Grassland Measurements of Photosynthesis and Respiration with Surface Chambers.

Field measurements of photosynthesis in turfgrass are often conducted with surface chambers that cover a small area of the canopy. Measurements may not be representative of overall photosynthesis where spatial variability is high. Furthermore, measurements with many portable photosynthesis systems may take up to four minutes, during which time the conditions that affect photosynthesis (e.g., air temperature) may change significantly inside the chamber. We fabricated a large turfgrass chamber that measured photosynthesis more quickly than a typical small chamber used in turfgrass; the chamber covered 34-times greater surface area than the smaller chamber. The benefits of the larger chamber potentially include: 1) measurements that cover greater surface areas and thus, reduce variability in photosynthesis measurements; and 2) faster measurements of photosynthesis, which may reduce undesirable temperature effects that may develop when chambers cover plots for longer measurement periods. Our objectives were to: 1) fabricate a large surface chamber for measuring canopy-level CO2 fluxes in turfgrass; 2) compare measurements in Kentucky bluegrass (Poa pratensis L.) of photosynthesis (sunlit chamber) and respiration (covered chamber) between the new surface chamber and a smaller surface chamber attached to a Licor 6400. Chamber sides constructed with clear Plexiglass; top covered with heat-stretched Propafilm-C. Equilibrium rates of CO2 decrease (sunlit chambers) and increase (shaded chambers) were reached rapidly, so that measurements of photosynthesis and respiration required only about 30 to 40 sec after the system was placed on the plot. Increases in air temperature were generally similar among chambers. In plot studies of turfgrass, evaluating treatment effects on photosynthesis using a combination of sunlit and shaded chamber measurements may have a distinct advantage over measurements with the sunlit chamber alone.