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 of several subtropical tree species was studied in soils of forest regrowths of three different age groups. Concentrations of NH4+ and NO3– in the soil generally increased with age of forest regrowth. However, during incubation concentrations fluctuated markedly. In the “soil only” treatment, the cumulative N mineralization, ammonification and nitrification rates were highest in soils of the 13-year-old regrowth, followed by those of the 16- and 7-year-old regrowths. Soils from all three regrowths planted with Quercus dealbata had greater N mineralization rates than soils planted with Pinus kesiya. Overall, leaf litter of Schima khasiana showed the highest release of N, followed by leaf litter of Q. griffithii; greatest immobilization of N was recorded for Rhododendron arboreum leaves and P. kesiya needles. The percentage of N accumulated/depleted from the leaf litter correlated positively with the initial N concentration, and correlated negatively with the lignin content and C/N ratio.