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Enhancing resilience in formerly degraded ecosystems is an important goal of restoration ecology. However, evidence for the recovery of resilience and its underlying mechanisms require long‐term experiments and comparison with reference ecosystems. We used data from an experimental prairie restoration that featured long‐term soil heterogeneity manipulations and data from two long‐term experiments located in a comparable remnant (reference) prairie to (1) quantify the recovery of ecosystem functioning (i.e., productivity) relative to remnant prairie, (2) compare the resilience of restored and remnant prairies to a natural drought, and (3) test whether soil heterogeneity enhances resilience of restored prairie. We compared sensitivity and legacy effects between prairie types (remnant and restored) and among four prairie sites that included two remnant prairie sites and prairie restored under homogeneous and heterogeneous soil conditions. We measured sensitivity and resilience as the proportional change in aboveground net primary productivity (ANPP) during and following drought (sensitivity and legacy effects, respectively) relative to average ANPP based on 4 pre‐drought years (2014–2017). In nondrought years, total ANPP was similar between remnant and restored prairie, but remnant prairie had higher grass productivity and lower forb productivity compared with restored prairie. These ANPP patterns generally persisted during drought. The sensitivity of total ANPP to drought was similar between restored and remnant prairie, but grasses in the restored prairie were more sensitive to drought. Post‐drought legacy effects were more positive in the restored prairie, and we attributed this to the more positive and less variable legacy response of forb ANPP in the restored prairie, especially in the heterogeneous soil treatment. Our results suggest that productivity recovers in restored prairie and exhibits similar sensitivity to drought as in remnant prairie. Furthermore, creating heterogeneity promotes forb productivity and enhances restored prairie resilience to drought. [ABSTRACT FROM AUTHOR]

Drought profoundly affects the morpho-physiological responses of desert plants in dryland. To scrutinize the morpho-physiological responses of nitrogen (N)-fixing legumes (Ammopiptanthus mongolicus, Caragana korshinskii), N-fixing non-legumes (Elaeagnus angustifolia, Hippophae rhamnoides), and non-N-fixing plants (Nitraria tangutorum, Haloxylon ammodendron) under varied drought stress levels (75%, 50%, 25% and 5% of soil water holding capacity), a pot experiment was conducted in greenhouse. Following prolonged water deficit, carbon (C) and N stoichiometry, metabolic rates, plant growth, and biomass distribution of unstressed and stressed plants were recorded. Intensified drought significantly reduced stem, root and whole-plant biomass, with no significant changes observed in leaf dry-fresh mass ratio, specific leaf area, intrinsic water use efficiency and root to shoot ratio. However, other traits were impacted differently, reflecting distinct adaptive strategies to drought among three plant functional types (PFTs). Patterns of trait-soil water content (SWC) relationships varied across different PFTs, with N-fixing non-legumes followed by N-fixing legumes displayed greater sensitivity to SWC variations than non-N-fixing plants. This resulted in a shift from a stronger trait-SWC relationship in N-fixing non-legumes and N-fixing legumes to a less correlated relationship in non-N-fixing plants. The diverse responses to drought among PFTs suggest a shift from N limitation to water limitation as SWC decreases. [ABSTRACT FROM AUTHOR]

Droughts are predicted to become more frequent and intense in many tropical regions, which may cause shifts in plant community composition. Especially in diverse tropical communities, understanding how traits mediate demographic responses to drought can help provide insight into the effects of climate change on these ecosystems. To understand tropical tree responses to reduced soil moisture, we grew seedlings of eight species across an experimental soil moisture gradient at the Luquillo Experimental Forest, Puerto Rico. We quantified survival and growth over an 8‐month period and characterized demographic responses in terms of tolerance to low soil moisture—defined as survival and growth rates under low soil moisture conditions—and sensitivity to variation in soil moisture—defined as more pronounced changes in demographic rates across the observed range of soil moisture. We then compared demographic responses with interspecific variation in a suite of 11 (root, stem, and leaf) functional traits, measured on individuals that survived the experiment. Lower soil moisture was associated with reduced survival and growth but traits mediated species‐specific responses. Species with relatively conservative traits (e.g., high leaf mass per area), had higher survival at low soil moisture whereas species with more extensive root systems were more sensitive to soil moisture, in that they exhibited more pronounced changes in growth across the experimental soil moisture gradient. Our results suggest that increasing drought will favor species with more conservative traits that confer greater survival in low soil moisture conditions. [ABSTRACT FROM AUTHOR]

Plant traits can be helpful for understanding grassland ecosystem responses to climate extremes, such as severe drought. However, intercontinental comparisons of how drought affects plant functional traits and ecosystem functioning are rare. The Extreme Drought in Grasslands experiment (EDGE) was established across the major grassland types in East Asia and North America (six sites on each continent) to measure variability in grassland ecosystem sensitivity to extreme, prolonged drought. At all sites, we quantified community‐weighted mean functional composition and functional diversity of two leaf economic traits, specific leaf area and leaf nitrogen content, in response to drought. We found that experimental drought significantly increased community‐weighted means of specific leaf area and leaf nitrogen content at all North American sites and at the wetter East Asian sites, but drought decreased community‐weighted means of these traits at moderate to dry East Asian sites. Drought significantly decreased functional richness but increased functional evenness and dispersion at most East Asian and North American sites. Ecosystem drought sensitivity (percentage reduction in aboveground net primary productivity) positively correlated with community‐weighted means of specific leaf area and leaf nitrogen content and negatively correlated with functional diversity (i.e., richness) on an intercontinental scale, but results differed within regions. These findings highlight both broad generalities but also unique responses to drought of community‐weighted trait means as well as their functional diversity across grassland ecosystems. [ABSTRACT FROM AUTHOR]

Drought profoundly affects the morpho-physiological responses of desert plants in dryland. To scrutinize the morpho-physiological responses of nitrogen (N)-fixing legumes (Ammopiptanthus mongolicus, Caragana korshinskii), N-fixing non-legumes (Elaeagnus angustifolia, Hippophae rhamnoides), and non-N-fixing plants (Nitraria tangutorum, Haloxylon ammodendron) under varied drought stress levels (75%, 50%, 25% and 5% of soil water holding capacity), a pot experiment was conducted in greenhouse. Following prolonged water deficit, carbon (C) and N stoichiometry, metabolic rates, plant growth, and biomass distribution of unstressed and stressed plants were recorded. Intensified drought significantly reduced stem, root and whole-plant biomass, with no significant changes observed in leaf dry-fresh mass ratio, specific leaf area, intrinsic water use efficiency and root to shoot ratio. However, other traits were impacted differently, reflecting distinct adaptive strategies to drought among three plant functional types (PFTs). Patterns of trait-soil water content (SWC) relationships varied across different PFTs, with N-fixing non-legumes followed by N-fixing legumes displayed greater sensitivity to SWC variations than non-N-fixing plants. This resulted in a shift from a stronger trait-SWC relationship in N-fixing non-legumes and N-fixing legumes to a less correlated relationship in non-N-fixing plants. The diverse responses to drought among PFTs suggest a shift from N limitation to water limitation as SWC decreases.

