Long-term legacies and short-term changes in soil microbial community structure and function after Japanese barberry invasion

Exotic invasive plants are well known but poorly understood drivers of change in plant community structure and ecosystem functions. Plants are particularly strong determinants of soil microbial community structure and function, and exotic invasive plants may alter soil microbial communities in ways that feed back to influence the plant community. Recent work has suggested that invasive species may promote their own growth through positive plant-soil feedback, but little is known about the temporal dynamics of feedback during invasion. In an ongoing study, we manipulated the understory plant community in invaded and uninvaded areas of Allamuchy State Forest in northwest New Jersey. We measured the response of soil microbial communities over time to invasion by Japanese barberry, as well as the legacy effect of the previous plant community on microbial community structure and function. Manipulation of the understory plant community did not produce significant changes in the soil microbial community structure after one year, though it did significantly change net ammonification rates after two years (p<0.05). In contrast, the legacy effect of the previous understory community was a strong determinant of soil community structure after one year. The soil microbial community structure in previously invaded sites was still significantly different from previously uninvaded sites after one year (Wilk’s λ < 0.001), despite manipulating the plant understory. Similarly, two years after replacing invasives with natives, the legacy effect of invasion was still a strong determinant of net nitrification (p<0.001), net ammonification (p = 0.001), and the enzyme activities of acid phosphatase, phenol oxidase, ß-glucosidase, and chitobiase (p<0.05). These results suggest that changes in soil microbial community structure and function do not occur as quickly as invasion does, but legacy effects after restoration may strongly influence soil microbial communities.