the wild type. Further, no changes occurred in stomatal complex size or proxies for photosynthetic capacity. Measurements of gas exchange at low CO2 concentrations that promote complete stomatal opening to normalize aperture size between genotypes were combined with modeling of maximum g sw from anatomical data. These data suggest that increased stomatal aperture is the only possible explanation for maintaining g sw when SD is reduced. Meta-analysis across C3 dicots, C3 monocots, and C4 monocots revealed that engineered reductions in SD are strongly correlated with lower g sw (r 2=0.60–0.98), but this response is damped relative to the change in anatomy. [ABSTRACT FROM AUTHOR]

Recent research has shown that optimizing photosynthetic and stomatal traits holds promise for improved crop performance. However, standard phenotyping tools such as gas exchange systems have limited throughput. In this work, a novel approach based on a bespoke gas exchange chamber allowing combined measurement of the quantum yield of PSII (F q' /F m'), with an estimation of stomatal conductance via thermal imaging was used to phenotype a range of bread wheat (Triticum aestivum L.) genotypes. Using the dual-imaging methods and traditional approaches, we found broad and significant variation in key traits, including photosynthetic CO2 uptake at saturating light and ambient CO2 concentration (A sat), photosynthetic CO2 uptake at saturating light and elevated CO2 concentration (A max), the maximum velocity of Rubisco for carboxylation (V cmax), time for stomatal opening (K i), and leaf evaporative cooling. Anatomical analysis revealed significant variation in flag leaf adaxial stomatal density. Associations between traits highlighted significant relationships between leaf evaporative cooling, leaf stomatal conductance, and F q' /F m', highlighting the importance of stomatal conductance and stomatal rapidity in maintaining optimal leaf temperature for photosynthesis in wheat. Additionally, g smin and g smax were positively associated, indicating that potential combinations of preferable traits (i.e. inherently high g smax, low K i, and maintained leaf evaporative cooling) are present in wheat. This work highlights the effectiveness of thermal imaging in screening dynamic g s in a panel of wheat genotypes. The wide phenotypic variation observed suggested the presence of exploitable genetic variability in bread wheat for dynamic stomatal conductance traits and photosynthetic capacity for targeted optimization within future breeding programmes. [ABSTRACT FROM AUTHOR]

Plants grown under field conditions experience fluctuating light. Understanding the natural genetic variations for a similarly dynamic photosynthetic response among untapped germplasm resources, as well as the underlying mechanisms, may offer breeding strategies to improve production using molecular approaches. Here, we measured gas exchange under fluctuating light, along with stomatal density and size, in eight wild tomato species and two tomato cultivars. The photosynthetic induction response showed significant diversity, with some wild species having faster induction rates than the two cultivars. Species with faster photosynthetic induction rates had higher daily integrated photosynthesis, but lower average water use efficiency because of high stomatal conductance under natural fluctuating light. The variation in photosynthetic induction was closely associated with the speed of stomatal responses, highlighting its critical role in maximizing photosynthesis under fluctuating light conditions. Moreover, stomatal size was negatively correlated with stomatal density within a species, and plants with smaller stomata at a higher density had a quicker photosynthetic response than those with larger stomata at lower density. Our findings show that the response of stomatal conductance plays a pivotal role in photosynthetic induction, with smaller stomata at higher density proving advantageous for photosynthesis under fluctuating light in tomato species. The interspecific variation in the rate of stomatal responses could offer an untapped resource for optimizing dynamic photosynthetic responses under field conditions. [ABSTRACT FROM AUTHOR]

Low nitrogen (N) is a major limitation of cotton sustainability and productivity. N-efficient genotype cultivation can enhance productivity under the economical N usage. This study was conducted to characterize 15 cotton genotypes for N use efficiency (NUE) under differential N (0.0125 and 0.125 g kg−1 of sand) supply. All studied traits significantly responded to genotypes and N treatments. Under low N conditions, plants experienced reduced seedling height, root weight, shoot weight and total biomass (TDM) production, chlorophyll content, photosynthetic efficiency, NPK content, and N uptake efficiency (NUpE). Thus, intercellular CO2 concentration, photosynthetic N use efficiency (PNUE), and NUtE enhanced in low N supply, although these changes varied in magnitude. Based on variations in TDM production (14.6–33.1%) and NUtE (3.3–20.4%), GH-Uhad, FH-Anmol, FH-Super, GH-Haadi, and SLH-Chandani were categorized as efficient and responsive (ER), while J-7, CIM-343, FH-155, FH-492, FH-444 found as inefficient and non-responsive. The efficient and non-responsive group contained FH-142, GH-Baghdadi, and FH-490 whereas FH-152 and Cyto-179 were classified as inefficient and responsive. The scoring method provided further insight into genotypic NUE related to biomass distribution, photosynthetic rate (Pn), NUpE, and NUtE under low N. The highest cumulative score (15-18) of ER genotypes for these attributes indicated selected traits orchestrated to determine the NUE. Moreover, agronomical and NUE-related traits were positively associated with Pn, suggesting that photosynthesis is a primary manipulator of plant growth which coordinates biomass production and NUE. Overall, cultivars exhibited greater genotypic variation for NUE, providing a scientific basis to evaluate the existing germplasm and proposing that cultivation of N-efficient genotypes can decrease N application and help cotton breeding for sustainable production. [ABSTRACT FROM AUTHOR]

