西双版纳外来入侵植物及其共存种叶片氮、磷化学计量特征

Foliar nitrogen and phosphorus stoichiometry of alien invasive plants and co-occurring natives in Xishuangbanna

诊断外来植物和本地种的资源利用方式是入侵生态学研究的热点问题。叶片氮(N)、磷(P)含量和化学计量特征可以反映受侵地区植物的N、P吸收能力和限制状况,为把握外来植物的入侵能力、为本地植物共存或消失的机制提供基础科学依据。该研究以我国西南地区典型外来入侵植物(飞机草(Chromolaena odorata)、紫茎泽兰(又叫破坏草,Ageratina adenophora))及其共存的本地植物为对象,探讨不同入侵条件下入侵种及其共存的本地植物的N、P利用策略。在云南西双版纳孔明山研究区,调查了无入侵条件下和飞机草与紫茎泽兰的不同入侵程度(按入侵种生物量比例划分)下的物种数量和生物量,分析了主要植物的叶片N、P含量和N:P值。结果显示:尽管群落地上生物量随飞机草和紫茎泽兰入侵程度增加而增加,但本地植物种数随飞机草和紫茎泽兰入侵程度增加而显著减少。飞机草与紫茎泽兰的叶片N、P平均含量无显著差异,但均显著高于无入侵条件下的本地植物以及与其共存的本地植物。两种入侵植物的N、P含量均随它们所占样方总生物量的比例增大而升高,本地植物N含量也有相似的变化趋势。当对比入侵和无入侵两类样方的同种植物N、P和N:P变化时发现多数本地种叶片P含量呈降低趋势,N含量和N:P呈升高趋势。根据叶片N、P绝对含量和N:P值及其随入侵的变化规律,推测入侵可能提高了植物的N可利用性,但本地植物仍然受N限制;入侵植物N:P值总体小于10与其具有相对于N吸收的较高的P吸收能力有关。该研究揭示了西南典型外来入侵植物具有较强的N、P吸收富集能力。

Aims How alien invasive plants and co-occurring native plants utilize nutrients is one of major issues in invasion ecology. Foliar nitrogen（N） and phosphorus（P） contents and stoichiometry can elucidate the uptake ability and limitation status of nutrients in plants, which provides basic knowledge for understanding the invading ability and co-occurrence or disappearance of plants. Methods Based on typical alien invasive plants（Chromolaena odorata, Ageratina adenophora） and native plants in southwestern China, this study focused on strategies of N and P utilization among invasive plants and native plants under different invasion conditions. The species compositions, aboveground biomass, leaf N and P contents and leaf N：P were investigated for plants in plots with no invasion and with different invasion extents（estimated by the plot-based percentage of invaders＇ biomass in total community） at Mt. Kongming in Xishuangbanna region, Yunnan Province, China. Important findings The species number decreased significantly with the invasion extent of both C. odorata andA. adenophora, although the aboveground biomass was greatly enhanced. Leaf N and P contents did not differ between the two studied invaders, but they showed significantly higher N and P levels than both co-occurring and only native species（P〈0.05）. Besides, leaf N and P contents of invaders increased with the invasion extent, and leaf N of native plants also showed an increasing trend with the invasion extent. When the influence of invasion was checked for the same species, leaf P contents decreased, whereas leaf N and N：P increased for most native plants under invasion. Based on the absolute foliar N and P contents, N：P values, we inferred that native plants were still limited by N, although N availability might be enhanced by invasion. Both invasive plants had leaf N：P values lower than 10, suggesting a higher P uptake relative to N uptake. All above results highlighted a higher N and P uptake of typical alien invasive plants in southwestern China.