DOWNWARD REGULATION OF PHOTOSYNTHESIS AND GROWTH AT HIGH CO2 LEVELS - NO EVIDENCE FOR EITHER PHENOMENON IN 3-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 CO2 have revealed the CO2-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 CO2 enrichment experiments with plants growing in pots.