Weak local adaptation to drought in seedlings of a widespread conifer

Tree seedlings from populations native to drier regions are often assumed to be more drought tolerant than those from wetter provenances. However, intraspecific variation in drought tolerance has not been well-characterized despite being critical for developing climate change mitigation and adaptation strategies, and for predicting the effects of drought on forests. We used a large-scale common garden drought-to-death experiment to assess range-wide variation in drought tolerance, measured by decline of photosynthetic efficiency, growth, and plastic responses to extreme summer drought in seedlings of 73 natural populations of the two main varieties of Douglas-fir (Pseudotsuga menziesii var. menziesii and var. glauca). Local adaptation to drought was weak in var. glauca and nearly absent in menziesii. Var. glauca showed higher tolerance to drought but slower growth than var. menziesii. Clinal variation in drought tolerance and growth species-wide was mainly associated with temperature rather than precipitation. A higher degree of plasticity for growth was observed in var. menziesii in response to extreme drought. Genetic variation for drought tolerance in seedlings within varieties is maintained primarily within populations. Selective breeding within populations may facilitate adaptation to drought more than assisted gene flow.

The WRKY17-WRKY50 complex modulates anthocyanin biosynthesis to improve drought tolerance in apple

Drought stress is increasing worldwide due to global warming, which severely reduces apple (Malus domestica) yield. Clarifying the basis of drought tolerance in apple could accelerate the molecular breeding of drought-tolerant cultivars to maintain apple production. We identified a transcription factor MdWRKY50 by yeast two-hybrid (Y2H) assays as an interactor of the drought-tolerant protein MdWRKY17, and confirmed their interaction by bimolecular fluorescence complementation (BiFC) and pull-down assays. MdWRKY50 was induced by drought and when overexpressed in apple, conferred transgenic apple plants enhanced drought tolerance by directly binding to the promoter of anthocyanin synthetic gene Chalcone synthase (MdCHS) to upregulate its expression for higher anthocyanin. Increased anthocyanin relieves apple plants from oxidative damage under drought stress. MdWRKY50 RNA-interference transgenic apple plants showed opposite phenotypes. The dimerization of MdWRKY50 with mutated MdWRKY17DP mimicking drought-induced phosphorylation by the mitogen-activated protein kinase kinase 2 (MEK2)-MPK6 cascade, compared with MdWRKY17AP and MdWRKY17, further promoted anthocyanin biosynthesis, suggesting dimerization with MdWRKY17 makes MdWRKY50 more powerful in promoting anthocyanin biosynthesis under drought stress. Taken together, we isolated an entire MEK2-MAPK6-MdWRKY17-MdWRKY50-MdCHS pathway for drought tolerance and generated transgenic apple germplasm with enhanced drought tolerance and higher anthocyanin levels.

Grafting seedling rootstock strengthens tolerance to drought stress in polyploid mulberry (Morus alba L.)

The economically adaptable mulberry (Morus alba L.) has a long history of grafting in China, yet the physiological mechanisms and advantages in drought tolerance remain unexplored. In our study, we investigated the responses of self-rooted 2X (diploid), 3X (triploid), and 4X (tetraploid) plants, as well as polyploid plants grafted onto diploid seedling rootstocks (2X/2X, 3X/2X, and 4X/2X) under drought stress. We found that self-rooted diploid plants exhibited the most severe phenotypic damage, lowest water retention, photosynthetic capacity, and the least effective osmotic stress adjustment compared to tetraploid and triploid plants. However, grafted diploid and triploid plants showed effective mitigation of drought-induced damage, with higher relative water content and improved soil water retention. Grafted plants also improved the photosystem response to drought stress through elevated photosynthetic potential, closed stomatal aperture, and faster recovery of chlorophyll biosynthesis in the leaves. Additionally, grafted plants altered osmotic protective compound levels, including starch, soluble sugar, and proline content, thereby enhancing drought resistance. Absolute quantification PCR indicated that the expression levels of proline synthesis-related genes in grafted plants were not influenced after drought stress, whereas they were significantly increased in self-rooted plants. Consequently, our findings support that self-rooted triploid and tetraploid mulberries exhibited superior drought resistance compared to diploid plants. Moreover, grafting onto seedling rootstocks enhanced tolerance against drought stress in diploid and triploid mulberry, but not in tetraploid. Our study provides valuable insights for a comprehensive analysis of physiological effects in response to drought stress between stem-roots and seedling rootstocks.

Polysome-bound mRNAs and translational mechanisms regulate drought tolerance in rice

Plants evolved several acquired tolerance traits for drought stress adaptation to maintain the cellular homeostasis. Drought stress at the anthesis stage in rice affects productivity due to the inefficiency of protein synthesis machinery. The effect of translational mechanisms on different pathways involved in cellular tolerance plays an important role. We report differential responses of translation-associated mechanisms in rice using polysome bound mRNA sequencing at anthesis stage drought stress in resistant Apo and sensitive IR64 genotypes. Apo maintained higher polysomes with 60 S-to-40 S and polysome-to-monosome ratios which directly correlate with protein levels under stress. IR64 has less protein levels under stress due to defective translation machinery and reduced water potential. Many polysome-bound long non-coding RNAs (lncRNA) were identified in both genotypes under drought, influencing translation. Apo had higher levels of N6-Methyladenosine (m6A) mRNA modifications that contributed for sustained translation. Translation machinery in Apo could maintain higher levels of photosynthetic machinery-associated proteins in drought stress, which maintain gas exchange, photosynthesis and yield under stress. The protein stability and ribosome biogenesis mechanisms favoured improved translation in Apo. The phytohormone signalling and transcriptional responses were severely affected in IR64. Our results demonstrate that, the higher translation ability of Apo favours maintenance of photosynthesis and physiological responses that are required for drought stress adaptation.

Drought reduces productivity and anti-herbivore defences, but not mycorrhizal associations, of perennial prairie forbs

During drought, plants allocate resources to aboveground biomass production and belowground carbohydrate reserves, often at the expense of production of defence traits. Additionally, drought has been shown to alter floral resources, with potential implications for plant-pollinator interactions. Although soil symbionts, such as arbuscular mycorrhizal (AM) fungi, can alleviate drought stress in plants, certain levels of drought may negatively impact this relationship, with potential cascading effects. Because of their importance to plant and animal community diversity, we examined effects of drought on biomass production, physical defence properties, nectar production, and associated AM fungal abundance of five common prairie forb species in a greenhouse study. Reduced soil moisture decreased vegetative biomass production. Production of trichomes and latex decreased under drought, relative to well-watered conditions. Ruellia humilis flowers produced less nectar under drought, relative to well-watered conditions. Intra-radical AM fungal colonization was not significantly affected by drought, although extra-radical AM fungal biomass associated with S. azurea decreased following drought. Overall, grassland forb productivity, defence, and nectar production were negatively impacted by moderate drought, with possible negative implications for biotic interactions. Reduced flower and nectar production may lead to fewer pollinator visitors, which may contribute to seed limitation in forb species. Reduced physical defences increase the likelihood of herbivory, further decreasing the ability to store energy for essential functions, such as reproduction. Together, these results suggest drought can potentially impact biotic interactions between plants and herbivores, pollinators, and soil symbionts, and highlights the need for direct assessments of these relationships under climate change scenarios.

Drought memory in Acanthostachys strobilacea, a CAM epiphytic bromeliad

Stress memory is the development of altered responses to stress due to previous exposure, which might result in increased tolerance. Biochemical and physiological parameters shown to be positively affected by stress memory include those of the antioxidant and nitrosative metabolism, photosynthetic pigments and osmolyte content. Epiphytic bromeliads likely present stress memory since they experience frequent droughts in the canopies. Thus, we aimed to evaluate if the epiphytic bromeliad Acanthostachys strobilacea (Schult. & Schult.f.) Klotzsch shows improved metabolic stress defence responses to a second drought and rewatering cycle compared to a single exposure. In a controlled environment chamber, 90-day-old plants were exposed to one or two drought-rewatering cycles of 14 days without irrigation and 5 days of rewatering each. Sampling occurred after the final drought and rewatering periods for one or two cycles treatments. The free amino acid, chlorophyll, and carotenoid levels and S-nitrosoglutathione reductase (GSNOR) activity were higher at the second drought than at the first exposure. The rise in nocturnal acidification (indicative of increased CAM activity) caused by the initial drought persisted through the second drought-rewatering cycle, implying a lasting memory effect on CAM activity. Furthermore, the second recovery did not induce glutathione accumulation, as in the first rewatering event, suggesting the pre-exposure to drought reduced this thiol's demand during a later recovery. Our results evidence metabolic changes related to drought stress memory in A. strobilacea, supporting this mechanism might be involved in the tolerance of epiphytic bromeliads to intermittent droughts.

