Responses of soil nitrogen cycling to changes in aboveground plant litter inputs: A meta-analysis

Alterations in aboveground plant litter inputs due to global climate change can strongly change soil nitrogen (N) cycling, which will influence soil processes and functions. However, a comprehensive evaluation for the effects of altered litter inputs on soil N cycling is not available. We evaluated these effects using a global meta-analysis based on 1829 observations from 119 studies across different ecosystems including forests, shrublands and grasslands. Results showed that litter addition significantly increased soil N pools including total N (TN), dissolved organic N (DON), ammonium (NH4+), nitrate (NO3–) and microbial biomass N (MBN) by 4–––24 %, while litter removal decreased them by 10–––42 %. High initial soil TN pool weakened the positive effect of litter addition on soil TN. Moreover, litter addition significantly increased soil net N mineralization (+19 %), DON leaching (+56 %) and nitrous oxide (N2O) emission (+27 %), whereas litter removal reduced net N mineralization (-10 %) and increased NO3– leaching (+51 %). The response of soil net N mineralization to litter addition was stronger in broadleaved forests than that in coniferous forests, and negatively correlated with mean annual temperature and precipitation. The responses of soil TN, NH4+, NO3–, MBN and N2O emission to litter manipulation increased with increasing litter input rates. Therefore, altered litter inputs had strong effects on soil N cycling and these effects were regulated by soil N status, ecosystems, climates and experimental conditions. Our results provide insights into understanding how altered plant litter input affects soil N cycling and help better assess the soil processes under global climate change.