Abstract Droughts are predicted to become more frequent and intense in many tropical regions, which may cause shifts in plant community composition. Especially in diverse tropical communities, understanding how traits mediate demographic responses to drought can help provide insight into the effects of climate change on these ecosystems. To understand tropical tree responses to reduced soil moisture, we grew seedlings of eight species across an experimental soil moisture gradient at the Luquillo Experimental Forest, Puerto Rico. We quantified survival and growth over an 8‐month period and characterized demographic responses in terms of tolerance to low soil moisture—defined as survival and growth rates under low soil moisture conditions—and sensitivity to variation in soil moisture—defined as more pronounced changes in demographic rates across the observed range of soil moisture. We then compared demographic responses with interspecific variation in a suite of 11 (root, stem, and leaf) functional traits, measured on individuals that survived the experiment. Lower soil moisture was associated with reduced survival and growth but traits mediated species‐specific responses. Species with relatively conservative traits (e.g., high leaf mass per area), had higher survival at low soil moisture whereas species with more extensive root systems were more sensitive to soil moisture, in that they exhibited more pronounced changes in growth across the experimental soil moisture gradient. Our results suggest that increasing drought will favor species with more conservative traits that confer greater survival in low soil moisture conditions.

[Objective] This study accurately quantified the degree of drought sensitivity of ecosystems to provide reference for early warning of ecological drought and reduction of ecological losses. [Method] The standardized ecological water deficit index (SEWDI) was constructed based on the ecological water deficit in Northwest China, and the ecological drought sensitivity was defined by combining water use efficiency (WUE) of vegetation. The Copula method was used to analyze the sensitivity of ecological drought by exploring the probability of WUE increase under the condition of increasing ecological drought. [Result] The ecological water deficit of vegetation in the Tarim Basin, Kunlun Mountains, Turpan Basin, Qaidam Basin and Hexi Corridor was high, with the highest monthly mean value of 75 mm. SEWDI was strongly correlated with WUE in most regions and areas with significantly positive correlation accounted for 24. 2% of the total region, mainly in Xinjiang, western Qinghai and southern Shaanxi. The areas with significantly negative correlation accounted for 36. 8% of the total region, mainly in the Loess Plateau. With the intensification of ecological drought, the sensitivity of WUE to ecological drought was not tnonotonically increased in different regions. The sensitivity of WUE to ecological drought increased with the increase of drought stress during the vegetation growth period, and the sensitivity of ecological drought in grassland was higher than that in forest land and cropland. The rate of increase in WUE probability from May to June was the fastest, and the monthly average rates of increase in WUE probability in the conditions of light drought-moderate drought, moderate drought-severe drought and severe drought-extreme drought were 0.09, 0.07, and 0.06, respectively. [Conclusion] WUE can well reflect the ecological drought sensitivity of vegetation under drought stress during the growing period and can be used as a factor to characterize ecological drought sensitivity. [ABSTRACT FROM AUTHOR]

Key message: Beech and pine respond differently to climate change. June precipitation is of particular influence for beech, and February/March temperature for pine. Climate warming exposes forests to increasing abiotic stress, demanding for difficult silvicultural decisions about the right choice of future timber species. Scots pine (Pinus sylvestris) and European beech (Fagus sylvatica) are major timber species in the North German Lowlands, which have suffered from recent hot droughts, thus raising concern about their suitability for future production forests in the region. We investigated the climate sensitivity of tree growth and long-term growth trends of ten paired beech and pine forests along a precipitation gradient in the North German Lowlands with the aim to compare the species' climate sensitivity and to search for species-specific climatic thresholds. In the majority of beech stands, basal area increment (BAI) has lost its positive trend since the 1980s or growth declined since then, while the BAI of pine has continually increased. Long-term change in June precipitation is in the study region a more important determinant of beech growth trends than the amount of MAP, while pine growth is largely dependent on the warmth of February/March. Yet, pine growth is also sensitive to dry mid summers, with sensitivity increasing toward low MAP. Climate sensitivity of growth has significantly declined since the 1980s in beech, while the dominant drought signal of June persisted in pine. We conclude that recent climate change is affecting radial growth of beech and pine differently with both species revealing signs of vulnerability to hot droughts, suggesting for the drier part of the study region the preference of more drought-tolerant hardwood timber species over beech and pine. [ABSTRACT FROM AUTHOR]

The frequency and intensity of drought events are increasing worldwide, challenging the adaptive capacity of several tree species. Here, we evaluate tree growth patterns and climate sensitivity to precipitation, temperature, and drought in the relict Moroccan fir Abies marocana. We selected two study sites, formerly stated as harboring contrasting A. marocana taxa (A. marocana and A. tazaotana, respectively). For each tree, dendrochronological methods were applied to quantify growth patterns and climate–growth sensitivity. Further, ddRAD-seq was performed on the same trees and close saplings to obtain single nucleotide polymorphisms (SNPs) and related genotype–phenotype associations. Genetic differentiation between the two studied remnant populations of A. marocana was weak. Growth patterns and climate–growth relationships were almost similar at the two sites studied, supporting a negative effect of warming. Growth trends and tree size showed associations with SNPs, although there were no relationships with phenotypes related to climatic sensitivity. We found significant differences in the SNPs subjected to selection in the saplings compared to the old trees, suggesting that relict tree populations might be subjected to genetic differentiation and local adaptation to climate dryness. Our results illustrate the potential of tree rings and genome-wide analysis to improve our understanding of the adaptive capacity of drought-sensitive forests to cope with ongoing climate change. [ABSTRACT FROM AUTHOR]

During the last two decades, inventory data show that droughts have reduced biomass carbon sink of the Amazon forest by causing mortality to exceed growth. However, process‐based models have struggled to include drought‐induced responses of growth and mortality and have not been evaluated against plot data. A process‐based model, ORCHIDEE‐CAN‐NHA, including forest demography with tree cohorts, plant hydraulic architecture and drought‐induced tree mortality, was applied over Amazonia rainforests forced by gridded climate fields and rising CO2 from 1901 to 2019. The model reproduced the decelerating signal of net carbon sink and drought sensitivity of aboveground biomass (AGB) growth and mortality observed at forest plots across selected Amazon intact forests for 2005 and 2010. We predicted a larger mortality rate and a more negative sensitivity of the net carbon sink during the 2015/16 El Niño compared with the former droughts. 2015/16 was indeed the most severe drought since 1901 regarding both AGB loss and area experiencing a severe carbon loss. We found that even if climate change did increase mortality, elevated CO2 contributed to balance the biomass mortality, since CO2‐induced stomatal closure reduces transpiration, thus, offsets increased transpiration from CO2‐induced higher foliage area. [ABSTRACT FROM AUTHOR]

Abstract Drought is a devastating recurring climate hazard, with enormous impacts on livelihoods and attainment of sustainable development goals (SDGs) in semi-arid areas. The current study was conducted to evaluate households’ livelihood vulnerability to droughts in an African semi-arid region. A total of 384 households from a drought-prone region in Northern Cameroon were randomly sampled and interviewed using a structured questionnaire. Livelihood vulnerability was evaluated from the collected households’ data using the Livelihood Vulnerability Index (LVI) and Intergovernmental Panel on Climate Change Vulnerability Index (IPCC-VI) methods. The LVI results showed that food insecurity, livelihood strategy and social networking were the major drivers of livelihood vulnerability. This was because almost all of the interviewed households relied on rain-fed agriculture and there was limited early drought warning information, which limited the achievements of some SDGs such as zero hunger, water accessibility and poverty alleviation. Adoption of drought-resilient and early maturing crops together with the use of agriculture extension officers to disseminate drought warnings are advised to reduce the effects of the livelihood vulnerability drivers and ensure sustainable development. The IPCC-VI showed that drought exposure and adaptive capacity were low while drought sensitivity was high among the surveyed households. The high sensitivity was due to food and water insecurity, while low adaptive capacity was due to a lack of formal education and a high dependency rate. Heavy investment in education and reducing the number of dependents through family planning and campaigning against polygamy could enhance households’ adaptive capacity. It was concluded that households’ livelihood vulnerability in the study area was due to high sensitivity and low adaptive capacity to drought. Drought reversed positive steps that had been taken to achieve various SDGs; however, heavy investment in other SDGs such as quality education and health could enhance households’ adaptive capacity and system sustainability in African semi-arid regions.

