Stomatal Conductance Research Articles

Vapor pressure deficit and temperature variability drive future changes to carbon sink stability in China’s terrestrial ecosystems

The stability of future carbon sinks is crucial for accurately predicting the global carbon cycle. However, the future dynamics and stability of carbon sinks remain largely unknown, especially in China, a significant global carbon sink region. Here, we examined the dynamics and stability of carbon sinks in China’s terrestrial ecosystems from 2015 to 2,100 under two CMIP6 scenarios (SSP245 and SSP585), using XGBoost and SHAP models to quantify the impact of climatic drivers on carbon sink stability. China’s future terrestrial ecosystems will act as a “carbon sink” (0.27–0.33 PgC/yr), with an initial increase that levels off over time. Although the carbon sink capacity increases, its stability does not consistently improve. Specifically, the stability of carbon sinks in future China’s terrestrial ecosystems transitions from strengthening to weakening, primarily occurring in areas with higher carbon sink capacity. Further analysis revealed that atmospheric vapor pressure deficit (VPD) and temperature (Tas) are the two primary factors influencing carbon sink stability, with significant differences in their impacts across different scenarios. Under the SSP245 scenario, variations in VPD (VPD.CV) regulate water availability through stomatal conductance, making it the key driver of changes in carbon sink stability. In contrast, under the SSP585 scenario, although VPD.CV still plays an important role, temperature variability (Tas.CV) becomes the dominant factor, with more frequent extreme climate events exacerbating carbon cycle instability. The study highlights the differences in driving factors of carbon sink stability under different scenarios and stresses the importance of considering these differences, along with the scale and stability of carbon sinks, when developing long-term carbon management policies to effectively support carbon neutrality goals.

Leaf-level physiological strategies related to productivity and plasticity of Populus in the Southeastern United States

IntroductionPopulus and its hybrids are attractive bioenergy crops and the southeastern United States has broad ability to supply bioenergy markets with woody biomass. Breeding and hybridization have led to superior eastern cottonwood (Populus deltoides W. Bartram ex Marshall) and hybrid poplars adapted to a wide variety of site types not suited for agricultural production. In order to maximize productivity and minimize inputs, genotypes need to efficiently use available site resources and tolerate environmental stresses. In addition, we need to determine plasticity of traits and their coordination across sites to select traits that will broadly characterize genotypes. Therefore, our study objectives were to determine (1) which leaf traits were correlated with growth, (2) if traits and genotypes exhibited significant plasticity across sites, and (3) how traits were coordinated within and across sites and Populus taxa.MethodsWe measured trees at two sites in northeastern Mississippi, United States: one upland and one alluvial terrace site. Genotypes included eastern cottonwoods as well as F1 crosses of eastern cottonwood and P. maximowiczii (Henry), P. nigra (L.) and P. trichocarpa (Torr. & Gray).ResultsWe found that sites differed in which leaf traits were correlated with productivity; with water use efficiency specifically being positively correlated with growth at an alluvial terrace site, but negatively correlated with growth at an upland site. Tree height growth, leaf isotope composition (δ13C and δ15N), as well as leaf mass per area (LMA) exhibited the least plasticity across sites, while physiological gas exchange parameters and leaf nitrogen concentration exhibited the highest plasticity. Broadly across taxa, leaf carbon isotope ratios were correlated with intrinsic water use efficiency, and stomatal conductance was positively correlated with photosynthetic nitrogen use efficiency across sites, while leaf nitrogen isotope ratios exhibited contrasting relationships with leaf nitrogen concentration.DiscussionOverall, these results allow us to refine selections of productive genotypes based on site conditions and site-specific relationships with physiological parameters to better match Populus taxa with sites and landowner objectives.

A global dataset of tree hydraulic and structural traits imputed from phylogenetic relationships

We present a dataset of plant hydraulic and structural traits imputed for 55,779 tree species based on TRY plant trait dataset observations and phylogenetic relationships. We collected plant trait values for maximum stomatal conductance (gsMAX), xylem pressure at 12%, 50%, and 88% conductance loss (P12, P50, P88), maximum observed rooting depth (rdMAX), photosynthetic Water Use Efficiency (WUE), maximum plant height (height), Specific Leaf Area (SLA), and leaf Nitrogen content (LeafN). We demonstrated that each of these traits exhibited remarkably large phylogenetic signals across all land plants. Based on the strength of this signal we then developed random forest (RF) models trained on TRY trait data to impute the traits of previously unstudied tree species using Phylogenetic Eigenvector Maps. We quantified imputed trait uncertainty by fitting RF model test dataset residuals to skew exponential power distributions accounting for heteroscedasticity, demonstrating encouraging lack of biases in the imputed dataset. The resulting dataset of imputed trait values can support global analyses of plant trait variations and species-level parameterization of earth systems models.

