Water Stress Intensity Research Articles

Geopolitical Risk and Foreign Direct Investment Inflows: The Moderating Role of Water and Energy Risks

ABSTRACTUsing a panel of 43 economies between 1985 and 2022, this article establishes a link between foreign direct investment (FDI) inflows and geopolitical risk. We distinguish the idiosyncratic component of geopolitical risk from the global geopolitical risk index provided by Caldara and Iacoviello (2022. American Economic Review, 112, 1194–1225.). We then incorporate both global and idiosyncratic risks into a static FDI regression model, controlling for other economic and institutional determinants. Our findings suggest that both global and idiosyncratic geopolitical risks pose significant obstacles to FDI inflows. Additionally, we investigate whether water and energy risks, when interacting with geopolitical risk, influence the behaviour of international investors. To test this hypothesis, we estimate the interaction effect of water stress and energy intensity as proxies for water and energy risks, respectively. Our findings imply that foreign investors perceive high energy intensity and water stress as moderating factors that could motivate host country policymakers to avoid involvement in geopolitical confrontations, thereby supporting peacebuilding to prevent or resolute conflicts.

The interaction effect of water deficit stress and seaweed extract on phytochemical characteristics and antioxidant activity of licorice (Glycyrrhiza glabra L.).

With increasing drought stress due to climate change and water scarcity, the agricultural sector has sought innovative strategies to mitigate the detrimental effects on crop productivity. One approach that has received significant attention is the use of fertilizers and biostimulants as potential means of alleviating drought stress. In this study, five different irrigation levels including 100% (control), 80% (slight stress), 60% (mild stress), 40% (moderate stress), and 20% (severe stress) of field capacity (FC) and seaweed extract (SWE) at three concentrations (0, 5, and 10 g/L) were applied to the pots containing one-year-old licorice (Glycyrrhiza glabra L.) plants in a factorial completely randomized design experiment with three replications for eight weeks. The glycyrrhizic acid content increased with water stress intensity without the application of SWE until severe (20% FC) water stress treatment. The application of 10 g/L SWE under 100% FC led to a significant increase in the glycyrrhizic acid value (32.5±0.889 mg/g DW) compared with non-SWE application (30.0±1.040 mg/g DW). The maximum glabridin content (0.270±0.010 mg/g DW) was obtained under irrigation of 20% field capacity with 10 g/L SWE application. In addition, the activity of the all studied enzymes such as APX (ascorbate peroxidase), CAT (catalase), POD (peroxidase), and SOD (superoxide dismutase) were boosted by increasing the water stress levels. The use of SWE further enhanced the increase of some of these metabolites and enzymes, which, in turn, helped the plant to tolerate stress conditions through the scavenging of more ROS (Reactive oxygen species), wherein for this purpose, the SWE 10 g/L was more effective than other concentration. The plants efficiently eliminated ROS driven from drought stress by both non-enzymatic and enzymatic systems.

Mixing oak and pine trees in Mediterranean forests increases aboveground hydraulic dysfunctions.

Increasing tree species diversity in Mediterranean forests could reduce drought-induced hydraulic impairments through improved microclimate and reduced competition for water. However, it remains unclear if and how species diversity modulates tree hydraulic functions and how impacts may shift during the growing season. Using unmanaged Mediterranean forest stands composed of one (i.e., monospecific) or four (i.e., multispecific) tree species, we examined the seasonal dynamics of in-situ hydraulic traits (predawn and midday leaf water potential - Ψpd and Ψmd, xylem- and leaf-specific hydraulic conductivity - KS and KL, percentage loss of conductivity - PLC, specific leaf area - SLA, and Huber value - HV) in four co-existing Pinus and Quercus species over two years. We mainly observed adverse impacts of species diversity with lower Ψpd, Ψmd, KS, KL, and higher PLC in multispecific compared to monospecific stands, especially for the two pines. These impacts were observed all along the growing season but were stronger duringthe driest periods of the summer. Beneficial impacts of diversity were rare and only occured for oaks (Q. faginea) after prolonged and intense water stress. Our findings reveal that mixing oaks and pines could mainly enhance hydraulic impairments for all species during the dry season, suggesting a potential decline in mixed Mediterranean forests under future climate.

