Water Gas Exchange Research Articles

Enhancing salinity tolerance in cultivated rice through introgression of African rice genes and application of moringa leaf extract

BackgroundSalinity is a major threat to rice growth and productivity. Utilizing wild rice-derived genes and biostimulants with high growth promoting- and stress-alleviating potential can significantly improve salinity tolerance in cultivated rice. Herein, we investigated the vegetative growth and physiological responses of Giza 177 (Oryza sativa, salinity sensitive, high-yielding cultivar) and a promising introgression salt tolerant line (sativa/glaberrima; SG 65) from a population of Giza 177 × African rice (Oryza glaberrima) under low (2.75 mS/cm) and high (5.5 mS/cm) salinity stress. The possible ameliorative effects of priming rice seeds in moringa leaf extract (MLE) on these responses were also tested.ResultsThe two salinity levels induced differential reduction in plant growth in both cultivars. In the MLE-unprimed plants, salinity induced 34–54% and 30–45% reductions in biomass accumulation in Giza 177 and SG 65, respectively. These responses were associated with significant differential reductions in relative water content, chlorophylls, carotenoids, and gas exchange parameters (transpiration rate, net photosynthetic rate, stomatal conductance, and intercellular CO2 concentration), ascorbic acid, and total protein. Conversely, salinity induced the accumulation of H2O2, malondialdehyde, proline, carbohydrate fractions, and membrane injury. MLE treatment mitigated the above salinity-induced adverse effects in both cultivars via reducing the salt-induced oxidative stress through the induction of non-enzymic (total phenols, and flavonoids) and enzymic antioxidants including ascorbate peroxidase, catalase, peroxidase, and polyphenol oxidase in both cultivars. SG 65 plants exhibited consistently higher salt tolerance and responsiveness to MLE than Giza 177.ConclusionsThis study reports significant differences in an array of critical physiological and biochemical indices that underpin the divergent responses between the two salinized cultivars. It demonstrates the potential of African rice-derived genomic fragments and MLE priming in mitigating salinity stress, highlighting their use as a sustainable strategy for increasing rice production in salt-affected soils.

Evaluation of seed dormancy-breaking techniques for enhancing germination potential, seedling growth, and vigour of Carissa carandas L.

Carissa carandas L. is a versatile evergreen shrub of the Apocynaceae family and its fruit is rich in vitamins and antioxidants. It is commonly propagated by seeds, which are characterized by low germination rates due to the presence of a hard seed coat that causes physical dormancy and limits water absorption and gas exchange. In this study, the effects of different dormancy-breaking treatments viz., chemical treatment with potassium nitrate and thiourea at two concentrations (1% and 2%), hormonal therapy with gibberellic acid (GA3) at two concentrations (500 and 1000 ppm) and physical treatments (hot water and simple water immersion) were investigated on germination and seedling growth using a Randomized Block Design (RBD) with three replications and the statistical significance of each treatment was tested at the five percent probability level (p ? 0.05). Key germination indices, seedling growth parameters, and seedling vigour were observed. Among all treatments, 2% KNO3 was most effective in breaking seed dormancy that achieved significantly higher (86.33%) germination with accelerated completion of germination in 18 days and the highest (4.80) mean daily germination (MDG). Thiourea 2% attained a germination percentage of 82.91% and MDG of 4.36 while GA3 treated seeds had a lower germination percentage and MDG than KNO3 and thiourea treatments. The significantly highest seedling length vigour index (LVI) of 1085.1 and weight vigour index (WVI) of 12.67 were also obtained in 2% KNO3 treated seeds which was followed by 2% thiourea with LVI of 1003.6 and WVI 10.12 . Both LVI and WVI were significantly lower in GA3 treatments compared to KNO3 and thiourea treatments. The significantly lowest germination percentage (61.19%), MDG (2.78), LVI (575.8), and WVI (3.67) were recorded in the control. This study offers valuable insights into the efficient techniques for seed dormancy breaking and optimizing seed propagation techniques for C. carandas L.

