Stomatal Conductance Research Articles

Evaluating Salinity Tolerance of Pomegranate Cultivars Using Subordinate Function Analysis and Machine Learning

ABSTRACT The application of machine learning in salinity tolerance evaluation studies is limited. To address this gap, a pot culture experiment was conducted with six pomegranate cultivars at Punjab Agricultural University Ludhiana, India, in 2020 and 2021. The data were subjected to subordinated function analysis (SFA), random forest regression (RFR), support vector regression (SVR) and general linear modeling (GLM) after 60 and 120 days of first saline water treatment. The SFA identified ‘Bhagwa’ as the most salt tolerant cultivar, followed by ‘Wonderful.’ The RFR highlighted leaf K, catalase activity, and relative growth rate (RGR) as key parameters influencing salinity tolerance of the tested cultivars after 60 days. The SVR demonstrated root S content and net assimilation rate as critical factors. After 120 days, both RFR and SVR identified stomatal conductance and relative growth rate as crucial markers displaying salinity tolerance of cultivars. Both RFR and SVR showed high predictive accuracy, especially after 120 days, compared to GLM. However, GLM provided a broader set of variables for a better understanding of the underlying mechanism across different time intervals. Therefore, this research emphasizes the importance of using both machine learning techniques and traditional statistical approaches to gain a deeper understanding of the subject.

Cuticular analysis of Late Pleistocene, Middle Holocene, and modern Nothofagus dombeyi leaves from Chile: Implications for understanding changes in plant function at different atmospheric CO2 concentrations

How will forests respond to increases in atmospheric CO2 concentrations over the next century? This question is the subject of intensive research, and is based mostly on the results of greenhouse experiments, landscape-level experiments and modeling. In this paper, we examined leaf morphological and physiological characteristics of Nothofagus dombeyi populations exposed to different atmospheric CO2 levels by analyzing leaf cuticle from a Late Pleistocene (∼15,500–13,200 cal yr BP) fossil site, a Middle Holocene (∼6700–4900 cal yr BP) fossil site, and a modern (2016) collection in mid-latitude Chile. Atmospheric CO2 concentrations were inferred as ∼230 ppm, ∼270 ppm and ∼ 400 ppm based on a comparison with icecore and instrumental records. Our findings show that as atmospheric CO2 concentrations increased by 74% during the transition from late glacial to modern conditions, stomatal density decreased by 24% and maximum stomatal conductance decreased by 42%. In contrast, we observed a 10% increase in stomatal size, a 195% increase in intrinsic water use efficiency, and an increase in leaf nitrogen content. Carbon discrimination decreased as CO2 levels increased contrary to our expectations underscoring that additional factors such as water availability and nutrients can affect carbon discrimination. We also tested the paleo-CO2 method of Franks that performed well under high CO2 conditions (∼400 ppm) but failed under low levels (∼230 ppm) of atmospheric CO2 indicating the need for a better understanding of photosynthesis during glacial times.

Coping with extremes: Responses of Quercus robur L. and Fagus sylvatica L. to soil drought and elevated vapour pressure deficit

Climate change, particularly droughts and heat waves, significantly impacts global photosynthesis and forest ecosystem sustainability. To understand how trees respond to and recover from hydrological stress, we investigated the combined effects of soil moisture and atmospheric vapour pressure deficit (VPD) on seedlings of the two major European broadleaved tree species Fagus sylvatica (FS) and Quercus robur (QR). The experiment was conducted under natural forest gap conditions, while soil water availability was strictly manipulated. We monitored gas exchange (net photosynthesis, stomatal conductance and transpiration rates), nonstructural carbohydrates (NSC) concentration in roots and stomatal morphometry (size and density) during a drought period and recovery. Our comparative empirical study allowed us to distinguish and quantify the effects of soil drought and VPD on stomatal behavior, going beyond theoretical models. We found that QR conserved water more conservatively than FS by reducing transpiration and regulating stomatal conductance under drought. FS maintained higher stomatal conductance and transpiration at elevated VPD until soil moisture became critically low. QR showed higher intrinsic water use efficiency than FS. Stomata density and size also likely played a role in photosynthetic rate and speed of recovery, especially since QR with its seasonal adjustments in stomatal traits (smaller, more numerous stomata in summer leaves) responded and recovered faster compared to FS. Our focal species showed different responses in NSC content under drought stress and recovery, suggesting possible different evolutionary pathways in coping with stress. QR mobilized soluble sugars, while FS relied on starch mobilization to resist drought. Although our focal species often co-occur in mixed forests, our study showed that they have evolved different physiological, morphological and biochemical strategies to cope with drought stress. This suggests that ongoing climate change may alter their competitive ability and adaptive potential in favor of one of the species studied.

