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Belowground mechamisms that enhance the success of an invasive forb.
Zimmerley, Sara*,1, Zabinski, Cathy1, 1 Montana State University, Bozeman
ABSTRACT- Centaurea maculosa (spotted knapweed) is an exotic forb that has invaded millions of hectares of rangeland in the Rocky Mountain region. Our work examines belowground mechanisms that increase C. maculosa's competitive abilities, and specifically, the role of arbuscular mycorrhizae (AM) in nutrient acquisition. Based on our previous research, we hypothesized that extraradical hyphae of C. maculosa AM would obtain P from a more distant source than the extraradical hyphae of Festuca idahoensis AM. Both C. maculosa and F. idahoensis were planted singly in pots divided by either a membrane barrier that excludes fine roots and hyphae, or a mesh barrier that excludes only roots. Across the barrier from the plant we applied one of three phosphorus treatments: no P amendments, rock phosphate (RP), or triple super phosphate (TSP). Plants were grown in an 8:1 sand-to-soil mixture, and given half-strength modified Hoagland's solution minus P, ensuring that plant P source was from the opposite side of the pot. After 13 weeks of growth, plant biomass differed significantly between P treatments, with greatest biomass when P was added as RP, and the smallest biomass when P was added as TSP. There were no differences in P content or % P between plants growing with mesh or membrane barriers, probably as a result of P mobility across the pots. When F. idahoensis was grown with TSP, significantly more P moved to the soil on the plant side in mesh-divided pots as compared to membrane dividers. This may be from greater P mobility across the mesh barrier, or from AM-hyphae facilitated transport, without a net increase in P content in the host plant. Our research continues by measuring differences in AM colonization levels and extraradical hyphae lengths between species and P treatments.
KEY WORDS: arbuscular mycorrhizae, Centaurea maculosa, nutrient acquisition, invasive species