Effects of nitrogen deposition on greenhouse-gas fluxes for forests and grasslands of North America

Abstract

Human activities have substantially elevated the atmospheric deposition of reactive nitrogen (N) onto terrestrial ecosystems of North America. Some of this N can stimulate carbon (C) storage in terrestrial ecosystems, but the fertilization effect of added N can be diminished by elevated concentrations of tropospheric ozone (O3) and by chronically high N deposition. In this review, we discuss spatial patterns and effects of N deposition and tropospheric O3 on net greenhouse-gas fluxes in North American forest and grassland ecosystems. While projected rates of ammonia emissions and deposition are expected to remain unchanged, projected declines in nitrogen oxide (NOx) emissions within the US will likely lead to reductions in total N deposition and O3. The net effect of these changes in N deposition onto forests and grasslands will likely initiate declines in C sequestration attributed to N deposition over the next 40 years. © The Ecological Society of America.