Nitrogen Addition Aggregates Microbial Carbon Limitation in Subtropical Soils : New Evidence from Microbial Necromass Decomposition

Microbial necromass has been increasingly recognized as an important source of soil organic carbon (C). However, how nitrogen (N) addition regulates microbial necromass decomposition and the size of different necromass pools remain poorly understood. Here, via an incubation of 13 C-labeled necromass in a laboratory with subtropical plantation (Cunninghamia lanceolata ) soils, we found that 7-year N addition stimulated the decomposition rate constant of the labile necromass (k1 ) pool, which was attributed to microbial C limitation. N addition also decreased the size of the labile necromass pool, but it enlarged the recalcitrant pool, while phosphorus (P) addition had no effect on k1 or the sizes of different necromass pools. Moreover, N interacted with P to affect the decomposition rate constant of the recalcitrant necromass pool, with a higher value with N treatments than with N+P treatments. Collectively, our study highlighted the importance of microbial necromass C on soil C cycle under N deposition