Effects of exotic plant Rhus typhina invasion on soil properties in different forest types

Rapid expansion of exotic invasive plants throughout the world is well acknowledged as one of the major threats to biodiversity and ecosystem stability. Plant-soil interactions play an important role in plant competition and distribution,and represent an important aspect of the invasion potential of exotic plants and ecosystem invasibility,one of the hot research topics in vegetation and invasion ecology. Rhus typhina,an exotic large shrub or small tree introduced from North America in 1959,was identified as a main afforestation species in Northern China. However,as its distribution keeps expanding,it has been increasingly realized as a potential invasive species in local habitats. In the present study,we examined the influence of R. typhina invasions in four different forest types on typical soil properties, including soil microbial community,soil enzyme activities,and soil chemical properties. In April 2012,soil samples were collected from four different types of forests( dominated by R. typhina,R. typhina + Robinia pseudoacacia,R. typhina + Quercus acutissima,R. typhina + Populus alba,respectively) in the Zhen Mountain,Yantai of Shandong Province. Subsequently,soil microbial community,soil enzyme activities,and soil chemical properties of each soil sample were analyzed in the laboratory. The results showed that the invasion of the exotic plant R. typhina affected soil properties by( 1) significantly increasing the amount of bacteria and actinomyces,but not the fungi; ( 2) significantly enhancing the soil enzyme activities of urease and catalase,while decreasing acid phosphatase; ( 3) accelerating the soil total C,total N,total P and nitrate N content,but decreasing the ammonium N content. The elevated nitrate N content may be caused by the altered composition of soil microbial community and the accelerating soil nitrification rate by R. typhina invasion. However,the ammonium N content was reduced after R. typhina invasion,suggesting that R. typhina prefers to absorb and utilize ammonium N in the soil. Collectively,our results strongly suggest that R. typhina can alter soil nutrient dynamics by modifying the composition of soil biota and the activities of soil enzymes,which in turn alter the soil properties. All these changes may endow R.typhina advantages in competition with native species during its establishment,inhibit native plants,and finally facilitate its invasion process in the field. Both management of exotic plant invasions and the restoration