ROOT ARCHITECTURE OF WARM-SEASON AND COOL-SEASON GRASSES - RELATIONSHIP TO MYCORRHIZAL DEPENDENCE

Root architecture of five warm-season and five cool-season grasses was compared. The cool-season grasses had significantly more primary and secondary roots than warm-season grasses, and the diameter of primary, secondary, and tertiary roots of cool-season grasses was significantly smaller than that of warm-season grasses. Soil microorganisms, mycorrhizae, and P fertilization did not affect root number or diameter of the cool-season grasses; root number of warm-season grasses did respond to mycorrhizae and P fertilization, but not soil microorganisms. Specific root length of cool-season grasses was not altered by mycorrhizae, soil microbes, or P fertilization, and was significantly greater than that of warm-season grasses, particularly those inoculated with mycorrhizae. Topological analysis of root architecture revealed that mycorrhizal symbiosis inhibited root branching in warm-season grasses but had no effect on rooting strategy of cool-season grasses. In contrast, P fertilization did not substantially alter root branching in warm- or cool-season grasses. Apparently, root architecture of the mycorrhizal-dependent warm-season grasses is quite plastic, allowing energy expenditure for root development to be conserved; the root architecture of the less mycorrhizal-dependent cool-season grasses appears to be fixed and does not alter to accommodate the symbiosis.