Increasing soil heterogeneity strengthens the inhibition of a native woody plant by an invasive congener

Aims Environmental heterogeneity can influence biological invasions by altering the interspecific competition between native and invasive species. Soils are a key component of the abiotic environment that can vary in small scales. However, it is not clear how the mechanisms that patch size of soil heterogeneity mediates competition between native and invasive plants. Methods We grew invasive Rhus typhina and native Rhus chinensis in intraspecific (two seedlings of the same species per pot) and interspecific competition (one seedling of each of the two species per pot) with three different soil treatments: homogeneous (Ho) and two soil heterogeneous (He1 and He2) treatments. In He1 and He2 treatments, the soil consisted of loam and peat patches but different patch sizes, and in Ho treatment, the soil was a uniform mixture of the two types of soil patches. Results We found R. typhina had greater overall performance and belowground investment compared to R. chinensis and outcompeted R. chinensis in the interspecific competition regardless of soil heterogeneity. The strength of interspecific competition increased with increasing soil heterogeneity, such that soil heterogeneity amplified the superiority of R. typhina over R. chinensis. Moreover, R. chinensis were more plastic in phenotype than R. typhina, indicating phenotypic plasticity did not confer advantages to R. typhina over R. chinensis across various soil heterogeneity. Conclusions Soil heterogeneity can facilitate the invasion of R. typhina by enhancing the advantages over R. chinensis and altering interspecific competition. Phenotypic divergence rather than plasticity plays an important role in mediating interspecific competition.