Mitigating Drought by Exogenous Potassium-mediated Improvements in Water Relation, Antioxidant Defense, Morpho-physiological and Biochemical Attributes of Black Gram [Vigna mungo (L.) Hepper

Background: Globally, drought stress (DS) incidence in early development and grain-filling stages of crops like black gram has posed a serious constraint to the growth and yield of legume crops. To ensure the food and nutritional security of the rising human population, requisites developing eco-friendly, pro-farmers and cost-effective DS mitigation strategies for imparting yield sustainability to black gram. Methods: In this trial, treatments included control group entailing control (normal watering), water spray (WA, positive control), control+50 mg L-1 K2SO4, control +100 mg L-1 K2SO4, control +150 mg L-1 K2SO4, while drought treatment included drought stress (plant exposed to 15-20% by suspending water supply), water spray (WA, positive control), drought +50 mg L-1 K2SO4, drought +100 mg L-1 K2SO4 and drought +150 mg L-1 K2SO4. Result: The results exhibited that the DS seriously declined plant growth, relative water content and water potential by 24.2% and 39.3%, respectively, inducing higher levels of malondialdehyde (MDA) content and hydrogen peroxide (H2O2) concentration that reduced cell membrane stability, stomatal conductance and photosynthetic rate, than the control. However, the foliar applied K significantly improved plant growth, plant water status, gas exchange and photosynthetic performance, chlorophyll content and antioxidant enzyme activity. Exogenous application of K further reduced lipid peroxidation, cell membrane injury and hydrogen peroxide by 12.7, 17.6 and 8.70%, respectively.

Dual regulation of stomatal development by brassinosteroid in Arabidopsis hypocotyls.

Stomata are epidermal pores that are essential for water evaporation and gas exchange in plants. Stomatal development is orchestrated by intrinsic developmental programs, hormonal controls, and environmental cues. The steroid hormone brassinosteroid (BR) inhibits stomatal lineage progression by regulating BIN2 and BSL proteins in leaves. Notably, BR is known to promote stomatal development in hypocotyls as opposed to leaves; however, its molecular mechanism remains elusive. Here, we show that BR signaling has a dual regulatory role in controlling stomatal development in Arabidopsis hypocotyls. We found that brassinolide (BL; the most active BR) regulates stomatal development differently in a concentration-dependent manner. At low and moderate concentrations, BL promoted stomatal formation by upregulating the expression of SPEECHLESS (SPCH) and its target genes independently of BIN2 regulation. In contrast, high concentrations of BL and bikinin, which is a specific inhibitor of BIN2 and its homologs, significantly reduced stomatal formation. Genetic analyses revealed that BIN2 regulates stomatal development in hypocotyls through molecular mechanisms distinct from the regulatory mechanism of the cotyledons. In hypocotyls, BIN2 promoted stomatal development by inactivating BZR1, which suppresses the expression of SPCH and its target genes. Taken together, our results suggest that BR precisely coordinates the stomatal development of hypocotyls using an antagonistic control of SPCH expression via BZR1-dependent and BZR1-independent transcriptional regulation.

Gas exchange velocities (k600), gas exchange rates (K600), and hydraulic geometries for streams and rivers derived from the NEON Reaeration field and lab collection data product (DP1.20190.001)

Abstract. Air–water gas exchange is essential to understanding and quantifying many biogeochemical processes in streams and rivers, including greenhouse gas emissions and metabolism. Gas exchange depends on two factors, which are often quantified separately: (1) the air–water concentration gradient of the gas and (2) the gas exchange velocity. There are fewer measurements of gas exchange velocity compared to concentrations in streams and rivers, which limits accurate characterization of air–water gas exchange (i.e., flux rates). The National Ecological Observatory Network (NEON) conducts SF6 gas-loss experiments in 22 of their 24 wadeable streams using standardized methods across all experiments and sites, and publishes raw concentration data from these experiments on the NEON data portal. NEON also conducts NaCl injections that can be used to characterize hydraulic geometry at all 24 wadeable streams. These NaCl injections are conducted both as part of the gas-loss experiments and separately. Here, we use these data to estimate gas exchange and water velocity using the reaRate R package. The dataset presented includes estimates of hydraulic parameters, cleaned raw concentration SF6 tracer-gas data (including removing outliers and failed experiments), estimated SF6 gas-loss rates, normalized gas exchange velocities (k600; m d−1) and normalized depth-dependent gas exchange rates (K600; d−1). This dataset provides one of the largest compilations of gas-loss experiments (n=339) in streams to date. This dataset is unique in that it contains gas exchange estimates from repeated experiments in geographically diverse streams across a range of discharges. In addition, this dataset contains information on the hydraulic geometry of all 24 NEON wadeable streams, which will support future research using NEON aquatic data. This dataset is a valuable resource that can be used to explore both within- and across-reach variability in the hydraulic geometry and gas exchange velocity in streams. The data are available at https://doi.org/10.6073/pasta/18dcc1871ee71cf0b69f2ee4082839d0 (Aho et al., 2024), and the reaRate R package code is available at https://doi.org/10.5281/zenodo.12786089 (Cawley et al., 2024).

