Incorporating photosynthetic acclimation improves stomatal optimisation models.

Stomatal opening in plant leaves is regulated through a balance of carbon and water exchange under different environmental conditions. Accurate estimation of stomatal regulation is crucial for understanding how plants respond to changing environmental conditions, particularly under climate change. A new generation of optimality-based modelling schemes determines instantaneous stomatal responses from a balance of trade-offs between carbon gains and hydraulic costs, but most such schemes do not account for biochemical acclimation in response to drought. Here, we compare the performance of six instantaneous stomatal optimisation models with and without accounting for photosynthetic acclimation. Using experimental data from 37 plant species, we found that accounting for photosynthetic acclimation improves the prediction of carbon assimilation in a majority of the tested models. Photosynthetic acclimation contributed significantly to the reduction of photosynthesis under drought conditions in all tested models. Drought effects on photosynthesis could not accurately be explained by the hydraulic impairment functions embedded in the stomatal models alone, indicating that photosynthetic acclimation must be considered to improve estimates of carbon assimilation during drought.

A new empirical framework to quantify the hydraulic effects of soil and atmospheric drivers on plant water status.

Metrics to quantify regulation of plant water status at the daily as opposed to the seasonal scale do not presently exist. This gap is significant since plants are hypothesised to regulate their water potential not only with respect to slowly changing soil drought but also with respect to faster changes in air vapour pressure deficit (VPD), a variable whose importance for plant physiology is expected to grow because of higher temperatures in the coming decades. We present a metric, the stringency of water potential regulation, that can be employed at the daily scale and quantifies the effects exerted on plants by the separate and combined effect of soil and atmospheric drought. We test our theory using datasets from two experiments where air temperature and VPD were experimentally manipulated. In contrast to existing metrics based on soil drought that can only be applied at the seasonal scale, our metric successfully detects the impact of atmospheric warming on the regulation of plant water status. We show that the thermodynamic effect of VPD on plant water status can be isolated and compared against that exerted by soil drought and the covariation between VPD and soil drought. Furthermore, in three of three cases, VPD accounted for more than 5 MPa of potential effect on leaf water potential. We explore the significance of our findings in the context of potential future applications of this metric from plant to ecosystem scale.

The role of invasive plant species in drought resilience in agriculture: the case of sweet briar (Rosa rubiginosa L.).

Sweet briar (Rosa rubiginosa) belongs to the group of wild roses. Under natural conditions it grows throughout Europe, and was introduced also into the southern hemisphere, where it has efficiently adapted to dry lands. This review focuses on the high adaptation potential of sweet briar to soil drought in the context of global climatic changes, especially considering steppe formation and desertification of agricultural, orchard, and horticultural areas. We provide a comprehensive overview of current knowledge on sweet briar traits associated with drought tolerance and particularly water use efficiency, sugar accumulation, accumulation of CO2 in intercellular spaces, stomatal conductance, gibberellin level, effective electron transport between photosystem II and photosystem I, and protein content. We discuss the genetics and potential applications in plant breeding and suggest future directions of study concerning invasive populations of R. rubiginosa. Finally, we point out that sweet briar can provide new genes for breeding in the context of depleting gene pools of the crop plants.

Compound droughts slow down the greening of the Earth.

Vegetation response to soil and atmospheric drought has raised extensively controversy, however, the relative contributions of soil drought, atmospheric drought, and their compound droughts on global vegetation growth remain unclear. Combining the changes in soil moisture (SM), vapor pressure deficit (VPD), and vegetation growth (normalized difference vegetation index [NDVI]) during 1982-2015, here we evaluated the trends of these three drought types and quantified their impacts on global NDVI. We found that global VPD has increased 0.22 ± 0.05 kPa·decade-1 during 1982-2015, and this trend was doubled after 1996 (0.32 ± 0.16 kPa·decade-1 ) than before 1996 (0.16 ± 0.15 kPa·decade-1 ). Regions with large increase in VPD trend generally accompanied with decreasing trend in SM, leading to a widespread increasing trend in compound droughts across 37.62% land areas. We further found compound droughts dominated the vegetation browning since late 1990s, contributing to a declined NDVI of 64.56%. Earth system models agree with the dominant role of compound droughts on vegetation growth, but their negative magnitudes are considerably underestimated, with half of the observed results (34.48%). Our results provided the evidence of compound droughts-induced global vegetation browning, highlighting the importance of correctly simulating the ecosystem-scale response to the under-appreciated exposure to compound droughts as it will increase with climate change.

