Leaf Gas Exchange Responses Research Articles

Elevated CO2 Concentration Enhances Drought Tolerance by Mitigating Oxidative Stress and Enhancing Carbon Assimilation in Foxtail Millet (Setaria italica)

ABSTRACTElevated CO2 concentration (eCO2) can modulate the response of crop plants to drought stress (DS). This study aimed to investigate the response of leaf gas exchange, chlorophyll fluorescence, antioxidant activities, osmotic adjustment substance, phytohormone and signal transduction regulatory enzymes, as well as related genes in foxtail millet to DS (water stress for 10 days), ambient condition (aCO2, 400 μmol mol−1) and eCO2 (600 μmol mol−1). eCO2 significantly increased the net photosynthetic rate, maximum net photosynthetic rate, chlorophyll a content, transpiration rate and stomatal conductance, but did not affect leaf instantaneous water‐use efficiency under DS. eCO2 also significantly enhanced the quantum yield of Photosystem II (PSII), photosynthetic electron transport, and proportion of open PSII reaction centers under DS. Moreover, eCO2 significantly increased abscisic acid (ABA) content, proline content, and the activities of peroxidase, superoxide dismutase, and calcium‐dependent protein kinase under DS, leading to a significant reduction in malondialdehyde content. eCO2 significantly increased the expressions of gene encoding ABA‐, stress‐ and ripening‐induced proteins and ABA‐responsive element binding factor under DS. Our results clearly demonstrated the vital role of eCO2 in mitigating the drought‐induced damage over ambient CO2 grown foxtail millet.

Leaf gas exchange responses to combined heat and drought stress in wheat genotypes with varied stomatal density

Stomata regulate the plant’s gas exchange and water balance, and their density may be a crucial factor in the response to abiotic stresses. The aim of this study was to investigate the response of leaf gas exchange of three spring wheat genotypes with different stomatal density to progressive drought and combined heat and drought stress. The stomatal conductance (gs) was the most sensitive parameter that declined with increasing drought stress. This negatively affected transpiration and leaf cooling, and limited photosynthesis (A) when gs decreased to < 550 mmol m−2 s−1. The treatments affected all three genotypes similarly over time irrespective of stomatal density. However, when related to the fraction of transpirable soil water (FTSW) in the pot, gs and A of the low and high stomatal density cultivars responded differently when heat was added to the drought stress. The high stomatal density cultivar showed no difference in maximum gs at FTSW > 0.3, and a similar decline of gs and A at FTSW < 0.3 in drought alone and combined drought and heat. The low stomatal density cultivar showed a higher maximum gs and the most severe decline of gs under combined heat and drought stress and a significantly slower decline of gs under drought alone, which was also reflected in a significantly slower reduction in A under drought compared to the combined stress. Overall, the drought response of stomatal closure dominated the physiological response under simultaneous heat and drought irrespective of stomatal density, and it was only in the combined stress that the maximum photochemical efficiency Fv/Fm was negatively affected. In conclusion, to elucidate the effect of drought and combined drought and heat on the leaf gas exchange in wheat cultivars with varied stomatal density, it is crucial to relate the parameters to the available soil water, not the duration of the drought.

Responses of leaf gas exchange and metabolites to drought stress in different organs of sugarcane and its closely related species Erianthus arundinaceus

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

Stomatal response to VPD in C4 plants with different biochemical sub-pathways.

C4 NAD-malic enzyme (NAD-ME) species occurs in drier regions and exhibit different drought responses compared to C4 NADP-malic enzyme (NADP-ME) species. However, a physiological mechanism explaining the geographical discrepancies remains uncertain. This study examined gas exchange patterns that might explain different distributions observed between two subtypes of C4 photosynthesis. We measured the response of leaf gas exchange to vapour pressure deficit (VPD) and CO2 in plants from six distinct C4 clades having closely related NAD-ME and NADP-ME species using a Li-Cor 6400 gas exchange system. We found that NAD-ME species exhibited greater relative reductions in stomatal conductance with increases in VPD than NADP-ME species but observed no consistent subtype differences in C4 cycle activity as indicated by the initial slope of the A response to intercellular CO2 concentration. Based on these results, we hypothesise the greater response of gs to increasing VPD may enable NAD-ME plants to outperform NADP-ME plants in hot, dry environments where VPD is normally high.

