Critical slowing down of the Amazon forest after increased drought occurrence.

Dynamic ecosystems, such as the Amazon forest, are expected to show critical slowing down behavior, or slower recovery from recurrent small perturbations, as they approach an ecological threshold to a different ecosystem state. Drought occurrences are becoming more prevalent across the Amazon, with known negative effects on forest health and functioning, but their actual role in the critical slowing down patterns still remains elusive. In this study, we evaluate the effect of trends in extreme drought occurrences on temporal autocorrelation (TAC) patterns of satellite-derived indices of vegetation activity, an indicator of slowing down, between 2001 and 2019. Differentiating between extreme drought frequency, intensity, and duration, we investigate their respective effects on the slowing down response. Our results indicate that the intensity of extreme droughts is a more important driver of slowing down than their duration, although their impacts vary across the different Amazon regions. In addition, areas with more variable precipitation are already less ecologically stable and need fewer droughts to induce slowing down. We present findings indicating that most of the Amazon region does not show an increasing trend in TAC. However, the predicted increase in extreme drought intensity and frequency could potentially transition significant portions of this ecosystem into a state with altered functionality.

LncRNA DANA1 promotes drought tolerance and histone deacetylation of drought responsive genes in Arabidopsis.

Although many long noncoding RNAs have been discovered in plants, little is known about their biological function and mode of action. Here we show that the drought-induced long intergenic noncoding RNA DANA1 interacts with the L1p/L10e family member protein DANA1-INTERACTING PROTEIN 1 (DIP1) in the cell nucleus of Arabidopsis, and both DANA1 and DIP1 promote plant drought resistance. DANA1 and DIP1 increase histone deacetylase HDA9 binding to the CYP707A1 and CYP707A2 loci. DIP1 further interacts with PWWP3, a member of the PEAT complex that associates with HDA9 and has histone deacetylase activity. Mutation of DANA1 enhances CYP707A1 and CYP707A2 acetylation and expression resulting in impaired drought tolerance, in agreement with dip1 and pwwp3 mutant phenotypes. Our results demonstrate that DANA1 is a positive regulator of drought response and that DANA1 works jointly with the novel chromatin-related factor DIP1 on epigenetic reprogramming of the plant transcriptome during the response to drought.

BAPID suppresses the inhibition of BRM on Di19-PR module in response to drought.

Drought is one of the most important abiotic stresses, and seriously threatens plant development and productivity. Increasing evidence indicates that chromatin remodelers are pivotal for plant drought response. However, molecular mechanisms of chromatin remodelers-mediated plant drought responses remain obscure. In this study, we found a novel interactor of BRM called BRM-associated protein involved in drought response (BAPID), which interacted with SWI/SNF chromatin remodeler BRM and drought-induced transcription factor Di19. Our findings demonstrated that BAPID acted as a positive drought regulator since drought tolerance was increased in BAPID-overexpressing plants, but decreased in BAPID-deficient plants, and physically bound to PR1, PR2, and PR5 promoters to mediate expression of PR genes to defend against dehydration stress. Genetic approaches demonstrated that BRM acted epistatically to BAPID and Di19 in drought response in Arabidopsis. Furthermore, the BAPID protein-inhibited interaction between BRM and Di19, and suppressed the inhibition of BRM on the Di19-PR module by mediating the H3K27me3 deposition at PR loci, thus changing nucleosome accessibility of Di19 and activating transcription of PR genes in response to drought. Our results shed light on the molecular mechanism whereby the BAPID-BRM-Di19-PRs pathway mediates plant drought responses. We provide data improving our understanding of chromatin remodeler-mediated plant drought regulation network.

Subgenomic Stability of Progenitor Genomes During Repeated Allotetraploid Origins of the Same Grass Brachypodium hybridum.

