PARENT SESSION
Oral Session #45: Herbivory: Effects on Plants. Presiding: T. Craig.
Wednesday, August 8, 2001. 8:00 AM to 12:00 PM. Hall of Ideas H.

Effects of defoliation on the invasive species, Centaurea maculosa: neighbors, allelopathy, compensatory growth and mycorrhizae.

Newingham, Beth¹, ¹

ABSTRACT- Herbivory can have negative, positive or no effect on plants, but the use of insects as biocontrols assumes that herbivory will have negative effects on target weeds and release neighboring natives from competition. Previous studies have shown that herbivory does not have strong negative effects on C. maculosa, one of the most invasive species in North America. I evaluated Centaurea's response to defoliation and herbivory in the context of compensatory growth, increased allelopathic effects on neighboring grasses, and mycorrhizae. In a greenhouse experiment, herbivory had a negative effect on C. maculosa when growing alone, but C. maculosa had a compensatory growth response when in competition with another C. maculosa, Festuca idahoensis or F. scabrella. Although C. maculosa had significant allelopathic effects on F. idahoensis, these negative effects did not increase after herbivory. Other experiments suggest that C. maculosa may parasitize F. idahoensis through mycorrhizal networks . In a final experiment, we reduced soil fungi with the fungicide, Benomyl, and clipped C. maculosa. Centaurea maculosa was only able to compensate for defoliation when soil fungi were not reduced; in other words, fungicide eliminated C. maculosa's ability to compensate. This suggests that mycorrhizae and/or other soil fungi play an important role in the compensatory response of C. maculosa. The complex interactions among fungi, native plants, and insect herbivores have important implications for the use of insects as biocontrols on C. maculosa.

KEY WORDS: compensatory growth, invasive plants, mycorrhizae, allelopathy