Relationships of mycorrhizal symbiosis, rooting strategy, and phenology among tallgrass prairie forbs

The response of 23 tallgrass prairie forbs to mycorrhizal symbiosis and P fertilization was assessed in steamed and non-sterile prairie soil. For each plant species, root diameters, root fibrousness, root to shoot ratio, plant dry weight, mycorrhizal root colonization, mycorrhizal dependence, P dependence, and phenology were measured. Using these data, cluster analysis, stepwise discriminant analysis, and canonical discriminant analysis of the data revealed that the forbs could be divided into three distinct groups based on mycorrhizal dependence, root morphology, and phenology in descending order of importance. Cluster groups 1 and 2 contained obligately and facultatively mycotrophic forbs, respectively, while the third group did not benefit from the symbiosis. Models for prediction of mycorrhizal dependence, constructed using stepwise regression analysis, were based largely on root fibrousness. A regression analysis comparing mycorrhizal dependence and root fibrousness was conducted, and group means and 95% confidence ellipses were examined for each group. These revealed that the mycorrhizal dependence and root fibrousness of groups 1 and 3 are relatively constant regardless of P level, while the response of forbs of group 2 is more plastic, i.e., mycorrhizal dependence decreases and root fibrousness increases as P level increases. The relationship between plant response to mycorrhizal symbiosis and life strategy or growth pattern is discussed. Key words: mycorrhizal dependency, vesicular–arbuscular mycorrhizae, root systems.