Climate change significantly threatens crops, mainly through drought stress, affecting barley, which is essential for food and feed globally. Ten barley cultivars were evaluated under normal and drought stress conditions during the 2019/20 and 2020/21 seasons, focusing on traits such as days to heading and maturity, plant height, number of spikes m−2, spike length, 1000-kernel weight, and biological and grain yield. Drought stress significantly reduced most of these traits. The genotypes showed significant differences in their responses to irrigation treatments, with the interaction between seasons and cultivars also being significant for most traits. The grain yield and 1000-kernel weight were among the least affected traits under drought stress, respectively. Notably, Giza138 and Giza126 showed strong drought tolerance, suitable for drought-resilient breeding. In season one, Giza126, Giza134, and Giza138 yielded 13%, 9%, and 11%, respectively, while Giza135 and Giza129 showed higher reductions at 31% and 39%. In season two, Giza126, Giza134, and Giza138 had reductions of 14%, 10%, and 13%, respectively, while Giza135 and Giza129 again exhibited higher reductions at 31% and 38%. These cultivars also showed strong performance across various stress tolerance indices, including the MP, YSI, STI, GMP, and YI. Giza 134 demonstrated the lowest values for the SDI and TOL, indicating superior drought stress tolerance. On the other hand, Giza 129 and Giza 135 were the most sensitive to drought stress, experiencing significant reductions across critical traits, including 6.1% in days to heading, 18.37% in plant height, 28.21% in number of kernel spikes−1, 38.45% in grain yield, and 34.91% in biological yield. In contrast, Giza 138 and Giza 2000 showed better resilience, with lower reductions in the 1000-kernel weight (6.41%) and grain yield (10.61%), making them more suitable for drought-prone conditions. Giza 126 and Giza 132 also exhibited lower sensitivity, with minimal reductions in days to heading (2%) and maturity (2.4%), suggesting potential adaptability to water-limited environments. Giza 126 maintained the highest root lengths and had the highest stomatal conductance. Giza 138 consistently had the highest chlorophyll content, with SPAD values decreasing to 79% under drought. Despite leading in shoot length, Giza 135 decreased to 42.59% under drought stress. In conclusion, Giza 126 and Giza 138 showed adaptability to water-limited conditions with minimal impact on phenological traits. Giza 126 had the longest roots and highest stomatal conductance, while Giza 138 consistently maintained a high chlorophyll content. Together, they and Giza 134 are valuable for breeding programs to improve barley drought tolerance. [ABSTRACT FROM AUTHOR]

• This work assessed the physiological properties of dark-colored caladium (dark green, pinkish-dark green, dark maroon, maroon, and green lime) and light-colored caladium (yellow, white, young pinkish green, pink, and red). • A higher rate of photosynthesis was positively correlated to the higher stomatal conductance and lower RGB in the dark-colored caladium group rather than the light-colored ones. • The main characteristics of the group of light-colored leaves were a high RGB, LUE, and leaf temperature. This work aims to analyze the physiological characteristics of caladium ornamental plants with different leaf colors. Ten leaf colors, i.e., dark maroon, maroon, red, pink, white, pinkish young green, yellow, lime green, pinkish dark green, and dark green, were arranged in a completely randomized design and subjected to colorimetric red–green–blue (RGB) and portable photosynthesis measurement. Caladium leaf color, defined by the colorimetric RGB value, significantly impacted leaf physiological properties. Heatmap analysis apparently clustered caladiums into dark-colored group and light-colored ones. Dark-colored caladiums, as indicated by lower RGB values, exhibited higher photosynthesis rate, stomatal conductance, and water use efficiency (WUE). In contrast, light-colored caladium show a higher RGB, leaf temperature and light use efficiency (LUE) than the dark ones. By considering their leaf color-based physiological adaptability, this work recommends moderate sunlight and adequate water conditions for growing light-colored caladiums, while dark caladiums potentially tolerate excess light and water scarcity. Further research, including quantitative pigment analysis, is necessary to verify this hypothesis. [ABSTRACT FROM AUTHOR]

This experiment was conducted at the Fruit Research Institute, MAREM, Eğirdir-Isparta, Turkey, to detect the effects of different glycine betaine doses in drought stress conditions on young pear trees in 2019. The pear trees used in the study were one-year-old Deveci (Pyrus Comminus L.) variety grafted onto OHxF 333 rootstock. There were three different irrigation treatments in the experiment. Treatments were I100 treatment—available soil water reached field capacity for each irrigation, 100% (control); I50 treatment—irrigated with 50% of the water used in the I100 treatment (50% water deficit, moderate stress); I25 treatment—irrigated with 25% of the water used in the I100 treatment (75% water deficit, severe stress). Four different GB doses were used: GB0: 0, control; GB1: 1 mg L−1; GB5: 5 mg L−1; and GB10: 10 mg L−1. GB was not applied to pear trees in the I100 treatment. That is, there were nine different treatments in this study. GB applications provided a 19% increase in Pn of both the I25 and I50 treatments. According to the results of gsw, gsw increased between 18.0% and 27.8% for GB50 and GB25 treatments, respectively. In total, 10.9% and 14.8% increasing rates in shoot length were detected in GB10 applications in both the 50% and 75% water deficit treatments. The highest trunk diameter and fresh root weight results were determined in 10 mg L−1 GB dose applications under 50% water deficit conditions (I50GB10). [ABSTRACT FROM AUTHOR]

