Impacts of Long-term Nitrogen and/or Phosphorus Additions on Litterfall Production and Decomposition Rates in a Tropical Monsoon Secondary Forest

Abstract:

Monsoon secondary forests are important ecosystems in tropical South China, but reports on their long- term response to nitrogen (N) and phosphorus (P) addition in terms of litter production and decomposition rates are scarce. This paper prbesents the results of a 12-year study on aboveground litter production and a 4-year study on decomposition rates in a long-term NP addition experiment in a tropical monsoon secondary forest in South China. The experiment employed a two-factor (N addition and P addition) and two-level (addition and no addition) design, including control, N-only addition, P-only addition, and combined NP addition treatments. The results showed that over 12 years, the total aboveground litter production for the four treatments was (11544±1115), (12649±1087), (13694±1456), and (11761±712) g/m², respectively. P addition significantly increased litter production, while N addition showed a trend of increasing litter production. There was a significant interaction between N and P addition, and the effects of NP addition did not vary with year or season. During the 4-year decomposition rate study, the decomposition rate constants for the four treatments were (1.44±0.07), (1.76±0.09), (2.10±0.10), and (1.81±0.08), respectively. P addition significantly affected litter decomposition rates, while N addition had no significant effect, and there was no significant interaction between N and P addition. Long-term P addition significantly increased aboveground litter production in this ecosystem, while long-term N addition had a weak effect. There was a significant interaction between N and P addition, and the effects of NP addition did not change with treatment duration or dry/wet seasons. Aboveground litter decomposition was mainly limited by P, with no response to increased N availability. Therefore, it was suggested that the effects of long-term NP addition on aboveground litter production and decomposition in tropical monsoon secondary forests, contributing to the understanding of long-term response mechanisms of this ecosystem to increased nutrient availability.