Probabilistic monitoring of meteorological drought impacts on water quality of major rivers in South Korea using copula models

The impacts of drought range from water supply for humans to ecosystems. Drought affects river water quality by disturbing the hydrological regime in a variety of ways, and can degrade water quality by reducing surface and groundwater availability. In particular, drought-induced low flows, reduced nutrient dilution, and extreme increases in water temperature affect various water quality parameters in streams. Furthermore, the effects of drought on stream water quality may vary from season to season and from stream segment to stream segment, which requires careful investigation. In this study, Environmental Drought Condition Index - water quality (EDCI-wq) is proposed using a bivariate copula joint probability model between meteorological drought index and river water quality. Using this, environmental drought with respect to water quality is defined, and it is confirmed that environmental drought with respect to water quality can be routinely monitored through time series analysis and mapping of the proposed EDCI-wq. In addition, in order to express the environmental drought condition more explicitly to the general public, the environmental drought condition is graded into four classes based on the EDCI-wq. Furthermore, the sensitivity of river water quality to meteorological drought was estimated using the copula joint probability model, which allowed us to identify river segments that are relatively more sensitive to meteorological drought events.

Nitrogen starvation modulates the sensitivity of rhizobacterial community to drought stress in Stevia rebaudiana

Alterations in water regimes or nitrogen (N) availability lead to shifts in the assemblage of rhizosphere microbial community; however, how the rhizosphere microbiome response to concurrent changes in water and N availability remains largely unclear. Herein, we investigated the taxonomic and functional characteristics of rhizobacteria associated with stevia (Stevia rebaudiana Bertoni) under varying combinations of water and N levels. Community diversity and predicted functions of rhizobacteria were predominantly altered by drought stress, with N-starvation modulating these effects. Moreover, N fertilization simplified the ecological interactions within rhizobacterial communities and heightened the relative role of stochastic processes on community assembly. In terms of rhizobacterial composition, we observed both common and distinctive changes in drought-responsive bacterial taxa under different N conditions. Generally, the relative abundance of Proteobacteria and Bacteroidetes phyla were depleted by drought stress but the Actinobacteria phylum showed increases. The rhizobacterial responses to drought stress were influenced by N availability, where the positive response of δ-proteobacteria and the negative response of α- and γ-proteobacteria, along with Bacteroidetes, were further heightened under N starvation. By contrast, under N fertilization conditions, an amplified negative or positive response to drought were demonstrated in Firmicutes and Actinobacteria phyla, respectively. Further, the drought-responsive rhizobacteria were mostly phylogenetically similar, but this pattern was modulated under N-rich conditions. Overall, our findings indicate an N-dependent specific restructuring of rhizosphere bacteria under drought stress. These changes in the rhizosphere microbiome could contribute to enhancing plant stress tolerance.

Molecular mechanism of drought resistance in soybean roots revealed using physiological and multi-omics analyses

Soybeans are one of the most cultivated crops worldwide and drought can seriously affect their growth and development. Many studies have elucidated the mechanisms through which soybean leaves respond to drought; however, little is known about these mechanisms in roots. We used two soybean varieties with different drought tolerances to study the morphological, physiological, and molecular response mechanisms of the root system to drought stress in seedlings. We found that drought stress led to a significant decrease in the root traits and an increase in antioxidant enzyme activity in the two varieties. Drought-resistant varieties accumulate large amounts of flavonoids and phenolic acids at the metabolic level, which causes variations in drought resistance. Additionally, differences in gene expression and drought-resistance pathways between the two varieties were clarified using transcriptome analysis. Through a multi-omics joint analysis, phenylpropanoid and isoflavonoid biosynthesis were identified as the core drought resistance pathways in soybean roots. Candidate genes and marker metabolites affecting drought resistance were identified. The phenylpropanoid pathway confers drought tolerance to roots by maintaining a high level of POD activity and mediates the biosynthesis of various secondary drought-resistant metabolites to resist drought stress. This study provides useful data for investigating plant root drought responses and offers theoretical support for plant breeding for drought resistance.

Understanding role of roots in plant response to drought: Way forward to climate-resilient crops

Drought stress leads to a significant amount of agricultural crop loss. Thus, with changing climatic conditions, it is important to develop resilience measures in agricultural systems against drought stress. Roots play a crucial role in regulating plant development under drought stress. In this review, we have summarized the studies on the role of roots and root-mediated plant responses. We have also discussed the importance of root system architecture (RSA) and the various structural and anatomical changes that it undergoes to increase survival and productivity under drought. Various genes, transcription factors, and quantitative trait loci involved in regulating root growth and development are also discussed. A summarization of various instruments and software that can be used for high-throughput phenotyping in the field is also provided in this review. More comprehensive studies are required to help build a detailed understanding of RSA and associated traits for breeding drought-resilient cultivars.

The Relationships between Drought Exposure, Fertility Preferences, and Contraceptive Behaviors: A Multicountry Study

The interplay between population dynamics and the environment has long interested demographers. Although studies have explored how climate patterns affect macrolevel population processes, such as mortality and migration, little is known about their impact on individual-level demographic behaviors. This study fills this research gap by examining the linkages between exposure to drought and women's fertility preferences and contraceptive behaviors in sub-Saharan Africa. We analyze data from the Demographic and Health Surveys Program, focusing on 17 countries in East, Southern, and West Africa. We investigate whether women's recent exposure to drought episodes in their community affects their fertility preferences and modern contraceptive use. Generally, the findings show that drought is relevant to understanding women's fertility preferences and behaviors in the vast majority of countries; however, drought exposure has variable impacts. Moreover, whereas in some countries, drought exposure encourages contraceptive behaviors that align with women's preferences, in select countries it is associated with behavior that is misaligned with women's stated preferences. Overall, the study emphasizes the importance of examining climate events as complex forces that have localized meanings for demographic outcomes.

Halotolerant Pseudomonas koreensis S4T10 mitigate salt and drought stress in Arabidopsis thaliana

Salt and drought are documented among the most detrimental and persistent abiotic stresses for crop production. Here, we investigated the impact of Pseudomonas koreensis strain S4T10 on plant performance under salt and drought stress. Arabidopsis thaliana Col-0 wild type and atnced3 mutant plants were inoculated with P. koreensis or tap water and exposed to NaCl (100 mM) for five days and drought stress by withholding water for seven days. P. koreensis significantly enhanced plant biomass and photosynthetic pigments under salt and drought stress conditions. Moreover, P. koreensis activated the antioxidant defence by modulating glutathione (GSH), superoxide dismutase (SOD), peroxidase (POD), and polyphenol oxidase (PPO) activities to scavenge the reactive oxygen species produced due to the stress. In addition, the application of P. koreensis upregulated the expression of genes associated with antioxidant responses, such as AtCAT1, AtCAT3, and AtSOD. Similarly, genes linked to salt stress, such as AtSOS1, AtSOS2, AtSOS3, AtNHX1, and AtHKT1, were also upregulated, affirming the positive role of P. koreensis S4T10 in streamlining the cellular influx and efflux transport systems during salt stress. Likewise, the PGPB inoculation was observed to regulate the expression of drought-responsive genes AtDREB2A, AtDREB2B, and ABA-responsive genes AtAO3, AtABA3 indicating that S4T10 enhanced drought tolerance via modulation of the ABA pathway. The results of this study affirm that P. koreensis S4T10 could be further developed as a biofertilizer to mitigate salt and drought stress at the same time.

Mesophyll conductance limits photosynthesis in fluctuating light under combined drought and heat stresses

Drought and heat stresses usually occur concomitantly in nature, with increasing frequency and intensity of both stresses expected due to climate change. The synergistic agricultural impacts of these compound climate extremes are much greater than those of the individual stresses. However, the mechanisms by which drought and heat stresses separately and concomitantly affect dynamic photosynthesis have not been thoroughly assessed. To elucidate this, we used tomato (Solanum lycopersicum) seedlings to measure dynamic photosynthesis under individual and compound stresses of drought and heat. Individual drought and heat stresses limited dynamic photosynthesis at the stages of diffusional conductance to CO2 and biochemistry, respectively. However, the primary limiting factor for photosynthesis shifted to mesophyll conductance under the compound stresses. Compared with the control, photosynthetic carbon gain in fluctuating light decreased by 38%, 73%, and 114% under the individual drought, heat, and compound stresses, respectively. Therefore, compound stresses caused a greater reduction in photosynthetic carbon gain in fluctuating light conditions than individual stress. These findings highlight the importance of mitigating the effects of compound climate extremes on crop productivity by targeting mesophyll conductance and improving dynamic photosynthesis.

Genome-wide profiling of histone (H3) lysine 4 (K4) tri-methylation (me3) under drought, heat, and combined stresses in switchgrass

BACKGROUND

Switchgrass (Panicum virgatum L.) is a warm-season perennial (C4) grass identified as an important biofuel crop in the United States. It is well adapted to the marginal environment where heat and moisture stresses predominantly affect crop growth. However, the underlying molecular mechanisms associated with heat and drought stress tolerance still need to be fully understood in switchgrass. The methylation of H3K4 is often associated with transcriptional activation of genes, including stress-responsive. Therefore, this study aimed to analyze genome-wide histone H3K4-tri-methylation in switchgrass under heat, drought, and combined stress.