We had assembled a synthetic bacterial community (SynComH) from the rhizosphere microbiota of Haloxylon ammodendron, which enhance drought tolerance in Arabidopsis thaliana under laboratory conditions. Here we assessed the efficacy of SynComH, alone or in combination with SynComS, a consortium of previously identified growth-promoting bacteria from Crocus sativus, in increasing maize plants' fitness under optimal and water-deficit conditions. We were also interested in unveiling the mechanisms by which the bacteria confer drought tolerance. We first performed detailed greenhouse experiments on maize plants that were artificially inoculated with SynComS, SynComH, and SynComH+S, and measured 22 different plant morphological, physiological, biochemical, and histological traits under optimal and water-deficit conditions. Data were analyzed by different univariate and multivariate statistical methods. Lastly, we tested the effects of the SynComs on maize in field in a split-plot experiment with two irrigation regimes as main plots and SynComs as subplots. Results from both greenhouse and field experiments showed that all three SynComs had growth-promoting properties and improved growth-related traits, but only SynComH and SynComH+S were effective in ameliorating the drought stress. SynComH substantially enhanced drought tolerance by increasing stomatal conductance, photosynthesis rate, and proline content, while decreasing transpiration rate, leading to up to 700% increase of water use efficiency. Morphological and histological investigations suggested that these positive effects are probably attributed to modulation of plant stomatal density and xylem structure by SynComH. Besides the significance for practical agronomic use, our results suggest unprecedented capabilities of non-pathogenic bacteria in modulation of plant stomatal density. [ABSTRACT FROM AUTHOR]

Water stress is one of the most significant abiotic stresses that disrupts the osmotic balance of plants and consequently reduces their growth and performance. In recent years, it has been found that serotonin, as a signaling and regulatory molecule, can play important roles in the growth and development of plants and enhance their tolerance to abiotic stresses. Saffron is a plant known for its medicinal and culinary properties. Its distinct flavor, aroma, and vibrant color make it a sought-after ingredient in various cuisines and traditional medicines. The aim of this study is to investigate the possible effect of serotonin growth regulator on some morphophysiological and biochemical characteristics of saffron plant under water stress conditions. Water stress was applied using polyethylene glycol 6000 at a level of 30%, w/v. Serotonin was also applied exogenously at a concentration of 100 µM in both foliar and root applications. The experimental findings demonstrated that water stress had a detrimental impact on various growth and photosynthetic parameters including FW, DW, SH, RWC, photosynthetic pigments content, Pn, Fv/Fm, C and Ci. Under these conditions, H2O2 content and ion leakage increased. The increase in the content of proline and sugars also confirmed that the saffron plant was placed in unfavorable growth conditions. Serotonin application in both foliar and root applications and especially root treatment under stressful conditions improved plant growth by activating enzymatic and non-enzymatic antioxidant systems. Overall, the exogenous application of serotonin increased the resistance of saffron plants to water stress. [ABSTRACT FROM AUTHOR]

Modern plant physiological theory stipulates that the resistance to water movement from plants to the atmosphere is overwhelmingly dominated by stomata. This conception necessitates a corollary assumption—that the air spaces in leaves must be nearly saturated with water vapour; that is, with a relative humidity that does not decline materially below unity. As this idea became progressively engrained in scientific discourse and textbooks over the last century, observations inconsistent with this corollary assumption were occasionally reported. Yet, evidence of unsaturation gained little traction, with acceptance of the prevailing framework motivated by three considerations: (1) leaf water potentials measured by either thermocouple psychrometry or the Scholander pressure chamber are largely consistent with the framework; (2) being able to assume near saturation of intercellular air spaces was transformational to leaf gas exchange analysis; and (3) there has been no obvious mechanism to explain a variable, liquid‐phase resistance in the leaf mesophyll. Here, we review the evidence that refutes the assumption of universal, near saturation of air spaces in leaves. Refining the prevailing paradigm with respect to this assumption provides opportunities for identifying and developing mechanisms for increased plant productivity in the face of increasing evaporative demand imposed by global climate change. Summary statement: Universal, near saturation of leaf air spaces is a long‐standing assumption in plant science. Here, we summarise historical and recent evidence which provides a compelling case for refuting this assumption and recognising significant unsaturation. Such recognition will enhance opportunities to promote plant productivity in the face of increasing evaporative demand. [ABSTRACT FROM AUTHOR]

Predicting how plants respond to drought requires an understanding of how physiological mechanisms and drought response strategies occur, as these strategies underlie rates of gas exchange and productivity. We assessed the response of 11 plant traits to repeated experimental droughts in four co-occurring species of central Australia. The main goals of this study were to: (i) compare the response to drought between species; (ii) evaluate whether plants acclimated to repeated drought; and (iii) examine the degree of recovery in leaf gas exchange after cessation of drought. Our four species of study were two tree species and two shrub species, which field studies have shown to occupy different ecohydrological niches. The two tree species (Eucalyptus camaldulensis Dehnh. and Corymbia opaca (D.J.Carr & S.G.M.Carr) K.D.Hill & L.A.S.Johnson) had large reductions in stomatal conductance (g s) values, declining by 90% in the second drought. By contrast, the shrub species (Acacia aptaneura Maslin & J.E.Reid and Hakea macrocarpa A.Cunn. ex R.Br.) had smaller reductions g s in the second drought of 52 and 65%, respectively. Only A. aptaneura showed a physiological acclimatation to drought due to small declines in g s versus ᴪpd (0.08 slope) during repeated droughts, meaning they maintained higher rates of g s compared with plants that only experienced one final drought (0.19 slope). All species in all treatments rapidly recovered leaf gas exchange and leaf mass per area following drought, displaying physiological plasticity to drought exposure. This research refines our understanding of plant physiological responses to recurrent water stress, which has implications for modelling of vegetation, carbon assimilation and water use in semi-arid environments under drought. [ABSTRACT FROM AUTHOR]

