A new type of cuvette for the measurement of daily variation of CO2 efflux from stems and branches in controlled temperature conditions

A miniaturized, porometer-compatible cuvette for measurements of CO2 efflux from woody plant parts at controlled temperature conditions is described. A copper cuvette equipped with a PID-controlled Peltier element regulates cortex temperature in three modes: (1) synchronized with ambient air temperature; (2) at a constant difference in the range of ±10°C from air temperature; and (3) constant at a temperature in a range of ±25°C difference from ambient air. This method allows investigation of (a) respiratory capacity of woody plant parts dependent on short-term temperature variations, (b) CO2 release from woody plant parts following exposure to the sun, and (c) acclimation of woody plant parts to long-term changes of temperature. By use of the copper cuvette, temperature gradients in the cortex are drastically reduced. Therefore, studies on the effect of metabolically and physico-chemically based processes on diurnal variations of CO2 efflux from woody plant parts can be carried out. Field experiments were carried out on trees of Betula pendula, B. ermanii, and B. litwinowii. At synchronized temperatures of ambient air and woody plant tissue, daytime reductions of CO2 efflux relative to night-time rates at a given temperature from branches of B. pendula and B. ermanii were observed. In July, CO2 efflux from branches of B. litwinowii under controlled temperature conditions from 3 to 27°C showed a characteristic exponential increase from 0.6 to 7.2 µmol CO2 m−2 s−1. During dormancy, long-term warming of branches of B. ermanii failed to increase metabolic activity.