Abstract: Rubber (Hevea brasiliensis)based agroforestry systems are regarded as an effective way to improve ecosystem functioning. However, few studies have examined soil water conservation function in this system. Here, we analyzed the direct and indirect factors affecting soil water conservation functions in two types of rubber plantations (pure rubber plantation and rubber Alpinia oxyphylla agroforestry system) in the central mountainous region of Hainan Island, based on structural equation model (SEM). The results showed that, compared to the rubber monoculture, soil water conservation function index of rubber-A. oxyphyllaagroforestry system increased by 1.09 times, indicating an increase of soil water conservation function in agroforestry system (P<0.05). The increases of litter quantity and fine root biomass accounted for the changes of soil bulk density and aggregate stability when A. oxyphylla was intercropped with rubber. Soil bulk density, soil aggregate stability and litter quantity accounted for 91% of the total variation of soil water conservation function. Those three variables can directly affect soil water conservation. Moreover, soil bulk density and litter quantity can also indirectly affect soil water conservation function through soil infiltration. We concluded that the species selected for intercropping in rubber plantations should have great fine root biomass and litter quantity so as to improve soil water conservation and enhance soil and water retention in the rubber plantations.  

Key words: niche, interspecific association, major species, shrimp, the offshore waters of southern Zhejiang Province