Effects of anthropogenic nitrogen (N) deposition and the ability of terrestrial ecosystems to store carbon (C) depend in part on the amount of N retained in the system and its partitioning among plant and soil pools. We conducted a meta-analysis of studies at 48 sites across four continents that used enriched 15N isotope tracers in order to synthesize information about total ecosystem N retention (i.e., total ecosystem 15N recovery in plant and soil pools) across natural systems and N partitioning among ecosystem pools. The greatest recoveries of ecosystem 15N tracer occurred in shrublands (mean, 89.5%) and wetlands (84.8%) followed by forests (74.9%) and grasslands (51.8%). In the short term (<1 week after 15N tracer application), total ecosystem 15N recovery was negatively correlated with fine-root and soil 15N natural abundance, and organic soil C and N concentration but was positively correlated with mean annual temperature and mineral soil C:N. In the longer term (3–18 months after 15N tracer application), total ecosystem 15N retention was negatively correlated with foliar natural-abundance 15N but was positively correlated with mineral soil C and N concentration and C: N, showing that plant and soil natural-abundance 15N and soil C:N are good indicators of total ecosystem N retention. Foliar N concentration was not significantly related to ecosystem 15N tracer recovery, suggesting that plant N status is not a good predictor of total ecosystem N retention. Because the largest ecosystem sinks for 15N tracer were below ground in forests, shrublands, and grasslands, we conclude that growth enhancement and potential for increased C storage in aboveground biomass from atmospheric N deposition is likely to be modest in these ecosystems. Total ecosystem 15N recovery decreased with N fertilization, with an apparent threshold fertilization rate of 46 kg N·ha-1·yr-1 above which most ecosystems showed net losses of applied 15N tracer in response to N fertilizer addition.
|Title||Sinks for nitrogen inputs in terrestrial ecosystems: a meta-analysis of 15N tracer field studies|
|Authors||P.H. Templer, M.C. Mack, F. S. Chapin, L.M. Christenson, J.E. Compton, H.D. Crook, W.S. Currie, C.J. Curtis, D.B. Dail, C. M. D'Antonio, B.A. Emmett, H.E. Epstein, C.L. Goodale, P. Gundersen, S.E. Hobbie, K. Holland, D.U. Hooper, B.A. Hungate, S. Lamontagne, K.J. Nadelhoffer, C.W. Osenberg, S.S. Perakis, P. Schleppi, J. Schimel, I.K. Schmidt, M. Sommerkorn, J. Spoelstra, A. Tietema, W.W. Wessel, D.R. Zak|
|Publication Subtype||Journal Article|
|Record Source||USGS Publications Warehouse|
|USGS Organization||Forest and Rangeland Ecosystem Science Center|