Multigenerational Effects of Elevated CO2 and N Supply on Leaf Gas Exchange Traits in Wheat Plants

ABSTRACTThe responses of leaf gas exchange of wheat (Triticum aestivum L.) to elevated atmospheric CO2 concentration (e[CO2]) were often investigated within a single generation, while the long‐term acclimation of photosynthesis to growth in e[CO2] over multiple generations has not been systematically studied. Here, five wheat cultivars were grown under either ambient (a[CO2], 400 ppm) or elevated (e[CO2], 800 ppm) CO2 concentration for three consecutive generations (G1 to G3) with two N‐fertilisation levels (1N–1 g N pot−1 and 2N–2 g N pot−1) in climate‐controlled greenhouses. Leaf gas exchange was determined in each generation of plants under different treatments. It was found that at both N levels, e[CO2] stimulated photosynthetic rate while reducing stomatal conductance, transpiration rate and leaf N concentration, resulting in an enhanced water use efficiency and photosynthetic N use efficiency. The N level modulated the intergenerational responses of photosynthetic capacity to e[CO2]; under low N supply, the maximum carboxylation rate (Vcmax), the maximum electron transport rate (Jmax) and the rate of triose phosphate utilisation (TPU) were significantly downregulated by e[CO2] from the first to the second generation, but recovered in the third generation; whereas at high N levels, photosynthetic acclimation was diminished with the progress of generations, with Vcmax, Jmax and TPU increased under e[CO2] in the third generation. These results suggest that intergenerational adaptation could alleviate the e[CO2]‐induced reduction of the photosynthetic capacity, but plants with different N status responded differently to adapt to the long‐term exposure to e[CO2]. Among the five cultivars, 325Jimai showed a better photosynthetic performance under e[CO2] over the three generations, while 02‐1Shiluan appeared to be more inhibited by CO2 elevation in the long term conditions. These findings provide new insights for breeding strategies in the future CO2‐enriched environments.

Integrated Ca, Mg, Cu, and Zn supply upregulates leaf anatomy and metabolic adjustments in Eucalyptus seedlings

Adaptive responses to abiotic stresses such as soil acidity in Eucalyptus—the most widely planted broad-leaf forest genus globally—are poorly understood. This is particularly evident in physiological and anatomical disorders that inhibit plant development and wood quality. We aimed to explore how the supply of Ca and Mg through liming (lime), combined with Cu and Zn fertilization (CZF), influences physiological and anatomical responses during Eucalyptus grandis seedlings growth in tropical acid soil. Therefore, related parameters of leaf area and leaf anatomy, stomatal size, leaf gas exchange, antioxidant system, nutrient partitioning, and biomass allocation responses were monitored. Liming alone in Eucalyptus increased specific leaf area, stomatal density on the abaxial leaf surface, and Ca and Mg content. Also, Eucalyptus exposed only to CZF increased Cu and Zn content. Lime and CZF increased leaf blade and adaxial epidermal thickness, and improved the structural organization of the spongy mesophyll, promoting increased net CO2 assimilation, and stomatal conductance. Fertilization with Ca, Mg, Cu, and Zn positively affects plant nutrition, light utilization, photosynthetic rate, and antioxidant performance, improving growth. Our results indicate that lime and CZF induce adaptive responses in the physiological and anatomical adjustments of Eucalyptus plantation, thereby promoting biomass accumulation.

