Endophytes and invasive plants: How do endophytic fungi affect the growth, environmental tolerance and competitive success of invasive knotweed?

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Invasive plants are causing substantial ecological and economic problems, and it is therefore important to understand what makes these plants so competitive and dominant. There is now increasing evidence that soil microbes play a key role in many plant invasions. However, much of this evidence is rather coarse, and we often do not know which specific groups of microorganisms promote plant invasiveness. One particular group of soil microbes that is very diverse and widespread but still little understood are fungal endophytes of the order Sebacinales. These species are usually difficult to isolate and cultivate, and therefore opportunities for experimental tests of their ecological effects have so far been rare. Here, we propose to conduct a project that will test for the effects of fungal endophytes on the growth, environmental tolerance and invasion success of exotic knotweeds (Fallopia ssp.), some of the worst invasive plants worldwide. We will work with a Sebacinales strain, Sebacina herbamans, that was recently isolated in our group. We know from preliminary work that S. herbamans can strongly affect plant growth, that it occurs in invasive knotweed, and that we are able to experimentally inoculate knotweed with S. herbamans. We also know that some (unknown) soil microbes promote dominance of invasive knotweed over native plants. Our project will consist of three complementary work packages: (1) A lab experiment in which we will test the effects of the endophytes on the growth of invasive knotweed under highly controlled conditions. (2) A more ecologically realistic garden experiment where we will test the effects of endophytes on the competitive ability and invasion success of knotweed in native plant communities under a range of different environmental conditions. (3) A field survey in which we will attempt to associate endophyte diversities and abundances with knotweed invasion success in the field. In the first two work packages, we will experimentally inoculate knotweed plants with S. herbamans, and we generally verify the success of these inoculations, and quantify endophyte colonization rates, through microscopy and quantitative real-time PCR. In the last work package, we will use next-generation sequencing methods to compare not only the distribution of S. herbamans but more broadly the diversity of all root-associated fungi across a broad range of invasive knotweed populations. Our project will uniquely combine invasion biology with endophyte research, and we hope that it will provide novel insights both in the ecology of endophytes and the determinants of plant invasion success.