Gradual Drought Research Articles

Impact of Soil Moisture Depletion on Various Yield Components and Water Usage to Trigger Pods in Chickpea (Cicer arietinum L.) Desi Genotypes

ABSTRACTChickpeas are well adapted to rainfed conditions, but a lack of moisture during the reproductive phase can result in lower pod setting and ultimately reduced grain yield. The exact reasons for this reduction are not fully understood, partly because of the lack of information on soil moisture content (SMC) and water use during podding. This study aimed to address this knowledge gap by quantifying the impact of gradual drought on various yield components of desi‐type genotypes using the fraction of transpirable soil water (FTSW) method. Two water treatments were applied at the start of anthesis: well‐watered (WW) and drought‐stressed (DS). The WW was maintained at 24% SMC, whereas the DS was dried to 3% SMC. The results showed that DS caused early podding (3.3 days less), with reductions in plant height (11.4 cm), leaf area (1249.5 cm2), flowers (18.6), pods (27.4), seeds (37.0), grain yield (0.2 g), aboveground dry biomass (11.4 g) and harvest index (0.2 g), while increasing flower abortion (14.6) and seed biomass (1.5 g). However, diverse genotypic responses were observed to treatments, as well as water usage, FTSW and SMC that triggered pods which ranged from 1.12 to 1.89 L, 0.05 to 0.43 and 4.0% to 12.2%, respectively. A positive association between days taken and the amount of water used to terminate pods indicated that quicker‐triggering genotypes, such as Rupali and Genesis 836, consumed less water to develop pods than Flipper, ICCV_06109 and PBA Slasher did. Conversely, the negative association between the amount of water used and the number of pods triggered, seeds and grain yield explained the superior performance of Rupali and Genesis 836. These genotypes extracted less water (FTSW = 0.36 and 0.43; SMC = 10.3% and 12.2%, respectively) to develop pods and maintained favourable photosynthesis at lower transpiration rates for longer periods, allowing them to use residual moisture more efficiently. Our research offers crucial insights that can be beneficial to breeders and physiologists, paving the way for future studies aimed at developing drought‐tolerant genotypes.

Zinc finger knuckle genes are associated with tolerance to drought and dehydration in chickpea (Cicer arietinum L.).

Chickpea (Cicer arietinum L.) is a very important food legume and needs improved drought tolerance for higher seed production in dry environments. The aim of this study was to determine diversity and genetic polymorphism in zinc finger knuckle genes with CCHC domains and their functional analysis for practical improvement of chickpea breeding. Two CaZF-CCHC genes, Ca04468 and Ca07571, were identified as potentially important candidates associated with plant responses to drought and dehydration. To study these genes, various methods were used including Sanger sequencing, DArT (Diversity array technology) and molecular markers for plant genotyping, gene expression analysis using RT-qPCR, and associations with seed-related traits in chickpea plants grown in field trials. These genes were studied for genetic polymorphism among a set of chickpea accessions, and one SNP was selected for further study from four identified SNPs between the promoter regions of each of the two genes. Molecular markers were developed for the SNP and verified using the ASQ and CAPS methods. Genotyping of parents and selected breeding lines from two hybrid populations, and SNP positions on chromosomes with haplotype identification, were confirmed using DArT microarray analysis. Differential expression profiles were identified in the parents and the hybrid populations under gradual drought and rapid dehydration. The SNP-based genotypes were differentially associated with seed weight per plant but not with 100 seed weight. The two developed and verified SNP molecular markers for both genes, Ca04468 and Ca07571, respectively, could be used for marker-assisted selection in novel chickpea cultivars with improved tolerance to drought and dehydration.

Appropriate Drought Training Induces Optimal Drought Tolerance by Inducing Stepwise H2O2 Homeostasis in Soybean.

Soybean is considered one of the most drought-sensitive crops, and ROS homeostasis can regulate drought tolerance in these plants. Understanding the mechanism of H2O2 homeostasis and its regulatory effect on drought stress is important for improving drought tolerance in soybean. We used different concentrations of polyethylene glycol (PEG) solutions to simulate the progression from weak drought stress (0.2%, 0.5%, and 1% PEG) to strong drought stress (5% PEG). We investigated the responses of the soybean plant phenotype, ROS level, injury severity, antioxidant system, etc., to different weak drought stresses and subsequent strong drought stresses. The results show that drought-treated plants accumulated H2O2 for signaling and exhibited drought tolerance under the following stronger drought stress, among which the 0.5% PEG treatment had the greatest effect. Under the optimal treatment, there was qualitatively describable H2O2 homeostasis, characterized by a consistent increasing amplitude in H2O2 content compared with CK. The H2O2 signal formed under the optimum treatment induced the capacity of the antioxidant system to remove excess H2O2 to form a primary H2O2 homeostasis. The primary H2O2 homeostasis further induced senior H2O2 homeostasis under the following strong drought and maximized the improvement of drought tolerance. These findings might suggest that gradual drought training could result in stepwise H2O2 homeostasis to continuously improve drought tolerance.