RESULTS

In total, ~ 1.3 million H3K4me3 peaks were identified in this study using SICER. Among them, 7,342; 6,510; and 8,536 peaks responded under drought (DT), drought and heat (DTHT), and heat (HT) stresses, respectively. Most DT and DTHT peaks spanned 0 to + 2000 bases from the transcription start site [TSS]. By comparing differentially marked peaks with RNA-Seq data, we identified peaks associated with genes: 155 DT-responsive peaks with 118 DT-responsive genes, 121 DTHT-responsive peaks with 110 DTHT-responsive genes, and 175 HT-responsive peaks with 136 HT-responsive genes. We have identified various transcription factors involved in DT, DTHT, and HT stresses. Gene Ontology analysis using the AgriGO revealed that most genes belonged to biological processes. Most annotated peaks belonged to metabolite interconversion, RNA metabolism, transporter, protein modifying, defense/immunity, membrane traffic protein, transmembrane signal receptor, and transcriptional regulator protein families. Further, we identified significant peaks associated with TFs, hormones, signaling, fatty acid and carbohydrate metabolism, and secondary metabolites. qRT-PCR analysis revealed the relative expressions of six abiotic stress-responsive genes (transketolase, chromatin remodeling factor-CDH3, fatty-acid desaturase A, transmembrane protein 14C, beta-amylase 1, and integrase-type DNA binding protein genes) that were significantly (P < 0.05) marked during drought, heat, and combined stresses by comparing stress-induced against un-stressed and input controls.

CONCLUSION

Our study provides a comprehensive and reproducible epigenomic analysis of drought, heat, and combined stress responses in switchgrass. Significant enrichment of H3K4me3 peaks downstream of the TSS of protein-coding genes was observed. In addition, the cost-effective experimental design, modified ChIP-Seq approach, and analyses presented here can serve as a prototype for other non-model plant species for conducting stress studies.

Photosynthetic gas exchange, plant water relations and osmotic adjustment of three tropical perennials during drought stress and re-watering

Planting vegetation on slopes is an effective way of improving slope stability while enhancing the aesthetic appearance of the landscape. However, plants growing on slopes are susceptible to natural drought stress (DS) conditions which commonly lead to water deficit in plant tissues that affect plant health and growth. This study investigated the photosynthetic gas exchange, plant water status and proline accumulation of three tropical perennials namely Clerodendrum paniculatum, Ipomoea pes-caprae and Melastoma malabathricum after being subjected to DS and re-watering (RW). During DS, there was a significant decrease in light-saturated photosynthetic CO2 assimilation rate (Asat), stomatal conductance (gs sat), and transpiration rate (Tr) for all three plant species. Leaf relative water content, shoot water potential, and leaf, stem and root water content also declined during DS. Proline concentration increased for all three species during DS, reaching especially high levels for C. paniculatum, suggesting that it heavily relies on the accumulation of proline to cope with DS. Most of the parameters recovered almost completely to levels similar to well-watered plants after RW, apart from M. malabathricum. Strong linear correlations were found between Asat and gs sat and between gs sat and Tr. Ultimately, C. paniculatum and I. pes-caprae had better drought tolerance than M. malabathricum.

Organic seed priming with curtailed seed rate compensated wheat grains productivity by upgrading anti-oxidant status against terminal drought at flowering and milking

Terminal irrigation drought stress is one of the most drastic abiotic stress to diminish the wheat crop development and grains yield in arid regions of the world. The use of moringa leaf extract (MLE30) via seed priming technique is investigated as an organic and sustainable approach for the mitigation of drought stress along with curtailed seed rate in wheat crop. The study investigated the interaction of organic seed priming: control (dry seeds), hydro-priming, MLE30-priming, seed rate: recommended @ 125 kg ha-1, curtailed @ 25 kg ha-1, and terminal irrigation drought (TID): normal irrigation, mild-TID, severe-TID in wheat crop at agronomic research station, Bahawalpur, Pakistan during the wheat winter season of 2021-2022 and 2022-2023. The application of organic MLE30-priming with curtailed seed rate enhanced antioxidant enzyme activity especially total soluble proteins by 15%, superoxide dismutase by 68%, peroxidase by 16%, catalase by 70%, ascorbic acid by 17% and total protein contents by 91% under severe-TID. Yield and yield-related morphological attributes performed better in MLE30-priming as compared to hydro-priming. An effective trend was observed in the plant's chlorophyll contents, K+, and water use efficiency after being treated with MLE30-priming followed by hydro-priming under curtailed seed rate. The higher benefit-cost ratio and net income return were observed with the application of MLE30-priming with curtailed seed rate under mild-TID and severe-TID. So, it is suggested to adopt the MLE30-priming technique along with a curtailed seed rate for improving the crop establishment, stress regulation, and economic return under limited availability of irrigation water. The project findings recommended that the application of exogenous application of organic MLE30-seed priming favored and compensated the maximum wheat grains production under curtailed seed rate @ 25 kg ha-1 and induced terminal drought stress at flowering and milking conditions.

Alleviating the drought stress and improving the plant resistance properties of Triticum aestivum via biopriming with aspergillus fumigatus

BACKGROUND

Wheat (Triticum aestivum L.) is one of the most widely grown and vital cereal crops, containing a high percentage of basic nutrients such as carbohydrates and proteins. Drought stress is one of the most significant limitations on wheat productivity. Due to climate change influences plant development and growth, physiological processes, grain quality, and yield. Drought stress has elicited a wide range of plant responses, namely physiological and molecular adaptations. Biopriming is one of the recent attempts to combat drought stress. Mitigating the harmful impact of abiotic stresses on crops by deploying extreme-habitat-adapted symbiotic microbes. The purpose of this study was to see how biopriming Triticum aestivum grains affected the effects of inoculating endophytic fungi Aspergillus fumigatus ON307213 isolated from stressed wheat plants in four model agricultural plants (Gemmiza-7, Sids-1, Sakha8, and Giza 168). And its viability in reducing drought stress through the use of phenotypic parameters such as root and shoot fresh and dry weight, shoot and root length, and so on. On a biochemical and physiological level, enzymatic parameters such as catalase and superoxidase dismutase are used. Total phenolics, flavonoids, and photosynthetic pigments are non-enzymatic parameters. Making use of molecular techniques such as reverse transcriptase polymerase chain reaction (RT-PCR).

RESULTS

It has been found that using Aspergillus fumigatus as a biological biopriming tool can positively impact wheat plants experiencing drought stress. The total biomass of stressed wheat plants that had been bio-primed rose by more than 40% as compared to wheat plants that had not been bio-primed. A. fumigatus biopriming either increased or decreased the amount of enzymatic and non-enzymatic substances on biochemical scales, aside from the noticeable increase in photosynthetic pigment that occurs in plants that have been bio-primed and stressed. Drought-resistant genes show a biopriming influence in gene expression.

CONCLUSIONS

This is the first paper to describe the practicality of a. fumigatus biopriming and its effect on minimizing the degrading effects of drought through water limitation. It suggests the potential applications of arid habitat-adapted endophytes in agricultural systems.

Enhancing drought, heat shock, and combined stress tolerance in Myrobalan 29C rootstocks with foliar application of potassium nitrate

BACKGROUND

Drought and heat stress are significant concerns to food security in arid and semi-arid regions, where global warming is predicted to increase both frequency and severity. To cope with these challenges, the use of drought-tolerant plants or technological interventions are essential. In this study, the effects of foliar potassium nitrate (KNO3) application on the stress tolerance and recovery of Myrobalan 29C rootstocks (Prunus cerasifera Ehrh.) were evaluated. These rootstocks are widely recognized for their adaptability and are extensively used in fruit production. To assess their response, the rootstocks were subjected to drought, heat shock, or a combination of both stressors. Additionally, they were treated with 1.0% KNO3 via foliar application. Throughout the stress and recovery periods, various morphological, physiological, and bio-chemical parameters were measured.

RESULTS

Based on our results, KNO3 treatment improved LRWC, Chl stability, SC, and key stress markers like proline, MDA, H2O2, along with antioxidant enzymes CAT, SOD, POD during both stress and recovery phases. Moreover, our results emphasized KNO3's critical role in hormone regulation under stress. KNO3 application significantly altered hormone levels, notably increasing ABA during drought and heat shock stress, essential for stress response and adaptation. In contrast, IAA, GA, and cytokinin's significantly increased during the recovery phase in KNO3-treated plants, indicating improved growth regulation and stress recovery. In addition, KNO3 application improved the recovery process of the rootstocks by restoring their physiological and biochemical functions.

CONCLUSION

This study suggests that the application of foliar KNO3 is an effective technique for enhancing the drought and heat tolerance as well as the recovery of Myrobalan 29C rootstocks. These results hold significant value for farmers, policymakers, and researchers, as they offer crucial insights into the development of drought-tolerant crops and the management of climate change's adverse effects on agriculture.