Soil water availability modulates the response of grapevine leaf gas exchange and PSII traits to a simulated heat wave

Background and aimsA better understanding of plant carbon assimilation, water status and photosystem performance responses to combined heat and drought stress would help to optimize grapevine management under such limiting conditions.MethodsGas exchange and chlorophyll fluorescence parameters were measured in potted grapevines, cv Sauvignon Blanc, before, during and after simulated six-day heat (Tmax = 40 °C) wave using heated well-watered (HW), heated drought-stressed (HD), non-heated well-watered (CW) and non-heated dry (CD) vines.ResultsPhotosynthesis and stomatal conductance in HW vines increased during the morning and dropped in the afternoon with respect to CW vines. Daily plant transpiration in HW almost doubled that of CW vines. When grapevines were already exposed to drought, the effects of the heat wave were negligible, with HD plants showing similar leaf photosynthesis and transpiration to their CD counterparts. Heat, but not drought stress, decreased the maximum (Fv/Fm) and effective photochemical quantum yield of PSII (φPSII), and also affected the use of absorbed energy. HW plants dissipated more radiative energy as heat, a protective mechanism of the photosystem, while HD vines increased the energy dissipated by non-regulated non-photochemical pathways, which might lead to photoinhibition damages. The different behavior could be due to the enhanced transpiration rate and consequent decrease in leaf temperature in HW as compared to HD vines. After the heat wave, only HW vines recovered the afternoon values of photosynthesis, stomatal conductance and φPSII to similar levels as those in CW vines.ConclusionDrought had a more significant effect than heat stress on photosynthesis, stomatal conductance and transpiration. The combined heat and drought stress, however, increased the proportion of energy lost by the leaves through harmful non-regulated dissipative pathways. With adequate soil water availability, grapevines withstood the heat wave period through an increase in leaf transpiration, which decreased leaf temperature and protected the PSII from heat damage.

Sap flow and leaf gas exchange response to a drought and heatwave in urban green spaces in a Nordic city

Abstract. Urban vegetation plays a role in offsetting urban CO2 emissions, mitigating heat through tree transpiration and shading, and acting as deposition surfaces for pollutants. The frequent occurrence of heatwaves and of concurrent drought conditions significantly disrupts the processes of urban trees, particularly their photosynthesis and transpiration rates. Despite the pivotal role of urban tree functioning in delivering essential ecosystem services, the precise nature of their response remains uncertain. We conducted sap flux density (Js) and leaf gas exchange measurements of four tree species (Tilia cordata, Tilia × europaea, Betula pendula, and Malus spp.) located in different urban green areas (Park, Street, Forest, and Orchard) in Helsinki, Finland. Measurements were made over two contrasting summers 2020 and 2021. Summer 2021 experienced a local heatwave and drought, whereas summer 2020 was more typical of Helsinki. In this study, we aimed to understand the responses of urban tree transpiration (measured with sap flux density) and leaf gas exchange to heatwave and drought conditions, and we examined the main environmental drivers controlling the tree transpiration rate during these periods. We observed varying responses of Js during the heatwave period at the four urban sites. When comparing the heatwave and no heatwave periods, a 35 %–67 % increase in Js was observed at the Park, Forest, and Orchard locations, whereas no significant change was seen at the Street site. Our results also showed that Js was higher (31 %–63 %) at all sites under drought conditions compared with non-dry periods. The higher Js values during the heatwave and dry periods were mainly driven by the high atmospheric demand for evapotranspiration, represented by the high vapor pressure deficit (VPD), suggesting that the trees were not experiencing severe enough heat or drought stress that stomatal control would have decreased transpiration. Accordingly, photosynthetic potential (Amax), stomatal conductance (gs), and transpiration (E) at the leaf level did not change during heatwave and drought periods, excluding the Park site where a significant reduction in gs was seen. VPD explained 55 %–69 % of the variation in the daily mean Js during heatwave and drought periods at all sites. At the Forest site, the increase in Js saturated after a certain VPD level, likely due to low soil water availability during these hot and dry periods. Overall, the heat and drought conditions were untypical of the region but not excessive enough to restrict stomatal control and transpiration, indicating that ecosystem services such as cooling were not at risk.

