|Pinter Jr, Paul|
|Wall, Gerard - Gary|
|Hunsaker, Douglas - Doug|
Submitted to: Agricultural and Forest Meteorology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/24/2000
Publication Date: 9/15/2000
Citation: Pinter Jr, P.J., Kimball, B.A., Wall, G.W., Lamorte, R.L., Hunsaker, D.J., Adamsen, F.J., Frumau, K.F., Vugts, H.F., Hendrey, G.R., Lewin, K.F. 2000. Free-air co2 enrichment (face): blower effects on wheat canopy microclimate and plant development. Agricultural and Forest Meteorology. 103(4):319-332. Interpretive Summary: Agricultural scientists researching the potential effects of global change on productivity of crops have usually conducted their experiments in growth chambers and greenhouses where carbon dioxide (CO2) levels could be manipulated conveniently. Unfortunately, results from such experiments are often confounded by artifacts caused by the enclosures themselves. For example, light is significantly reduced, temperatures rise by several degrees, and wind patterns are changed. For the past decade, however, a new experimental approach, Free Air Carbon dioxide Enrichment (FACE), has resolved many of these problems and has provided a realistic, cost-effective method for evaluating the effects of elevated atmospheric CO2 concentrations on plant growth, yield, and water requirements. With current FACE technology, CO2-enriched air is injected around the perimeter of circular plots, and natural wind disperses the CO2 across the experimental area. Under the calm, nighttime wind conditions found in FACE wheat experiments at Maricopa, Arizona, the blowers used to inject CO2 exerted subtle effects on the microclimate similar to the way that wind machines protect orchards from frost. Blowers were found to alter air and leaf temperatures and change patterns of dewfall. Moreover, there is evidence that these microclimatic changes accelerated plant maturity. Advantages of the FACE approach still outweigh disadvantages. However, these findings emphasize the importance of evaluating even minor environmental perturbations caused by experimental equipment. Results will help scientists design appropriate strategies for conducting global change research using similar technologies.
Technical Abstract: Free Air Carbon dioxide Enrichment (FACE) provides a method for evaluating the effects of supra-ambient CO2 concentrations on growth, development, yield, and water use of crops with very few of the problems normally associated with chambers. There are no walls interfering with incident radiation and no artificial constraints on rooting depth. With FACE technology, CO2-enriched air is injected at the perimeter of circular plots, and natural wind disperses the CO2 across the experimental area. Under the stable, nighttime wind conditions found in FACE wheat experiments at Maricopa, Arizona, the blowers used to inject CO2 exerted subtle effects on the microclimate in a manner analogous to wind machines used for orchard frost protection. Plots with blowers had nighttime foliage and air temperatures 0.6 to 1.0 degree C warmer than controls without blowers and also displayed differences in dewfall, plant development, and senescence [as measured with the normalized difference vegetation index (NDVI)]. Natural wind and turbulence appear to overcome the blower effect during daytime and on some nights. Aerial thermal imagery (8-12um) acquired during the 1998 FACE sorghum experiment provided additional evidence of the blower effect on canopy temperatures. Since increased foliage temperatures also occur when elevated CO2 induces partial stomatal closure and transpiration is reduced, all instances of leaf temperature elevation in CO2-enriched plots cannot be ascribed solely to the presence of blowers. It is concluded that proper controls for FACE facilities should have similar air flows to those used in the FACE plots. Advantages and disadvantages to nighttime CO2 enrichment are discussed.