The Impacts Of Latitudinal Gradients And Environmental Heterogeneity On The Invasion Of Alternanthera Philoxeroides

With the rapid economical globalization and climate change, some species have directly or indirectly been introduced into a new environment, causing serious damage to environment, ecosystem health and global biodiversity. Under climate change, alien invasive species may pose new threats environments.In our study, we took the invasive plant alligator weed, Alternanthera philoxeroides as an example to examine the effects of latitudinal gradient and habitat heterogeneity on the impact of plant invasion. We totally set 126 terrestrial and aquatic plots (10 m×10 m) through a consecutive field investigation spanning three years (2012s-2014s) along a large latitudinal latitude (N21°-N37°) in 10 Provinces in China. We used the TWINSPAN (Two-way Indicator Species Analysis), canonical correspondence (CCA) and redundancy analysis (RDA) to analyze the invader performance, species composition, community diversity, and the effects of habitat heterogeneity. We also conducted experiment with wanning and nitrogen addition, to examine the effect of climate warming and nitrogen deposition on A. philoxeroides to predict its invasion under global change. The main research conclusions were as follows:1. We totally recorded 235 plant species in A. philoxeroides community from 126 plots which were belonged to 60 families and 183 genera. The families with higher species richness were Poaceae (30 genera 35 sp), Asteraceae (19 genera 28 sp), Labiatae (13 genera 15 sp), Polygonaceae (3 general 3 sp), Leguminosae (10 general 0 sp), Cyperaceae (5 genera 10 sp). Digitaria sanguinalis was the main accompanying species of terrestrial A. philoxeroides. Using TWINSPAN we found 10 associations in terrestrial A. philoxeroides community with "A. philoxeroides+D. sanguinalis" as the main type.In aquatic habitats Paspalum paspaloides was the main accompanying species, and "A. philoxeroides+P. paspaloides+Oenanthe javanica" was the main aquatic type in a total of 6 communities.2. Surveys along the latitudinal gradients showed that A. philoxeroides invasion in terrestrial habitat increased with latitude rising between N21°-N35°, then, it began to decline. A small scale invasion could improve community diversity, but A. philoxeroides reduced community alpha species diversity sharply when its invasion cover exceeded a certain threshold (7%). Canonical correspondence analysis indicated that the plant species in invasion community gradually switched from mesophyte to hygrophyte with latitude rising. All the four alpha diversity indices and Godron community stability declined with latitude increasing.3. Compared to terrestrial habitat, the species composition of aquatic A. philoxeroides community was relative simple. Among four diversity indices, the Patrick richness index and Shannon-Wiener diversity index of aquatic community were all lower than terrestrial community, but aquatic invasion stability was higher than that in terrestrial habitats. The invasion of A. philoxeroides in aquatic habitat also had the "first promoting then suppression" effect on native plant diversity. The Pielou evenness index and aquatic native diversit were mostly vulnerable for A. philoxeroides invasion. The occurrence of Agasicles hygrophila in aquatic habitat significantly increased with latitude rising. Redundancy analysis (RDA) indicated that the environmental factors mainly determining species diversity and plant species’ distributions of terrestrial A. philoxeroides community were ammonia nitrogen, nitrate nitrogen and latitude, respectively. For aquatic A. philoxeroides community, the main factors were longitude, ammonia nitrogen, nitrate nitrogen, respectively.4. Field experiments showed that warming promoted the accumulating of A. philoxeroides’belowground biomass when it was planted with the native D. sanguinalis, but A. philoxeroides" growth rate (biomass) decreased by the increasing richness of accompanying species. Nitrogen addition could significantly improve D. sanguinalis’’biomass but reduce A. philoxeroides’biomass in mixed cultures. With the increasing of D. sanguinalis’density, there was more significantly negative effect of nitrogen enrichment on A. philoxeroides. Relative yield (RY) indicated that warming increased A. philoxeroides’interspecific competition but nitrogen increased D. sanguinalis’competition. Based on these results, we could predict that under the background of rapid global environment change in the future, warming may accelerate A. philoxeroides invasion while nitrogen deposition will slow down this invasion progress.In conclusion, our study clearly showed that the latitudinal gradient and habitat heterogeneity could significantly affect A. philoxeroides’performance and its impact on community structure and species diversity. The results have important implications for predicting the invasive A. philoxeroides’occurrence under global environment change and for preventing and managing invasive plants in the future.