Ecotype effects on photosynthesis performance using A/PFFD among Pinus nigra Arn.

This study aimed to provide insights on intraspecific variability of photosynthesis performance of 19 provenances of black pine planted in a common garden. The experiment was conducted in an experimental trial located at Souiniet (the southern limit of its range) Photosynthetic capacity char­acterized by light-saturated net photosynthetic rates, associated light compensation points and apparent quantum yield was monitored by measuring the response of leaf gas exchange to light levels. Amax was the highest in provenances Puget Theniers (nigra ssp), Saint-Guilhem (salzmanni ssp), Marghese and les barres (laricio ssp). The lowest value was recorded in Olette of the subspecies salzmanni. Needles from two provenances Crimea (pallasiana ssp) and Les Barres (ssp laricio) revealed the highest apparent quantum yield (ɸ), followed by Brougatlès Ales (salzmanni ssp), Trenta Coste (ssp laricio), Les barres and Puget Theniers (nigra ssp). The lowest apparent quantum Yield was recorded in Laricio subspecies (Cosenza; Les barres and Bois frerot). The highest value of dark respiration (Rd) was shown in provenance Les barres (laricio ssp), while Grancia and Tavola of the laricio subspecies reported the lowest one. Provenances Tavola (laricio ssp) and Puget Theniers (nigra ssp) exhibited the highest LCP. The provenance Crimée (pallasiana ssp) and Aspromonto (laricio ssp) recorded the lowest values. The maximum values of photosynthesis are positively correlated with the total chlorophyll contents and Leaf Mass area. Our study illustrates that Photosynthesis performance showed a difference between 19 provenances of black pine; it seems that black pine photosynthetic performance is eco-typical independent.

Functional consequences of light intensity on soybean leaf hydraulic conductance: Coordinated variations in leaf venation architecture and mesophyll structure

Leaf hydraulic conductance (Kleaf) is a critical determinant of photosynthesis. Prior research has assessed the influence of light intensity on Kleaf by affecting leaf veins. However, whether the mesophyll structure is associated with leaf hydraulic acclimation to different light intensities remains unclear. We investigated the responses of leaf gas exchange and Kleaf to different growth light intensities and checked for the correlation of Kleaf with leaf structural traits in soybean. Low light significantly reduced Kleaf, but Kleaf and stomatal conductance remain coordinated. Low light decreased the stomatal density to match the balance between in water supply and carbon gain capacity. The decline in Kleaf under low growth light condition was partly due to for the reduction of the water movement through leaf veins because of reduced leaf vein thickness and density and xylem conduit size. In addition, low light reduces the mesophyll cell‐to‐cell connectivity and increased the volume fraction of intercellular air space. As a result, the area available for liquid‐phase flow decreases, and subsequently decreased Kleaf. The present study highlights the coordination role between leaf venation architecture and mesophyll structure influencing Kleaf in response to light intensity.

GrapevineXL reliably predicts multi-annual dynamics of vine water status, berry growth, and sugar accumulation in vineyards.

Climate and water availability greatly affect each season's grape yield and quality. Using models to accurately predict environment impacts on fruit productivity and quality is a huge challenge. We calibrated and validated the functional-structural model, GrapevineXL, with a data set including grapevine seasonal midday stem water potential (Ψxylem), berry dry weight (DW), fresh weight (FW), and sugar concentration per volume ([Sugar]) for a wine grape cultivar (Vitis vinifera cv. Cabernet Franc) in field conditions over 13years in Bordeaux, France. Our results showed that the model could make a fair prediction of seasonal Ψxylem and good-to-excellent predictions of berry DW, FW, [Sugar] and leaf gas exchange responses to predawn and midday leaf water potentials under diverse environmental conditions with 14 key parameters. By running virtual experiments to mimic climate change, an advanced veraison (i.e. the onset of ripening) of 14 and 28days led to significant decreases of berry FW by 2.70% and 3.22%, clear increases of berry [Sugar] by 2.90% and 4.29%, and shortened ripening duration in 8 out of 13 simulated years, respectively. Moreover, the impact of the advanced veraison varied with seasonal patterns of climate and soil water availability. Overall, the results showed that the GrapevineXL model can predict plant water use and berry growth in field conditions and could serve as a valuable tool for designing sustainable vineyard management strategies to cope with climate change.

