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Objective To explore the effects of new composite hydrogel on the physiological characteristics of tobacco seedlings under drought stress, and to provide theoretical basis for alleviating the toxicity of drought stress to tobacco. Method A total of 10 treatments including CK control and three different hydrogels added at 0.1%, 0.5% and 0.9% of soil dry mass: commercial hydrogel HS, new composite hydrogel HM (polyvinyl alcohol-acrylic acid-molecular sieve hydrogel) and HB (polyvinyl alcohol-acrylic acid-biochar hydrogel) were designed by pot experiment to study the effects of new composite hydrogels on tobacco under drought stress The effects of the new composite hydrogels on biomass accumulation, root development, photosynthetic system and oxidative stress of tobacco under drought stress were investigated. Result Under the same dosage conditions, HM and HB treatments were effective in increasing the fresh mass, dry mass and total water content of tobacco under drought stress compared to HS treatment. Compared with CK, HM and HB treatments could increase the fresh mass by a maximum of 153.91% and 126.34%, respectively. Under the same dosage conditions, HM and HB treatments significantly increased the total root length, total root surface area, average root diameter, root tip number and root volume, and improved the root vigor of tobacco compared with HS treatments; photosynthetic parameters and SPAD values of tobacco increased significantly and improved leaf stomatal status; SOD (superoxide dismutase), POD (peroxidase) and CAT (catalase) activities and soluble protein amounts of tobacco increased and MDA (malondialdehyde) amounts decreased significantly, which enhanced the resistance of tobacco. Conclusion Adding 0.9% HM and HB hydrogels to soil dry weight can effectively reduce the impact of drought stress on tobacco and improve tobacco drought resistance. [ABSTRACT FROM AUTHOR]

Extreme droughts, of increased frequency due to climate change, are threatening the sustainability of dryland plantations worldwide by exacerbating water scarcity. Here we aim to disentangle the impacts of combinations of terracing and mulching on water use strategy and their response to extreme droughts in a rainfed jujube (Ziziphus jujuba Mill.) plantation on the semiarid Loess Plateau of China, using 3‐year in situ field observations. Pruned jujube branches and maize straw were mulched on half‐moon terraces to form two combined treatments, referred to as JBT and MST, respectively. The efficacy of these two combinations on the water use strategy of jujube trees was compared with terracing alone (SHT) and control (no terrace). We found that under extreme drought there was clearly reduced soil water storage (SWS) for different treatments. However, the combined treatments showed significantly (p <.05) higher SWS than the SHT and control. Furthermore, the combined treatments enhanced soil water use in deep layers during both normal and drought years, thus helping jujube trees to resist droughts. Moreover, under extreme drought there was greatly reduced transpiration whereas for moderate drought increased transpiration at both seasonal and annual scales. Nonetheless, the combined treatments were associated with enhanced transpiration compared to the SHT and control during drought periods. Finally, jujube trees exhibited isohydric behavior which also helped them to cope with prolonged droughts. Overall, the findings here may provide insights into land management of dryland plantations worldwide under climate change. [ABSTRACT FROM AUTHOR]

Background and aims: Changes in climate and land-use are altering soil respiration patterns and thus affecting C sequestration rates globally. This study aims to understand the effect of revegetation induced land-use change on the response of soil respiration to precipitation pulses during an extreme-drying-and-rewetting period.Methods: Soil respiration (SR) in cropland, grassland, shrubland, and orchard were intensively monitored along with environmental variables during an extreme drought period with precipitation pulse on China’s Loess Plateau.Results: SR was strongly correlated to soil water content for all land-uses. However, the relationship was highly dependent on land-use types: SR was only strongly suppressed in cropland and orchard when moisture content exceeded 10.8 and 13.7%, respectively, whereas no clear suppression was observed under other land-uses. As a result, the C loss in grassland and shrubland was 49.1-78.9% higher than in cropland following significant precipitation events. In addition, SR was negatively and weakly correlated with soil temperature, indicating the change in the dominant control on SR due to extreme drought.Conclusions: Land-use change alters the response of soil respiration to soil moisture during extreme-drying-and-rewetting periods in this revegetated ecosystem. Its effect on respiration pulses will amplify as extreme climate events increase in the future, which may potentially alter the existing C balance. [ABSTRACT FROM AUTHOR]

Highlights • Water sources and stem mortality of exotic and native species to drought was assessed. • Stable isotopes, in situ soil moisture observations and fine roots were measured. • Clear seasonality in water use was observed for both exotic and native species. • Extreme drought reduced the plasticity of mature A. gmelinii in water source use. • Extreme drought caused clear stem mortality to native species but not to exotic species. Abstract Droughts of increasing frequency and severity are expected to have a great impact on vegetation restoration in semiarid ecosystems by reducing water availability to plants. Understanding the functional plasticity of root systems in plant water uptake and the response to extreme droughts is of critical importance for predicting revegetation dynamics under future extreme climates. Sampling was undertaken over a two-year period to investigate the seasonality of water use strategy and growing status of one mature exotic shrub species Caragana korshinskii and one native subshrub species Artemisia gmelinii in both its young and mature growing stages. We investigated stable isotopes, made in situ soil water observations, and recorded functional root distribution. The spring and summer drought in 2015, especially the record low precipitation in July, allowed us to examine the impact of extreme drought on plant water sources and stem mortality. The results revealed that both exotic and native species exhibited significant seasonal patterns in water source use, following shifts in soil water content; they were overall positively correlated with soil water availability. The exotic species C. korshinskii used more soil water from subsurface layers compared to the native species A. gmelinii. The prolonged drought reduced the plasticity of water use strategy and resulted in clear stem mortality of both the young and mature native species but not the exotic species. The results indicate that the native shrub A. gmelinii is less resistant to extreme natural drought than exotic shrub C. korshinskii and hence could be more severely affected by future extreme climatic episodes. This implies that vegetation restoration may be greatly disturbed by extreme droughts in semiarid ecosystems. [ABSTRACT FROM AUTHOR]