Changes in Photosynthetic Efficiency, Biomass, and Sugar Content of Sweet Sorghum Under Different Water and Salt Conditions in Arid Region of Northwest China

Sweet sorghum (Sorghum bicolor L. Moench) has significant cultivation potential in arid and saline–alkaline regions due to its drought and salt tolerance. This study aims to evaluate the mechanisms by which increased soil salinity and reduced irrigation affect the growth, aboveground biomass, and stem sugar content of sweet sorghum. A two-year field experiment was conducted, with four salinity levels (CK: 4.17 dS/m, S1: 5.83 dS/m, S2: 7.50 dS/m, and S3: 9.17 dS/m) and three irrigation levels (W1: 90 mm, W2: 70 mm, and W3: 50 mm). The results showed that increased salinity and reduced irrigation significantly reduced both the emergence rate and aboveground biomass, with the decreases in the emergence rate ranging from 11.0% to 36.2% and the reductions in the aboveground biomass ranging from 15.9% to 43.8%. Additionally, increased soil salinity led to reductions in stem sugar content of 6.3% (S1), 8.8% (S2), and 12.8% (S3), respectively. The results also indicated that photosynthetic efficiency, including the net photosynthetic rate (Pn), stomatal conductance (Gs), and chlorophyll content (SPAD), was significantly hindered under increased water and salt stress, with the Pn decreasing by up to 50.4% and the SPAD values decreasing by up to 36.3% under the highest stress conditions. These findings underscore the adverse impacts of increased soil salinity and reduced irrigation on sweet sorghum’s growth, photosynthetic performance, and sugar accumulation, offering critical insights for optimizing its cultivation in arid and saline environments.

The physiological and molecular responses of potato tuberization to projected future elevated temperatures.

Potato (Solanum tuberosum L.) is one of the most important food crops globally and is especially vulnerable to heat stress. However, substantial knowledge gaps remain in our understanding of the developmental mechanisms associated with tuber responses to heat stress. This study used whole-plant physiology, transcriptomics, and phytohormone profiling to elucidate how heat stress affects potato tuber development. When plants were grown in projected future elevated temperature conditions, abscisic acid (ABA) levels decreased in leaf and tuber tissues, whereas rates of leaf carbon assimilation and stomatal conductance were not significantly affected compared to those plants grown in historical temperature conditions. While plants grown in projected future elevated temperature conditions initiated more tubers per plant on average, there was a 66% decrease in mature tubers at final harvest compared to those plants grown in historical temperature conditions. We hypothesize that reduced tuber yields at elevated temperatures are not due to reduced tuber initiation, but due to impaired tuber filling. Transcriptomic analysis detected significant changes in the expression of genes related to ABA response, heat stress and starch biosynthesis. The tuberization repressor genes SELF PRUNING 5G (StSP5G) and CONSTANS-LIKE1 (StCOL1) were differentially expressed in tubers grown in elevated temperatures. Two additional known tuberization genes, IDENTITY OF TUBER 1 (StIT1) and TIMING OF CAB EXPRESSION 1 (StTOC1), displayed distinct expression patterns under elevated temperatures compared to historical temperature conditions but were not differentially expressed. This work highlights potential gene targets and key developmental stages associated with tuberization to develop potatoes with greater heat tolerance.

