|Long, S - UNIVERSITY OF ILLINOIS|
Submitted to: New Phytologist
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 26, 2004
Publication Date: February 1, 2005
Citation: Ainsworth, E.A., Long, S.P. 2005. What have we learned from fifteen years of free-air CO2 enrichment (FACE)? A meta-analytic review of the responses of photosynthesis, canopy properties and plant production to rising CO2. New Phytologist. 165:351-372. Interpretive Summary: This review summarizes the results of 120 articles describing plant responses to elevated atmospheric carbon dioxide concentration under fully open air conditions in free-air CO2 enrichment (FACE) experiments. The results of this analysis confirm some results from previous studies performed in growth chambers and greenhouses, but there were also some differences in the responses of plants to elevated [CO2] in the open air. Importantly, C4 species, which include maize and sorghum, showed little response to elevated [CO2]. Other grain crops also did not show increases in yield to the degree predicted from previous studies. Therefore, stimulation of crop yields due to elevated atmospheric [CO2] in the future may not be as high as currently assumed.
Technical Abstract: Free-air CO2 enrichment (FACE) experiments allow study of the effects of elevated [CO2] on plants and ecosystems grown under natural conditions without enclosure. Data from 120 primary, peer-reviewed articles describing physiology and production in the 12 large-scale FACE experiments (475-600 ppm) were collected and summarized using meta-analytic techniques. The results confirm some results from previous chamber experiments: light-saturated carbon uptake, diurnal C assimilation, growth and above-ground production increased, while specific leaf area and stomatal conductance decreased in elevated [CO2]. There were differences in FACE. Trees were more responsive than herbaceous species to elevated [CO2]. Grain crop yields increased far less than anticipated from prior enclosure studies. The broad direction of change in photosynthesis and production in elevated [CO2] may be similar in FACE and enclosure studies, but there are major quantitative differences: trees were more responsive than other functional types; C4 species showed little response; and the reduction in plant nitrogen was small and largely accounted for by decreased Rubisco. The results from this review may provide the most plausible estimates of how plants in their native environments and field-grown crops will respond to rising atmospheric [CO2]; but even with FACE there are limitations, which are also discussed.