Physiological response of winter wheat (Triticum aestivum L.) during vegetative growth to gradual, persistent and intermittent drought

Drought priming at the vegetative growth stage has been demonstrated to be an effective water regulation strategy to enhance drought resistance in wheat. Therefore, exploring the stress response of winter wheat to different soil water changes during this stage can improve the drought priming strategies. This study examined the physiological response of winter wheat during two seasons of greenhouse pot experiments (2018–2019, 2019–2020) in the following four treatments: adequate water supply (control, C), persistent drought (P), intermittent drought (I), and gradual drought (G). An adequate water supply (75–85 % FC, field capacity) was always maintained for treatment C. Before jointing, plants in treatment P were maintained in a drought state (55–65 % FC), while in treatment I, plants underwent a change in soil water status from 55–65% FC to re-watering up to 75–85 % FC and back to 55–65 % FC. After entering the jointing stage, plants in treatments P and I were re-watered to 75–85 % FC. There was no water supplied in treatment G throughout the experiment. The soil water content (SWC) in treatment G gradually decreased with time (100–34 % FC). At the same time, abscisic acid (ABA), and osmotic substances accumulated exponentially with the reduction of SWC, the activity of antioxidant protective enzymes increased significantly, and the change in the stomatal closure rate was faster than the decrease in photosynthetic rate (Pn). Drought priming before jointing in treatments P and I prompted photosynthetic compensation after re-watering at the jointing stage, with the highest Pn in treatment I, followed by treatment P, and lastly, treatment C. The drought-re-watering cycle stimulated the stress response indicators in primed plants; hence, they were significantly higher than the stable levels in non-primed plants. Specifically, the ABA level in the leaves increased faster than the other indicators under repeated drought. Moreover, the relationship between photosynthesis and ABA was stronger than with antioxidative enzymes and osmolytes. Besides, increasing the number of drought-re-watering cycles enabled the primed plants to achieve a higher maximum Pn after re-watering and enhanced the association between soluble sugar and Pn. Overall, increasing the frequency of drought-re-watering enhanced the drought priming effect on the wheat stress response. Besides, there is a time difference in the response of different drought stress indicators to soil water changes. The findings in this study provide an empirical reference for better utilization of drought priming strategies to stimulate crop production.

The Physiological Responses of Zea Mays L. and Cucumis Sativus L. on Drought Stress and Re-Watering

Drought leads to deficit water availability and its detrimental effects seriously threaten plant growth. This study assessed the physiological, biochemical, and antioxidant adjustments in different types of photosynthetic plants between Zea mays L. (C4) and Cucumis sativus L. (C3 plant) under response to short-term drought stress. Analyses of relative water content (RWC), proline, and ascorbic acid (AsA) were performed to explore how these plants react to drought. Fifteen-day-old plants were subjected to full irrigation or gradual drought periods for 2-d, 4-d, 6-d, and 8-d following by recovery for 7-d. The results revealed that drought significantly reduces leaf RCW in both plants. Re-watered Z. mays after 8-d drought was higher than C. sativus and reestablished RCW by 23% of stressed plant although remained lower by 9% of the well-watered plant. While, proline and AsA contents in Z. mays were higher than those in C. sativus in drought treatment at 8-d (2.05 µmol/g FW) and 6-d (3174.60 AsA/100 g FW), respectively, that could demonstrate osmotic adjustment ability in this C4 species. The increased proline in both plants also indicates a good strategy for plants to recover. Rewatering gave a decrease AsA and could be expected that plants restore cellular activity after oxidative injury. Based on our study, proline is the most informative biochemical marker to differentiate plant response to drought and Z. mays adjusted defense mechanism to drought rather than C. sativus due to higher accumulation of proline, better antioxidant activity, and improved RCW after recovery.

Identification of HvLRX, a new dehydration and light responsive gene in Tibetan hulless barley (Hordeum vulgare var. nudum).