A light-induced decrease in the photochemical reflectance index (PRI) can be used to estimate the energy-dependent component of non-photochemical quenching under heat stress and soil drought in pea, wheat, and pumpkin.

The remote sensing of a plant's physiological state is a key problem of precision agriculture. The photochemical reflectance index (PRI), which is based on the intensities of the reflected light at 531 and 570 nm, is an important tool for the remote sensing of photosynthetic processes in plants. In particular, the PRI can be strongly connected with the non-photochemical quenching of chlorophyll fluorescence (NPQ) and the quantum yield of photosystem II (ФPSII); however, this connection is dependent on illumination, the intensity of stressor actions, the time scale of measurements, etc. The aim of the present work was to analyze the connection of PRI with the energy-dependent component of NPQ (NPQF) and ФPSII under heating and soil drought conditions. Pea, wheat, and pumpkin seedlings, which were grown under controlled conditions, were investigated. A PAM fluorometer Dual-PAM-100 and spectrometer S-100 were used for measurements of photosynthetic parameters and PRI, respectively. It was shown that heat stress increased the NPQF and the magnitude of light-induced changes in PRI (ΔPRI) and decreased ФPSII in pea seedlings. The decreased ФPSII and increased ΔPRI were observed in wheat after heating, but significant changes in NPQF were absent; the significant decrease in ФPSII was observed in pumpkin seedlings, while there were no significant changes in the other parameters. ΔPRI and NPQF after heating were significantly correlated. However, a significant correlation of the absolute values of PRI with photosynthetic parameters was absent. The soil drought increased NPQF and the magnitude of ΔPRI and decreased ФPSII in peas. ΔPRI was strongly correlated with photosynthetic parameters, but this correlation was absent for the absolute value of PRI. Thus, ΔPRI is strongly connected with the magnitude of NPQF and can be used as an estimator of this parameter.

Animal wastes as fertilizers enhance growth of young walnut trees under soil drought conditions.

BACKGROUND: Using nutrient-rich animal wastes as organic fertilizers in agricultural practices is a sustainable method for soil amendment and avoiding environmental pollution. In order to evaluate their practical effect, we applied different proportions of animal waste as fertilizers to wet or dry soils that were either planted or not planted with young walnut trees. RESULTS: The results showed that animal waste could increase soil C accumulation and carbon to nitrogen (C/N) ratio and reduce soil organic nitrogen and total nitrogen contents as well as the nitrogen to phosphorus (N/P) ratio in the planted group soil. This framework of soil C and N composition (a high C/N ratio) resulted in high N and Mg contents as well as high Cu and Zn contents in the leaves of the young trees as well as a high dry matter weight/leaf N ratio, causing increased leaf photosynthesis, reduced transpiration and relatively high water use efficiency under soil drought conditions. Also, animal wastes as fertilizers caused the branching of walnut to switch from elongation growth to thickening growth under soil drought conditions. CONCLUSIONS: Principal component analysis and redundancy analysis demonstrated the mechanism by which the soil C/N ratio mediates the flux of available nutrients from the soil to the plant and thereby regulates plant dry matter accumulation and branching architecture under soil drought conditions. The results of this study provide new insights into the improvement of hilly soils using animal waste. © 2020 Society of Chemical Industry.

Exogenous 2-(3,4-Dichlorophenoxy) triethylamine ameliorates the soil drought effect on nitrogen metabolism in maize during the pre-female inflorescence emergence stage.

