Intensive rubber cultivation degrades soil nematode communities in Xishuangbanna, southwest China

Fifty years after the introduction, rubber monoculture now covers more than 400,000 ha of previously tropical seasonal rainforest, representing 20% of the land in Xishuangbanna, southwest China. However, little is known about effects of this widespread rubber monoculture on soil ecosystems. Here, we used soil nematodes as indicator species to assess effects of different rubber plantation types on soil ecosystems. Four land-use types (rubber monoculture, rubber and tea mixture, rubber polyculture and natural forest) at three sites were selected to compare soil nematode communities. Nematode communities were significantly different among the four land-use types. Natural forest had highest nematode abundance and taxa richness, followed by rubber polyculture, rubber and tea mixture and rubber monoculture. Compared to natural forest, rubber monoculture after 15-20 years reduced nematode taxa richness by as much as 33%. This was accompanied by reduced soil C and N, indicating loss of soil nutrients and ecological functioning. Nematode ecological indices (H′, MI and PPI) suggested a common pattern that natural forest was the most stable and undisturbed ecosystem, followed by rubber polyculture, rubber and tea mixture and rubber monoculture. Nematode trophic groups and SI indicated that food-web structures changed from complex in natural forest to much more simple in rubber monoculture. Finally, based on our results, two protective measures have been proposed to local government and farmers for rubber plantation and management in Xishuangbanna: 1. plant various cash crops such as tea, coffee, and cocoa into rubber monocultures; 2. decrease the management intensity and adjust strategies to restore surface vegetation, and ultimately convert rubber monoculture to rubber polyculture.