PLANT-RESPONSE TO HERBIVORY AND BELOWGROUND NITROGEN CYCLING

Field data came from Wind Cave National Park, South Dakota. Laboratory estimates of net nitrogen mineralization were highest in soils from the more altered areas of prairie dog colonies (Cynomys ludovicianus) and lowest in adjacent, lightly grazed, uncolonized grassland. The ratio of CO2:net N mineralized, an index of immobilization, was highest in the uncolonized grassland, lowest in the altered core areas. Soil moisture was an important modifier of in situ field estimates of net N mineralization. Root biomass, an important C source for decomposers in perennial grasslands, was lowest in the altered core area and highest in adjacent uncolonized grassland. Decreased N immobilization and increased net N mineralization in laboratory incubations likely resulted from decreased root C inputs in grazer areas, which limited C availability to decomposers. -from Authors