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Arbuscular mycorrhizal fungi enhance spotted knapweed growth across a riparian chronosequence


Arbuscular mycorrhizal fungi (AMF) mediate nutrient uptake that accelerates plant growth and reproduction. Thus, AMF may promote plant invasions often observed along rivers. We assessed the importance of AMF in improving growth of the invasive species, spotted knapweed (Centaurea stoebe), during succession of riparian vegetation along a flood plain in Montana, USA. We grew spotted knapweed with and without AMF in soils collected from riparian sites ranging from 1 to 72 years old and measured the plant’s growth response to AMF. We observed variability in relative effects of AMF, with greatest growth benefits in recently deposited alluvial sediments. We then separated effects of soil and inoculum source by growing spotted knapweed with soils and inocula collected from young or old sites and found that growth responses were greatest in young soils regardless of inoculum source. Our results demonstrate that AMF directly benefit growth of spotted knapweed, especially in soils that typify early successional sites on this alluvial flood plain.

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We thank Jake Corwin, Daniel Warnock, Jeff Piotrowski, Dan Bowling, Tyler Huggins, and Sonia Purin for assistance in the field and laboratory, and Keith Geluso and several anonymous reviewers for comments on earlier versions of the manuscript. We thank colleagues at the Flathead Lake Biological Station, as well as the John Dalimata Family, for support of research at Nyack Flood Plain. The study was funded by the U.S. National Science Foundation (DEB 0613943) and supported by the Alexander von Humboldt Foundation.

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Correspondence to Mary J. Harner.

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Harner, M.J., Mummey, D.L., Stanford, J.A. et al. Arbuscular mycorrhizal fungi enhance spotted knapweed growth across a riparian chronosequence. Biol Invasions 12, 1481–1490 (2010).

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  • Arbuscular mycorrhizal fungi
  • Centaurea
  • Floodplain
  • Mycorrhizal responsiveness
  • Riparian
  • Spotted knapweed