Foliar application of phosphoric acid mitigates oxidative stress induced by herbicides in soybean, maize, and cotton crops

Foliar fertilization presents a potential solution in alleviating oxidative stress triggered by herbicide exposure. Enhancing our comprehension of the interplay between foliar fertilization, oxidative stress, and herbicide application is pivotal for enhancing crop yield. Carfentrazone, a herbicide, prompts the buildup of reactive oxygen species, leading to detrimental effects on cell membranes and the manifestation of chlorotic spots on leaves. This research administered carfentrazone-ethyl to soybean, maize, and cotton to induce stress. The herbicide application was followed by foliar application of phosphorus (H3PO4) to evaluate its effect on phytotoxicity recovery. The evaluations included leaf nutritional analyses, gas exchange measurements (photosynthesis, stomatal conductance, substomatal CO2 concentration, and Leaf transpiration), photosynthetic pigments (chlorophylls and carotenoids), oxidative stress indicators (MDA, H2O2, SOD, CAT and APX), and productivity parameters (height, number of branches, pods, grains, 100-grain weight, and yield), in addition to the activity of the enzyme Rubisco (ribulose-1,5-bisphosphate carboxylase/oxygenase), which is crucial for carbon fixation and the photosynthetic efficiency of plants. Phosphorus (P) improved chlorophyll levels by up to 28.8% and Rubisco activity by up to 24.8%, leading to increases in the net photosynthetic rate by up to 40.2%, stomatal conductance, water use efficiency, and carboxylation. In addition, foliar P fertilization enhanced antioxidant metabolism, with reductions in markers of oxidative stress (H2O2 and MDA) by up to 39.1%. Collectively, these effects of foliar P fertilization increased the productivity of the three crops by up to 55.9%, indicating that foliar supplementation with P is an effective strategy to mitigate phytotoxicity symptoms.. In soybeans at the V4 and V6 stages, it has been shown to improve net photosynthesis, enhance Rubisco activity, and reduce oxidative stress. In maize, the V4 stage proved to be more effective, increasing Rubisco activity and improving productivity. For cotton, the B1 stage was more beneficial, resulting in increased boll weight and fiber yield. This study introduces an innovative approach of foliar P-supplementation to mitigate herbicide-induced oxidative stress in crops. This management strategy enhances crop resilience, improves yield stability, and provides a sustainable solution to a critical challenge in modern agriculture.

Cross‐Generational Effect of Water Deficit Priming on Physiology of Peanut Plants Under Water Stress

ABSTRACTWater deficit priming through regulated deficit irrigation has been shown to be beneficial for peanut cultivation, leading to improved water‐use efficiency during the crop cycle and enhanced stress acclimation. The effects of priming using water deficit can be heritable, but little is known about stress priming effects on the physiology and growth of successive generations undergoing water stress. Two experiments were conducted to assess cross‐generational priming by determining physiological and growth responses of offspring of primed and non‐primed peanut plants of two genotypes, COC‐041 and New Mexico Valencia C (NMV‐C), both previously found to be strongly responsive to priming. Seeds were collected from parental plants subjected to mild water stress by regulated deficit irrigation (primed) or adequate irrigation (non‐primed). These seeds were then planted, and the offspring were monitored for physiological and growth responses to water stress, including on a whole‐plant basis using a high‐throughput physiological phenotyping platform and on individual leaves by periodic single‐leaf measurements. Measurements included whole‐plant transpiration (plant‐Tr), root water uptake, leaf transpiration, stomatal conductance and net CO2 assimilation (leaf‐Tr, leaf‐gs, and leaf‐A), leaf water and osmotic potential (leaf‐Ψw and leaf‐Ψo), leaf osmotic adjustment, leaf relative water content (leaf‐RWC) and cumulative plant‐Tr. Offspring of both genotypes from primed parent plants had faster early establishment, with more uniform germination, and more rapid initial seedling growth compared to offspring from non‐primed parent plants. Although offspring of both non‐primed and primed plants of both genotypes exhibited a significant reduction of plant‐Tr, gas exchange, leaf‐Ψw, leaf‐Ψo, and leaf‐RWC when exposed to water stress, offspring of primed plants showed increased water use efficiency through reduced leaf‐gs, leaf‐Tr and plant‐Tr while maintaining leaf‐A under water stress. Despite offspring of both primed and non‐primed plants being susceptible to severe water stress, offspring of primed plants exhibited overall enhanced water use efficiency, leading to greater dry biomass production per gram of transpired water and a trend of less growth reduction due to water stress compared to offspring of non‐primed plants, especially for the genotype COC‐041. This study shows the potential of water deficit priming to promote cross‐generational changes in physiological function under limited water availability, by enhancing crop stress acclimation in the next plant generation.

