Neiff Juan José, Casco Sylvina Lorena, Poi de Neiff Alicia
Consejo Nacional de Investigaciones Cientificas y Técnicas, Centro de Ecologia Aplicada del Litoral, C.C. 291, Corrientes, Argentina.
Rev Biol Trop. 2008 Jun;56(2):613-23. doi: 10.15517/rbt.v56i2.5612.
Floodplain lakes are especially dynamic due to the irregular flow regime of the Paraná River and its location along the geomorphologic gradient between the lakes and the river. The response of Eichhornia crassipes (Mart.) Solms (one of the most frequent aquatic plant) was studied in two floodplain lakes with different flooding regimes. Samples were taken between March 1997 and December 2001 on 13 different hydrologic conditions during prolonged hydrologic connection and prolonged hydrologic isolation. Leaf height, leaf density, biomass and nutrient content of the mature leaves of E. crassipes were measured and related to water level fluctuation and the hydrologic connectivity. The lake more connected with the main channel had a long lasting inundation phase. In this condition the surface area covered by water increased more than three times compared to prolonged hydrologic isolation condition. As river water entered the floodplain lakes, dissolved inorganic nitrogen increased to high values, especially NO3-, whereas the isolation condition was characterised by a decrease in NO3 concentrations to undetectable levels. Compared to plants growing in the more isolated lake, those growing in the more connected lake had a significantly lower leaf density, longer leaves, less root biomass and lower ratio between below-ground and above-ground biomasses. However, total and leaf biomasses were not significantly different between sites. In each lake, differences in leaf height, leaf biomass and root biomass between prolonged hydrologic connection and isolation, as well as the insignificant relationship between leaf size and leaf density, indicate that the morphological traits of E. crassipes respond to pluri-annual water level fluctuations. The highest nutrient concentration in mature leaves was registered at the end of the prolonged hydrologic connection in the more connected lake. During the prolonged isolation, leaves had more lignin and a higher L:N ratio than at high waters, at the same sites. The success of E. crassipes in occupying habitats subjected to wide and erratic fluctuations in water level, such as the Parana River floodplain, appears to be related to its ability to modify morphological traits according to water level.
由于巴拉那河不规则的水流状态及其位于湖泊与河流之间地貌梯度上的位置，河漫滩湖泊具有特别的动态性。在两个具有不同洪水状况的河漫滩湖泊中研究了凤眼莲（Eichhornia crassipes (Mart.) Solms，最常见的水生植物之一）的响应情况。在1997年3月至2001年12月期间，在长时间水文连通和长时间水文隔离的13种不同水文条件下采集样本。测量了凤眼莲成熟叶片的叶高、叶密度、生物量和养分含量，并将其与水位波动和水文连通性相关联。与主河道联系更紧密的湖泊有一个持续时间长的淹没阶段。在这种情况下，与长时间水文隔离条件相比，被水覆盖的表面积增加了三倍多。随着河水进入河漫滩湖泊，溶解无机氮增加到很高的值，尤其是NO3-，而隔离条件的特征是NO3浓度降低到无法检测的水平。与生长在隔离程度更高湖泊中的植物相比，生长在联系更紧密湖泊中的植物叶密度显著更低、叶片更长、根生物量更少且地下与地上生物量之比更低。然而，不同地点之间的总生物量和叶生物量没有显著差异。在每个湖泊中，长时间水文连通和隔离之间叶高、叶生物量和根生物量的差异，以及叶大小与叶密度之间不显著的关系，表明凤眼莲的形态特征对多年水位波动有响应。在联系更紧密的湖泊中，长时间水文连通结束时成熟叶片中的养分浓度最高。在长时间隔离期间，相同地点的叶片比高水位时含有更多木质素和更高的L:N比。凤眼莲成功占据水位波动大且不稳定的栖息地，如巴拉那河河漫滩，似乎与其根据水位改变形态特征的能力有关。
