Document: PEG-3-54-8

Evidence of a mycorrhizal mechanism for the adaptation of Andropogon gerardii to high and low-nutrient prairies.

SCHULTZ, P.A.* ¹, R.M.MILLER ², J.D.JASROW ², C.V.RIVETTA ² and J.D.BEVER ¹

University of California, Irvine, CA 92697-2525 USA ¹
Argonne National Laboratory, Argonne IL 60439 ²

Abstract:
Andropogon gerardii is highly dependent upon its association with arbuscular mycorrhizal fungi (AMF) when grown on phosphorus-deficient soils in Kansas, but on Illinois soils with greater phosphorus supply rates, the growth of A. gerardii is not dependent on mycorrhizal infection. We grew ecotypes of A. gerardii obtained from Kansas and Illinois in a controlled environment on their own and each other's soils, with and without mycorrhizal infection. Each ecotype grew comparatively better in its own soil indicating adaptation to their soils of origin. Overall, A. gerardii benefited more from AMF in Kansas soil than Illinois soil. The two ecotypes, however, did not benefit equally from mycorrhizal infection, the Kansas isolate was three times more responsive to mycorrhizal infection in the Kansas soil than was the Illinois isolate. Our results indicate that plant adaptation to the nutrient levels of their local soils is due at least in part to a shift in their dependence on mycorrhizal fungi. In the course of adapting to the nutrient rich soils of Illinois, A. gerardii has apparently evolved a reduced dependence upon these fungi and greater reliance on a more highly branched root system for phosphorus uptake. This reduced dependence was seen in a root system that was significantly more branched than the Kansas ecotype. In contrast, the Kansas ecotype had a coarser root system and invested proportionately greater carbon in the symbiotic association with AMF as measured by spore production. This study provides the first demonstration that plants can adapt to changing soil nutrient levels by shifting their dependence on AM fungi This result has broad implications for our understanding of the role of these fungi in agricultural systems and the adaptation of plants to a changing environment.

Keywords: mycorrhizae, adaptation, soil phosphorus, soil, prairie, _Andropogon gerardii_

This abstract is being presented at: 10:15 AM in session:
Oral Session #8: Mycorrhizal Fungi.