Pea Seed Priming with Pluronic P85-Grafted Single-Walled Carbon Nanotubes Affects Photosynthetic Gas Exchange but Not Photosynthetic Light Reactions.

Nanotechnology is rapidly advancing towards the development of applications for sustainable plant growth and photosynthesis optimization. The nanomaterial/plant interaction has been intensively investigated; however, there is still a gap in knowledge regarding their effect on crop seed development and photosynthetic performance. In the present work, we apply a priming procedure with 10 and 50 mg/L Pluronic-P85-grafted single-walled carbon nanotubes (P85-SWCNT) on garden pea seeds and examine the germination, development, and photosynthetic activity of young seedlings grown on soil substrate. The applied treatments result in a distorted topology of the seed surface and suppressed (by 10-19%) shoot emergence. No priming-induced alterations in the structural and functional features of the photosynthetic apparatus in 14-day-old plants are found. However, photosynthetic gas exchange measurements reveal reduced stomatal conductance (by up to 15%) and increased intrinsic water use efficiency (by 12-15%), as compared to hydro-primed variants, suggesting the better ability of plants to cope with drought stress-an assumption that needs further verification. Our study prompts further research on the stomatal behavior and dark reactions of photosynthesis in order to gain new insights into the effect of carbon nanotubes on plant performance.

Knock-out of SlDMR6-1 in tomato promotes a drought-avoidance strategy and increases tolerance to Late Blight

The DOWNY MILDEW RESISTANCE 6 (DMR6) protein is a 2-oxoglutarate (2OG) and Fe(II)-dependent oxygenase, involved in salicylic acid (SA) metabolism. SA is recognized as an abiotic stress-tolerance enhancer, and in tomato the inactivation of DMR6 was found increase its level and induce disease-resistance against several pathogens. By applying the CRISPR/Cas9 technique, we generated Sldmr6-1 tomato mutants and tested their tolerance to drought as well as to Late Blight. Wild-type tomato cultivar ‘San Marzano’ and its Sldmr6-1 mutants were subjected to water deprivation for 7 days. WT plants exhibited severe wilting, while T2Sldmr6-1 mutants showed turgid leaves and maintained higher Soil Relative Water Content. Eco-physiological measurements highlighted that Sldmr6-1 mutants adopted a water saving behavior reducing transpiration rate by decreasing stomatal conductance. Under drought stress the assimilation rate decreased as well, resulting in no alteration of the CO2 concentration in the sub-stomatal chamber and increasing the Water Use Efficiency. Furthermore, in Sldmr6-1 mutants the drought stress induced up-regulation of the anti-oxidant related genes SlAPX and SlGST as well as down-regulation of SlCYP707A2 gene, which is involved in ABA catabolism. At last we highlighted, for the first time in tomato, that Sldmr6-1 mutants exhibited a reduced susceptibility to Phytophthora infestans, the causal agent of Late Blight.

Two Carya Species, Carya hunanensis and Carya illinoinensis, Used as Rootstocks Point to Improvements in the Heat Resistance of Carya cathayensis.

