Decrease In Stomatal Conductance Research Articles

Assimilatory deficit and energy regulation in young Handroanthus chrysotrichus plants under flooding stress.

Flooding negatively influences the growth and development of several plant species. Here, we show that the flood tolerance of young Handroanthus chrysotrichus plants involves growth deficit, carbon assimilation reductions, starch remobilization, and energy regulation. The effect of hypoxia was evaluated in a controlled experiment consisting of plants subjected to normoxia and water-logging, with later recovery. We measured morphological changes, gas exchange, photosynthetic pigments, soluble carbohydrates and starch contents, the activity of the enzymes alcohol dehydrogenase (ADH), and pyruvate decarboxylase (PDC), and ATP and ADP levels. While control plants showed normal appearance and growth, flooded plants exhibited a drastic decrease in growth, necrosis of some root tips, hypertrophic lenticels on the stems, and foliar chlorosis. Oxygen deprivation in root cells led to a significant decrease in stomatal conductance. The low Amax rates caused a decline in foliar soluble sugar content at 20days and a subsequent increase in the leaves and roots, coinciding with starch degradation at 40days. We also observed increases of 220.5% in ADH and 292% in PDC activities in the roots at 20 and 40days of flooding. The activation of anaerobic metabolism in stressed plants was an essential mechanism for ATP regulation in both tissues used to maintain a minimal metabolism to cope with hypoxia to the detriment of growth. The post-stress recovery process in H. chrysotrichus occurred slowly, with gas exchange gradually resumed and anaerobic metabolism and sugar content maintained to improve energy regulation.

Ultraviolet radiation causes leaf warming due to partial stomatal closure.

Variation in solar ultraviolet radiation induces a wide-range of plant responses from the cellular to whole-plant scale. We demonstrate here for the first time that partial stomatal closure caused by ultraviolet radiation exposure results in significant increases in leaf temperature. Significant leaf warming in response to ultraviolet radiation was consistent in tomato (Solanum lycopersicum L.) across different experimental approaches. In field experiments where solar ultraviolet radiation was attenuated using filters, exposure to ultraviolet radiation significantly decreased stomatal conductance and increased leaf temperature by up to 1.5°C. Using fluorescent lamps to provide ultraviolet radiation treatments, smaller but significant increases in leaf temperature due to decreases in stomatal conductance occurred in both multi-day controlled environment growth room experiments and short-term (<2 hours) climate cabinet irradiance response experiments. We show that leaf warming due to partial stomatal closure is independent of any direct warming effects of ultraviolet radiation manipulations. We discuss the implications of ultraviolet radiation-induced warming both for horticultural crop production and understanding broader plant responses to ultraviolet radiation.

Response of Tropical Rainfall to Reduced Evapotranspiration Depends on Continental Extent

AbstractFuture projections of precipitation change over tropical land are often enhanced by vegetation responses to CO2 forcing in Earth system models. Projected decreases in rainfall over the Amazon basin and increases over the Maritime Continent are both stronger when plant physiological changes are modeled than if these changes are neglected, but the reasons for this amplification remain unclear. The responses of vegetation to increasing CO2 levels are complex and uncertain, including possible decreases in stomatal conductance and increases in leaf area index due to CO2 fertilization. Our results from an idealized atmospheric general circulation model show that the amplification of rainfall changes occurs even when we use a simplified vegetation parameterization based solely on CO2-driven decreases in stomatal conductance, indicating that this mechanism plays a key role in complex model projections. Based on simulations with rectangular continents we find that reducing terrestrial evaporation to zero with increasing CO2 notably leads to enhanced rainfall over a narrow island. Strong heating and ascent over the island trigger moisture advection from the surrounding ocean. In contrast, over larger continents rainfall depends on continental evaporation. Simulations with two rectangular continents representing South America and Africa reveal that the stronger decrease in rainfall over the Amazon basin seen in Earth system models is due to a combination of local and remote effects, which are fundamentally connected to South America’s size and its location with respect to Africa. The response of tropical rainfall to changes in evapotranspiration is thus connected to size and configuration of the continents.

High-frequency stable isotope signals in uneven-aged forests as proxy for physiological responses to climate in Central Europe.