Leaf functional traits highlight phenotypic variation of two tree species in the urban environment

Urbanization is transforming landscapes globally, altering environmental conditions that affect ecosystem functioning, particularly in urban areas where trees are crucial for regulating microclimates, improving air quality, and sustaining biodiversity. This study investigates the environmental differences and tree leaf structure and morphology in urban and suburban sites in the Chicago Metropolitan Region. The leaf functional traits of Norway Maple and Little − leaved Linden were studied in three locations in the summer of 2023: an urban park (University of Illinois Chicago, Chicago, IL), a suburban park (Morton Arboretum, Lisle, IL), and a suburban residential site (Lombard, IL). The urban site had higher daytime and nighttime air, and land surface temperatures compared to the suburban sites with significant fluctuations observed across the sites. Cumulative growing degree days, a measure of potential photosynthetically active days, were also higher in the urban park than in the suburban sites between March and August. Norway Maple trees growing in the urban site displayed higher specific leaf area (SLA) and lower leaf dry matter content (LDMC) than in the suburban sites, resulting in thinner leaves. Similarly, Little−leaved Linden trees in the suburban residential site displayed higher SLA and lower LDMC than those in the suburban park. The values of gas exchange traits − namely photosynthetic assimilation, transpiration rates, and stomatal conductance − of Norway Maple were higher at the urban site compared to suburban sites as temperatures increased during the summer. Norway Maple gas exchange values decreased as the growing season progressed, as expected by ontogeny. In contrast, Little−leaved Linden maintained similar leaf gas exchange values throughout the growing season. Both species in the urban site exhibited lower instantaneous water use efficiency and reduced LDMC, suggesting greater water loss in response to elevated temperatures compared to suburban park and residential sites. Comparisons with existing global trait databases emphasize the need for localized data to accurately capture site−specific responses. Although some traits aligned with database values, others deviated significantly, underscoring the importance of comprehensive, site−specific datasets for robust ecosystem modeling and management strategies.

Influences of conifer encroachment and removal on oak woodland ecophysiology and biodiversity—a case study from northern California, U.S.A.

Oregon white oak (Quercus garryana) woodlands are threatened by conifer encroachment established during decades of fire exclusion. Widespread restoration efforts are underway to remove conifers from many oak woodlands in California, Oregon, and Washington. Using water potential, stomatal conductance, stable isotopes, and three metrics of biodiversity, we investigated the effects of Douglas‐fir (Pseudotsuga menziesii) encroachment and removal at the ecosystem scale across 3 years in a northern California woodland. We found that heavily encroached stands had the highest water potential and often the lowest stomatal conductance, compared to moderately encroached and open stands. Xylem water stable isotopes indicated that oaks and Douglas‐firs were likely not directly competing for water, as oaks appeared to use a relatively deeper water source. Under certain climatic conditions, heavily encroached oaks were more vulnerable to water stress than oaks in open or moderately encroached stands. Following low‐intensity conifer removal, thinned stands had slightly lower predawn water potential and higher gas exchange compared to unthinned stands, particularly under dry conditions. For ecosystem biodiversity, understory plant and bird diversity did not meaningfully vary with encroachment or thinning, but mammal diversity was greater in encroached stands compared to open stands. Findings from this work demonstrate that negative impacts of conifer encroachment on oaks are not due to increased competition for water, conifer removal is physiologically beneficial for shaded oaks, and that heavier thinning treatments are likely needed to yield long‐term responses and influence biodiversity.

Multidimensional role of selenium nanoparticles to promote growth and resilience dynamics of Phaseolus vulgaris against sodium fluoride stress

High fluoride (F) concentrations negatively affect the seed germination, plant growth, development, and yield of crops. Phaseolus vulgaris L. is an F-sensitive crop frequently grown on marginal lands affected by F salts. Selenium (Se) is a vital elicitor of the antioxidative enzymes involved in scavenging free radicals to alleviate abiotic stress. Recent studies have demonstrated that engineered nanoparticles (NPs) have the potential to induce tolerance to abiotic stress in plants. Phytosynthesis of NPs is a novel and sustainable approach to mitigate abiotic stresses. The present study was intended to assess the role of green synthesized Se-nanoparticles (Se-NPs) in improving the physiochemical attributes, growth, and F stress tolerance of P. vulgaris growing in 200 ppm sodium fluoride (NaF) stress. NaF toxicity reduced Chl a, Chl b, and carotenoid content by 88.8%, 95.5%, and 96% compared to control with maximum improvement obtained through phyto-nano seed priming and foliar spray of 70 ppm Se-NPs. The joint treatment of NPs application through seed priming and foliar spray improved stomatal conductance (14.2%) and transpiration rate (11.7%) in plants subjected to NaF stress. The protein content (91.02%) and DPPH activity (33.72%) decreased under NaF stress, which was improved by phyto-nano seed priming and foliar spray (14.10%). Furthermore, the integrated application of Se-NPs seed priming and foliar spray increased nutritional content (P, K, Ca, Mg, and Zn), proline, ascorbic acid, and phenol yet reduced the level of NaF in plants. Se-NPs at 70 ppm were found to be more effective than 60 ppm in all modes of applications. Our results reveal a perception that Se-NPs increase P. vulgaris growth in NaF stress conditions, perhaps through a multipronged approach: improving photosynthetic content, nutrient uptake, and yield of P. vulgaris. Consequently, the findings of this study may be used for breeding and screening F-tolerant cultivars.