Enhancing maize resilience to drought stress: the synergistic impact of deashed biochar and carboxymethyl cellulose amendment

Drought stress poses a significant challenge to maize production, leading to substantial harm to crop growth and yield due to the induction of oxidative stress. Deashed biochar (DAB) in combination with carboxymethyl cellulose (CMC) presents an effective approach for addressing this problem. DAB improves soil structure by increasing porosity and water retention and enhancing plant nutrient utilization efficiency. The CMC provides advantages to plants by enhancing soil water retention, improving soil structure, and increasing moisture availability to the plant roots. The present study was conducted to investigate the effects of DAB and CMC amendments on maize under field capacity (70 FC) and drought stress. Six different treatments were implemented in this study, namely 0 DAB + 0CMC, 25 CMC, 0.5 DAB, 0.5 DAB + 25 CMC, 1 DAB, and 1 DAB + 25 CMC, each with six replications, and they were arranged according to a completely randomized design. Results showed that 1 DAB + 25 CMC caused significant enhancement in maize shoot fresh weight (24.53%), shoot dry weight (38.47%), shoot length (32.23%), root fresh weight (19.03%), root dry weight (87.50%) and root length (69.80%) over control under drought stress. A substantial increase in maize chlorophyll a (40.26%), chlorophyll b (26.92%), total chlorophyll (30.56%), photosynthetic rate (21.35%), transpiration rate (32.61%), and stomatal conductance (91.57%) under drought stress showed the efficiency of 1 DAB + 25 CMC treatment compared to the control. The enhancement in N, P, and K concentrations in both the root and shoot validated the effectiveness of the performance of the 1 DAB + 25 CMC treatment when compared to the control group under drought stress. In conclusion, it is recommended that the application of 1 DAB + 25 CMC serves as a beneficial amendment for alleviating drought stress in maize.

Characterization of sucrose nonfermenting-1-related protein kinase 2 (SnRK2) gene family in Haynaldia villosa demonstrated SnRK2.9-V enhances drought and salt stress tolerance of common wheat

BACKGROUND

The sucrose nonfermenting-1-related protein kinase 2 (SnRK2) plays a crucial role in responses to diverse biotic/abiotic stresses. Currently, there are reports on these genes in Haynaldia villosa, a diploid wild relative of wheat.

RESULTS

To understand the evolution of SnRK2-V family genes and their roles in various stress conditions, we performed genome-wide identification of the SnRK2-V gene family in H. villosa. Ten SnRK2-V genes were identified and characterized for their structures, functions and spatial expressions. Analysis of gene exon/intron structure further revealed the presence of evolutionary paths and replication events of SnRK2-V gene family in the H. villosa. In addition, the features of gene structure, the chromosomal location, subcellular localization of the gene family were investigated and the phylogenetic relationship were determined using computational approaches. Analysis of cis-regulatory elements of SnRK2-V gene members revealed their close correlation with different phytohormone signals. The expression profiling revealed that ten SnRK2-V genes expressed at least one tissue (leave, stem, root, or grain), or in response to at least one of the biotic (stripe rust or powdery mildew) or abiotic (drought or salt) stresses. Moreover, SnRK2.9-V was up-regulated in H. villosa under the drought and salt stress and overexpressing of SnRK2.9-V in wheat enhanced drought and salt tolerances via enhancing the genes expression of antioxidant enzymes, revealing a potential value of SnRK2.9-V in wheat improvement for salt tolerance.

CONCLUSION

Our present study provides a basic genome-wide overview of SnRK2-V genes in H. villosa and demonstrates the potential use of SnRK2.9-V in enhancing the drought and salt tolerances in common wheat.

The E3 ligase TaGW2 mediates transcription factor TaARR12 degradation to promote drought resistance in wheat

Drought stress limits crop yield, but the molecular modulators and their mechanisms underlying the trade-off between drought resistance and crop growth and development remain elusive. Here, a grain width and weight2 (GW2)-like really interesting new gene finger E3 ligase, TaGW2, was identified as a pivotal regulator of both kernel development and drought responses in wheat (Triticum aestivum). TaGW2 overexpression enhances drought resistance but leads to yield drag under full irrigation conditions. In contrast, TaGW2 knockdown or knockout attenuates drought resistance but remarkably increases kernel size and weight. Furthermore, TaGW2 directly interacts with and ubiquitinates the type-B Arabidopsis response regulator TaARR12, promoting its degradation via the 26S proteasome. Analysis of TaARR12 overexpression and knockdown lines indicated that TaARR12 represses the drought response but does not influence grain yield in wheat. Further DNA affinity purification sequencing combined with transcriptome analysis revealed that TaARR12 downregulates stress-responsive genes, especially group-A basic leucine zipper (bZIP) genes, resulting in impaired drought resistance. Notably, TaARR12 knockdown in the clustered regularly interspaced short palindromic repeat (CRISPR)/CRISPR-associated nuclease 9 (Cas9)-mediated tagw2 knockout mutant leads to significantly higher drought resistance and grain yield compared to wild-type plants. Collectively, these findings show that the TaGW2-TaARR12 regulatory module is essential for drought responses, providing a strategy for improving stress resistance in high-yield wheat varieties.

Crown die-back of peri-urban forests after combined heatwave and drought was species-specific, size-dependent, and also related to tree neighbourhood characteristics

The Rhine River valley of Germany has been facing recurrent and intense spells of drought and heatwaves threatening the health of trees in peri-urban forests. Crown damage intensified by climate change accelerates tree mortality, threatening its ecological, economic, and social benefits; however, the pattern of crown die-back in peri-urban forests remained unclear. We performed a field inventory to estimate the crown die-back of 2578 trees of 51 species from 68 randomly selected peri-urban forest plots in Karlsruhe region on the right bank of the Rhine, after the catastrophic summer heatwave and drought of 2018. We related crown die-back to species-specific drought tolerance, wood anatomical traits, tree size, canopy surface temperature, tree density, Shannon's diversity and Gini coefficient for tree height. Regression results indicate that small-size trees were found to be more susceptible to canopy damage than large trees, with a 1-meter increase in tree height associated with a 0.8 % reduction in crown die-back. This size-dependent process is also species-specific. Among the 12 species with significant (p < 0.05) linear relationship between height and die-back, 9 species demonstrated negative correlations and 3 species showed positive relationships. Species tolerant to drought or cavitation (e.g., trees with diffuse porous xylem, 21 species) had significantly lower crown dieback. For example, with a 1-point-scale increase in drought tolerance crown die-back declined 14.35 %. Trees that experienced high canopy surface temperature and grew with high tree density and species diversity (Shannon's diversity) had more crown die-back. However, high structural diversity (Gini coefficient) was related to lower crown die-back. Our results suggested that future research should focus more on tree species-specific hydraulic and thermal traits and tree density and structure management to improve tree health and species selection in peri-urban forests under future climate change.

Independent and combined effects of microplastics pollution and drought on soil bacterial community

Global terrestrial ecosystems are simultaneously threatened by multiple environmental pressures, with microplastics (MPs) pollution and drought possibly being the most pressing, both of which may have unanticipated effects on soil organisms. Here, we investigated the responses of diversity, composition and functions of soil bacterial community to MPs pollution (including two MPs types: polyethylene (PE) and polylactic acid (PLA); two MPs sizes: < 20 μm and <300 μm) and drought in microcosms. We found that only 20 μm PLA MPs significantly decreased soil bacterial diversity by 17.4 % and altered soil bacterial community composition, while PE MPs and 300 μm PLA MPs had no significant effects. The copiotrophic bacteria (i.e., Proteobacteria and Firmicutes) were enriched in the 20 μm PLA MPs pollution soils due to the enhanced dissolved organic carbon contents. Moreover, our results showed that the 20 μm PLA MPs also affected the potential phenotypes and functions of soil bacterial community, increasing the potentially pathogenic, stress-tolerant, containing mobile elements and forming biofilms phenotypes, and promoting membrane transport and signal transduction pathways. These results suggested that the effects of MPs on soil bacterial community varied depending on MPs types and sizes. However, drought significantly increased soil bacterial diversity by 10.3 % and affected soil bacterial community composition in the 20 μm PLA MPs pollution soils. We also found that drought inhibited the levels of potentially pathogenic, containing mobile elements and forming biofilms phenotypes in the 20 μm PLA MPs pollution soils. Taken together, these findings reveal that drought may alleviate the adverse effects of MPs pollution on soil bacterial community, which enhances our understanding of the interactive effects of multiple global change factors on agroecosystem functions.

Hydro-meteorological droughts across the Baltic Region: The role of the accumulation periods

Based on the physical and geographical conditions, the Baltic Region is categorised as a humid climate zone. This means that, there is usually more precipitation than evaporation throughout the year, suggesting that droughts should not occur frequently in this region. Despite the humid climate in the region, the study focused on assessing the spatio-temporal patterns of droughts. The drought events were analysed across the Baltic Region, including Sweden, Finland, Lithuania, Latvia, and Estonia. This analysis included two drought indices, the Standardized Precipitation Index (SPI) and the Streamflow Drought Index (SDI), for different accumulation periods. Daily data series of precipitation and river discharge were used. The spatial and temporal analyses of selected drought indices were carried out for the Baltic Region. In addition, the decadal distribution of drought classes was analysed to disclose the temporal changes and spatial extent of drought patterns. The Pearson correlation between SPI and SDI was applied to investigate the relationship between meteorological and hydrological droughts. The analysis showed that stations with more short-duration SPI or SDI cases had fewer long-duration cases and vice versa. The number of SDI cases (SDI ≤ -1) increased in the Western Baltic States and some WGSs in Sweden and Finland from 1991 to 2020 compared to 1961-1990. The SPI showed no such tendencies except in Central Estonia and Southern Finland. The 6-month accumulation period played a crucial role in both the meteorological and hydrological drought analyses, as it revealed prolonged and widespread drought events. Furthermore, the 9- and 12-month accumulation periods showed similar trends in terms of drought duration and spatial extent. The highest number of correlation links between different months was found between SPI12-SDI9 and SPI12-SDI12. The results obtained have deepened our understanding of drought patterns and their potential impacts in the Baltic Region.