Both homeologous exchanges and homeologous expression bias are generally found in most allopolyploid species. Whether homeologous exchanges and homeologous expression bias differ between repeated allopolyploid speciation events from the same progenitor species remains unknown. Here, we detected a third independent and recent allotetraploid origin for the model grass Brachypodium hybridum. Our homeologous exchange with replacement analyses indicated the absence of significant homeologous exchanges in any of the three types of wild allotetraploids, supporting the integrity of their progenitor subgenomes and the immediate creation of the amphidiploids. Further homeologous expression bias tests did not uncover significant subgenomic dominance in different tissues and conditions of the allotetraploids. This suggests a balanced expression of homeologs under similar or dissimilar ecological conditions in their natural habitats. We observed that the density of transposons around genes was not associated with the initial establishment of subgenome dominance; rather, this feature is inherited from the progenitor genome. We found that drought response genes were highly induced in the two subgenomes, likely contributing to the local adaptation of this species to arid habitats in the third allotetraploid event. These findings provide evidence for the consistency of subgenomic stability of parental genomes across multiple allopolyploidization events that led to the same species at different periods. Our study emphasizes the importance of selecting closely related progenitor species genomes to accurately assess homeologous exchange with replacement in allopolyploids, thereby avoiding the detection of false homeologous exchanges when using less related progenitor species genomes.

Structure and dynamics of microbial communities associated with the resurrection plant Boea hygrometrica in response to drought stress.

MAIN CONCLUSION: The resurrection plant Boea hygrometrica selectively recruits and assembles drought-specific microbial communities across the plant-soil compartments, which may benefit plant growth and fitness under extreme drought conditions. Plant-associated microbes are essential for facilitating plant growth and fitness under drought stress. The resurrection plant Boea hygrometrica in natural habitats with seasonal rainfall can survive rapid desiccation, yet their interaction with microbiomes under drought conditions remains unexplored. This study examined the bacterial and fungal microbiome structure and drought response across plant-soil compartments of B. hygrometrica by high-throughput amplicon sequencing of 16S rRNA gene and internal transcribed spacer. Our results demonstrated that the diversity, composition, and functional profile of the microbial community varied considerably across the plant-soil compartments and were strongly affected by drought stress. Bacterial and fungal diversity was significantly reduced from soil to endosphere and belowground to aboveground compartments. The compartment-specific enrichment of the dominant bacteria phylum Cyanobacteriota and genus Methylorubrum in leaf endosphere, genera Pseudonocardia in rhizosphere soil and Actinoplanes in root endosphere, and fungal phylum Ascomycota in the aboveground compartments and genera Knufia in root endosphere and Cladosporium in leaf endosphere composed part of the core microbiota with corresponding enrichment of beneficial functions for plant growth and fitness. Moreover, the recruitment of dominant microbial genera Sphingosinicella and Plectosphaerella, Ceratobasidiaceae mycorrhizal fungi, and numerous plant growth-promoting bacteria involving nutrient supply and auxin regulation was observed in desiccated B. hygrometrica plants. Our results suggest that the stable assembled drought-specific microbial community of B. hygrometrica may contribute to plant survival under extreme environments and provide valuable microbial resources for the microbe-mediated drought tolerance enhancement in crops.

Regulation of a single inositol 1-phosphate synthase homeologue by HSFA6B contributes to fibre yield maintenance under drought conditions in upland cotton.

