Effects of external N and P on decomposition of mixed leaf litters of Michelia macclurei and Pinus massoniana woodlands

Objective  To investigate the effects of external nitrogen(N) and phosphorus(P) on decomposition rate of mixed leaf litters of Michelia macclurei and Pinus massoniana woodlands, and analyze changes in N,P and potassium(K) contents during deposition process, in order to understand the response mechanism of leaf litter decomposition to external N and P, and provide reference for forest resource management.

Method  Mixed leaf litters of M. macclurei and P. massoniana were placed in woodlands of M. macclurei and P. massoniana. Four 5 m×5 m plots were set in each wood land and were sprayed with N, P or N+P. The decomposition rates and changes in N, P, K contents of leaf litters were compared.

Result  Twenty-four months after treatments, the amounts of leaf litter residue were N addition (4.99 g) > control (4.14 g) > N+P addition (2.17 g) > P addition (1.16 g) in M. macclurei woodland, and N addition (2.72 g) > control (1.21 g) > N+P addition (0.36 g) > P addition (0.16 g) in P. massoniana woodland. N addition inhibited decomposition of mixed leaf litters under M. macclurei and P. massoniana woodlands, whereas P and N+P additions both accelerated decomposition of mixed leaf litters with a faster decomposition rate compared to N+P addition. The amounts of leaf litter residue in P. massoniana woodland were less than those in M. macclurei woodland. Twenty-four months after treatments, N contents of mixed leaf litters treated with N, P and N+P additions were 13.72, 12.34 and 13.70 g·kg^–1 respectively in M. macclurei woodland, and 12.63, 13.46, and 14.54 g·kg^–1 respectively in P. massoniana woodland, Which were greater than the initial N content of mixed leaf litters (9.90 g·kg^–1). The P content of mixed leaf litters treated with P and N+P additions increased from the initial value of 0.38 to 0.86 and 0.74 g·kg^–1 respectively in M. macclurei woodland, and increased from 0.38 to 1.37 and 1.05 g·kg^–1 respectively in P. massoniana woodland. K contents of mixed leaf litters changed irregularly.

Conclusion  Decomposition of M. macclurei leaf litter can be accelerated and decomposition rate of mixed leaf litters can be enhanced by mixed-planting M. macclurei and P. massoniana.