Abstract: Taking barnyard grass (Echinochloa crus-galli), allelopathic rice (Oryza sativa) PI312777, and non-allelopathic rice Liaojing-9 as test materials, this paper studied the changes of microbial biomass C and of dehydrogenase, urease and invertase activities in soils under 1∶1 rice-barnyard grass coexistence. The results showed that with the coexistence of barnyard grass, the microbial biomass C in rhizosphere soil of PI312777 was decreased by 50.52% (P<0.01), while that in inter-row soil was increased. The microbial biomass C in rhizosphere soil of Liaojing-9 was also decreased by 38.99%(P<0.01), but no significant difference was observed in inter-row soil. The dehydrogenase activity in rhizosphere soils of the two rice varieties were decreased by 20% or more (P<0.05), but the urease and invertase activities in rhizosphere soil of PI312777 were significantly stimulated (P<0.01). The invertase activity in rhizosphere soil of Liaojing-9 was inhibited by coexisting barnyard grass, but urease activity had less change. As a result, the allelopathic traits of rice variety led to a significant decrease of microbial biomass C and an increase of urease and invertase activities in rhizosphere soil under barnyard grass coexistence, implying that soil microbial biomass and enzymes might play essential roles in species interactions between rice and barnyard grass, and allelopathic rice had its advantage in resistance to barnyard grass.

Key words: central region of Yunnan Province, ecological evaluation, lake basin, eco-environmental quality, ecological monitoring