Drought stress substantially impacts crop physiology resulting in alteration of growth and productivity. Understanding the genetic and molecular crosstalk between stress responses and agronomically important traits such as fibre yield is particularly complicated in the allopolyploid species, upland cotton (Gossypium hirsutum), due to reduced sequence variability between A and D subgenomes. To better understand how drought stress impacts yield, the transcriptomes of 22 genetically and phenotypically diverse upland cotton accessions grown under well-watered and water-limited conditions in the Arizona low desert were sequenced. Gene co-expression analyses were performed, uncovering a group of stress response genes, in particular transcription factors GhDREB2A-A and GhHSFA6B-D, associated with improved yield under water-limited conditions in an ABA-independent manner. DNA affinity purification sequencing (DAP-seq), as well as public cistrome data from Arabidopsis, were used to identify targets of these two TFs. Among these targets were two lint yield-associated genes previously identified through genome-wide association studies (GWAS)-based approaches, GhABP-D and GhIPS1-A. Biochemical and phylogenetic approaches were used to determine that GhIPS1-A is positively regulated by GhHSFA6B-D, and that this regulatory mechanism is specific to Gossypium spp. containing the A (old world) genome. Finally, an SNP was identified within the GhHSFA6B-D binding site in GhIPS1-A that is positively associated with yield under water-limiting conditions. These data lay out a regulatory connection between abiotic stress and fibre yield in cotton that appears conserved in other systems such as Arabidopsis.

SNAC1-OsERF103-OsSDG705 module mediates drought response in rice.

Drought stress profoundly hampers both plant growth and crop yield. To combat this, plants have evolved intricate transcriptional regulation mechanisms as a pivotal strategy. Through a genetic screening with rice genome-scale mutagenesis pool under drought stress, we identified an APETALA2/Ethylene Responsive Factor, namely OsERF103, positively responds to drought tolerance in rice. Combining chromatin immunoprecipitation sequencing and RNA sequencing analyses, we pinpointed c. 1000 genes directly influenced by OsERF103. Further results revealed that OsERF103 interacts with Stress-responsive NAC1 (SNAC1), a positive regulator of drought tolerance in rice, to synergistically regulate the expression of key drought-related genes, such as OsbZIP23. Moreover, we found that OsERF103 recruits a Su(var)3-9,enhancer of zeste and trithorax-domain group protein 705, which encodes a histone 3 lysine 4 (H3K4)-specific methyltransferase to specifically affect the deposition of H3K4me3 at loci like OsbZIP23 and other genes linked to dehydration responses. Additionally, the natural alleles of OsERF103 are selected during the domestication of both indica and japonica rice varieties and exhibit significant geographic distribution. Collectively, our findings have unfurled a comprehensive mechanistic framework underlying the OsERF103-mediated cascade regulation of drought response. This discovery not only enhances our understanding of drought signaling but also presents a promising avenue for the genetic improvement of drought-tolerant rice cultivars.

AtCIPK20 regulates microtubule stability to mediate stomatal closure under drought stress in Arabidopsis.

Drought stress is a common abiotic challenge that profoundly impacts plant growth and development. As sessile organisms, plants rely on various physiological and morphological adaptations to cope with drought conditions. The CIPK (calcineurin B-like protein-interacting protein kinase) family proteins play a pivotal role in mediating plant responses to abiotic stress through modulation of cellular membrane events via the CBL-CIPK complex. However, reports documenting the CIPKs' regulation of non-membrane events are scant. In this study, we discovered a novel subcellular localisation pattern of the AtCIPK20 protein of Arabidopsis, specifically to cortical microtubules (cMT), which is distinct from previously reported localisation patterns of plant CIPKs. AtCIPK20 regulates ABA-induced loss of cMT organisation in guard cells, thereby facilitating stomatal closure, mitigating leaf water loss, and protecting plants from drought stress in Arabidopsis. The C-terminal regulatory domain of AtCIPK20 governs its cMT targeting, whereas the interaction of AtCIPK20 with its CBL partners disrupts this localisation. Notably, the cMT targeting characteristic of AtCIPK20 is not exclusive, as several other CIPK members in Arabidopsis, maize, and rice exhibit similar localisation patterns. These findings broaden our current understanding of the role of plant CIPK members in abiotic stress resistance and suggest that future exploration of CIPK molecular functions should adopt a more comprehensive perspective.

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

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

Nutritional changes in trees during drought-induced mortality: A comprehensive meta-analysis and a field study.

