Decomposition responses of pine (Pinus massoniana) needles with two different nutrient-status to N deposition in a tropical pine plantation in southern China

The effect of nitrogen (N) deposition on the decomposition of pine (Pinus massoniana) needles in a tropical pine plantation was studied. The pine needles with two different nutrient status (nutrient-rich and nutrient-poor) were used, followed by 3-levels of N treatments (Control: no N addition, Low N: 5 g N m(-2) y(-1), and Medium-N: 10 g N m(-2) y(-1) experimental inputs), which had been applied for 26 months continuously before this experiment and continued throughout the decomposition measurement. The main objective was to test the hypothesis that decomposition of nutrient-rich needles would be more sensitive to cumulative N deposition than the decomposition of nutrient-poor needles. Nitrogen addition had negative effect on mass loss, and the release of N and P from decomposing nutrient-rich needles but little or no effect on the decomposition of nutrient-poor needles. In addition, a negative effect in the initial decomposition phase and a positive effect in later decay stages were found on C release. The negative effect was stronger on nutrient-rich needles than on nutrient-poor needles, but the reverse was true for the positive effect. Our results suggest that response of litter decomposition to N deposition may vary depending on the nutrient status of the litter.