3 - Terrestrial Higher Plant Respiration and Net Primary Production

Abstract

A large fraction of carbon (C) assimilated in higher plant photosynthesis is released into the atmosphere as carbon dioxide during subsequent plant respiration. Thus, plant respiration is a large negative component of the C budget of plants and ecosystems. It contributes to the control of ecosystem net primary production (NPP) because NPP is gross primary production (GPP) minus plant respiration. The relationship between ecosystem NPP and GPP is therefore dictated by respiration. Plant respiration is the metabolic link between GPP and NPP. It is also a large component of a plant's C budget; perhaps, typically, 50–70% of carbon assimilated in GPP is released into the atmosphere as carbon dioxide during subsequent plant respiration. Because of great uncertainty concerning in situ measurements of respiration (Ra) and photosynthesis (P), it is hard to quantify more precisely their role in C cycles of various ecosystems. This chapter judges the available data to be too imprecise to assess properly whether the Ra/P ratio at present is conservative within or among ecosystems. Moreover, environmental change such as warming and increasing carbon dioxide concentration may affect Ra and P differently, so the Ra/ P ratio may change in the future. In any case, future studies of the relationship between Ra and NPP or GPP will be more enlightening than simple measurements of respiration rate.