第七届青年地学论坛

 Soil nitrogen (N) cycling mediated by microbial turnover is crucial for N availability and plant growth in natural ecosystems, yet how and to what extent the plant litter input alters the soil N turnover remains not fully understood. Here we compiled 2557 paired observations from 142 published articles to assess the global effect of leaf and root litter input on soil N pools across forests and grasslands. We found that leaf litter addition significantly increased soil C/N ratio, total nitrogen (TN), microbial biomass nitrogen (MBN) and dissolved organic nitrogen (DON) concentrations by 5.98%, 7.89%, 31.43% and 35.01%, respectively, but decreased nitrate (NO₃^-) concentration by 37.40%. However, leaf litter removal significantly reduced TN, MBN and NO₃^- concentrations by 10.17%, 28.50% and 14.96%, respectively, but increased ammonium (NH₄⁺) by 8.05%. On the contrary, root litter removal significantly increased TN, DON and NO₃^- concentrations by 24.23%, 21.99% and 39.33%, respectively, but reduced MBN by 24.80%. Thus, the effect of leaf litter removal on soil N pool was greater than that of root litter removal. Consequently, litter input increased soil C/N ratio and further changed soil stoichiometry, stimulating microorganisms acquiring available N from the ambient environment by preferentially assimilating available N (such as DON) directly from plant litter input with less investment to mining soil organic N. By contrast, removing leaf litter reduced MBN and DON concentrations and promoted microbial mining of soil organic N to produce more assimilable N. These results suggest differential influence of leaf input alternation on microbial strategy of N acquisition from the ambient environment in forests and grasslands.
 

soil nitrogen turnover, microbial assimilation, plant litter, leaf addition, leaf removal, root removal