CO 2 Exchange of Seedling Pines in the Laboratory as Related to Lower Elevational Limits

Abstract

CO2 exchange of leafy branches intact on potted plants was measured with an infrared gas analyzer to determine if there were differences in adaptation to low elevations. Species studied were: Pinus attenuata, knobcone pine; P. coulteri, coulter pine; P. lambertiana, sugar pine, listed in order of increasing minimum elevation. Knobcone pine showed the greatest acclimation to low temperatures; coulter pine acclimated better than sugar pine. Sugar pine was most efficient at photosynthesis in reduced light intensities. Young seedlings of knobcone and coulter pine, with 100% primary leaves, were more efficient than sugar pine seedlings of comparable age which had developed some secondary leaves. Plants of all three species showed a similar pattern of decline in rate of photosynthesis during each 8-hr experimental photoperiod. Coulter and knobcone pines showed somewhat greater drought tolerance than sugar pine both as seedlings and as saplings. Knobcone and coulter pines are better adapted to low elevations than sugar pine.