Short-term effects of CO_2 concentration elevation, warming and transgenic Bt rice cropping on soil labile organic carbon and nitrogen, and nematode communities
Interactions of global change and transgenic Bt rice (Huahui-1, HH1) cropping on soil ecosystem remain largely unexplored. Here we conducted an OTC (Open Top Chamber) experiment to evaluate the effects of transgenic Bt rice cropping on soil labile organic carbon and nitrogen, and nematode communities under elevation of temperature and [CO_2] with two rice varieties including non-Bt rice (MH63) and its transgenic Bt line (HH1). Results showed that (1) Under the condition of elevated [CO_2] and warming, transgenic Bt rice cropping significantly affected the content of soil dissolved organic carbon, dissolved organic nitrogen and NO_3~- -N. Significantly interactions of transgenic Bt rice, warming and elevated [CO_2] were observed for the content of soil dissolved organic carbon and dissolved organic nitrogen. Further, the transgenic Bt rice reduced microbial biomass carbon and nitrogen significantly under ambient temperature and [CO_2]; whereas warming and [CO_2] elevation reversed that trend. (2) At ambient temperatures and [CO_2], the total number of nematodes in soil grown with transgenic Bt rice cropping were significantly more than those in soil grown with the parental line. Herbivorous nematodes tended to increase under the condition of warming and elevated [CO_2], though not reaching to a significant level. Transgenic Bt rice and warming significantly increased the Nematode Channel Ratio, demonstrating the shift from bacteria-dominated to fungi-dominated energy channel. But [CO_2] elevation and transgenic Bt rice significantly increased the nematode Enrichment Index. In conclusion, climate change modified the responses of soil labile organic matter and nematode community to transgenic Bt rice cropping, though it does not lead to negative effects on soil based on the results of short-term experimental duration.