Exogenously Applied Triacontanol Mitigates Cadmium Toxicity in Vigna radiata L. by Optimizing Growth, Nutritional Orchestration, and Metal Accumulation

Cadmium (Cd) is one of the foremost phytotoxic elements. Its proportion in agricultural soil is increasing critically due to anthropogenic activities. Cd stress is a major crop production threat affecting food security globally. Triacontanol (TRIA) is a phytohormone that promotes growth, development, and metabolic processes in plants. The current study explicates the mitigation of Cd toxicity in Vigna radiata L. (mung bean) seedlings through the application of TRIA by a seed priming technique under Cd stress. The role of TRIA in improving metabolic processes to promote Vigna radiata (mung bean, green gram) vegetative growth and performance under both stressed and unstressed conditions was examined during this study. To accomplish this, three doses of TRIA (10, 20, and 30 µmol L−1) were used to pretreat V. radiata seeds before they were allowed to grow for 40 days in soil contaminated with 20 mg kg−1 Cd. Cd stress lowered seed germination, morphological growth, and biomass in V. radiata plants. The maximum root and shoot lengths, fresh and dry weights of roots, and shoot and seed germination rates were recorded for TRIA2 compared with those of TRIA1 and TRIA3 under Cd stress. In Cd-stressed V. radiata plants, TRIA2 increased the content of chlorophyll a (2.1-fold) and b (3.1-fold), carotenoid (4.3-fold), total chlorophyll (3.1-fold), and gas exchange attributes, such as the photosynthetic rate (2.9-fold), stomatal conductance (6.0-fold), and transpiration rate (3.5-fold), compared with those in plants treated with only Cd. TRIA seed priming increased nutrient uptake (K1+, Na1+, Mg2+, and Zn2+), total phenolic content, total soluble protein content, and DPPH (2,2-diphenyl-1-picrylhydrazyl) activity. Additionally, TRIA2 significantly reduced the quantity of Cd in the plants (3.0-fold) and increased the metal tolerance index (6.6-fold) in plants contrasted with those in the Cd-treated plants. However, TRIA2 promoted plant growth and biomass production by lowering Cd-induced stress through modifying the plant antioxidant machinery and reducing oxidative stress. The improved yield characteristics of V. radiata seedlings treated with TRIA suggest that exogenous TRIA may be used to increase plant tolerance to Cd stress.

Leaf warming in the canopy of mature tropical trees reduced photosynthesis due to downregulation of photosynthetic capacity and reduced stomatal conductance.

Tropical forests play a large role in the global carbon cycle by annually absorbing 30% of our annual carbon emissions. However, these forests have evolved under relatively stable temperature conditions and may be sensitive to current climate warming. Few experiments have investigated the effects of warming on large, mature trees to better understand how higher temperatures affect these forests in situ. We targeted four tree species (Endiandra microneura, Castanospermum australe, Cleistanthus myrianthus and Myristica globosa) of the Australian tropical rainforest and warmed leaves in the canopy by 4°C for 8 months. We measured temperature response curves of photosynthesis and respiration, and determined the critical temperatures for chloroplast function based on Chl fluorescence. Both stomatal conductance and photosynthesis were strongly reduced by 48 and 35%, respectively, with warming. While reduced stomatal conductance was likely in response to higher vapour pressure deficit, the biochemistry of photosynthesis responded to higher temperatures via reduced Vcmax25 (-28%) and Jmax25 (-29%). There was no shift of the Topt of photosynthesis. Concurrently, respiration rates at a common temperature did not change in response to warming, suggesting limited respiratory thermal acclimation. This combination of physiological responses to leaf warming in mature tropical trees may suggest a reduced carbon sink with future warming in tropical forests.