Both macronutrients and micronutrients are essential for tree growth and development through participating in various ecophysiological processes. However, the impact of the nutritional status of trees on their ability to withstand drought-induced mortality remains inconclusive. We thus conducted a comprehensive meta-analysis, compiling data on 11 essential nutrients from 44 publications (493 independent observations). Additionally, a field study was conducted on Pinus sylvestris L. trees with varying drought-induced vitality loss in the "Visp" forest in southern Switzerland. No consistent decline in tree nutritional status was observed during tree mortality. The meta-analysis revealed significantly lower leaf potassium (K), iron (Fe), and copper (Cu) concentrations with tree mortality. However, the field study showed no causal relationships between nutritional levels and the vitality status of trees. This discrepancy is mainly attributed to the intrinsic differences in the two types of experimental designs and the ontogenetic stages of target trees. Nutrient reductions preceding tree mortality were predominantly observed in non-field conditions, where the study was conducted on seedlings and saplings with underdeveloped root systems. It limits the nutrient uptake capacity of these young trees during drought. Furthermore, tree nutritional responses are also influenced by many variables. Specifically, (a) leaf nutrients are more susceptible to drought stress than other organs; (b) reduced tree nutrient concentrations are more prevalent in evergreen species during drought-induced mortality; (c) of all biomes, Mediterranean forests are most vulnerable to drought-induced nutrient deficiencies; (d) soil types affect the direction and extent of tree nutritional responses. We identified factors that influence the relationship between tree nutritional status and drought survival, and proposed potential early-warning indicators of impending tree mortality, for example, decreased K concentrations with declining vitality. These findings contribute to our understanding of tree responses to drought and provide practical implications for forest management strategies in the context of global change.

Growing at the arid edge: Anatomical variations in leaves are more extensive than in stems of five Mediterranean species across contrasting moisture regimes.

PREMISE: Increasing aridity in the Mediterranean region affects ecosystems and plant life. Various anatomical changes in plants help them cope with dry conditions. This study focused on anatomical differences in leaves and xylem of five co-occurring Mediterranean plant species namely Quercus calliprinos, Pistacia palaestina, Pistacia lentiscus, Rhamnus lycioides, and Phillyrea latifolia in wet and dry sites. METHODS: Stomatal density, stomatal length, leaf mass area, lamina composition, percentage of intercellular air spaces, and mesophyll cell area in leaves of plants in wet and dry sites were analyzed. Xylem anatomy was assessed through vessel length and area in branches. RESULTS: In the dry site, three species had increased stomatal density and decreased stomatal length. Four species had increased palisade mesophyll and reduced air space volume. In contrast, phenotypic changes in the xylem were less pronounced; vessel length was unaffected by site conditions, but vessel diameter decreased in two species. Intercellular air spaces proved to be the most dynamic anatomical feature. Quercus calliprinos had the most extensive anatomical changes; Rhamnus lycioides had only minor changes. All these changes were observed in comparison to the species in the wet site. CONCLUSIONS: This study elucidated variations in anatomical responses in leaves among co-occurring Mediterranean plant species and identified the most dynamic traits. Understanding these adaptations provides valuable insights into the ability of plants to thrive under changing climate conditions.

Abscisic acid regulates secondary cell-wall formation and lignin deposition in Arabidopsis thaliana through phosphorylation of NST1.

Plant secondary cell-wall (SCW) deposition and lignification are affected by both seasonal factors and abiotic stress, and these responses may involve the hormone abscisic acid (ABA). However, the mechanisms involved are not clear. Here we show that mutations that limit ABA synthesis or signaling reduce the extent of SCW thickness and lignification in Arabidopsis thaliana through the core ABA-signaling pathway involving SnRK2 kinases. SnRK2.2. 3 and 6 physically interact with the SCW regulator NAC SECONDARY WALL THICKENING PROMOTING FACTOR 1 (NST1), a NAC family transcription factor that orchestrates the transcriptional activation of a suite of downstream SCW biosynthesis genes, some of which are involved in the biosynthesis of cellulose and lignin. This interaction leads to phosphorylation of NST1 at Ser316, a residue that is highly conserved among NST1 proteins from dicots, but not monocots, and is required for transcriptional activation of downstream SCW-related gene promoters. Loss of function of NST1 in the snd1 mutant background results in lack of SCWs in the interfascicular fiber region of the stem, and the Ser316Ala mutant of NST1 fails to complement this phenotype and ABA-induced lignin pathway gene expression. The discovery of NST1 as a key substrate for phosphorylation by SnRK2 suggests that the ABA-mediated core-signaling cascade provided land plants with a hormone-modulated, competitive desiccation-tolerance strategy allowing them to differentiate water-conducting and supporting tissues built of cells with thicker cell walls.

