Allelopathy has been regarded as a mechanism for successful exotic plant invasion. However, it is not clear if and what effects of allelopathic substances may exert on soil nutrient. The exotic plant Mikania micrantha H.B.K. (M. micrantha) has invaded many forests in south China, and recent studies have suggested it has allelopathic potential for other plants and soil microbial community. Thus, we hypothesized that M. micrantha could influence soil nutrients and N transformation through allelopathy. We measured total C and N, NO3−, NH4+ and pH of the soil beneath M. micrantha and the adjacent open soil, and then measured the above soil properties after treating soil with 3 concentrations of aqueous extracts of M. micrantha (T1: 0.005 g ml−1; T2: 0.025 g ml−1; T3: 0.100 g ml−1). In addition, a bioassay was conducted to determine the allelopathic potential of the soil beneath M. micrantha. The results showed that M. micrantha significantly affected soil nutrients and N transformation. Soil beneath M. micrantha had inhibitory effects on seed germination and seedling growth of test plant, and had significantly higher C, N, ammonia, net nitrification rate than those of open soil. The plant extracts decreased soil pH, and T1 decreased it the most, and it increased soil C and N, and T1 represented the greatest increase in both C and N. The extracts also increased both NO3− and NH4+ in soil, whereas no significant difference existed among the 3 extract treatments. Compared to the water control, the soil net mineralization rate was higher under T1, while lower under T2 and T3. However, the extracts increased the soil nitrification rates under all the treatments (T1, T2 and T3). Our results suggest that the water soluble allelochemicals of M. micrantha improve soil nutrient availability, through which the invasive plant M. micrantha may successfully invade and establish in new habitats.
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We thank Prof. Jiang-Ming Mo and Zhong-Liang Huang for their valuable suggestions and help in the study. We also thank the colleagues of Dinghushan Forest Experimental Station for their help in completing the experiments. The study was supported by the National Natural Science Foundation of China (30670385, U0633002) and the Key Program of Ministry of Education of China (704037).
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