A Crop Water Stress Index for Hazelnuts Using Low-Cost Infrared Thermometers.

Incorporating data-driven technologies into agriculture presents a promising approach to optimizing crop production, especially in regions dependent on irrigation, where escalating heat waves and droughts driven by climate change pose increasing challenges. Recent advancements in sensor technology have introduced diverse methods for assessing irrigation needs, including meteorological sensors for calculating reference evapotranspiration, belowground sensors for measuring plant available water, and plant sensors for direct water status measurements. Among these, infrared thermometry stands out as a non-destructive remote sensing method for monitoring transpiration, with significant potential for integration into drone- or satellite-based models. This study applies infrared thermometry to develop a crop water stress index (CWSI) model for European hazelnuts (Corylus avellana), a key crop in Oregon, the leading hazelnut-producing state in the United States. Utilizing low-cost, open-source infrared thermometers and data loggers, we aim to provide hazelnut farmers with a practical tool for improving irrigation efficiency and enhancing yields. The CWSI model was validated against plant water status metrics such as stem water potential and gas exchange measurements. Our results show that when stem water potential is below -6 bar, the CWSI remains under 0.2, indicating low plant stress, with corresponding leaf conductance rates ranging between 0.1 and 0.4 mol m2 s-1. Additionally, un-irrigated hazelnuts were stressed (CWSI > 0.2) from mid-July through the end of the season, while irrigated plants remained unstressed. The findings suggest that farmers can adopt a leaf conductance threshold of 0.2 mol m2 s-1 or a water potential threshold of -6 bar for irrigation management. This research introduces a new CWSI model for hazelnuts and highlights the potential of low-cost technology to improve agricultural monitoring and decision-making.

Differential eco-physiological performance of eight Eucalyptus species grown in Tunisian’s arid regions

Successful production of Eucalyptus in drylands requires a thorough understanding of the mechanisms involved in their tolerance to abiotic stress as well as drought. The present study aimed to investigate the effects of dry conditions on morpho-physiological characteristics of eight 5-year-old Eucalyptus species trees, Eucalyptus camaldulensis Dehn., Eucalyptus gomphocephala DC., Eucalyptus torquata Luehm., Eucalyptus microtheca F.Muell., Eucalyptus occidentalis Endl., Eucalyptus diversifolia Bonpl., Eucalyptus sargentii Maiden., and Eucalyptus torwood (Spontaneous hybrid), grew in the same arid microhabitat (a plot) characterized by poor soil. The experiments were conducted in summer 2022, a year that was characterized by a low rainfall rate. Thus, at regular intervals, several parameters were assessed. Plant water status, leaf water relations, gas exchanges, and chlorophyll fluorescence in relation to trees growth performance and leaf traits. Results revealed a distinct resistance level to aridity for the studied species, trees were able to grow showing a clear inter-specific variability. Regarding all species, E. camaldulensis, exhibited a particular behavior to preserve their internal functionality. It displayed simultaneously a rapid growth performance with an ability to develop thinner leaves and earlier stomatal closure under water deficit. Although, E. microtheca, E. gomphocephala, and E. diversifolia’ growth were low, but trees attempted to maintain a stable inter-dependence functions for survival. For E. occidentalis, E. torquata, E. sargentii, and E. torwood, we suggest that a physiological acclimation took place under severe conditions, they showed convergence responses for many parameters. Their ability to maintain good leaves’ succulence and thickness is clearly attributed to a significant RWC (71.5% to 82.4%) related to important LTD, LDMC, and SLW, enabling trees to have important stomata conductance and maintain respectful growth performance. Overall, this comparative study of multiple Eucalyptus species revealed significant variability in their functional and adaptive responses to water deficiency and dry weather conditions, which aids in selecting species that are more appropriate to arid natural environments.