Leaf Gas Exchange and Photosystem II Fluorescence Responses to CO2 Cycling.

Experimental systems to simulate future elevated CO2 conditions in the field often have large, rapid fluctuations in CO2. To examine possible impacts of such fluctuations on photosynthesis, the intact leaves of the field-grown plants of five species were exposed to two-minute cycles of CO2 between 400 and 800 μmol mol-1, lasting a total of 10 min, with photosynthesis, stomatal conductance and PSII fluorescence measured at the end of each half-cycle and also 10 min after the end of the cycling. Prior to the cyclic CO2 treatments, the steady-state responses of leaf gas exchange and fluorescence to CO2 were determined. In four of the five species, in which stomatal conductance decreased with increasing CO2, the cyclic CO2 treatments reduced stomatal conductance. In those species, both photosynthesis and the photochemical efficiency of PSII were reduced at limiting internal CO2 levels, but not at saturating CO2. In the fifth species, there was no change in stomatal conductance with CO2 and no change in either photosynthesis or PSII efficiency at any CO2 level with CO2 cycling. It is concluded that in many, but not all, species, fluctuations in CO2 may reduce photosynthesis at low CO2, partly by decreasing the photochemical efficiency of photosystem II as well as by decreasing stomatal conductance.

The Interactive Effects of Deficit Irrigation and Bacillus pumilus Inoculation on Growth and Physiology of Tomato Plant.

The effects of inoculating plant growth promoting rhizobacteria (PGPR) and soil water deficits on crop growth and physiology remain largely unknown. Here, the responses of leaf gas exchange, growth, and water use efficiency (WUE) of tomato plants to Bacillus pumilus (B.p.) inoculation under four irrigation strategies (I1-I4) were investigated in a greenhouse. Results showed that soil water deficits, especially at I4 (20%, v/v), significantly decreased leaf stomatal conductance (gs), transpiration rate (Tr), and photosynthetic rate (An), and the decrease of gs and Tr were more pronounced than An. Reduced irrigation regimes significantly lowered dry matter and plant water use both in the non-B.p. control and the B.p. plants, while reduced irrigation significantly increased plant WUE, and B.p. inoculation had little effect on this parameter. Synergistic effects of PGPR and deficit irrigation on leaf gas exchange, leaf abscisic acid content, and stomatal density were found in this study, and specifically, B.p. treated plants at I4 possessed the highest WUE at stomatal and leaf scales, suggesting that B.p. inoculation could optimize water use and partly alleviate the negative effects of soil water deficit. These findings provide useful information for effective irrigation management and the application of PGPR in agriculture in the future.

Leaf Gas Exchange and Growth Responses of Tomato Plants to External Flavonoids Application as Biostimulators under Normal and Salt-Stressed Conditions

The exogenous application of natural metabolites, such as phenolic compounds, is a useful strategy to stimulate growth and reduce the adverse effects of abiotic stress on crops, such as salinity. Salinity stress is one of the most damaging abiotic stresses to plants, causing reductions in growth by changes in the physiology, biochemistry, and gene expression. In this work, we investigated the effect of the foliar application of flavonoids (CropBioLife, CBL) on control and salt-stressed (NaCl 60 mM) tomato plants grown in controlled conditions. The results showed that CBL mainly influenced the stimulation of photosynthesis, increasing CO2 fixation and promoting growth. Furthermore, a higher stomata number in an open state was found in CBL-treated plants in relation to the higher CO2 fixation, which also resulted in a higher H2O uptake due to increasing stomatal conductance and nutrient uptake that plants need for growth. The results were due to the increase of phenolic metabolism and the expression of most of the aquaporins, which could be the triggering signal for the rest to the changes observed. The effect of the biostimulation of CBL under salinity was related to higher levels of photosynthesis, the increase of some mineral nutrients, and the increase of some PIP aquaporins expression, although no effect on growth was observed. The results of this work showing the mechanism of action of flavonoids in tomato plants open a new line of investigation with great importance for the future of agronomy.