By killing or weakening trees, drought could change the partitioning of growth between tree sizes or species, thereby altering stand structure. Growth partitioning, often quantified using the growth dominance coefficient (DC) or the shape of tree size versus growth relationships (SGR), indicates the relative contribution of differently sized trees to the total stand growth. Changes in growth partitioning due to droughts are rarely examined but provide valuable information that links tree‐ and stand‐level responses to droughts.The objective of this study was to test whether the 2018 European megadrought altered the growth partitioning among tree sizes and species. For this purpose, we first evaluated whether DC or SGR can be calculated from small sample sizes of trees typical of individual forest inventory plots.DC, and particularly SGR, were sensitive to sample size, forest type (even‐aged and uneven‐aged), target variable (tree diameter, basal area or stem mass) and range of tree sizes within the sample. SGR could therefore not be used for our analyses. We found no differences in DC prior to and during the 2018 drought. However, when considering only beech (Fagus sylvatica)‐dominated stands, DC was lower during post‐drought years than during the 2018 drought.The growth of larger trees, especially beech, was more negatively affected during post‐drought years. Therefore, an extreme drought event can indeed alter the growth partitioning within forest stands. The DC indicates such changes in partitioning and, hence, which trees can be selected for commercial thinning, or released from competition, to minimize potential impacts of droughts. [ABSTRACT FROM AUTHOR]

Seeds provide the basis of genetic diversity in perennial grassland communities and their traits may influence ecosystem resistance to extreme drought. However, we know little about how drought effects the community functional composition of seed traits and the corresponding implications for ecosystem resistance to drought.We experimentally removed 66% of growing season precipitation for 4 years across five arid and semi‐arid grasslands in northern China and assessed how this multi‐year drought impacted community‐weighted means (CWMs) of seed traits, seed trait functional diversity and above‐ground net primary productivity (ANPP).Experimental drought had limited effects on CWM traits and the few effects that did occur varied by site and year. For three separate sites, and in different years, drought reduced seed length and phosphorus content but increased both seed and seed‐coat thickness. Additionally, drought led to increased seed functional evenness, divergence, dispersion and richness, but only in some sites, and mostly in later years following cumulative effects of water limitation. However, we observed a strong negative relationship between drought‐induced reductions in ANPP and CWMs of seed‐coat thickness, indicating that a high abundance of dominant species with thick seeds may increase ecosystem resistance to drought. Seed trait functional diversity was not significantly predictive of ANPP, providing little evidence for a diversity effect.Our results suggest that monitoring community composition with a focus on seed traits may provide a valuable indicator of ecosystem resistance to future droughts despite inconsistent responses of seed trait composition overall. This highlights the importance of developing a comprehensive seed and reproductive traits database for arid and semi‐arid grassland biomes. Read the free Plain Language Summary for this article on the Journal blog. [ABSTRACT FROM AUTHOR]

The paper is dealing with the effects of the late drought stress on the productivity and yield components of 12 varieties and 7 lines of winter bread wheat, which differ in morphophysiological characteristics. It was found that drought stress created in the late period decreased productivity, number of spikes per sheaf, number of spikelets per spike, number and mass of grains per spike and mass of 1000 grains by 19.9%, 7.7%, 4.9%, 12.8%, 21,6%, and 10.01%, respectively. As can be seen, of the components directly affected by water stress, the productivity and grain mass per spike were the most depressed, while number of spikes per unit area and number of spikelets per spike was relatively stable. Under late drought stress, Gobustan and Gyrmyzy gul 1 varieties, 7thWON-SA No.465 and Ferrigineum 2/19 lines manifested the highest productivity (557, 515, 607, and 549 g/m², respectively). Under drought stress, the most depressed values for 1000-grain mass were found for the genotypes Tale 38, Gyrmyzy gul 1, 12thIWWYT No.8, and Ferrigineum 2/19, while the least depressed values were found for Sonmez 01, Gobustan, 4thFEFWSN No.50 and 7thWON-SA No.477. [ABSTRACT FROM AUTHOR]

Understanding present and future impacts of drought on the terrestrial carbon budget is of great significance to the evaluation of terrestrial ecosystem disturbance and terrestrial carbon sink. Here, we evaluate the effect of vegetation net primary productivity (NPP) associated with drought through the difference between the mean NPP in the drought and normal years during a specific time period (30 years). Then, the NPP effects in different vegetation types and climatic zones under baseline stage (1981–2010) and future climate scenarios (RCP2.6, RCP4.5, and RCP8.5) is assessed. The results indicate that the negative NPP extremes are captured in most regions, except for the high‐latitude in the Northern Hemisphere. The NPP loss caused by extreme droughts in 2071–2100 is largest under RCPs, followed by the effects of severe and moderate droughts. Regionally, central United States, southern Africa, central Asia, India, Amazon tropical rainforest, and Australia are projected to experience a significant increase in negative NPP extremes and most of these regions are in arid and semi‐arid and tropical rain forest areas. In contrast, tropical Asia suffers little drought effects. For different vegetation, Evergreen Broadleaf Forest, Closed Shrubland, Open Shrubland, Croplands, and Grassland are the most affected by drought. The largest NPP loss occurs in most part of regions under RCP4.5 scenario, not RCP8.5. Climate change is projected to play the largest role in aggravating the risk of drought‐induced NPP reduction. And meanwhile, the adverse effects of drought on vegetation may be resisted through rational fertilizer utilization and land management in future. Plain Language Summary: Drought is already the most widespread factor affecting terrestrial net primary productivity (NPP) via direct physiological effects, such as water limitation and heat stress. Nevertheless, the effects of drought on terrestrial ecosystems under future climate change are still highly uncertain. In this study, we assess and compare the present and future impact of drought on vegetation net primary productivity. The results suggest that global drought events are projected to be intensified and frequent in the coming decades. Drought‐related NPP reduction is prevalent especially in the arid and semi‐arid areas and tropical regions at the end of 21st century. Extreme drought depresses NPP most under RCPs, followed by severe and moderate droughts. For vegetation, the adverse impact on NPP induced by drought under RCPs is increasingly significant in Evergreen Broadleaf Forest, Grassland, Savanna, and Cropland. Climate change is projected to play the largest role in aggravating the risk of drought‐induced NPP reduction. These results highlight the growing vulnerability of ecosystem productivity to droughts, implying increased adverse impacts of these climate extremes on terrestrial carbon sinks. Key Points: Net primary productivity (NPP) reduction associated with drought is prevalent especially in the arid and semi‐arid areas and tropical regionsAdverse impact of drought on NPP under RCPs is large in Evergreen Broadleaf Forest, Shrubland, Grassland, and CroplandThe largest NPP loss occurs under RCP4.5. Climate change plays the largest role in aggravating the risk of drought‐induced NPP reduction [ABSTRACT FROM AUTHOR]

