Drought Adaptation Strategies Research Articles

Agro-climatic zone-wise drought hazards in Karnataka under historical and future climate scenarios

This study performed the spatio-temporal analysis of drought hazards across the agro-climatic zones (ACZs) of Karnataka under historical and future climate scenarios. The India Meteorological Department’s high-resolution gridded data for1989-2019 was used for historical drought occurrence analysis. Coordinated Regional Climate Downscaling Experiment ensemble data of the Representative Concentration Pathway (RCP) 4.5 and 8.5 scenarios were used for analysing future drought hazards in the near (2031-2060) and end term (2061-2099) periods. The standardised precipitation index (SPI) was used to calculate the frequency of droughts at different accumulation periods of 1, 3, 6, 9, and 12 months. Subsequently, the ACZ-wise drought hazard index (DHI) was calculated and mapped geospatially using ArcGIS. The results indicated that moderate drought events have the highest frequencies of occurrence, followed by severe and extreme drought events for all accumulation periods. During 1989-2019, 54.8%, 28.3% and 16.7% of droughts were moderate, severe, and extreme, respectively. An increase of 2.6% and 2.4% in the frequency of moderate droughts is projected under the RCP4.5 and 8.5 scenarios, respectively, in the end term. Under both historical and future climate scenarios, a high frequency of extreme droughts was observed in the long accumulation periods (SPI-9 and SPI-12), whereas the frequency of moderate droughts was observed to be high in the short accumulation periods (SPI-1 and SPI-3). Under the historical scenario, the frequency of droughts in the extreme category was high in the southern transition, central dry, and north eastern dry zones, severe category in the northern dry, southern transition, and coastal zones, and moderate category in the north transition, hill, and southern dry zones. Among the 30 districts of Karnataka, Chitradurga, Udupi, Tumakuru, Ballari, Koppala, Raichuruand Gadaga districts have very high DHI. This study sheds light on the potential consequences of climate change on drought scenarios in the Karnataka state’s agro-climate zones and urges for zone specific drought adaptation and mitigation strategies to strengthen the State resilience.

VULNERABLITY OF RURAL LIVELIHOODS IN NINH THUAN PROVINCE TO DROUGHT

The risk of drought poses a significant challenge to agricultural production in Ninh Thuan Province. Therefore, this study aims to identify the factors that influence farmers’ livelihood outcomes due to the impact of drought. Data were collected from a survey of 231 farmers randomly selected from the districts of Thuan Nam, Thuan Bac, and Ninh Hai. In addition to descriptive statistics, a Tobit regression model was used to identify the factors influencing livelihood outcomes during mild and severe droughts. The results showed that farmers’ livelihood outcomes were generally low. The regression identified the financial (β=0.230 and 0.205), social (β=0.200 and 0.291), and human capital (β=0.195 and 0.196) impacts on farmers’ livelihood outcomes from both mild and severe droughts. During mild drought years, seasonal adjustment (β=-0.009) and migration (β=0.013) were found to significantly influence livelihood outcomes. In severe drought years, government support (β=-0.030) negatively affected livelihood outcomes. There is a need to establish an early warning system for climate change and extreme weather events while simultaneously disseminating information widely to farmers so that they can take timely measures to cope. Enhancing human capital by raising awareness and skills in adapting to drought and developing comprehensive abilities to implement drought adaptation strategies is needed.

Biological and environmental controls on nighttime water-use behaviors in Populus simonii in semi-arid areas of the Chinese Loess plateau