Coffee is a key agricultural product in national and international markets. Physiological parameters, such as plant growth indicators, can signal interruptions in these processes. This study aimed to characterize the temperature obtained by a thermal camera embedded in a remotely piloted aircraft (RPA) and evaluate its relationship with the water potential (WP) and stomatal conductance (gs) of an experimental coffee plantation using geostatistical techniques. The experiment was conducted at the Federal University of Lavras, Minas Gerais, Brazil. A rotary-wing RPA with an embedded thermal camera flew autonomously at a height of 10 m and speed of 10 m/s. Images were collected on 26 November 2019 (rainy season), and 11 August 2020 (dry season), between 9:30 am and 11:30 am. Data on gs and WP were collected in the field. The thermal images were processed using FLIR Tools 5.13, and temperature analysis and spatialization were undertaken using geostatistical tools and isocolor maps by Kriging interpolation in R 4.3.2 software. Field data were superimposed on final crop temperature maps using QuantumGIS version 3.10 software. The study found that with decreasing WP, stomatal closure and reduction in gs occurred, increasing the temperature due to water deficit. The temperature distribution maps identified areas of climatic variations indicating water deficit. [ABSTRACT FROM AUTHOR]

Leaf ontogeny of tropical evergreen tree species lasts several months with changes in size, shape, colouration and internal tissue distribution of leaves. Leaf initiation in Saraca asoca generally occurs once in a year during February–April, followed by very limited leafing thereafter. We measured the rate of photosynthesis, chlorophyll a fluorescence, energy quenching and PSII functions during the leaf ontogeny process. Observations were taken up to 35 days after opening of lamina (DAOL). Significant increase in the synthesis and accumulation of photosynthetic pigments but negative net photosynthesis was noticed during initial days of the ontogeny. The leaf moved from heterotrophy to autotrophy with gradual improvement of PSII functions. The ratio of intercellular CO2 (C i) and ambient CO2 (C a) showed significant change at ≥11 DAOL. Increase in the age of the leaf (between 5 and 28 DAOL) caused decrease in O-J rise and corresponding increase in J-I and I-P rise as well as of fluorescence maximum (F M) of the OJIP curve. The improvement of the electron transport components of the donor side of PSII was seen with increase in the functional oxygen evolving complex. The functional improvements of the donor and acceptor side of PSII during leaf ontogeny are discussed. The leaf ontogeny in Saraca asoca usually occurs once in a year and involves variation in PSII function. The developing leaves metabolically switch from heterotrophy to autotrophy. During leaf development, the carotenoids are accumulated earlier than chlorophylls. With the development of leaf, the PSII function improves leading to increased efficiency of oxygen evolving complex and photoelectron transport. [ABSTRACT FROM AUTHOR]

• VPD and R g predominantly drive variations in tree-level transpiration. • Soil moisture availability did not limit tree-level transpiration. • Xylem sap flow exhibited a strong correlation with VPD, R g , and RH. • Significant correlation (P < 0.001) was observed between actual and potential transpiration. • Apple tree water usage was higher in the early season compared to mid- and late seasons. Understanding the environmental drivers and hydraulic dynamics of plants is pivotal for elucidating future water use strategies and refining precise irrigation techniques. In our investigation, we focused on the daily and seasonal fluctuations in sap flow (SF) using compensation heat-pulse techniques on 7-year-old 'Gamhong' apple trees. Predictions of stand transpiration were integrated using the Penman-Monteith grass reference evapotranspiration. Additionally, we measured leaf-level diurnal and seasonal stomatal conductance (g s), leaf water potential (Ψ Leaf), and transpiration rate (E) to explore the relationship between plant-level transpiration and orchard microclimate. Diurnal SF exhibited a pattern similar to global radiation (R g) and vapor pressure deficit (VPD), increasing in the morning with a peak in the afternoon and decreasing towards evening. Seasonal water use varied, with rates of 10.62 ± 0.282 L day-1 in early (May–June), 8.40 ± 0.222 L day-1 in mid- (July–August), and 5.96 ± 0.154 L day-1 in late season (September–October). Plant water consumption was influenced by weather conditions and evaporative demand driven by atmospheric VPD and R g. Clear and sunny days resulted in higher water use (10.23 ± 0.291 L day-1) compared to partially sunny but windy days (9.85 ± 0.32 L day-1) and cloudy/rainy days (5.37 ± 0.176 L day-1). Plant transpiration strongly correlated with VPD (R² = 0.565), R g (R² = 0.616), relative humidity (R ² = 0.623), and wind velocity (u, R ² = 0.684), while no significant correlation was observed with air temperature (T a , R ² = 0.19) or soil moisture status (Ψ soil , R² = 0.19). VPD and R g emerged as the primary drivers, with Ψ soil playing a minor role and not limiting tree-level transpiration. Leaf-level g s , Ψ Leaf , and E displayed similar diurnal trends. In our study, the integrated daily sap flow provided valuable insights into plant-water relations differently across growing seasons and its relationship with reference evapotranspiration (E o). The Penman–Monteith equation, using grass reference evapotranspiration indicated a positive correlation (R ² = 0.764, P < 0.001) between actual and estimated transpiration. However, the slope of the relationship differed significantly from 1.0, suggesting that E o per unit leaf area of grass corresponds to E 288 = E o /2.88 (L m-2 of leaf area d-1), which underestimated evapotranspiration. [ABSTRACT FROM AUTHOR]