Over the coming decades, climate change can decrease forest productivity and stability in many semiarid regions. Tree-ring width (TRW) analysis allows estimation of tree sensitivity to droughts, including resistance (Rt) and resilience (Rc) indexes. It helps to find adaptive potential of individual trees and forest populations. On a forest stand scale, it is affected by habitat conditions and species' ecophysiological characteristics, and on individual scale by tree genotype, age, and size. This study investigated TRW response to droughts in forest-steppe and sub-taiga of southern Siberia for keystone species Scots pine (Pinus sylvestris L.), Siberian larch (Larix sibirica Ledeb.), and silver birch (Betula pendula Roth.). Chronologies reacted positively to the Standardized Precipitation-Evapotranspiration Index (SPEI) of the previous July–September and current April–July. Depressed tree growth across region and droughts lasting over both intra-seasonal intervals were registered in 1965, 1974, and 1999. TRW-based Rt and Rc for these droughts did not reveal age- or size-related patterns. Higher growth stability indexes were observed for birch in sub-taiga and for conifers in forest-steppe. Larch at all sites had disadvantage against pine for 1965 and 1999 droughts aggravated by pest outbreaks, but adapted better to drought in 1974. Site aridity affected both tree growth stability and intensity of climatic response. [ABSTRACT FROM AUTHOR]

Abstract Understanding present and future impacts of drought on the terrestrial carbon budget is of great significance to the evaluation of terrestrial ecosystem disturbance and terrestrial carbon sink. Here, we evaluate the effect of vegetation net primary productivity (NPP) associated with drought through the difference between the mean NPP in the drought and normal years during a specific time period (30 years). Then, the NPP effects in different vegetation types and climatic zones under baseline stage (1981–2010) and future climate scenarios (RCP2.6, RCP4.5, and RCP8.5) is assessed. The results indicate that the negative NPP extremes are captured in most regions, except for the high‐latitude in the Northern Hemisphere. The NPP loss caused by extreme droughts in 2071–2100 is largest under RCPs, followed by the effects of severe and moderate droughts. Regionally, central United States, southern Africa, central Asia, India, Amazon tropical rainforest, and Australia are projected to experience a significant increase in negative NPP extremes and most of these regions are in arid and semi‐arid and tropical rain forest areas. In contrast, tropical Asia suffers little drought effects. For different vegetation, Evergreen Broadleaf Forest, Closed Shrubland, Open Shrubland, Croplands, and Grassland are the most affected by drought. The largest NPP loss occurs in most part of regions under RCP4.5 scenario, not RCP8.5. Climate change is projected to play the largest role in aggravating the risk of drought‐induced NPP reduction. And meanwhile, the adverse effects of drought on vegetation may be resisted through rational fertilizer utilization and land management in future.

Global climate change is expected to result in increased temperatures and variation in precipitation. In the Desert Southwest region of the United States, climate change may result in drier conditions. Eragrostis lehmanniana (Lehmann lovegrass) is an invasive species that has extensively colonized the southwestern United States, including Bouteloua eriopoda (black grama) grasslands. While both E. lehmanniana and B. eriopoda evolved in arid conditions, drier conditions may influence this invader–native system in unforeseen ways. Using a combination of precipitation pivot point (PPP) and drought sensitivity (DS) analysis, we compared responses of B. eriopoda and E. lehmanniana to altered precipitation regimes including long‐term drought treatments in the northern Chihuahuan Desert, New Mexico. We defined PPP as the critical point in precipitation amount below which plant percent cover decreased and above which it increased. We used DS, defined as the square millimeters of cover lost when precipitation decreased by 1 mm, to elucidate the direct response of biomass to drought on either side of the PPP. We estimated mean monsoon PPPs of 62.5 and 63.7 mm for B. eriopoda and E. lehmanniana, respectively. We estimated mean annual (1 October–30 September) PPPs of 108.6 and 108.5 mm for B. eriopoda and E. lehmanniana, respectively. Bouteloua eriopoda mean DS was 4.71 mm2/mm. Eragrostis lehmanniana mean DS was 1.56 mm2/mm. Results suggest that it is unlikely that extended drought will benefit E. lehmanniana over B. eriopoda and both species may decline under extreme drought. [ABSTRACT FROM AUTHOR]

Abstract Global climate change is expected to result in increased temperatures and variation in precipitation. In the Desert Southwest region of the United States, climate change may result in drier conditions. Eragrostis lehmanniana (Lehmann lovegrass) is an invasive species that has extensively colonized the southwestern United States, including Bouteloua eriopoda (black grama) grasslands. While both E. lehmanniana and B. eriopoda evolved in arid conditions, drier conditions may influence this invader–native system in unforeseen ways. Using a combination of precipitation pivot point (PPP) and drought sensitivity (DS) analysis, we compared responses of B. eriopoda and E. lehmanniana to altered precipitation regimes including long‐term drought treatments in the northern Chihuahuan Desert, New Mexico. We defined PPP as the critical point in precipitation amount below which plant percent cover decreased and above which it increased. We used DS, defined as the square millimeters of cover lost when precipitation decreased by 1 mm, to elucidate the direct response of biomass to drought on either side of the PPP. We estimated mean monsoon PPPs of 62.5 and 63.7 mm for B. eriopoda and E. lehmanniana, respectively. We estimated mean annual (1 October–30 September) PPPs of 108.6 and 108.5 mm for B. eriopoda and E. lehmanniana, respectively. Bouteloua eriopoda mean DS was 4.71 mm2/mm. Eragrostis lehmanniana mean DS was 1.56 mm2/mm. Results suggest that it is unlikely that extended drought will benefit E. lehmanniana over B. eriopoda and both species may decline under extreme drought.

In soybean, studies on drought-responses are conducted during vegetative season. Information related to genes triggered in response to water-deficit (WD) in flower and pod is lacking. We performed an RNASeq and an agro-physiological characterization at stages R2 and R4 of soybean cultivar BR16, under WD. Physiological results showed a decrease in gas exchange parameters. Agronomical results showed WD impaired yield. Global Gene Ontology analyses indicated that most of the Differential Expressed Genes (DEGs) were down-regulated in flowers but up-regulated in pods. qRT-PCR revealed that WD triggered hormone biosynthesis changes. Mechanisms such as a decrease in glyceollin levels and cell wall instability were observed. This data showed tissue-specific mechanisms correlated with phenotypic responses such as drought escape, early flowering hormone-induced, and loss in grain weight. We presented here a comprehensive expression profile of flowers and pods soybean genes, which could guide researchers in the development of plants more tolerant to drought.

