Drought modifies the impacts of soil nutrient heterogeneity on native and alien plant growth in the absence of competition

Soil nutrient heterogeneity has generally been shown to benefit alien plants more than native ones. However, whether drought, an important aspect of climate change, alters these effects remains an open question. We used a greenhouse experiment with two alien and two native herbaceous plants. Plants were grown either alone or in a mixture (one alien plant and one native plant) in homogeneous and heterogeneous soils, with or without drought. We found that shoot mass of the native plant Alternanthera sessilis and the alien plant Celosia argentea were 27.4% and 76.6% lower in heterogeneous soils than homogenous soils, respectively, indicating a negative effect of soil nutrient heterogeneity. However, these negative effects were eliminated when the plants were grown alone in drought conditions. By contrast, soil nutrient heterogeneity, drought and competition had little effect on the growth of the native plant Achyranthes bidentata and the alien plant Amaranthus retroflexus. These results suggest that plant species differ in their growth responses to complex environmental changes. These results may have implications for understanding plant invasion outcomes in heterogeneous environments under global climate changes.