Water Relations and Physiological Traits Associated with the Yield Components of Winter Wheat (Triticum aestivum L.)

Water stress in agricultural systems may occur slowly or abruptly. Plant reactions to stress differ with regard to its level and duration. The level of plant susceptibility to water deprivation primarily depends on the management of the water content and metabolism adjustments. The aim of this study was to determine the correlation between water-based plant parameters and the yield components of 90 genotypes of winter wheat (Triticum aestivum L.). Since the loss of water is frequently used as a selection criterion to assess drought tolerance, the relationships between the yield and leaf water content, osmotic potential, and gas exchange characteristics were examined. Genotypes 1, 25, 34, 36, 42, 43, 46, 57, 66, 73, and 90 showed 33–45% larger numbers of grains/plant, 19–25% higher weights of grains/plant, and 4% higher thousand grain weights compared to other genotypes. The higher values of the yield components were accompanied by 20–30% lower leaf water content, 39–52% lower osmotic potential, and 4–39% lower water use efficiency. The principal component analysis revealed that the wheat genotypes had noticeable differences in a few physiological parameters that depended on the sowing date. Electrolyte leakage showed a substantial correlation with the sowing date, suggesting that it may not be a suitable factor for the prediction of drought tolerance. The factors that distinguished the examined genotypes the most were the leaf water content, osmotic potential, and water use efficiency. In addition, a significant correlation was observed between the mentioned parameters and yield components. As a result, these parameters may be helpful in genotype characterization in relation to water stress susceptibility, offering a trustworthy plant selection test.

Exploring the Interplay of Bud Load and Pruning Type in Shaping ‘Xinomavro’ (Vitis vinifera L.) Vine Growth, Yield, and Berry Composition

‘Xinomavro’ (V. vinifera L.) is an important native red wine grape variety in Northern Greece, particularly in PDO (protected designation of origin) regions. Despite its significance, there is limited research on the effects of pruning type and severity on ‘Xinomavro’ vine physiology, yield, and berry quality across diverse environmental conditions. This study aimed to address this knowledge gap and provide growers with crucial information for optimizing vineyard management practices. The study was conducted over two consecutive years (2016 and 2017) in a vineyard in Thessaloniki, Northern Greece. Four treatments (B12: 12 buds on 6 spurs, B24: 24 buds on 12 spurs, M12: 12 buds on 2 canes, and M24: 24 buds on 4 canes) combining two bud load levels (12 or 24 count nodes) and two pruning types (short spurs or long canes) were applied to ‘Xinomavro’ vines in a complete block randomized design. The vine water status, gas exchange, canopy characteristics, yield components, and berry composition were measured. Bud load and pruning type significantly influenced vine canopy development, microclimate, and yield components. Short pruning with high bud load (B24) resulted in denser canopies and higher yields, whereas cane pruning (M12 and M24) led to more open canopies and improved berry quality indicators. Treatment effects on berry composition were inconsistent across years but showed a tendency for higher anthocyanin and total phenol content in cane-pruned vines. This study demonstrates that pruning type (short or long fruiting units) may have a greater impact on vine growth, yield, and berry composition than bud load alone in ‘Xinomavro’ vines. Cane pruning appears to be a more effective strategy for achieving vine balance and potentially improving grape quality under given experimental conditions.

Drought tolerance and recovery capacity of two ornamental shrubs: Combining physiological and biochemical analyses with online leaf water status monitoring for the application in urban settings

When plants are transferred from nursery to urban environments, they often face drought stress due to inadequate maintenance, such as insufficient irrigation. Using drought tolerant species may help mitigate the adverse impact of drought stress in urban settings. Additionally, utilizing novel technologies for water status monitoring may help optimize irrigation schedules to prevent transplanting failures. This study investigated the physiological and biochemical responses of two ornamental shrubs, Photinia x fraseri and Viburnum tinus, subjected to water stress of increasing severity and rewatering. Water relations, gas exchanges, chlorophyll fluorescence and biochemical analyses were conducted alongside real-time monitoring of water status using leaf-water-meter sensors (LWM).The progression of water stress had a notable negative impact on leaf gas exchanges and water relations in both species. Notably, P. fraseri avoided photoinhibition by reducing chlorophyll content and actual efficiency of PSII. Adjustments in leaf phenolic compounds played a significant role in enhancing drought tolerance of both species due to their antioxidant and photoprotective properties.Upon rewatering, both species exhibited complete recovery in their physiological functions, underscoring their remarkable tolerance and resilience to drought stress. Additionally, LWM sensors efficiently tracked the dehydration levels, exhibiting a rising trend during the water stress progression and a subsequent decline after rewatering for both species. These findings confirm the reliability of LWM sensors in monitoring physiological status of plants in outdoor contexts, making them a suitable tool for use in urban settings.