The frequency and intensity of drought events are increasing worldwide, challenging the adaptive capacity of several tree species. Here, we evaluate tree growth patterns and climate sensitivity to precipitation, temperature, and drought in the relict Moroccan fir Abies marocana. We selected two study sites, formerly stated as harboring contrasting A. marocana taxa (A. marocana and A. tazaotana, respectively). For each tree, dendrochronological methods were applied to quantify growth patterns and climate–growth sensitivity. Further, ddRAD-seq was performed on the same trees and close saplings to obtain single nucleotide polymorphisms (SNPs) and related genotype–phenotype associations. Genetic differentiation between the two studied remnant populations of A. marocana was weak. Growth patterns and climate–growth relationships were almost similar at the two sites studied, supporting a negative effect of warming. Growth trends and tree size showed associations with SNPs, although there were no relationships with phenotypes related to climatic sensitivity. We found significant differences in the SNPs subjected to selection in the saplings compared to the old trees, suggesting that relict tree populations might be subjected to genetic differentiation and local adaptation to climate dryness. Our results illustrate the potential of tree rings and genome-wide analysis to improve our understanding of the adaptive capacity of drought-sensitive forests to cope with ongoing climate change.

Forest composition in the eastern United States (US) has been shifting from an oak–hickory to maple–beech assemblage, but whether there are species-specific differences within these oak–hickory stands in their responses and recovery from drought remains unclear. Here, we examined drought responses and resilience derived from radial growth of 485 co-occurring Carya ovata and Quercus alba individual trees at 15 forests in the eastern US. Water availability over the growing season (May to August) of the current year controls growth variability of both C. ovata and Q. alba. Drought that occurred in June caused the greatest growth reduction for both species while interspecific differences inof drought-induced growth reduction was found in July, where Q. alba experienced stronger reduction than C. ovata. Both species are resilient to early growing season drought, but late growing season drought caused larger drought legacy effects for Q. alba. The increasing drought frequency and intensity will have a more prominent impact in oak–hickory stands in the eastern US. The species composition of a forest along with species-specific responses and recovery is likely to be a critical control on forest productivity and species abundance. [ABSTRACT FROM AUTHOR]

The mid-elevation forest of California's Sierra Nevada poses a bioclimatic paradox. Mid-elevation trees experience a montane Mediterranean climate, with near-freezing winter days and rain-free summers. The asynchrony between warmth and water input suggests low primary production, limited by photosynthetic dormancy in winter cold, and again in summer and early autumn with drought, yet this forest is characterized by tall trees and high biomass. We used eddy covariance in a mid-elevation Sierra stand to understand how winter cold and summer drought limit canopy photosynthesis and production. The trees exhibited canopy photosynthesis year-round. Trees avoided winter dormancy, and daytime CO2uptake continued despite a deep snowpack and near-freezing temperatures. Photosynthesis on sunny days continued at half of maximum rates when air temperature was 0 °C. Likewise, the vegetation avoided summer drought dormancy, and high rates of daytime CO2uptake and transpiration continued despite a 5-month period with only negligible water input. We attribute this drought avoidance to deep rooting and availability of deep soil water. Year-round photosynthesis helps explain the large biomass observed in the Sierra Nevada, and implies adaptive strategies that may contribute to the resiliency or vulnerability of Sierran vegetation to climate change.

In soybean, studies on drought-responses are conducted during vegetative season. Information related to genes triggered in response to water-deficit (WD) in flower and pod is lacking. We performed an RNASeq and an agro-physiological characterization at stages R2 and R4 of soybean cultivar BR16, under WD. Physiological results showed a decrease in gas exchange parameters. Agronomical results showed WD impaired yield. Global Gene Ontology analyses indicated that most of the Differential Expressed Genes (DEGs) were down-regulated in flowers but up-regulated in pods. qRT-PCR revealed that WD triggered hormone biosynthesis changes. Mechanisms such as a decrease in glyceollin levels and cell wall instability were observed. This data showed tissue-specific mechanisms correlated with phenotypic responses such as drought escape, early flowering hormone-induced, and loss in grain weight. We presented here a comprehensive expression profile of flowers and pods soybean genes, which could guide researchers in the development of plants more tolerant to drought. [ABSTRACT FROM AUTHOR]

In this study, using Analytic Hierarchy Process (AHP) and Geographic Information System (GIS), the sensitivity to the occurrence of different types of droughts including meteorological drought (Med), hydrological drought (Hyd), and agricultural drought (Agd) were evaluated. In this research, at first, some of the effective indicators in each type of droughts were selected (four indicators in Med, three indicators in Hyd, and seven indicators in Agd), then using the ArcGIS 10.3 software, the sensitivity map of drought for each indicator were prepared (all indicators classified in four classes including mild, moderate, severe, and very severe). Then, using the AHP method the weight of each indicator in each type of droughts was determined and the final map of drought sensitivity for different types of droughts was prepared by superposition the maps of effective indicators in each drought. The final map of drought sensitivity was prepared by superposition the Med, Hyd, and Agd sensitivity maps (after determining the weight of each using AHP). In the Med, 43.29% of the study area (Fars province, Iran) was classified in the moderate class of drought sensitivity and 56.71% in the severe class. In the Hyd, 0.46%, 33.25%, 62.49%, and 3.80% of the study area were classified in the mild, moderate, severe, and very severe classes (respectively), and in the Agd, 1.18%, 50.23%, and 48.59% of the study area were classified in the mild, moderate, and severe classes. The results showed that in final drought sensitivity, the Med with a weight equal to 0.36 was the most effective variable, and based on the final map, 38.26% and 61.74% of the study area were classified in the moderate and severe classes of drought sensitivity. [ABSTRACT FROM AUTHOR]

Abstract Background Understanding the mechanisms underlying plant water use in response to drought is critical to predicting the trend of ecosystem development under a changing environment, while the responses of water use in clonal plants with interconnected ramets to drought are far less clear than trees. Method In this study, we conducted manipulated drought by excluding 50% annual throughfall at a stand level in a Moso bamboo (Phyllostachys heterocycla) forest, to determine how water use of the Moso bamboo responds to drought stress, and whether bamboo culms of different developmental stages show synchronized responses given the existence of physiological integration. Three developmental stages of bamboo culms (i.e., young, mature and old) were investigated and measurements were made on sap flow density (J s), leaf water potential at predawn (ψ pre) and midday (ψ mid), leaf water potential at turgor loss (ψ TLP), leaf stomatal density and size, and the maximum stomatal conductance (g w(max)) was calculated. Results Under the manipulative drought conditions, the values of J s significantly decreased in the mature culms but not in the young and old culms. g w(max) remained unchanged in mature culms, and increased in the young and old culms. Drought significantly reduced ψ mid of the young culms, resulting in more negative ψ TLP in the young culms compared with the old ones. Conclusions The results imply that the young culms adopted the drought tolerance strategy, while the old culms tended to adopt the drought avoidance strategy. Both the young and old culms are capable of maintaining relatively stable J s under drought by structural and physiological adjustments. Our findings demonstrate the variable responses of water use in bamboo culms of different developmental stages to drought, suggesting an unsynchronized responses of water use to water stress among culms in clonal plants.