The potential of processed mineral construction and demolition waste to increase the water capacity of urban tree substrates - A pilot scale study in Munich

Construction and demolition waste (CDW) represents one of the most significant waste streams worldwide. Due to a high brick content, CDW amended soil substrates are expected to improve water retention, benefitting urban trees.In this two-year field study evaluating the effects of CDW on the water holding capacities of urban tree substrates, six substrate mixtures are tested. Three test substrates contained a standard CDW mixture with 30 % and three 60 % bricks. Soil water contents were monitored and plant available water contents (PAWC) were analysed. From soil water contents and PAWC, the relative extractable water contents (REW), and subsequently the number of days with REW < 40 % and water stress intensity (WSI) are calculated.The substrates with enhanced brick content showed higher PAWC. However, the effect of brick on PAWC was only significant at a minimum of 30 % bricks in the substrate. Pore size distribution of the brick fraction confirmed the assumed relationship between addition of brick and increased PAWC. Substrates with an enhanced brick content showed reduced numbers of days with REW < 40 % and a reduction in WSI.Our findings demonstrate that CDW has potential to foster water holding capacities of urban tree substrates.

Water stress effect on the quality and quantity of lemongrass essential oils in glass greenhouses: Juvenile and adult stages

The detrimental effects of water stress on the survival and productivity of many medicinal and aromatic crops of pharmacological interest are becoming increasingly important given the socioeconomic issues involved. The scarcity of precipitation and its irregularity endanger the life and productivity of certain medicinal plants of pharmaceutical interest with high economic value. Indeed, the biosynthesis of essential oils is influenced by various environmental factors, namely, an increase in the intensity of water stress. This natural constraint could have a positive impact on the synthesis of essential oils as well as on their chemical composition. In this article, we propose the study of the impact of this abiotic constraint on the quality and quantity of essential oils at the juvenile and adult stages of lemongrass, known for its therapeutic effects, by gas chromatography (GC). This study revealed a reduction in the yield of essential oil from citronella depending on the increase in the intensity of water stress at the juvenile and adult stages, except at the adult stage for severe drying, with a significant increase in the αcitral of 27% for the moderate treatment for adult lemongrass, and the increase in the βcitral increased by 37% for the severe treatment for adult lemongrass compared to the controls.

Zinc and amino acids improve the growth, physiological, and biochemical attributes of corn under different irrigation levels

The global challenge of food security is threatened by drought stress. Exogenous application of zinc and amino acids could alleviate the negative impacts of water shortage on the growth, physiological, and biochemical attributes of plants. Based on this hypothesis, a field study was conducted to assess the effects of chelated zinc applied through irrigation systems and foliar amino acids on the growth, physiological and biochemical attributes of corn, under three irrigation levels at the recommended irrigation level (100%), and at 75% and 50% of the recommended rate. The treatments were arranged in randomized complete block design in triplicate. Treatment effects on yield varied with intensity and duration of water stress. An irrigation level of 100% means the normal supply of recommended water. In results, the implementation of irrigation levels on corn led to varying impacts on yield, depending on the intensity and duration of the water stress. Plants responded by reallocating nutrient accumulation within their tissues, which played a crucial role in mitigating the negative effects of water stress. The application of zinc and amino acids individually showed positive effects on corn improvement, as these promoted antioxidant defense systems and enhanced corn yield. However, the combined application of foliar amino acids and soil-applied zinc, particularly under the 75% irrigation level, had a tremendous effect on various examined parameters. There was an increase in catalase by 65.9%, superoxide dismutase by 17.1%, and peroxidase by 15.1%, resulting in improved corn yield by 114.6% and decreased hydrogen peroxide contents by 74.2% compared to control. In conclusion, adopting 75% of the applied water and treating corn plants with a combination of zinc and amino acids resulted in the highest yield, nutrient accumulation, antioxidant enzymes, chlorophyll contents, relative water contents, and carbohydrate levels.

Identifying physiological traits related with drought tolerance and water‐use efficiency in floral hemp (Cannabis sativa L.)