BACKGROUND: Nitrogen (N) metabolism plays an important role in plant drought tolerance. 2-(3,4-Dichlorophenoxy) triethylamine (DCPTA) regulates many aspects of plant development; however, the effects of DCPTA on soil drought tolerance are poorly understood, and the possible role of DCPTA on nitrogen metabolism has not yet been explored. RESULTS: In the present study, the effects of DCPTA on N metabolism in maize (Zea mays L.) under soil drought and rewatering conditions during the pre-female inflorescence emergence stage were investigated in 2016 and 2017. The results demonstrated that the foliar application of DCPTA (25 mg/L) significantly alleviated drought-induced decreases in maize yield, shoot and root relative growth rate (RGR), leaf relative water content (RWC), net photosynthetic rate (Pn), stomatal conductance (Gs) and transpiration rate (Tr), and nitrate (NO3-), nitrite (NO2-), soluble protein contents, and nitrate reductase (NR), nitrite reductase (NiR), isocitrate dehydrogenase (ICDH), alanine aminotransferase (AlaAT) and aspartate aminotransferase (AspAT) activities. In addition, the foliar application of DCPTA suppressed the increases of intercellular CO2 concentration (Ci), ammonium (NH4+) and free amino acid contents, and the glutamate dehydrogenase (GDH) and protease activities of the maize. Simultaneously, under drought conditions, the DCPTA application improved the spatial and temporal distribution of roots, increased the root hydraulic conductivity (Lp), flow rate of root-bleeding sap and NO3- delivery rates of the maize. Moreover, the DCPTA application protected the chloroplast structure from drought injury. CONCLUSIONS: The data show, exogenous DCPTA mitigates the repressive effects of drought on N metabolism by maintained a stabilized supply of 2-oxoglutarate (2-OG) and reducing equivalents provided by photosynthesis via favorable leaf water status and chloroplast structure, and NO3- uptake and long-distance transportation from the roots to the leaves via the production of excess roots, as a result, DCPTA application enhances drought tolerance during the pre-female inflorescence emergence stage of maize.

Transcriptome Analysis Reveals Drought-Responsive Pathways and Key Genes of Two Oat (Avena sativa) Varieties.

To cope with the yield loss caused by drought stress, new oat varieties with greater drought tolerance need to be selected. In this study, two oat varieties with different drought tolerances were selected for analysis of their phenotypes and physiological indices under moderate and severe soil drought stress. The results revealed significant differences in the degree of wilting, leaf relative water content (RWC), and SOD and CAT activity between the two oat genotypes under severe soil drought stress; moreover, the drought-tolerant variety exhibited a significant increase in the number of stomata and wax crystals on the surface of both the leaf and guard cells; additionally, the morphology of the guard cells was normal, and there was no significant disruption of the grana lamella membrane or the nuclear envelope. Furthermore, transcriptome analysis revealed that the expression of genes related to the biosynthesis of waxes and cell-wall components, as well as those of the WRKY family, significantly increased in the drought-tolerant variety. These findings suggest that several genes involved in the antioxidant pathway could improve drought tolerance in plants by regulating the increase/decrease in wax and cell-wall constituents and maintaining normal cellular water potential, as well as improving the ability of the antioxidant system to scavenge peroxides in oats.

Trigger thresholds and their dynamics of vegetation production loss under different atmospheric and soil drought conditions.

Many evidences have shown that both atmospheric and soil droughts can constrain vegetation growth and further threaten its ability to sequester carbon. However, the trigger thresholds of vegetation production loss under different atmospheric and soil drought conditions are still unknown. In this study, we proposed a Copula and Bayesian equations-based framework to investigate trigger thresholds of various vegetation production losses under different atmospheric and soil drought conditions. The trigger thresholds dynamics and their possible causes were also investigated. To achieve this goal, we first simulated the gross primary production, soil moisture, and vapor pressure deficit over China during 1961-2018 using an individual-based, spatially explicit dynamic global vegetation model. The main drivers of the dynamic change in trigger thresholds were then explored by Random Forest model. We found that soil drought caused greater stress on gross primary production loss than atmospheric drought, with a larger impact area and higher probability of damage. In terms of spatial distribution, the risk probability of gross primary production loss was higher in eastern China than in western China, and the drought trigger threshold was also smaller in eastern China. In addition, the trigger thresholds for atmospheric and soil drought in most regions exhibited a decreasing trend from 1961 to 2018, while the CO2 fertilization enhanced the drought tolerance of vegetation. The reduction in CO2 fertilization effect slowed down the downward trend of trigger threshold for soil drought, while the increase in temperature exacerbated the downward trend of trigger threshold for atmospheric drought. This study highlighted the larger effect of soil drought on vegetation production loss than atmospheric drought and implied that climate change can modulate the trigger threshold of vegetation production losses under drought conditions. These findings provide scientific guidance for managing the increasing risk of drought on vegetation and optimizing watershed water allocation.