Recent studies have revealed that the active nighttime water-use behaviors by trees have critical physio-ecological significance in survival and growth in adversity. However, the characteristics and biophysical control of nighttime water-use of silvicultural trees are not clear. We continuously monitored sap flow and leaf water potential (predawn and midday) of Populus simonii of different tree sizes as well as environmental factors during the 2021 and 2022 growing seasons (May-September) in a semi-arid area of Loess Plateau. Our results showed that both nighttime water-use (WUn) and the ratio of nighttime to daily water-use (WUn%) increased significantly with tree size, and had larger values in the drought year than in the normal year. The WUn% of different tree sizes ranged from 10.24 to 13.01% and can reach up to 36.49% during prolonged soil drought. Besides, the WUn% of different tree sizes were significantly positively and negatively correlated with nighttime vapor pressure deficit (VPDn) and soil water content, respectively. By partitioning the components of WUn, we found that as tree size increased, the stem water refilling (RE) and nighttime transpiration increased obviously, but the ratio of RE to WUn (RE%) did not change. The RE of different tree sizes constituted the major part of WUn with an average RE% of 65.7–68.0%, and the RE% was larger in the drought year than in the normal year. Additionally, the RE% of different tree sizes increased with decreasing predawn leaf water potential (Ѱpd) during the soil dry stage and with increasing VPDn during the soil wet stage. Given the increased risk of atmospheric drought and soil drought, it can be expected from our findings that the nighttime water-use behaviors of trees become more active in the future, which represents a significant performance of drought adaptation strategies of silvicultural species.

Gamma-aminobutyric acid modulates antioxidant and osmoprotective systems in seedlings of Triticum aestivum cultivars differing in drought tolerance

The stress-protective effects of plant neurotransmitters, including gamma-aminobutyric acid (GABA) have been intensively examined in recent years. However, studies on the GABA influence on stress protective systems in bread wheat cultivars with different drought adaptation strategies are still lacking. The aim of this work was to estimate the GABA effect on the state of antioxidant and osmoprotective systems in etiolated seedlings of two wheat cultivars differing significantly in drought tolerance, namely Doskonala (non-drought-resistant) and Tobak (drought-resistant) under model drought induced by PEG 6000. Two-day-old seedlings were transferred to 15% PEG 6000 and incubated for two days in the absence or presence of GABA. Treatment with 0.1 and 0.5 mM GABA significantly reduced the growth-inhibitory effect of PEG 6000 on the roots and shoots of both cultivars, but to a greater extent on those of non-resistant Doskonala. It was shown that GABA treatment reduced drought-induced accumulation of H2O2 and MDA, stabilized SOD and GPX activity, the level of sugars, anthocyanins and flavonoids in seedlings of both cultivars. Meanwhile GABA treatment enhanced the stress-induced increase in proline content in the Doskonala cultivar, but decreased it in the Tobak, completely prevented stress induced decrease in anthocyanins and flavonoids level in the Tobak and only partially in Doskonala cultivar. Thus, the stabilization of the stress-protective systems functioning in the wheat cultivars and variety-dependent differences in response to GABA were revealed. Keywords: anthocyanins, antioxidant system, drought resistance, gamma-aminobutyric acid, oxidative stress, proline, Triticum aestivum

Resilience of rainfed agriculture in northern part of Cyprus: a comprehensive drought severity level impact analysis and adaptive strategies

Resilience of rainfed agriculture in northern part of Cyprus: a comprehensive drought severity level impact analysis and adaptive strategies

Patterns, timing, and environmental drivers of growth in two coexisting green-stemmed Mediterranean alpine shrubs species.

The Mediterranean alpine is one of the most vulnerable ecosystems under future environmental change. Yet, patterns, timing and environmental controls of plant growth are poorly investigated. We aimed at an improved understanding of growth processes, as well as stem swelling and shrinking patterns, by examining two common coexisting green-stemmed shrub species. Using dendrometers to measure daily stem diameter changes, we separated these changes into water-related shrinking and swelling and irreversible growth. Implementing correlation analysis, linear mixed effects models, and partial least squares regression on time series of stem diameter changes, with corresponding soil temperature and moisture data as environmental predictors, we found species-specific growth patterns related to different drought-adaptive strategies. We show that the winter-cold-adapted species Cytisus galianoi uses a drought tolerance strategy combined with a high ecological plasticity, and is, thus, able to gain competitive advantages under future climate warming. In contrast, Genista versicolor is restricted to a narrower ecological niche using a winter-cold escape and drought avoidance strategy, which might be of disadvantage in a changing climate. Pregrowth environmental conditions were more relevant than conditions during growth, controlling the species' resource availability. Thus, studies focusing on current driver constellations of growth may fail to predict a species' ecological niche and its potential future performance.

Two common, often coexisting grassland plant species differ in their evolutionary potential in response to experimental drought.