AbstractHemp (Cannabis sativa L.) is a reemerging crop that was once deeply rooted in many global civilizations. Due to climate change and the increasing risk of water‐deficit situations, it is important to use water judiciously. Hemp production has interested many producers; however, due to its past illegal status, there is a lack of research‐based knowledge about the physiological parameters that are affected by drought and which parameters could be responsible for drought tolerance. Therefore, our objective was to study and understand the effects of different drought intensities and timings on physiological parameters such as water‐use efficiency (WUE), photosynthesis, stomatal conductance, and fluorescence parameters and determine if cultivar variation exists as this could mean the possibility of selection for drought‐tolerant cultivars. In addition, we tested if carbon isotope discrimination can be used to predict whole plant WUE as this technique is quick and allows moderate throughput for selection. Hemp cultivars BaOx and Cherry Mom were grown in a greenhouse from July to October during 2021 and 2022 under different water stress intensities and timings. During the water stress period, WUE was determined by the gravimetric method and photosynthetic traits were measured using two portable gas analyzers (LI‐6800). Moderate water stress (30%–50% field capacity) was found to have the least effect on physiological parameters studied, while intense water stresses significantly reduced many physiological parameters such as photosynthesis, stomatal conductance (gs), and electron transport rate (ETR). It was found that the cultivar BaOx had a greater WUE than Cherry Mom. This was confirmed with carbon isotope discrimination measurements, which were demonstrated to estimate WUE accurately, and therefore, this technique could be used for germplasm screening. Drought first decreased gs, which caused the reduction in photosynthesis, although cultivar variation in these traits was not observed. Twenty days after drought, negative effects on fluoresce parameters such as ETR were observed with the cultivar Cherry Mon being more affected. This study states that hemp is negatively affected by different timings and intensities of drought; however, there is physiological variation in the response between cultivars. More research is needed to investigate the sources of genotypic variation in physiological parameters to find the sources of drought tolerance.

Diversified cropping systems effect on the water status of mandarin trees under deficit irrigation

The diversified cropping systems has several environmental benefits, but there is no certainty about their effect on the water status of trees, especially in areas with permanent low availability of irrigation water. Therefore, our objective was to evaluate the effect of the establishment of diversified cropping systems in a traditional monoculture (MC) of adult mandarin trees on its water status and yield under sustained deficit irrigation (SDI) and regulated deficit irrigation (RDI). Six treatments were tested during three consecutive seasons: (i) a mandarin monoculture under SDI (MC-SDI), with permanent bare alleys and irrigated at ∼70 % ETc during the entire season (actual amount of irrigation water available in the area); (ii) a diversified mandarin crop (D1-SDI), irrigated as MC-SDI, with a rotation of fava bean and barley/vetch in the alleys; and (iii) a second diversified mandarin crop (D2-SDI), irrigated as MC-SDI, with a seasonal rotation of fava bean, purslane and cowpea. Additionally, three RDI treatments were evaluated, denoted as (iv) MC-RDI, (v) D1-RDI and (vi) D2-RDI, irrigated as MC-SDI, except during the stage II of fruit growth, when it was reduced by 50 % with an irrigation threshold of a solar midday stem water potential of ∼ –1.5 MPa. The mandarin yield was not affected by the effect of diversified cropping systems, but the RDI reduced it on average by 30.1 % with respect to SDI. The alley cropping of fava bean and barley/vetch during winter and spring under sustained deficit irrigation conditions reduced the water stress intensity of mandarin trees by 26.9 % over the entire season, while cultivation of purslane or cowpea during summer increased it by 60–144 %. Both diversifications required a greater amount of water than the monoculture, in these terms an additional reduction in the irrigation of mandarin trees, as in the RDI treatment, allowed to solve this additional water requirement, but promoted an increase in the water stress intensity of the trees, which may affect their productivity in the mid and long-term.

Influence of No-Till System with or without Cover Crops on Stomata Sensitivity of Glyphosate-Tolerant Soybeans to Vapor Pressure Deficit

Soybeans are vulnerable to drought and temperature increases potentially induced by climate change. Hydraulic dysfunction and stomatal closure to avoid excessive transpiration are the main problems caused by drought. The vulnerability of soybeans to drought will depend on the intensity and duration of water stress. The purpose of this study was to determine if the use of cover crops (CCs) can influence the gas exchange potential of glyphosate-tolerant soybeans when the vapor pressure deficit (Vpd) increases. This two-year study was conducted in an open experimental field comprising direct seeding plots with or without CCs. Stomatal conductance (Gs) was measured five times on the same identified leaves following glyphosate-based herbicide application. These leaves were then collected in order to observe the stomata and foliar traits with a scanning electron microscope. The Vpd was calculated concomitantly to Gs measurements at the leaf surface. The results suggest that the use of CCs promotes phenotypic change in soybean leaves (more elaborate venation and a higher abaxial stomatal density), which in turn may enhance their tolerance to drier conditions. In 2019, Gs could be up to 29% higher in plots with CCs compared to those without CCs with similar Vpd values. This study shows that the benefits of using CCs can be observed via the morphological development strategies of the crop plants and their higher tolerance to drought.

