A year long study was conducted to examine how large herbivores and landscape factors affect soil C and N dynamics in grasslands of Yellowstone National Park. Results from the in situ experiment indicated that average net N mineralization among grazed plots (3.8 g N .m-2.yr-1) was double that of fenced, ungrazed plots (1.9 g N .m-2.yr-1) and dramatically increased between-site variation of that rate. Herbivores improved the organic matter quality of soil and reduced C respired/N mineralized ratios by an average of 21%. The greatest landscape influence on in situ net mineralization (2.2g N .m-2.yr-1) was similar to the average grazer impact on that rate (1.9 g N .m-2.yr-1). These results suggest that variation in net N mineralization among diverse sites is principally a function of differences in immobilization rates, while effects of grazers on net mineralization may be due to variation in gross mineralization. Findings indicate that the regulatory influences of herbivores on soil N dynamics may be underestimated, particularly for grasslands supporting large herds of ungulates.
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