Agricultural land-use legacies shape plant-soil interactions: Mechanisms underlying invasive plant performance in human-modified landscapes

Background/Question/Methods

Although historic land-use patterns are known to shape the diversity and distribution of invasive plants, mechanistic links between land-use legacies and present-day invasion success are largely unknown. Here, we evaluate how agricultural land-use legacies shape plant-soil interactions as a putative mechanism underlying invasive plant performance in human-modified landscapes. We conducted this experiment in a controlled greenhouse environment using plants and soil collected from 16 remnant and post-agricultural sites situated in the upland longleaf pine savannas of Fort Bragg, North Carolina. We altered the biotic condition of the soil collected from each remnant and post-agricultural site by imposing a soil treatment with three levels: control, soil sterilization, and microbial inoculation. Individuals of two native (Lespedeza capitata and Tephrosia virginiana) and three non-native (Crotalaria spectabilis, Lespedeza bicolor, and Lespedeza cuneata) nitrogen-fixing legume species were grown separately under each combination of land-use category and soil condition. After four months of growth, plant responses to treatment combinations were evaluated in terms of root nodulation and above- and belowground biomass production.

Results/Conclusions

For each study species, biomass production and nodulation rates were greater in soil collected from remnant than from post-agricultural sites. For the remnant sites, inoculation had negligible effects on native and non-native plant responses, but soil sterilization greatly reduced plant biomass production and root nodulation. In contrast, plant responses to soil condition were more variable among plant species grown in soil collected from post-agricultural sites. However, among these sites, soil sterilization generally elicited weak plant responses, and soil inoculation tended to increase plant biomass production and root nodulation. Our results suggest historic agriculture can lead to persistent changes in soil microbial communities and that the relative lack of beneficial microbes (e.g. rhizobia) may serve to limit the performance of both native and non-native legume species in post-agricultural habitats.