Tibetan hulless barley (Hordeum vulgare var. nudum), adjusting to the harsh environment on Qinghai-Tibet Plateau, is a good subject for analyzing drought tolerance mechanism. Several unannotated differentially expressed genes (DEGs) were identified through our previous RNA-Seq study using two hulless barley accessions with contrasting drought tolerance. One of these DEGs, HVU010048.2, showed up-regulated pattern under dehydration stress in both drought tolerant (DT) and drought susceptible (DS) accessions, while its function in drought resistance remains unknown. This new gene was named as HvLRX (light responsive X), because its expression was induced under high light intensity while suppressed under dark. To provide preliminary bioinformatics prediction, expression pattern, and drought resistance function of this new gene. Bioinformatics analysis of HvLRX were conducted by MEGA, PlantCARE, ProtParam, CELLO et al. The expression pattern of HvLRX under different light intensity, dehydration shock, gradual drought stress, NaCl stress, polyethylene glycol (PEG) 6000 stress and abscisic acid (ABA) treatment was investigated by quantitative reverse transcription-polymerase chain reaction (RT-qPCR). The function of HvLRX was analyzed by virus induced gene silencing (VIGS) in hulless barley and by transgenic method in tobacco. Full cDNAs of HvLRX were cloned and compared in three hulless barley accessions. Homologues of HvLRX protein in other plants were excavated and their phylogenetic relationship was analyzed. Several light responsive elements (ATC-motif, Box 4, G-box, Sp1, and chs-CMA1a) were identified in its promoter region. Its expression can be promoted under high light intensity, dehydration shock, gradual drought stress, PEG 6000, and NaCl stress, but was almost unchanged in ABA treatment. HvLRX-silenced plants had a higher leaf water loss rate (WLR) and a lower survival rate (SR) compared with controls under dehydration stress. The infected leaves of HvLRX-silenced plants lost their water content quickly and became withered at 10 dpi. The SR of HvLRX overexpressed transgenic tobacco plants was significantly higher than that of wild-type plants. These results indicated HvLRX play a role in drought resistance. Besides, retarded vegetative growth was detected in HvLRX-silenced hulless barley plants, which suggested that this gene is important for plant development. This study provided data of bioinformatics, expression pattern, and function of HvLRX. To our knowledge, this is the first report of this new dehydration and light responsive gene.

Comparative Transcriptome and Weighted Gene Co-expression Network Analysis Identify Key Transcription Factors of Rosa chinensis 'Old Blush' After Exposure to a Gradual Drought Stress Followed by Recovery.

Rose is one of the most fundamental ornamental crops, but its yield and quality are highly limited by drought. The key transcription factors (TFs) and co-expression networks during rose’s response to drought stress and recovery after drought stress are still limited. In this study, the transcriptomes of leaves of 2-year-old cutting seedlings of Rosa chinensis ‘Old Blush’ from three continuous droughted stages (30, 60, 90 days after full watering) and rewatering were analyzed using RNA sequencing. Weighted gene co-expression network analysis (WGCNA) was used to construct a co-expression network, which was associated with the physiological traits of drought response to discovering the hub TFs involved in drought response. More than 45 million high-quality clean reads were generated from the sample and used for comparison with the rose reference genome. A total of 46433 differentially expressed genes (DEGs) were identified. Gene Ontology (GO) term enrichment and Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis indicated that drought stress caused significant changes in signal transduction, plant hormones including ABA, auxin, brassinosteroid (BR), cytokinin, ethylene (ET), jasmonic acid (JA) and salicylic acid (SA), primary and secondary metabolism, and a certain degree of recovery after rewatering. Gene co-expression analysis identified 18 modules, in which four modules showed a high degree of correlation with physiological traits. In addition, 42 TFs including members of NACs, WRKYs, MYBs, AP2/ERFs, ARFs, and bHLHs with high connectivity in navajowhite1 and blue modules were screened. This study provides the transcriptome sequencing report of R. chinensis ‘Old Blush’ during drought stress and rewatering process. The study also identifies the response of candidate TFs to drought stress, providing guidelines for improving the drought tolerance of the rose through molecular breeding in the future.

