Respiration is important in the overall carbon balance of plants, and can be separated into growth (R g ) and maintenance respiration (R m ) . Estimation of R g and R m throughout plant development is difficult with traditional approaches. Here, we describe a new method to determine ontogenic changes in R g and R m . The CO 2 exchange rate of groups of 28 `Cooler Peppermint' vinca plants [ Catharanthus roseus (L.) G. Don.] was measured at 20 min intervals for 2 weeks. These data were used to calculate daily carbon gain (DCG, a measure of growth rate) and cumulative carbon gain (CCG, a measure of plant size). Growth and maintenance respiration were estimated based on the assumption that they are functions of DCG and CCG, respectively. Results suggested a linear relationship between DCG and R g . Initially, R m was three times larger than R g , but they were similar at the end of the experiment. The decrease in the fraction of total available carbohydrates that was used for R m resulted in an increase in carbon use efficiency from 0.51 to 0.67 mol·mol -1 during the 2-week period. The glucose requirement of the plants was determined from R g , DCG, and the carbon fraction of the plant material and estimated to be 1.39 g·g -1 , while the maintenance coefficient was estimated to be 0.031 g·g -1 ·d -1 at the end of the experiment. These results are similar to values reported previously for other species. This suggests that the use of semicontinuous CO 2 exchange measurements for estimating R g and R m yields reasonable results.
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Iersel et al. (2000) studied this question.