Spatiotemporal patterns of net primary productivity of subtropical forests in China and its response to drought

Net primary productivity (NPP) is an important indicator used to evaluate the carbon sequestration capacity of forest ecosystems. Subtropical forest ecosystems play an indispensable role in maintaining the global carbon balance, while frequently occurring drought events in recent years have seriously damaged their productivity. However, the spatiotemporal patterns of NPP, as well as its response to drought, remain uncertain. In this study, the multiscale drought characteristics in subtropical China during 1981-2015 were analyzed based on the standardized precipitation evapotranspiration index. Then, simulated and analyzed the spatiotemporal NPP of subtropical forests by the boreal ecosystem productivity simulator model. Finally, the response of NPP to drought was analyzed based on multiple statistical indices. The results show that most regions in subtropical China experienced mild and moderate drought during 1981-2015. In particular, the extent of drought severity has shown a noticeable increasing trend after 2000. The forest NPP ranged from 622.64 to 1323.82 gC·m-2·a-1, with an overall increase rate of 16.15 gC·m-2·a-1; in particular, the contribution of the western forest NPP became increasingly important. Drought stress has limited the growth of subtropical forest NPP in China, with summer and wet season time scales of drought having the greatest impact on forest NPP anomalies, followed by autumn time scales. The limitation is mostly because the drought duration continually increased, leading to differences in the impact of drought on forest NPP before and after 2000, with declines of 59.55 % and 82.45 %, respectively, mainly concentrated in southwestern regions, such as Yunnan, Guangxi, and Sichuan provinces. This study quantitatively analyzed the impact of drought on subtropical forest NPP, and provides scientific basis for subtropical forest response and adaptation to climate change.

Nitrogen enrichment delays the drought threshold responses of leaf photosynthesis in alpine grassland plants

Extreme drought is found to cause a threshold response in photosynthesis in ecosystem level. However, the mechanisms behind this phenomenon are not well understood, highlighting the importance of revealing the drought thresholds for multiple leaf-level photosynthetic processes. Thus, we conducted a long-term experiment involving precipitation reduction and nitrogen (N) addition. Moreover, an extreme drought event occurred within the experimental period. We found the presence of drought thresholds for multiple leaf-level photosynthetic processes, with the leaf light-saturated carbon assimilation rate (Asat) displaying the highest threshold (10.76 v/v%) and the maximum rate of carboxylation by Rubisco (Vcmax) showing the lowest threshold (5.38 v/v%). Beyond the drought thresholds, the sensitivities of leaf-level photosynthetic processes to soil water content could be greater. Moreover, N addition lowered the drought thresholds of Asat and stomatal conductance (gs), but had no effect on that of Vcmax. Among species, plants with higher leaf K concentration traits had a lower drought threshold of Asat. Overall, this study highlights that leaf photosynthesis may be suppressed abruptly as soil water content surpasses the drought threshold. However, N enrichment helps to improve the resistance via delaying drought threshold response. These new findings have important implications for understanding the nonlinearity of ecosystem productivity response and early warning management in the scenario of combined extreme drought events and continuous N deposition.

Understanding genetic diversity in drought-adaptive hybrid parental lines in pearl millet

Information on genetic diversity and population structure is helpful to strategize enhancing the genetic base of hybrid parental lines in breeding programs. The present study determined the population structure and genetic diversity of 109 pearl millet hybrid parental lines, known for their better adaptation and performance in drought-prone environments, using 16,472 single nucleotide polymorphic (SNP) markers generated from GBS (genotyping-by-sequencing) platforms. The SNPs were distributed uniformly across the pearl millet genome and showed considerable genetic diversity (0.337), expected heterozygosity (0.334), and observed heterozygosity (0.031). Most of the pairs of lines (78.36%) had Identity-by-State (IBS) based genetic distances of more than 0.3, indicating a significant amount of genetic diversity among the parental lines. Bayesian model-based population stratification, neighbor-joining phylogenetic analysis, and principal coordinate analysis (PCoA) differentiated all hybrid parental lines into two clear-cut major groups, one each for seed parents (B-lines) and pollinators (R-lines). Majority of parental lines sharing common parentages were found grouped in the same cluster. Analysis of molecular variance (AMOVA) revealed 7% of the variation among subpopulations, and 93% of the variation was attributable to within sub-populations. Chromosome 3 had the highest number of LD regions. Genomic LD decay distance was 0.69 Mb and varied across the different chromosomes. Genetic diversity based on 11 agro-morphological and grain quality traits also suggested that the majority of the B- and R-lines were grouped into two major clusters with few overlaps. In addition, the combined analysis of phenotypic and genotypic data showed similarities in the population grouping patterns. The present study revealed the uniqueness of most of the inbred lines, which can be a valuable source of new alleles and help breeders to utilize these inbred lines for the development of hybrids in drought-prone environments.

The first global multi-timescale daily SPEI dataset from 1982 to 2021

Global warming accelerates water cycle, causing more droughts globally that challenge monitoring and forecasting. The Standardized Precipitation Evapotranspiration Index (SPEI) is used to assess drought characteristics and response time of natural and economic systems at various timescales. However, existing SPEI datasets have coarse spatial or temporal resolution or limited spatial extent, restricting their ability to accurately identify the start or end dates or the extent of drought at the global scale. To narrow these gaps, we developed a global daily SPEI dataset (SPEI-GD), with a 0.25° spatial resolution from 1982 to 2021 at multiple timescales (5, 30, 90, 180 and 360 days), based on the precipitation from European Center for Medium Weather Forecasting Reanalysis V5 (ERA5) dataset and the potential evapotranspiration from Singer's dataset. Compared to widely used SPEIbase dataset, the SPEI-GD can improve the spatial-temporal resolution and the accuracy of SPEI in areas where meteorological sites are lacking. The SPEI-GD significantly correlates with site-based SPEI and soil moisture. Our dataset solidly supports sub-seasonal and daily-scale global and regional drought research.

Isolation and Structure Determination of Drought-Induced Multihexose Benzoxazinoids from Maize (Zea mays)

Benzoxazinoids (BXDs) are plant specialized metabolites exerting a pivotal role in plant nutrition, allelopathy, and defenses. Multihexose benzoxazinoids were previously observed in cereal-based food products such as whole-grain bread. However, their production in plants and exact structure have not been fully elucidated. In this study, we showed that drought induced the production of di-, tri-, and even tetrahexose BXDs in maize roots and leaves. We performed an extensive nuclear magnetic resonance study and elucidated the nature and linkage of the sugar units, which were identified as gentiobiose units β-linked (1″ → 6') for the dihexoses and (1″ → 6')/(1‴ → 6″) for the trihexoses. Drought induced the production of DIMBOA-2Glc, DIMBOA-3Glc, HMBOA-2Glc, HMBOA-3Glc, and HDMBOA-2Glc. The induction was common among several maize lines and the strongest in seven-day-old seedlings. This work provides ground to further characterize the BXD synthetic pathway, its relevance in maize-environment interactions, and its impact on human health.

Rapidly mining candidate cotton drought resistance genes based on key indicators of drought resistance

BACKGROUND

Focusing on key indicators of drought resistance is highly important for quickly mining candidate genes related to drought resistance in cotton.

RESULTS

In the present study, drought resistance was identified in drought resistance-related RIL populations during the flowering and boll stages, and multiple traits were evaluated; these traits included three key indicators: plant height (PH), single boll weight (SBW) and transpiration rate (Tr). Based on these three key indicators, three groups of extreme mixing pools were constructed for BSA-seq. Based on the mapping interval of each trait, a total of 6.27 Mb QTL intervals were selected on chromosomes A13 (3.2 Mb), A10 (2.45 Mb) and A07 (0.62 Mb) as the focus of this study. Based on the annotation information and qRT‒PCR analysis, three key genes that may be involved in the drought stress response of cotton were screened: GhF6'H1, Gh3AT1 and GhPER55. qRT‒PCR analysis of parental and extreme germplasm materials revealed that the expression of these genes changed significantly under drought stress. Cotton VIGS experiments verified the important impact of key genes on cotton drought resistance.

CONCLUSIONS

This study focused on the key indicators of drought resistance, laying the foundation for the rapid mining of drought-resistant candidate genes in cotton and providing genetic resources for directed molecular breeding of drought resistance in cotton.

