杂草五爪金龙对入侵地植物群落和土壤肥力的影响

五爪金龙（Ipomoeacairica）是粤东地区入侵性极强的外来杂草。在野外调查的基础上，选取5个被五爪金龙种群重度入侵地作为样地，并以5个相邻的无五爪金龙和其他外来植物入侵的地段作为对照，采用样方法对样地内的植物进行群落学调查并计算多样性指数，采集样地内的土壤样品进行土壤酶活性与理化指标测定，探讨五爪金龙入侵地生态因子间的相互作用关系，评价五爪金龙入侵对入侵地生态系统的影响。结果表明，与未入侵对照样地比较，五爪金龙入侵导致入侵地植物丰富度和多样性显著或极显著下降（P〈0．05或P〈0．01），对本土植物的排斥效应明显；除森林公园样地外，其余样地与土壤肥力密切相关的土壤蔗糖酶、脲酶、磷酸酶及硝酸还原酶4种酶活性均明显升高，增幅为26．91％～55．52％；五爪金龙种群的入侵明显提高了其入侵地土壤全氮、碱解氮、全钾及有效钾含量，降低了全磷、有效磷及有机质含量，且与对照样地间差异均达显著或极显著水平（P〈0．05或P〈0．01）。推测五爪金龙可能通过改变其入侵地的植物群落结构，改善土壤酶活性及养分水平，从而形成对自身生长发育和种群扩张有利的微生态环境。

Impacts of Invasion of Ipomoea cairica on Plant Community and Soil Fertility.

Ipomoea cairica （Convolvulaceae） , a perennial herbaceous liana, has become a major invasive weed with strong invasiveness in the east part of Guangdong Province, China. In a field investigation, five patches of land that had been heavily invaded by I. cairica were chosen as sample plots, and five adjacent patches of land free of I. cairica or other invasive plants were set as control group. Coenological survey of the plants in all the 10 plots was performed using the quadrat method for calculation of species diversity index, and soil samples were collected from the sample plots for analysis of soil enzyme activity and physico-chemical indices, so as to explore interactions between I. cairica and eco-factors of the invaded area and evaluate impacts of the invasion on ecosystem. Results show that the invasion decreased plant richness and diversity to a significant（ P 〈 0. 05 ） or an extremely significant extent（ P 〈 0. 01 ）, and its effect of crowding out native species was especially obvious. In all the sample plots, except for the forest park plot, the invasion increased the activities of invertase, urase, phosphatase and nitrate reductase （ NR）, which are closely related with soil fertility, notably by 26. 91% -55.52%. Besides, it increased the contents of TN, AN, TK and AK, but reduced the contents of TP, AP and OM in the soil, all to a significant （P 〈 0.05 ） or extremely significant extent （P 〈 0. 01 ）. The findings suggest that inva- sire weed I. cairica can alter the structure and composition of the community and improve soil enzyme activities and soil nutrient levels, thus forming a micro-ecoenvironment that is beneficial to development and growth of the plant per se and expansion of its population.