Structural and Functional Shifts in the Microbial Community of a Heavy Metal-Contaminated Soil Exposed to Short-Term Changes in Air Temperature, Soil Moisture and UV Radiation.

The interplay between metal contamination and climate change may exacerbate the negative impact on the soil microbiome and, consequently, on soil health and ecosystem services. We assessed the response of the microbial community of a heavy metal-contaminated soil when exposed to short-term (48 h) variations in air temperature, soil humidity or ultraviolet (UV) radiation in the absence and presence of Enchytraeus crypticus (soil invertebrate). Each of the climate scenarios simulated significantly altered at least one of the microbial parameters measured. Irrespective of the presence or absence of invertebrates, the effects were particularly marked upon exposure to increased air temperature and alterations in soil moisture levels (drought and flood scenarios). The observed effects can be partly explained by significant alterations in soil properties such as pH, dissolved organic carbon, and water-extractable heavy metals, which were observed for all scenarios in comparison to standard conditions. The occurrence of invertebrates mitigated some of the impacts observed on the soil microbial community, particularly in bacterial abundance, richness, diversity, and metabolic activity. Our findings emphasize the importance of considering the interplay between climate change, anthropogenic pressures, and soil biotic components to assess the impact of climate change on terrestrial ecosystems and to develop and implement effective management strategies.

Effects of soil drought on cottonseed kernel carbohydrate metabolism and kernel biomass accumulation.

Cottonseed is the main coproduct of cotton production. The carbohydrate metabolism provides carbon substrate for the accumulation of cottonseed kernel biomass which was the basis of cottonseed kernel development. However, the responses of drought stress on carbohydrate metabolism in kernels are still unclear. To address this, two cotton cultivars (Dexiamian 1 and Yuzaomian 9110) were cultivated under three water treatments including soil relative water content (SRWC) at (75 ± 5)% (control), (60 ± 5)% (mild drought) and (45 ± 5)% (severe drought) to investigate the effects of soil drought on cottonseed kernel carbohydrate metabolism and kernel biomass accumulation. Results suggested that drought restrained the accumulation of cottonseed kernel biomass which eventually decreased cottonseed kernel biomass at maturity. In detail, the down-regulation of sucrose phosphate synthase (SPS) activity led to the inhibition of sucrose synthesis, while the up-regulation of invertase (INV) promoted the sucrose decomposite, which reduced the sucrose content eventually under drought. Though hexose content was increased, phosphoenolpyruvic acid (PEP) content was decreased under drought by downregulating 6-phosphofructokinase (PFK) and pyruvate kinase (PK) activities, which hindered the conversion of hexose to PEP. The large decrease of sucrose and PEP contents hindered the accumulation of kernel biomass. The related substances contents and enzyme activities in carbohydrate metabolism of Yuzaomian 9110 were more susceptible to drought stress than Dexiamian 1.

Putrescine transformation to other forms of polyamines in filling grain embryos functioned in enhancing the resistance of maize plants to drought stress.

Polyamines (PAs), one of plant growth regulators, play an important role in the plant resistance to drought stress. However, the precise function of putrescine (Put) transformation to other forms of PAs is not clear in filling maize grain embryos. In this study, two maize (Zea mays L.) cultivars, Yedan No. 13 (drought-resistant) and Xundan No. 22 (drought-sensitive), were used as experimental materials. Maize was planted in big plastic basins during whole growth period, and from the 25th day after fertilization, the plants were treated with drought (-1.0 MPa), PAs and inhibitors for 12 d. The experiments were performed during three consecutive years. The changes in the levels of three main free PAs, Put, spermidine (Spd) and spermine (Spm), covalently conjugated PAs (perchloric acid-soluble), covalently bound PAs (perchloric acid-insoluble), the activities of arginine decarboxylase, S-adenosylmethionine decarboxylase, and transglutaminase were investigated in embryos of filling grains. During drought stress, free Put increased from 109 to 367 nmol g-1 FW and from 107 to 142 nmol g-1 FW in Xundan 22 and in Yedan 13, respectively. Meanwhile, free Spd, free Spm and bound Put increased 2.7, 3.0 and 4.2 times in Yedan 13, respectively, and they merely increased about 1.5 times in Xundan 22. These results suggested that free Spd/Spm and bound Put, which were transformed from free Put, were possibly involved in drought resistance. Exogenous Spd treatment enhanced the drought-induced increase in endogenous free Spd/Spm content in drought-sensitive Xundan 22, coupled with the increase in drought resistance, as judged by the decrease in ear leaf relative plasma membrane permeability and increases in ear leaf relative water content, 1000-grain weight and grain number per ear. The suggestion was further testified with methylglyoxal-bis guanylhydrazone and o-phenanthrolin treatments. Collectively, it could be inferred that transformation of free Put to free Spd/Spm and bound Put in filling grain embryos functioned in enhancing the resistance of maize plants to soil drought.