Evaluation of drought-tolerant varieties based on root system architecture in cotton (Gossypium hirsutum L.)

BACKGROUND

Root system architecture (RSA) exhibits significant genetic variability and is closely associated with drought tolerance. However, the evaluation of drought-tolerant cotton cultivars based on RSA in the field conditions is still underexplored.

RESULTS

So, this study conducted a comprehensive analysis of drought tolerance based on physiological and morphological traits (i.e., aboveground and RSA, and yield) within a rain-out shelter, with two water treatments: well-watered (75 ± 5% soil relative water content) and drought stress (50 ± 5% soil relative water content). The results showed that principal component analysis identified six principal components, including highlighting the importance of root traits and canopy parameters in influencing drought tolerance. Moreover, the systematic cluster analysis was used to classify 80 cultivars into 5 categories, including drought-tolerant cultivars, relatively drought-tolerant cultivars, intermediate cultivars, relatively drought-sensitive cultivars, and drought-sensitive cultivars. Further validation of the drought tolerance index showed that the yield drought tolerance index and biomass drought tolerance index of the drought-tolerant cultivars were 8.97 and 5.05 times higher than those of the drought-sensitive cultivars, respectively.

CONCLUSIONS

The RSA of drought-tolerant cultivars was characterised by a significant increase in average length-all lateral roots, a significant decrease in average lateral root emergence angle and a moderate root/shoot ratio. In contrast, the drought-sensitive cultivars showed a significant decrease in average length-all lateral roots and a significant increase in both average lateral root emergence angle and root/shoot ratio. It is therefore more comprehensive and accurate to assess field crop drought tolerance by considering root performance.

Thawing permafrost can mitigate warming-induced drought stress in boreal forest trees

Perennially frozen soil, also known as permafrost, is important for the functioning and productivity of most of the boreal forest, the world's largest terrestrial biome. A better understanding of complex vegetation-permafrost interrelationships is needed to predict changes in local- to large-scale carbon, nutrient, and water cycle dynamics under future global warming. Here, we analyze tree-ring width and tree-ring stable isotope (C and O) measurements of Gmelin larch (Larix gmelinii (Rupr.) Rupr.) from six permafrost sites in the northern taiga of central Siberia. Our multi-parameter approach shows that changes in tree growth were predominantly controlled by the air and topsoil temperature and moisture content of the active soil and upper permafrost layers. The observed patterns range from strong growth limitations by early summer temperatures at higher elevations to significant growth controls by precipitation at warmer and well-drained lower-elevation sites. Enhanced radial tree growth is mainly found at sites with fast thawing upper mineral soil layers, and the comparison of tree-ring isotopes over five-year periods with different amounts of summer precipitation indicates that trees can prevent drought stress by accessing water from melted snow and seasonally frozen soil. Identifying the active soil and upper permafrost layers as central water resources for boreal tree growth during dry summers demonstrates the complexity of ecosystem responses to climatic changes.

Increased cover of native and exotic plants on the rims of harvester ant (Hymenoptera: Formicidae) nests under grazing and drought

Harvester ants create habitats along nest rims, which some plants use as refugia. These refugia can enhance ecosystem stability to disturbances like drought and grazing, but their potential role in invasion ecology is not yet tested. Here we examine the effects of drought and grazing on nest-rim refugia of 2 harvester ant species: Pogonomyrmex occidentals and P. rugosus. We selected 4 rangeland sites with high harvester ant nest densities in northern Arizona, USA, with pre-existing grazing exclosures adjacent to heavily grazed habitat. Our objective was to determine whether nest refugia were used by native or exotic plant species for each site and scenario of drought and grazing. We measured vegetation cover on nest surfaces, on nest rims, and at 3 distances (3, 5, and 10 m) from nests. At each site, we sampled 2 treatments (grazed/excluded) during 2 seasons (drought/monsoon). We found that nest rims increased vegetation cover compared with background levels at all sites and in almost all scenarios of treatment and season, indicating that nest rims provide important refugia for plants from drought and cattle grazing. In some cases, plants enhanced on nest rims were native grasses such as blue gramma (Bouteloua gracilis) or forbs such as sunflowers (Helianthus petiolaris). However, nest rims at all sites enhanced exotic species, particularly Russian thistle (Salsola tragus), purslane (Portulaca oleracea), and bull thistle (Cirsium vulgare). These results suggest that harvester ants play important roles in invasion ecology and restoration. We discuss potential mechanisms for why certain plant species use nest-rim refugia and how harvester ant nests contribute to plant community dynamics.

The effect of heterogeneous severe drought on all-cause and cardiovascular mortality in the Northern Rockies and Plains of the United States

Drought is a distinct and complicated climate hazard that regularly leads to severe economic impacts. Changes in the frequency and occurrence of drought due to anthropogenic climate change can lead to new and unanticipated outcomes. To better prepare for health outcomes, more research is needed to develop methodologies to understand potential consequences. This study suggests a new methodology for assessing the impact of monthly severe drought exposure on mortality in the Northern Rockies and Plains of the United States from 2000 to 2018. A two-stage model with the power prior approach was applied to integrate heterogeneous severe drought pattern and estimate overall risk ratios of all-cause and cardiovascular mortality related to multiple drought indices (the US Drought Monitor, 6- and 12-month Standardized Precipitation-Evapotranspiration Index, 6- and 12 month Evaporative Demand Drought Index). Under severe drought, the risk ratios of all-cause mortality are 1.050 (95 % Cr: 1.031 to 1.071, USDM), 1.041 (95 % Cr: 1.022 to 1.060, 6-SPEI), 1.009 (95 % Cr: 0.989 to 1.031, 12SPEI), 1.045 (95 % Cr: 1.022 to 1.067, 6-EDDI), and 1.035 (95 % Cr: 1.009 to 1.062, 12-EDDI); cardiovascular mortality are 1.057 (95 % Cr: 1.023 to 1.091, USDM), 1.028 (95 % Cr: 0.998 to 1.059, 6-SPEI), 1.005 (95 % Cr: 0.973 to 1.040, 12-SPEI), 1.042 (95 % Cr: 1.005 to 1.080, 6-EDDI), and 1.004 (95 % Cr: 0.959 to 1.049, 12-EDDI). Our results showed that (i) a model with properly accounted for heterogeneous exposure pattern had greater risk ratios if statistically significant; (ii) a mid-term (6-month) severe drought had higher risk ratios compared to longer-term (12-month) drought; and (iii) different severe droughts affect populations in a different way. These results expand the existing knowledge of drought relationship to increasing mortality in the United States. The findings from this study highlight the need for communities and policymakers to establish effective drought-prevention initiatives in this region.

Drought limits vegetation carbon sequestration by affecting photosynthetic capacity of semi-arid ecosystems on the Loess Plateau

Drought is the driver for ecosystem production in semi-arid areas. However, the response mechanism of ecosystem productivity to drought remains largely unknown. In particular, it is still unclear whether drought limits the production via photosynthetic capacity or phenological process. Herein, we assess the effects of maximum seasonal photosynthesis, growing season length, and climate on the annual gross primary productivity (GPP) in vegetation areas of the Loess Plateau using multi-source remote sensing and climate data from 2001 to 2021. We found that maximum seasonal photosynthesis rather than growing season length dominates annual GPP, with above 90 % of the study area showing significant and positive correlation. GPP and maximum seasonal photosynthesis were positively correlated with self-calibrating Palmer Drought Severity Index (scPDSI), standardized precipitation and evapotranspiration index (SPEI) in >95 % of the study area. Structural equation model demonstrated that both drought indices contributed to the annual GPP by promoting the maximum seasonal photosynthesis. Total annual precipitation had a positive and significant effect on two drought indices, whereas the effects of temperature and radiation were not significant. Evidence from wood formation data also confirmed that low precipitation inhibited long-term carbon sequestration by decreasing the maximum growth rate in forests. Our findings suggest that drought limits ecosystem carbon sequestration by inhibiting vegetation photosynthetic capacity rather than phenology, providing a support for assessing the future dynamics of the terrestrial carbon cycle and guiding landscape management in semi-arid ecosystems.

The role of edaphic variables and management practices in regulating soil microbial resilience to drought - A meta-analysis

Environmental disturbances such as drought can impact soil health and the resistance (ability to withstand environmental stress) and resilience (ability to recover functional and structural integrity after stress) of soil microbial functional activities. A paucity of information exists on the impact of drought on soil microbiome and how soil biological systems respond to and demonstrate resilience to drought stress. To address this, we conducted a systematic review and meta-analysis (using only laboratory studies) to assess the response of soil microbial biomass and respiration to drought stress across agriculture, forest, and grassland ecosystems. The meta-analysis revealed an overall negative response of microbial biomass in resistance (-31.6 %) and resilience (-0.3 %) to drought, suggesting a decrease in soil microbial biomass content. Soil microbial respiration also showed a negative response in resistance to drought stress indicating a decrease in soil microbial respiration in agriculture (-17.5 %), forest (-64.0 %), and grassland (-65.5 %) ecosystems. However, it showed a positive response in resilience to drought, suggesting an effective recovery in microbial respiration post-drought. Soil organic carbon (SOC), clay content, and pH were the main regulating factors of the responses of soil microbial biomass and respiration to drought. In agriculture ecosystem, soil pH was primarily correlated with soil microbial respiration resistance and resilience to drought, potentially influenced by frequent land preparation and fertilizer applications, while in forest ecosystem SOC, clay content, and pH significantly impacted microbial biomass and respiration resistance and resilience. In grassland ecosystem, SOC was strongly associated with biomass resilience to drought. The impact of drought stress on soil microbiome showed different patterns in natural and agriculture ecosystems, and the magnitude of microbial functional responses regulated by soil intrinsic properties. This study highlighted the importance of understanding the role of soil properties in shaping microbial responses to drought stress for better ecosystem management.