For terrestrial plant communities, the increase in frequency and intensity of drought events is considered as one of the most severe consequences of climate change. While single-species studies demonstrate that drought can lead to relatively rapid adaptive genetic changes, the evolutionary potential and constraints to selection need to be assessed in comparative approaches to draw more general conclusions. In a greenhouse experiment, we compare the phenotypic response and evolutionary potential of two co-occurring grassland plant species, Bromus erectus and Trifolium pratense, in two environments differing in water availability. We quantified variation in functional traits and reproductive fitness in response to drought and compared multivariate genetic variance-covariance matrices and predicted evolutionary responses between species. Species showed different drought adaptation strategies, reflected in both their species-specific phenotypic plasticity and predicted responses to selection indicating contrasting evolutionary potential under drought. In T. pratense we found evidence for stronger genetic constraints under drought compared to more favourable conditions, and for some traits plastic and predicted evolutionary responses to drought had opposing directions, likely limiting the potential for adaptive change. Our study contributes to a more detailed understanding of the evolutionary potential of species with different adaptive strategies in response to climate change and may help to inform future scenarios for semi-natural grassland ecosystems.

Addressing the effects of soil organic carbon on water retention in US Pacific Northwest wheat–soil systems

Soil organic carbon (SOC) is considered a significant contributor to soil water retention. However, generalizations about the role of SOC in available water-holding capacity (AWHC) may have inaccurately portrayed this relationship. We aim to reexamine the relationship between SOC and water retention using the National Cooperative Soil Survey (NCSS) Database. We focus on regional soil groups within the Pacific Northwest wheat production region, including Haploxerolls, Argixerolls, Haplocambids, and Durixerolls. We evaluated 77 sites based on SOC, total nitrogen (TN), pH, texture, bulk density (BD), field capacity (FC), permanent wilting point (PWP), and AWHC. Our findings indicate that texture and BD were the most significant contributors to AWHC variation, while SOC played a secondary role in explaining this variation. Mid-infrared (MIR) spectroscopy coupled with a random forest (RF) algorithm was used to evaluate the importance of spectral bands in determining changes in FC and PWP. This analysis identified mineral bands related to inner-surface hydroxyl groups in kaolinite (3700 cm −1) and Si-O-Si overtones (1870 cm −1) as the most important spectral contributors to PWP. The water retention at FC was associated with organic absorbances relevant to soil aggregation, such as polysaccharide C–O (~1035 cm −1), while mineral bands were relatively less influential. This study highlights the need to reexamine the impact of SOC as well as the interaction between soil texture and compaction on soil water retention to elucidate the underlying mechanisms responsible for AWHC, thus providing insight into future drought adaptation strategies.

Agricultural drought severity in NE Italy: Variability, bias, and future scenarios

This study investigated the variability of agricultural drought severity, as depicted by vegetation indices, and the bias in identifying drought events when considering a stationary vs nonstationary climate reference. The work leveraged gridded climate data (NCEP CFSv2, CHIRPS 1981–2022), soil properties (OpenLandMap), satellite imagery (Sentinel2/Landsat, 2000–2022), and future climate projections (NEX-GDDP, 2050) together with local knowledge of selected farms, to augment drought monitoring techniques and identify potential issues for agriculture. For the study domain, significant differences were observed when comparing drought characteristics using stationary and nonstationary drought indexes, with biases being not ubiquitous in either space or time of year. When developing sustainable drought mitigation and adaptation strategies, decision-makers should carefully address this uncertainty to avoid a possible underestimation of drought magnitude. Results showed a drought increase (∼50%) by the mid and late twenty-first century. Projection of future climate highlighted an even more significant impact (∼80%) with a wide variability of risk across the domain. As drought impact was also related to soil organic carbon (SOC), our results suggest that improving SOC content could be a sustainable strategy for enhancing soil drought resilience, especially in areas commonly characterized by low concentrations of organic carbon and nutrients. The analysis highlighted that drought impacts were also modulated by investment in irrigation infrastructure and irrigation efficiency. Researchers and land managers could apply the proposed analysis design to address historical, current and future indicators of vegetation conditions within irrigated regions. By providing spatio-temporal information on the patterns of drought impacts and their bias, this study supports identifying priority regions for targeted drought risk reduction and adaptation options, including water resources and soil management sustainability criteria, to move towards more resilient agricultural systems.

