Consequences of aboveground invasion by non-native plants into restored vernal pools do not prompt changes in belowground processes

Given the frequent overlap between biological plant invasion and ecological restoration efforts it is important to investigate their interactions to sustain desirable plant communities and modify long-term legacies both above and belowground. To address this relationship, we used natural reference, invaded, and constructed vernal pools in the Central Valley of California to examine potential changes in direct and indirect plant effects on soils associated with biological invasion and active restoration ecosystem disturbances. Our results showed that through a shift in vegetation composition and changes in the plant community tissue chemistry, invasion by non-native plant species has the potential to transform plant inputs to soils in vernal pool systems. In particular, we found that while non-native litter decomposition was driven by seasonal and interannual variability, associated with changes in precipitation, the overall decomposition for non-native litter was drastically lower than native species. This shift has important implications for long-term alterations in plant-based inputs to soils in a negative feedback to nutrient cycling. Moreover, these results were independent of historic active restoration efforts. Despite the consistent shift in plant litter decomposition rates and community composition, we did not detect associated shifts in belowground function associated with invasion by non-native plants. Instead, soil C:N ratios and microbial biomass did not differ between invaded and reference naturally occurring pools but were reduced in the manipulated restored pools independent of invasion levels. Our results suggest that while there is an observed invasive positive feedback aboveground, this trajectory is not necessarily represented belowground and restoration legacies were still dominant ten years after practices were applied. Restoration practices that limit invasive plant feedbacks and account for soil legacy recovery, therefore offer the best solution for disturbed ephemeral ecosystems.

Methods
All data presented here were collected associated from a long-term restoration vernal pool field site located on Travis Air Force Base, in Solano Co. California. Field samples  including plant materials and soils were collected and processed as described in the associated paper.