Evaluation of drought and salinity tolerance potentials of different soybean genotypes based upon physiological, biochemical, and genetic indicators

The present study has evaluated different soybean genotypes to understand the salt and drought tolerance mechanisms based on physiological traits (photosynthesis, stomatal conductance, chlorophyll, and cell membrane stability), antioxidant enzymes (superoxide dismutase, catalase, and peroxidase), reactive oxygen species (H2O2 and O2•−), osmolytes (glycine betaine, proline, and Na+/K+), plant water relations (relative water content, water potential, and solute potential) and expression of related genes (GmCAT1, GmPOD1, GmSOD, GmP5CS, GmNHX1, GmAKT1, GmDREB1, and GmARF1). The experiment was conducted in a two-factorial arrangement using randomized complete block design (RCBD) with genotypes as one factor and salt, drought, and control treatments as the other factor. All physiological traits, relative water content, and water potential decreased significantly in all soybean genotypes due to individual and combined treatments of drought and salt stress, with significantly less decrease in soybean genotypes G4620RX, DM45X61, and NARC-21. Besides that, the activity of antioxidant enzymes, production of ROS, accumulation of osmolytes, solute potential, and Na+/K+ ratio were increased significantly in all soybean genotypes under salt and water deficit conditions. As a whole, the soybean genotypes G4620RX, DM45X61, and NARC-21 showed the maximum enzymatic activity with less increase in ROS and Na+/K+ in addition to a high accumulation of osmolytes and an increase in solute potential. Correspondingly, the genotypes exhibiting high physiological and biochemical tolerance to drought and salt stresses showed the high expression of genes imparting the stress tolerance. Moreover, correlation, heatmap, and principal component analysis further confirmed the varying physiological and biochemical responses of all soybean genotypes under individual and combined applications of drought and salinity stresses. Overall, the present study confirmed that plants opt for the integrated physiological, biochemical, and genetic approaches to counteract the harmful effects of environmental stresses.

Difference in summer heatwave-induced damage between desert native and urban greening plants in an arid desert region.

Summer heatwaves have caused a distinct mortality between urban greening and native plants. However, there are insufficient studies revealing the underlying mechanisms. We hypothesized that differentiation in hydraulic traits and their integration cause the varied heatwave-induced damages between the two plant types. To prove it, three desert native species and five urban greening species were selected as the experimental objects. Then, the number of damaged individuals caused by summer heatwaves were investigated based on the 100 individuals for each species. The hydraulic traits (including hydraulic transport, photosynthetic and leaf traits) of 3-5 mature individuals were measured for each species. The comparative analysis (independent sample t test and one-way ANOVA) and the collaborative analysis (Pearson correlation and network analysis) were used to reveal the differences in heatwave-induced damage, hydraulic traits and their integration between urban greening and native plants. Our results showed that the heatwave-induced damage to urban greening plants was larger than that to native species. Water potentials of leaf and branch in pre-dawn and midday, P50, leaf dry matter content, net photosynthetic rate, transpiration rate and stomatal conductance of desert native species were significantly lower than those of urban greening plants (P < 0.05), while twig specific hydraulic conductivity, Huber value, wood density, intrinsic water use efficiency and the specific leaf area showed opposite patterns (P < 0.05). Trait integration of desert native species (0.63) was much higher than greening plants (0.24). Our results indicate that artificial urban greening plants are more susceptible to drought stress caused by heatwaves than native desert species. In the context of global climate change, in order to maintain the stability and function of urban ecosystems in extreme climate, the screening of greening plants should start from the perspective of hydraulics and trait integration, and more native species with strong drought adaptability should be planted.

Genotypic variability in cotton's transpiration response under progressive soil drying.