Plant drought adaptation strategies regulate alpine grassland water yield in the Qinghai Lake Basin, northeastern Qinghai-Tibet Plateau

Study regionThe Qinghai Lake Basin, northeast Qinghai-Tibetan Plateau. Study focusVegetation dynamic induced change on catchment water yield (including surface runoff and groundwater runoff) is one of the research hotspots in the field of hydrology and ecology. However, few studies have explored the underlying biological mechanism by which plant regulate water yield. In this study, we examined the impact of different plant drought adaptation strategies on watershed water yield in the Qinghai Lake Basin, using both the ecohydrological model, water balance method and surface runoff experiments. New hydrological insightswe defined two type of plant drought adaptation strategies: drought-avoiding strategy can maximize the soil moisture and therefore minimize vegetation water stress, while drought-tolerating strategy tends to increase productivity by tolerating a certain degree of water stress. The result shows that plants employing drought-avoiding strategy have significantly higher water yield and water yield coefficient (the ratio of water yield to precipitation) than plants adopting drought-tolerating strategy, regardless of meadow or steppe species. Meanwhile, for all grassland species in the study region, plants with drought-avoiding strategy have less vegetation cover and net primary productivity than plants with drought-tolerating strategy, which reflect the trade-off between avoiding water stress and achieving competitive advantages. Our findings offer insights into the biological mechanism by which vegetation regulates water yield, and provide vital guidance for watershed management.

Meteorological Drought Variability over Africa from Multisource Datasets

This study analyses the spatiotemporal variability of meteorological drought over Africa and its nine climate subregions from an ensemble of 19 multisource datasets (gauge-based, satellite-based and reanalysis) over the period 1983–2014. The standardized precipitation index (SPI) is used to represent drought on a 3-month scale. We analyse various drought characteristics (duration, events, frequency, intensity, and severity) for all drought months, and moderate, severe, and extreme drought conditions. The results show that drought occurs across the continent, with the equatorial regions displaying more negative SPI values, especially for moderate and severe droughts. On the other hand, Eastern Sahara and Western Southern Africa portray less negative SPI values. The study also reveals that extreme drought months have the largest interannual variability, followed by all drought months and severe drought months. The trend analysis of SPI shows a significantly increasing trend in drought episodes over most regions of Africa, especially tropical areas. Drought characteristics vary greatly across different regions of Africa, with some areas experiencing longer and more severe droughts than others. The equatorial region has the highest number of drought events, with longer durations for severe and extreme drought months. The Eastern Sahara region has a low number of drought events but with longer durations for moderate, severe, and extreme drought months, leading to an overall higher drought severity over the area. In contrast, Western Southern Africa and Madagascar display a consistently low drought severity for all categories. The study demonstrates the importance of conducting drought analysis for different drought levels instead of using all drought months. Drought management and adaptation strategies need to enhance community resilience to changing drought situations and consider drought variability in order to mitigate different impacts of drought across the continent.

Robust management strategies promoting ecological resilience and economic efficiency of a mixed conifer-broadleaf forest in Southwest Germany under the risk of severe drought

Robust decision-making in forestry seeks solutions that reduce the risk of environmental damage and economic losses, which matters for designing forest adaptation measures. We propose a state-of-the-art methodology to identify robust drought adaptive strategies. First, we used a process-based model with an ensemble of climate change scenarios to simulate managed forest dynamics. Second, we quantified the ecological resilience and financial return as net present value (NPV), applying business-as-usual (BAU) and alternative adaptation strategies to regenerate the overstorey layer (trees ≥ 30 cm dbh) of the forest (e.g., “active”, “reactive”, and “do-nothing”). Afterward, we analyzed robustness by searching for the strategy with minimum worst-case losses of ecological and economic signposts. Our analysis found a reduced forest drought resilience under BAU and “do-nothing” strategies, determining a high probability of economic failure (∼ −49% and ∼ −67% loss in NPV respectively). While, an early “active” strategy would increase the NPV (∼ +10%), and a highly-intense “reactive” strategy would have minimal losses (∼ −2%). Finally, we found that local conditions influence the signpost performance magnitude but do not vary the robust solution. We conclude that our methodology facilitates applying a robustness analysis in forestry, and drought adaptation should occur rather sooner than later, considering constant revision.

