NET PHOTOSYNTHESIS OF SOUR ORANGE TREES MAINTAINED IN ATMOSPHERES OF AMBIENT AND ELEVATED CO2 CONCENTRATION

Eight sour orange trees planted directly into the ground at Phoenix, Arizona, as small seedlings in July 1987 have been enclosed by four clear-plastic-wall, open-top chambers since November of that year. Half of the trees have been continuously supplied with a CO2-enriched atmosphere consisting of an extra 300 cm3 of CO2 per m3 of air. Data from a comprehensive inventory of all above-ground plant parts at the conclusion of two full years of growth under these conditions have revealed that the net effect of the CO2-enriched air was to more than double the normal production of biomass over that time interval. Here we report net photosynthesis measurements made throughout the last summer of the period, which suggest that the primary impetus for this large growth response was an equivalent enhancement of the net photosynthetic rates of the CO2-enriched trees.