Crop yields in food and fibre production systems throughout the world are significantly limited by soil water deficits. Identifying water conservation mechanisms within existing genotypes is pivotal in developing varieties with improved performance in water-limited conditions. The objective of this study was to screen Australian germplasm for variability in the transpiration response to progressive soil drying using a glasshouse dry-down experiment. It tests the hypothesis that water conservation traits may provide tolerance to water stress, particularly when combined with other drought stress traits. Three glasshouse experiments were conducted to identify whether there are differences in the fraction of transpirable soil water (FTSW) threshold values for transpiration decline among six cotton genotypes. We also assessed whether genotype dependent responses to progressive soil drying are evident from leaf-level physiology, by measurement of gas exchange parameters. Significant variation in the FTSW threshold for transpiration decline between six genotypes was found, ranging from 0.13 to 0.29. Genotypic variation in the response to soil drying was also observed from leaf level physiology, with reductions in stomatal conductance and photosynthetic rate coinciding with when the FTSW threshold was reached. Genotypes that limit transpiration at high FTSW can conserve water earlier in the season to maintain productivity during extended dry periods. Therefore, these genotypes may provide physiological traits that improve productivity in water-limited environments. This research is important as rainfall and water resources for irrigated agriculture are predicted to decline. The development of drought tolerant germplasm for the Australian cotton industry will be beneficial in the projected increasingly frequent limited water environments resulting from a changing climate.

Interannual Variation of Stomatal Traits Impacts the Environmental Responses of Apple Trees.

Stomata are fundamental to plant-water relations and represent promising targets to enhance crop water-use efficiency and climate resilience. Here, we investigated stomatal density (SD) variation in 269 apple accessions across 3 years (2019-2021), which demonstrated significant differences between accessions but consistency over time. We selected 2 subsets of 20 accessions, each with contrasting SD: high stomatal density (HSD; 370-500 mm-2) and low stomatal density (LSD; 192-316 mm-2). SD groups were compared in stomatal function, leaf physiology and crop productivity across two seasons (2021-2022). LSD had lower stomatal conductance (gs) and higher intrinsic water-use efficiency in both years (p < 0.05). Hotter and drier conditions in 2022 reduced gs similarly in both groups (-22% HSD, -21% LSD), but also created a difference in net carbon assimilation (Anet) that was not present in 2021 (HSD + 1.7 μmol CO2 m-2 s-1, p < 0.05). LSD constraints on Anet were reflected in carbon isotope discrimination (δ13C, p < 0.001) and annual decline in fruit yield (-35%, p < 0.001). Our results demonstrate the suitability of SD as a trait to improve WUE, but also identifies a trade-off between water savings and productivity, which requires consideration for breeding.

Key role played by mesophyll conductance in limiting carbon assimilation and transpiration of potato under soil water stress

IntroductionThe identification of the physiological processes limiting carbon assimilation under water stress is crucial for improving model predictions and selecting drought-tolerant varieties. However, the influence of soil water availability on photosynthesis-limiting processes is still not fully understood. This study aimed to investigate the origins of photosynthesis limitations on potato (Solanum tuberosum) during a field drought experiment.MethodsGas exchange and chlorophyll fluorescence measurements were performed at the leaf level to determine the response of photosynthesis-limiting factors to the decrease in the relative extractable water (REW) in the soil.ResultsDrought induced a two-stage response with first a restriction of CO2 diffusion to chloroplasts induced by stomatal closure and a decrease in mesophyll conductance, followed by a decrease in photosynthetic capacities under severe soil water restrictions. Limitation analysis equations were revisited and showed that mesophyll conductance was the most important constraint on carbon and water exchanges regardless of soil water conditions.DiscussionWe provide a calibration of the response of stomatal and non-stomatal factors to REW to improve the representation of drought effects in models. These results emphasize the need to revisit the partitioning methods to unravel the physiological controls on photosynthesis and stomatal conductance under water stress.

Leaf Orientation Method as a Proxy for Sensing Nitrogen and Water Deficit in Tomato Plants