Photosynthetic performance of quinoa (Chenopodium quinoa Willd.) after exposure to a gradual drought stress followed by a recovery period

Drought is an abiotic scourge, one of the major environmental stress factors that adversely affect plant growth and photosynthesis machinery through a disruption of cell organelles, arrangement thylakoid membranes and the electron transport chain. Herein, we probed the effect of drought stress on photosynthetic performance of Chenopodium quinoa Willd. Beforehand, plants were subjected to water deficit (as 15% Field Capacity, FC) for one (D-1W) or two weeks (D-2W), and were then re-watered at 95% FC for 2 weeks. Light and electron microscopy analysis of leaves showed no apparent changes in mesophyll cell organization and chloroplast ultrastructure after one week of drought stress, while a swelling of thylakoids and starch accumulation were observed after the prolonged drought (D-2W). The latter induced a decrease in both PSI and PSII quantum yields which was accompanied by an increase in F0 (minimum fluorescence) and a decline in Fm (maximum fluorescence). Drought stress influenced the fluorescence transients, where the major changes at the OJIP prompt FI level were detected in the OJ and IP phases. Prolonged drought induced a decrease in chl a fluorescence at IP phase which was readjusted and established back after re-watering and even more an increase was observed after 2 weeks of recovery. The maximum quantum yield of primary photochemistry (φPo) was unaffected by the different drought stress regimes. Drought induced an increase in the ABS/RC and DI0/RC ratios which was concurrent to a stable φPo (maximum quantum yield of PSII primary photochemistry). A substantial decrease in PI(ABS) was detected especially, during severe drought stress (D-2W) suggesting a drop in the PSII efficiency and the level of electron transport through the plastoquinone pool (PQ pool) towards oxidized PSI RCs (P700+). The immunoblot analysis of the main PSII proteins revealed considerable changes in the D1, D2, CP47, OEC, PsbQ and LHCII proteins under drought. These changes depend on the stress duration and recovery period. The main message of this investigation is the elevated recovery capacities of PSII and PSI photochemical activities after re-watering.

Drought-Induced Regulatory Cascades and Their Effects on the Nutritional Quality of Developing Potato Tubers.

Competition for scarce water resources and the continued effects of global warming exacerbate current constraints on potato crop production. While plants’ response to drought in above-ground tissues has been well documented, the regulatory cascades and subsequent nutritive changes in developing tubers have been largely unexplored. Using the commercial Canadian cultivar “Vigor”, plants were subjected to a gradual drought treatment under high tunnels causing a 4 °C increase in the canopy temperature. Tubers were sampled for RNAseq and metabolite analysis. Approximately 2600 genes and 3898 transcripts were differentially expressed by at least 4-fold in drought-stressed potato tubers, with 75% and 69% being down-regulated, respectively. A further 229 small RNAs were implicated in gene regulation during drought. Expression of several small RNA clusters negatively correlated with expression of their six target patatin genes, suggesting involvement in the regulation of storage proteins during drought. The comparison of protein homologues between Solanum tuberosum L. and Arabidopsis thaliana L. indicated that down-regulated genes were associated with phenylpropanoid and carotenoid biosynthesis. As is indicative of reduced flow through the phenylpropanoid pathway, phenylalanine accumulated in drought-stressed tubers. This suggests that there may be nutritive implications to drought stress occurring during the potato tuber bulking phase in sensitive cultivars.

Nitrogen fixation sensitivity related to water use efficiency at reproductive development in soybean

Soybean [Glycine max (L.) Merr.] nitrogen fixation is sensitive differentially to drought among different genotypes at different growth and development stages, which directly affects soybean yield. Acetylene reduction activity (ARA) response to a gradual drought and rewatering period at late podding (late R<sub>3</sub>) and late seed fill (late R<sub>5</sub>) were evaluated in two different water use efficiency (WUE) genotypes. Drought-stressed plants with high WUE (PI 372413) decreased ARA more insensitively than that of low WUE (PI 548534), and drought-stressed plants with low WUE (PI 548534) maintained low ARA level after stress alleviation at late R<sub>5</sub>. The recovery ability of N<sub>2</sub> fixation was a genotypic difference with WUE at late reproductive development (late R<sub>5</sub>), especially. Analysing relation between fraction of transpirable soil water (FTSW) and relative ARA, it was confirmed that PI 372413 with high WUE was more insensitive to water deficit and had drought tolerance by N<sub>2</sub> fixation and recovery ability with a threshold of 0.139–0.147 FTSW than PI 548534 with a threshold of 0.192–0.209 FTSW. The ability to recover N<sub>2</sub> fixation following drought during the reproductive developmental stage would be of an important value in the actual planting environment.

Comparative Proteomics of Root Apex and Root Elongation Zones Provides Insights into Molecular Mechanisms for Drought Stress and Recovery Adjustment in Switchgrass.