Picea abies (L.) Karst. and Fagus sylvatica (L.) are important tree species in Europe, and the foreseen increase in temperature and vapour pressure deficit (VPD) could increase the vulnerability of these species. However, their physiological performance under climate change at temperate and productive sites is not yet fully understood, especially in uneven-aged stands. Therefore, we investigated tree-ring width and stable isotope chronologies (δ13C/δ18O) of these two species at 10 sites along a climate gradient in Central Europe. In these uneven-aged stands, we compared the year-to-year variability of dominant and suppressed trees for the last 80years in relation to the sites' spatial distribution and climate. δ18O and δ13C were generally consistent across sites and species, showing high sensitivity to summer VPD, whereas climate correlations with radial growth varied much more and depended on mean local climate. We found no significant differences between dominant and suppressed trees in the response of stable isotope ratios to climate variability, especially within the annual high-frequency signals. In addition, we observed a strikingly high coherence of the high-frequency δ18O variations across long distances with significant correlations above 1500km, whereas the spatial agreement of δ13C variations was weaker (~700km). We applied a dual-isotope approach that is based on known theoretical understanding of isotope fractionations to translate the observed changes into physiological components, mainly photosynthetic assimilation rate and stomatal conductance. When separating the chronologies in two time windows and investigating the shifts in isotopes ratios, a significant enrichment of either or both isotope ratios over the last decades can be observed. These results, translated by the dual-isotope approach, indicate a general climate-driven decrease in stomatal conductance. This improved understanding of the physiological mechanisms controlling the short-term variation of the isotopic signature will help to define the performance of these tree species under future climate.

Salinity Stress Affects Photosynthesis, Malondialdehyde Formation, and Proline Content in Portulaca oleracea L.

In this investigation, the effect of salt stress on Portulaca oleracea L. was monitored at salinity levels of 100 and 300 mM NaCl. At a concentration of 100 mM NaCl there was a decrease in stomatal conductance (gs) simultaneously with an increase in CO2 assimilation (A) at the beginning of salt exposure (day 3). However, the leaf water potential (ψw), the substomatal concentration of CO2 (Ci), the maximum quantum yield of photosystem II (Fv/Fm), and the proline and malondialdehyde (MDA) content remained unchanged. Exposure to 300 mM NaCl caused a decrease in gs from day 3 and a decrease in water potential, CO2 assimilation, and Fv/Fm from day 9. There was a large increase in proline content and a significantly higher MDA concentration on days 6 and 9 of salt stress compared to the control group. After 22 days of exposure to 300 mM NaCl, there was a transition from the C4 cycle to crassulacean acid metabolism (CAM), manifested by a rapid increase in substomatal CO2 concentration and negative CO2 assimilation values. These results document the tolerance of P. oleracea to a lower level of salt stress and the possibility of its use in saline localities.

In situ determination of guard cell ion flux underpins the mechanism of ABA-mediated stomatal closure in barley plants exposed to PEG-induced drought stress

ABA regulates stomatal movement by affecting ion transport in guard cells; yet in situ measurement of ABA-mediated dynamics of guard cell ion transport and the involvement of other phytohormones in regulating stomatal aperture under drought stress are still lacking. In this study, hydroponically grown plants of wild type barley Steptoe (WT) and its correspondent ABA-deficient barley mutant Az34 were treated with 10% polyethylene glycol (PEG) 6000 for 0, 2, 4, and 24 h or 9 d to mimic short- and long-term drought stress. The K+, H+ and Ca2+ fluxes in the guard cell were monitored in situ by noninvasive micro-test technology. Upon 10% PEG treatment, leaf ABA concentration ([ABA]leaf) of both barley genotypes increased dramatically after 2 h and reached the highest level after the 24 h. Compared to the control, a significant increase in Ca2+ influx in both genotypes was observed after 2 h exposure to PEG, and reached the largest value after 4 h in WT. The increase of [ABA]leaf coincided with the increase of K+ efflux and Ca2+ influx and the decrease of stomatal conductance in WT under short-term drought stress, though the concentrations of IAA, GA3 and ZR in WT were all increased at 4 h. K+ efflux of guard cells was significantly greater in WT than in Az34 at 24 h after PEG treatment. The results elucidate the role of ABA in mediating ion transports in guard cells, hereby regulating the stomatal movement in barley exposed to drought stress.

