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Drought is considered to be one of the most devastating natural hazards, and it is predicted to become increasingly frequent and severe in the future. Understanding the plant gas exchange and water status response to drought is very important with regard to future climate change. We conducted a meta-analysis based on studies of plants worldwide and aimed to determine the changes in gas exchange and water status under different drought intensities (mild, moderate and severe), different photosynthetic pathways (C3 and C4) and growth forms (herbs, shrubs, trees and lianas). Our results were as follows: 1) drought negatively impacted gas exchange and water status, and stomatal conductance (gs) decreased more than other physiological traits and declined to the greatest extent in shrubs and C3 plants. Furthermore, C4 plants had an advantage compared to C3 plants under the same drought conditions. 2) The decrease in gs mainly reduced the transpiration rate (Tr), and gs could explain 55% of the decrease in the photosynthesis (A) and 74% of the decline in Tr. 3). Finally, gas exchange showed a close relationship with the leaf water status. Our study provides comprehensive information about the changes in plant gas exchange and water status under drought.

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Stomata control the cycling of water and carbon between plants and the atmosphere; however, no consistent conclusions have been drawn regarding the response of stomatal frequency to climate change. Here, we conducted a meta-analysis of 1854 globally obtained data series to determine the response of stomatal frequency to climate change, which including four plant life forms (over 900 species), at altitudes ranging from 0 to 4500 m and over a time span of more than one hundred thousand years. Stomatal frequency decreased with increasing CO concentration and increased with elevated temperature and drought stress; it was also dependent on the species and experimental conditions. The response of stomatal frequency to climate change showed a trade-off between stomatal control strategies and environmental factors, such as the CO concentration, temperature, and soil water availability. Moreover, threshold effects of elevated CO and temperature on stomatal frequency were detected, indicating that the response of stomatal density to increasing CO concentration will decrease over the next few years. The results also suggested that the stomatal index may be more reliable than stomatal density for determination of the historic CO concentration. Our findings indicate that the contrasting responses of stomata to climate change bring a considerable challenge in predicting future water and carbon cycles.

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Understanding the changes in microbial community composition that occur during succession can help elucidate the mechanisms that drive successional dynamics.However, the mechanisms underlying community assemblages and promoting temporal succession are often overlooked in microbial ecology, and comparisons of the relative roles of bacteria and fungi during long-term secondary succession are rare.Using both 16S and ITS rRNA gene sequencing, we studied shifts in bacterial and fungal communities in a well-established secondary successional chronosequence that spanned approximately 160 years in an ecosystem. Our results showed that the abundance of both bacteria and fungi increased with succession in the early stages but then reached a relatively stable state in later successional stages. Diversity showed a fairly linear increase with succession, and there were inconsistent changes between the bacterial and fungal communities. During succession, soil bulk density, soluble carbon, total nitrogen and plant richness had large effects on the microbial community. The abundance of most phyla showed parabolic trends with succession; however, Verrucomicrobia and Basidiomycota showed linear increases with succession, and Cercozoa and Chytridiomycota showed linear decreases with succession.These microbial taxa may be considered collaborative development microbial biomarkers of secondary succession. The predicted microbial functions related to C and N cycle genes showed corresponding changes in succession, which need further study. Our findings suggest that the relationships between soil physicochemical properties and microbial communities mutually influence one another, leading to their ongoing relationship in the course of secondary succession.

Aim The continuous increase in anthropogenic nitrogen (N) may have a substantial impact on soil carbon (C) fluxes; thus, understanding the dynamics of soil C fluxes under N enrichment is important. Our main goal was to resolve the conflicting results presented to date and to expand our knowledge about the response of soil respiration (Rs) to N enrichment, which may be affected by the physico‐chemical properties of soil and environmental factors. Methods We assembled a large dataset for meta‐analysis, including 563 datasets on annual and seasonal Rs with N enrichment from 154 published papers at 163 sites, covering seven types of biomes world‐wide. Results (1) N enrichment was not significantly related to global Rs but we found a negative relationship in forests and a positive one in other biomes. (2) Rs showed a negative correlation with the N levels in forests and croplands and a positive correlation with the N levels in deserts; heterotrophic respiration exhibited negative correlations with N levels globally, and its response was correlated with the incubation environment. (3) The response of Rs to N enrichment was also correlated with mean annual temperature and soil properties, with 15 °C being the threshold for switching between increasing and decreasing Rs. (4) The estimated total C flux for global terrestrial lands was 97.01 Pg C year−1, and 1 kg of N enrichment at ha−1 year−1 induced an average efflux of 1.33 kg C ha−1 year−1. Main conclusions The response of Rs to future N enrichment should be predicted separately for each biome. The association between changes in Rs and temperature and soil properties under N enrichment makes soil C flux a more complex challenge in the context of future increases in temperature and N deposition.

A dry soil layer (DSL) is a common soil desiccation phenomenon that generally forms at a particular depth in the soil profile because of climatic factors and poor land management, and this phenomenon can influence the water cycle and has been observed on the Loess Plateau of China and other similar regions around the world. Therefore, an investigation of the DSL formation depth (DSLFD), thickness (DSLT) and mean water content (MWDSL) on the Loess Plateau can provide valuable information. This paper synthesized 69 recent publications (1,149 observations of DSLs from 73 sites) that focused on DSLs in this region, and the results indicated that DSLs are significantly affected by climatic and vegetation factors. The mean annual precipitation had a significant positive relationship with DSLFD (p = 0.0003) and MWDSL (p<0.0001) and a negative relationship with DSLT (p = 0.0071). Crops had the lowest DSLT and highest MWDSL values compared with other vegetation types. A significant correlation was observed between the occurrence of DSLs and the years since planting for grasses, shrubs, trees and orchards, and the severity of DSLs increased with increasing planting years and wheat yield. Our results suggest that optimizing land-use management can mitigate DSL formation and development on the Loess Plateau. Understanding the dominant factors affecting DSLs will provide information for use in guidelines for the sustainable development of economies and restoration of natural environments experiencing water deficiencies.