[Effects of broadleaved tree plantation on soil phosphorus fractions and availability in diffe-rent soil layers in a logged Cunninghamia lanceolata woodland].

Phosphorus (P) limitation is one of the major issues for the management of subtropical plantations. Understanding the effects of tree species transition from conifer to broadleaved trees on soil P fraction and availability in different soil layers are of great significance for the sustainable development of subtropical forests. We compared changes in soil chemical properties, P fraction and availability across 0-100 cm soil profile between Mytilaria laosensis and Cunninghamia lanceolata plantations, which were initially reforested from C. lanceolata plantation in the spring of 1993. The results showed that soil organic P content in both plantations decreased significantly with soil depth. Compared with C. lanceolata, the M. laosensis plantation significantly increased soil available P content by 35.7% and 86.2% in the 0-10 and 10-20 cm, respectively. The contents of soil labile P and moderately labile P decreased significantly with soil depth in both plantations. The contents of labile P and moderately labile P were significantly higher in the surface soil (0-20 cm), while the non-labile P in the 80-100 cm was increased by 13.6%, and the free iron content in the 20-80 cm significantly decreased. Results of redundancy analysis showed that dissolved organic carbon and free iron were the most important factors influencing P fraction in those plantations. Tree species transition from C. lanceolata to M. laosensis could change the pattern of soil P fraction in soil profile, and greatly enhance soil P availability.