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Effects of Native Grazers on Grassland N Cycling in Yellowstone National Park

1997; Wiley; Volume: 78; Issue: 7 Linguagem: Inglês

10.2307/2265959

1939-9170

Douglas A. Frank, R. D. Evans,

Isotope Analysis in Ecology

EcologyVolume 78, Issue 7 p. 2238-2248 Article EFFECTS OF NATIVE GRAZERS ON GRASSLAND N CYCLING IN YELLOWSTONE NATIONAL PARK Douglas A. Frank, Douglas A. Frank Biological Research Labs, Syracuse University, Syracuse, New York 13244-1220 USASearch for more papers by this authorR. David Evans, R. David Evans Biological Sciences, University of Arkansas, Fayetteville, Arkansas 72701 USASearch for more papers by this author Douglas A. Frank, Douglas A. Frank Biological Research Labs, Syracuse University, Syracuse, New York 13244-1220 USASearch for more papers by this authorR. David Evans, R. David Evans Biological Sciences, University of Arkansas, Fayetteville, Arkansas 72701 USASearch for more papers by this author First published: 01 October 1997 https://doi.org/10.1890/0012-9658(1997)078[2238:EONGOG]2.0.CO;2Citations: 173Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat Abstract We investigated the effects of native ungulates on grassland N cycling in Yellowstone National Park by examining natural 15N abundance (δ15N) of soils and plants inside and outside long-term (32–36 yr) exclosures. Across six topographically diverse sites, grazers increased δ15N of soil (0–20 cm) by 0.7‰, which was substantial considering that values for ungrazed soil ranged 2.4‰ (2.4–4.8‰). The magnitude of grazer 15N enrichment was positively related (r2 = 0.70) to the intensity of herbivore activity during the study, indexed by the amount of dung (g/m2) deposited at the sites. We also found that soil δ15N of ungulate urine and dung patches was significantly higher than that of control areas. Grazers probably increased soil δ15N by promoting N loss from the soil via leaching, ammonia volatilization, and/or denitrification. Each of these processes results in the removal of 15N depleted products from the soil and, consequently, 15N enrichment of the remaining soil. In contrast to soil results, grazers reduced plant 15N by an average of 0.7‰, probably due to isotopically light, soil NO3− (compared to soil NH4+) constituting a more important N source for plants in grazed grassland relative to those in ungrazed grassland. These findings indicate that native grazers increased N loss from this north-temperate grassland as a result of accelerated losses on urine- and dung-affected microsites and, potentially, from elevated N loss throughout the grazed landscape due to grazers promoting N cycling. Furthermore, these results suggest that herbivores increase plant NO3− assimilation, which may positively affect primary productivity in this grazed ecosystem. Citing Literature Volume78, Issue7October 1997Pages 2238-2248 RelatedInformation