Aspen Bibliography


Coarse and Fine Root Respiration in Aspen (Populus Tremuloides)

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Tree Physiology





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Coarse and fine root respiration rates of aspen (Populus tremuloides Michx.) were measured at 5, 15 and 25 °C. Coarse roots ranged from 0.65 to 4.45 cm in diameter, whereas fine roots were less than 5 mm in diameter. To discrim- inate between maintenance and growth respiration, root respi- ration rates were measured during aboveground growing periods and dormant periods. An additional measurement of coarse root respiration was made during spring leaf flush, to evaluate the effect of mobilization of resources for leaf expan- sion on root respiration. Fine roots respired at much higher rates than coarse roots, with a mean rate at 15 °C of 1290 μmol CO2 m–3 s–1 during the growing period, and 660 μmol CO2 m–3 s–1 during the dormant period. The temperature response of fine root respiration rate was nonlinear: mean Q10 was 3.90 for measurements made at 5–15 °C and 2.19 for measurements made at 15–25 °C. Coarse root respiration rates measured at 15 °C in late fall (dormant season) were higher (370 μmol CO2 m–3 s–1) than rates from roots collected at leaf flush and early summer (200 μmol CO2 m–3 s–1). The higher respiration rates in late fall, which were accompanied by decreased total non- structural carbohydrate (TNC) concentrations, suggest that respiration rates in late fall included growth expenditures, re- flecting recent radial growth. Neither bud flush nor shoot growth of the trees caused an increase in coarse root respiration or a decrease in TNC concentrations, suggesting a limited role of coarse roots as reserve storage organs for spring shoot growth, and a lack of synchronization between above- and be- lowground growth. Pooling the data from the coarse and fine roots showed a positive correlation between nitrogen concen- tration and respiration rate.