Global Positive Effects of Litter Inputs on Soil Nitrogen Pools and Fluxes.

Soil nitrogen (N) pools and fluxes are strongly influenced by litter inputs in natural ecosystems. However, general responses of soil N pools and fluxes to litter inputs from both above- and belowground are still lacking at a global scale. Here, we compiled 2791 paired observations from 145 published articles to assess global effects of altered leaf litter and roots inputs on soil N pools and fluxes. We found that litter addition increased soil N pools and fluxes globally, with a 30.6% increase in soil microbial biomass N (MBN) pool, a 28.9% increase in dissolved organic N (DON) pool, a 15.8% increase in ammonia (NH4+) pool and a 12.6% increase in nitrous oxide (N2O) fluxes. In contrast, litter removal decreased soil MBN, DON and nitrate (NO3−) pools and N2O fluxes by 9.6%, 9.2%, 9.1% and 16.9%, respectively. Moreover, the increases in soil N pools in response to leaf litter addition and root removal were greater than their decreases in response to leaf litter removal. Soil N pools in forests, especially mixed forests, responded more positively to litter addition than those in grasslands. However, the negative effects of litter removal on soil N pools were contingent upon environmental conditions. In particular, the negative effects of litter removal on soil DON and NO3− pools were stronger in region with warmer and wetter climates and in soils with higher pH. Our synthesis highlights the globally positive effects of litter inputs on soil N pools and fluxes and the importance of litter type, climate factors and soil pH in understanding soil N pools and fluxes responses. These changes have important implications for soil N supply under global change-induced increases in litterfall. [ABSTRACT FROM AUTHOR]