Mechanisms to change farmers' drought adaptation behaviors in Sistan and Baluchistan Province, Iran

IntroductionFrequent droughts in Iran have imposed economic and social losses on farmers. To mitigate drought implications, farmers' behaviors should be shifted towards drought adaptation. This research mainly aimed to study mechanisms for changing farmers' drought adaptation behaviors in Sistan and Baluchistan Province.MethodsThe research was conducted among farmers in this province (N = 950). The sample whose size was estimated at 275 farmers by Krejcie and Morgan's table was taken by the stratified random sampling technique. The research instrument was a researcher-made questionnaire. Data were analyzed by SPSS23 and AMOS23 software. The comprehensive action determination model was validated by confirmatory factor analysis. Furthermore, structural equation modeling was used to explore the components influencing farmers' drought adaptation behaviors.Results and discussionAccording to the results, personal norms, attitudes, objective barriers, and subjective barriers had positive and significant effects on the farmers' intention to apply drought adaptation strategies. As well, the farmers' adaptation behaviors were influenced by their behavioral intentions, objective barriers, and subjective barriers. It can be concluded that changing the mechanism of farmers' behaviors toward drought adaptation is shaped by the processes included in the comprehensive action determination model in which norms, habits, situational influences, and intentional processes are involved.

Adapting to Climate Change in the Semi-Arid Northern Kenya

Climate change in the semi-arid northern Kenya is evidenced by increasing frequency and duration of severe droughts. The effects are devastating with the region experiencing massive loss of livestock, total crop failures and increased levels of hunger and starvation resulting in near collapse of livelihood sources which is mainly pastoralism. This study investigated the most appropriate drought adaptive strategies that pastoralists in the semi-arid northern Kenya depend on to subsist. Data was collected from the counties of Garissa, Samburu, Turkana, Isiolo, Marsabit, West Pokot, Laikipia and Baringo where drought is persistent. The study used a cross-sectional design where past and current data was obtained through face-to-face and telephone interviews from purposively sampled respondents and observations. Document information collected supplemented the information obtained from the respondents. The pastoralists embrace adaptive strategies that are easy, accessible and affordable. The traditional adaptive strategies such as food preservation and herd composition and management predominate. These strategies are preferred because of their ease of implementation and also culturally acceptable. With increasing drought severity and other factors like increase in population growth, there has been decline in grazing areas limiting transhumance activities. This has stemmed the adoption of non-pastoral activities such as crop farming, craftwork, poultry keeping, petty trade and dependence on external assistance. The traditional adaptive strategies play a key role in surviving the droughts. Due to their pastoral nature, the non-pastoral sedentary practices do not fit their lifestyles and are less practiced especially by men but taken up much better by women who are left at home. Therefore, efforts to enhance pastoral resilience in the semi-arid areas should strengthen the traditional practices as well as capacity building on the non-pastoral activities.

Exacerbated drought accelerates catastrophic transitions of groundwater-dependent ecosystems in arid endorheic basins