Growing-season drought and nitrogen addition interactively impair grassland ecosystem stability by reducing species diversity, asynchrony, and stability

Aboveground net primary productivity controls the amount of energy available to sustain all living organisms, and its sustainable provision relies on the stability of grassland ecosystems. Human activities leading to global changes, such as increased nitrogen (N) deposition and the more frequent occurrence of extreme precipitation events, with N addition increasing the sensitivity of ecosystem production stability to changes in the precipitation regime. However, whether N addition, in combination with seasonal precipitation increases or severe drought, affects ecosystem stability remains unclear. In this study, we conducted a six-year environmental change monitoring experiment in a semiarid grassland in northern China to test the effects of N addition, seasonal drought, and precipitation increases on the temporal stability of ecosystem productivity. Our study revealed that an interaction between drought and N addition reduced species diversity, species asynchrony, species stability, and thus ecosystem stability. These environmental change drivers (except for precipitation increase) induced a positive relationship between species asynchrony and diversity, whereas N addition interactively with drought and precipitation increase led to a negative relationship between diversity and species stability. Only N addition interactively with drought induced a positive species diversity-ecosystem stability relationship because lower species stability was overcome by increased species asynchrony. Our study is great importance to illustrate that production temporal stability tends to be inhibited with drought, though interactively with nutrient N addition. These findings highlight the primary role of asynchronous dynamics among species in modulating the effects of environmental change on diversity-stability relationships.

Climatic drivers of cork growth depend on site aridity

Cork is one of the main non-timber forest products in the world. Most of its production is concentrated in the Iberian Peninsula, a climate change hotspot. Climate warming may lead to increased aridification and reduce cork production in that region. However, we still lack assessments of climate-cork relationships across ample geographical and climatic gradients explicitly considering site aridity. We quantified cork growth by measuring cork ring width and related it to climate variables and a drought index using dendrochronology. Four cork oak (Quercus suber) forests located from north eastern Spain to south western Morocco (31.5-41.5° N) and subjected to different aridity levels were sampled. Warm conditions in spring to early summer, when cork is formed, reduced cork width, whereas high precipitation in winter and spring enhanced it. The response of cork to increased water availability in summer peaked (r = 0.89, p = 0.00002) in the most arid and continental site considering 14-month long droughts. A severe drought caused a disproportionate loss of cork production in this site, where for every five-fold decrease in the drought index, the cork-width index declined by a factor of thirteen. Therefore, site aridity determines the responses of cork growth to the soil water availability resulting from accumulated precipitation during winter and spring previous to cork growth and until summer. In general, this cumulative water balance, which is very dependent on temperature and evapotranspiration rate, is critical for cork production, especially in continental, dry sites. The precipitation during the hydrological year can be used as a proxy of cork production in similar sites. Assessments of climate-cork relationships in the western Mediterranean basin could be used as analogues to forecast the impacts of aridification on future cork production.

Higher latewood to earlywood ratio increases resistance of radial growth to severe droughts in larch

As drought has caused great losses of tree growth across the world, the mechanism of how trees adapt to drought has been extensively investigated. However, how trees change their late- to earlywood ratio (LER) to adapt to severe drought events remains poorly understood. We used a network of Larix principis-rupprechtii earlywood and latewood width data from 1979 to 2018, covering most of the distribution of planted larch across North China, to investigate how latewood proportion affected trees' resistance to drought. The interactions among LER, minimum temperature, vapor pressure deficit (VPD), growing season length, and their contributions to drought resistant (Rt) were estimated using structural equation models. The results show a significant increase in LER of the juvenile wood throughout the first 15 growth rings after which it stabilizes. The LER decreased significantly with elevation for the juvenile wood. March-May temperature and VPD were the main determinant in the LER of mature wood. The sensitivity of radial growth to droughts was positively changed with LER when LER was below 0.50, but negatively changed with LER when LER is above 0.50. We confirmed that high LER increases resistance of tree growth to severe droughts in L. principis-rupprechtii. Our results highlight that a higher proportion of latewood is formed in dry years, and this high drought sensitivity of LER in turn led to an increased resistance to drought. This combination of reduced radial growth during dry years, while the latewood proportion remains increases maybe an adaptive strategy of larch trees to cope with severe droughts.

Slower growth prior to the 2018 drought and a high growth sensitivity to previous year summer conditions predisposed European beech to crown dieback

The record-breaking drought in 2018 caused premature leaf discoloration and shedding (early browning) in many beech (Fagus sylvatica L.) dominated forests in Central Europe. However, a high degree of variability in drought response among individual beech trees was observed. While some trees were severely impacted by the prolonged water deficits and high temperatures, others remained vital with no or only minor signs of crown vitality loss. Why some beech trees were more susceptible to drought-induced crown damage than others and whether growth recovery is possible are poorly understood. Here, we aimed to identify growth characteristics associated with the variability in drought response between individual beech trees based on a sample of 470 trees in northern Switzerland. By combining tree growth measurements and crown condition assessments, we also investigated the possible link between crown dieback and growth recovery after drought. Beech trees with early browning exhibited an overall lower growth vigor before the 2018 drought than co-occurring vital beech trees. This lower vigor is mainly indicated by lower overall growth rates, stronger growth declines in the past decades, and higher growth-climate sensitivity. Particularly, warm previous year summer conditions negatively affected current growth of the early-browning trees. These findings suggest that the affected trees had less access to critical resources and were physiologically limited in their growth predisposing them to early browning. Following the 2018 drought, observed growth recovery potential corresponded to the amount of crown dieback and the local climatic water balance. Overall, our findings emphasize that beech-dominated forests in Central Europe are under increasing pressure from severe droughts, ultimately reducing the competitive ability of this species, especially on lowland sites with shallow soils and low water holding capacity.

DNA methylation: an emerging paradigm of gene regulation under drought stress in plants

Drought is an enormous threat to global crop production. In order to ensure food security for the burgeoning population, we must develop drought tolerant crop varieties. This necessitates the identification of drought-responsive genes and understanding the mechanisms involved in their regulation. DNA methylation is a widely studied mechanism of epigenetic regulation of gene expression, which is known to play vital role in conferring tolerance to various biotic and abiotic stress factors. The recent advances in next-generation sequencing (NGS) technologies, has allowed unprecedented access to genome-wide methylation marks, with single base resolution. The most important roles of DNA methylation have been studied in terms of gene body methylation (gbM), which is associated with regulation of both transcript abundance and its stability. The availability of mutants for the various genes encoding enzymes involved in methylation of DNA has allowed ascertainment of the biological significance of methylation. Even though a vast number of reports have emerged in the recent past, where both genome-wide methylation landscape and locus specific changes in DNA methylation have been studied, a conclusive picture with regards to the biological role of DNA methylation is still lacking. Compounding this, is the lack of sufficient evidence supporting the heritability of these epigenetic changes. Amongst the various epigenetic variations, the DNA methylation changes are observed to be the most stable. This review describes the drought-induced changes in DNA methylation identified across different plant species. We also briefly describe the stress memory contributed by these changes. The identification of heritable, drought-induced methylation marks would broaden the scope of crop improvement in the future.

Expression Patterns and Molecular Mechanisms Regulating Drought Tolerance of Soybean [Glycine max (L.) Merr.] Conferred by Transcription Factor Gene GmNAC19

NAC transcription factors are commonly involved in the plant response to drought stress. A transcriptome analysis of root samples of the soybean variety 'Jiyu47' under drought stress revealed the evidently up-regulated expression of GmNAC19, consistent with the expression pattern revealed by quantitative real-time PCR analysis. The overexpression of GmNAC19 enhanced drought tolerance in Saccharomyces cerevisiae INVSc1. The seed germination percentage and root growth of transgenic Arabidopsis thaliana were improved in comparison with those of the wild type, while the transgenic soybean composite line showed improved chlorophyll content. The altered contents of physiological and biochemical indices (i.e., soluble protein, soluble sugar, proline, and malondialdehyde) related to drought stress and the activities of three antioxidant enzymes (i.e., superoxide dismutase, peroxidase, and catalase) revealed enhanced drought tolerance in both transgenic Arabidopsis and soybean. The expressions of three genes (i.e., P5CS, OAT, and P5CR) involved in proline synthesis were decreased in the transgenic soybean hairy roots, while the expression of ProDH involved in the breakdown of proline was increased. This study revealed the molecular mechanisms underlying drought tolerance enhanced by GmNAC19 via regulation of the contents of soluble protein and soluble sugar and the activities of antioxidant enzymes, providing a candidate gene for the molecular breeding of drought-tolerant crop plants.

