Photosynthetic and respiratory activities and gross production in relation to temperature conditions were investigated in the population of an evergreen herb, Pyrola japonica, growing on the floor of a deciduous forest in the warm temperate region of central Japan. Analysis of the temperature-photosynthesis relationship of P. japonica leaves during the growing season indicated distinct seasonal changes in the temperature optimum for photosynthesis. This population was found to be acclimatable to ambient air temperatures exceeding 15C, but this acclimation became less pronounced under thermal conditions below 15 C. This plant possessed narrow photosynthetic optima in the warm season but wide optima in the cold season. The shape of the temperature-respiration curve did not vary significantly with the months except for April. The Q10 for respiration between 10 C and 20 C was calculated to be 1.93-2.65. Annual dry matter loss associated with respiration was estimated to amount to 159.1 g d.w.m-2 based on the measurements of the seasonal changes in the respiratory activity of each organ. Gross production of this population was estimated to be 219.3 g d.w.m-2 year-1 as the sum total of the net production (60.2 g d.w.m-2year-1) and the respiration. Monthly gross production was high in the early growing season, and low and stable in winter.
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