Abstract
The responses of litter decomposition to nitrogen (N) and phosphorus (P) additions were examined in an old-growth tropical forest in southern China to test the following hypotheses: (1) N addition would decrease litter decomposition; (2) P addition would increase litter decomposition, and (3) P addition would mitigate the inhibitive effect of N addition. Two kinds of leaf litter, Schima superba Chardn. & Champ. (S.S.) and Castanopsis chinensis Hance (C.C.), were studied using the litterbag technique. Four treatments were conducted at the following levels: control, N-addition (150 kg N ha−1 yr−1), P-addition (150 kg P ha−1 yr−1) and NP-addition (150 kg N ha−1 yr−1 plus 150 kg P ha−1 yr−1). While N addition significantly decreased the decomposition of both litters, P addition significantly inhibited decomposition of C.C., but did not affect the decomposition of S.S. The negative effect of N addition on litter decomposition might be related to the high N-saturation in this old-growth tropical forest; however, the negative effect of P addition might be due to the suppression of “microbial P mining”. Significant interaction between N and P addition was found on litter decomposition, which was reflected by the less negative effect in NP-addition plots than those in N-addition plots. Our results suggest that P addition may also have negative effect on litter decomposition and that P addition would mitigate the negative effect of N deposition on litter decomposition in tropical forests.
Highlights
Nutrient limitation, especially nitrogen (N) and phosphorus (P), to primary production and other ecological processes is widespread in terrestrial ecosystems [1,2]
For example in China, the emissions of reactive N increased from 14 Tg N yr21 in 1961 to 68 Tg N yr21 in 2000 and is expected to reach 105 Tg N yr21 in 2030 [7], leading to a high deposition of N (30–73 kg N ha21 yr21) in some sub-tropical forests of southern China [8]
As expected N addition decreased litter decomposition in the present study, which is consistent with previous studies in the same forest [24,27]
Summary
Especially nitrogen (N) and phosphorus (P), to primary production and other ecological processes is widespread in terrestrial ecosystems [1,2]. N is generally believed to be the main limiting nutrient in temperate forests [3], but the tropical forests more typically exhibit N-rich and P limitation [4]. While most studies have focused on the role of N on temperate ecosystems, nutrient limitation in tropical forest is not well studied. Atmospheric deposition of N has increased drastically and is projected to increase further in tropical and subtropical regions in the coming decades [5,6]. Increased N deposition has begun to alter nutrient status in these regions, which increases the N cycling rate [9], and enhances P limitation in tropical forests. Some studies have demonstrated that elevated inputs of N to tropical forests would decrease P concentrations in soils and leaves [10,11], suggesting the existence of a complex relationship between N deposition and P availability, and interactions that affect ecosystem processes in tropical forests
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