Grafting as a crucial horticultural technique has been widely used in the cultivation of Carya cathayensis (Chinese hickory), which is a unique and important economic tree in the northeast of Zhejiang Province and the south of Anhui Province. However, the existing literature lacks research on the potential impact of various rootstocks on the thermal tolerance of Chinese hickory. The objectives of this study were to evaluate heat tolerance in four distinct groups of Chinese hickory, including C. cathayensis grafted onto Carya hunanensis and Carya illinoinensis, one self-grafted group (C. cathayensis grafted onto C. cathayensis), and one non-grafted group (C. cathayensis). We examined photosynthesis parameters, phytohormones, and differentially expressed genes in the four various hickory groups subjected to 25 °C, 35 °C, and 40 °C heat stress (HS). The results demonstrated that grafting onto C. hunanensis and C. illinoinensis exhibited a higher net photosynthetic rate and stomatal conductance, lower intercellular CO2 concentration, and smaller changes in plant hormone content compared to self-grafted and non-grafted group under HS. The transcriptome results revealed that the majority of differentially expressed genes (DEGs) associated with photosynthetic pathways exhibited downregulation under HS, while the degree of variation in grafted groups using C. hunanensis and C. illinoinensis as rootstocks was comparatively lower than that observed in self-grafted and non-grafted groups. The alteration in the expression patterns of DEGs involved in plant hormone synthesis and metabolism under HS corresponded to changes in plant hormone contents. Overall, Chinese hickory grafted onto C. hunanensis and C. illinoinensis exhibited enhanced resistance to high-temperature stress at the juvenile stage.

Ecophysiological Recovery of Micropropagated Olive Cultivars: Field Research in an Irrigated Super-High-Density Orchard

This research focuses on the seasonal patterns of the ecophysiological recovery of four olive cultivars (Arbequina, Coratina, Frantoio, and Urano), both micropropagated and self-rooted, grown in a mature, irrigated, super high-density (SHD) orchard under Mediterranean conditions (Southern of Italy). The aim was to observe the impact of the micropropagation method on the ecophysiological responses. Ecophysiological parameters, including leaf water potential (LWP), stomatal conductance (gs), net photosynthetic rate (Pn), and transpiration rate (E) were assessed. Self-rooted trees consistently exhibited superior gs, E, and Pn recovery compared to the micropropagated ones. ‘Arbequina’ maintained elevated levels of Pn under water-deficit conditions. ‘Coratina’ exhibited increases in gs and E after irrigation. ‘Frantoio’ demonstrated recovery capabilities, with lower LWP and higher Pn under stress. ‘Urano’ micropropagated trees achieved higher gs values in mid-summer, while self-rooted trees sustained higher Pn later in the season. This field research highlighted the important role of the propagation method in optimizing the physiological performance of olive cultivars in SHD orchards. Furthermore, it highlighted the necessity of long-term studies on the effects of propagation methods and their interactions with other farming practices.

Predicting Grapevine Physiological Parameters Using Hyperspectral Remote Sensing Integrated with Hybrid Convolutional Neural Network and Ensemble Stacked Regression

Grapevine rootstocks are gaining importance in viticulture as a strategy to combat abiotic challenges, as well as enhance scion physiology. Direct leaf-level physiological parameters like net assimilation rate, stomatal conductance to water vapor, quantum yield of PSII, and transpiration can illuminate the rootstock effect on scion physiology. However, these measures are time-consuming and limited to leaf-level analysis. This study used different rootstocks to investigate the potential application of aerial hyperspectral imagery in the estimation of canopy level measurements. A statistical framework was developed as an ensemble stacked regression (REGST) that aggregated five different individual machine learning algorithms: Least absolute shrinkage and selection operator (Lasso), Partial least squares regression (PLSR), Ridge regression (RR), Elastic net (ENET), and Principal component regression (PCR) to optimize high-throughput assessment of vine physiology. In addition, a Convolutional Neural Network (CNN) algorithm was integrated into an existing REGST, forming a hybrid CNN-REGST model with the aim of capturing patterns from the hyperspectral signal. Based on the findings, the performance of individual base models exhibited variable prediction accuracies. In most cases, Ridge Regression (RR) demonstrated the lowest test Root Mean Squared Error (RMSE). The ensemble stacked regression model (REGST) outperformed the individual machine learning algorithms with an increase in R2 by (0.03 to 0.1). The performances of CNN-REGST and REGST were similar in estimating the four different traits. Overall, these models were able to explain approximately 55–67% of the variation in the actual ground-truth data. This study suggests that hyperspectral features integrated with powerful AI approaches show great potential in tracing functional traits in grapevines.

Greater aperture counteracts effects of reduced stomatal density on WUE: a case study on sugarcane and meta-analysis.

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 (gsw). However, the quantitative relationship between reduced SD, gsw, 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 (SbEFP2) in sugarcane reduced SD by 26-38% but did not affect gsw compared to wildtype. 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 gsw from anatomical data. These data suggest that increased stomatal aperture is the only possible explanation for maintaining gsw when SD is reduced. Meta-analysis across C3 dicots, C3 monocots, and C4 monocots revealed engineered reductions in SD are strongly correlated with lower gsw (r2=0.60-0.98), but this response is damped relative to the change in anatomy.