Over the coming decades, climate change can decrease forest productivity and stability in many semiarid regions. Tree-ring width (TRW) analysis allows estimation of tree sensitivity to droughts, including resistance (Rt) and resilience (Rc) indexes. It helps to find adaptive potential of individual trees and forest populations. On a forest stand scale, it is affected by habitat conditions and species’ ecophysiological characteristics, and on individual scale by tree genotype, age, and size. This study investigated TRW response to droughts in forest-steppe and sub-taiga of southern Siberia for keystone species Scots pine (Pinus sylvestris L.), Siberian larch (Larix sibirica Ledeb.), and silver birch (Betula pendula Roth.). Chronologies reacted positively to the Standardized Precipitation-Evapotranspiration Index (SPEI) of the previous July–September and current April–July. Depressed tree growth across region and droughts lasting over both intra-seasonal intervals were registered in 1965, 1974, and 1999. TRW-based Rt and Rc for these droughts did not reveal age- or size-related patterns. Higher growth stability indexes were observed for birch in sub-taiga and for conifers in forest-steppe. Larch at all sites had disadvantage against pine for 1965 and 1999 droughts aggravated by pest outbreaks, but adapted better to drought in 1974. Site aridity affected both tree growth stability and intensity of climatic response.

Forest composition in the eastern United States (US) has been shifting from an oak–hickory to maple–beech assemblage, but whether there are species-specific differences within these oak–hickory stands in their responses and recovery from drought remains unclear. Here, we examined drought responses and resilience derived from radial growth of 485 co-occurring Carya ovata and Quercus alba individual trees at 15 forests in the eastern US. Water availability over the growing season (May to August) of the current year controls growth variability of both C. ovata and Q. alba. Drought that occurred in June caused the greatest growth reduction for both species while interspecific differences inof drought-induced growth reduction was found in July, where Q. alba experienced stronger reduction than C. ovata. Both species are resilient to early growing season drought, but late growing season drought caused larger drought legacy effects for Q. alba. The increasing drought frequency and intensity will have a more prominent impact in oak–hickory stands in the eastern US. The species composition of a forest along with species-specific responses and recovery is likely to be a critical control on forest productivity and species abundance.

High-resolution hydroclimate proxy records are essential for distinguishing natural hydroclimate variability from possible anthropogenically-forced changes, since instrumental precipitation observations are too short to represent the whole spectrum of natural variability. In Northern Europe, progress in this field has been hampered by a relative lack of long and truly moisture-sensitive proxy records. In this study, we provide the first assessment of the dendroclimatic potential of Blue Intensity (BI) and partial ring-width measurements (latewood and earlywood width series) from a network of cold and drought-prone Pinus sylvestris L. sites in Sweden. Our results show that all tree-ring parameters and sites share a clear and strong sensitivity to warm-season precipitation. The ΔBI parameter, in particular, shows considerable potential for hydroclimate reconstructions, here permitting a cross-validated precipitation reconstruction capable of explaining 56% (1901–2010 period) of regional-scale warm-season high-frequency precipitation variance. Using ΔBI as an alternative to ring-width improves the predictive skill with nearly a 20 percentage points increase in explained variance, reduces signal instability over time as well as allows a broader seasonal window (May–July) to be reconstructed. Additionally, we found that earlywood BI also reflect a positive late winter through early summer temperature signal. These findings emphasize that tree-rings, and in particular wood density parameters such as from BI, are capable of providing fundamental information to advance our understanding of hydroclimate variability in regions with a cool and rather humid climate regime that traditionally has been overlooked in studies of past droughts. Increasing the spatio-temporal coverage of hydroclimate records in northern Europe, and taking full advantage of the opportunities offered by the wood densitometric properties should be considered a research priority. [ABSTRACT FROM AUTHOR]

Summary: Over recent decades, biomass gains in remaining old-growth Amazonia forests have declined due to environmental change. Amazonia's huge size and complexity makes understanding these changes, drivers, and consequences very challenging. Here, using a network of permanent monitoring plots at the Amazon–Cerrado transition, we quantify recent biomass carbon changes and explore their environmental drivers. Our study area covers 30 plots of upland and riparian forests sampled at least twice between 1996 and 2016 and subject to various levels of fire and drought. Using these plots, we aimed to: (1) estimate the long-term biomass change rate; (2) determine the extent to which forest changes are influenced by forest type; and (3) assess the threat to forests from ongoing environmental change. Overall, there was no net change in biomass, but there was clear variation among different forest types. Burning occurred at least once in 8 of the 12 riparian forests, while only 1 of the 18 upland forests burned, resulting in losses of carbon in burned riparian forests. Net biomass gains prevailed among other riparian and upland forests throughout Amazonia. Our results reveal an unanticipated vulnerability of riparian forests to fire, likely aggravated by drought, and threatening ecosystem conservation at the Amazon southern margins. [ABSTRACT FROM AUTHOR]

Water scarcity has become a limiting factor for increasing crop production. Yield losses due to drought stress can best be resolved by breeding new, drought-tolerant cultivars, however, the genetic gains in drought resistance of different maize cultivars especially under precise water control conditions were not systematically studied. The objectives of this study were to assess 1) the change in yield and WUE of different cultivars from the 1970s through the 2010s under precise water control conditions and 2) find out the main factors affecting the yield and WUE change of different cultivars. We selected nine hybrids from different eras for a detailed field study under three different water treatments (full irrigation, moderate drought, and intense drought) in a rainout shelter at Hengshui (115°40′E, 37°44′N) in southern Hebei province in 2018 and 2019. We compared the grain yield and water use efficiency (WUE) of different cultivars from the 1970s through the 2010s under drought-stress (moderate drought and intense drought) and fully-irrigated conditions. The maize yield and WUE showed a significant linear increase with the year of release. The average yield gains were 111, 113.4 and 121.3 kg ha−1yr−1 under fully-irrigated, moderate and intense drought conditions while the WUE gains were 0.31, 0.38 and 0.72 kg ha−1 mm−1 yr−1 respectively. The yield reduction ratio showed a significant linear decrease from the 1970 s through the 2010s under both moderate water deficit and intense water deficit which were 0.51 % and 0.99 % yr−1, indicating that modern cultivars had better drought resistance than older ones. With increased water stress, the yield gap and yield reduction ratio between full irrigation and drought treatments (moderate drought and intense drought) increased significantly. The significant increase in the number of ears per hectare and the number of kernels per ear was the main reason for maize yield increase with the year of release from 1970s to 2010s under drought treatments. Under drought stress, the uniformity of yield component decreased significantly compared to the fully-irrigated treatment. In addition, an overly large leaf area was not conducive to drought resistance. Modern cultivars had better drought resistance than older ones. Selecting hybrids with higher uniformity and smaller leaf area was beneficial to improve the maize drought resistance. The results of this study will be beneficial for the breeding and selecting drought-resistant cultivars. • The maize yield and WUE showed significant linear increases with the year release. • Modern cultivars had better drought resistance than the old ones. • Too large leaf area was not conducive to the drought resistance. [ABSTRACT FROM AUTHOR]