Switchgrass plants were grown in a Sandwich tube system to induce gradual drought stress by withholding watering. After 29 days, the leaf photosynthetic rate decreased significantly, compared to the control plants which were watered regularly. The drought-treated plants recovered to the same leaf water content after three days of re-watering. The root tip (1cm basal fragment, designated as RT1 hereafter) and the elongation/maturation zone (the next upper 1 cm tissue, designated as RT2 hereafter) tissues were collected at the 29th day of drought stress treatment, (named SDT for severe drought treated), after one (D1W) and three days (D3W) of re-watering. The tandem mass tags mass spectrometry-based quantitative proteomics analysis was performed to identify the proteomes, and drought-induced differentially accumulated proteins (DAPs). From RT1 tissues, 6156, 7687, and 7699 proteins were quantified, and 296, 535, and 384 DAPs were identified in the SDT, D1W, and D3W samples, respectively. From RT2 tissues, 7382, 7255, and 6883 proteins were quantified, and 393, 587, and 321 proteins DAPs were identified in the SDT, D1W, and D3W samples. Between RT1 and RT2 tissues, very few DAPs overlapped at SDT, but the number of such proteins increased during the recovery phase. A large number of hydrophilic proteins and stress-responsive proteins were induced during SDT and remained at a higher level during the recovery stages. A large number of DAPs in RT1 tissues maintained the same expression pattern throughout drought treatment and the recovery phases. The DAPs in RT1 tissues were classified in cell proliferation, mitotic cell division, and chromatin modification, and those in RT2 were placed in cell wall remodeling and cell expansion processes. This study provided information pertaining to root zone-specific proteome changes during drought and recover phases, which will allow us to select proteins (genes) as better defined targets for developing drought tolerant plants. The mass spectrometry proteomics data are available via ProteomeXchange with identifier PXD017441.

Pliocene flora and paleoenvironment of Zanda Basin, Tibet, China

This paper describes a plant megafossil assemblage from the Pliocene strata of Xiangzi, Zanda Basin in the western Qinghai-Tibet Plateau. Twenty-one species belonging to 12 genera and 10 families were identified. Studies show that the Pliocene vegetation in Zanda Basin was mostly deciduous shrub composed of Cotoneaster , Spiraea , Caragana , Hippophae , Rhododendron , Potentilla fruticosa , etc. Leaf sizes of these taxa were generally small. Paleoclimate reconstruction using Coexistence Analysis and CLAMP showed that this area had higher temperature and precipitation in the Pliocene than today, and distinct seasonal precipitation variability was established. The reconstructed paleoelevation of Zanda Basin in the Pliocene was similar to modern times. In the context of central Asian aridification, the gradual drought in the area beginning in the late Cenozoic caused vegetation to transition from shrub to desert, and the flora composition also changed.

Relating Whole-plant Photosynthesis to Physiological Acclimations at Leaf and Cellular Scales under Drought Stress in Bedding Plants

Bedding plants are at increased risk for exposure to drought stress during production because they are grown in small containers. Physiological mechanisms of bedding plants at leaf and cellular scales that regulate whole-plant photosynthesis under drought conditions are not well understood. This information can be useful for screening bedding plant cultivars with improved drought-tolerance and generate guidelines to mitigate drought stress during production. We subjected drought-sensitive salvia (Salvia splendens ‘Bonfire Red’) and drought-tolerant vinca (Catharanthus roseus ‘Cooler Peppermint’) to gradual drought stress inside whole-plant gas exchange chambers. Substrate water content (Θ), whole-plant net photosynthesis (Pn_avg), whole-plant respiration (Rd_avg), and daily carbon gain (DCG) were measured continuously, whereas stomatal conductance (gS) to water, leaf water (ΨL), osmotic (ΨS), and turgor (ΨP) potentials were measured at the start and end of the drought phase. In addition, ΨS was measured before exposure to stress and after thoroughly rehydrating plants. Dark-adapted quantum efficiency (dark-adapted ΦPSII) was measured after rehydrating plants. The results indicated that, at whole-plant scale, vinca continued to uptake water at lower Θ levels than the Θ level that resulted in wilting of salvia. There were no differences in Rd_avg; however, Pn_avg and DCG of salvia decreased at a higher Θ level than that of vinca. This indicated that salvia experienced drought stress at a higher Θ level than did vinca. At the leaf scale, there were no differences in ΨL; however, a more negative ΨS (P = 0.06) and significantly higher ΨP were observed in vinca (compared to salvia) under drought conditions. In addition, ΨS was not different between species before exposure to drought, whereas ΨS of rehydrated leaves after exposure to drought in vinca was significantly lower than that in salvia. Moreover, ΨS of rehydrated leaves after exposure to drought was significantly lower than that observed before exposure to drought in vinca. This indicated osmotic adjustment (OA) in vinca under drought conditions. Dark-adapted ΦPSII was lower in salvia than in vinca after exposure to drought, indicating damage to photosynthetic mechanisms. Our results suggested that increased OA likely helped to maintain higher ΨP under drought conditions and continuation of water uptake at lower Θ in vinca compared to salvia. In addition, healthier photosynthetic mechanisms of vinca (compared to salvia) under drought conditions likely resulted in its higher Pn_avg and DCG at lower Θ. Screening for OA and dark-adapted ΦPSII may be useful for developing drought-tolerant bedding plant cultivars.