Reducing stomatal density by expression of a synthetic Epidermal Patterning Factor increases leaf intrinsic water use efficiency and reduces plant water use in a C4 crop.

Enhancing crop water use efficiency (WUE) is a key target trait for climatic resilience and expanding cultivation on marginal lands. Engineering lower stomatal density to reduce stomatal conductance (gs) has improved WUE in multiple C3 crop species. However, reducing gs in C3 species often reduces photosynthetic carbon gain. A different response is expected in C4 plants because they possess specialized anatomy and biochemistry which concentrates CO2 at the site of fixation. This modifies the photosynthesis (AN) relationship with intracellular CO2 concentration (ci) so that photosynthesis is CO2-saturated and reductions in gs are unlikely to limit AN. To test this hypothesis, genetic strategies were investigated to reduce stomatal density in the C4 crop sorghum. Constitutive expression of a synthetic epidermal patterning factor (EPF) transgenic allele in sorghum, led to reduced stomatal densities, reduced gs, reduced plant water use and avoidance of stress during a period of water deprivation. In addition, moderate reduction in stomatal density did not increase stomatal limitation to AN. However, these positive outcomes were associated with negative pleiotropic effects on reproductive development and photosynthetic capacity. Avoiding pleiotropy by targeting expression of the transgene to specific tissues could provide a pathway to improved agronomic outcomes.

The influence of plant water stress on vegetation–atmosphere exchanges: implications for ozone modelling

Abstract. Evapotranspiration is important for Earth's water and energy cycles as it strongly affects air temperature, cloud cover, and precipitation. Leaf stomata are the conduit of transpiration, and their opening is sensitive to weather and climate conditions. This feedback can exacerbate heat waves and can play a role in their spatiotemporal propagation. Sustained high temperatures strongly favour high ozone levels, with significant negative impacts on air quality and thus on human health. Our study evaluates the process representation of evapotranspiration in the atmospheric chemistry–climate European Centre for Medium-Range Weather Forecasts – Hamburg(ECHAM)/Modular Earth Submodel System (MESSy) Atmospheric Chemistry model. Different water stress parameterizations are implemented in a stomatal model based on CO2 assimilation. The stress factors depend on either soil moisture or leaf water potential, which act on photosynthetic activity, and mesophyll and stomatal conductance. The new functionalities reduce the initial overestimation of evapotranspiration in the model globally by more than an order of magnitude, which is most important in the Southern Hemisphere. The intensity of simulated warm spells over continents is significantly improved. For ozone, we find that a realistic model representation of plant water stress suppresses uptake by vegetation and enhances photochemical production in the troposphere. These effects lead to an overall increase in simulated ground-level ozone, which is most pronounced in the Southern Hemisphere over the continents. More sophisticated land surface models with multi-layer soil schemes could address the uncertainties in representing plant dynamics representation due to too-shallow roots. In regions with low evaporative loss, the representation of precipitation remains the largest uncertainty.

Escherichia coli Inoculation Decreases the Photosynthetic Performance on Tomato Plants: Clarifying the Impact of Human Commensal Bacteria on Transient Plant Hosts

