Mikania sesquiterpene lactones enhance soil bacterial diversity and fungal and bacterial activities

Allelopathy is frequently invoked as important for successful invasion by non-native plants. Yet, the effects of specific phytochemicals of invasive plants on soil microbes remain unexplored. Here we used manipulative experiments and next generation sequencing analyses to investigate how sesquiterpene lactones (STLs) of invasive Mikania micrantha influence soil microbial diversity and activity. We showed that Mikania STLs significantly increase the regulation of soil microbial activity. Using the specific STL, dihydromikanolide, we also found that the presence of this phytochemical increased bacterial richness but decreased soil fungal richness. Dihydromikanolide also increased the abundance of beneficial soil bacteria and fungi associated with nutrient cycling and supply, while lowering pathogen abundance. Bacterial functional groups, such as those involved in carbon, nitrogen, phosphorus, and sulfur metabolism, was similar in experimentally treated dihydromikanolide soils and Mikania-invaded soils collected from the field, but significantly higher than those in uninvaded soils. Soil fungi, on the other hand, appeared to be less sensitive to dihydromikanolide than bacteria. Mikania STLs, in particular dihydromikanolide, substantially affect soil microbial structure and function. Our findings provide a new perspective for understanding the effects of invasive plants on soil microbial communities via allelopathy.