Current agriculture intensifies crop cultivation to meet food demand, leading to unsustainable use of chemical fertilizers. This study investigates a few physiological and agronomic responses of common wheat following the inoculation with plant growth-promoting bacteria to reduce nitrogen inputs. A field trial was conducted in 2022–2023, in Legnago (Verona, Italy) on Triticum aestivum var. LG-Auriga comparing full (180 kg ha−1) and reduced (130 kg ha−1) N doses, both with and without foliar application at end tillering of the N-fixing bacterium Methylobacterium symbioticum. Biofertilization did not improve shoot growth, while it seldom increased the root length density in the arable layer. It delayed leaf senescence, prolonged photosynthetic activity, and amplified stomatal conductance and PSII efficiency under the reduced N dose. Appreciable ACC-deaminase activity of such bacterium disclosed augmented nitrogen retrieval and reduced ethylene production, explaining the ameliorated stay-green. Yield and test weight were unaffected by biofertilization, while both glutenin-to-gliadin and HMW-to-LMW ratios increased together with dough tenacity. It is concluded that Methylobacterium symbioticum can amplify nitrogen metabolism at a reduced nitrogen dose, offering a viable approach to reduce chemical fertilization under suboptimal growing conditions for achieving a more sustainable agriculture. Further research over multiple growing seasons and soil types is necessary to corroborate these preliminary observations. [ABSTRACT FROM AUTHOR]

Climate change is considered a threat for viticulture by altering phenology, yield, and key physiological processes. The plant responses depend on the genotype characteristics and the microclimate of crop area. In this research, "Castellana Negra", "Negramoll", and "Tintilla" were cultivated for 102 days, and physiological variables were assessed under natural conditions. Results indicated similar trends in growth between "Negramoll" and "Tintilla", while "Castellana Negra" grew slowly and possessed fewer leaves compared to the other genotypes. Stomatal conductance was constant among the genotypes, excepting "Negramoll", which demonstrated lower values at d 76 compared to "Castellana Negra" and "Tintilla", coinciding with the elevated leaf temperature. Regarding the hormonal changes, "Castellana Negra" accumulated the highest concentration of salicylic acid (SA) compared to "Negramoll" and "Tintilla", which showed similar content. Furthermore, an antagonistic change between SA and jasmonic acid (JA) was observed in all genotypes, as well as between abscisic acid (ABA) and JA at the beginning and end of the trial. The variations in micronutrients did not show a clear tendency between cultivars. Therefore, to thoroughly elucidate the role of phytohormones and other physiological factors in the growth and development of these genotypes under varying environmental conditions, long-term experiments could be conducted. [ABSTRACT FROM AUTHOR]

Drought conditions can severely impact rubber (Hevea brasiliensis) plantations, leading to economic loss in Malaysia. The study aimed to assess the impact of varying soil moisture levels on the physiological characteristics of five latex timber clones (LTCs) of rubber, with the goal of identifying the most suitable clone for specific soil moisture conditions. These conditions include (1) field capacity, (2) 75% available water (AW), (3) 50% AW, (4) 25% AW, and (5) wilting point, with the ultimate objective of optimizing cultivation methods and fostering sustainable rubber production in Malaysia. The five clones under investigation include RRIM3001, RRIM2025, RRIM2001, RRIM928, and PB350. Leaf chlorophyll content, stomatal conductance, and net photosynthesis were measured 4 and 8 months after treatment (MAT). The findings indicated significant effects of moisture stress on various physiological attributes, including total chlorophyll content, relative chlorophyll content, stomatal conductance, and net photosynthesis rate. At 4 and 8 MATs, the clones subjected to field capacity exhibited the highest values for these physiological characteristics, followed by those exposed to 75% available water, with the lowest values observed at the wilting point. RRIM3001 consistently exhibited the highest total chlorophyll content, stomatal conductance, and net photosynthesis among the clones at both sampling dates. The highest net photosynthesis was observed in the RRIM3001 clone under field capacity conditions. Furthermore, a significant positive correlation was identified between total chlorophyll and relative chlorophyll contents, as well as between net photosynthesis and stomatal conductance. These findings carry practical implications for water management during the initial growth phase of rubber seedlings and for replanting initiatives in rubber plantations. [ABSTRACT FROM AUTHOR]

