Document: BET-3-42-39

Mycorrhizae determine compensatory responses of American and French Centaurea maculosa after clipping.

NEWINGHAM, B.A.* ¹, C.A.ZABINSKI ², R.MICHALET ³ and R.M.CALLAWAY ¹

University of Montana, Missoula, MT 59812 USA ¹
Montana State University, Bozeman, MT 59717 USA ²
Universite Joseph Fourier, BP53-38041, Grenoble, France ³

Abstract:
Centaurea maculosa (spotted knapweed) is a non-native, invasive plant in North America that is native to Europe and Asia. We investigated the responses of C. maculosa collected from the US to clipping, mycorrhizae, and interspecific competition with Festuca idahoensis. In a greenhouse experiment, we planted North American C. maculosa with or without F. idahoensis and with or without mycorrhizae in North American soil. We simulated herbivory by clipping all C. maculosa leaves, except one, in half of the pots. We found interactions between neighbor and mycorrhizae (P=0.003) and mycorrhizae and herbivory (P=0.055). In the absence of mycorrhizae, C. maculosa's biomass was negatively affected by clipping with or without F. idahoensis. In contrast, C. maculosa had a compensatory growth response to clipping in the presence of mycorrhizae both in the presence and absence of F. idahoensis. In a similar experiment, we compared the responses of C. maculosa collected from the US to C. maculosa collected in France to clipping. Both Centaureas were planted either alone or with the French grass, Festuca ovina, in French soil, with or without mycorrhizae. We found strong positive effects of mycorrhizae (P<0.001) and F. ovina (P=0.023) on Centaurea biomass. In the absence of mycorrhizae, both the American and French C. maculosa compensated for clipping with or without F. ovina. However, the biomass of both Centaureas was negatively affected by clipping in the presence of mycorrhizae and F. ovina. Our results suggest that fungal and microbial communities in the soil differ between North America and Eurasia and may affect the response of C. maculosa to herbivory. The compensatory growth response by C. maculosa has implications for the use of insects as biocontrols.

Keywords: herbivory, mycorrhizae, Centaurea maculosa, competition

This abstract is being presented at: 8:30 AM in session:
Oral Session #8: Mycorrhizal Fungi.