Plant Stomatal Conductance Research Articles

Characterization of carbon and oxygen isotopes of plant on climate and plant physiology at the southeastern margin of Qinghai-Tibet Plateau, China

To investigate the correlation between carbon and oxygen isotope compositions of plant cellulose and climatic factors as well as plant physiological indices on the southeastern margin of the Qinghai-Tibet Plateau, we examined plant species in eight sampling sites with similar latitudes and different longitudes in this region. Through the characteristics of δ13C and δ18O values, fractionation values (Δ13C and Δ18O) in leaf cellulose, we discussed water use efficiency (WUE) and the environmental factors, the variation of carbon and oxygen isotopes in the southeastern margin of the Qinghai-Tibet Plateau with elevation and longitude, and revealed the indication degrees of isotopic signals to different environments and vegetation physiology. By using the semi-quantitative model of carbon and oxygen dual isotopes, we investigated the physiological adaptation mechanisms of plants to varying environmental conditions. The results demonstrated that both Δ13C and Δ18O of cellulose decreased with increasing elevation and longitude, and Δ13C was more influenced by longitude, while Δ18O was more susceptible to elevation variation. Additionally, Δ13C and Δ18O were significantly and positively correlated with temperature (TEM), precipitation (PRE), potential evapotranspiration (PET), and relative humidity (RH). PRE was the dominant meteorological factor driving the variation of Δ13C, while RH was the dominant meteorological factor influencing Δ18O variation. In contrast to Δ13C, WUE showed a stronger correlation with elevation than with longitude, which increased as elevation and longitude increased. According to the carbon-oxygen model, plant stomatal conductance (gs) and photosynthetic capacity (Amax) decreased with increasing precipitation and relative humidity, while the values increased with increasing elevation and longitude. The combined analysis of carbon and oxygen isotopes of organic matters would yield additional environmental and gas exchange information for studies on climate tracing and vegetation physiology studies on the southeastern margin of the Qinghai-Tibet Plateau.

Stomatal response to VPD is not triggered by changes in soil-leaf hydraulic conductance in Arabidopsis or Callitris.

Stomatal closure under high VPDL (leaf to air vapour pressure deficit) is a primary means by which plants prevent large excursions in transpiration rate and leaf water potential (Ψleaf) that could lead to tissue damage. Yet, the drivers of this response remain controversial. Changes in Ψleaf appear to drive stomatal VPDL response, but many argue that dynamic changes in soil-to-leaf hydraulic conductance (Ks-l) make an important contribution to this response pathway, even in well-hydrated soils. Here, we examined whether the regulation of whole plant stomatal conductance (gc) in response to typical changes in daytime VPDL is influenced by dynamic changes in Ks-l. We use well-watered plants of two species with contrasting ecological and physiological features: the herbaceous Arabidopsis thaliana (ecotype Columbia-0) and the dry forest conifer Callitris rhomboidea. The dynamics of Ks-l and gc were continuously monitored by combining concurrent in situ measurements of Ψleaf using an open optical dendrometer and whole plant transpiration using a balance. Large changes in VPDL were imposed to induce stomatal closure and observe the impact on Ks-l. In both species, gc was observed to decline substantially as VPDL increased, while Ks-l remained stable. Our finding suggests that stomatal regulation of transpiration is not contingent on a decrease in Ks-l. Static Ks-l provides a much simpler explanation for transpiration control in hydrated plants and enables simplified modelling and new methods for monitoring plant water use in the field.

Stevia rebaudiana under a CO2 Enrichment Atmosphere: Can CO2 Enrichment Overcome Stomatic, Mesophilic and Biochemical Barriers That Limit Photosynthesis?

Due to the desire to live a healthier lifestyle, the search for nonglycosidic sweeteners has increased stevioside production in recent years. The main goal of this study was to demonstrate that S. rebaudiana grown in a CO2-enriched environment can overcome stomatic, mesophilic and biochemical barriers that limit photosynthesis (AN). We show that in an environment with a CO2-enriched atmosphere (800 and 1200 µmol CO2 mol−1), the genotype 16 (G16) shows an increase of 17.5% in AN and 36.2% in stomatal conductance in plants grown in 800 µmol CO2 mol−1 when compared to non-enriched plants. In conjunction with this issue, the plants show an efficient mechanism of dissipating excess energy captured by the photosystems. Photosystem II efficiency was increased at 1200 µmol CO2 mol−1 when compared to non-enriched plants, both in genotype 4 (25.4%) and G16 (211%). In addition, a high activity of Calvin–Benson enzymes, a high production of sugars and an enhanced production of steviosides were combined with high horticultural yield. Both genotypes (G4 and G16) showed excellent physiological indicators, with high superiority in G16. Thus, our study has demonstrated that S. rebaudiana could adapt to global climate change scenarios with higher temperatures caused by higher atmospheric CO2.