Minimizing VPD Fluctuations Maintains Higher Stomatal Conductance and Photosynthesis, Resulting in Improvement of Plant Growth in Lettuce.

Vapor pressure deficit (VPD) is considered to be one of the major environmental factors influencing stomatal functions and photosynthesis, as well as plant growth in crop and horticultural plants. In the greenhouse cultivation, air temperature and relative air humidity are regulated by switching on/off the evaporative systems and opening/closing the roof windows, which causes VPD fluctuation. However, it remains unclear how VPD fluctuation affects photosynthetic and growth performance in plants. Here, we examined the effects of the VPD fluctuation on the photosynthetic and growth characteristics in lettuce (Lactuca sativa L.). The parameters for gas exchange and chlorophyll fluorescence and biomass production were evaluated under the conditions of drastic (1.63 kPa for 6 min and 0.63 for 3 min) or moderate (1.32 kPa for 7 min and 0.86 kPa for 3 min) VPD fluctuation. The drastic VPD fluctuation induced gradual decrease in stomatal conductance and thus CO2 assimilation rate during the measurements, while moderate VPD fluctuation caused no reduction of these parameters. Furthermore, data showed moderate VPD fluctuation maintained leaf expansion and the efficiency of CO2 diffusion across leaf surface, resulting in enhanced plant growth compared with drastic VPD fluctuation. Taken together, fine regulation of VPD can be crucial for better plant growth by maintaining the photosynthetic performance in lettuce. The present work demonstrates the importance of VPD control during plant cultivation in plant factories and greenhouses.

Bromoacetic acid inhibits pyruvate orthophosphate dikinase and reduces photosynthetic activity in maize

Pyruvate orthophosphate dikinase (PPDK) catalyzes the conversion of pyruvate to phosphoenolpyruvate, and its activity is essential to maintain photosynthetic CO2 assimilation in C4 plants. Thus, it has been described as a promising target for the development of selective herbicides for C4 weeds. We evaluated whether bromoacetic acid, a known PPDK inhibitor of Clostridium symbiosum, can also inhibit the PPDK of a C4 plant, maize, in in vitro experiments. We also evaluated the effects of foliar application of 0.5–10 mM bromoacetic acid on the leaf pyruvate content and gas exchange of maize plants. Bromoacetic acid reduced maize PPDK activity in vitro in a dose-dependent manner; the degree of inhibition ranged from 13.6 to 73.6% with 0.5–10 mM bromoacetic acid. The foliar application of bromoacetic acid increased the leaf pyruvate content, suggesting that this compound may also inhibit PPDK activity in vivo. As a consequence, impairments to the gas exchange parameters of maize plants were noted, with a marked reduction in the photosynthetic rate and an increase in the intercellular CO2 concentration. Despite the abrupt decrease in stomatal conductance and transpiration, the plants showed large dehydration and reduction of leaf fresh weight after 48 h of application to bromoacetic acid. Our data allow us to affirm that bromoacetic acid has a potent herbicidal effect on a C4 plant, maize; the most likely mechanism of action is the inhibition of PPDK.

Mechanisms of specific systemic response in wheat plants under different locally acting heat stimuli

Mechanisms of the specific systemic response of plant to different adverse factors are poorly understood. We studied the mechanisms acting in wheat (Triticum aestivum L.) under the action of local burn and gradual heating. Both stimuli induce a variation potential (VP) propagation and a biphasic (fast and long-term phases) photosynthetic response in non-stimulated zones of plant with stimulus-specific parameters of the latter: the fast phase or long-term phase predominance in responses induced by burn or heating, respectively. The burn-induced VP and photosynthetic response attenuate with distance, while the heating-induced VP and photosynthetic response were of more stable amplitude in distant part of the stimulated plant. VP propagation in both cases induced apoplast alkalization with dynamics well corresponding to such of VP and of the fast phase of photosynthetic response. Gradual heating induced a significant rise in jasmonate production along with a decrease in stomatal conductance with characteristic times well corresponding to the long-term phase of the photosynthetic response. We suppose that the VP-induced pH shift is responsible for in the induction of the fast phase, while jasmonate production for the long-term phase of the photosynthetic response. The revealed differences in the systemic response to stressors studied, apparently, reflect two distinct plant adaptation strategies to fast and slow-growing stimuli. The immediate response in the tissue nearest to the damage zone is the most important under a fast-growing stimulus. The fundamentally different situation is under a slowly-growing stimulus which provokes long-term changes in the plant that ensure the preparation of the whole organism for impending environmental changes.

