Two-year interactions between invasive Solidago canadensis and soil decrease its subsequent growth and competitive ability

Plant-soil interaction (PSI) has been implicated as a causative mechanism promoting plant invasions, and some mechanisms underlying PSI effects remain unclear. Here, we attempted to address how altered soil microbes and nutrients influence PSI effects. Soil was cultured by an invasive forb Solidago canadensis for two years. We conducted an experiment, in which S. canadensis and Chinese natives were grown either alone or together in control and cultured soils, and determined the growth of S. canadensis and five natives and the competitive ability of S. canadensis. We analyzed the microbial community composition and nutrients of two types of soils. Compared to the control soil, the soil cultured by S. canadensis decreased the subsequent growth of S. canadensis and five Chinese natives, as well as the competitive ability of S. canadensis against Chinese natives. Soil microbial community composition was significantly altered due to soil culturing. Total fatty acids, bacteria, Gram-negative bacteria and Gram-positive bacteria had no responses to soil culturing; fungi, aerobic bacteria and fungi/bacteria ratio significantly decreased with soil culturing; anaerobes and Gram-negative/positive bacteria ratio greatly increased with soil culturing. Soil nitrogen (N) dramatically decreased with soil culturing, whereas soil phosphorus (P) was unchanged. These results suggest that negative PSI effects may be linked to decreases in soil fungi, aerobic bacteria and soil N and increases in soil anaerobic bacteria and the ratio of Gram-negative/positive bacteria. Our findings provide an initial indication that S. canadensis-soil interaction alone could exhibit limited contributions to its success in the early stage of invasion.