Precision field management and modeling crop growth requires precise, efficient, timely, nondestructive, and cost-effective measurements of structural component including leaf area index (LAI) and leaf orientation based on the foliage mean tilt angle (MTA), which is defined as the average leaf inclination angle of a canopy. Two experiments were carried out to investigate 1) the influence of different nitrogen (N) fertigation levels and 2) cycles of water deficit on leaf orientation (specifically, MTA) of young tomato (Solanum lycopersicum cv. Florida 47). N rates were 10, 50, 100, 200, and 300 mg·L−1 (mg N per liter of water) and irrigation treatments were well-watered and deficit irrigation. MTA was measured using the LAI-2200C Plant Canopy Analyzer. Across the experimental period, low N supply to leaves reduced the angle between leaf petiole and stem (high MTA) and produced plants with more erect leaves compared with N-sufficient plants. The MTA for the 10 mg·L−1–N treatment ranged from 54.3° to 73.6° and higher levels of N (50 to 300 mg·L−1–N) had MTA between 36.4° and 51.9°. Compared with lower N level (10 mg·L−1), LAI of tomato plants fertigated with a nutrient solution containing 300 mg·L−1–N increased by 3.6- to 4.9-fold across the study period. Similarly, canopy normalized difference vegetation index (NDVI) and leaf N% values at 300 mg·L−1–N were 2- to 3-fold higher than at 10 mg·L−1–N. However, MTA did not consistently differ across the 100 to 300 mg·L−1–N rates. In terms of water treatments, MTA of well-watered plants ranged from 32.3° to 40.5° whereas the same plants at water-deficit level had MTA between 45.7° and 51.8°. Although the relationship between MTA and canopy LAI, NDVI as well as leaf N was inconsistent or not significant under well-watered and water-deficit conditions, leaf gas exchange components (photosynthesis, stomatal conductance, and transpiration) showed a significant negative relationship (R2, 0.39–0.81, P &lt; 0.001) with MTA. Overall, leaf orientation, specifically MTA, was modulated by N levels (highest at 10 mg·L−1; lowest at 300 mg·L−1–N) and cycles of water deficit and therefore, MTA determination hold promise as a nondestructive method to assess N and water deficit in young tomato plants.

From intercropping to monocropping: the effects of Pseudomonas strain to facilitate nutrient efficiency in peanut and soil

As an oilseed crop, the yield and quality of peanuts are severely constrained by nutrient deficiencies, particularly in calcareous soils in northern China. Maize-peanut intercropping is an effective strategy to enhance mineral nutrient efficiency in peanuts via plant-microbe interaction, but the underlying mechanisms remain elusive. Here, we conducted experiments using a Pseudomonas strain (Pse.IP6) with diverse beneficial characteristics, which was isolated from the rhizosphere of intercropped peanuts. Additionally, Pse.IP6 exhibits high phylogenetic similarity with the Amplicon Sequence Variants 48 (ASV48) which belongs to Pseudomonas and is positively correlated with Fe in plants and soil in intercropping. To confirm the plant growth-promoting potential of Pse.IP6 and its role in intercropping advantage, we constructed pot experiments. Results revealed that Pse.IP6 promoted shoot growth and root development, as well significantly enhanced SPAD value, net photosynthetic rate, stomatal conductance, and transpiration rate of peanut leaves. Moreover, the application of Pse.IP6 resulted in a notable accumulation of nitrogen (N), phosphorus (P), and potassium (K) in shoot and active iron (Fe) in leaves, accompanied by an increased K-N ratio. The primary reason for the nutrient promotion is the enhancement of the bioavailability of nitrate, ammonium, P, K, and Fe in the rhizosphere. Collectively, our findings demonstrate that Pse.IP6, enriched in intercropping peanut, is a plant growth-promoting bacteria, represented by transferring the intercropping advantage on nutrients activation to monocropping peanuts. Our results offer insights into plant-rhizobacteria interaction mechanisms and therefore provide a rhizobacteria-based pathway to improve nutrient efficiency and productivity of crops.

Assessing the impact of salinity stress on some morpho-physiological traits of two chickpea genotypes under hydroponic conditions

Evaluating the performance of crop species to salinity stress is considered an intricate task due to differences in performance, response and susceptibility at different phenological stages of chickpea crop. Assessment of the performance of chickpea genotypes in response to NaCl-induced salinity stress at the initial vegetative phase is of great importance to have a crystal idea about the threshold level of tolerance. An experiment was carried out under hydroponic conditions to evaluate the performance of two chickpea genotypes (ELMO and ORION), in response to different salinity levels (0, 25, 50 and 75 mM NaCl) as factorial arrangement under completely randomized design with three replications. The average of shoot and root dry matter weight was significantly higher for the ELMO genotype at the control treatment (1.143, 0.4133 g respectively), while it was significantly lower in the two genotypes ORION and ELMO at the highest salinity level (0.267 and 0.2700; 0.0433 and 0.0533 g respectively). The root to shoot ratio was significantly higher in both genotypes in the control and the lowest salt level (25 mM NaCl), without significant differences among them (47.98, 43.30, 37.10 and 36.25% respectively). The relative water content and stomatal conductance were significantly higher in the ORION genotype (88.01%; 335.40 mmol m-2 s-1) compared to ELMO (84.09%; 299.10 mmol m-2 s-1), and increasing salinity level caused a proportional decline in both traits, where they were significantly lower at the highest salt level (75Mm) (77.45%; 87.50 mmol m-2 s-1). Results indicate genotypic variability in response to NaCl-induced salinity stress under hydroponic conditions and the physiological traits are more expressive and reliable as selection criteria than morphological ones.

