外来植物火炬树水浸液对土壤微生态系统的化感作用

引种自北美的外来植物火炬树(Rhus typhina L.)是中国北方主要造林树种之一.然而,近年来分布区的不断扩大暗示着该树种的潜在入侵性.以火炬树为对象,研究火炬树不同浓度(0、0.005、0.025、0.1g/mL)的鲜枝叶水浸液对土壤微生物群落结构、酶活性、土壤养分含量及土壤矿化的影响.研究结果表明:随着水浸液浓度的提高,火炬树增加了细菌和真菌的数量;火炬树对所测土壤酶活性产生了不同程度的影响,脲酶和磷酸酶均有随着水浸液浓度的提高而增大的趋势,而蔗糖酶活性受影响不明显;随水浸液浓度升高,火炬树显著提高了土壤全碳、全钾、速效氮、有效磷、速效钾的含量,对土壤含水量、pH值、全氮与全磷没有显著影响;同时,火炬树通过促进微生物的矿化速率,提高了土壤无机氮的供给.以上结果表明,火炬树可以改变土壤的微生物组成和土壤酶活性并影响土壤相关营养元素循环,从而为自身的入侵创造有利条件.本研究揭示外来植物火炬树水浸液对土壤微生态系统的影响,从化感间接作用角度为火炬树的潜在入侵性提供进一步的数据支持.

Allelopathic effects of aqueous extract of exotic plant Rhus typhina L. on soil micro-ecosystem

Biological invasion represents one of the most serious threats to ecological diversity, and the invasion ecology research has become one of the central issues of contemporary environmental sciences. Multiple hypotheses have been put forward to explain the remarkable success in many exotic invasive species, but one, allelopathy, proposes that some invaders gain growth advantage through possessing allelopathic, defensive or antimicrobial chemicals to which native organisms have not adapted. This hypothesis has been regarded as an important mechanism for successful exotic plant invasions. Filter paper bioassays, though repeatedly performed in laboratory in many studies, were insufficient to evaluate the allelopathic potential for lacking the incorporation of natural soil, which consists of important space and carrier for manifestation of allelopathy. 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 the distribution keeps expanding, it has been increasingly realized as a potential invasive species in the introduced habitats. Previous research indicated that the aqueous extracts of leaves and stems of R. typhina significantly inhibited the growth of tested plants in filter paper bioassay experiments. In the present study, the allelopathic potential of R. typhina on soil microbes, enzyme activities, soil nutrients and N transformation was investigated after 80 days' aqueous extract treatment. The aqueous extracts of leaves and stems of R. typhina were sprayed in 18 pots filled with the same soil (300 mL extracts per pot) with compression sprayer. Each extract concentration was sprayed in 6 pots. The concentrations of the extracts were 0.005 g/mL, 0.025 g/mLand 0.1 g/mL, respectively. Distilled water was sprayed in 6 additional pots, which was served as control (300 ml water per pot). Spray treatment was conducted at the beginning and repeated thirty days later during the experiment, and a rainproof shelter was put up above all the pots for two weeks after each spray treatment to avoid extract leaching by rain. Results showed that the aqueous extracts of R. typhina had effects on soil micro-ecosystem by (1) increasing the amount of bacteria and fungi in a concentration dependant manner; (2) significantly enhancing the enzyme activities of urease and acid phosphatase along with its increasing concentration but not of invertase; (3) accelerating the soil total C, total K, available N, available P and available K content, as well as the inorganic nitrogen supply through significantly increased soil mineralization, but not soil water content, pH, total N and total P. All these suggested that R. typhina could modify the composition of soil biota, the activities of soil enzyme and turnover of soil nutrition, which in turn may facilitate its invasion in the field. Although a large number of studies have demonstrated allelopathic effects of R. typhina extract in laboratory, our experiments with field soils help to put forward these allelopathic effects into the context of natural conditions. This study provided experimental-based evidence both for assessment of impacts of exotic plant R. typhina on soil micro-ecosystem and for prediction of invasive potential of the species.