Role of carbohydrate supply in white and brown root respiration of ponderosa pine.

•  Respiration of intact ponderosa pine (Pinus ponderosa) fine roots (< 2.5 mm) was measured to determine the role of recently fixed carbohydrate in maintaining root metabolism of growing white (WR) and recently suberized brown roots (BR). •  The CO2 efflux and O2 uptake of individual roots were followed continuously over 24 h after carbohydrate supply was altered by exposing shoots to light/dark treatments and by root excision. •  In situ respiration of individual WR and BR averaged 86.0 ± 2.6 and 21.1 ± 1.5 mol CO2  g-1  h-1 , respectively. Growth respiration was estimated to be approximately two-thirds the rate of WR respiration. Attached WR and BR respiration did not decline significantly over 24 h under continuous light. The WR respiration significantly decreased during a dark period. All roots maintained relatively constant respiration rates for at least 6 h after excision. Respiratory quotient (RQ; CO2  : O2 ) was not different between attached (0.84 ± 0.014) and detached (0.85 ± 0.017) roots. CO2 environment of the cuvette did not influence WR or BR respiration. •  The WR appear to be more sensitive to supply of current photosynthate than BR. Shoot light environment needs to be considered when measuring root and soil CO2 efflux.