| Arbuscular mycorrhizal fungi (AMF) are mutualistic with most land plants. The hyphae reaching beyond the rhizosphere transport minerals, particularly phosphorus, to the plant. The host plant supplies the fungi with photosynthate. Field experiments, common garden experiments, and greenhouse experiments were performed to investigate the role of AM fungi in the growth and fitness of Bouteloua curtipendula (Michx.) Torr., a grass species rare in New York State.; Nellie Hill, the study site in Dutchess County, yielded two gene pools of B. curtipendula; and commercial seed (Prairie Nursery) was obtained from native populations in Nebraska. In long-term factorial experiments, I manipulated AMF colonization using the fungicide benomyl, controlled plant water relations, and varied soil phosphorus availability. I measured various aspects of plant growth, size, reproductive output and survivorship as response variables.; The gene pools responded differently to AMF colonization. All had increased growth when fully colonized with AMF and not droughted. When droughted, the Nellie Hill 1 gene pool did not increase growth when fully colonized with AMF, but did respond to additional phosphorous with better survival regardless of mycorrhizal state. It was concluded that Nellie Hill 1 plants benefited from hyphal uptake of phosphorous but may have responded to drought with reduced photosynthesis, and so had no increase of biomass. When droughted and with abundant AMF, the photosynthate drain to the AMF lessened survival so that the plants performed no better than with reduced AMF.; The Nellie Hill 2 gene pool had increased growth and survival with abundant AMF regardless of water availability. When plants had reduced AMF, added phosphorous increased survival. Plants from Prairie Nursery also had increased growth and survival when fully infected, regardless of water availability; however, with reduced AMF, added phosphorous did not increase survival. It was concluded that Prairie Nursery plants benefited from AMF, but not by hyphal uptake of phosphorous. This study documents a high degree of poorly understood, intraspecific variability in the dynamics of the plant root-AMF symbiosis. |
