Do novel weapons that degrade mycorrhizal mutualisms promote species invasion?
- 334 Downloads
Non-native plants often dominate novel habitats where they did not co-evolve with the local species. The novel weapons hypothesis suggests that non-native plants bring competitive traits against which native species have not adapted defenses. Novel weapons may directly affect plant competitors by inhibiting germination or growth, or indirectly by attacking competitor plant mutualists (degraded mutualisms hypothesis). Japanese knotweed (Fallopia japonica) and European buckthorn (Rhamnus cathartica) are widespread plant invaders that produce potent secondary compounds that negatively impact plant competitors. We tested whether their impacts were consistent with a direct effect on the tree seedlings (novel weapons) or an indirect attack via degradation of seedling mutualists (degraded mutualism). We compared recruitment and performance using three Ulmus congeners and three Betula congeners treated with allelopathic root macerations from allopatric and sympatric ranges. Moreover, given that the allelopathic species would be less likely to degrade their own fungal symbiont types, we used arbuscular mycorrhizal (AMF) and ectomycorrhizal (ECM) tree species to investigate the effects of F. japonica (no mycorrhizal association) and Rhamnus cathartica (ECM association) on the different fungal types. We also investigated the effects of F. japonica and R. cathartica exudates on AMF root colonization. Our results suggest that the allelopathic plant exudates impact seedlings directly by inhibiting germination and indirectly by degrading fungal mutualists. Novel weapons inhibited allopatric seedling germination but sympatric species were unaffected. However, seedling survivorship and growth appeared more dependent on mycorrhizal fungi, and mycorrhizal fungi were inhibited by allopatric species. These results suggest that novel weapons promote plant invasion by directly inhibiting allopatric competitor germination and indirectly by inhibiting mutualist fungi necessary for growth and survival.
KeywordsAllelochemicals Mycology Invasive species Fallopia japonica Polygonum cuspidatum Reynoutria japonica Rhamnus cathartica
We thank Dr. James Berry at the University of Buffalo for use of the Dorsheimer Laboratory/Greenhouse. We also thank two anonymous reviewers for helpful comments that improved the manuscript.
The data generated and analyzed for the current study are available in the SUNY Buffalo State Digital Commons [http://digitalcommons.buffalostate.edu].
PP conceived the ideas and designed methodology; PP collected the data; PP and RW analyzed the data; PP and RW led the writing of the manuscript. All authors contributed critically to the drafts and gave final approval for publication.
- Cipollini K, Titus K, Wagner C (2012) Allelopathic effects of invasive species (Alliaria petiolata, Lonicera maackii, Ranunculus ficaria) in the Midwestern United States. Allelopath J 29:63–75Google Scholar
- Coyle BF, Sharik TL, Feret PP (1982) Variation in leaf morphology among disjunct and continuous populations of river birch (Betula nigra). Silvae Genet 31:122–125Google Scholar
- Dallali S, Lahmayer I, Mokni R, Marichali A, Ouerghemmi S (2014) Phytotoxic effects of volatile oil from Verbena spp. on the germination and radicle growth of wheat, maize, linseed and canary grass and phenolic content of aerial parts. Allelopath J 34:95–105Google Scholar
- Duke SO, Dayan FE (2006) Modes of action of phytotoxins from plants. In: Reigosa MJ, Pedrol N, Gonzalez L (eds) Allelopathy: a physiological process with ecological implications. Springer, DordrechtGoogle Scholar
- Fox J, Weisberg S (2011) An R companion to applied regression. Sage, Thousand OaksGoogle Scholar
- Mitchell CE, Power AG (2006) Disease dynamics in plant communities. In: Collinge S, Ray C (eds) Disease ecology: community structure and pathogen dynamics. Oxford University Press, New YorkGoogle Scholar
- R Core Team Version 3.3.2 (2016) R: A language and environment for statistical computing. R Foundation for Statistical Computing, Vienna, AustriaGoogle Scholar
- Rabotnov T (1982) Importance of the evolutionary approach to the study of allelopathy. Sov J Ecol 12:127–130Google Scholar
- Schnitzer A, Muller S (1998) Ecology and biogeography of highly invasive plants in Europe: giant knotweeds from Japan (Fallopia japonica and F-sachalinensis). Revue d’écologie 53:3–38Google Scholar
- Sera B (2012) Effects of soil substrate contaminated by knotweed leaves on seed development. Pol J Environ Stud 21:713–717Google Scholar
- Smith SE, Read D (2008) Mycorrhizal symbiosis, 3rd edn. Academic Press, New YorkGoogle Scholar