INFLUENCE OF LEAF-LITTER QUALITY ON N MINERALIZATION IN SOILS OF SUBTROPICAL HUMID FOREST REGROWTHS

Laboratory net N mineralization as influenced by leaf litter quality o f several subtropical tree species was studied in soils of forest regr owths of three different age groups. Concentrations of NH4+ and NO3- i n the soil generally increased with age of forest regrowth. However, d uring incubation concentrations fluctuated markedly. in the ''soil onl y'' treatment, the cumulative N mineralization, ammonification and nit rification rates were highest in soils of the 13-year-old regrowth, fo llowed by those of the 16- and 7-year-old regrowths. Soils from all th ree regrowths planted with Quercus dealbata had greater N mineralizati on rates than soils planted with Pinus kesiya. Overall, leaf litter of Schima khasiana showed the highest release of N. followed by leaf lit ter of e. griffithii; greatest immobilization of N was recorded for Rh ododendron arboreum leaves and P. kesiya needles. The percentage of N accumulated/depleted from the leaf litter correlated positively with t he initial N concentration, and correlated negatively with the lignin content and C/N ratio.