ABSTRACT
Growth respiration is mainly related to the growth rate of organs, whereas maintenance respiration is related to the mass of the organ and temperatures affecting the organ. According to Mohren (1987), growth respiration (Rg) is: Rg = CPF x ΔW, where CPF is the CO2 production factor in kg CO2 per kg ΔW of mass growth. He estimated the CPF values for the needles, branches, stems and roots of Douglas fi r [Pseudotsuga menziesii (Mirb.) Franco] as falling in the range of 0.3469-0.3866 [kg CO2 (kg ΔW)
–1], the values for stems and branches being smaller than those for needles and roots. For example, the CO2 produced [kg CO2] in needle growth is: Rg = 0.3866 x ΔW. Rearranging Equation (7.2): ΔW = Ph – Rm – Rg = Ph – Rm – 0.3866 x ΔW. This yields: ΔW = 0.721 x (Ph – Rm). Consequently, the share of growth respiration is 27.9% and the share of mass growth 72.1% of the usable photosynthesis. The share of growth respiration is close to the value (25%) suggested by Ryan (1991) for estimating its share in annual total respiration losses (see further Ryan et al. 1997).
