Authors studied the response of two grass species differing in growth forms and photosynthetic pathway to simulated cattle urine deposition in a native semi-arid grassland of Wyoming. The species were Agropyron smithii, a spreading, rhizomatous C3 grass, and Bouteloua gracilis, a cespitose C4 grass. They are codominants in this grassland and A. smithii is the most important forage species in the study site. Simulated urine increased tiller density of both species, with B. gracilis increasing in the first growing season while A. smithii was not increased until the second year. Above-ground biomass, N yield, and tiller height of A. smithii increased in urine patches. Leaf production was not affected by treatment. Urine return by grazing animals, mediated by plant morphological and ecophysiological processes, may produce a mosaic of patches or microecosystems not only structurally, but functionally, different from the surrounding grassland matrix.
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