PLANT SPECIES-SPECIFIC CHANGES IN ROOT-INHABITING FUNGI IN A CALIFORNIA ANNUAL GRASSLAND - RESPONSES TO ELEVATED CO2 AND NUTRIENTS

Five co-occurring plant species from an annual mediterranean grassland were grown in monoculture for 4 months in pots inside open-top chambe rs at the Jasper Ridge Biological Preserve (San Mateo County, Californ ia). The plants were exposed to elevated atmospheric CO2 and soil nutr ient enrichment in a complete factorial experiment. The response of ro ot-inhabiting non-mycorrhizal and arbuscular mycorrhizal fungi to the altered resource base depended strongly on the plant species. Elevated CO2 and fertilization altered the ratio of non-mycorrhizal to mycorrh izal fungal colonization for some plant species, but not for others. P ercent root infection by non-mycorrhizal fungal increased by over 500% for Linanthus parviflorus in elevated CO2, but decreased by over 80% for Bromus hordeaceus. By contrast, the mean percent infection by myco rrhizal fungi increased in response to elevated CO2 for all species, b ut significantly only for Avena barbata and B. hordeaceus. Percent inf ection by mycorrhizal fungi increased, decreased, or remained unchange d for different plant hosts in response to fertilization. There was ev idence of a strong interaction between the two treatments for some pla nt species and non-mycorrhizal and mycorrhizal fungi. This study demon strated plant species-and soil fertility-dependent shifts in belowgrou nd plant resource allocation to different morphogroups of fungal symbi onts. This may have consequences for plant community responses to elev ated CO2 in this California grassland ecosystem.