Dynamics of decomposition and nutrient release of leaf litter in Kandelia obovata mangrove forests with different ages in Jiulongjiang Estuary, China

Rates of in-situ decomposition and nutrient (organic C, N and P) release of leaf litter were seasonally compared among three planted Kandelia obovata mangrove forests (K12, K24 and K48 with forest ages of 12, 24 and 48 years, respectively) and one natural mature K. obovata forest (KM) in Jiulongjiang Estuary, China. The average values of half-time (T50) of leaf litter decomposition in spring, summer, autumn and winter were 29.8, 18.7, 23.9 and 47.4d, respectively. Decomposition rates were lower in the older forests (with T50 values of 30.1 and 31.1d averaged by all seasons in K48 and KM, respectively) than in the younger ones (with T50 values 29.8 and 28.8d averaged by all seasons in K12 and K24, respectively), especially in summer and autumn. The annual mean T50 of nutrient release of leaf litter during decomposition followed an order of KM > K48 > K24 > K12. During leaf litter decomposition, C releases were very similar to dry weight losses, while N releases were slower and P releases were much faster than dry weight losses. With the development of restored mangrove forests, decomposition and nutrient release of leaf litter became slow, which may increase the chance of leaf litter being exported into the surrounding waters.