Rising CO2 concentration in the atmosphere is a matter of global concern and poses apprehension about how plants will adapt to the changing environment. Various studies have proved that under high CO2 levels, plant physiology alters and affects plant functioning. However, under elevated CO2, the stomatal characters and their relation with physiological responses are still not yet clear. To find out these changes in the stomatal parameters at ambient and two elevated CO2 (550 ppm and 700 ppm) levels, four genotypes of maize (Zea mays L.) viz. DHM-117, Harsha, Varun and M-24 were grown in open-top chambers. In the study, it was observed that the stomatal density increased, stomatal size altered, stomatal conductance (gs) and transpiration rate (Tr) decreased under elevated CO2 (eCO2) while photosynthetic rate (Pn), water use efficiency (WUE), yield and biomass, of which especially the reproductive biomass increased. Under eCO2, stomatal and physiological changes were genotypic and CO2 concentration specific. Increased stomatal density at eCO2 was mainly due to increased abaxial stomatal density. The improved Pn and reduced Tr at 550 ppm improved the WUE in the plants, while this response was not observed at 700 ppm. These results elucidate that this C4 crop responded positively to up to 550 ppm of CO2 concentrations, and beyond this, the impact was minimal. [ABSTRACT FROM AUTHOR]

Capsicum annuum L. has worldwide distribution, but drought has limited its production. There is a lack of research to better understand how this species copes with drought stress, whether it is reversible, and the effects of mitigating agents such as salicylic acid (SA). Therefore, this study aimed to understand the mechanisms of action of SA and rehydration on the physiology of pepper plants grown under drought conditions. The factorial scheme adopted was 3 × 4, with three water regimes (irrigation, drought, and rehydration) and four SA concentrations, namely: 0 (control), 0.5, 1, and 1.5 mM. This study evaluated leaf water percentage, water potential of shoots, chlorophylls (a and b), carotenoids, stomatal conductance, chlorophyll a fluorescence, and hydrogen peroxide (H2O2) concentration at different times of day, water conditions (irrigation, drought, and rehydration), and SA applications (without the addition of a regulator (0) and with the addition of SA at concentrations equal to 0.5, 1, and 1.5 mM). In general, exogenous SA application increased stomatal conductance (gs) responses and modified the fluorescence parameters (ΦPSII, qP, ETR, NPQ, D, and E) of sweet pepper plants subjected to drought followed by rehydration. It was found that the use of SA, especially at concentrations of 1 mM in combination with rehydration, modulates gs, which is reflected in a higher electron transport rate. This, along with the production of photosynthetic pigments, suggests that H2O2 did not cause membrane damage, thereby mitigating the water deficit in pepper plants. Plants under drought conditions and rehydration with foliar SA application at concentrations of 1 mM demonstrated protection against damage resulting from water stress. Focusing on sustainable productivity, foliar SA application of 1 mM could be recommended as a technique to overcome the adverse effects of water stress on pepper plants cultivated in arid and semi-arid regions. [ABSTRACT FROM AUTHOR]

Main conclusion: The high intrinsic water-use efficiency of Erianthus may be due to the low abaxial stomatal density and the accumulation of leaf metabolites such as betaine and gamma-aminobutyric acid. Sugarcane is an important crop that is widely cultivated in tropical and subtropical regions of the world. Because drought is among the main impediments limiting sugarcane production in these regions, breeding of drought-tolerant sugarcane varieties is important for sustainable production. Erianthus arundinaceus, a species closely related to sugarcane, exhibits high intrinsic water-use efficiency (iWUE), the underlying mechanisms for which remain unknown. To improve the genetic base for conferring drought tolerance in sugarcane, in the present study, we performed a comprehensive comparative analysis of leaf gas exchange and metabolites in different organs of sugarcane and Erianthus under wet and dry soil-moisture conditions. Erianthus exhibited lower stomatal conductance under both conditions, which resulted in a higher iWUE than in sugarcane. Organ-specific metabolites showed gradations between continuous parts and organs, suggesting linkages between them. Cluster analysis of organ-specific metabolites revealed the effects of the species and treatments in the leaves. Principal component analysis of leaf metabolites confirmed a rough ordering of the factors affecting their accumulations. Compared to sugarcane leaf, Erianthus leaf accumulated more raffinose, betaine, glutamine, gamma-aminobutyric acid, and S-adenosylmethionine, which function as osmolytes and stress-response compounds, under both the conditions. Our extensive analyses reveal that the high iWUE of Erianthus may be due to the specific accumulation of such metabolites in the leaves, in addition to the low stomatal density on the abaxial side of leaves. The identification of drought-tolerance traits of Erianthus will benefit the generation of sugarcane varieties capable of withstanding drought stress. [ABSTRACT FROM AUTHOR]