Rewatering after drought: Unravelling the drought thresholds and function recovery-limiting factors in maize leaves.

Drought and subsequent rewatering are common in agriculture, where recovery from mild droughts is easier than from severe ones. The specific drought threshold and factors limiting recovery are under-researched. This study subjected maize plants to varying drought degrees before rewatering, and measuring plant water status, gas exchange, hydraulic conductance, hormone levels, and cellular damage throughout. We discovered that stomatal reopening in plants was inhibited with leaf water potentials below about -1.7 MPa, hindering postdrought photosynthetic recovery. Neither hydraulic loss nor abscisic acid (ABA) content was the factor inhibited stomatal reopening on the second day following moderate drought stress and rewatering. But stomatal reopening was significantly correlated to the interaction between hydraulic signals and ABA content under severe drought. Extended drought led to leaf death at about -2.8 MPa or 57% relative water content, influenced by reduced rehydration capacity, not hydraulic failure. The lethal threshold remained relatively constant across leaf stages, but the recoverable safety margin (RSM), that is, the water potential difference between stomatal closure and recovery capacity loss, significantly decreased with leaf aging due to delayed stomatal closure during drought. Our findings indicate hydraulic failure alone does not cause maize leaf death, highlighting the importance of RSM in future research.

High heat tolerance, evaporative cooling, and stomatal decoupling regulate canopy temperature and their safety margins in three European oak species.

Heatwaves and soil droughts are increasing in frequency and intensity, leading many tree species to exceed their thermal thresholds, and driving wide-scale forest mortality. Therefore, investigating heat tolerance and canopy temperature regulation mechanisms is essential to understanding and predicting tree vulnerability to hot droughts. We measured the diurnal and seasonal variation in leaf water potential (Ψ), gas exchange (photosynthesis Anet and stomatal conductance gs), canopy temperature (Tcan), and heat tolerance (leaf critical temperature Tcrit and thermal safety margins TSM, i.e., the difference between maximum Tcan and Tcrit) in three oak species in forests along a latitudinal gradient (Quercus petraea in Switzerland, Quercus ilex in France, and Quercus coccifera in Spain) throughout the growing season. Gas exchange and Ψ of all species were strongly reduced by increased air temperature (Tair) and soil drying, resulting in stomatal closure and inhibition of photosynthesis in Q. ilex and Q. coccifera when Tair surpassed 30°C and soil moisture dropped below 14%. Across all seasons, Tcan was mainly above Tair but increased strongly (up to 10°C > Tair) when Anet was null or negative. Although trees endured extreme Tair (up to 42°C), positive TSM were maintained during the growing season due to high Tcrit in all species (average Tcrit of 54.7°C) and possibly stomatal decoupling (i.e., Anet ≤0 while gs >0). Indeed, Q. ilex and Q. coccifera trees maintained low but positive gs (despite null Anet), decreasing Ψ passed embolism thresholds. This may have prevented Tcan from rising above Tcrit during extreme heat. Overall, our work highlighted that the mechanisms behind heat tolerance and leaf temperature regulation in oak trees include a combination of high evaporative cooling, large heat tolerance limits, and stomatal decoupling. These processes must be considered to accurately predict plant damages, survival, and mortality during extreme heatwaves.

Leaves and roots metabolomic signatures underlying rootstock-mediated water stress tolerance in grafted pepper plants