Hyperpolarization electrical signals induced by local action of moderate heating influence photosynthetic light reactions in wheat plants.

Local action of stressors induces fast changes in physiological processes in intact parts of plants including photosynthetic inactivation. This response is mediated by generation and propagation of depolarization electrical signals (action potentials and variation potentials) and participates in increasing plant tolerance to action of adverse factors. Earlier, we showed that a local action of physiological stimuli (moderate heating and blue light), which can be observed under environmental conditions, induces hyperpolarization electrical signals (system potentials) in wheat plants. It potentially means that these signals can play a key role in induction of fast physiological changes under the local action of environmental stressors. The current work was devoted to investigation of influence of hyperpolarization electrical signals induced by the local action of the moderate heating and blue light on parameters of photosynthetic light reactions. A quantum yield of photosystem II (ФPSII) and a non-photochemical quenching of chlorophyll fluorescence (NPQ) in wheat plants were investigated. It was shown that combination of the moderate heating (40°C) and blue light (540 µmol m-2s-1) decreased ФPSII and increased NPQ; these changes were observed in 3-5 cm from border of the irritated zone and dependent on intensity of actinic light. The moderate soil drought (7 days) increased magnitude of photosynthetic changes and shifted their localization which were observed on 5-7 cm from the irritated zone; in contrast, the strong soil drought (14 days) suppressed these changes. The local moderate heating decreased ФPSII and increased NPQ without action of the blue light; in contrast, the local blue light action without heating weakly influenced these parameters. It meant that just local heating was mechanism of induction of the photosynthetic changes. Finally, propagation of hyperpolarization electrical signals (system potentials) was necessary for decreasing ФPSII and increasing NPQ. Thus, our results show that hyperpolarization electrical signals induced by the local action of the moderate heating inactivates photosynthetic light reactions; this response is similar with photosynthetic changes induced by depolarization electrical signals. The soil drought and actinic light intensity can influence parameters of these photosynthetic changes.

Soil versus atmospheric drought: A test case of plant functional trait responses.

Climate change alters mean global surface temperatures, precipitation regimes, and atmospheric moisture. Resultant drought affects the composition and diversity of terrestrial ecosystems worldwide. To date, there have been no assessments of the combined impacts of reduced precipitation and atmospheric drying on functional trait distributions of any species in an outdoor experiment. Here, we examined whether soil and atmospheric drought affected the functional traits of a focal grass species (Poa secunda) growing in monoculture and eight-species grass communities in outdoor mesocosms. We focused on specific leaf area (SLA), leaf area, stomatal density, root:shoot ratio, and fine root:coarse root ratio responses. Leaf area and overall growth were reduced with soil drying. Root:shoot ratio only increased for P. secunda growing in monoculture under combined atmospheric and soil drought. Plant energy allocation strategy (measured using principal components) differed when P. secunda was grown in combined soil and atmospheric drought conditions compared with soil drought alone. Given a lack of outdoor manipulations of this kind, our results emphasize the importance of atmospheric drying on functional trait responses more broadly. We suggest that drought methods focused purely on soil water inputs may be imprecisely predicting drought effects on other terrestrial organisms as well (other plants, arthropods, and higher trophic levels).

Effects of Elevated Temperature and High and Low Rainfall on the Germination and Growth of the Invasive Alien Plant Acacia mearnsii.

