Soil Ecology Group

Successful invasion by exotic plant species can modify the abundance and composition of soil microbial communities. Eupatorium adenophora and Chromolaena odorata are exotics and have become highly invasive plants in China. Several studies have investigated mechanisms of their successful invasions including phenotypic plasticity, genetic differentiation, and allelopathy, but little is known about effects on soil microorganisms.

Dr. XIAO Haifeng of Soil Ecology Group in Xishuangbanna Tropical Botanical Garden (XTBG) and his colleagues used two invasive (E. adenophora and C. odorata) and two native plant species (Eupatorium japonicum and Eupatorium heterophyllum) to compare the soil feedback (to plant growth) before and after microbial-community exposure to sterilization of the soil and to plant-root exudates. They found that soil sterilization significantly increased biomass of native Eupatorium japonicum and Eupatorium heterophyllum but did not affect these two invasive species’ biomass. After root exudates from these plants had acted on the soil microbial community for 10 months, soil sterilization significantly decreased the growth of E. adenophora and C. odorata but still significantly increased the biomass of two native species. Denaturing gradient gel electrophoresis revealed that these four plant species modified fungal rather than bacterial communities. Subsequent sequencing results indicated that C. odorata soils had more dominant arbuscular mycorrhiza fungal (AMF) species compared with other plant species. These results strongly suggest that invasive E. adenophora and C. odorata produced plant-soil benefit themselves, which may be among the belowground mechanisms contributing to their success as invasive species.

The study entitled “Soil fungi rather than bacteria were modified by invasive plants, and that benefited invasive plant growth” has been published online in Plant and Soil.

Large areas of rubber monoculture and high-intensity management have already been established in Xishuangbanna ((21°08′–22°36′ N, 99°56′–101°50′E) for half a century. Rubber monoculture now covers more than 400,000 ha, or 20% of land in Xishuangbanna. Previous studies demonstrated that, compared to primary tropical forests, rubber plantations significantly decrease diversity of plant species, birds, bats, insects and spiders. However, little is known about effects of this widespread rubber monoculture on soil ecosystems.

Dr. XIAO Haifeng of Soil Ecology Group in Xishuangbanna Tropical Botanical Garden (XTBG) and his colleagues used soil nematodes as indicator species to assess effects of different rubber plantation types on soil ecosystems. They compared soil nematode communities in different rubber plantations (rubber monoculture, rubber and tea mixture, rubber polyculture) and natural forest.

Nematode communities were distinctly different among the four land-use types and significantly correlated with all the examined environmental factors except litter quantity, which suggested that rubber management practices significantly affected soil C, N, pH, soil moisture and vegetation (including plant diversity and quantity of plant litter and roots) and thus affected soil nematode communities. Their results provided evidence to the local government and plantation managers that vegetation diversity had positive effects such as relatively high soil nutrient (N) levels and biodiversity in rubber plantations. They advised local government and plantation managers to: 1) plant various cash crops such as tea, coffee, and cocoa into rubber monocultures, which is consistent with the local government recently proposing environmentally friendly rubber plantations.

The study entitled “Intensive rubber cultivation degrades soil nematode communities in Xishuangbanna, southwest China” has been published online in Soil Biology and Biochemistry.