• Two Haloxylon species exhibited distinct water use strategies but analogous bistable transitions. • Drought accelerates catastrophic shifts in both Haloxylon ecosystems by reducing resilience. • Natural and anthropogenic forcings are aggravating drought in groundwater-dependent ecosystems. • Drought adaptation strategies for such ecosystems must account for maintaining resilience. Drought has become a major threat to regional sustainable development in drylands. Ecological drought, emphasizing the process of drought impacts on ecosystems in coupled human-natural systems, has been posing large risks to the stability of groundwater-dependent ecosystems (GDEs) in drylands. Yet, the interconnected avenues via which ecological drought drives vegetation transition, ecological resilience and ecosystem services in GDEs with species-specific traits remain elusive, especially in arid endorheic basins. Here, we combine comprehensive field measurements derived from representative groundwater depth transects in Central Asia and simulations obtained from the stochastic eco-hydrological models and the Langevin approach, we find that two groundwater-dependent species, the salt-tolerant Haloxylon ammodendron and salt-sensitive Haloxylon persicum , exhibit contrasting water use strategies being driven by variations in eco-physiological traits and environmental regimes. Nonetheless, both the low-resilient H. ammodendron and high-resilient H. persicum vegetation tend to show bistable transition corresponding to vegetated and bare soils under drought stress with stochastic noises and time delays. Alarmingly, ecological drought is accelerating catastrophic transitions in both Haloxylon ecosystems induced by diminishing ecological flows, depleting soil moisture, and aggravating salinization, together with climate forcing. In particular, exacerbated drought stress reduces ecological resilience, enhances the likelihood of catastrophic shifts, and reduces ecosystem services of GDEs in arid endorheic basins. Our results highlight that ecological drought adaptation strategies must account for resilience maintenance by balancing water scarcity, water overuse, and water/soil quality to avoid accelerating regime shifts in dryland ecosystems.

Drought Stress and Adaptation Strategies in Kumi and Amuria Districts of Uganda

This study investigated smallholder farmers’ drought adaptation strategies in 246 randomly selected households in Kumi and Amuria districts of Teso sub region of Uganda. Primary and secondary data were collected, the former through individual interviews, focus group discussions and key informant interview and the latter through document review. The results revealed that drought stress was above -4 kilo pascal within the period 2006–2016. The adaptation strategies appliedincluded cultivation of food crops that can be preserved and offering of labour on other people’s farms as a survival strategy. Promotion of early warning mechanisms; easy access to farm inputs; group formation and consolidation; and affordable irrigation technology are recommended to enhance farmers’ resilience

Multiple drought indices and their teleconnections with ENSO in various spatiotemporal scales over the Mekong River Basin

Drought may lead to severe and diverse impacts on agriculture, economy, and society across different regions and periods, posing predictive and adaptive challenges. In recent years, severe droughts have affected >60 million people in the Mekong River Basin (MRB). Additionally, El Niño Southern Oscillation (ENSO) episodes had distinct influences on the occurrence and intensity of drought variability in the regions. Understanding the spatiotemporal characteristics of droughts across the MRB is critical to improving management and mitigation actions. This study aims to investigate spatiotemporal drought characteristics in the MRB and their teleconnection with the ENSO. Three multiple drought indices, including the Standardized Precipitation Index (SPI) for meteorological drought, Standardized Soil Water Index (SSWI) for agricultural drought, and Standardized Runoff Index (SRI) for hydrological drought were calculated to quantify drought events, drought frequency, and drought severity. The overall patterns showed more events and larger intensity were identified by the SPI than those by the SRI or the SSWI, while the higher frequency was observed by the SRI. The Middle Mekong basins seem to experience more drought events, while higher levels of frequency and intensity of droughts were observed in the Upper Mekong Basin. The correlation analysis between ENSO index and precipitation suggested that the strongest ENSO events in Dec-Jan-Feb may result in developments of meteorological drought in Mar-Apr-May, and further led to hydrological and agricultural drought in Apr-May-Jun. Such ENSO effects had significant influences on drought variabilities in southern MRB and were insignificant in the north. The multiple drought indices show skills in identifying spatial and temporal drought characteristics from meteorological, agricultural, and hydrological perspectives, and potential for drought outlook further considering their ENSO teleconnections. The results can be applied to the development of drought monitoring methods and adaptive strategies to mitigate drought impacts through scientific and quantitative assessments.

Higher association and integration among functional traits in small tree than shrub in resisting drought stress in an arid desert

