Effects Of Multiple Climate Changes On Soil Microbial Communities In A Typical Temperate Grassland In The United States

Future Cliamte changes can simultaneously affect soil nutrient cycling,such as soil carbon and nitrogen,triggering complex consequences on ecosystems structure and multiple functions.Yet few studies have focused on how multiple climate changes would affect taxonomic and functional diversity of soil microbial communities at the decadal scale,along with mechanism underlying microbe-mediated geochemical cycling.To address these questions,we present a long-term?14 years?,manipulative field study examining the responses of microbial communities to elevated CO₂,nitrogen deposition,precipitation,warming and fire in a grassland ecosystem at the Jasper Ridge Global Change Experiment?JRGCE?site in California,USA.Using high-throughput sequencing and Geo Chip 4.6,we analyzed the impacts of aforementioned five drivers on microbial taxonomic communities and functional genes.???After 14 years'experiment,soil microbial taxonomic communities were significantly changed by N deposition,precipitation,elevated CO₂ and fire,but not by warming or interactive effects of those drivers.The overall microbial taxonomic response to combined global change drivers was mostly determined by the single dominant driver with the largest effect,i.e.,N deposition.In contrast,microbial functional genes were significantly changed by both single main effects and multiple interactive effects,which differed substantially from the taxonomic level.?ii?Eelevated CO₂?275 ppm higher than ambient level?decreased the relative abundances for taxa with higher ribosomal RNA operon?rrn?copy number,but increased the relative abundances for taxa with lower rrn copy number.As a consequence,the abundance-weighted average rrn copy number of significantly changed OTUs declined from 2.27 at ambient CO₂ to 2.01 at elevated CO₂,indicating a shift in the microbial community towards slow-growing taxa.The nitrogen?N?fixation gene nif H and the ammonium-oxidizing gene amo A significantly decreased under elevated CO₂ by 12.6%and 6.1%,respectively.Concomitantly,nitrifying enzyme activity and denitrifying enzyme activity decreased under elevated CO₂ by 48.3%and25.6%,respectively.Further,a large number of microbial genes related to carbon?C?degradation were also affected by elevated CO₂,whereas those related to C fixation remained largely unchanged.?iii?9 months post-fire,soil microbial communities were altered considerably,with community assembly process analysis showing that environmental selection pressure was higher in burned sites.However,a small subset of highly connected taxa?46 genus?was able to withstand the disturbance.In addition,fire decreased the relative abundances of most functional genes associated with C degradation and N cycling,implicating a slow-down of microbial processes linked to soil C and N dynamics.In contrast,fire stimulated above-and below-ground plant growth,likely enhancing plant-microbe competition for soil inorganic N.To synthesize those findings,we performed structural equation modeling,which showed that plants but not microbial communities were responsible for significantly higher soil respiration rates in burned sites.This study comprehensively investigated the response of microbial communities,at both taxonomic and functional level,to multiple global climate changes in a temperate semi-arid grassland,established a mechanistic understanding of microbe-mediated soil carbon and nitrogen cycling and unveiled the importance and necessity to involve microbes in the model evaluation of multiple ecosystem functions.