GROWTH AND MAINTENANCE COMPONENTS OF LEAF RESPIRATION OF COTTON GROWN IN ELEVATED CARBON-DIOXIDE PARTIAL-PRESSURE

Elevated atmospheric carbon dioxide partial pressures have been shown to have variable direct and indirect effects on plant respiration rates. In this study, growth, leaf respiration, and leaf nitrogen and carbohydrate partitioning were measured in Gossypium hirsutum L. grown in 35 and 65Pa CO2 for 30 d. Growth and maintenance coefficients of leaf respiration were estimated using gas exchange techniques both at night and during the day. Elevated CO2 stimulated biomass production (107%) and net photosynthetic rates (35-50%). Total day-time respiration (R(d)) was not significantly affected by growth CO2 partial pressure. However, night respiration (R(n)) of leaves grown in 65 Pa CO2 Was significantly greater than that of plants grown in 35 Pa CO2. Correlation of R(d) and R(n) with leaf expansion rates indicated that plants in both CO2 treatments had equivalent growth respiration coefficients but maintenance respiration was significantly greater in elevated CO2. Increased maintenance coefficients in elevated CO2 appeared to be related to increased starch accumulation rather than to changes in leaf nitrogen.