Influence of certain environmental factors on photosynthesis and photorespiration in Simmondsia chinensis

The response of net photosynthesis and apparent light respiration to changes in O₂], light intensity, and drought stress was determined by analysis of net photosynthetic CO₂ response curves. Low O₂] treatment resulted in a large reduction in the rate of photorespiratory CO₂ evolution. Lightintensity levels influenced the maximum net photosynthetic rate at saturating CO₂]. These results indicate that CO₂], O₂] and light intensity affect the levels of substrates involved in the enzymatic reactions of photosynthesis and photorespiration. Intracellular resistance to CO₂ uptake decreased in low O₂] and increased at low leaf water potentials. This response reflects changes in the efficiency with which photosynthetic and photorespiratory substrates are formed and utilized. Water stress had no effect on the CO₂ compensation point or the CO₂] at which net photosynthesis began to saturate at high light intensity. The relationship between these data and recently published in-vitro kinetic measurements with ribulose-diphosphate carboxylase is discussed.Abbreviations C _w intracellular CO₂ concentration - F _gross gross photosynthesis - F _net net photosynthesis - I light intensity - R _L light respiration rate - r _c carboxylation resistance - r ₈ leaf gas-phase resistance - r _i intracellular resistance; to CO₂ uptake - r _t resistance to CO₂ flux between the intercellular spaces and the carboxylation sites - T _L leaf temperature - _t leaf water potential - CO₂ compensation point