Grafting onto pepper rootstock NIBER® is an effective strategy to mitigate water stress effects on the grafted variety. In this work, we comparatively explored the metabolomic responses to water stress in the pepper variety “Maestral F1” (V) grafted onto NIBER® (V/N) and self-grafted (V/V) by untargeted metabolomics on leaves and roots. Leaf water status was also evaluated by relative water content (RWC) and gas exchange measurements. Under water stress, the V/N water use efficiency (WUE) and leaf RWC were higher than V/V, in agreement with major stomata closure and water retention in leaves. V/N showed a tolerance response, which was manifested in the untargeted metabolomic analysis. NIBER® modulated the grafted variety response to water stress as reflected in the differential metabolomic profiles in leaves and roots. The V/N-enriched metabolic pathways showed that the NIBER® response to water stress involved cutin and suberin biosynthesis, which act as protection layers, and jasmonic acid (JA) and jasmonates biosynthesis to favor signaling pathways. NIBER® did not induce flavonols and chlorophyll b synthesis, but likely promoted anthocyanins biosynthesis and maintained an undisturbed chlorophyll a:chlorophyll b ratio. Moreover, NIBER® increased vitamin B6, anthocyanins and stearic acid concentration in the variety leaves, whereas siroheme content rose in roots to improve nitrogen assimilation. Further studies are required to understand the contribution of secondary metabolites, such as phenylpropanoids, glycoalkaloids, and nitrogen-containing secondary metabolites, to NIBER® water stress tolerance.

Salicylic acid improves cowpea productivity under water restriction in the field by modulating metabolism.

Salicylic acid has shown promise in alleviating water stress in cultivated plants. However, there is a lack of studies confirming its effectiveness in cowpea plants grown in field conditions. Therefore, this research aimed to evaluate the use of salicylic acid as a water stress mitigator in cowpea cultivars under different irrigation depths in field conditions. Four cowpea cultivars (BRS Novaera, BRS Tapaihum, BRS Pujante, and BRS Pajeú) were subjected to different treatments: control (W100: 100% replacement of crop evapotranspiration - ETc), W50 (50% of ETc), W50+SA2 (50% of ETc + 276 mg L-1 of SA), and W50+SA4 (50% of ETc + 552 mg L-1 of SA). The treatments were combined in a 4×4 factorial scheme with three replications, arranged in a randomized block design. Water restriction had a negative impact on the water status, growth, gas exchange, and production of the cultivars while also leading to changes in the antioxidant metabolism and osmolyte concentration. The application of SA enhanced antioxidant activity and the synthesis of osmotic adjusters under stress conditions. The most effective concentration was 276 mg L-1 in stage R2 and 552 mg L-1 in stage V7, respectively. The BRS Pujante cultivar showed increased productivity under water restriction with SA application, while the BRS Tapaihum was the most tolerant among the cultivars studied. In summary, our findings underscore the importance of using SA to mitigate the effects of water restriction on cowpea cultivation. These discoveries are crucial for the sustainability of cowpea production in regions susceptible to drought, which can contribute to food security. We further add that the adoption of new agricultural practices can enhance the resilience and productivity of cowpea as an essential and sustainable food source for vulnerable populations in various parts of the world.

Characteristics, Relationships, and Anatomical Basis of Leaf Hydraulic Traits and Economic Traits in Temperate Desert Shrub Species.

Shrubs are a key component of desert ecosystems, playing a crucial role in controlling desertification and promoting revegetation, yet their growth is often impeded by drought. Leaf hydraulic traits and economic traits are both involved in the process of water exchange for carbon dioxide. Exploring the characteristics, relationships, and anatomical basis of these two suites of traits is crucial to understanding the mechanism of desert shrubs adapting to the desert arid environment. However, the relationship between these two sets of traits currently remains ambiguous. This study explored the leaf hydraulic, economic, and anatomical traits of 19 desert shrub species. The key findings include the following: Relatively larger LT values and smaller SLA values were observed in desert shrubs, aligning with the "slow strategy" in the leaf economics spectrum. The relatively high P50leaf, low HSMleaf, negative TLPleaf, and positive HSMtlp values indicated that severe embolism occurs in the leaves during the dry season, while most species were able to maintain normal leaf expansion. This implies a "tolerance" leaf hydraulic strategy in response to arid stress. No significant relationship was observed between P50leaf and Kmax, indicating the absence of a trade-off between hydraulic efficiency and embolism resistance. Certain coupling relationships were observed between leaf hydraulic traits and economic traits, both of which were closely tied to anatomical structures. Out of all of the leaf traits, LT was the central trait of the leaf traits network. The positive correlation between C content and WPleaf and HSMleaf, as well as the positive correlation between N content and HSMtlp, suggested that the cost of leaf construction was synergistic with hydraulic safety. The negative correlation between SLA, P content, GCL, and SAI suggested a functional synergistic relationship between water use efficiency and gas exchange rate. In summary, this research revealed that the coupling relationship between leaf hydraulic traits and economic traits was one of the important physiological and ecological mechanisms of desert shrubs for adapting to desert habitats.

