摘要
Biological nitrogen fixation(BNF)facilitated by diazotrophs,which convert N2 to ammonia,plays a key role in nutrient supply of terrestrial ecosystems.However,the differential contributions of rare versus abundant subcommunities to nitrogen fixation dynamics remain poorly characterized,especially in alpine ecosystem.This study examined BNF changes and shifts in abundant and rare soil diazotrophic taxa along an aridity gradient(arid,semi-arid,semi-humid,and humid)across the Tibetan Plateau.We found a significantly higher N fixation rate,vegetation coverage and biomass,nifH gene abundance,and diazotroph diversity in semi-arid and arid habitats than in semi-humid and humid habitats.Rare subcommunity composition explained more of the variation in N fixation rates than did the abundant subcommunities,suggesting greater roles of diazotrophic rare taxa in supplying nitrogen availability in alpine grasslands.The main influence factors of nitrogen fixation are aridity,plant coverage and soil C:N ratio.Structural equation modeling indicated that soil factors(e.g.,bulk density,C:N ratio)and climatic factors(aridity and temperature)affected the composition of rare subcommunity through altering plant coverage and biomass,consequently affecting soil nitrogen fixation.This study establishes rare diazotrophs as critical regulators of soil nitrogen fixation and deciphers their mediation in climate-altered N-cycling processes in alpine ecosystems.
基金
supported by the National Natural Sciences Foundation of China(Grant No.42177449)
the National Natural Sciences Foundation of China(Grant No.42130717)
Shaanxi Provincial Science Fund for Distinguished Young Scholars(Grant No.2024JC-JCQN-35).
