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ROLE OF CARBOHYDRATE SUPPLY IN WHITE AND BROWN ROOT RESPIRATION OF PONDEROSA PINE
Citation:
Lipp, C. C. AND C P. Andersen. ROLE OF CARBOHYDRATE SUPPLY IN WHITE AND BROWN ROOT RESPIRATION OF PONDEROSA PINE. NEW PHYTOLOGIST 160:523-531, (2003).
Description:
Respiratory responses of fine ponderosa pine (Pinus ponderosa Laws) roots of differing morphology were measured to evaluate response to excision and to changes in the shoot light environment. Ponderosa pine seedlings were subject to either a 15:9 h light/dark environment over 24 h or continuous light for 24 h while root respiration was monitored. The specific rate of CO2 release from individual ponderosa pine new white roots and brown roots, measured in situ, averaged 80- 90 mmol CO2 g dwt -1 h-1 and 20-30 mmol CO2 g dwt -1 h-1, respectively. Respiration of white roots in situ did not decline significantly over 24 h with seedlings under continuous light. However, significant decreases in white root respiration were evident during the dark night period for those seedlings under a diurnal light treatment. Older, brown roots did not exhibit diurnal responses in respiration. Excised roots, whether white or brown, maintained relatively constant respiration rates for about the first six h after excision from the seedling. It appeared that root excision did not significantly alter respiration rates for several hours. While the source of respiratory substrate was expected to differ between attached and detached roots, the apparent source of respiratory substrate did not change as evidenced by similar respiratory quotient (RQ) values between attached and detached roots. The pattern of decline in root respiration after excision was different from observed patterns of decline in attached roots in darkness. Differences in the patterns of decline suggest that the supply or use of current photosynthate may not be a factor regulating short-term respiratory responses in pine. Light-related responses suggest that a shoot factor may be influencing root respiration rates in new roots, possibly the result of shoot-to-root signaling.