Abstract:Rhizosphere is the important interface between plant roots and the soil environment. To detect the effects of cultivar alternation and continuous cropping on soil fertility maintenance and the soil environment of poplar (Populus deltoids) plantation, we compared soil nutrient, enzyme activity and microbe abundance of the rhizosphere and bulk soils from the poplar plantations under cultivar alternation continuous cropping (ACC) and non-alternation continuous cropping (NACC). The results showed that both ACC and NACC led to soil degradation, but the extent of NACC was higher than ACC. The nutrients in rhizosphere and bulk soils of NACC decreased significantly more than ACC. Rhizosphere effects of soil organic matter in NACC was significantly larger than ACC, In contrast, the rhizosphere effects of soil available N, P and K were significantly lower in NACC than ACC.. As for the soil enzyme activity, NACC led to a significant decline in catalase, urease and alkaline phosphatase activity while an increase in polyphenol oxidase and peroxidase activity in rhizosphere and bulk soils. The same pattern occurred in ACC, but the amplitude of decline or increase was much smaller. In addition, the rhizosphere effects of soil enzyme activity in NACC demonstrated the same pattern as that of ACC, but with a larger range of variation. For soil microbe abundance, the same patterns occurred in ACC and NACC. Both of the two continuous cropping models led to decrease of soil microbe abundance in rhizosphere and bulk soils. The percentage abundance of soil bacteria was decreased while that of fungi was increased indicating a transition from the bacterial functioning soil to the fungi functioning soil. The rhizosphere effects of soil microbes in NACC were significantly higher than ACC, which could be attributed to the difference of root exudates. We concluded that continuous cropping of poplar plantations would lead to soil degradation, possibly be mitigated by cultivar alternation, which should be considered in future managements.