Benefits of microbial additions for the restoration of ecosystem functions relies on the ability of microbes to establish and spread in novel environments. However, little research has explored if microbes from undisturbed systems can spread and perform beneficial functions in degraded systems, or whether microbial spread and functional response depends upon the biotic and abiotic environment of target sites. Here we utilized transplanted tallgrass prairie monoliths to ask if the inclusion of prairie monoliths and their associated microbial communities alter the function of the recipient sites. Prairie monoliths, 1.5 meters wide, by 1.5 meters deep, were transplanted into recipient sites with different land use histories: recently disturbed, abandoned post-agricultural, and restored post-agricultural. For each monolith, soil cores were collected along a transect spanning across the monolith edge and into the recipient site. We used microbial extracellular enzyme activity (EEA), soil nutrient composition and microbial biomass carbon (MBC) to assess changes in microbial function of the recipient site in comparison to the prairie monolith. Given that nutrient environments of the recipient sites differ from those of the monoliths, we hypothesized that the strength of response at the monolith-recipient site edge should be greatest in sites more recently/heavily disturbed in comparison to the intact prairie, such that microbial function should be least similar across the edge interface in the most recently disturbed site and most similar in the restored post-agricultural site.
Results/Conclusions
Microbial EEA across monolith-recipient edges differed among recipient sites. However, contrary to our hypothesis, monolith-recipient edges did not follow consistent patterns based on disturbance trajectory. We identified four clear patterns in EEA across the edges: similar EEAs across the edge, distinct edges, a directionally resistant response, or a synergistic response (edge function not predicted by monolith or the recipient site). The specific pattern depended on both the recipient site and the enzyme of interest. In the recently disturbed site, changes in EEAs across the edge differed among BGase, NAGase, and phosphatase activity. In the post agricultural site, all three EEAs were distinctly different when moving from the prairie to the recipient site. Lastly, in the restored sites edges were either enzymatically distinctly or similar, depending on the specific EEA. Our results suggest that the efficacy of prairie monolith microbial communities and their functions to restore degraded systems may depend on the level of disturbance of the recipient site. This study highlights the functional role of soil microbes in enhancing ecological restoration.