EFFECTS OF PLANTATION AGES, DENSITIES AND MANAGEMENT STRATEGIES ON CARBON SEQUESTRATION IN TROPICAL MANGO AND WAX APPLE ORCHARD ECOSYSTEMS

Mango (Mangiferaindica L.) and wax apple (Syzygiumsamarangense Merrill and Perry) are two of the main fruit crops in tropical Asia region and their orchard ecosystems may have a great potential for carbon (C) emission or sequestration. In this study, we present results on C fluxes in the ecosystems of these two typical tropical orchards. Trials were carried out in Sanya at the southern extremity of Hainan Island, China, on mango and wax apple orchards at different ages, plant densities and management strategies (pruning material return or organic fertilizer application). The total net primary productivity (NPP) of different orchard systems ranged from 6.62 to 9.73 t DM ha(-1) y(-1), while soil respiration ranged between 2.46 and 4.14 g CO(2)m(-2) d(-1). The sparse and intensive mango systems (MS and MI, 444 and 1000 trees ha(-1), respectively) were weak C sources, with the net C emission of 0.72 and 0.64 t C ha(-1) y(-1), respectively. A C return of 1.21 t C ha(-1) y(-1) from pruned residues led the intensive mango orchard system become a net C sink (0.54 t C ha(-1) y(-1)). The C sequestration in wax apple orchards were higher than that of mango orchards, mainly due to a C supply of 3.64 t C ha(-1) y(-1) from organic fertilizer. C sequestration by wax apple orchard was higher in the young (WY, 2-4 years old, 2.29 t C h(-1) y(-1)) than in the mature system (WM, 6-8 years old, 0.99 t C ha(-1) y(-1)), as a result of higher C fixation in above-ground permanent structures, more C return from floor vegetation and less C emission from soil respiration.