Abstract: Global warming has, in many cases, accelerated the spread of introduced invasive plant species, while the species diversity can produce bio-resistance to the invasive species. Exploring the effects of climate warming-biodiversity interactions on biological invasions is beneficial for predicting invasion outcomes and formulating effective bio-control measures. Here, 59 sampling plots were selected across a geographic range from 21° N to 37° N in China, the objective was to study the relationships between species diversity and invasiveness of the alien weed Alternanthera philoxeroides in field community. Temperature and species diversity data were examined in artificial community, to examine the effects of increased temperature and native plant species diversity on A. philoxeroides invasion. It was found that: 1) Values of Shannon-Wiener diversity index within A. philoxeroides communities ranged from 0-2.434, and the coverage and branches of A. philoxeroides both significantly decreased as species diversity increased, while the latitude and latitude×species diversity interaction did not significantly affect the invasiveness. 2) Increased temperature was associated with a significant reduction of both height and maximum stem length of A. philoxeroides, as well as the heights of resident plants Digitaria sanguinalis, Sonchus oleraceus and Eleusine indica. Increased species diversity significantly reduced the height, numbers of clonal ramets and maximum stem length of A. philoxeroides, thus weakened its invasiveness. An interaction between latitude and species diversity significantly increased A. philoxeroides branches when growing in the monoculture, and a species-specific interaction with latitude significantly shortened the maximum stem length of S. oleraceus in the artificial community. 3) Increased temperature had no significant effect on either A. philoxeroides or native plant species biomass. A. philoxeroides biomass decreased with increased species diversity, but its root/stem ratio increased, indicating that A. philoxeroides allocated relatively more resources to underground storage in response to the interspecies competition. In conclusion, these results indicate that a higher biodiversity is helpful for reducing A. philoxeroides invasiveness, but increased temperature may weaken the competitive resistance of resident plants. Thus, protection of native plant species diversity should receive more attentions to counteract the potential facilitating effects of global warming on the spread of A. philoxeroides.

Key words: biological invasions, Alternanthera philoxeroides, warming, latitudinal gradient, species diversity