Mycorrhizal dependence and growth habit of warm-season and cool-season tallgrass prairie plants

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Abstract
Warm-season [Andropogon gerardi, Panicum virgatum, Sorghastrum mutans, Bouteloua curtipendula] (C4) and cool-season [Koeleria cristata, Bromus inermis, Festuca arundinacea, Lolium perenne, Agropyron smithii, Elymus cinereus] (C3) mycorrhizal grasses were 63-215 and 0.12-4.1 times larger in dry weight than non-inoculated controls, respectively. Nonmycorrhizal warm-season plants did not grow and frequently died, while cool-season plants grew moderately well in the absence of mycorrhizal symbiosis. Like warm-season grasses, tallgrass prairie forbs [Liatris aspera, Dalea purpurea, Baptisia leucantha] were highly dependent on mycorrhizal symbiosis, even though they are not known to employ the C4 photosynthetic pathway. Thus, phenology may be more critical than photosynthetic pathway in determining mycorrhizal dependence. Warm-season grasses and forbs had coarser, less frequently branched root systems than cool-season grasses, supporting the hypothesis that mycorrhizal dependence is related to root morphology. Cool-season grasses may have developed more fibrous root systems because mycorrhizal nutrient uptake was not effective in the colder temperate environment in which they evolved. In contrast, warm-season plants and dependence on mycorrhizal fungi may have coevolved, because both symbionts are of tropical origin.