Revealing plant adaptation strategies to drought has become one of the research hotspots in assessing the impact of global change on forest ecosystems. However, it is not clear whether the drought adaptation strategies are consistent across life forms. The scientific question of this study is whether small tree and shrub adopt different strategies to cope with drought stress. To answer it, we analyzed the differences of change pattern in four types of functional traits (leaf, photosynthetic, hydraulic and carbohydrate traits), as well as the asscoiation and integration among traits across a drought stress gradient between the most common small tree (Haloxylon ammodendron) and shrub (Alhagi sparsifolia Shap.) species in an arid desert of northwest China. Our results showed that the adaptation of photosynthetic and carbohydrate traits were the same in the two species, but leaf and hydraulic traits were different. Association and integration among traits were obviously higher in small tree than shrub because the former suffered more severe drought stress. All the functional traits of small tree can be integrated into two independent drought adaptation groups, which can be named drought resistance-nutrient accumulation group and hydraulic adaptation group, respectively. These two groups were all obviously related to drought adaptation, and can be considered as two adaptive strategies evolved by small tree to cope with drought stress. In contrast, all traits of shrub can be classified into four independent adaptive groups. However, it is difficult to associate all of them as drought adaptation strategies. In conclusion, shrub had a stronger drought tolerance, and showed an independent trait adaptability relative to small tree, with no close accociation between traits. Oppositely, the traits of small tree were closely related to each other. The trade-offs and compensations among traits greatly helpled small tree to reduce drought stress.

Flexible drought deciduousness in a neotropical understory herb.

PremiseAdaptive divergence across environmental gradients is a key driver of speciation. Precipitation seasonality gradients are common in the tropics, yet drought adaptation is nearly unexplored in neotropical understory herbs. Here, we examined two recently diverged neotropical spiral gingers, one adapted to seasonal drought and one reliant on perennial water, to uncover the basis of drought adaptation.MethodsWe combined ecophysiological trait measurements in the field and greenhouse with experimental and observational assessments of real‐time drought response to determine how Costus villosissimus (Costaceae) differs from C. allenii to achieve drought adaptation.ResultsWe found that drought‐adapted C. villosissimus has several characteristics indicating flexible dehydration avoidance via semi‐drought‐deciduousness and a fast economic strategy. Although the two species do not differ in water‐use efficiency, C. villosissimus has a more rapid growth rate, lower leaf mass per area, lower stem density, higher leaf nitrogen, and a strong trend of greater light‐saturated photosynthetic rates. These fast economic strategy traits align with both field‐based observations and experimental dry‐down results. During drought, C. villosissimus displays facultative drought‐deciduousness, losing lower leaves during the dry season and rapidly growing new leaves in the wet season.ConclusionsWe revealed a drought adaptation strategy that has not, to our knowledge, previously been documented in tropical herbs. This divergent drought adaptation evolved recently and is an important component of reproductive isolation between C. villosissimus and C. allenii, indicating that adaptive shifts to survive seasonal drought may be an underappreciated axis of neotropical understory plant diversification.

Molecular plasticity to soil water deficit differs between sessile oak (Quercus Petraea (Matt.) Liebl.) high- and low-water use efficiency genotypes.

Water use efficiency (WUE) is an important adaptive trait for soil water deficit. The molecular and physiological bases of WUE regulation in crops have been studied in detail in the context of plant breeding. Knowledge for most forest tree species lags behind, despite the need to identify populations or genotypes able to cope with the longer, more intense drought periods likely to result from climate warming. We aimed to bridge this gap in knowledge for sessile oak (Quercus petraea (Matt.) Liebl.), one of the most ecologically and economically important tree species in Europe, using a factorial design including trees with contrasted phenotypic values (low and high WUE) and two watering regimes (control and drought). By monitoring the ecophysiological response, we first qualified genotypes for their WUE (by using instantaneous and long-term measures). We then performed RNA-seq to quantify gene expression for the three most extreme genotypes exposed to the two watering regimes. By analyzing the interaction term, we were able to capture the molecular strategy of each group of plants for coping with drought. We identified putative candidate genes potentially involved in the regulation of transpiration rate in high-WUE phenotypes. Regardless of water availability, trees from the high-WUE phenotypic class overexpressed genes associated with drought responses, and in the control of stomatal density and distribution, and displayed a downregulation of genes associated with early stomatal closure and high transpiration rate. Fine physiological screening of sessile oaks with contrasting WUE, and their molecular characterization (i) highlighted subtle differences in transcription between low- and high-WUE genotypes, identifying key molecular players in the genetic control of this trait and (ii) revealed the genes underlying the molecular strategy that evolved in each group to potentially cope with water deficit, providing new insight into the within-species diversity in drought adaptation strategies.