Arbuscular mycorrhizal fungi facilitate growth and competitive ability of an exotic species Flaveria bidentis

•A study was carried out to determine the impact of mycorrhiza on invasion.•Higher AMF colonization on exotic Flaveria bidentis roots vs native Setaria viridis.•Flaveria bidentis outcompetes S. viridis upon AMF colonization.•AMF-inoculation provides competitive advantages to exotic species.

Understanding of mechanisms through which arbuscular mycorrhizal fungi (AMF) facilitate establishment and growth of exotic species is important in invasion ecology. We have poor understanding of mechanisms that mediate positive or negative impact of AMF to exotic or native species. We ask whether the quantitative and or qualitative differences in the AMF colonization to exotic Flaveria bidentis and native Setaria viridis provide competitive advantage to the invader over native species. Flaveria bidentis, a native of South America, is an aggressive invader in North China. Native S. viridis is widely distributed in farmlands, roadsides and wastelands, and also found in Flaveria bidentis invaded areas. We hypothesize that exotic species alter AMF composition, which facilitate the establishment and growth of exotic species and reduces the competitiveness of native species. Experiments were carried out to: (i) quantify AMF colonization in roots of field-grown F. bidentis or S. viridis, (ii) isolate DNA sequences of AMF species from roots and soils of exotic F. bidentis and native S. viridis to carry out phylogenetic studies, and (iii) study the effect of AMF Rhizophagus intraradices spores on the physiological performance traits of both exotic F. bidentis and native S. viridis. Our results suggest that certain AMF clones had higher colonization (85%) in roots of F. bidentis than S. viridis (21.1%). AMF-inoculation (130 spores per 100 g soil) enhanced the net photosynthetic rate in the native S. viridis when grown in monoculture but reduced its net photosynthetic rate when grown in competition with exotic F. bidentis. A lower corrected index of relative competition intensity in exotic F. bidentis, and higher levels of foliar nutrient accumulation was observed in response to AMF inoculation than native S. viridis. We show that higher AMF colonization in F. bidentis provides competitive advantage over native S. viridis. This study is important because it establishes the impact of AMF colonization on physiological and ecological performance of the invader.