Study on Growth Characteristics of Some Brassica Species under Moisture Stress and Elevated Carbondioxide

Brassica juncea and Brassica campestries is two important oil seed crop of North-West India experiences intermittent moisture stress during its growing period. Thus a study was carried out to ameliorate the moisture stress through elevated CO2 applying Free Air CO2 Enrichment (FACE) technology. The consequences of CO2 enrichment were related to the rate of accelerated photosynthesis under both irrigated and moisture stress situation with significant decreases in stomatal conductance. The elevated CO2 brought about a significant enhancement in all the plant growth parameters studied, and also ameliorates the of moisture stress. The carbon dioxide enrichment improves the productivity of Brassica cultivars viz. ‘Pusa Gold’ and ‘RH-30’ through changes in various yield attributes and also nullifying the adverse effect of moisture stress.

Assessing suitability of Andrographis paniculata genotypes for rain-fed conditions in semi-arid climates

Medicinal plants are generally suggested for degraded land or areas having low rain-fall. Andrographis paniculata is an important medicinal plant known for its diterpene lactone i.e. andrographolide. We exposed 26 genotypes of A. paniculata to rain-fed condition during early-season rain-fed (ESRF) and mid-season rain-fed (MSRF) conditions and compared with the control to assess their suitability in semi-arid climate region of Gujarat, India. The study was performed during two consecutive years 2016–2017 in split plot design with rain-fed conditions as main-plot treatment and genotypes as sub-plot treatment in three replications. The gaseous exchange parameters taken at 85∼100 days after transplanting exhibited mean photosynthesis rate was 20.5 μmol CO2 m−2 s−1 ranging between 15.9 μmol CO2 m−2 s−1 and 24.0 μmol CO2 m−2 s−1. Exceeding 7% decrease in stomatal conductance was recorded compared to the control plants under imposed rain-fed condition. The mean value of transpiration rate was 4.8 mmol H2O m−2 s−1. The mean value of water use efficiency was 4.6. MSRF condition decreased leaf water potential from −0.517 to −1.189 Mpa. The dry herbage decreased by 29.2% due to MSRF condition as compared the control. The andrographolide yield per plant suffered significantly and under ESRF condition it reduced mainly due to reduction in andrographolide content. Reduced andrographolide yield per plant in MSRF condition was mainly due to reduction in herbage yield. Results revealed that ESRF and MSRF condition characterized by erratic rainfall pattern and dry spell is not beneficial for quality production in A. paniculata. Based on the least decrease in andrographolide, yield two genotypes viz., AP 6 and AP 12 identified to be suitable for ESRF condition and two genotypes viz., AP 19 and AP 6 suitable for MSRF condition. Overall, four genotypes, AP 35, AP 39, AP 61 and AP 24 were suitable as the promising genotypes having high andrographolide yield.

Effects of Postharvest Water Deficits on the Physiological Behavior of Early-Maturing Nectarine Trees.

The physiological performance of early-maturing nectarine trees in response to water deficits was studied during the postharvest period. Two deficit irrigation treatments were applied, moderate and severe, and these were compared with a control treatment (fully irrigated). Stem water potential and leaf gas exchange (net CO2 assimilation rate, ACO2; transpiration rate, E; and stomatal conductance, gs) were measured frequently. Drought avoidance mechanisms included a decrease in stomatal conductance, especially in the case of the severe deficit treatment, which also showed a strong dependence of ACO2 on gs. Intrinsic water-use efficiency (ACO2/gs) was more sensitive than instantaneous water-use efficiency (ACO2/E) as an indicator to detect water deficit situations in nectarine trees. However, in contrast to the results obtained for other deciduous fruit trees, a poor correlation was found between ACO2/E and ACO2/gs, despite the important relation between E and gs. ACO2/E was also weakly correlated with gs, although this relationship clearly improved when the vapor pressure deficit (VPD) was included, along with gs as the independent variable. This fact reveals that apart from stomatal closure, E depends on the boundary layer conductance (gb), which is mediated by VPD through changes in wind speed. This suggests low values of the decoupling coefficient for this water-resilient species.