Water stress changes the relationship between photosynthesis and stomatal conductance

Understanding the relationship between stomatal conductance (gs) and photosynthesis (An) under water stress conditions can improve the accuracy of land surface models for estimating the gas exchange of crop canopies with the atmosphere. However, little is known about the effect of water stress on this relationship in crops. A glasshouse experiment was, therefore, conducted to investigate changes in the linear relationship between gs and An owing to water stress in rice and the association with soil moisture content. Severe (SWS), mild (MWS), and no water stress (NWS) conditions were applied from flowering onwards and the gas exchange in fully developed flag leaves was assessed weekly. The Ball-Woodrow-Berry linear model was used to assess the relationship between gs and An under different treatments. SWS had a significant effect and reduced the slope of the linear relationship between gs and An by 30 % compared with NWS. Only in SWS were An and gs strongly correlated with soil water content. Our study revealed that changes in the linear relationship through a reduction in the slope imply a conservative water-use strategy for rice under intense water stress. We propose that crop models that use the linear relationship should consider the impact of water stress conditions when simulating yields and estimating CO2 and H2O fluxes from crop canopies.

Effect of deficit irrigation and mulching on the agronomic and physiological response of mandarin trees as strategies to cope with water scarcity in a semi-arid climate

In order to increase the crop water productivity (WPc) of the agricultural systems, and to support farmers in minimizing uncertainty of water availability, we conducted a three-years experiment in a commercial adult mandarin orchard to quantify the effect of sustained and severe deficit irrigation in combination with the use of geotextile mulch on the agronomic and physiological response of the crop. For this purpose, five treatments were tested: (i) a control (CTL) irrigated at 100% of the crop evapotranspiration (ETc) during the entire season; ii) sustained deficit irrigation (SDI), irrigated at ∼70% of CTL; (iii) regulated deficit irrigation (RDI), irrigated as SDI, except during the initial period of the second fruit growth stage, when trees were irrigated at 35% of the CTL, maintaining a moderate water stress level of around –1.5 MPa of stem water potential (Ψs), until fruits reached 70% of their final size. In addition, two geotextile mulch treatments were established, using the same irrigation criteria as the SDI and RDI treatments. The available irrigation water supplied about 66% of the crop evapotranspiration, but if it is managed under a SDI regime with the incorporation of mulching it is possible to increase the crop sustainability and reduce the pressure over the water resources. Since SDI did not reduce the yield with respect to the CTL treatment, it increased WPc by 35% and the incorporation of mulch significantly increased the water status of the soil and the crop, thus reducing the intensity of water stress by 18% on average, which was expressed in a higher leaf gas exchange rate and was also a factor that significantly increased crop production variables and WPc.

Drought stress-responsive abscisic acid and salicylic acid crosstalk with the phenylpropanoid pathway in soybean seeds.

Crosstalk between hormones and secondary metabolites regulates the interactions between plants and stress. However, little is known about the effects of hormone crosstalk on the concentration of flavonoids in seeds. In this study, we identified abscisic acid (ABA) as a negative regulator of flavonoid accumulation in soybean seeds under drought-stress conditions. Alterations in flavonoid accumulation at several intensities of water stress, followed by a recovery period, were measured during the soybean seed-filling stage. Low soil moisture (SM 10%) significantly decreased the total flavonoid content in seeds. The decline in flavonoid content was proportional to the severity of drought stress and was dependent on the activities of phenylalanine ammonia-lyase (PAL) and chalcone synthase (CHS), two key phenylpropanoid pathway enzymes. The expression of phenylalanine ammonia-lyase 1 (GmPAL1), chalcone isomerase 1A (GmCHI1A), and chalcone synthase 8 (GmCHS8) was associated with phenolic and flavonoid accumulation in soybean seeds of plants subjected to drought stress. Interestingly, the expression levels of GmCHS8 were highly correlated with flavonoid levels under drought stress and water recovery conditions. Cinnamic acid, which is a biosynthesis precursor shared by both phenylpropanoid metabolism and salicylic acid (SA) biosynthesis, decreased under drought stress conditions. Notably, exogenous ABA suppressed the expression of GmPAL1, which encodes the first rate-limiting enzyme in the phenylpropanoid biosynthesis pathway and affects downstream products such as SA and flavonoids. In conclusion, drought stress altered the phenylpropanoid-derived compounds, at least with regard to flavonoid and SA accumulation in seeds, which was regulated by antagonistic interactions with ABA.