The impact of climate change on the germination and growth of invasive alien plants varies depending on the plant species and invasion process. We experimentally assessed the responses of the invasive alien plant Acacia mearnsii to future climate change scenarios-namely, elevated temperature as well as high and low rainfall. Acacia mearnsii was grown at an elevated air temperature (+2 °C), high rainfall (6 mm per day), and low rainfall (1.5 mm per day), and its germination and growth performance were measured over five months. We further examined changes in soil nutrients to assess if the above-mentioned climate change scenarios affected soils. Both elevated temperature and high rainfall did not influence A. mearnsii germination and seedling growth. In contrast, we observed reductions in A. mearnsii germination and growth in the low rainfall treatment, an indication that future drought conditions might negatively affect A. mearnsii invasion. We noted that elevated temperature and rainfall resulted in varied effects on soil properties (particularly soil C, N, Ca, and Mg content). We conclude that both elevated temperature and high rainfall may not enhance A. mearnsii invasion through altering germination and growth, but a decrease in A. mearnsii invasiveness is possible under low rainfall conditions.

Structural and Functional Responses of the Heteromorphic Leaves of Different Tree Heights on Populus euphratica Oliv. to Different Soil Moisture Conditions.

Populus euphratica Oliv., a pioneer species of desert riparian forest, is characterized heterophylly. To understand the adaptation strategies of the heteromorphic leaves of P. euphratica to soil drought, we assessed the structural and functional characteristics of the heteromorphic leaves at different heights in suitable soil moisture conditions (groundwater depth 1.5 m) and drought conditions (groundwater depth 5 m), which include morphology, anatomical structure, photosynthetic capacity, water use efficiency, osmotic adjustment capacity, and endogenous hormones. These results indicate that leaf area, leaf thickness, fence tissue, palisade-to-sea ratio, main vein xylem area, vessel area, net photosynthetic rate, transpiration rate, and proline, MDA, IAA, GA3, and ZR contents showed a positive correlation with the tree height under the two soil moisture conditions, but leaf shape index, leaf water potential (LWP), and ABA content showed a decreasing trend. In addition, the main vein vascular bundle area, main vein xylem area, and contents of malondialdehyde, ABA, GA3, and IAA were significantly greater under soil drought conditions than normal soil water content. Under soil drought stress, the heteromorphic leaves of P. euphratica showed more investment in anatomical structure and greater water use efficiency, proline, and hormone contents, and synergistic changes to maintain high photosynthetic efficiency. This is an adaptation strategy to water stress caused by soil drought and tree height changes.

Modified Photochemical Reflectance Indices as New Tool for Revealing Influence of Drought and Heat on Pea and Wheat Plants.

In environmental conditions, plants can be affected by the action of numerous abiotic stressors. These stressors can induce both damage of physiological processes and adaptive changes including signaling-based changes. Development of optical methods of revealing influence of stressors on plants is an important task for plant investigations. The photochemical reflectance index (PRI) based on plant reflectance at 531 nm (measuring wavelength) and 570 nm (reference wavelength) can be effective tool of revealing plant stress changes (mainly, photosynthetic changes); however, its efficiency is strongly varied at different conditions. Earlier, we proposed series of modified PRIs with moderate shifts of the measuring wavelength and showed that these indices can be effective for revealing photosynthetic changes under fluctuations in light intensity. The current work was devoted to the analysis of sensitivity of these modified PRIs to action of drought and short-term heat stress. Investigation of spatially-fixed leaves of pea plants showed that the modified PRI with the shorter measuring wavelength (515 nm) was increased under response of drought and heat; by contrast, the modified PRI with the longer wavelength (555 nm) was decreased under response to these stressors. Changes of investigated indices could be related to parameters of photosynthetic light reactions; however, these relations were stronger for the modified PRI with the 555 nm measuring wavelength. Investigation of canopy of pea (vegetation room) and wheat (vegetation room and open-ground) supported these results. Thus, moderate changes in the measuring wavelengths of PRI can strongly modify the efficiency of their use for the estimation of plant physiological changes (mainly photosynthetic changes) under action of stressors. It is probable that the modified PRI with the 555 nm measuring wavelength (or similar indices) can be an effective tool for revealing photosynthetic changes induced by stressors.

