Growing on patch boundaries of heterogeneous soils promotes root growth but not the total biomass of naturalized alien and native plants

Abstract

Background and aims: Soil heterogeneity has been found to promote plant invasion, as many naturalized alien species benefit more from nutrient-rich patches than native species do. However, it remains unclear whether naturalized alien species also benefit more from growing on patch boundaries than from growing in the patch centres of heterogeneous soils. Methods: We experimentally tested whether the planting position changes the effect of soil heterogeneity on the growth of native and naturalized alien plants. We created pots with heterogeneous soils consisting of patches of sand, peat-based potting substrate (peat) and a 1:1 sand-peat mixture, and homogenous soils consisting of the mixture only. In each pot, we planted three plants of one of five native or five naturalized alien species, either on the boundaries between or in the centres of the soil patches. Results: Individual plant growth increased when the plant had direct access to the peat patches. This positive effect of peat on plant growth tended to be more pronounced for the naturalized alien species than for the natives. The populations of naturalized alien species also tended to benefit more, in terms of total biomass, from soil heterogeneity than the natives did. Belowground biomass of the plant populations, was not significantly affected by soil heterogeneity, but was larger when plants grew on the patch boundaries instead of in the centres. Conclusion: Our study suggests that soil heterogeneity promotes the growth of naturalized alien plants over native plants. Moreover, being positioned on the boundary of strongly contrasting patches might provide benefits to plant growth.