Leaf litter production and decomposition in a Riverine Mangrove forest in India

Leaf litter constitutes a major fraction in total litter production in mangrove forests. Its contribution to NPP of mangrove forests and carbon sequestration is less studied. These aspects were investigated for Kunhimangalam mangrove forest in Kerala, India. We quantified the leaf litter production and estimated the decomposition rates of leaf litter from Aegiceras corniculatum, Avicennia officinalis, Excoecaria agallocha and Rhizophora mucronata. These four species together constituted 92.49% of abundance in Kunhimangalam. The average annual leaf litter production was 8.83 +/- 0.95 t ha(-1)yr(-1), 78% of the total litter produced. Leaf litter production was negatively correlated with soil pH (R-2 = 0.531) and rainfall (R-2 = 0.561). Temperature, salinity and humidity did not show any remarkable influence. The rate of decomposition varied significantly among these species (F = 2497.79, p < 0.01) but as for the mixed leaf litter category (a mixture of leaves from the above four species in equal weight), the rate of decomposition was the highest. The pattern of leaf litter decomposition observed in mixed, R. mucronata and E. agallocha categories best fitted to the exponential decay model indicating an initial phase of faster decomposition followed by a terminal slow phase. The leaf litter of A. corniculatum and A. officinalis categories fitted best to the linear regression model showing a steady pace throughout the period of decomposition. Leaf litter of these four species together contributed 3.56 +/- 0.01 t C ha(-1) y(-1) to NPP. Higher production of leaf litter in Kunhimangalam showed higher potential for carbon sequestration. However, only less than 1% (0.62%) of the leaf litter was decomposed when macrobenthos were excluded from the system. The destiny of the rest 99% appeared critical as this determined the capacity of Kunhimangalam mangrove forest to act as a source or sink for carbon.