Abstract: Vegetation restoration can effectively prevent soil erosion and improve ecological environment in eroded red soil regions. Enhancement of soil nitrogen (N) mineralization capacity and N availability is a key pathway to improve the growth and development of vegetation in barren soil, which is of great significance to ecosystem restoration of eroded land. The amount and rate of soil net N mineralization in Pinus massoniana forests under different recovery years (Y0, Y16, and Y34) and different treatments of understory vegetation (Dicranopteris dichotoma) were examined by in situ closedtop core incubation method. The interactive effects of vegetation restoration years, understory vegetation cover, and seasonal changes on soil N mineralization were analyzed. The results showed that vegetation restoration improved soil nutrients in the erosion-degraded land. The highest value of net N mineralization appeared in summer and autumn, but negative value was observed in spring. Vegetation restoration significantly increased the amount of soil net N mineralization, with ammonification playing a dominant role in the process of net N mineralization. The net ammonification rate and net mineralization rate showed similar seasonal pattern. The nitrification rate decreased with increasing recovery years. The amount and rate of net N mineralization in the forest gap without vegetation cover were lower than that in the forest covered with D. dichotoma. The removal of D. dichotoma reduced the amount and rate of net N mineralization. Results of analysis of variance showed that recovery years, seasons, and their interaction significantly affected the amount and rate of soil net N mineralization (P<0.001), but the manipulation of D. dichotoma had no effects (P>0.05). Soil N transformation in P. massoniana forest changed seasonally, and thus forest management should be carried out in accordance with seasonal change. D. dichotoma coverage under the forest plays an important role in the soil N recovery of P. massoniana forest.

Key words: eroded red soil, vegetation restoration, soil nitrogen mineralization, seasonal dynamics, Dicranopteris dichotoma.