Role of bio-stimulants on the advancement of vegetable production: A review

Abstract. Since climate of the globe is changing abruptly, causing tremendous challenges (biotic and abiotic stresses) on the production of vegetable crops, it seems to be difficult to ensure the food security for the rapidly growing population of the world if sustainable production systems are adopted. Though farmers are indiscriminately applying inorganic fertilizers and plant protection chemicals to replenish the fertility of their fields and protect their plants from pests, the issue of sustainable production seems to have been forgotten. Thus, the use of organic factors of production is a must in order to overcome the challenges so that production of healthy products can be maintained in an eco-friendly manner through the utilization of Bio-stimulators. Bio-stimulants have a crucial role in enhancing the growth, development and overall performance of different vegetable crops belonging to different families; Solanaceae, Alliaceae, Amaranthaceae, and Brassicaceae. The most commonly utilized bio-stimulants in the field of agriculture worldwide are humic substances (humic acid and fulvic acid), plant or animal-based protein hydrolysates, macro and micro-algal extracts (seaweed extracts), silicon, arbuscular mycorrhizal fungi and plant growth-promoting rhizobacteria. Bio-stimulants have important role in enhancing the growth characteristics, yielding potential, biochemical compositions (concentrations of ascorbic acid, and carotenoid content) in tomato plants and in other plants belonging to Solanaceae family like eggplant. Application of different types of bio-stimulants results in the improvement of growth, yields and chlorophyll and allicin contents in the Alliaceae species (onion and garlic). In the vegetable crops belonging to the family of Amaranthaceae (Spinach and Amaranthus), bio-stimulants have important impacts in the improvement of seed germination, increasing of plant height, photosynthetic pigments, yield and nutritional composition. Increased plant growth, photosynthetic rate and stomatal conductance, yield parameters, phenolic and flavonoid compounds and seed fatty acid concentration are also the results of bio-stimulant applications in the brassica species (cabbage, broccoli, rapeseed, mustard). Thus, the sustainable agriculture systems could be guaranteed by using bio-stimulants to boost the production of vegetable crops both quantitatively and qualitatively.

Drought-mediated oxidative stress and its scavenging differ between citrus hybrids with medium and late fruit maturation

Drought stress is a major environmental factor limiting citrus productivity. Still, differences in drought sensitivity between citrus hybrids of different maturation periods have so far not been reported. Here, we selected a medium-maturing (Fertile orange: FO (Citrus reticulata cv. Fertile orange) and a late-maturing citrus hybrid (Newhall Navel orange: NO (Citrus sinensis Osbeck cv. Newhall) and determined the physiological and biochemical traits of leaves, roots, wood and bark. Our results showed that drought significantly decreased net photosynthetic rate (Pn), stomatal conductance (Gs) and transpiration rate (Tr) of citrus leaves. Oxidative stress upon drought was indicated by enhanced foliar malondialdehyde (MDA) and hydrogen peroxide contents, as well as a stimulation of the anti-oxidative system. This stimulation included the contents of dehydroascorbic acid (DHA), glutathione (GSH) and oxidized glutathione (GSSG) in leaves, roots, wood and bark, as well as activities of antioxidative enzymes of glutathione reductase (GR), dehydroascorbate reductase (DHAR), superoxide dismutase (SOD) and peroxidase (POD). The late maturing NO hybrid not only showed better general physiological performance as indicated by increased Pn in leaves, but also higher biochemical ROS scavenging and osmotic capacity as indicated by increased ascorbic acids (ASA), DHA, and proline contents, as well as activities of enzymes of SOD, POD, ASA/DHA and GSH/GSSG ratios in the investigated tissues compared to the FO hybrid under drought and control conditions. Analysis of molecular mechanisms of signaling, regulatory and functional genes expression are suggested for future studies to elucidate the complex interplay of molecular, biochemical and physiological responses of citrus hybrids to drought.