Influence of Burning-Induced Electrical Signals on Photosynthesis in Pea Can Be Modified by Soil Water Shortage.

Local damage to plants can induce fast systemic physiological changes through generation and propagation of electrical signals. It is known that electrical signals influence numerous physiological processes including photosynthesis; an increased plant tolerance to actions of stressors is a result of these changes. It is probable that parameters of electrical signals and fast physiological changes induced by these signals can be modified by the long-term actions of stressors; however, this question has been little investigated. Our work was devoted to the investigation of the parameters of burning-induced electrical signals and their influence on photosynthesis under soil water shortage in pea seedlings. We showed that soil water shortage decreased the amplitudes of the burning-induced depolarization signals (variation potential) and the magnitudes of photosynthetic inactivation (decreasing photosynthetic CO2 assimilation and linear electron flow and increasing non-photochemical quenching of the chlorophyll fluorescence and cyclic electron flow around photosystem I) caused by these signals. Moreover, burning-induced hyperpolarization signals (maybe, system potentials) and increased photosynthetic CO2 assimilation could be observed under strong water shortage. It was shown that the electrical signal-induced increase of the leaf stomatal conductance was a potential mechanism for the burning-induced activation of photosynthetic CO2 assimilation under strong water shortage; this mechanism was not crucial for photosynthetic response under control conditions or weak water shortage. Thus, our results show that soil water shortage can strongly modify damage-induced electrical signals and fast physiological responses induced by these signals.

Metabolite profiling of semi-leafless pea (Pisum sativum L.) under progressive soil drought and subsequent re-watering.

Four semi-leafless pea (Pisum sativum L.) cultivars at the vegetative stage of growth were exposed to progressive soil drought, which lasted for 18 days until the plants began to wilt, after which a 7-day period of the recovery from stress followed, when plant watering was resumed. The soil drought negatively affected plant growth, slowing down the rate of shoot elongation, decreasing the accumulation of fresh and dry weight, inhibiting the development of new leaves, and delaying the flowering of plants. Changes in the levels of 41 polar metabolites (identified by GC-MS) were established by the GC-FID method in the shoot tip, stem, stipules and tendrils, separately. Drought caused re-arrangement in the metabolism in all parts of the pea shoot, leading to a significant increase in the content of total polar metabolites. Although changes in most metabolites in the same parts of shoot were not identical among the pea cultivars studied, some metabolites were uniformly accumulated until 18th day of drought and decreased after recovery. They were i) proline and malate in all, while myo-inositol in most parts of shoot (of all the pea cultivars), ii) sucrose and glycine in the shoot tip, iii) homoserine in the stem and iv) GABA in stipules. These findings signify that the pea adjustment to progressive soil drought includes both accumulation of osmolytes and osmoprotectants and translocation of some of them (proline, sucrose, myo-inositol) to the shoot tip, thereby protecting the youngest tissues from damage caused by water deficit.

The influence of soil drought stress on the leaf transcriptome of faba bean (Vicia faba L.) in the Qinghai-Tibet Plateau.

Water deficit has a significant impact on growth, development and yield of fava bean (Vicia fava L.) in arid and semi-arid climates. The aim of this study was to identify differentially expressed genes in the Qinghai 13 genotype under soil drought through leaf transcriptome analysis. A total of 256.95 M clean reads were obtained and assembled into 176334 unigenes, with an average length of 766 bp. A total of 9126 (4439 upregulated and 4687 downregulated) differentially expressed genes (DEGs) were identified in faba bean leaves under soil drought. In total, 324 putative transcription factors were identified and classified as belonging to different transcription factor families. According to GO and KEGG analysis, the soil drought stress-inducible DEGs encoded proteins mainly involved in regulating photosynthesis, osmotic adjustment, detoxification, autophagy and other functions. In addition, a large portion of DEGs appeared to be novel because they could not be annotated in any functional databases, therefore, suggesting a specific response to soil drought in faba bean. Finally, RNA-seq analysis was validated by quantitative reverse-transcription PCR analysis. This work provides comprehensive and valuable information for understanding the molecular mechanisms which faba bean uses to respond to soil drought.