Foliar Concentrations of Selected Elements, Assessment of Oxidative Stress Markers and Role of Antioxidant Defense System is Associated with Fly Ash Stress Tolerance in Withania somnifera

Increased dependence on thermal power has resulted in a significant increase in the generation of fly ash (FA), which exacerbates environmental pollution. In order to mitigate this source of pollution, we propose covering FA dumps with a layer of planted vegetation. Due to varying degrees of tolerance and their sessile nature, plants are themselves susceptible to stress from pollution. This suggests that an investigation to assess the role of wild growing plants for management of FA dumps, where selected wild plants could be grown to mitigate consequences of FA. The present study assesses oxidative damage and the foliar concentration of metals in Withania somnifera growing wild at the Badarpur Thermal Power Plant (BTPP) compared to those growing at a control site. Plants growing at the BTPP showed significantly higher foliar concentrations of Pb, Mn, and Fe, and low concentrations of Ni and Cd. The plants at the BTPP site showed signs of oxidative stress as indicated by enhanced levels of malondialdehyde and electrolyte leakage from cells. The CO2 assimilation rate, net photosynthetic rate, rate of transpiration, stomatal conductance decrease, while water use efficiency, and air pollution tolerance index increase. Among air pollution tolerance index parameters, relative water content showed a significant increase with FA pollution stress at the BTPP. A significant decrease was observed in leaf morphology single leaf area, leaf length, and leaf width and biochemical parameters (Chlorophyll a, Chlorophyll b, total chlorophyll, and carotenoids. Moreover, FA pollution stress induces oxidative stress in W. somnifera through a significant and enhanced production of reactive oxygen species (ROS). According to our observations, the ability of W. somnifera to effectively coordinate superoxide dismutase, ascorbate peroxidase, and glutathione reductase activities involved in the scavenging of ROS along with the enhanced increment of nonenzyme activities (total ascorbic acid, proline, and oxidized glutathione) could be related to FA stress tolerance in W. somnifera.

Aluminum-induced stomatal closure is related to low root hydraulic conductance and high ABA accumulation

Many studies ask how aluminum (Al) reduces the root growth, but as Al is mostly retained in the root system, physiological explanations for the also expected Al-induced decrease in stomatal conductance (gs) are unclear, mainly in well-watered conditions. We exposed tomato plants (Solanum lycopersicum) to 0, 25, 50 and 100 μM Al in nutrient solution to investigate whether Al impairs root hydraulic conductance (Lpr), affecting leaf water potential (Ψleaf) and possibly inducing abscisic acid (ABA) accumulation in roots and/or leaves. We also measured ABA delivery rate, xylem sap pH and the root/leaf area ratio in order to explain the low gs in plants exposed to Al. Declines in Lpr and gs were proportional to the increase in Al concentration, and all Al treatments similarly decreased Ψleaf, indicating the plant’s attempt to reduce water loss through transpiration while accumulating more ABA. Despite Al-induced increases in root ABA, the root-to-shoot delivery of ABA did not enhance, but Al caused root xylem sap alkalization. Despite the stability of root/leaf area ratio across a range of Al concentrations (0, 25 and 50 μM Al), the leaf hydration and stomatal opening was not conserved. Here we provide the first evidence that decreases in Lpr and increases in ABA might explain Al-induced stomatal closure.

Varying responses to combined water-stress and herbivory in maize for spider mite species that differ in host specialization

Water-stress commonly affects crops grown in arid and semi-arid regions. Apart from the direct impact of this abiotic stress on yield, a diverse community of herbivores can outbreak under these conditions, and plant responses to abiotic stress may alter plant defense responses that deter herbivores. Outbreaks of both generalist and specialist spider mites are strongly associated with hot and dry conditions in the field settings. To understand how water-stress impacts maize responses to spider mites, we conducted parallel greenhouse and field experiments with maize plants (B73 inbred line) subjected to optimal irrigation and water-stress conditions (50-60% and 5-10% volumetric water content (VWC), and 25-32% and 10-15% VWC, in the greenhouse and field, respectively). In addition to recording B73 responses to water-stress alone, we measured the population growth of the generalist twospotted spider mite (Tetranychus urticae, TSM) and the specialist Banks grass mite (Oligonychus pratensis, BGM) on optimally watered and water-stressed plants. We also measured plant defense protein activities (peroxidase (POD), polyphenol oxidase (PPO), chitinase (CHI) and trypsin inhibitor (TI)) at 1, 3, and 7 days post mite introduction for each irrigation treatment. For B73 plants exposed to water-stress, we observed increases in leaf temperature, leaf water potential, POD activity, as well as decreases in stomatal conductance and stem height. Populations of both mite species increased more rapidly on water-stressed B73 plants. While optimally irrigated B73 plants responded with similar plant defense activity to both mite species, combinations of plant water-stress and TSM herbivory resulted in increases in CHI and TI activity that were not observed for the respective treatments with BGM. Collectively, our results highlight a role for species-specific factors, possibly associated with herbivore host plant breadth, in impacting plant responses to herbivory in combination with an abiotic stress.

