Simulated nitrogen deposition significantly suppresses the decomposition of forest litter in a natural evergreen broad-leaved forest in the Rainy Area of Western China

Background and aims

Litter, an essential component of forest ecosystems, plays an important role in maintaining soil fertility, sequestering carbon (C) and improving soil biodiversity. However, litter decomposition is affected by increased nitrogen (N) deposition. Numerous reports have presented N deposition experiments in different forest ecosystems to investigate the effects of N deposition on litter decomposition, but the effects remain unclear, especially in ecosystems receiving increasingly higher levels of ambient N deposition. To address this gap, we performed a litterbag experiment to understand the effects of increasing N deposition on the litter decomposition process in natural evergreen broad-leaved forest in the Rainy Area of Western China.

Methods

A 2-year field litter decomposition experiment was conducted using the litterbag method. Four levels of N deposition were established: control (CK; 0 kg·N·ha^?1·year^?1), low N deposition (LN; 50 kg·N·ha^?1·year^?1), medium N deposition (MN; 150 kg·N·ha^?1·year^?1), and high N deposition (HN; 300 kg·N·ha^?1·year^?1). The simulated N depositions ranged from 50% to 320% of the ambient rate of wet N deposition.

Results

Simulated N deposition significantly increased the remaining mass, C, N, lignin and cellulose of the litter. The LN treatment decreased the remaining phosphorus (P); conversely, the HN treatment increased it. In the late stage of the study period, the mass remaining was positively closely correlated to the lignin and cellulose remaining during the decomposition process.

Conclusions

Simulated N deposition significantly suppressed the litter decomposition in the natural evergreen broad-leaved forest, despite the high rate of ambient N deposition, and the inhibitory effects increased with the N deposition levels. The suppressive effect of N deposition on litter decomposition may be primarily explained by the inhibition of lignin and cellulose degradation by the exogenous inorganic N. With ongoing N deposition in future, N deposition may have a potentially significant impact on C and N cycles in such forest ecosystems.