Tree growth, wood anatomy and carbon and oxygen isotopes responses to drought in Mediterranean riparian forests

Mediterranean riparian forests have been altered by past use and are also negatively impacted by climate and hydrological droughts. However, we lack data on their historical changes in extent combined with multi-proxy, long-term assessments of tree growth and leaf gas exchange responses to climate, drought severity and river flow. These evaluations must also consider their current stand structure and the amount of lying deadwood which are proxies of river dynamics and forest maturity. To fill these research gaps, we studied four riparian tree species (Populus alba, Populus nigra, Fraxinus angustifolia and Ulmus minor) inhabiting a Mediterranean riparian forest located in north-eastern Spain. We quantified and analyzed: stand structure; lying deadwood; radial growth; relationships between growth, climate variables, the SPEI drought index and river flow; stable C (δ13C) and O (δ18O) isotopes in wood of P. alba, P. nigra and F. angustifolia; and earlywood anatomy in F. angustifolia. Mature sites were dominated by P. nigra and F. angustifolia and showed the highest amount of decayed lying deadwood. Radial growth was reduced by drought and low spring-summer river flow. We found the highest growth responses to 3- (P. nigra, r = 0.62; P. alba, r = 0.46) or 12-month SPEI (F. angustifolia, r = 0.54; U. minor, r = 0.53). The coordinated decrease in δ18O and intrinsic water-use efficiency (WUE) in P. alba and P. nigra could involve an increase in stomatal conductance rate. P. alba and P. nigra were more enriched in δ18O than F. angustifolia, suggesting the former used more enriched shallow groundwater in dry periods. The F. angustifolia WUE and P. nigra δ18O series were positively and negatively correlated with the SPEI, respectively. The F. angustifolia hydraulic diameter decreased in response to drought, whereas its vessel density and WUE were positively associated. Overall, P. nigra and F. angustifolia were the species most responsive to drought.

Elevated CO2 enhanced water use efficiency of wheat to progressive drought stress but not on maize.

Global rising atmospheric CO2 concentration ([CO2]) and drought stress exert profound influences on crop growth and yield. The objective of the present study was to investigate the responses of leaf gas exchange and plant water use efficiency (WUE) of wheat (C3) and maize (C4) plants to progressive drought stress under ambient (a[CO2], 400 ppm) and elevated (e[CO2], 800 ppm) atmospheric CO2 concentrations. The fraction of transpirable soil water (FTSW) was used to evaluate soil water status in the pots. Under non-drought stress, e[CO2] increased the net photosynthetic rate (An) solely in wheat, and dry matter accumulation (DMA), whereas it decreased stomatal conductance (g s) and water consumption (WC), resulting in enhanced WUE by 27.82% for maize and 49.86% for wheat. After onset of progressive soil drying, maize plants in e[CO2] showed lower FTSW thresholds than wheat, at which e.g. gs (0.31 vs 0.40) and leaf relative water content (0.21 vs 0.43) starts to decrease, indicating e[CO2] conferred a greater drought resistance in maize. Under the combination of e[CO2] and drought stress, enhanced WUE was solely found in wheat, which is mainly associated with increased DMA and unaffected WC. These varied responses of leaf gas exchange and WUE between the two species to combined drought and e[CO2] suggest that specific water management strategies should be developed to optimize crop WUE for different species in a future drier and CO2-enriched environment.

