Downward Regulation of Photosynthesis and Growth at High CO(2) Levels : No Evidence for Either Phenomenon in Three-Year Study of Sour Orange Trees.

Numerous photosynthesis and growth measurements of sour orange (Citrus aurantium L.) trees maintained in ambient air and air enriched with an extra 300 microliters per liter of CO(2) have revealed the CO(2)-enriched trees to have consistently sequestered approximately 2.8 times more carbon than the control trees over a period of three full years. Under field conditions in the natural environment, plants may not experience the downward regulation of photosynthetic capacity typically observed in long-term CO(2) enrichment experiments with plants growing in pots.