Gene Expression Profiling in Sugarcane Genotypes During Drought Stress and Rehydration

The study aimed to assess the molecular responses of sugarcane genotypes exposed to water stress and rehydration. Six sugarcane varieties that show differential tolerance to drought were planted in the pots with three replications and subjected to gradual drought by withholding water for 2, 6 and 10 days and rehydration for 2, 6 and 10 days after the onset of treatment (DAT) at 60 days after planting. To analyze the physiological status, relative water content and cellular membrane injury were measured. Among the six varieties, two varieties, viz. Co 06022 and Co 99004, retained high relative water content and cell membrane injury recorded was also low during severe drought stress. Sugarcane variety Co 8021 was the most vulnerable to drought stress. The relative water content reduced drastically at 2 days of stress and also maximum membrane injury was observed as stress progressed. Signs of wilting were observed in 2 days, while Co 06022 and Co 99004 showed slight wilting only at 10 days of stress. Examination of differentially expressed genes and transcription factors indicated that ABRE-binding factor, trehalose 6-phosphate synthase, DREB2, SNAC1, dehydrin and early responsive to dehydration (ERD4) showed high-level transcript accumulation during initial stress and gradually declined as stress progressed to 10 days in most genotypes. Invertase and calmodulin functional proteins were overexpressed at both stress and recovery stages. Expression levels of most genes reverted back to their control levels during recovery. Results were validated in shoots and leaves by quantitative real-time PCR.

Shoot and Root Growth in Common Bean (Phaseolus vulgaris L.) Exposed to Gradual Drought Stress

Drought condition during the dry season is a major constraint for intensifying agricultural activities at riparian wetlands in Indonesia, particularly for annual vegetables, including common bean (Phaseolus vulgaris L.). Besides inhibiting growth and reducing yield, drought also causes alteration of the shoot and root growth and development. The objective of this study was to evaluate responses of common bean to three durations of drought stress and the bean ability to recover after termination of the stress treatments. Gradual drought stress treatments were imposed by withholding all water sources to the treated plants. Three durations of drought stress imposed were 4, 8, and 12 days. The ability of the stress-treated plants to recover was evaluated at 7 days after termination of each treatment. The result of this study revealed that common bean was able to tolerate and recover from gradual water deficit for up to 8 days; however, prolonged water deficit for 12 days inhibited the growth of above-ground organs in common bean. Despite root regrowth during the recovery period, plants previously treated with 12 days of drought were unable to recover but those treated with shorter drought stress period were able to recover.

Effects of drying-rewetting on leaf litter decomposition and nutrient releases in forest plantations in Horqin Sandy Land, China

Soil drying-rewetting is a common phenomenon in arid and semi-arid regions. Under the background of global climate change, it is predicted that the intensity of soil drying-rewetting cycle in Horqin Sandy Land will be further strengthened in the future. In this study, we conducted an in-situ soil column incubation experiment for 180 days to investigate the effects of soil drying-rewetting on leaf litter decomposition and nutrient releases of Populus simonii and Pinus sylvestris var. mongo-lica in Horqin Sandy Land. There were three treatments: Constantly moist treatment (CM, 60% water holding capacity during whole incubation period), mild drying-rewetting treatment (DW1, gra-dual drought for 10 days plus 60% WHC for 20 days) and heavy drying-rewetting treatment (DW2, gradual drought for 20 days plus 60% WHC for 10 days). To evaluate their delayed effects, leaf litter in all three treatments were incubated for 60 days under same and constant humid condition (60% WHC) after four cycles of soil drying-rewetting. The responses of litter decomposition to soil drying-rewetting cycles and nutrient releases of P. simonii and P. sylvestris var. mongolica were similar during the drying and rewetting period. Litter mass loss and the release of C, lignin and total phenol were decreased by 17.4%, 23.8%, 35.2% and 32.7% in DW2 treatment compared with CM treatment. There was no significant difference in release of leaf litter N or P among the drying-rewetting treatments. There were consistent changes of litter mass loss and nutrient releases among the treatments at the end of drying-rewetting and delayed incubation period. However, litter decomposition rate and litter C and lignin release rates were increased in DW2 treatment compared with CM treatment during the delayed incubation period, indicating a short-term delayed effect.

