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Researchers from Xishuangbanna Tropical Botanical Garden (XTBG) of the Chinese Academy of Sciences revealed that water availability combined with phosphorus limitation or herbivory created an advantage for alien plant species over natives.

Using two invasive plant species and five co-occurring native species, researchers conducted a large-scale common garden experiment in XTBG. They grew the plants alone, with intraspecific competition or with interspecific competition, and exposed the plants to three stressors, i.e., drought, phosphorus limitation and herbivory. The research is in the Journal of Environmental Management.

Researchers found that water availability was the key factor for the invasion success of alien plant species. Under well-watered conditions, the invasive plants significantly outperformed native species in competitive interactions as their competitive advantages were dramatically boosted by high water availability. These advantages disappeared under drought stress.

For common stressors like nutrient limitations or being eaten by herbivores, researchers found that they didn't necessarily hinder invasive plants. When combined with ample water, these stressors actually widened the performance gap between invaders and natives.

Moreover, researchers found evidence that the presence of non-specific herbivores (snails that eat both native and invasive plants) reduced the invaders' advantage linked to escaping natural enemies, but this was overridden by the strong positive effect of water combined with herbivory pressure.

"Our findings suggest that non-limiting water conditions, especially in combination with phosphorus limitation or herbivore presence, may allow the successful invasion of alien species. The dry season might be an effective period for removing invasive species," said Zheng Yulong from XTBG.