Whole-plant respiration and its temperature sensitivity during progressive carbon starvation.

Plant respiration plays a critical role in the C balance of plants. Respiration is highly temperature sensitive and small temperature-induced increases in whole-plant respiration could change the C balance of plants that operate close to their light-compensation points from positive to negative. Nonstructural carbohydrates are thought to play an important role in controlling respiration and its temperature sensitivity, but this role has not been studied at the whole-plant level. We measured respiration of whole Ardisia crenata Sims. seedlings and tested the hypothesis that darkness-induced C starvation would decrease the temperature sensitivity of whole-plant respiration. Compared with control plants, sugar and starch concentrations in darkened plants declined over time in all organs. Similarly, whole-plant respiration decreased. However, the temperature sensitivity of whole-plant respiration, expressed as the proportional increase in respiration per 10°C warming (Q10), increased with progressive C starvation. We hypothesise that growth respiration was suppressed in darkened plants and that whole-plant respiration represented maintenance respiration almost exclusively, which is more temperature sensitive. Alternatively, changes in the respiratory substrate during C starvation or increased involvement of alternative oxidase pathway respiration may explain the increase in Q10. Carbohydrates are important for respiration but it appears that even in C-starved A. crenata plants, carbohydrate availability does not limit respiration during short-term warming.