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Species coexistence depends on the comprehensive effects of biological properties and habitat heterogeneity. Based on a large-scale field survey (21°-35° N), we compared the differences on morphological and stoichiometric characteristics between the invasive aquatic species Alternanthera philoxeroides and the native co-occurring species Paspalum paspaloides , and examined the effects of environmental factors on such differences. The results showed that the coverage and importance value (IV) of A . philoxeroides were all significantly greater than P . paspa-loides (34.3% and 104.0%, respectively), whereas the height of P . paspaloides was significantly greater than A . philoxeroides (13.8%). Moreover, the total nitrogen concentration (TN) and N:P of A . philoxeroides were significantly greater than those of P . paspaloides (55.1% and 55.8%, respectively), whereas the total carbon concentration (TC) and C:N of P . paspaloides were significantly greater than those of A . philoxeroides (4.1% and 83.8%, respectively). A . philoxeroides coverage increased with the increases of longitude, and its abundance increased with the increases of water nitrate concentration and longitude, while its IV increased with the increases of water ammonium concentration. However, the coverage, abundance, and IV of P . paspaloides decreased with the increases of ammonium concentration. C:N of A . philoxeroides decreased with the increase of ammonium concentration. Increased mean annual temperature and mean annual precipitation increased C:N but decreased N:P of P . paspa-loides. The C:P of both species decreased with the increases of ammonium concentration and electrical conductivity. N:P of A . philoxeroides was little affected by environment. These results indicated that A . philoxeroides had greater coverage and N absorption capacity than P . paspaloides , and that enriched water nitrogen would aggravate the invasion of A . philoxeroides. Meanwhile, P . paspaloides improved its C-assimilate reserves and chose the growth competition strategy for resisting A . philoxeroides invasion under the superior hydrothermal conditions. Different responses to environmental changes contributed to their coexistence in aquatic ecosystem.

The article researched the effect of Iris pseudacorus L., Paspalum distichum L., Leersia hexandra Swartz, Ludwigia peploides and Hydrocotyle vulgaris on the nitrogen and phosphorus repression in sandy soil from lower reaches of Yangtze River and clay from stored littoral zone. The result indicated that plants had a significant inhibitory effect on total phosphorus release from sediment, with concentration in overlaying water below 0.02 mg·L -1 in Paspalum distichum L., Hydrocotyle vulgaris, Iris pseudacorus group, below 0.03 mg·L -1 in Leersia hexandra Swartz, Ludwigia peploides group; with release rate below 0.1 d -1 in Leersia hexandra Swartz and Ludwigia peploides group, below 0.05 d -1 in Paspalum distichum L., Hydrocotyle vulgaris , Iris pseudacorus group. While the plants were proved to aggravate total nitrogen release by accumulating in sediment, with concentration in overlaying water below 0.4 mg·L -1 in Paspalum distichum and Iris pseudacorus L. group; with release rate below 0.02 mg·L -1 . Root weight density, root length density, root surface area density were major factors, which increased the proportion of particles in sediment with diameter of below 50 μm, therefore decreased sediment resuspension against hydraulic disturbance; the root system also enriched total nitrogen in sediment and absorbed phosphorus from sediment. These five kinds of plants in terrestrial-aquatic transverse actually repressed nitrogen and phosphorus release from sediment in two ways mentioned above, Paspalum distichum L. and Iris pseudacorus L. possessed the best effect due to their developed root system, followed by Leersia hexandra Swartz and Hydrocotyle vulgaris , and Ludwigia peploides had the least effect.