Mineral accumulation, relative water content and gas exchange are the main physiological regulating mechanisms to cope with salt stress in barley

Salinity has become a major environmental concern for agricultural lands, leading to decreased crop yields. Hence, plant biology experts aim to genetically improve barley’s adaptation to salinity stress by deeply studying the effects of salt stress and the responses of barley to this stress. In this context, our study aims to explore the variation in physiological and biochemical responses of five Tunisian spring barley genotypes to salt stress during the heading phase. Two salinity treatments were induced by using 100 mM NaCl (T1) and 250 mM NaCl (T2) in the irrigation water. Significant phenotypic variations were detected among the genotypes in response to salt stress. Plants exposed to 250 mM of NaCl showed an important decline in all studied physiological parameters namely, gas exchange, ions concentration and relative water content RWC. The observed decreases in concentrations ranged from, approximately, 6.64% to 40.76% for K+, 5.91% to 43.67% for Na+, 14.12% to 52.38% for Ca2+, and 15.22% to 38.48% for Mg2+ across the different genotypes and salt stress levels. However, under salinity conditions, proline and soluble sugars increased for all genotypes with an average increase of 1.6 times in proline concentrations and 1.4 times in soluble sugars concentration. Furthermore, MDA levels rose also for all genotypes, with the biggest rise in Lemsi genotype (114.27% of increase compared to control). Ardhaoui and Rihane showed higher photosynthetic activity compared to the other genotypes across all treatments. The stepwise regression approach identified potassium content, K+/Na+ ratio, relative water content, stomatal conductance and SPAD measurement as predominant traits for thousand kernel weight (R2 = 84.06), suggesting their significant role in alleviating salt stress in barley. Overall, at heading stage, salt accumulation in irrigated soils with saline water significantly influences the growth of barley by influencing gas exchange parameters, mineral composition and water content, in a genotype-dependent manner. These results will serve on elucidating the genetic mechanisms underlying these variations to facilitate targeted improvements in barley's tolerance to salt stress.

Sweet Cherry Plants Prioritize Their Response to Cope with Summer Drought, Overshadowing the Defense Response to Pseudomonas syringae pv. syringae.

Disease severity and drought due to climate change present significant challenges to orchard productivity. This study examines the effects of spring inoculation with Pseudomonas syringae pv. syringae (Pss) on sweet cherry plants, cvs. Bing and Santina with varying defense responses, assessing plant growth, physiological variables (water potential, gas exchange, and plant hydraulic conductance), and the levels of abscisic acid (ABA) and salicylic acid (SA) under two summer irrigation levels. Pss inoculation elicited a more pronounced response in 'Santina' compared to 'Bing' at 14 days post-inoculation (dpi), and those plants inoculated with Pss exhibited a slower leaf growth and reduced transpiration compared to control plants during 60 dpi. During differential irrigations, leaf area was reduced 14% and 44% in Pss inoculated plants of 'Bing' and 'Santina' respectively, under well-watered (WW) conditions, without changes in plant water status or gas exchange. Conversely, water-deficit (WD) conditions led to gas exchange limitations and a 43% decrease in plant biomass compared to that under WW conditions, with no differences between inoculation treatments. ABA levels were lower under WW than under WD at 90 dpi, while SA levels were significantly higher in Pss-inoculated plants under WW conditions. These findings underscore the influence on plant growth during summer in sweet cherry cultivars that showed a differential response to Pss inoculations and how the relationship between ABA and SA changes in plant drought level responses.

