火炬树入侵黑松幼林过程中对土壤化学性质的影响

Effects of Rhus typhina invasion into young Pinus thunbergii forests on soil chemical properties

外来植物入侵对生态系统和环境造成严重影响。成功的入侵植物常常可通过改变土壤化学性质来促进自身的竞争和入侵能力。最近几年火炬树（Rhus typhina L.）已经成为北方入侵木本植物之一，火炬树克隆繁殖形成居于绝对优势地位的单优群落已严重威胁着生物多样性和生态系统功能。在本文中，我们研究了火炬树入侵黑松（Pinus thunbergii Parlatore）幼林对土壤化学性质的影响。2011年4月，在山东烟台蓁山，于火炬树入侵程度不同的黑松幼林（在未入侵、轻度、中度、重度入侵下，火炬树盖度分别为0%、30%、50%~70%、90%以上），分别采样表层土壤并带回实验室分析其化学性质。结果表明：火炬树的入侵显著提高了土壤硝态氮（从未入侵下的0.63 mg/kg 提高到重度入侵下的0.98 mg？kg-1）和有效磷（从未入侵下的0.589 mg？kg-1提高到重度入侵下的1.189 mg？kg-1）的含量，降低了土壤铵态氮（从未入侵下的9.25 mg？kg-1降低到重度入侵下的2.97 mg？kg-1）的含量，而对土壤pH、有机质和全氮含量没有显著影响。火炬树入侵导致铵态氮降低可能是由于火炬树更易于吸收利用土壤铵态氮；硝态氮含量升高是因为火炬树入侵提高了土壤的硝化速率。同时火炬树入侵导致土壤有效磷升高，说明火炬树能够通过活化分解土壤含磷化合物来满足自身生长的需求。本研究表明，火炬树入侵能显著改变土壤化学性质，火炬树入侵对根际土壤化学性质的影响及其自身的适应性特征等可能是其能够入侵成功和快速扩张蔓延的生态机制之一。

Exotic plant invasions severely threaten ecosystems and the environment. Successful invasive plants often promote their competitive ability and invasiveness through altering soil chemical properties. In recent years Rhus typhina has become one of the invasive woody plant species in North China. The monodominant communities formed by R. typhina through vegetative propagation have extremely threatened biodiversity and ecosystem functioning. In this study, we examined the influence of R. typhina invasion into young Pinus thunbergii forests on soil chemical properties. In April 2011, soils were collected under young P. thunbergii forests with R. typhina invasion by different extents in the Zhen Mountain, Yantai of Shandong Province （coverage of R. typhina reached 0%, 30%, 50% to 70%, and above 90% under non-invaded, slightly invaded, moderately invaded, and severely invaded plots, respectively）, and their chemical properties were analyzed in the laboratory. The results showed that R. typhina invasion significantly elevated soil nitrate nitrogen with values ranging from 0.63 mg？kg-1 in non-invaded plots to 0.98 mg？kg-1 in severely invaded plots, increased available phosphorus contents with values ranging from 0.589 mg？kg-1 in non-invaded plots to 1.189 mg？kg-1 in significantly invaded plots, reduced the content of soil ammonium nitrogen from an initial value of 9.25 mg？kg-1 in non-invaded plots to 2.97 mg？kg-1 in severely invaded plots, but did not significantly influence the soil pH, total nitrogen and organic matter contents. That reduced ammonium nitrogen content due to R. typhina invasion may be attributed to enhanced capabilities of plant absorbance and utilization on soil ammonium nitrogen. Concurrently, the elevated nitrate nitrogen content might be a result of increase in soil nitrification rate caused by R. typhina invasion. Moreover, R. typhina invasion elevated the soil available phosphorus, indicating R. typhina could be able to meet its needs of growth through activating and decomposing soil phosphorus compounds. The present study suggests that the influence of R. typhina invasion on soil chemical properties, in combination with its own adaptive traits, may be one of the ecological mechanisms elucidating its successful invasion and rapid expansion.