The Promising B-Type Response Regulator hst1 Gene Provides Multiple High Temperature and Drought Stress Tolerance in Rice

High temperatures, drought, and salt stresses severely inhibit plant growth and production due to the effects of climate change. The Arabidopsis ARR1, ARR10, and ARR12 genes were identified as negative salt and drought stress regulators. However, in rice, the tolerance capacity of the hst1 gene, which is orthologous to the ARR1, ARR10, and ARR12 genes, to drought and multiple high temperature and drought stresses remains unknown. At the seedling and reproductive stages, we investigated the drought (DS) high temperature (HT) and multiple high temperature and drought stress (HT+DS) tolerance capacity of the YNU31-2-4 (YNU) genotype, which carries the hst1 gene, and its nearest genomic relative Sister Line (SL), which has a 99% identical genome without the hst1 gene. At the seedling stage, YNU demonstrated greater growth, photosynthesis, antioxidant enzyme activity, and decreased ROS accumulation under multiple HT+DS conditions. The YNU genotype also demonstrated improved yield potential and grain quality due to higher antioxidant enzyme activity and lower ROS generation throughout the reproductive stage under multiple HT+DS settings. Furthermore, for the first time, we discovered that the B-type response regulator hst1 gene controls ROS generation and antioxidant enzyme activities by regulating upstream and downstream genes to overcome yield reduction under multiple high temperatures and drought stress. This insight will help us to better understand the mechanisms of high temperature and drought stress tolerance in rice, as well as the evolution of tolerant crops that can survive increased salinity to provide food security during climate change.

Remote sensing-based drought hazard monitoring and assessment in a coastal plain: A principal component approach

Accurate drought information is essential for preventing agricultural and societal losses. The indicators of how severe a drought is the deficiency in precipitation, soil moisture, and vegetation stress. The indicators were evaluated using the Precipitation Condition Index (PCI), Vegetation Condition Index (VCI), and Temperature Condition Index (TCI).The indices were combined using Principal Component Analysis to create the Synthetic Drought Index (SDI) for the evaluation of drought severity. The indices were estimated using multi-source remote sensing data from the Tropical Rainfall Measuring Mission (TRMM) and Operational Land Imager (OLI) of various years. Temporal analysis showed that the district is drought-prone and deficiency of 65% of precipitation in northeast monsoon of 2016 and below average non-monsoon rainfall in 2017, caused drought and affected 223.5 Km2 in 2017. Below average precipitation in northeast monsoon of 2018 and below average non-monsoon rainfall in 2019, caused drought and affected 423 Km2 in 2019. The northeast coastal regions of Ottapidaram, Thoothukudi, and Vilathikulam taluks of the district were more severely prone to drought. Failure of monsoon is the root cause of water deficit in water bodies. The semi-arid coastal climate accelerates the evaporation of water in water bodies and causes soil moisture deficit that leads to drought in the coastal district. A sequential evaluation of this index can be used to identify the onset of drought and mitigate the effect of drought.

Chasing high and stable wheat grain mineral content: Mining diverse spring genotypes under induced drought stress

Climate change-induced drought has an effect on the nutritional quality of wheat. Here, the impact of drought at different plant stages on mineral content in mature wheat was evaluated in 30 spring-wheat lines of diverse backgrounds (modern, old and wheat-rye-introgressions). Genotypes with rye chromosome 3R introgression showed a high accumulation of several important minerals, including Zn and Fe, and these also showed stability across drought conditions. High Se content was found in genotypes with chromosome 1R. Old cultivars (K, Mg, Na, P and S) and 2R introgression lines (Fe, Ca, Mn, Mg and Na) demonstrated high mineral yield at early and late drought, respectively. Based on the low nutritional value often reported for modern wheat and negative climate effects on the stability of mineral content and yield, genes conferring high Zn/Fe, Se, and stable mineral yield under drought at various plant stages should be explicitly explored among 3R, 1R, old and 2R genotypes, respectively.

Accumulation of Phosphorylated SnRK2 Substrate 1 Promotes Drought Escape in Arabidopsis

Plants adopt optimal tolerance strategies depending on the intensity and duration of stress. Retaining water is a priority under short-term drought conditions, whereas maintaining growth and reproduction processes takes precedence over survival under conditions of prolonged drought. However, the mechanism underlying changes in the stress response depending on the degree of drought is unclear. Here, we report that SNF1-related protein kinase 2 (SnRK2) substrate 1 (SNS1) is involved in this growth regulation under conditions of drought stress. SNS1 is phosphorylated and stabilized by SnRK2 protein kinases reflecting drought conditions. It contributes to the maintenance of growth and promotion of flowering as drought escape by repressing stress-responsive genes and inducing FLOWERING LOCUS T (FT) expression, respectively. SNS1 interacts with the histone methylation reader proteins MORF-related gene 1 (MRG1) and MRG2, and the SNS1-MRG1/2 module cooperatively regulates abscisic acid response. Taken together, these observations suggest that the phosphorylation and accumulation of SNS1 in plants reflect the intensity and duration of stress and can serve as a molecular scale for maintaining growth and adopting optimal drought tolerance strategies under stress conditions.

Emerging trends and spatial shifts of drought potential across global river basins

Droughts have devastating effects on various sectors and are difficult to quantify and track because of the invisible and slow but prevalent propagation. This dilemma is more significant in the case of the complex interactions between land and atmosphere mechanisms, which are inadequately considered in previous drought metrics. Here, we investigate the spatiotemporal variability of the recently devised metric called 'Drought Potential Index (DPI)', which incorporates the antecedent land water storage and current precipitation. Using the spatial weighted centroid method, we elucidate the emerging spatial movement of the DPI within 168 major global river basins and analyze its influential factors. Improved drought detection and performance disparity of DPI as compared with multi-scale (i.e., 1, 3, 6, 9, 12-month) Standardized Precipitation Index, ensemble soil moisture anomaly, and Total Storage Deficit Index corroborate the robustness and improved insights of DPI. Higher increasing trends in DPI are detected over dryland basins (0.39 ± 0.43 %/a) than in the humid zones (0.15 ± 0.34 %/a). Six hotspot basins, namely, Don, Yellow, Haihe, Rio Grande, Sao Francisco, and Ganges river basins, are identified with increasing (2.1-3.5%/a) DPI during 2003-2021. The interannual occurrence of the highest DPI, spatial shifts, and relative contribution of DPI's constituent variables correspond well to the climatic and anthropogenic changes in humid and dry land basins. The absolute latitudinal/longitudinal shifts of ∼2° (as high as ∼3.2/4.9°) in DPI in 30% (47 out of 168 basins) of the global basins highlight the need for analyzing the water scarcity problems from both the perspectives of long-term trends and spatial shifts. Our findings provide a global assessment of the spatiotemporal shifts of drought potential and will be beneficial to understanding the anthropogenic and climatic influences on water resource management under a changing environment.

The underexposed nature-based solutions: A critical state-of-art review on drought mitigation

Droughts are the most expensive climate disasters as they leave long-term and chronic impacts on the ecosystem, agriculture, and human society. The intensity, frequency, and duration of drought events have increased over the years and are expected to worsen in the future on a regional and planetary/global scale. Nature-based solutions (NBS) such as wetland and floodplain restorations, green infrastructures, rainwater harvesting, etc., are highlighted as effective solutions to cope with the future impacts of these events. While the role of NBS in coping with the impacts of other disasters, such as floods, has been extensively studied, there has been a lack of comprehensive review of NBS targeting drought. The following paper provides a unique critical state-of-the-art literature review of individual drought-related NBS around the world, in Europe, and particularly in Belgium, and assesses the critical differences between the NBS applied globally and in Flanders. An extensive literature review was conducted to systematically analyze NBS, listing the type, the location, the status of the implementation, and the possible recommendations proposed to optimize future NBS applications. Finally, a comparison is made between small- and large-scale applications of NBS. By analyzing all these aspects, especially the level of effectiveness and recommendations, insight was gained into the future potential of NBS and possible improvements. The research indicated a lack of scientific publications, especially in Belgium. Hence, grey literature was also included in the literature review. Only four papers included a quantitative assessment regarding the effectiveness of drought on a global level, all stating a positive impact on groundwater recharge. In contrast, at regional and country levels, the performance of NBS was not quantified. The number of large-scale implementations is low, where landscape- or watershed-scale holistic approaches to drought mitigation are still scarce. Some successfully implemented projects are only very local and have a long realization time, two aspects that limit achieving visible impact at a larger scale. Among the many NBS, wetlands are recognized as highly effective in coping with drought but are still degraded or lost despite their significant restoration potential. A common effectiveness evaluation framework shall be followed, which gives policymakers a clear view of the different NBS investment options. Furthermore, a more collaborative approach is recommended globally, including different stakeholder groups, with specific attention to the local communities. To conclude, future research should increase the evidence base and implementation of drought-mitigating NBS.