Abstract: Human activities have changed soil nitrogen (N) and phosphorus (P) availability, which potentially affects ecosystem nutrient cycling. To explore nutrient limitation status of different forest types, we evaluated the response of soil and foliar N and P contents to N and P addition in an 11-year continuous fertilization experiment in both primary and secondary montane rainforests. We found that (1) N addition did not affect soil and foliar N and P contents in both primary and secondary forests. In contrast, P addition significantly increased soil available P contents but had no effect on foliar N and P contents in both forests. (2) Foliar N∶P ratios were higher than 16 in CK treatment of both forests. Foliar N∶P significantly decreased after P and NP additions in both forests. N addition significantly increased foliar N∶P of the secondary forest, but not in the primary forest. (3) Soil available N was significantly correlated with available P in the secondary forest, but not in the primary forest. In contrast, there was a significant negative correlation between foliar N∶P and soil available P in both forests. In summary, our findings indicate that P is the limiting factor for plant growth in tropical mountain rainforests. P addition could effectively alleviate P limitation. In addition, N addition aggravated P limitation in the secondary forest but not in the primary forest. This study provides an important reference for understanding nutrient limitation pattern of ecosystems in the context of global change.

Key words: nitrogen addition, phosphorus addition, tropical rainforest, nutrient limitation, N∶P ratio