Effects of microclimatic factors on stomatal conductance of plants in vertical greenery systems in humid subtropical areas

• Reduced irrigation in winter does not significantly affect VGS. • The transpiration in winter is about 1/3 of that in other seasons. • The E of southwest-oriented VGS is 41% higher in the afternoon than morning. • A stomatal model in VGS in humid subtropical areas is proposed. Plant transpiration through stomata is crucial in land surface physical processes and the hydrosphere-atmosphere-biosphere water vapor cycle. Applying stomatal models to vertical greenery systems (VGSs) is challenging because of the unique plant habitat. However, VGSs are widely used in subtropical areas; thus, plant transpiration in these systems should be investigated. Field measurements are used to determine the relationship between stomatal conductance ( g s ) and different microclimatic factors: solar radiation ( I ), air temperature ( T a ), relative humidity (RH), and soil volumetric water content ( θ ). A stomatal model based on multiple nonlinear regression is proposed, and its accuracy for different VGS plant species is verified with field measurements. The model's root mean square error (RMSE) is 57% lower than that of existing models. The latent heat flux from transpiration ( E ) of VGS in different seasons and orientations are calculated, and design strategies are proposed to utilize the cooling potential of VGS better. The prediction accuracy of the water vapor transfer, thermal comfort, and building energy consumption can be improved by incorporating the proposed model into an urban canopy model (UCM) and building energy model (BEM). It will provide guidelines for sustainable urban planning and VGS design regarding heat island mitigation and building energy savings.

Emergence of the physiological effects of elevated CO2 on land-atmosphere exchange of carbon and water.

Elevated atmospheric CO2 (eCO2 ) influences the carbon assimilation rate and stomatal conductance of plants, thereby affecting the global cycles of carbon and water. Yet, the detection of these physiological effects of eCO2 in observational data remains challenging, because natural variations and confounding factors (e.g., warming) can overshadow the eCO2 effects in observational data of real-world ecosystems. In this study, we aim at developing a method to detect the emergence of the physiological CO2 effects on various variables related to carbon and water fluxes. We mimic the observational setting in ecosystems using a comprehensive process-based land surface model QUINCY to simulate the leaf-level effects of increasing atmospheric CO2 concentrations and their century-long propagation through the terrestrial carbon and water cycles across different climate regimes and biomes. We then develop a statistical method based on the signal-to-noise ratio to detect the emergence of the eCO2 effects. The eCO2 effect on gross primary productivity (GPP) emerges at relatively low CO2 increase (∆[CO2 ] ~ 20 ppm) where the leaf area index is relatively high. Compared to GPP, the eCO2 effect causing reduced transpiration water flux (normalized to leaf area) emerges only at relatively high CO2 increase (∆[CO2 ] >> 40 ppm), due to the high sensitivity to climate variability and thus lower signal-to-noise ratio. In general, the response to eCO2 is detectable earlier for variables related to the carbon cycle than the water cycle, when plant productivity is not limited by climatic constraints, and stronger in forest-dominated rather than in grass-dominated ecosystems. Our results provide a step toward when and where we expect to detect physiological CO2 effects in in-situ flux measurements, how to detect them and encourage future efforts to improve the understanding and quantification of these effects in observations of terrestrial carbon and water dynamics.