Accurate Long-Read RNA Sequencing Analysis Reveals the Key Pathways and Candidate Genes under Drought Stress in the Seed Germination Stage in Faba Bean.

Faba bean is an important pulse. It provides proteins for the human diet and is used in industrial foodstuffs, such as flours. Drought stress severely reduces the yield of faba bean, and this can be efficiently overcome through the identification and application of key genes in response to drought. In this study, PacBio and Illumina RNA sequencing techniques were used to identify the key pathways and candidate genes involved in drought stress response. During seed germination, a total of 17,927 full-length transcripts and 12,760 protein-coding genes were obtained. There were 1676 and 811 differentially expressed genes (DEGs) between the varieties E1 and C105 at 16 h and 64 h under drought stress, respectively. Six and nine KEGG pathways were significantly enriched at 16 h and 64 h under drought stress, which produced 40 and 184 nodes through protein-protein interaction (PPI) analysis, respectively. The DEGs of the PPI nodes were involved in the ABA (abscisic acid) and MAPK (mitogen-activated protein kinase) pathways, N-glycosylation, sulfur metabolism, and sugar metabolism. Furthermore, the ectopic overexpression of a key gene, AAT, encoding aspartate aminotransferase (AAT), in tobacco, enhanced drought tolerance. The activities of AAT and peroxidase (POD), the contents of cysteine and isoleucine, were increased, and the contents of malonaldehyde (MDA) and water loss decreased in the overexpressed plants. This study provides a novel insight into genetic response to drought stress and some candidate genes for drought tolerance genetic improvements in this plant.

Influence of Drought Stress on the Rhizosphere Bacterial Community Structure of Cassava (Manihot esculenta Crantz).

Drought presents a significant abiotic stress that threatens crop productivity worldwide. Rhizosphere bacteria play pivotal roles in modulating plant growth and resilience to environmental stresses. Despite this, the extent to which rhizosphere bacteria are instrumental in plant responses to drought, and whether distinct cassava (Manihot esculenta Crantz) varieties harbor specific rhizosphere bacterial assemblages, remains unclear. In this study, we measured the growth and physiological characteristics, as well as the physical and chemical properties of the rhizosphere soil of drought-tolerant (SC124) and drought-sensitive (SC8) cassava varieties under conditions of both well-watered and drought stress. Employing 16S rDNA high-throughput sequencing, we analyzed the composition and dynamics of the rhizosphere bacterial community. Under drought stress, biomass, plant height, stem diameter, quantum efficiency of photosystem II (Fv/Fm), and soluble sugar of cassava decreased for both SC8 and SC124. The two varieties' rhizosphere bacterial communities' overall taxonomic structure was highly similar, but there were slight differences in relative abundance. SC124 mainly relied on Gamma-proteobacteria and Acidobacteriae in response to drought stress, and the abundance of this class was positively correlated with soil acid phosphatase. SC8 mainly relied on Actinobacteria in response to drought stress, and the abundance of this class was positively correlated with soil urease and soil saccharase. Overall, this study confirmed the key role of drought-induced rhizosphere bacteria in improving the adaptation of cassava to drought stress and clarified that this process is significantly related to variety.

Ca2+-independent ZmCPK2 is inhibited by Ca2+-dependent ZmCPK17 during drought response in maize.