Abstract In the Northeastern U.S., drought is expected to increase in frequency over the next century, and therefore, the responses of trees to drought are important to understand. There is recent debate about whether land-use change or moisture availability is the primary driver of changes in forest species composition in this region. Some argue that fire suppression from the early twentieth century to present has resulted in an increase in shade-tolerant and pyrophobic tree species that are drought intolerant, while others suggest precipitation variability as a major driver of species composition. From this debate, an emerging hypothesis is that mesophication and increases in the abundance of mesophytic genera (e.g., Acer, Betula, and Fagus) resulted in forests that are more vulnerable to drought. This review examines the published literature and factors that contribute to drought vulnerability of Northeastern U.S. forests. We assessed two key concepts related to drought vulnerability, including drought tolerance (ability to survive drought) and sensitivity (short-term responses to drought), with a focus on Northeastern U.S. species. We assessed drought-tolerance classifications for species, which revealed both consistencies and inconsistencies, as well as contradictions when compared to actual observations, such as higher mortality for drought-tolerant species. Related to drought sensitivity, recent work has focused on isohydric/anisohydric regulation of leaf water potential. However, based on the review of the literature, we conclude that drought sensitivity should be viewed in terms of multiple variables, including leaf abscission, stomatal sensitivity, turgor pressure, and dynamics of non-structural carbohydrates. Genera considered drought sensitive (e.g., Acer, Betula, and Liriodendron) may actually be less prone to drought-induced mortality and dieback than previously considered because stomatal regulation and leaf abscission in these species are effective at preventing water potential from reaching critical thresholds during extreme drought. Independent of drought-tolerance classification, trees are prone to dieback and mortality when additional stressors are involved such as insect defoliation, calcium and magnesium deficiency, nitrogen saturation, and freeze-thaw events. Overall, our literature review shows that multiple traits associated with drought sensitivity and tolerance are important as species may rely on different mechanisms to prevent hydraulic failure and depleted carbon reserves that may lead to mortality.

Summary: Water deficit is a major environmental threat affecting crop yields worldwide. In this study, a drought stress‐sensitive mutant drought sensitive 8 (ds8) was identified in rice (Oryza sativa L.). The DS8 gene was cloned using a map‐based approach. Further analysis revealed that DS8 encoded a Nck‐associated protein 1 (NAP1)‐like protein, a component of the SCAR/WAVE complex, which played a vital role in actin filament nucleation activity. The mutant exhibited changes in leaf cuticle development. Functional analysis revealed that the mutation of DS8 increased stomatal density and impaired stomatal closure activity. The distorted actin filaments in the mutant led to a defect in abscisic acid (ABA)‐mediated stomatal closure and increased ABA accumulation. All these resulted in excessive water loss in ds8 leaves. Notably, antisense transgenic lines also exhibited increased drought sensitivity, along with impaired stomatal closure and elevated ABA levels. These findings suggest that DS8 affects drought sensitivity by influencing actin filament activity. Significance Statement: DS8 encodes a NAP1‐like protein that affects drought sensitivity by its involvement in leaf epidermal development and stomatal closure in rice, revealing a molecular mechanism concerning the SCAR/WAVE‐Arp2/3 complex in the drought stress response. [ABSTRACT FROM AUTHOR]

Abstract Consequences of climate change will severely affect forest ecosystems in the near future, yet our understanding of how and why trees are responding to their abiotic environment is still limited. Intra-specific variation (ITV) in the growth response of trees to warming and drought has been widely neglected so far, but could play a key role for adapting forests to future climate conditions. We analyzed tree rings from four conifers (Picea abies , Abies alba , Larix decidua , Pseudotsuga menziesii) regarding their intra-specific adaptation potential when trees are growing at the warm and dry margins of species distributions. Our study comprises data from four common garden experiments (45 provenances and a total of 743 trees) and assessed growth response at different temporal scales from decades (long-term) to only a few event years (short-term) and finally for density fluctuations within one year (sudden response). We observed significant variation among provenances at all time-scales, but with varying degree among species. However, variation in short-term response (drought years) was remarkably unstable across all species, when the seasonal variation of drought occurrence was considered. Silver-fir and Douglas-fir showed significant associations between seed-source climate and growth response as well as trade-offs between early- and latewood growth reaction which strongly suggests that growth responses are adaptive. Intra-specific variation in conifers in response to drought will probably be sufficient to mitigate climate change consequences on forest growth, but growth-environment interactions as well as dependencies between temporal scales could create major pitfalls for adaptive forest management in the future. Graphical abstract Unlabelled Image Highlights • Intra-specific variation in response to warming and drought has been assessed by using dendroclimatological approaches. • Our study comprises data from common garden experiments including 4 conifer species (45 provenances and a total of 743 trees). • Variation in growth response is addressed at three different timescales ranging from decades to single years. [ABSTRACT FROM AUTHOR]

Drought stress results in significant losses in agricultural production, and especially that of cotton. The molecular mechanisms that coordinate drought tolerance remain elusive in cotton. Here, we isolated a drought-response gene GhKLCR1, which is a close homolog of AtKLCR1, which encodes a kinesin light chain-related protein enriched with a tetratrico peptide-repeat region. A subcellular localization assay showed that GhKLCR1 is associated with the cell membrane. A tissue-specific expression profile analysis demonstrated that GhKLCR1 is a cotton root-specific gene. Further abiotic and hormonal stress treatments showed that GhKLCR1 was upregulated during abiotic stresses, especially after polyethylene glycol treatments. In addition, the glucuronidase (GUS) staining activity increased as the increment of mannitol concentration in transgenic Arabidopsis plants harboring the fusion construct PGhKLCR1::GUS. The root lengths of 35S::GhKLCR1 lines were significantly reduced compared with that of wild type. Additionally, seed germination was strongly inhibited in 35S::GhKLCR1 lines after 300-mmol L−1 mannitol treatments as compared with Columbia-0, indicating the sensitivity of GhKLCR1 to drought. These findings provide a better understanding of the structural, physiological and functional mechanisms of kinesin light chain-related proteins. [ABSTRACT FROM AUTHOR]

Water use demand has increased steadily in Canterbury, New Zealand, over the last 20 years resulting in insufficient water availability. Prevailing irrigation management strategies in Canterbury consider soil moisture measurement up to a certain extent with no regard to crop’s development stages and sensitivity to water shortage; therefore, lacking to address the spatial and temporal variability of crop’s irrigation demand. This paper proposes an agent-based model that can be used to prioritise irrigation allocation to different crops on a farm. The proposed agent-based model takes into account the crop’s drought sensitivity, growth stage, soil type and the crop coefficient value when allocating water. It prioritises the crops based on their water requirements and generates an irrigation plan based on the predetermined water reduction. Our preliminary results showed that using this agent-based model, a significant water saving can be achieved even when water reduction is in effect, without impacting on production. [ABSTRACT FROM AUTHOR]

Climate extremes are predicted to become more frequent and intense in future. Thus, understanding how trees respond to adverse climatic conditions is crucial for evaluating possible future changes in forest ecosystem functioning. Although much information about climate effects on the growth of temperate trees has been collected in recent decades, our understanding of the influence of forest management legacies on climate-growth relationships is still limited. We used individual tree-ring chronologies from managed and unmanaged European beech forests, located in the same growth district (i.e. with almost identical climatic and soil conditions), to examine how forest management legacies (recently managed with selection cutting, >20 years unmanaged, >50 years unmanaged) influence the radial growth of Fagus sylvatica during fluctuating climatic conditions. On average, trees in managed stands had higher radial growth rate than trees in unmanaged stands during the last two decades a 50%. However, the beech trees in the unmanaged stands were less sensitive to drought than those in the managed stands. This effect was most pronounced in the forest with longest management abandonment (>50 years), indicating that the drought sensitivity of mature beech trees is in these forests the lower, the longer the period since forest management cessation is. Management-mediated modifications in crown size and thus water demand are one likely cause of the observed higher climate sensitivity of beech in the managed stands. Our results indicate a possible trade-off between radial growth rate and drought tolerance of beech. This suggests that reducing stem density for maximizing the radial growth of target trees, as is common practice in managed forests, can increase the trees' drought sensitivity. In the prospect of climate change, more information on the impact of forest management practices on the climate-growth relationships of trees is urgently needed. [ABSTRACT FROM AUTHOR]

