Three Phases of Plant Response to Atmospheric CO(2) Enrichment.

Several years of research on seven different plants (five terrestrial and two aquatic species) suggest that the beneficial effects of atmospheric CO(2) enrichment may be divided into three distinct growth response phases. First is a well-watered optimum-growth-rate phase where a 300 parts per million increase in the CO(2) content of the air generally increases plant productivity by approximately 30%. Next comes a nonlethal water-stressed phase where the same increase in atmospheric CO(2) is more than half again as effective in increasing plant productivity. Finally, there is a water-stressed phase normally indicative of impending death, where atmospheric CO(2) enrichment may actually prevent plants from succumbing to the rigors of the environment and enable them to maintain essential life processes, as life ebbs from corresponding ambient-treatment plants.