Calcium oscillations are induced by different stresses. Calcium-dependent protein kinases (CDPKs/CPKs) are one major group of the plant calcium decoders that are involved in various processes including drought response. Some CPKs are calcium-independent. Here, we identified ZmCPK2 as a negative regulator of drought resistance by screening an overexpression transgenic maize pool. We found that ZmCPK2 does not bind calcium, and its activity is mainly inhibited during short term abscisic acid (ABA) treatment, and dynamically changed in prolonged treatment. Interestingly, ZmCPK2 interacts with and is inhibited by calcium-dependent ZmCPK17, a positive regulator of drought resistance, which is activated by ABA. ZmCPK17 could prevent the nuclear localization of ZmCPK2 through phosphorylation of ZmCPK2T60. ZmCPK2 interacts with and phosphorylates and activates ZmYAB15, a negative transcriptional factor for drought resistance. Our results suggest that drought stress-induced Ca2+ can be decoded directly by ZmCPK17 that inhibits ZmCPK2, thereby promoting plant adaptation to water deficit.

Genome architecture and diverged selection shaping pattern of genomic differentiation in wild barley.

Divergent selection of populations in contrasting environments leads to functional genomic divergence. However, the genomic architecture underlying heterogeneous genomic differentiation remains poorly understood. Here, we de novo assembled two high-quality wild barley (Hordeum spontaneum K. Koch) genomes and examined genomic differentiation and gene expression patterns under abiotic stress in two populations. These two populations had a shared ancestry and originated in close geographic proximity but experienced different selective pressures due to their contrasting micro-environments. We identified structural variants that may have played significant roles in affecting genes potentially associated with well-differentiated phenotypes such as flowering time and drought response between two wild barley genomes. Among them, a 29-bp insertion into the promoter region formed a cis-regulatory element in the HvWRKY45 gene, which may contribute to enhanced tolerance to drought. A single SNP mutation in the promoter region may influence HvCO5 expression and be putatively linked to local flowering time adaptation. We also revealed significant genomic differentiation between the two populations with ongoing gene flow. Our results indicate that SNPs and small SVs link to genetic differentiation at the gene level through local adaptation and are maintained through divergent selection. In contrast, large chromosome inversions may have shaped the heterogeneous pattern of genomic differentiation along the chromosomes by suppressing chromosome recombination and gene flow. Our research offers novel insights into the genomic basis underlying local adaptation and provides valuable resources for the genetic improvement of cultivated barley.

Leaves as bottlenecks: The contribution of tree leaves to hydraulic resistance within the soil-plant-atmosphere continuum.

Within vascular plants, the partitioning of hydraulic resistance along the soil-to-leaf continuum affects transpiration and its response to environmental conditions. In trees, the fractional contribution of leaf hydraulic resistance (Rleaf ) to total soil-to-leaf hydraulic resistance (Rtotal ), or fRleaf (=Rleaf /Rtotal ), is thought to be large, but this has not been tested comprehensively. We compiled a multibiome data set of fRleaf using new and previously published measurements of pressure differences within trees in situ. Across 80 samples, fRleaf averaged 0.51 (95% confidence interval [CI] = 0.46-0.57) and it declined with tree height. We also used the allometric relationship between field-based measurements of soil-to-leaf hydraulic conductance and laboratory-based measurements of leaf hydraulic conductance to compute the average fRleaf for 19 tree samples, which was 0.40 (95% CI = 0.29-0.56). The in situ technique produces a more accurate descriptor of fRleaf because it accounts for dynamic leaf hydraulic conductance. Both approaches demonstrate the outsized role of leaves in controlling tree hydrodynamics. A larger fRleaf may help stems from loss of hydraulic conductance. Thus, the decline in fRleaf with tree height would contribute to greater drought vulnerability in taller trees and potentially to their observed disproportionate drought mortality.

Drought response in Arabidopsis displays synergistic coordination between stems and leaves.

