Effects of Atmospheric CO(2) Enrichment on Photosynthesis, Respiration, and Growth of Sour Orange Trees.

Numerous net photosynthetic and dark respiratory measurements were made over a period of 4 years on leaves of 24 sour orange (Citrus aurantium) trees; 8 of them growing in ambient air at a mean CO(2) concentration of 400 microliters per liter, and 16 growing in air enriched with CO(2) to concentrations approaching 1000 microliters per liter. Over this CO(2) concentration range, net photosynthesis increased linearly with CO(2) by more than 200%, whereas dark respiration decreased linearly to only 20% of its initial value. These results, together with those of a comprehensive fine-root biomass determination and two independent aboveground trunk and branch volume inventories, suggest that a doubling of the air's current mean CO(2) concentration of 360 microliters per liter would enhance the growth of the trees by a factor of 3.8.