Hourly water-carbon interactions modulate decadal water-use efficiency trends inferred from ecosystem-scale measurements

Plant stomatal conductance regulates photosynthesis and transpiration. This physiological link affects ecosystem responses to microclimate and harmonizes carbon, energy, and water exchanges between the biosphere and atmosphere. The relationship between water losses via transpiration and carbon gains via photosynthesis can be quantified by plant water-use efficiency (WUE). While leaf- and ecosystem-scale observations both suggest rising WUE in recent decades, WUE trends inferred from the ecosystem scale are much larger than those inferred from the leaf scale or implied by theory. The unexpectedly large ecosystem-scale WUE trends complicate interpretation of ecophysiological responses to changing environmental conditions. Here, we analyze ecosystem-scale WUE inferred from 40 FLUXNET sites, each with at least 10 years of measurements. Our results demonstrate that observed ecosystem-scale WUE trends are more sensitive to hourly weather conditions than longer-term changes in atmospheric carbon dioxide or vapor pressure deficit. Our analysis shows that Earth System Models participating in CMIP6 did not capture the observed WUE sensitivity to inter-site variability and microclimatic conditions. Collectively, our findings suggest that ecosystem-scale WUE trends reflect water-carbon interactions across multiple temporal scales, and disentangling factors contributing to emergent ecosystem responses is needed to infer ecophysiological relationships and model structures from observations.

Climate Drivers Contribute in Vegetation Greening Stalls of Arid Xinjiang, China: An Atmospheric Water Drying Effect

Xinjiang, an arid region of China, has experienced a substantial warming–wetting trend over the past five decades. However, climate change has affected vegetation growth/greening in arid Central Asia in unexpected ways due to complex ecological effects. We found a significant greening trend (consistent increase in the normalized difference vegetation index or NDVI) from 1982 to 1996, during the growing season; however, the NDVI consequently decreased and plateaued from 1997 to 2015, especially in naturally vegetated regions. Atmospheric vapor pressure deficit (VPD) is a critical driver of vegetation growth, is a direct measure of atmospheric aridity, and has increased sharply in recent decades. A partial correlation analysis indicated a significant relationship between growing season NDVI and VPD from 1997 to 2015. This implies that decreased VPD corresponds to increasing NDVI, and increasing VPD corresponds to a decrease and plateauing in the NDVI trend. Using the partial derivative equation method, our results suggest that the trend in growing season NDVI was affected primarily by increasing VPD (contributing 87.57%) from 1997 to 2015, especially in the grassland and desert biomes. Rising temperatures lead to a greater VPD, resulting in exacerbated evaporative water loss. Soil drought and atmospheric aridity limit plant stomatal conductance and could effectively lead to a decrease in the greening trend and increased vegetation mortality in arid Xinjiang. Our results emphasize the importance of VPD as a limiting factor of greening trends in arid regions. The influence of VPD on vegetation growth should be considered when evaluating arid ecosystem functioning under global warming.

Interactive Effects of Intraspecific Competition and Drought on Stomatal Conductance and Hormone Concentrations in Different Tomato Genotypes

Plant physiological responses to various stresses are characterized by interaction and coupling, while the intrinsic mechanism remains unclear. The effects of intraspecific competition on plant growth, stomatal opening, and hormone concentrations were investigated with three tomato genotypes (WT-wild type, Ailsa Craig; FL-a abscisic acid (ABA) deficient mutant, flacca; NR-a partially ethylene-insensitive genotype) under two water regimes (full irrigation, irrigation amount = daily transpiration; deficit irrigation, 60% of irrigation amount in full irrigation) in this study. Three kinds of competitions were designed, i.e., root and canopy competition, non-root competition, and non-canopy competition, respectively. Intraspecific competition reduced plant leaf area and stomatal conductance (gs) of wild-type tomato, accompanied by ABA accumulation and ethylene evolution. Intraspecific competition-induced decrease in gs was absent in FL and NR, indicating ABA and ethylene involved in plant response to intraspecific competition. As soil water becomes dry, the competition decreased gs by elevating ABA and ethylene accumulations. Under severe drought, the competition-induced decline in gs was covered by the severe drought-induced decrease in gs, as hydraulic signals most probably dominate. The absence of canopy competition insignificantly influenced plant stomatal opening of well-watered tomato, as canopy separation minimized the plant neighbor sensing by ethylene and other signals. Whereas under water deficit condition, the absence of canopy competition significantly reduced ABA accumulation in roots and then stomatal conductance, indicating the belowground neighbor detection signals maybe enhanced by soil drought. The absence of root competition increased ethylene evolution, confirming the importance of ethylene in neighbor detection and plant response to environmental stress.