A systematic assessment of drought termination in the United Kingdom

Abstract. Drought termination can be associated with dramatic transitions from drought to flooding. Greater attention may be given to these newsworthy and memorable events, but drought terminations that proceed gradually also pose challenges for water resource managers. This paper defines drought termination as a distinctive phase of the event. Using observed river flow records for 52 UK catchments, a more systematic and objective approach for detecting drought terminations is demonstrated. The parameters of the approach are informed by a sensitivity analysis that ensures a focus on terminations of multi-season to multi-year droughts. The resulting inventory of 467 drought terminations provides an unprecedented historical perspective on this phenomenon in the UK. Nationally and regionally coherent drought termination events are identifiable, although their characteristics vary both between and within major episodes. Contrasting drought termination events in 1995–1998 and 2009–2012 are examined in greater depth. The data are also used to assess potential linkages between metrics of drought termination and catchment properties. The duration of drought termination is moderately negatively correlated with elevation (rs = −0.47) and catchment average rainfall (rs = −0.42), suggesting that wetter catchments in upland areas of the UK tend to experience shorter drought terminations. More urbanized catchments tend to have gradual drought terminations (contrary to expectations of flashy hydrological response in such areas), although this may also reflect the type of catchments typical of lowland England. Significant correlations are found between the duration of the drought development phase and both the duration (rs = −0.29) and rate (rs = 0.28) of drought termination. This suggests that prolonged drought development phases tend to be followed by shorter and more abrupt drought terminations. The inventory helps to place individual events within a long-term context. The drought termination phase in 2009–2012 was, at the time, regarded as exceptional in terms of magnitude and spatial footprint, but the Thames river flow record identifies several comparable events before 1930. The chronology could, in due course, provide a basis for exploring the complex drivers, long-term variability, and impacts of drought termination events.

Drought-Induced Leaf Proteome Changes in Switchgrass Seedlings.

Switchgrass (Panicum virgatum) is a perennial crop producing deep roots and thus highly tolerant to soil water deficit conditions. However, seedling establishment in the field is very susceptible to prolonged and periodic drought stress. In this study, a “sandwich” system simulating a gradual water deletion process was developed. Switchgrass seedlings were subjected to a 20-day gradual drought treatment process when soil water tension was increased to 0.05 MPa (moderate drought stress) and leaf physiological properties had expressed significant alteration. Drought-induced changes in leaf proteomes were identified using the isobaric tags for relative and absolute quantitation (iTRAQ) labeling method followed by nano-scale liquid chromatography mass spectrometry (nano-LC-MS/MS) analysis. Additionally, total leaf proteins were processed using a combinatorial library of peptide ligands to enrich for lower abundance proteins. Both total proteins and those enriched samples were analyzed to increase the coverage of the quantitative proteomics analysis. A total of 7006 leaf proteins were identified, and 257 (4% of the leaf proteome) expressed a significant difference (p < 0.05, fold change <0.6 or >1.7) from the non-treated control to drought-treated conditions. These proteins are involved in the regulation of transcription and translation, cell division, cell wall modification, phyto-hormone metabolism and signaling transduction pathways, and metabolic pathways of carbohydrates, amino acids, and fatty acids. A scheme of abscisic acid (ABA)-biosynthesis and ABA responsive signal transduction pathway was reconstructed using these drought-induced significant proteins, showing systemic regulation at protein level to deploy the respective mechanism. Results from this study, in addition to revealing molecular responses to drought stress, provide a large number of proteins (candidate genes) that can be employed to improve switchgrass seedling growth and establishment under soil drought conditions (Data are available via ProteomeXchange with identifier PXD004675).

