Sinks for nitrogen inputs in terrestrial ecosystems: a meta-analysis of N tracer field studies

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 N isotope tracers in order to synthesize information about total ecosystem N retention (i.e., total ecosystem N recovery in plant and soil pools) across natural systems and N partitioning among ecosystem pools. The greatest recoveries of ecosystem N 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 N tracer application), total ecosystem 15N recovery was negatively correlated with fine-root and soil N 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 N tracer application), total ecosystem N retention was negatively correlated with foliar natural-abundance N but was positively correlated with mineral soil C and N concentration and C :N, showing that plant and soil natural-abundance N and soil C:N are good indicators of total ecosystem N retention. Foliar N concentration was not significantly related to ecosystem N tracer recovery, suggesting that plant N status is not a good predictor of total ecosystem N retention. Because the largest ecosystem sinks for N Manuscript received 24 June 2011; revised 10 February 2012; accepted 13 February 2012. Corresponding Editor: R. D. Evans. 27 E-mail: [email protected]