The commensal/pathogenic Escherichia coli affects humans and animals, being present in diverse environmental niches, possibly surviving due to its adaptation to transient plant hosts like crops, increasing the risk of foodborne diseases. E. coli interaction with the plant host remains unknown, particularly the impacts on photosynthesis. We hypothesize that E. coli influences the tomato transient host’s photosynthetic capacity. To validate this hypothesis, we exposed 57-day-old tomato plants (Solanum lycopersicum) to different inoculation conditions, namely, non-inoculated plants (negative control, C−); plants directly injected with E. coli SL6.1 (107 CFU/mL) (positive control, C+); plants irrigated one time with E. coli SL6.1 (107 CFU/mL); and plants chronically irrigated with E. coli SL6.1 (104 CFU/mL). No significant changes were observed in chlorophyll fluorescence, pigments’ contents, morphological aspects, and fruiting in all conditions. However, irrigated plants (chronically and one-time contaminated) had decreased stomatal conductance (gs, 31.07 and 34.42 mol m−2 s−1, respectively, vs. 53.43 and 48.08 mol m−2 s−1 in C− and C+, respectively), transpiration rate (E, 0.32 and 0.35 mol m−2 s−1 in chronically and one-time contaminated conditions vs. 0.57 and 0.48 mol m−2 s−1 in C− and C+, respectively), and a trend of increased intrinsic carboxylation (Ci, 384 and 361 ppm in chronically and one-time irrigated plants vs. 321 and 313 ppm in C− and C+, respectively). The one-time inoculated plants presented more severe effects than the remaining conditions, with lower net photosynthetic rate (PN, 0.93 vs. 3.94–5.96 μmol (CO2) m−2 s−1 in the other conditions), intrinsic water use efficiency (iWUE, 33.1 vs. 74.51–184.40 μmol (CO2)/ mmol (H2O) in the chronically irrigated and the control plants), and intrinsic carboxylation efficiency (iCE, 0.003 vs. 0.012–0.022 μmol (CO2)/ppm in the remaining conditions). Our data support that some observed effects are similar to those associated with phytopathogenic bacteria. Lastly, we propose that the decrease in some parameters of gas exchange requires direct contact with the leaf/stomata, and is mainly observed for high concentrations of E. coli.

Models of osmotic stress as a tool for proteomics and metabolomics of legume seeds

Drought poses a significant challenge to the sustainable development of modern agriculture and to the achievement of high crop yields. Water deficit causes osmotic stress and triggers plant physiological responses characterized by reduced water potential, diminished stomatal conductance, and decreased photosynthetic efficiency. Long-term adaptation to osmotic stress entails intricate metabolic rearrangements, leading to the accumulation of osmoprotectants, activation of antioxidant systems, and increased biosyntheses of stress-protective proteins. The severity and duration of drought, along with plant genotype and developmental stage, influence the plant response to stress, consequently affecting crop yield and quality. Particularly in the context of legumes, which are crucial for human and animal nutrition, understanding adaptive strategies to water deficit is essential for the cultivation of drought-resistant genotypes, primarily because these crops predominantly thrive in semi-arid regions. Proteomics and metabolomics approaches, in turn, serve as valuable tools, offering critical insights into the molecular dynamics governing plant responses to drought stress. Furthermore, the use of reliable drought simulation models is imperative for the effective evaluation of legume response to water scarcity, aiding the cultivation of drought-tolerant varieties. This review highlights the perspectives of utilizing different osmotic stress models to investigate proteome and metabolome alteration within seeds of food legumes.

Biochemical versus stomatal acclimation of dynamic photosynthetic gas exchange to elevated CO2 in three horticultural species with contrasting stomatal morphology.

Understanding photosynthetic acclimation to elevated CO2 (eCO2) is important for predicting plant physiology and optimizing management decisions under global climate change, but is underexplored in important horticultural crops. We grew three crops differing in stomatal density-namely chrysanthemum, tomato, and cucumber-at near-ambient CO2 (450 μmol mol-1) and eCO2 (900 μmol mol-1) for 6 weeks. Steady-state and dynamic photosynthetic and stomatal conductance (gs) responses were quantified by gas exchange measurements. Opening and closure of individual stomata were imaged in situ, using a novel custom-made microscope. The three crop species acclimated to eCO2 with very different strategies: Cucumber (with the highest stomatal density) acclimated to eCO2 mostly via dynamic gs responses, whereas chrysanthemum (with the lowest stomatal density) acclimated to eCO2 mostly via photosynthetic biochemistry. Tomato exhibited acclimation in both photosynthesis and gs kinetics. eCO2 acclimation in individual stomatal pore movement increased rates of pore aperture changes in chrysanthemum, but such acclimation responses resulted in no changes in gs responses. Although eCO2 acclimation occurred in all three crops, photosynthesis under fluctuating irradiance was hardly affected. Our study stresses the importance of quantifying eCO2 acclimatory responses at different integration levels to understand photosynthetic performance under future eCO2 environments.

Carboxymethyl Chitosan Improves Sugar Beet Tolerance to Drought by Controlling Enzyme Activity and Stomatal Conductance

Carboxymethyl Chitosan Improves Sugar Beet Tolerance to Drought by Controlling Enzyme Activity and Stomatal Conductance

Effects of arbuscular mycorrhizal fungi in the rhizosphere of two olive (Olea europaea) varieties Arbequina and Barnea under water deficit conditions.

