Managing the soil microbiome to overcome legacy effects of beachgrass invasion

Background/Question/Methods

Point Reyes National Seashore (PRNS) contains some of the highest quality remaining coastal dune habitat in the USA. However, it has been seriously threatened by the encroachment of European beachgrass and freeway iceplant. PRNS embarked in 2001 on an ambitious restoration program, removing 110 hectares of invaded habitat from former native dune habitat over the past 20 years using mechanical and herbicide interventions. Although the beachgrass was successfully suppressed, the original dune habitats were never restored. Standing dead beachgrass remains intact up to 8 years after herbicide treatment. Due to the important role of soil microorganisms and extracellular enzymes in decomposition, we hypothesized that the legacy effect from beachgrass invasion inhibiting the activities of decomposers lead to current decomposition deficiency. We collected soil samples from the sites that were uninvaded, treated with herbicide 2, 4, and 8 years ago, and invaded but not treated. Soil microbial communities and extracellular enzymes were investigated using amplicon sequencing and microplate fluorescence assays, respectively.

Results/Conclusions

Compared to both uninvaded sites and invaded but untreated sites, herbicide-treated sites had a lower abundance of putative wood saprotrophic fungi and lower activities of enzymes involved in sugar, protein, and xylose degradation. In conjunction with our previous studies on soil chemical properties and soil microbial communities across invasion gradients, the legacy effects of both beachgrass invasion and herbicide treatment require additional attention. As the next step, we will verify our observation and investigate if soil microorganism transfer will be a solution to decomposition deficiency and legacy effects of beachgrass invasion.