Climate forcing controls on carbon terrestrial fluxes during shale weathering

Climate influences near-surface biogeochemical processes and thereby determines the partitioning of carbon dioxide (CO2) in shale, and yet the controls on carbon (C) weathering fluxes remain poorly constrained. Using a dataset that characterizes biogeochemical responses to climate forcing in shale regolith, we implement a numerical model that describes the effects of water infiltration events, gas exchange, and temperature fluctuations on soil respiration and mineral weathering at a seasonal timescale. Our modeling approach allows us to quantitatively disentangle the controls of transient climate forcing and biogeochemical mechanisms on C partitioning. We find that ~3% of soil CO2 (1.02 mol C/m2/y) is exported to the subsurface during large infiltration events. Here, net atmospheric CO2 drawdown primarily occurs during spring snowmelt, governs the aqueous C exports (61%), and exceeds the CO2 flux generated by pyrite and petrogenic organic matter oxidation (~0.2 mol C/m2/y). We show that shale CO2 consumption results from the temporal coupling between soil microbial respiration and carbonate weathering. This coupling is driven by the impacts of hydrologic fluctuations on fresh organic matter availability and CO2 transport to the weathering front. Diffusion-limited transport of gases under transient hydrological conditions exerts an important control on CO2(g) egress patterns and thus must be considered when inferring soil CO2 drawdown from the gas phase composition. Our findings emphasize the importance of seasonal climate forcing in shaping the net contribution of shale weathering to terrestrial C fluxes and suggest that warmer conditions could reduce the potential for shale weathering to act as a CO2 sink.

Identifying Bioactive Compounds in Common Bean (Phaseolus vulgaris L.) Plants under Water Deficit Conditions

Deficit irrigation (DI) strategies are becoming increasingly common in areas where water resources are limited. The application of moderate levels of DI can result in water savings with a small reduction in yield but with a higher quality of the product. The aim of this work was to evaluate the effect of applying a certain level of water deficit (40% water holding capacity) on the yield and quality of the common bean (Phaseolus vulgaris L.), specifically the cultivar ‘Triunfo-70’. Bioactive compounds were investigated by applying an LC-MS-based untargeted metabolomics approach as an analytical tool for identifying novel markers associated with a water deficit in beans. The results showed that beans harvested 30 days after DI application experienced water stress, as indicated by the decrease in the leaf water potential and gas exchange values (stomatal conductance and photosynthesis). In addition, the number of pods per plant was significantly reduced by the DI treatment. The water deficit induced significant alterations in various bioactive compounds (including organic acids, polyphenols, hydroxybenzoic acids, lipids, and phospholipids) when compared to the control treatment. Additionally, twelve new biomarkers were identified in this study for the first time in the common bean under DI. These findings suggested that DI acted as an elicitor, increasing phenylpropanoid metabolism, while concurrently reducing the production of compounds associated with fatty acid metabolism. Additionally, new metabolites were tentatively identified in common beans. This study represents the successful application of the untargeted metabolomics approach to finding bioactive secondary metabolites in beans under different irrigation conditions.

Amphibians Exhibit Extremely High Hydric Costs of Respiration.

Terrestrial environments pose many challenges to organisms, but perhaps one of the greatest is the need to breathe while maintaining water balance. Breathing air requires thin, moist respiratory surfaces, and thus the conditions necessary for gas exchange are also responsible for high rates of water loss that lead to desiccation. Across the diversity of terrestrial life, water loss acts as a universal cost of gas exchange and thus imposes limits on respiration. Amphibians are known for being vulnerable to rapid desiccation, in part because they rely on thin, permeable skin for cutaneous respiration. Yet, we have a limited understanding of the relationship between water loss and gas exchange within and among amphibian species. In this study, we evaluated the hydric costs of respiration in amphibians using the transpiration ratio, which is defined as the ratio of water loss (mol H2O d-1) to gas uptake (mol O2 d-1). A high ratio suggests greater hydric costs relative to the amount of gas uptake. We compared the transpiration ratio of amphibians with that of other terrestrial organisms to determine whether amphibians had greater hydric costs of gas uptake relative to plants, insects, birds, and mammals. We also evaluated the effects of temperature, humidity, and body mass on the transpiration ratio both within and among amphibian species. We found that hydric costs of respiration in amphibians were two to four orders of magnitude higher than the hydric costs of plants, insects, birds, and mammals. We also discovered that larger amphibians had lower hydric costs than smaller amphibians, at both the species- and individual-level. Amphibians also reduced the hydric costs of respiration at warm temperatures, potentially reflecting adaptive strategies to avoid dehydration while also meeting the demands of higher metabolic rates. Our results suggest that cutaneous respiration is an inefficient mode of respiration that produces the highest hydric costs of respiration yet to be measured in terrestrial plants and animals. Yet, amphibians largely avoid these costs by selecting aquatic or moist environments, which may facilitate more independent evolution of water loss and gas exchange.