Differences in above- and below-ground responses to ozone between two populations of a perennial grass

Our study examined the influence of elevated ozone levels on the growth and mycorrhizal colonization of two populations of Elymus glaucus L. (blue wil drye). We hypothesized that ozone would reduce carbon availability to the p lants, particularly below ground, and would affect mycorrhizal colonization . Because of the wide geographic range of E. glaucus, two populations of pl ants were selected from areas of contrasting ozone histories to examine int raspecies variation in response to ozone. Two populations of E. glaucus (so uthern California versus northern California) exposed in a factorial experi ment involving ozone, mycorrhizal inoculation with Glomus intraradices Sche nck and Smith, and plant source population. Ozone had a subtle effect on le af area and number of tillers but did not affect overall root:shoot ratio i n either population. The impact of ozone on above-ground growth characteris tics was most pronounced in the southern population that came from a high-o zone environment, while below-ground responses such as reduced arbuscular c olonization was most pronounced in the northern population which originated in a low-ozone environment. Further analysis of soil characteristics from the northern population of plants revealed a significant reduction in activ e soil bacterial biomass and an increase in total fungi per gram dry weight soil, suggesting a possible role for ozone in altering soil processes. Whe ther or not population differences in response to ozone were due to genetic shifts resulting from prior ozone remains to be determined. However, these subtle but important differences in population response to ozone above- an d below-ground have significant implications in any attempt to generalize p lant response, even within a species. Future research efforts need to inclu de better characterization of intraspecific variation in response to ozone as well as possible adaptive strategies that may result from chronic ozone exposure.