外来植物火炬树(Rhus typhina L.)入侵对不同林型土壤性质的影响

生物入侵在世界范围内广泛发生,严重威胁当地生物多样性和生态系统稳定性。植物与土壤之间的相互作用在决定植物的竞争力以及分布格局中起着重要作用,是影响外来植物入侵力和生态系统可入侵性的一个重要方面。目前,有关研究已成为植被生态学与入侵生态学的研究热点。引自北美的外来植物火炬树(Rhus typhina L.)已成为我国北方主要的入侵木本植物之一。比较了火炬树单优林型、火炬树+刺槐(Robinia pseudoacacia L.)混交林、火炬树+麻栎(Quercus acutissima Carruth.)混交林、火炬树+银白杨(Populus alba L.)混交林4种不同林型的土壤微生物群落结构、土壤酶活性和土壤养分含量特征。结果表明:火炬树单优林土壤细菌、放线菌数量明显高于各混交林型,而真菌数量无显著差异;土壤酶活性方面,火炬树单优林脲酶、过氧化氢酶活性高,土壤磷酸酶活性低;火炬树的入侵显著提高了土壤全碳、全氮、全磷和硝态氮含量,同时明显降低了土壤铵态氮含量。硝态氮含量的增高可能与火炬树入侵造成土壤微生物群落组成变化、土壤硝化速率高有关;而火炬树入侵降低了土壤铵态氮含量,说明该物种可能更易于吸收利用铵态氮。以上研究结果表明,火炬树可以改变土壤生态系统的微生物群落组成和土壤酶活性并影响土壤相关营养元素循环,从而可能使其在与当地植物的竞争中获得优势,为自身的入侵创造有利条件。

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 of native invaded communities should be sufficient to manage the effects of exotic plant species on the soil. This study has theoretical and practical implications for studying the mechanisms underlying biological invasions and the risk-assessment and management of exotic plant R. typhina respectively.