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Submitted to: Agricultural and Forest Meteorology
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 4/7/2011 Publication Date: 12/1/2011 Citation: Bunce, J.A. 2011. Some performance characteristics of an area distributed free air carbon dioxide enrichment (FACE) system. Agricultural and Forest Meteorology. 151:1152-1157. Interpretive Summary: The concentration of carbon dioxide in the atmosphere continues to rise rapidly. Developing varieties of crops better adapted to higher carbon dioxide concentrations could increase food production. Existing experimental systems for exposing crop plants outdoors to elevated concentrations of carbon dioxide are limited in size because they add carbon dioxide only to the perimeter of plots, and the concentration achieved decreases substantially with distance from the perimeter. Larger experimental systems would allow more rapid progress by facilitating the simultaneous comparison of more varieties. A new system was developed and tested in which carbon dioxide addition was distributed evenly across the whole experimental plot. Tests indicated good uniformity of carbon dioxide concentration, and minimal disturbance of other environmental factors. Technical Abstract: Free air carbon dioxide enrichment (FACE) systems rely primarily on wind to distribute carbon dioxide across treatment plots. Most FACE designs inject carbon dioxide at the perimeter of the plot, and low wind speeds can result in large horizontal gradients of carbon dioxide concentration. These gradients can be reduced by using blowers to inject carbon dioxide or a mixture of carbon dioxide and air into the plot, but this process can alter the microclimate enough to affect plant growth. This report describes a new FACE system in which carbon dioxide emitters are evenly distributed across a plot in a square array to provide an area-source of carbon dioxide. A variable mixture of carbon dioxide and air is supplied continuously to each emitter at a constant low total volume flow. Tests showed good horizontal uniformity of carbon dioxide concentration except for a small radius around each emitter. Temporal variation in carbon dioxide concentration in the daytime at the center of the plot was similar to that of other FACE designs. Instantaneous measurements made with an open path carbon dioxide analyzer indicated a frequency distribution strongly skewed toward low concentrations compared with the one minute averages. Canopy air temperatures on nights with low wind did not differ in plots with and without flow to the emitters, indicating minimal disturbance of the canopy microclimate. A square array FACE system could be scaled to any horizontal dimension without compromising the horizontal uniformity of carbon dioxide concentration, and could be useful in large-scale screening of germplasm for carbon dioxide responsiveness under field conditions. |