Leaf-to-air vapor pressure deficit differently affects barley depending on soil water availability

Plant response to drought may be altered by the variation in air temperature and humidity and these interactions may be more frequent and intense with expected climate changes. The study examines impact of temporal changes in air temperature and air humidity on spring barley grown in dry and wet soil.The impact of two hours long changes in air temperature and relative humidity (RH) was evaluated on spring barley grown in soil of optimum and limited soil water availability. The alterations in stomatal conductance, transpiration photosynthesis, leaf temperature in response of air humidity and air temperature were analyzed.Air RH strongly differentiated leaf stomatal conductance in plants grown in well-watered soil. Despite the low impact of air RH on leaf conductance in plants grown in dry soil, a significant decline in transpiration with an increase in air RH occurred. The increase in air RH induced significant increase in leaf temperature in well-watered plants. Changes in leaf vapor pressure deficit (LVPD) differently affected stomatal conductance (gH2O) in plants grown in soil with optimum and limited water availability.Temporal changes in air humidity and temperature differently affected barley grown under optimum and limited water availability.

Container volume affects drought experiments in grapevines: Insights on xylem anatomy and time of dehydration.

Plant stress experiments are commonly performed with plants grown in containers to better control environmental conditions. Nevertheless, the container can constrain plant growth and development, and this confounding effect is generally ignored, particularly in studies on woody species. Here, we evaluate the effect of the container volume in drought experiments using grapevine as a model plant. Grapevines grown in small (7 L, S) or large (20 L, L) containers were subjected to drought stress and rewatering treatments. We monitored plant stomatal conductance (g s), midday stem water potential (Ψs), and photosynthetic rate (A N) throughout the experiment. The effect of the container volume on the stem and petiole xylem anatomy, as well as on the total leaf area (LA), was assessed before drought imposition. The results showed that LA did not differ between plants in L or S containers, but S vines exhibited a higher theoretical hydraulic conductance at the petiole level. Under drought L and S similarly reduced g s and A N, but plants in S containers reached lower Ψs than those in L. Nevertheless, upon rewatering droughted plants in S containers exhibited a faster stomata re‐opening than those in L, probably as a consequence of the differences in the stress degree experienced and the biochemical adjustment at the leaf level. Therefore, a suitable experimental design should consider the container volume used in relation to the desired traits to be studied for unbiased results.

Plant stomatal conductance determined transpiration and photosynthesis both contribute to the enhanced negative air ion (NAI)

Negative air ion (NAI) has been widely recognized to be regulated by plant photosynthesis. However, their quantified relationship had seldom been validated. In this study, plant photosynthesis-related traits (including leaf area-specific photosynthesis An, transpiration rates El, stomatal conductance gs, photosynthetic electron transport rate ETR) and leaf area-specific NAI (NAIc) were measured to qualify their relations with ten different species in a thermostat. Sap flow measurement was conducted on 15 individuals of Camellia japonica L. in an open-top chamber (OTC) to inverse sap flow based-stomatal conductance (GSf), as a proxy of whole individual photosynthesis. We also conducted gas exchange measurements on these individuals and compared them with their GSf. Three micro-meteorological parameters, including air temperature (Ta), relative humidity (RH) and radiation (Ra) and NAI were synchronously monitored with sap flow measurement. Significant differences were observed in NAIc among the 10 species, and was highly determined by their An, El and gs. However, since RH in the thermostat was stable at 70%, we could concluded that the NAIc difference among species was determined by the gs-related photosynthesis, rather than the El- related transpiration. In the OTC experiment, before the C. japonica individuals were moved in, Ta, RH and Ra accounted for 89% of the total NAI variation. However, after the C. japonica were moved in, the contribution of the three parameters decreased to 40%, and the new model only provided 46% of NAI variation. Since gs and An of C. japonica individuals were well explained by the GSf (R2 = 0.94 and 0.91 respectively), which proved GSf a good proxy of gs and An. GSf during the daytime was then considered in the model, and 76.88% of NAI variances were accounted. Even though some limitations such as the disturbance of air quantity index (AQI) still exist in our study, we provided a more efficient way to inverse the NAI dynamics in the region of vegetation.

