Drought Effects On Ecological Stoichiometry In Terrestrial Ecosystems And Soil Microbial Structures

Drought events are anticipated to become more severe and frequent by the end of this century,but our understandings of the responses of ecological stoichiometry and soil microbial structures to drought remain incomplete.Here,we firstly presented a meta-analysis derived from 379 paired observations of 79 studies to explore responses of C:N stoichiometry in plant-soil-microorganism systems to drought,and tested the effects of altered precipitation on C:N:P of plants-soilsmicroorganisms by collecting 848 observations from 160 studies.At the same time,according to the predictions of our meta-analysis,we selected a poplar plantation of subtropical region as the sample plot,employed 30% and 50% throughfall reduction manipulation experiments to simulate different intensities of droughts,and calculated the microbial C use efficiency(CUE)and N use efficiency(NUE)based on the C:N stoichiometry of soil,microbial biomass,and extracellular enzyme activity across different soil depths(0-15,15-30,and 30-45cm).Finally,we explored the responses of soil microbial communities to droughts in the poplar plantation.We found that:(1)C and N concentrations and C:N ratios of plant organs,soil,and extracellular enzyme activities all decreased under drought,while the microbial biomass C:N ratio increased.Moreover,the magnitudes of these responses generally increased with drought intensity and drought duration.These drought effects were consistent across ecosystem types(forests and grasslands)and climate conditions(MAT and MAP).(2)C:N and C:P ratios of different ecosystem compartments were more sensitive to moderately increased precipitation than moderately reduced precipitation,whereas they exhibited a higher response to extremely decreased precipitation than extremely increased precipitation,supporting the precipitations of double asymmetry model.Moreover,such responses were more pronounced under higher drought intensities and experimental duration.The effects of precipitation changes on C:N:P stoichiometry in above-and belowground were consistent with ecosystem types(forests and grasslands)and climate conditions.(3)Under drought conditions,microbial CUE and NUE increased.Moreover,CUE and NUE were primarily driven by changes in soil moisture,p H,microbial biomass C:N,enzyme C:N activity,and fungi:bacteria ratio under drought conditions.(4)Drought increased the fungi to bacteria ratios,Gram+:Gram-bacteria,and relative abundances of acidobacteria phylum and GP1 class,but reduced the relative abundances of proteobacteria phylum and alphaproteobacterial class.Soil moisture and labile organic C and N contents all decreased,whereas soil p H and microbial biomass C:N increased under different levels of droughts.These drought effects are more pronounced with drought intensity and kept consistent with soil depths.Soil moisture,p H,labile organic C and labile organic N accounted for the majority of the variabilities in the microbial communities.Collectively,our results suggest that,at global scale,drought reduced C:N ratios and precipitation change had a asymmetric effect on C:N:P stoichiometry in plants-soil-microorganism system;at local scale,different levels of droughts reduced C:N ratios in soil and extracellular enzyme,but increased microbial biomass C:N,thus increasing microbial CUE and NUE,and further making the microbial community show a water-tolerant shift.In conclusion,soil stoichiometry determines soil microbial community structure,and changes in soil microbial community structure affect soil stoichiometry.