水陆生境和氮沉降对香菇草(Hydrocotyle vulgaris)入侵湿地植物群落的影响

大气氮沉降对湿地外来植物入侵的影响已成为生态学研究的热点之一。选用梭鱼草(Pontederia cordata)、水菖蒲(Acorus calamus)、黄花鸢尾(Iris wilsonii)和粉绿狐尾藻(Myriophyllum aquaticum)模拟湿地植物群落,设置有无香菇草入侵、水生和陆生生境(水位分别为15 cm和0 cm)及有无氮沉降处理(15 g N m~(-2)a(-1)和0)交叉组成的8种处理组合,进行为期70d的温室控制实验,以分析水陆生境及氮沉降对香菇草入侵湿地植物群落的影响。结果表明:(1)水生生境下,香菇草的总生物量、叶生物量、叶片数和节点数与陆生生境相比显著降低;水生生境下氮沉降处理对香菇草各指标无显著影响,陆生生境下氮沉降处理的香菇草叶片数、节点数显著多于无氮沉降处理。(2)实验周期内氮沉降和香菇草入侵没有对群落的多样性指数及群落内4种湿地植物的生物量产生显著影响;水生生境下植物群落的总生物量及梭鱼草和粉绿狐尾藻的生物量与陆生生境相比显著提高。(3)水生生境下香菇草的相对优势度相比陆生生境下显著下降;氮沉降只在陆生生境下显著提高了香菇草的相对优势度。因此,香菇草向水生生境扩散和入侵的能力不强,其入侵在短时间内对湿地植物群落影响较小。研究结果可以为入侵植物生态学研究提供案例借鉴。

The effects of habitat type and nitrogen deposition on the invasion of Hydrocotyle vulgaris in wetland plant communities

Biological invasions can have strong negative impacts on native biodiversity and ecosystem functions. Water level and nitrogen deposition are important factors that can affect plant invasions in wetlands. Hydrocotyle vulgaris of the Apiaceae family is a perennial herb introduced to China that can be established and multiplied rapidly in a variety of habitats. Although it is considered highly invasive, few studies have tested the effects of habitat and nitrogen deposition on invasion by H. vulgaris. We designed a greenhouse experiment to test the following hypotheses: nitrogen deposition promotes invasion by H. vulgaris in both flooded and unflooded habitats; and invasion by H. vulgaris affects the growth of native plants in both flooded and unflooded habitats. Four perennial, herbaceous species were selected to measure the competitive effect of H. vulgaris in wetland communities:Pontederia cordata, Acorus calamus, Iris wilsonii, and Myriophyllum aquaticum. These are among the most common species that co-exist with H. vulgaris in the XiXi National Wetlands Park. We assessed two levels of invasion by H. vulgaris (present or absent) with two levels of flooding (water levels of 0 cm [not flooded] and 15 cm [flooded]) and two levels of nitrogen deposition (0 and 15 g N/m² as NH₄NO₃). We measured the stem length, leaf area, numbers of leaves and nodes, and relative dominance of H. vulgaris; and the biomass and diversity of the other four plant species. Compared to the non-flooded treatment, the total mass, leaf mass, numbers of leaves and nodes, and relative dominance of H. vulgaris were significantly lower in the flooded treatment. Nitrogen deposition significantly increased the numbers of leaves and nodes in the unflooded treatment. Total mass of the other plant species combined and of P. cordata and M. aquaticum individually were significantly greater in flooded than in unflooded treatments. Neither nitrogen deposition nor the presence of H. vulgaris affected the biomass or diversity of the other four plant species. These results suggest that invasion by H. vulgaris might not exert significant adverse effects on native wetland plant communities in the short term and that flooding might decrease invasion by H. vulgaris. Control of the water level might also be a helpful measure to control H. vulgaris invasion in wetlands.