The synergy between drought-responsive traits across different organs is crucial in the whole-plant mechanism influencing drought resilience. These organ interactions, however, are poorly understood, limiting our understanding of drought response strategies at the whole-plant level. Therefore, we need more integrative studies, especially on herbaceous species that represent many important food crops but remain underexplored in their drought response. We investigated inflorescence stems and rosette leaves of six Arabidopsis thaliana genotypes with contrasting drought tolerance, and combined anatomical observations with hydraulic measurements and gene expression studies to assess differences in drought response. The soc1ful double mutant was the most drought-tolerant genotype based on its synergistic combination of low stomatal conductance, largest stomatal safety margin, more stable leaf water potential during non-watering, reduced transcript levels of drought stress marker genes, and reduced loss of chlorophyll content in leaves, in combination with stems showing the highest embolism resistance, most pronounced lignification, and thickest intervessel pit membranes. In contrast, the most sensitive Cvi ecotype shows the opposite extreme of the same set of traits. The remaining four genotypes show variations in this drought syndrome. Our results reveal that anatomical, ecophysiological, and molecular adaptations across organs are intertwined, and multiple (differentially combined) strategies can be applied to acquire a certain level of drought tolerance.

Elevated [CO2] negatively impacts C4 photosynthesis under heat and water stress without penalizing biomass.

Elevated [CO2] (eCO2) and water stress reduce leaf stomatal conductance (gs), which may affect leaf thermoregulation during heat waves (heat stress). Two sorghum lines, with different leaf width were grown in a glasshouse at a mean day temperature of 30 °C, under different [CO2] and watering levels, and subjected to heat stress (43 °C) for 6 d at the start of the reproductive stage. We measured leaf photosynthetic and stomatal responses to light transients before harvesting the plants. Photosynthesis at growth conditions (Agrowth) and biomass accumulation were enhanced by eCO2 under control conditions. Heat stress increased gs, especially in wider leaves, and reduced the time constant of stomatal opening (kopen) at ambient [CO2] but not eCO2. However, heat stress reduced photosynthesis under water stress and eCO2 due to increased leaf temperature and reduced evaporative cooling. eCO2 prevented the reduction of biomass under both water and heat stress, possibly due to improved plant and soil water status as a result of reduced gs. Our results suggest that the response of the C4 crop sorghum to future climate conditions depends on the trade-off between low gs needed for high water use efficiency and drought tolerance, and the high gs needed for improved thermoregulation and heat tolerance under an eCO2 future.

Soil moisture determines the recovery time of ecosystems from drought.

Recovery time, the time it takes for ecosystems to return to normal states after experiencing droughts, is critical for assessing the response of ecosystems to droughts; however, the spatial dominant factors determining recovery time are poorly understood. We identify the global patterns of terrestrial ecosystem recovery time based on remote sensed vegetation indices, analyse the affecting factors of recovery time using random forest regression model, and determine the spatial distribution of the dominant factors of recovery time based on partial correlation. The results show that the global average recovery time is approximately 3.3 months, and that the longest recovery time occurs in mid-latitude drylands. Analysis of affecting factors of recovery time suggests that the most important environmental factor affecting recovery time is soil moisture during the recovery period, followed by temperature and vapour pressure deficit (VPD). Recovery time shortens with increasing soil moisture and prolongs with increasing VPD; however, the response of recovery time to temperature is nonmonotonic, with colder or hotter temperatures leading to longer recovery time. Soil moisture dominates the drought recovery time over 58.4% of the assessed land area, mostly in the mid-latitudes. The concern is that soil moisture is projected to decline in more than 65% regions in the future, which will lengthen the drought recovery time and exacerbate drought impacts on terrestrial ecosystems, especially in southwestern United States, the Mediterranean region and southern Africa. Our research provides methodological insights for quantifying recovery time and spatially identifies dominant factors of recovery time, improving our understanding of ecosystem response to drought.