Photosynthesis in Climatic Races of Mimulus. I. Effect of Light Intensity and Temperature on Rate

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Abstract
Responses of 6 climatic races of Mimulus cardinalis Dougl. whose native habitats range from 31[degree] to 38[degree]N and from 45 to 2220 m elevation were compared. The light intensity required to saturate photosynthesis in each race increased about 10-fold from 0[degree] to 40[degree]. The saturating intensity at 40[degree] varied among races from 3500 to 5900 ft. candles, increasing with elevation of the native habitat. The rate of ligh-saturated photosynthesis was measured from 0[degree] to about 50[degree]. All 6 races showed maximum CO2 uptake at or near 30[degree]. The decline in rate at low and high temperatures was larger in races from higher elevations. The rate at 0[degree] ranged from 11 to 20% of maximum. Apparent photosynthesis became zero at 46[degree]-49[degree].

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