Effect of an invasive plant on individual species and plant community structure through alteration of abiotic and biotic soil properties

Background/Question/Methods

Invasive plant species play a key role in the worldwide decline of native biodiversity and significantly alter the functioning of the ecosystems they invade. While much work has been devoted to understanding the direct effects of invasives on natives through competition, less is known about how invasives may affect natives via indirect effects such as the modification of abiotic and biotic soil properties. Understanding how invasives influence native plant communities through soil-mediated effects will provide important insights into the forces underlying plant community assembly and enlighten efforts to control invasives and restore native habitats. Here, we tested how an invasive nitrogen-fixing legume, Lespedeza cuneata, influenced native plants through the alteration of soil properties. We established a greenhouse experiment where two soil backgrounds (Lespedeza cuneata or native prairie) were crossed with two soil treatments (sterilized or live). Nine native species and L. cuneata were grown in individual pots in each of the four soil treatments to assess how above- and below-ground biomass was affected. Then, all ten species were grown together in communities to test if the individual response to the soil treatment predicted performance in communities, providing insights into how soil properties affect plant community assembly. 

Results/Conclusions

Grown individually, species performed better in L. cuneata than in native soil, producing 31% more aboveground and 27% more belowground biomass. This was likely driven by nutrients; K and NO₃ were greater in L. cuneata soil. Species also produced 44% more aboveground and 81% more belowground biomass in live than in sterile soil. Treatments interactively influenced aboveground biomass; when native soil was sterilized, there was a 40% decrease relative to live soil, whereas there was only a 23% decrease in L. cuneata soil. Species responded differently to the treatments in both magnitude and direction. Interestingly, L. cuneata’s response was the largest. It produced 850% more aboveground and 1050% more belowground biomass in live than in sterile soil. It also experienced a positive feedback when grown in its own soil, producing 65% more aboveground biomass than when grown in native soil. The rank order of biomass production was largely conserved when plants were grown together; species that received large benefits in the soil treatments outperformed those that received less benefit. These results suggest that soil properties can affect plant community composition and that soil remediation may be necessary to control L. cuneata.