Abstract Nowadays, climate change is the primary factor shaping the future of food and nutritional security. To investigate the interactive effects of various climate variables on photosynthetic efficiency, an experiment was conducted using 10 dryland wheat genotypes. These genotypes were exposed to different conditions: temperatures of 25 ± 3 °C and 34 ± 3 °C, carbon dioxide concentrations of 380 ± 50 ppm and 800 ± 50 ppm, and irrigation regimes of 50% field capacity and well-watered. Our results indicated that the wheat genotypes responded differently to both individual and combined climate stress factors. The traditional winter wheat genotype *Sardari*, along with the newly developed dryland wheat genotype *Ivan*, exhibited resilience to anticipated climate conditions. This resilience was reflected in enhancements in photochemical quantum efficiency parameters (Y(II), qP, and qL) under combined stress conditions. Resilient genotypes demonstrated superior regulation of the stomatal conductance (GS) and electron transport rate (ETR) under elevated temperature and CO2 levels. Principal component analysis (PCA) revealed significant correlations between chlorophyll fluorescence parameters and climate factors, such as NPQ with temperature, Y(NO) with CO2, qL in response to drought stress, and both qP and Y(II) with the interactions among temperature, CO2, and drought stress. Elevated CO2 reduced the ETR and GS across all genotypes. Our findings underscore the importance of assessing not only fundamental chlorophyll fluorescence parameters like Fm and Fo but also the efficiency of NPQ and Y(II) to understand climate change impacts on dryland wheat genotypes. We suggest that these parameters could serve as valuable biomarkers for breeding programs aimed at improving plant adaptation to future dryland climate conditions.

Abstract Background Climate change and the growing demand for agricultural water threaten global food security. Understanding water use characteristics of major crops from leaf to field scale is critical, particularly for identifying crop varieties with enhanced water-use efficiency (WUE) and stress tolerance. Traditional methods to assess WUE are either by gas exchange measurements at the leaf level or labor-intensive manual pot weighing at the whole-plant level, both of which have limited throughput. Results Here, we developed a microcontroller-based low-cost system that integrates pot weighing, automated water supply, and real-time monitoring of plant water consumption via Wi-Fi. We validated the system using major crops (rice soybean, maize) under diverse stress conditions (salt, waterlogging, drought). Salt-tolerant rice maintained higher water consumption and growth under salinity than salt-sensitive rice. Waterlogged soybean exhibited reduced water use and growth. Long-term experiments revealed significant WUE differences between rice varieties and morphological adaptations represented by altered shoot-to-root ratios under constant drought conditions in maize. Conclusions We demonstrate that the system can be used for varietal differences between major crops in their response to drought, waterlogging, and salinity stress. This system enables high-throughput, long-term evaluation of water use characteristics, facilitating the selection and development of water-saving and stress-tolerant crop varieties.

Rising temperatures can affect stomatal and nonstomatal control over photosynthesis, through stomatal closure in response to increasing vapor pressure deficit (VPD), and biochemical limitations, respectively. To explore the independent effects of temperature and VPD, we conducted leaf-level temperature-response measurements while controlling VPD on three tropical tree species. Photosynthesis and stomatal conductance consistently decreased with increasing VPD, whereas photosynthesis typically responded weakly to changes in temperature when a stable VPD was maintained during measurements, resulting in wide parabolic temperature-response curves. We have shown that the negative effect of temperature on photosynthesis in tropical forests across ecologically important temperature ranges does not stem from direct warming effects on biochemical processes but from the indirect effect of warming, through changes in VPD. Understanding the acclimation potential of tropical trees to elevated VPD will be critical to anticipate the consequences of global warming for tropical forests.

Abstract Water stress is one of the most significant abiotic stresses that disrupts the osmotic balance of plants and consequently reduces their growth and performance. In recent years, it has been found that serotonin, as a signaling and regulatory molecule, can play important roles in the growth and development of plants and enhance their tolerance to abiotic stresses. Saffron is a plant known for its medicinal and culinary properties. Its distinct flavor, aroma, and vibrant color make it a sought-after ingredient in various cuisines and traditional medicines. The aim of this study is to investigate the possible effect of serotonin growth regulator on some morphophysiological and biochemical characteristics of saffron plant under water stress conditions. Water stress was applied using polyethylene glycol 6000 at a level of 30%, w/v. Serotonin was also applied exogenously at a concentration of 100 µM in both foliar and root applications. The experimental findings demonstrated that water stress had a detrimental impact on various growth and photosynthetic parameters including FW, DW, SH, RWC, photosynthetic pigments content, Pn, Fv/Fm, C and Ci. Under these conditions, H2O2 content and ion leakage increased. The increase in the content of proline and sugars also confirmed that the saffron plant was placed in unfavorable growth conditions. Serotonin application in both foliar and root applications and especially root treatment under stressful conditions improved plant growth by activating enzymatic and non-enzymatic antioxidant systems. Overall, the exogenous application of serotonin increased the resistance of saffron plants to water stress.

Abstract The removal of pollutants from the environment has become a global demand. The current study aimed to relieve the Ni toxicity effect on the germination, growth, and grain yield of maize by using Azolla pinnata as a phytoremediator. Azolla-treated and untreated nickel solutions [0 (control), 24, 70, 140 and 190 ppm] were applied for germination and pot experiments. Electron microscope examination cleared the Ni accumulation in Azolla’s cell vacuole and its adsorption on the cell wall. The inhibition of the hydrolytic enzyme activity reduces maize germination; maximal inhibition was 57.1% at 190 ppm of Ni compared to the control (100%). During vegetative growth, Ni stimulated the generation of H2O2 (0.387 mM g−1 F Wt at 190 ppm of Ni), which induced maximal lipid peroxidation (3.913 µMDA g−1 F Wt) and ion leakage (74.456%) compared to control. Chlorophyll content and carbon fixation also showed significant reductions at all Ni concentrations; at 190 ppm, they showed maximum reductions of 56.2 and 63%, respectively. However, detoxification enzymes’ activity such as catalase and antioxidant substances (phenolics) increased. The highest concentration of Ni (190 ppm) had the most effect on constraining yield, reaching zero for the weight of 100 grains at 190 ppm of Ni. Azolla-treated Ni solutions amended all determinant parameters, indicating a high percentage of changes in hydrolytic enzyme activity (125.2%) during germination, chlorophyll content (77.6%) and photosynthetic rate (120.1%). Growth measurements, carbon fixation, and yield components showed a positive association. Thus, we recommended using Azolla as a cost-effective and eco-friendly strategy to recover Ni-polluted water.

