Integrated Effects of Atmospheric CO2 Concentration on Plant and Ecosystem Respiration

Abstract

Atmospheric CO2 concentrations have been increasing since the industrial revolution due to fossil fuel burning and deforestation. Elevated levels of atmospheric [CO2] are likely to enhance photosynthesis and plant growth, which, in turn should result in increased specific and whole-plant respiration rates. However, a large body of literature has shown that specific respiration rates of plant tissues can be considerably reduced when plants are exposed to or grown at high [CO2]. Reductions in respiration by [CO2] have been explained by either direct inhibitory effects of [CO2] on respiratory processes or by indirect effects associated with changes in the chemical composition of tissues of plants grown at high [CO2]. The observed reductions in plant respiration rates by elevated [CO2] can represent a large biospheric sink for atmospheric carbon. Although doubling current ambient levels of atmospheric [CO2] could inhibit some mitochondrial enzymes directly in the short-term, the magnitude of the direct effect of [CO2] on tissue respiration has now been shown to be largely explained by measurement artifacts, diminishing the impact that direct effects would have on the carbon cycle. A reduction in construction and maintenance costs of tissues of plants grown at high [CO2] can explain an indirect reduction of respiration. Such indirect effects, however, may be offset by the larger biomass of plants exposed to elevated [CO2]. A lack of clear understanding of the physiological control of plant respiration, of the role(s) of non-phosphorylating pathways, and effects associated with plant size, makes it difficult to predict how respiration and the processes it supports respond to elevated [CO2]. Therefore, the role of plant respiration in augmenting or controlling the sink capacity of terrestrial ecosystems is still uncertain.