High nitrogen deposition decreases the contribution of fungal residues to soil carbon pools in a tropical forest ecosystem

• High rates N (High-N) deposition decreased ratios of fungal/bacterial amino sugars.
• High-N deposition decreased fungal residues/SOC ratio.
• High-N deposition decreased total microbial residues' contribution to SOC.

Soil carbon (C) dynamics are closely mediated by microorganisms and microbial residues could constitute a significant pool of soil organic C (SOC). However, little is known about the nitrogen (N) deposition effect on the contribution of microbial residues to SOC balance in tropical forest ecosystems. Here, we assessed microbial residues using amino sugar biomarkers in surface soils of a tropical forest ecosystem under 11-year continuous N addition at different rates (0, 50, 100 and 150 kg N ha−1 yr−1). Nitrogen addition didn't affect either fungal or bacterial residues in soil apparently, but high-N addition (150 kg N ha−1 yr−1) significantly decreased the contribution of fungal residues to SOC indicated by both ratios of fungal/bacterial amino sugars and fungal residues/SOC. Consequently, high-N addition whittled down microbial contribution to SOC pools. Those findings may have implications for our predictions of global change impacts on soil C dynamics.