Acclimation to Ex Vitro Conditions in Ninebark

Acclimation is the final phase of micropropagation and often decisive for its economic output. The aim of the experiments was to evaluate the effect of abscisic acid (ABA) and supplementary light on acclimation and leaf anatomy of the in vitro-rooted plants of ninebark (Physocarpus opulifolius L.). The initial material came from 8–10-week-old in vitro cultures on ½MS supplemented with 1 mg·L−1 IBA. After potting, plantlets were sprayed with ABA solutions or distilled water and were grown either under natural daylight or under supplemental sodium light at 230 μmol·m−2·s−1 between 2 and 9 p.m. All measurements and anatomical observations were done after eight weeks in the greenhouse. Supplementary lighting significantly increased the percentage of acclimatized plants, plant height and the internode number. Plant growth was also positively affected by 1 mg·L−1 ABA. During acclimation, the photosynthesis rate increased while the transpiration and stomatal conductance dropped. The assimilation pigment contents increased under supplemental lighting while ABA had no detectable effect. However, relative to water controls, ABA increased photosynthesis, reduced transpiration, and stomatal conductance in plants growing under both light conditions. Leaves from the in vitro plants were about two times thinner than those from plants growing in soil, with only a single layer of the palisade parenchyma, hence with lower proportion in relation to the spongy parenchyma. Supplementary light during acclimation increased leaf thickness but only in the water control while it decreased it in the ABA-treated plants. ABA increased the mesophyll thickness but only in plants growing under natural light. In conclusion, supplementary light and treatment with ABA enhance acclimation of micropropagated ninebark plants.

Use of mycorrhizal fungi and compost for improving the growth and yield of tomato and its resistance to Verticillium dahliae

The impact of soil amendment with compost and/or application of arbuscular mycorrhizal fungi (AMF) on the resistance of tomato to Verticillium dahliae was evaluated. The frequency and intensity of mycorrhization decreased in V. dahliae inoculated plants. Application of compost and AMF significantly improved plant growth, stomatal conductance and chlorophyll fluorescence compared to infected and non infected controls. The combination of these biostimulants reduced the disease severity and incidence and the leaf alteration index compared to pathogen-infected control plants. Mycorrhized and compost amended soil recorded a maximum decrease in plants malonyldialdehyde accumulation in the presence of V. dahliae. The combination of compost and AMF resulted in a significant improvement of superoxide dismutase, catalase, peroxidase and polyphenoloxidase activities in tomato leaves and roots compared to the control treatment in the presence of the pathogen. Similarly, yield and quality of tomato fruits were significantly improved by the dual application of compost and AMF.

The Yield Responses to Crop Bioremediation Practices on Haplustept and Fluvaquent Saline-Sodic Soils

ABSTRACT Crop production in salty-sodic soils causes poor crop growth due to ion imbalance, water stress, low hormonal and enzymatic balances. The use of rhizobacteria promoting plant growth in saline and sanitary areas (PGPR) is an economical and environmentally friendly approach that increases and eliminates the tolerance of plants to salt. Field experiments were conducted to determine the response of barley, maize and sorghum crop yields to the application of the bacteria (Halobacillus sp), which was preliminarily experimented by a greenhouse study, on two big soil groups (Haplustept and Fluvaquent). The experiment was established with four different treatments; T0 (control-no application), T1 (the gypsum application), T2 (the PGPR application), and T3 (the gypsum + PGPR application) on the high saline and sodic soils in a semi-arid region. The observations of the present study indicate positive impacts of PGPR applications on crop yield and soil productivity. The gypsum + PGPR treatment was the most effective treatment obtaining higher yields owing to significant improvement in the plant photosynthetic activity, chlorophyll content, stomatal conductance, enzymes, hormones, amino and organic acids, and crop-soil productivity. The seed inoculation with the Halobacillus sp bacteria cultures help in alleviation of stress and enhance crop productivity under the short-term gypsum application on Haplustept and Fluvaquent saline-sodic soils.

Enhanced Nitric Oxide Synthesis Through Nitrate Supply Improves Drought Tolerance of Sugarcane Plants.

