Quantitative evaluation of the counterbalance between photosynthetic stimulation and depression caused by low partial pressure of O_2 and CO_ 2 in alpine atmospheres

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To evaluate the effects of low atmospheric pressure on leaf photosynthesis, we compared the photosynthesis of identical leaves of Fagus crenata at lowland (0 m a.s.l.) and at highland (2360 m a.s.l.). At the high altitude, the atmospheric pressure and partial pressure of CO_2 at intercellular air spaces in the leaf (C_<i360>) decreased to 77% and 78% of those at the low altitude, respectively. On the other hand, the efficiency of photosynthetic CO_2-utilization was apparently higher at the high altitude because of a mitigation of the O_2-inhibition of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) under low ambient partial pressure of O_2. This stimulation of photosynthesis partly compensated a photosynthetic depression due to the low C_<i360>, and the net assimilation rate (A_<n360>) at the high altitude retained 94% of the value at the low altitude. A theoretical model indicated that the stimulation of photosynthesis at high altitudes depend on internal conductance (g_i) and/or on Rubisco content. The model demonstrated that low atmospheric pressure at high altitudes caused severe restrictions of photosynthesis when leaves had a small g_i and/or a large amount of Rubisco, whichever are repeatedly reported in alpine plants.
国立極地研究所の論文