Cumulative effects of nitrogen additions on litter decomposition in three tropical forests in southern China

A field-scale experiment with nitrogen (N) addition treatments was performed in three forest types - a pine (Pinus massoniana Lamb.) forest, a pine-broadleaf mixed forest (mixed) and a mature monsoon evergreen broadleaf forest (mature) - in tropical China. Two kinds of leaf litter, Schima superba Chardn. & Champ. and Castanopsis chinensis Hance, were studied using the litterbag technique after more than 2 years of continuous N additions. The objective of this study was to understand the cumulative effect of N addition on litter decomposition in the tropical forests and to determine if the initial effects of N addition changes over time. Results indicated that leaf litter decomposition was significantly faster in the mature forest than in the mixed or pine forests. The mean fraction of mass remaining after 12-months of decomposition was: mature (0.22) < mixed (0.50) < pine (0.51) for the two litters. Nitrogen addition significantly depressed litter decomposition in the pine forest and the mature forest, but had no significant effect in the mixed forest. These results suggest that N deposition has significant cumulative effect on litter decomposition.