LAGGING EFFECT OF NUTRIENT RELEASE IN TROPICAL SEASONAL FOREST SOILS IN XISHUANGBANNA, SOUTHWEST CHINA

This study assessed how litterfall production and nutrient concentration of leaf litter and soil vary with seasonality of rainfall in primary and secondary tropical forests of south-west China. A total of five 20 m x 20 m plots were established in each of the primary and secondary tropical forests. Leaf litter and top soil were sampled from each plot at monthly intervals for one year. Total annual litterfall production was 6.03 and 8.29 tonnes ha(-1) year(-1) in the primary and secondary tropical forests respectively. Total litterfall showed marked peaks at the end of the dry season with smaller peaks at the end of the rainy season. Leaf nutrients (phosphorus, potassium and calcium) were slightly varied between the two sites. Soil nutrients peaked in the middle of the rainy season, i.e. about two months later than the onset of the rainy season, suggesting a lagging effect of nutrient release. Consequently, we postulated that there was nutrient pulse in tropical seasonal forest soils every year, which was driven by alternating dry and rainy seasons in the predominantly monsoon climate areas