A Comparative Biogeographical Study On The Mechanism Of The Enhanced Competitive Ability In An Invasive Plant

Why invasive plants are often more competitive in their introduced range than in their native range has been being a central question in understanding plant invasive biology. Researchers have offered various hypotheses to explain the increased competitive ability of invasive plant species. One of the most important hypothesis is the Novel Weapon Hypothesis which refers that allelopathy from invasive plant could promote the invasive plant’s competition against native competitors. Arbuscular mycorrhizal fungi (AMF) are important and ubiquitous soil microorganisms that form symbioses with many plant species in terrestrial ecosystems. It also plays an important role in plant successful invasion. The comparative biogeographical approach is often used to evaluate the various mechanisms explaining the reason(s) behind any successful plant invasion. Nowadays, less study has used comparative biogeographical approach to evaluate the role of allelopathy and mycorrhizal symbiosis played in the enhanced compatitive ability of invasive plant.Here, in our study, we used invasive plant Solidago canadensis as model plant, and used a comparative biogeographical approach and common garden experiments to evaluate (1) the relationship between allelopathy and the enhanced competitive ability in invasive plants;(2) the relationship between mycorrhizal symbiosis and the enhanced competitive ability in invasive plants;(3) the relationship between the interaction of allelopathy and mycorrhizal symbiosis and the enhanced competitive ability in invasive plants. The main results obtained were as bellows:1Enhanced allelopathy in invasive S. canadensis may promote its competitive abilityThe hight and biomass of S. canadensis from invasive range China was higher than that from the USA. Allelochemical contents (total phenolics, total flavones and total saponins) and allelopathic effects were greater in S. canadensis from China than those from the USA. Inhibition of Kummerowia striata germination using S. canadensis extracts or previously grown in soil was greater using samples from China than from the USA. The competitive ability of S. canadensis against K. striata was also greater for plants originating from China than those from the USA. Allelopathy could explain about46.1%of the difference.2Invasive S. canadensis colonized genetically similar AMF community in invasive and native ranges, and probably through enhanced AMF dependence to increase its competitive ability in their introduced rangeMDS analysis showed that even though the AMF community in the soils differed greatly from two continents,S. canadensis had similar AMF assemblages in native and invasive ranges. When S. canadensis from USA and China planted in the same environment from both ranges, the differences of AMF communities in S. canadensis from USA and China were non-significant (P>0.05). Four AMF phylotypes were always shown and most abundant in all roots samples (43%of AM fungal sequences belonged to these four AMF phylotypes) of S. canadensis from both USA and China.Invasive S. canadensis from China had higher AMF dependence than S. canadensis from USA. The higher AMF dependence promoted the growth and15N absorption. Interestingly, we found AMF dependence mediated the competition of S. canadensis from USA and China differently. AMF enhanced the growth and competitive ability of S. canadensis originating from China but did not enhance the growth and competitive ability of S. canadensis from USA.3Allelopathy from invasive S. canadensis may promote competition indirectly via promoting mycorrhizal symbiosisThe decreased concentrations of the main allelochemicals in soil changed the AMF community in S. canadensis roots. Allelochemicals from invasive S. canadensis did not promote the AMF Glomus versiforme and G. geosporum but promoted G. mosseae and G. diaphanum in the soil and also in S. canadensis roots. Allelopathy reduced S. canadensis competitive ability in the presence but not in the absence of AMF.