Nitric oxide (NO) is an important signaling molecule associated with many biochemical and physiological processes in plants under stressful conditions. Nitrate reductase (NR) not only mediates the reduction of NO3− to NO2− but also reduces NO2− to NO, a relevant pathway for NO production in higher plants. Herein, we hypothesized that sugarcane plants supplied with more NO3− as a source of N would produce more NO under water deficit. Such NO would reduce oxidative damage and favor photosynthetic metabolism and growth under water limiting conditions. Sugarcane plants were grown in nutrient solution and received the same amount of nitrogen, with varying nitrate:ammonium ratios (100:0 and 70:30). Plants were then grown under well-watered or water deficit conditions. Under water deficit, plants exhibited higher root [NO3−] and [NO2−] when supplied with 100% NO3−. Accordingly, the same plants also showed higher root NR activity and root NO production. We also found higher photosynthetic rates and stomatal conductance in plants supplied with more NO3−, which was associated with increased root growth. ROS accumulation was reduced due to increases in the activity of catalase in leaves and superoxide dismutase and ascorbate peroxidase in roots of plants supplied with 100% NO3− and facing water deficit. Such positive responses to water deficit were offset when a NO scavenger was supplied to the plants, thus confirming that increases in leaf gas exchange and plant growth were induced by NO. Concluding, NO3− supply is an interesting strategy for alleviating the negative effects of water deficit on sugarcane plants, increasing drought tolerance through enhanced NO production. Our data also provide insights on how plant nutrition could improve crop tolerance against abiotic stresses, such as drought.

Impact of a Soil Conditioner Integrated into Fertilization Scheme on Orange and Lemon Seedling Physiological Performances.

Growers in Florida face unique challenges regarding maintaining proper citrus nutrition. Poor draining soils with low fertility, low C.E.C., and high rates of leaching are common in this region. In response to these challenges, interest has grown in products labeled as soil conditioners. Using a completely randomized experimental design, this greenhouse study tested the effects of 5 different combinations of a traditional fertilizer (TF) and a new soil conditioner (SC) on lemon and orange seedling physiology. Eight-month-old ‘Bearss’ lemon and ‘Valencia’ sweet orange grafted on sour orange rootstocks were employed, and five repetitions were used for each treatment. Plant biomass (dry weight), height, stem diameter, chlorophyll content, stomatal conductance and nutrient uptake were analyzed after 120 days of treatment. The results show that SC has a positive impact upon both chlorophyll levels and stomatal conductance values in both orange and lemon seedlings. However, based on dry weight growth data, we can only conclude that the SC was effective for orange seedlings at 50% TF and 0.5% SC. Based on this short 120-day evaluation, the SC achieved positive growth promotion for orange (50% TF) but not for lemon seedlings.

Legacy effects of historical grazing alter leaf stomatal characteristics in progeny plants.

Grazing, one of the primary utilization modes of grassland, is the main cause of grassland degradation. Historical overgrazing results in dwarf phenotype and decreased photosynthesis of perennial plants. However, it remains unknown what the mechanism underlying of this legacy effect is, and the role of stomata in the resulting decreased photosynthesis also remains unclear. To address these questions, differences in stomatal density, length and width on both adaxial and abaxial epidermis were compared between overgrazing and ungrazed Leymus chinensis offspring by using rhizome buds cultivated in a greenhouse, and the correlation between photosynthetic capacity and stomatal behavior was also investigated. Our results showed that historical grazing significantly impacted phenotype, photosynthesis and stomatal traits of L. chinensis. The offspring plants taken from overgrazed parents were dwarfed compared to those taken from ungrazed parents, and the photosynthesis and stomatal conductance of plants with a grazing history decreased by 28.6% and 21.3%, respectively. In addition, stomatal density and length on adaxial and abaxial leaf surfaces were significantly increased; however, stomatal width on abaxial leaf surfaces of overgrazed L. chinensis was significantly decreased compared with ungrazed individuals. Moreover, the expression patterns of eight genes related to stomatal regulation were tested: seven were down-regulated (2–18 times) and one was up-regulated (three times). Genes, involved in ABC transporter and receptor-like serine/threonine protein kinase were down-regulated. These results suggest that legacy effects of historical grazing affect the stomatal conductance by decreasing the stomatal width in progeny plants, which thus results in lower photosynthesis. Furthermore, changes of stomatal traits and function were regulated by the inhibition of ABC transporter and serine/threonine protein kinase. These findings are helpful for future exploration of the possible mechanisms underlying the response of grassland plants to long-term overgrazing.

