Abstract
The important roles of plant-soil microbe interactions have been documented in exotic plant invasion, but we know very little about how soil mutualists enhance this process (i.e. enhanced mutualism hypothesis). To test this hypothesis we conducted two greenhouse experiments with Solidago canadensis (hereafter Solidago), an invasive forb from North America, and Stipa bungeana (hereafter Stipa), a native Chinese grass. In a germination experiment, we found soil microbes from the rhizospheres of Solidago and Stipa exhibited much stronger facilitative effects on emergence of Solidago than that of Stipa. In a growth and competition experiment, we found that soil microbes strongly facilitated Solidago to outgrow Stipa, and greatly increased the competitive effects of Solidago on Stipa but decreased the competitive effects of Stipa on Solidago. These findings from two experiments suggest that in situ soil microbes enhance the recruitment potential of Solidago and its ability to outcompete native plants, thereby providing strong evidence for the enhanced mutualism hypothesis. On the other hand, to some extent this outperformance of Solidago in the presence of soil microbes seems to be unbeneficial to control its rapid expansion, particularly in some ranges where this enhanced mutualism dominates over other mechanisms.
Highlights
Plant invasion is a threat to the conservation of ecosystems and an economic problem [1,2]
We know very little about enhanced mutualisms in the context of invasion [but see 8, 13], and it is not yet understood that how interactions between plants and soil microbes influence the competitive outcomes between invasive plants and native plants
Our results that soil microbes significantly enhanced emergence, growth, and competitive ability of Solidago provide strong evidence for the enhanced mutualism hypothesis. These findings suggest that the successful invasion of Solidago can in part be attributable to in situ soil microbes in its introduced range
Summary
Plant invasion is a threat to the conservation of ecosystems and an economic problem [1,2]. Invasive plants often perform better where they are introduced than where they are native, thereby shifting from minor components of communities at home to dominants where introduced [3] To explain this success a variety of nonmutually exclusive hypotheses have been proposed, like enemy release, evolution of novel traits, disturbance, novel weapons, and empty niches in invaded communities [4,5]. We know very little about enhanced mutualisms in the context of invasion [but see 8, 13], and it is not yet understood that how interactions between plants and soil microbes influence the competitive outcomes between invasive plants and native plants These interactions may depend on specific plants and specific soils, which in turn can alter the performance of plants [4,9,14]. How these interactions affect recruitment and competitive outcomes of invasive and native plants is very interesting, little is known about these aspects
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