Abstract: Quantifying gaseous loss of soil nitrogen (N) is important for understanding forest ecosystem N cycling. However, relatively few studies have investigated N gas loss, especially N₂. In this study, using a soil incubation experiment in laboratory, we examined soil N gaseous loss and its responses to water addition in two tropical montane forests in Jianfengling, Hainan Island. The results showed that in ambient soil water contents, soil N gas emission rates were relatively low, and N₂O and N₂ emission rates were -0.004-0.03 and 0-0.022 nmol N·h^-1·g^-1, respectively. After water addition, N₂O and N₂ emission rates increased sharply by more than 70 and 40 times, respectively. Soil N gas emissions were affected by forest types and seasons. N gas emission rates in secondary forest were higher than those in primary forest, and were higher in wet season than in dry season, but with no significant difference. Our results indicated that tropical forest soil N gaseous losses were mainly controlled by soil water content. In order to accurately estimate soil N gas losses of tropical forest ecosystems, we should consider the influence of heavy precipitation.

Key words: Pinus tabuliformis plantation, regression modeling, aboveground biomass, leave-one-out cross validation, GF-2