Projecting China’s future water footprints and water scarcity under socioeconomic and climate change pathways using an integrated simulation approach

Future changes in climate and socioeconomic systems will exacerbate water scarcity. Previous studies on China’s water footprint and scarcity often consider only climate change or socioeconomic factors in isolation. Here, we address these issues by coupling an integrated assessment model, the Global Change Analysis Model, with a global hydrological model to project China’s future water footprints and water scarcity, considering both climate change and socioeconomic factors. We simulated China’s water footprints under 52 scenarios, which include four global climate models (GCMs) and 13 combinations of Shared Socioeconomic Pathway (SSP)–Representative Concentration Pathway (RCPs) scenarios. We then projected the intensity of water stress (WSI), defined as a ratio of water footprint to renewable water volume, based on the simulations of the SSP2-RCP6.0 scenario. Our results align well with statistical data on water footprint variations between 2005 and 2020. China’s water footprints are likely to peak around 2030 and then decrease. We find through a scenario matrix analysis that emission-mitigation measures will significantly impact the water footprint, particularly in the electricity sector, which will become the largest water use sector in the future. This means that the low carbon energy option on China’s path to carbon neutrality may aggravate water scarcity. Water stress in China is projected to be greatest in 2025–2035, and all northern basins will experience water scarcity. Projections based on all GCMs consistently show a decline in WSI in China after 2050.

Precise control of water stress in the field reveals different response thresholds for forage yield and digestibility of maize hybrids.

With dwindling global freshwater supplies and increasing water stress, agriculture is coming under increasing pressure to reduce water use. Plant breeding requires high analytical capabilities. For this reason, near-infrared spectroscopy (NIRS) has been used to develop prediction equations for whole-plant samples, particularly for predicting dry matter digestibility, which has a major impact on the energy value of forage maize hybrids and is required for inclusion in the official French catalogue. Although the historical NIRS equations have long been used routinely in seed company breeding programmes, they do not predict all variables with the same accuracy. In addition, little is known about how accurate their predictions are under different water stress-environments. Here, we examined the effects of water stress and stress intensity on agronomic, biochemical, and NIRS predictive values in a set of 13 modern S0-S1 forage maize hybrids under four different environmental conditions resulting from the combination of a northern and southern location and two monitored water stress levels in the south. First, we compared the reliability of NIRS predictions for basic forage quality traits obtained using the historical NIRS predictive equations and the new equations we recently developed. We found that NIRS predicted values were affected to varying degrees by environmental conditions. We also showed that forage yield gradually decreased as a function of water stress, whereas both dry matter and cell wall digestibilities increased regardless of the intensity of water stress, with variability among the tested varieties decreasing under the most stressed conditions. By combining forage yield and dry matter digestibility, we were able to quantify digestible yield and identify varieties with different strategies for coping with water stress, raising the exciting possibility that important potential selection targets still exist. Finally, from a farmer's perspective, we were able to show that late silage harvest has no effect on dry matter digestibility and that moderate water stress does not necessarily result in a loss of digestible yield.

A novel Multiple Attribute Decision-making approach for assessing the effectiveness of advertising to a target audience on drinking water consumers’ behavior considering age and education level

One effective way to cope with water scarcity is to enhance water use efficiency by reforming water customer habits. Owing to the semi-arid climate of Iran, the drinking water consumption rate of urban households is greater than the routine average daily per capita consumption of water. With limited water supply and poor consumption habits, the country needs to reform its water management practices. On the other hand, the influence of advertising types, especially mass media, to improve water consumers' behavior in society is undeniable. Herein, the current study examines the effectiveness of using four advertisement strategies (animation, celebrities, social networks, and conceptual advertising) to modify the public's drinking water consumption. The statistical population in this study included urban households in four critical cities subjected to intense water stress, including Tehran, Isfahan, Shiraz, and Kermanshah. In order to evaluate the impact of the advertisement strategy on residents, the most important questions were extracted and used to prepare a questionnaire with 24 indicators. Afterward, a novel Multiple Attribute Decision-making (MADM) based methods was designed to consider the importance weights of age and education level on respondents to estimate the questionnaire accuracy. The dominant strategy by applying age and education level influence for each city was using animation in Tehran, followed by a conceptual advertisement in Isfahan and Shiraz, and the social network in Kermanshah. Further, as a statistical examination using SPSS software, the Spearman test was employed to analyze the questionnaire and its results without the impact of age and education level. The results obtained in the developed technique compared with the analyzed results of statistical test showed that the application of age and education level will significantly impact advertising comprehension and validation of results.

