Monday, November 5, 2007
99-2
Effect of Plant Shading on Greenhouse Gas Emissions.
For sampling of greenhouse gases, vented chambers are the most common technique because of their simplicity and economic practicality. Most chambers are made of opaque materials such as plastic or aluminum. When deployed, the interior of the chamber becomes dark. If plants are present, they are shaded which may effect gas emissions by the plant (photosynthesis versus respiration). The experiment took place in Shelton, NE on a seed-corn field that was replanted mid-season to sorghum because of hail damage. Aluminum or clear acrylic vented chambers were used to eliminate or permit sunlight during sample collection, respectively. There were no notable differences between chambers for N2O and CH4 emissions. The aluminum chambers had higher CO2 emissions (71.5 and 84.4 kg ha-1 d-1) than the clear chambers (42.4 and 36.5 kg ha-1 d-1) on the two latest sample dates (June 21 and July 14, respectively), when plants were largest. This indicates that shading of the plants from aluminum chambers is causing respiration to occur during chamber deployment, while photosynthesis is still occurring in the clear chambers. If total emissions from agroecosystems are a goal, then emissions by plants and soils should be considered. This data shows that overestimation of CO2 flux can occur if opaque chambers are used for sampling during daylight.
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