入侵植物空心莲子草春季沿纬度变化的群落特征

Variation characteristics of an invasive Alternanthera philoxeroides community along latitudinal gradients in spring

纬度和季节是影响生物入侵的重要环境因子。以往对入侵植物空心莲子草Alternanthera philoxeroides的研究多集中于秋季入侵旺盛期,较少关注其春季的入侵表现(入侵态势、生物入侵-物种多样性关系等)。在中国22°~30°N范围内(广东、广西、湖南、湖北),共设置15个入侵样地与15个对照样地,探讨了春季陆生空心莲子草入侵群落沿纬度的变化特征及入侵对群落多样性(α物种多样性指数)、稳定性(Godron坐标值)的影响。结果表明:(1)春季空心莲子草入侵态势随纬度上升而加剧;入侵群落的Simpson多样性指数、Shannon多样性指数和Pielou均匀度指数与纬度显著负相关(P<0.05),而对照群落的这3个多样性指数与纬度显著正相关(P<0.05),2种群落的Patrick丰富度指数与纬度均无显著相关性。(2)在群落整体水平上,空心莲子草入侵造成本土群落的4个多样性指数显著下降,但小规模入侵(入侵盖度<25%)可以提高群落多样性;群落多样性指数随空心莲子草盖度的增加呈现出先上升后下降的单峰变化趋势;入侵样地和对照样地的Godron坐标值相接近,表明春季空心莲子草入侵并未对群落稳定性产生较大影响。(3)入侵区共记录植物45种,空心莲子草优势度最高;对照区共记录植物125种,优势种为结缕草Zoysia japonica,鹅观草Roegneria kamoji和葎草Humulus scandens;春季2种群落的植物在典型对应分析(CCA)排序图中沿纬度各自形成界限明显的3个分布区,入侵群落中物种分布的斑块化程度更高;空心莲子草靠近排序图的中心位置,表明它拥有较为宽广的纬度适应性。这些研究结果有助于预测外来入侵植物的群落动态,同时也有利于制定有效的入侵防治措施以保护本土生物多样性。

Latitude and season are the crucial environmental factors that affect biological invasions,such as Alternanthera philoxeroides,a malignant invasive weed native to South America and now widely found in several provinces of China.To explore variation characteristics of an A.philoxeroides community along latitudinal gradients and also to test its invasive effect on native plant diversity（α diversity indices） and community stability（Godron coordinate values） in spring,a latitudinal field survey was conducted in April with 15 invasive and 15 control plots selected in the 22°-30° N（spanning Guangdong,Guangxi,Hunan,and Hubei Provinces） terrestrial habitats of South China.Analysis included the ordination method of canonical correspondence analysis（CCA） based on species and environmental matrixes,as well as the curve regression between A.philoxeroides cover and α diversity indices（the Simpson,Shannon,Pielou,and Patrick indices）.Results showed that：1）species cover of Alternanthera philoxeroides increased with increasing latitude from 22°-30° N of China with the Simpson,Shannon,and Pielou indices all significantly and negatively correlated（P=0.012,r=-0.629;P=0.020,r=-0.591;P=0.024,r=-0.579,respectively） to latitude in the invasive community but significantly and positively correlated（P=0.041,r=0.533;P=0.020,r=0.591;P=0.010,r=0.641,respectively） in the control community.The Patrick index had no significant correlation with latitude.2） Invasion decreased species diversity at the whole community level（t=7.811,P〈0.001）.However,a slight invasion（A.philoxeroides cover25%）improved diversity,and with invasion cover increasing,species diversity indices were unimodal.In spring the Godron values between invasive and control communities were similar.3） Invasive plots recorded 45 plant species;whereas,control plots recorded 125 plant species.Plant species of these two community types formed three separate distribution areas in the CCA two-dimensional diagrams with the invasive community having a higher distribution density.A.philoxeroides was near to the central position indicating it had a wider latitudinal adaptability.These findings would be helpful for predicting dynamics of an invasive plant community and also very important for biological invasion control and native biodiversity protection.