Germination of grass species from dry and wet grasslands in response to osmotic stress under present and future temperatures.

Seed germination is controlled by the soil microclimate, which is expected to change with the temperature increase and rainfall irregularity predicted for the future. Because changes in soil characteristics directly affect species recruitment, vegetation dynamics and resilience, we investigated how caryopses of native grasses from dry and wet grasslands respond to water stress under current and future temperature regimes. Caryopses were collected from 10 grass species in dry and wet grasslands, subjected or not to a fire event, and tested for germination at increasing osmotic potential (0 to -1.0 MPa) at current (17°/27°C night/day) and future (23°/33°C) simulated temperatures. The viability and germination percentages of caryopses from both dry and wet grassland species were progressively reduced as osmotic stress increased, irrespective of temperature regime. The viability of caryopses from wet grassland species was reduced under the future temperature regime, irrespective of osmotic potential. The slow germination of caryopses of dry grassland species at the present temperature regime was absent when they were incubated in the future temperature regime. More intense water stress reduced the survival of caryopses for both dry and wet grassland grass species. The predicted future temperature regime reduced the viability of wet grassland species and altered the germination strategy of dry grassland species. These results indicate that increasing water stress and temperature predicted for the future may compromise the recruitment potential of dry and wet grassland species and directly impact the dynamics and resilience of these ecosystems.

Berry flavonoids are differently modulated by timing and intensities of water deficit in Vitis vinifera L. cv. Sangiovese.

In this work, we tested the effect of different regulated deficit irrigation (RDI) regimes on berry flavonoid content and its relative biosynthetic pathways. Vines were subjected to six irrigation regimes over two consecutive years: a) full irrigation during the entire irrigation period (FI); b) moderate (RDI-1M) or c) severe (RDI-1S) water deficit between berry pea-size and veraison; d) severe water deficit during the lag-phase (RDI-LS); and e) moderate (RDI-2M) or f) severe (RDI-2S) water deficit from veraison through harvest. Berries from both RDI-1 treatments showed the highest accumulation of anthocyanins, upregulating the expression of many genes of the flavonoid pathway since the beginning of veraison until harvest, far after the water deficit was released. Although to a lesser degree than RDI-1, both post-veraison water deficit treatments increased anthocyanin concentration, particularly those of the tri-substituted forms, overexpressing the F3'5'H hydroxylases. The moderate deficit irrigation treatments enhanced anthocyanin accumulation with respect to the severe ones regardless of the period when they were applied (pre- or post-veraison). The water deficit imposed during the lag-phase downregulated many genes throughout the flavonoid pathway, showing a slight reduction in anthocyanin accumulation. The measurements of cluster temperature and light exposure highlighted that under deficit irrigation conditions, the effects induced by water stress prevailed over that of light and temperature in regulating anthocyanin biosynthesis. Flavonol concentration was higher in RDI-1S berries due to the upregulation of the flavonol synthases and the flavonol-3-O-glycosyltransferases. In this case, the higher cluster light exposure induced by water deficit in RDI-1S berries had a major role in flavonol accumulation. We conclude that the timing and intensity of water stress strongly regulate the berry flavonoid accumulation and that proper management of deficit irrigation can modulate the phenylpropanoid and flavonoid pathways.