(Z)-3-Hexen-1-ol accumulation enhances hyperosmotic stress tolerance in Camellia sinensis.

Volatile components in fresh leaves are involved in the regulation of many stress responses, such as insect damage, fungal infection and high temperature. However, the potential function of volatile components in hyperosmotic response is largely unknown. Here, we found that 7-day hyperosmotic treatment specifically led to the accumulation of (Z)-3-hexen-1-ol, (E)-2-hexenal and methyl salicylate. Transcriptome and qRT-PCR analyses suggested the activation of linolenic acid degradation and methyl salicylate processes. Importantly, exogenous (Z)-3-hexen-1-ol pretreatment dramatically enhanced the hyperosmotic stress tolerance of tea plants and decreased stomatal conductance, whereas (E)-2-hexenal and methyl salicylate pretreatments did not exhibit such a function. qRT-PCR analysis revealed that exogenous ABA induced the expressions of related enzyme genes, and (Z)-3-hexen-1-ol could up-regulate the expressions of many DREB and RD genes. Moreover, exogenous (Z)-3-hexen-1-ol tremendously induced the expressions of specific LOX and ADH genes within 24h. Taken together, hyperosmotic stress induced (Z)-3-hexen-1-ol accumulation in tea plant via the activation of most LOX, HPL and ADH genes, while (Z)-3-hexen-1-ol could dramatically enhance the hyperosmotic stress tolerance via the decrease of stomatal conductance and MDA, accumulation of ABA and proline, activation of DREB and RD gene expressions, and probably positive feedback regulation of LOXs and ADHs. KEY MESSAGE: Hyperosmotic stress induced (Z)-3-hexen-1-ol accumulation in Camellia sinensis via the up-regulation of most LOX, HPL and ADH genes, while (Z)-3-hexen-1-ol could dramatically enhance the hyperosmotic stress tolerance via the decrease of stomatal conductance, accumulation of proline, activation of DREB and RD gene expressions, and probably positive feedback regulation of LOXs and ADHs.

Dry matter production and physiological responses to a wide range of irrigation levels in two Japanese soybean cultivars

ABSTRACT Two pot experiments were conducted to compare dry matter production and physiological responses to a wide range of irrigation levels (100% of field capacity (control: iC), 80% (i8), 60% (i6), 40% (i4), and 20% (i2) of irrigation for iC) from the beginning of the bloom stage to the full seed stage of two Japanese determinate soybean cultivars, Hatsusayaka and Sachiyutaka. The phenological stages of both cultivars were delayed correspondingly with the reduction in irrigation levels. Seed yield and total dry matter (TDM) decreased correspondingly with the reduction in irrigation, with some exceptions in which maximum results were achieved with i8 rather than iC for some traits, though the differences between i8 and iC were not significant. The proportional decrease in TDM in line with irrigation levels was due to the decrease in photosynthesis rate (Pn), and the decrease in Pn was closely related to the decrease in stomatal conductance. The response of grain yield to irrigation levels was approximated by a linear-plateau model, which indicated that these traits increased proportionally with the amount of irrigation up to a certain level, and after that, it reached a threshold. Our results showed that Hatsusayaka had higher leaf water potential and TDM than Sachiyutaka in some irrigation levels, but no evidence was found which indicates a significant difference on drought tolerance between Hatsusayaka and Sachiyutaka.

Influences of Saccharomyces cerevisiae on gas exchange and water-use efficiency in Vicia faba L.

