Polley and Detling examined the effects of defoliation on growth and nitrogen nutrition in populations of Agropyron smithii (western wheatgrass) collected from a heavily grazed black-tailed prairie dog (Cynomys ludovicianus) colony (on-colony) and a nearby lightly grazed, uncolonized colony (off-colony). Defoliated and nondefoliated plants were grown at low soil N availability and similar sized defoliated individuals of A. smithii from a grazing-exclosure population as a common competitor. Plants from prairie dog colonies accumulated biomass at a faster relative rate than did plants from uncolonized sites, in part, because of a 250% greater mean relative growth rate of blades and more than 200% greater rate of biomass production per unit blade biomass. Total N accumulation was greater in defoliated ON-than OFF-colony individuals. Colony plants initially had a greater proportion of biomass and N remaining after defoliation in the roots. Initial differences between populations in the distribution of biomass and N were eliminated as colony plants concentrated 24-day accumulation of biomass and N in aboveground structures. The authors state that on-colony plants appear adapted to a high rate of resource capture from nitrogen in feces in urine.
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