Effect of progressive drying of pedunculate oak (Quercus robur L.) and holm oak (Quercus rotundifolia Lam.) forest soils on the composition of the oribatid mite community (Acari: Oribatida) in laboratory conditions

ABSTRACTSoil moisture is an important factor in soil systems. To examine the effects of a progressive loss of moisture (gradual drought) on the soil oribatid community of two ecosystems (pedunculate oak and holm oak forests), a laboratory experiment was carried out to (1) record changes in abundance, diversity and species composition and (2) determine drought-resistant and drought-sensitive species. In both ecosystems, the maximum values for species abundance were at the beginning of the experiment; by the end of the experiment, only a few species remained. The species that disappeared first were Damaeus onustus, Microppia minus, Suctobelba regia, Suctobelba trigona, Liochthonius brevis, Quadroppia pseudocircumita, Rhinoppia obsoleta and Suctobelbella subcornigera. Those that survived until the end of the experiment were Hermanniella dolosa, Odontocepheus elongatus and Tectocepheus velatus. The progressive rate of water loss (drought) was similar in both experiments. Species richness decreased in drier conditions. The communities remained intact until Day 30, even though the sample water content decreased by 83% in the pedunculate oak and 90.1% in holm oak soils during the first 15 days. The species diversity and community balance were altered after 30 days as a result of a reduction in numbers of both individuals and species, and the reductions were severe after 45 days.

UV-B辐射和干旱对丹参生长和叶片中酚酸类成分的影响

Ultraviolet B and drought stress are common environmental stresses in arid and semi-arid regions of northwestern China. A pot experiment was conducted to investigate the separate and combined effects of UV-B radiation and drought stress on physiological characteristics of Salvia miltiorrhiza Bunge in this region,and on the accumulation of phenolic compounds in its leaves. In this experiment,the UV-B radiation was performed with two intensities,2.60 k J / m2( T1) and4.10 k J / m2( T2),meanwhile,three gradual drought stress treatments were carried out with field water capacity ranging from40% to 75%. The involved physiological characteristics included plant height,leaf area index,shoot biomass,root biomass,total biomass,root: shoot ratio,and those photosynthetic indices,such as net photosynthetic rate( Pn),transpiration rate( Tr),stomatal conductance( Gs) and intercellular CO2concentration( Ci). The phenolic compounds detected in leaves contained salvianolic acid B( SAB), rosmarinic acid( RA), caffeic acid( CA) and 3,4-trihydroxybenzenepropanoic acid( DSS). The results showed that both UV-B radiation and drought stress had cross-talk on the growth of S. miltiorrhiza,and the least plant height was found in the combined treatment( 40% T2),which significantly decreased 47.82%. Drought stress and UV-B radiation reduced leaf area 40.22% and 71.51%,respectively,and the leastvalue occurred in the combined treatment 75% T2. Similarly,the least root: shoot ratio also happened in combined treatment75% T1 and the least total plant biomass did in 40% T2. In terms of the effects of UV-B and drought stress on photosynthetic indices,similar tendency was observed among Pn,Tr and Gs,but Ci had reverse trend with these three indices. The three indices were found reaching the largest at growth season,but decreased to the lowest at harvest period in the combined 40%T2 treatment. Both UV-B and drought stress could promote the accumulation of four phenolic compounds,in which the former had more prominent influence. Both contents of SAB and RA increased 4.28 and 8 folds,respectively,under UV-B radiation,which were significantly higher than 1. 12 and 1. 51 folds in drought stress treatment. The SAB and RA accumulation reached the highest level( 4.75 and 3.15 μg / g,respectively) in the combined treatment 75% T2. Statistical data also exhibited that there was a cross-talk in accumulation of phenolic compounds between UV-B and drought stress. The SAB content increased 4.28 folds in T2 radiation intensity,while only 2.18 folds were observed in T1. The content increased1.12 and 0.52 folds in drought stress treatment with 40% and 55% field water capacity,respectively. If combined UV-B radiation and drought stress,the SAB content would increased 2. 69 and 1. 67 folds in 40% T2 and 55% T2 treatments,respectively. In conclusion,there was a cross-talk between UV-B radiation and drought stress,which had combined effects on the growth of S. miltiorrhiza and accumulation of phenolic compounds in leaves. Relatively,UV-B radiation had stronger influence than drought stress. Either UV-B radiation or drought stress had negative effect on plant growth. The higher UV-B radiation intensity( T2,4. 10 k J / m2) was helpful to accumulation of SAB,but the amount of accumulation would be decreased with the increase of drought stress intensity.