To examine the hypothesis that microbes can function as antitranspirants regulating stomatal behavior, we studied the effect of Saccharomyces cerevisiae strain BY4741 on gas exchange and water-use efficiency (WUE) in Vicia faba L. Stomatal aperture and photosynthetic parameters were analyzed every day for 7 days after treatment. In the present study, spraying yeast decreased the stomatal aperture. On the 4th, 5th, 6th, and 7th days after the foliar application of yeast, a decreased in net photosynthetic rate (Pn) was observed. This decrease was accompanied with decreases in stomatal conductance (gs), intercellular CO2 concentration (Ci), and transpiration (Tr). The carboxylation efficiency (CE) was reduced by yeast on the 1st day after treatment. On the 1st, 2nd, and 3rd days of treatment, the yeast dramatically decreased the maximum photochemical efficiency of photosystem (PS) II (Fv/Fm) and increased non-photochemical quenching (NPQ); however, these parameters eventually recovered to their normal levels. The marked decrease of qP was observed on the 1st and 2nd days after yeast treatment. At the beginning of the treatment, the yeast decreased electron the transport rate (ETR), but later increased it. Both concentrations of yeast (1×106 and 1×1010 CFU mL−1) increased the WUE on the 4th, 5th, 6th, and 7th days of treatments. At the concentrations of 1×106 CFU mL−1, yeast acted as a more effective antitranspirant, showing higher WUE, than at the concentration of 1 × 1010 CFU mL−1. Pn was positively correlated with Tr and gs on the 7th day of the treatment. Moreover, Tr was much more sensitive to yeast than was Pn. In general, the foliar application of yeast resulted in decreased Tr and increased WUE. The yeast-induced decrease in photosynthesis is mainly caused by stomatal closure, suggesting that yeast can be used as an antitranspirant or a priming agent for improving drought tolerance in plants.

Interactive Effects of the CO2 Enrichment and Nitrogen Supply on the Biomass Accumulation, Gas Exchange Properties, and Mineral Elements Concentrations in Cucumber Plants at Different Growth Stages

The concentration changes of mineral elements in plants at different CO2 concentrations ([CO2]) and nitrogen (N) supplies and the mechanisms which control such changes are not clear. Hydroponic trials on cucumber plants with three [CO2] (400, 625, and 1200 μmol mol−1) and five N supply levels (2, 4, 7, 14, and 21 mmol L−1) were conducted. When plants were in high N supply, the increase in total biomass by elevated [CO2] was 51.7% and 70.1% at the seedling and initial fruiting stages, respectively. An increase in net photosynthetic rate (Pn) by more than 60%, a decrease in stomatal conductance (Gs) by 21.2–27.7%, and a decrease in transpiration rate (Tr) by 22.9–31.9% under elevated [CO2] were also observed. High N supplies could further improve the Pn and offset the decrease of Gs and Tr by elevated [CO2]. According to the mineral concentrations and the correlation results, we concluded the main factors affecting these changes. The dilution effect was the main factor driving the reduction of all mineral elements, whereas Tr also had a great impact on the decrease of [N], [K], [Ca], and [Mg] except [P]. In addition, the demand changes of N, Ca, and Mg influenced the corresponding element concentrations in cucumber plants.

Effect of water deficit on some physiological and biochemical responses of the yellow diploid potato (Solanum tuberosum L. Group Phureja)

Water availability is one of the main limitations of potato yields due to the high sensitivity of this crop to water deficit. The objective of this study was to determine the effect of water deficit on some physiological and biochemical responses in yellow diploid potato plants (Solanum tuberosum L. Group Phureja) of the cultivars Criolla Colombia, Criolla Dorada and Criolla Ocarina. Plants at tuber initiation were subjected to two treatments: continuous irrigation and water deficit imposed by withholding water at tuber initiation for 17 d. The results showed that plants under water deficit increased chlorophyll concentration, malondialdehyde and proline content. However, these plants showed a decrease in stomatal conductance, leafarea, total dry mass and exhibited a higher root/shoot ratio in all potato cultivars. In addition, all the cultivars also showed a decrease in yield, which was associated with sensitivity to water stress. Although the high content of proline and high root/shoot ratio may be associated with tolerance to water deficit, this association was not observed in these cultivars, probably due to the high reduction of stomatal conductance, which limited the production of photoassimilates, plant growth, and,therefore, the yield.