Carbon dioxide and light curves and leaf gas exchange responses to shade levels in bell pepper (Capsicum annuum L.)

Vegetable crops grown under shade nets typically show increased yield and quality. However, little is known about the photosynthetic responses at various CO2 and light levels under nets. This study aimed to determine carbon dioxide (A/Cc) and light (A/I) curves and leaf gas exchange response of bell pepper plants grown under nets at various shade levels. Experiments were conducted in the spring-summer of 2016 and 2018 in Tifton, Georgia (GA), USA, with five shade treatments [0 % (open field), 30 %, 47 %, 63 %, and 80 %]. The A/Cc curves revealed that plants grown at 30 % shade and in the open field had similar carboxylation, electron transport, and triose phosphate utilization rates. The A/I curves showed that gross and net photosynthesis were highest at 30 % shade. The 30 % shade had similar stomatal conductance, intercellular CO2, electron transport rate, and water use efficiency compared to the open field. The A/Cc and A/I curves and the leaf gas exchange parameters explained the intrinsic causes for the higher net photosynthesis at 30 % shade than in open-field bell pepper. The information from A/Cc-curves, A/I-curves, and leaf gas exchange is applicable in modeling photosynthesis and predicting primary productivity for C3 plants in elevated-CO2 and altered-light environments.

Leaf gas exchange, water status, and oil yield responses to rewatering after irrigation cut-off periods in a superintensive drip-irrigated olive (cv. Arbequina) orchard

Leaf gas exchange, water status, and oil yield responses to rewatering after irrigation cut-off periods in a superintensive drip-irrigated olive (cv. Arbequina) orchard

The response of ABA and hydraulic indicator-mediated leaf gas exchange and nonstructural carbohydrate of Ginkgo biloba saplings to drought and rehydration

The response of ABA and hydraulic indicator-mediated leaf gas exchange and nonstructural carbohydrate of Ginkgo biloba saplings to drought and rehydration

Elevated CO2 effect on the response of stomatal control and water use efficiency in amaranth and maize plants to progressive drought stress

Rising CO2 concentration ([CO2]) in the atmosphere may modulate the response of crop plants to drought stress. This study aimed to investigate the response of leaf gas exchange and plant growth of two C4 species representing both dicot (amaranth) and monocot (maize) to progressive drought under two different [CO2] (ambient (a[CO2], 400 ppm) and elevated (e[CO2], 800 ppm)). The soil water status in the pots was expressed as the fraction of transpirable soil water (FTSW). The results showed that as compared to a[CO2], e[CO2] significantly increased net photosynthetic rate (An) at non-stress condition (An max) for both species, while the increase was more pronounced in maize than in amaranth. Stomatal conductance (gs) at non-stress condition was significantly lower at e[CO2] in both species. The FTSW threshold, at which An starts to decrease, was higher in maize grown at e[CO2] than at a[CO2], whereas it was not affected in amaranth. In both species, gs decreased at higher FTSW threshold when grown at e[CO2] than at a[CO2]. e[CO2] decreased stomatal density (SD) in amaranth but increased it in maize; drought increased SD in amaranth but not in maize. Intrinsic water use efficiency (WUEi) was significantly enhanced by e[CO2] and drought stress at FTSW ranged from 0.0 to 0.6, particularly in maize. e[CO2] increased leaf area of well-watered plants in maize and decreased specific leaf area in amaranth. In amaranth, water consumption of well-watered plants was increased and plant WUE was decreased at e[CO2]. The varied responses of leaf gas exchange and WUE to soil water deficits and e[CO2] among the two C4 species imply their different mechanisms in stomatal control over carbon gain versus water loss in dicot and monocot plants, which is essentially important for selecting crop species and developing strategies to optimize crop WUE in a future drier and CO2-enriched climate. The more physiological and biochemical response from soil, stomatal to plant scale related to various environments would be considered in further investigation.