入侵植物南美蟛蜞菊对NH+4-N和NO-3-N的响应

为了阐明外来入侵植物是否对不同形态氮源具有偏向选择性，研究了外来入侵植物南美蟛蜞菊（Wedelia trilobata）对2种不同形态氮源（NH+4/NO-3）的响应. 结果表明:（1）南美蟛蜞菊在全铵营养条件下的生物量显著高于全硝营养条件；（2）南美蟛蜞菊在全铵营养和全硝营养条件下总生物量和叶绿素含量（SPAD）均显著高于本地种蟛蜞菊（Wedelia chinensis）；（3）在全铵营养条件下，南美蟛蜞菊根部游离氨基酸含量显著高于蟛蜞菊；与蟛蜞菊相比，在全硝营养条件下南美蟛蜞菊根部和叶部的硝酸还原酶活性显著升高，硝态氮累积显著减少. 结果表明南美蟛蜞菊为喜铵植物，具有较强的铵态氮同化能力和硝态氮还原能力，对全铵或全硝的极端环境有较强的调节能力，这可能是南美蟛蜞菊入侵成功的重要机制之一，也说明NH+4-N占优势的土壤生境更易遭受南美蟛蜞菊入侵，可能是南美蟛蜞菊在定居和扩散进程中的一个重要变化.

Responses of the Invasive Plant Wedelia Trilobata to NH4+-N and NO3--N

The response of invasive plant Wedelia trilobata to two different nitrogen forms (NH+4/NO-3) were investigated. The results showed that (1) W.trilobata had significantly larger biomass under the condition of the whole ammonium nutrition than under the condition of the whole nitrate nutrition; (2) Whether W.trilobata under the condition of the whole ammonium nutrition or nitrate nutrition, its total biomass and chlorophyll content (SPAD) was significantly higher than the native plant species Wedelia chinensis; (3) Under the condition of whole ammonium nutrition, free amino acid in roots of W.trilobata increased significantly compared to W.chinensis, whereas under the condition of the whole nitrate nutrition the activity of nitrate reductase in both roots and leaves of W.trilobata also increased significantly but its nitrate accumulation decreased significantly compared to W.chinensis. It was concluded that W.trilobata might be of a plant absorbing NH+4-N preferentially. Compared to the native species, W.trilobata had higher ability of ammonium assimilation and tolerance, and nitrate deoxidization, and also had stronger ability of adaptation to the extreme environment, which might be one of the important mechanisms why W.trilobata became invasive. It was implied that the soil habitats where NH+4-N was dominant might be vulnerable to be invaded by invasive species. This might be a crucial change of invasive plants during the process of settlement and spread.