Rising CO2 concentration in the atmosphere is a matter of global concern and poses apprehension about how plants will adapt to the changing environment. Various studies have proved that under high CO2 levels, plant physiology alters and affects plant functioning. However, under elevated CO2, the stomatal characters and their relation with physiological responses are still not yet clear. To find out these changes in the stomatal parameters at ambient and two elevated CO2 (550 ppm and 700 ppm) levels, four genotypes of maize (Zea mays L.) viz. DHM-117, Harsha, Varun and M-24 were grown in open-top chambers. In the study, it was observed that the stomatal density increased, stomatal size altered, stomatal conductance (gs) and transpiration rate (Tr) decreased under elevated CO2 (eCO2) while photosynthetic rate (Pn), water use efficiency (WUE), yield and biomass, of which especially the reproductive biomass increased. Under eCO2, stomatal and physiological changes were genotypic and CO2 concentration specific. Increased stomatal density at eCO2 was mainly due to increased abaxial stomatal density. The improved Pn and reduced Tr at 550 ppm improved the WUE in the plants, while this response was not observed at 700 ppm. These results elucidate that this C4 crop responded positively to up to 550 ppm of CO2 concentrations, and beyond this, the impact was minimal.

Abstract Biochar (BC) applications in soil has positive effects on plant performance, particularly for loose soil in agricultural context. However, how biochar types affect plant performance of non-crop species and soil–plant carbon relationships is not clear. We selected five different BC types and three plant species to investigate the responses of plant performance and the soil–plant carbon relationship to BC effects. The result demonstrated that peanut shell BC led to the death of both R. tomentosa and C. edithiae, due to a reduction in nutrient uptake caused by higher soil electricity conductivity (2001.7 and 976.3 µS cm−1). However, the carbon content of S. arboricola increased by 57% in peanut shell BC-amended soil, suggesting that S. arboricola has a higher tolerance for soil salinity. Wood BC-amended soil led to better stomatal conductance (gs) and leaf area index (LAI) of both R. tomentosa and C. edithiae due to the higher water retention in the soil (22.68% and 20.79%). This illustrated that a higher amount of water retention brought by wood BC with a great amount of pore volume might be the limited factor for plant growth. The relationship between gs and LAI suggested that gs would not increase when LAI reached beyond 3. Moreover, wood and peanut shell BC caused a negative relationship between soil organic carbon and plant carbon content, suggesting that plants consume more carbon from the soil to store it in the plant. Overall, wood BC is recommended for plant growth of R. tomentosa and C. edithiae, and peanut shell BC is suggested for S. arboricola carbon storage. Graphical Abstract

Abstract Climate change has become a concern, emphasizing the need for the development of crops tolerant to drought. Therefore, this study is designed to explore the physiological characteristics of quinoa that enable it to thrive under drought and other extreme stress conditions by investigating the combined effects of irrigation water levels (100%, 75%, and 50% of quinoa's water requirements, WR as I1, I2 and I3) and different planting methods (basin, on-ridge, and in-furrow as P1, P2 and P3) on quinoa's physiological traits and gas exchange. Results showed that quinoa’s yield is lowest with on-ridge planting and highest in the in-furrow planting method. Notably, the seed protein concentrations in I2 and I3 did not significantly differ but they were 25% higher than those obtained in I1, which highlighted the possibility of using a more effective irrigation method without compromising the seed quality. On the other hand, protein yield (PY) was lowest in P2 (mean of I1 and I2 as 257 kg ha−1) and highest in P3 (mean of I1 and I2 as 394 kg ha−1 , 53% higher). Interestingly, PY values were not significantly different in I1 and I2, but they were lower significantly in I3 by 28%, 27% and 20% in P1, P2, and P3, respectively. Essential plant characteristics including plant height, stem diameter, and panicle number were 6.1–16.7%, 6.4–24.5%, and 18.4–36.5% lower, respectively, in I2 and I3 than those in I1. The highest Leaf Area Index (LAI) value (5.34) was recorded in the in-furrow planting and I1, while the lowest value was observed in the on-ridge planting method and I3 (3.47). In I3, leaf temperature increased by an average of 2.5–3 oC, particularly during the anthesis stage. The results also showed that at a similar leaf water potential (LWP) higher yield and dry matter were obtained in the in-furrow planting compared to those obtained in the basin and on-ridge planting methods. The highest stomatal conductance (gs) value was observed within the in-furrow planting method and full irrigation (I1P3), while the lowest values were obtained in the on-ridge and 50%WR (I3P2). Finally, photosynthesis rate (An) reduction with diminishing LWP was mild, providing insights into quinoa’s adaptability to drought. In conclusion, considering the thorough evaluation of all the measured parameters, the study suggests using the in-furrow planting method with a 75%WR as the best approach for growing quinoa in arid and semi-arid regions to enhance production and resource efficiency.