In general, trees growing at or near their limit of distribution are more sensitive to climate than those growing at their ecological core. Here we examined the growth-climate relationship of European beech (Fagus sylvatica L.) close to its northern distribution limit in southern Sweden. Tree-ring width chronologies were developed from four well-separated sites where the species was dominant (Djupeåsen, DJ; Baldringe, BLD; Komperskulla, KSK and Ryssberget Nature Reserve, RYSS). The chronologies extended from 52 years (BLD) to 150 years (RYSS). Significant negative relationships were found between tree growth and previous summer (July and August) temperatures at three sites. July temperature of the year of growth had a negative relationship with beech growth at BLD and DJ. In contrast, current summer (July and August) precipitation was positively correlated with beech growth at DJ and KSK. This sensitivity of European beech to drought at its northern limit is in line with the previous research. However, following the exceptionally dry summer in southern Sweden in 1970, a marked growth decrease was noted as well as a shift in the relationship between beech growth and current growing-season temperature. Our results show that that the radial growth of European beech has become more sensitive to drought and precipitation than temperature at its northern distribution limit in the last several decades. [ABSTRACT FROM AUTHOR]

Lignin is a complex phenolic polymer that forms interwoven networks in the cell wall and is crucial to plant development and stress responses. The root tissues of safflower contain a high concentration of lignin, which may contribute to drought regulation mechanism in safflower. Cytochrome P450 is the largest oxidase family, which is often dubbed with a significant role in plant metabolism. However, little is known about the molecular mechanism of CYP450-mediated regulation of drought stress tolerance in safflower roots. In this study, a putative CtCYP71A1 gene from safflower was identified by combining genome-wide and transcriptomic analysis. In safflower, a total of 16 CtCYP71A enzyme coding genes were identified. The conserved structural topology of CtCYP71As reveals several signature motifs that are crucial to plant growth and stress response. The expression of CtCYP71A1 was shown to be diversely expressed in different tissues, however, it was significantly up-regulated in roots under normal condition. Similarly, in response to PEG stress, the expression of CtCYP71A1 in roots gradually increased, whereas it was upregulated initially and subsequently downregulated with ABA, GA3, and SA stress. In addition, the phenotypic analysis and root morphology of CtCYP71A1 overexpressed Arabidopsis lines showed enhanced drought tolerance with improved lignin content than that of wild-type and antisense plants, which was further confirmed by expression analysis, and various physiological indexes. Similarly, overexpression of CtCYP71A1 resulted in the positive regulation of several other genes involved in lignin biosynthesis compared to WT and antisense plants. Furthermore, drought sensitivity was observed in safflower roots with CtCYP71A1 virus-induced gene silencing assay. Together, these findings revealed important insights into the crucial role of CtCYP71A1 in drought tolerance via lignin accumulation in safflower. • Genome and transcriptome-wide analysis identified 16 putative CtCYP71A genes in safflower. • CtCYP71A1 demonstrates upregulation in safflower roots under drought stress. • Suppression of CtCYP71A1 resulted in drought susceptibility in safflower. • Overexpression of CtCYP71A1 led to improved drought tolerance and high lignin accumulation in Arabidopsis. • CtCYP71A1 is likely regulating drought stress tolerance by promoting lignin biosynthesis in safflower. [ABSTRACT FROM AUTHOR]

Abstract The ability of plants to acquire and use water is critical in determining life‐history traits such as growth, flowering, and allocation of biomass into reproduction. In this context, a combination of functionally linked traits is essential for plants to respond to environmental changes in a coordinated fashion to maximize resource use efficiency. We analyzed different water‐use traits in Arabidopsis ecotypes to identify functionally linked traits that determine water use and plant growth performance. Water‐use traits measured were (i) leaf‐level water‐use efficiency (WUEi) to evaluate the amount of CO2 fixed relative to water loss per leaf area and (ii) short‐term plant water use at the vegetative stage (VWU) as a measure of whole‐plant transpiration. Previously observed phenotypic variance in VWU, WUEi and life‐history parameters, highlighted C24 as a valuable ecotype that combined drought tolerance, preferential reproductive biomass allocation, high WUEi, and reduced water use. We therefore screened 35 Arabidopsis ecotypes for these parameters, in order to assess whether the phenotypic combinations observed in C24 existed more widely within Arabidopsis ecotypes. All parameters were measured on a short dehydration cycle. A segmented regression analysis was carried out to evaluate the plasticity of the drought response and identified the breakpoint as a reliable measure of drought sensitivity. VWU was largely dependent on rosette area, but importantly the drought sensitivity and plasticity measures were independent of the transpiring leaf surface. A breakpoint at high rSWC indicated a more drought‐sensitive plant that closed stomata early during the dehydration cycle and consequently showed stronger plasticity in leaf‐level WUEi parameters. None of the sensitivity, plasticity, or water‐use measurements were able to predict the overall growth performance; however, there was a general trade‐off between vegetative and reproductive biomass. PCA and hierarchical clustering revealed that C24 was unique among the 35 ecotypes in uniting all the beneficial water use and stress tolerance traits, while also maintaining above average plant growth. We propose that a short dehydration cycle, measuring drought sensitivity and VWU is a fast and reliable screen for plant water use and drought response strategies.

Abstract Forecast increases in the frequency, intensity, and duration of droughts with climate change may have extreme and extensive ecological consequences. There are currently hundreds of published, ongoing, and new drought experiments worldwide aimed to assess ecological sensitivity to drought and identify the mechanisms governing resistance and resilience. To date, the results from these experiments have varied widely, and thus, patterns of drought sensitivities and the underlying mechanisms have been difficult to discern. Here we examined 89 published drought experiments, along with their associated historical precipitation records to (1) identify where and how drought experiments have been imposed, (2) determine the extremity of drought treatments in the context of historical climate, and (3) assess the influence of ambient precipitation variability on the magnitude of drought experiments. In general, drought experiments were most common in water‐limited ecosystems, such as grasslands, and were often short‐term, as 80% were 1–4 yr in duration. When placed in a historical context, the majority of drought experiments imposed extreme drought, with 61% below the 5th, and 43% below the 1st percentile of the 50‐yr annual precipitation distribution. We also determined that interannual precipitation variability had a large and potentially underappreciated effect on the magnitude of drought treatments due to the co‐varying nature of control and drought precipitation inputs. Thus, detecting significant ecological effects in drought experiments is strongly influenced by the interaction between experimental drought magnitude, precipitation variability, and key ecological thresholds. The patterns that emerged from this study have important implications for the design and interpretation of drought experiments and also highlight critical gaps in our understanding of the ecological effects of drought.