Multifaceted characteristics of aridity changes and causal mechanisms in Chinese drylands

The water cycle is accelerating in the context of global warming. However, how the multifaceted characteristics of aridity, particularly atmospheric, hydrological, and ecological drying, change and interact with each other are largely unknown. A gap we bridged was discovering the causal relationships underlying the atmosphere-hydrosphere-biosphere nexus from the nonlinear dynamic system perspective based on convergent cross mapping (CCM). Dryland area in China has expanded since 1982, while the vegetation greenness indicated by leaf area index has been increasing during the same period. The results showed that the causality among atmospheric, hydrological, and ecological drying in different subtypes of drylands was different. In arid and semi-arid regions: vegetation changes were mainly driven by soil moisture (SM) and vapor pressure deficit (VPD), and VPD regulated SM. In hyper-arid and dry sub-humid areas: VPD dominated vegetation changes. VPD increases did not contribute to SM loss under the intense water stress in hyper-arid regions, as the soil water supply cannot meet the atmospheric water demand. In dry sub-humid areas, human disturbances have attenuated the dependence of vegetation changes on SM variability. This research pioneers complex nonlinear dynamic analyses on the multifaceted characteristics of ecosystems, which can deepen our understanding of atmosphere-vegetation-soil interactions in drylands and guide the sustainable management of dryland ecosystems in China and elsewhere.

Biochemical responses of hairgrass (Deschampsia caespitosa) to hydrological change.

Plant growth and development are closely related to water availability. Water deficit and water excess are detrimental to plants, causing a series of damage to plant morphology, physiological and biochemical processes. In the long evolutionary process, plants have evolved an array of complex mechanisms to combat against stressful conditions. In the present study, the duration-dependent changes in ascorbate (AsA) and glutathione (GSH) contents and activities of enzymes involved in the AsA-GSH cycle in hairgrass (Deschampsia caespitosa) in response to water stress was investigated in a pot trial using a complete random block design. The treatments were as follows: (1) heavily waterlogging, (2) moderate waterlogging, (3) light waterlogging, (4) light drought, (5) moderate drought, (6) heavily drought, and (7) a control (CK) with plant be maintained at optimum water availability. The hairgrass plants were subjected to waterlogging or drought for 7, 14, 21 and 28 days and data were measured following treatment. Results revealed that hairgrass subjected to water stress can stimulate enzymatic activities of ascorbate peroxidase (APX), glutathione peroxidase (GPX), glutathione reductase (GR), dehydroascorbate reductase (DHAR), monodehydroascorbate reductase (MDHAR) and L-galactono-1, 4-lactone dehydrogenase (GalLDH), switched on the ascorbate-glutathione (AsA-GSH) cycle and the L-galactose synthesis, up-regulated the contents of AsA and GSH, and maintained higher ratios of ascorbate to dehydroascorbate (AsA/DHA) and reduced glutathione to oxidized glutathione (GSH/GSSG) to alleviate potential oxidative damage. However, the light waterlogging did not induce hairgrass under stress to switch on the AsA-GSH pathway. In general, the critic substances and enzyme activities in AsA-GSH metabolic pathway increased as the increase of water stress intensity. As the increase of exposure duration, the critic antioxidant substances content and enzyme activities increased first and then maintained a relatively stable higher level. Our findings provide comprehensive information on biochemical responses of hairgrass to hydrological change, which would be a major step for accelerating ecological restoration of degradation alpine marshes in the Qinghai-Tibetan Plateau.

Increasing evapotranspiration decouples the positive correlation between vegetation cover and warming in the Tibetan plateau.

Plant growth generally responds positively to an increase in ambient temperature. Hence, most Earth system models project a continuous increase in vegetation cover in the future due to elevated temperatures. Over the last 40 years, a considerable warming trend has affected the alpine ecosystem across the Tibetan Plateau. However, we found vegetation growth in the moderately vegetated areas of the plateau were negatively related to the warming temperatures, thus resulting in a significant degradation of the vegetative cover (LAI: slope = −0.0026 per year, p < 0.05). The underlying mechanisms that caused the decoupling of the relationship between vegetation growth and warming in the region were elaborated with the analysis of water and energy variables in the ecosystem. Results indicate that high temperatures stimulated evapotranspiration and increased the water consumption of the ecosystem (with an influence coefficient of 0.34) in these degrading areas, significantly reducing water availability (with an influence coefficient of −0.68) and limiting vegetation growth. Moreover, the negative warming effect on vegetation was only observed in the moderately vegetated areas, as evapotranspiration there predominantly occupied a larger proportion of available water (compared to the wet and highly vegetated areas) and resulted in a greater increase in total water consumption in a warmer condition (compared to dry areas with lower levels of vegetation cover). These findings highlight the risk of vegetation degradation in semi-arid areas, with the degree of vulnerability depending on the level of vegetation cover. Furthermore, results demonstrate the central role of evapotranspiration in regulating water stress intensity on vegetation under elevated temperatures.