Interspecific variation in plant responses to mycorrhizal colonization in tallgrass prairie

Symbiotic associations between plants and arbuscular mycorrhizal fungi are ubiquitous and ecologically important in many grasslands. Differences in sp ecies responses to mycorrhizal colonization can have a significant influenc e on plant community structure. The growth responses of 36 species of warm- and cool-season tallgrass prairie grasses and 59 tallgrass prairie forbs t o arbuscular mycorrhizal (AM) fungal colonization were assessed in greenhou se studies to examine the extent of interspecific variation in host-plant b enefit from the symbiosis and patterns of mycorrhizal dependence among host plant life history (e.g., annual, perennial) and taxonomic (e.g., grass, f orb, legume, nonlegume) groups and phenological guilds. There was a strong and significant relationship between phenology of prairie grasses and mycor rhizal responsiveness. however this relationship was less apparent in forbs . Perennial warm-season C-4 grasses and forbs generally benefited significa ntly from the mycorrhizal symbiosis. whereas biomass production of the cool -season C-3 grasses was not affected. The root systems of the cool-season g rasses were also less highly colonized by the AM fungi, as compared to the warm-season grasses or forbs. Unlike the native perennials, annuals were ge nerally not responsive to mycorrhizal colonization and were lower in percen tage root colonization than the perennial species. Plant growth responsiven ess and AM root colonization were positively correlated for the nonlegumino us species, with this relationship being strongest for the cool-season gras ses. In contrast, root colonization of prairie legumes showed a significant , but negative, relationship to mycorrhizal growth responsiveness.