Assessing plant-soil feedbacks following biological invasions: Implications for restoration

Background/Question/Methods

Sericea lespedeza (Lespedeza cuneata), a nitrogen-fixing perennial legume, was introduced into the United States for forage production, land reclamation, and erosion control. Prolific seed production, high phenolic polymers, and high specific leaf area are some of the invasive traits which allow sericea to outcompete native plant species. However, little is known about belowground alterations following sericea invasion. Understanding potential plant-soil feedbacks may be a critical aspect of the restoration of native ecosystems. Therefore, we conducted both field and greenhouse studies to assess plant-soil feedbacks. Our field study assessed abiotic (N, P, K, and soil pH) and biotic (microbial communities using phospholipid fatty acid analysis) soil components. Soil was collected from areas with: 1) sericea invaded; 2) sericea removed using herbicide; and 3) non-invaded prairie. Our greenhouse study assessed plant-soil feedbacks indirectly through biomass production of six native and three non-native grasses planted into soil collected from the same sites as field study. Plants were grown for 16 weeks, at which time total biomass was determined. Percent root colonization by arbuscular mycorrhizal (AM) fungi was determined microscopically. We hypothesized plant-soil feedbacks function through altering soil nutrients and microbial communities and that plant growth would be enhanced in soils invaded by sericea.

Results/Conclusions

Our results indicate higher nitrogen and lower pH in soil from sericea invaded and sericea removed sites relative to native prairie. Also, phosphorus was higher in sericea invaded soil relative to native prairie soil. Phospholipid fatty acid analysis indicated lower AM fungal abundance in sericea invaded and in soils following sericea removal, relative to native prairie. Similarly, with the exception of switchgrass, native and non-native grass species had lower percent AM root colonization when grown in sericea invaded soil relative to native soil. Our hypotheses were supported as all nine species produced greater total biomass when grown in soils with a history of sericea invasion, as compared to production in soil from native sites. One year following the removal of sericea using herbicide did not result in restoration of native soil properties; there were few differences in soil nutrient availability and microbial communities in sites following chemical removal of sericea, compared to sites currently dominated by this invasive species. Further research is needed to address long-term shifts in soil properties following sericea removal to assess likelihood of successful establishment of native species.