The concept that nitrogen (N) availability can limit plant productivity is well established based on (1) N fertilization that stimulates productivity and (2) increases in productivity along gradients of soil fertility. Nitrogen limitations to plant productivity are regulated by processes such as mineralization, immobilization, and plant physiological adjustments. However, this production-centric perspective might not fully explain patterns in carbon (C) sequestration in terrestrial ecosystems. Carbon sequestration involves both plant and soil pools. The plant pool, which is the main concern of production research, can be much smaller than the soil pool. To quantify terrestrial C sequestration, therefore, we have to develop an ecosystem perspective to examine how C and N interact in both plant and soil pools.

Key words: atmospheric CO₂; carbon sequestration; ecosystem development; elevated CO₂; forest; global change; grassland; net primary production; nitrogen cycling; nitrogen use efficiency; progressive nitrogen limitation; soil carbon.