Increases in multiple resources promote competitive ability of naturalized non-native plants

Invasion by non-native plants is frequently attributed to increased resource availability. Still, our understanding is mainly based on effects of single resources and on plants grown without competition despite the fact that plants rely on multiple resources and usually grow in competition. How multiple resources affects competition between native and non-native plants remains largely unexplored. Here, with two similar common garden experiments, one in China and one in Germany, we tested whether nutrient and light availabilities affected the competitive outcomes, in terms of biomass production, between native and naturalized non-native plants. We found that under low resource availability or with addition of only one type of resource non-natives were not more competitive than natives. However, with a joint increase of nutrients and light intensity, non-natives were more competitive than natives. Our finding indicates that addition of multiple resources could greatly reduce the niche dimensionality (i.e. number of limiting factors), favoring dominance of non-native species. It also indicates that habitats experiencing multiple global changes might be more vulnerable to plant invasion.