Effects of canopy nitrogen addition on soil fauna and litter decomposition rate in a temperate forest and a subtropical forest

Abstract

Traditionally, experiments testing the impacts of nitrogen (N) deposition on ecosystem processes have been conducted by adding N directly to forest floors, yet, in reality, atmospheric N passes through the canopy layer before it reaches the forest floor. Furthermore, we know little about how N-deposition mediated changes in soil fauna communities affect litter decomposition. Here, we use a novel experiment to contrast canopy addition of N (CAN) to understory addition of N (UAN) in a subtropical forest and a temperate forest to investigate the impact of N-deposition approaches and N-concentrations on soil fauna and leaf litter decomposition rate. We found that CAN increased the soil fauna diversity and accelerated litter decomposition whereas UAN did not significantly affect soil fauna or litter decomposition. In addition, N-deposition concentration significantly influenced soil fauna density, H′ diversity, and species richness at the subtropical forest, but only affected H′ diversity of soil fauna at the temperate forest. The high N-deposition concentration treatment in the subtropical forest and low N-deposition concentration treatment in our temperate forest had significantly higher decomposition rates compared with the control (no N) treatment. We assert that addition of N through the canopy is a more realistic approach for simulating the actual processes of atmospheric N-deposition in forests. Future experiments using CAN methods will provide an improved understanding of the effect of N-deposition on soil fauna-decomposition interactions and inform reliable predictions of the consequences of global change on soil ecosystems.