Studies of a semiarid shortgrass plant community (Central Plains Experimental Range, Colorado, USA) and a mesic tallgrass community (Konza Prairie Research Natural Area, Kansas, USA) are described. Soil C and N pools were measured from soil cores taken below rhizomatous and caespitose grass species from both grazed and ungrazed sites. Physiological plasticity was determined for the roots of both grass types by exposure to ammonium sulfate solution and rhizome and root morphological plasticity was determined on the long-term grazed sites. Caespitose grasses [Schizachyrium scoparium and Bouteloua gracilis] accumulated larger pools of nutrients in soils directly beneath plants than rhizomatous grasses [Andropogon gerardii and Pascopyrum smithii [Elymus smithii]] did in rhizomes. Caespitose and rhizomatous grasses had inconsistent modifications of nutrient pools on grazed compared with ungrazed sites, which indicated the occurrence of either species- or system-specific responses. Neither grass type expressed morphological or physiological root plasticity in the mesic community but both grass types expressed morphological root plasticity and the rhizomatous grass displayed significant physiological root plasticity in the semiarid plant community