One strategy to improve olive (Olea europaea ) tree drought tolerance is through the symbiosis of arbuscular mycorrhizal fungi (AMF), which helps alleviate water deficit through a combination of morphophysiological effects. Cuttings of olive varieties Arbequina (A) and Barnea (B) were grown with (+AMF) or without (-AMF) inoculum in the olive grove rhizosphere soil. One year after establishment, pots were exposed to four different water regimes: (1) control (100% of crop evapotranspiration); (2) short-period drought (20days); (3) long-period drought (25days); and (4) rewatering (R). To evaluate the influence of AMF on tolerance to water stress, stem water potential, stomatal conductance and the biomarkers for water deficit malondialdehyde, proline, soluble sugars, phenols, and flavonoids were evaluated at the end of the irrigation regimes. Stem water potential showed higher values in A(+) and B(+) in all water conditions, and the opposite was true for stomatal conductance. For proline and soluble sugars, the stem water potential trend is repeated with some exceptions. AMF inoculum spore communities from A(+ and -) and B(+ and -) were characterised at the morphospecies level in terms of richness and abundance. Certain morphospecies were identified as potential drought indicators. These results highlight that the benefits of symbiotic relationships between olive and native AMF can help to mitigate the effects of abiotic stress in soils affected by drought.

Unveiling Genotypic Response of Chickpea to Moisture Stress Based on Morpho‐Physiological Parameters in the Eastern Indo‐Gangetic Plains

ABSTRACTIn the eastern Indo‐Gangetic plains, chickpea is grown postrice cultivation mostly under rainfed condition with residual soil moisture which adversely affects branching as well as pod and seed development, ultimately resulting in substantial yield losses. The current study analysed the moisture stress response of 12 chickpea genotypes with control for different morpho‐physiological traits in two sets of field experiments carried out during the year 2017–18 and 2018–19. The current study observed varying response of chickpea genotypes under moisture stress condition with average yield reduction from 11.79% to 24.77%. Mean yield of genotypes under stress condition showed a strong positive association with yield index (1.00**) and stress tolerance index (0.915**). The biplot principal component analysis revealed maximum potential of three chickpea genotypes (DBGC 1, Pusa 256 and DBGC 2) for grain yield and biological yield under moisture stress condition. The correlation analysis showed a significant association of yield with physiological parameters such as photosynthetic rate (0.363**), stomatal conductance (0.364**) and transpiration rate (0.292*). The three higher yielding genotypes relatively maintained biological yield, yield plant−1, 100 seed weight and photosynthesis rate and showed reduced rates of stomatal conductance and transpiration under moisture stress condition. The study found variable genotypic response to moisture stress and showed that yield index as well as stress tolerance index was more effective to identify superior genotypes for moisture stress condition. The superior genotypes identified in the present study may be considered for rainfed areas of eastern Indo‐Gangetic plains and can be used in future chickpea breeding programs for drought tolerance.

Physiological and anatomical responses of Passiflora tripartita var. mollissima (Passifloraceae) in water deficit

Introduction: Passiflora tripartita var. mollissima (banana passionfruit) is one of the most promising exotic tropical fruits from the diversity of the Passifloraceae family in South America, because of its organoleptic properties and antioxidant activity. Objective: To evaluate the physiological and anatomical responses of banana passionfruit plants under water deficit to better understand the mechanisms that mitigate this stress and affect the production of crops subject to climate change and global warming. Methods: Three-month-old seedlings of banana passionfruit were subjected to a soil water deficit through an irrigation reduction at 70 % for 49 days under greenhouse conditions. Morphology (leaf area, height, and number of leaves) and physiological (stomatal conductance, Fv/Fm, total chlorophyll content) measurements were made through time, and after the irrigation treatments were measured biomass parameters and anatomical foliar traits. Results: The plants experienced a decrease in height, leaf area, number of leaves, leaf area index, and relative water content, that are common responses in plants subjected to reduced irrigation. Additionally, the plants exhibited certain mechanisms that can be attributed to water deficit tolerance such as higher root: shoot ratio, stomatal closing, an increase in stomatal density, a reduction in mesophyll tissue thickness, and a decrease in the number of vessels and its diameter as they enable the banana passionfruit to reduce water loss and decrease the probability of cavitation in xylem vessels. Conclusions: banana passionfruit plants could implement strategies against water scarcity, allowing them to survive and endure challenging environmental conditions