Leaf gas exchange recovery of soybean from water-deficit stress

ABSTRACT As the risk of drought attributable to climate change increases, the development of high-yielding, drought-adapted cultivars will be critical for minimizing yield losses in crops like soybean (Glycine max (L.) Merr.). In this study, the ability of soybean genotypes to recover transpiration and leaf gas exchange capacity following re-watering from soil drying was investigated. The plants were subjected to controlled water-deficit stress and recovery in growth-chamber experiments. Transpiration was measured on five soybean genotypes and photosynthesis rates on two select genotypes. After water re-supply, transpiration was initially low but increased until a stable rate was reached on day 3, to about 50% to 100% of the rates of reference plants that had not been stressed. The largest difference in maximum transpiration recovery was between the varieties USDA-N8002 and Benning compared to the landrace Geden Shirazu, with Geden Shirazu having the lowest recovery. Photosynthesis and vapor-pressure-deficit response measurements did not show that restricted plant stomatal conductance was responsible for the limitation observed in Geden Shirazu recovery. Since all genotypes showed rapid recovery from water-deficit stress in 3 d, more rapid recovery was not indicated as a major candidate for improving soybean drought tolerance. However, the extent of recovery varied among genotypes and those genotypes that fully recovered to rates of well-watered plants such as Benning and USDA-N8002 would seemingly be advantageous for drought conditions.

The effect of plant physiological responses to rising CO2 on global streamflow

River flow statistics are expected to change as a result of increasing atmospheric CO2 but uncertainty in Earth system model projections is high. While this is partly driven by changing precipitation, with well-known Earth system model uncertainties, here we show that the influence of plant stomatal conductance feedbacks can cause equally large changes in regional flood extremes and even act as the main control on future low latitude streamflow. Over most tropical land masses, modern climate predictions suggest that plant physiological effects will boost streamflow, overwhelming opposing effects of soil drying driven by the effects of CO2 on atmospheric radiation, warming and rainfall redistribution. The relatively unknown uncertainties in representing eco-physiological processes must therefore be better constrained in land-surface models. To this end, we identify a distinct plant physiological fingerprint on annual peak, low and mean discharge throughout the tropics and identify river basins where physiological responses dominate radiative responses to rising CO2 in modern climate projections. Climate change is expected to impact river flows. Here, it is shown that plant physiological responses to increased CO2, rather than atmospheric changes, are the primary drivers of mean, peak and low flows throughout the tropics.

Intact leaf gas exchange provides a robust method for measuring the kinetics of stomatal conductance responses to abscisic acid and other small molecules in Arabidopsis and grasses

BackgroundGuard cells perceive external and internal stimuli and regulate stomatal conductance in plants. With the use of gas exchange analyzers, time-resolved stomatal conductance responses to light intensity, [CO2] concentration and relative humidity changes can be measured. This is more difficult to achieve when measuring stomatal responses to small soluble molecules such as the plant hormone abscisic acid (ABA) or the bacterial peptide flagellin 22 (flg22), in particular when investigating mutants with response phenotypes.ResultsA method to evaluate the dynamic effects of small molecules on stomatal conductance in a time-resolved fashion using gas exchange analyzers is presented here. ABA-induced stomatal closure was investigated by adding ABA to the transpiration stream of intact leaves placed in a microcentrifuge tube containing water. Strong ABA responses were resolved in time- and in a dose-dependent manner in wild-type Arabidopsis leaves, whereas the same response was not observed in leaves of the ABA-insensitive mutant open stomata 1-3 (ost1-3). Moreover, when leaves of the Plasma membrane Intrinsic Protein (PIP) aquaporin quadruple mutant pip1;1 pip1;2 pip2;1 pip2;2 were tested, robust wild-type-like responses to ABA were observed. When the bacterial peptide flg22 was added to the transpiration stream of intact wild-type leaves, a strong flg22-induced stomatal closure effect was observed. Finally, the proposed technique was further developed and optimized for evaluation of stomatal conductance responses to small molecules in leaves of grasses using the reference plant Brachypodium distachyon.ConclusionsDue to the variable size of stomata in Arabidopsis and the limited dynamic response of stomata in isolated epidermal strips, evaluation of the effect of small molecules on stomatal physiology has been challenging and has led in some cases to inconsistent results. Moreover, potential signals from the mesophyll are missing when using epidermal peels to evaluate stomatal aperture responses. Here we propose a less invasive technique which allows for time-resolved measurements of stomatal conductance responses to small molecules optimized for both Arabidopsis and Brachypodium distachyon leaves.