Submitted to: Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/6/1998
Publication Date: N/A
Interpretive Summary: There is renewed interest in evaluating terrestrial CO2 fluxes and ecosystem productivity as a basis for understanding the global carbon cycle and ecosystem responses to increasing CO2. ARS global change research includes the goal of determining the importance of crops, rangeland and forest in carbon cycling and greenhouse gas increases. Measurement of CO2 on rangeland is difficult, and data are lacking for carbon dynamics on rangeland at this time. We designed a large chamber which can be used in remote rangeland settings to determine net carbon dioxide flux over entire shrub canopies. The chamber provides a unique method to circulate air through a shrub canopy. The design includes a system to simultaneously measure changes in leaf and air temperature and relative humidity in addition to CO2. This chamber will allow ARS and other scientists to collect new information regarding net carbon dioxide flux on rangeland and crops. The chamber design has been adopted for use by four other ARS locations. This technology is being used to measure gas exchange as related to management inputs on rangeland. These data are essential for strategic planning for agriculture in the face of certain increases in carbon dioxide.
Technical Abstract: Net carbon exchange of terrestrial ecosystems will likely change as atmospheric CO2 levels increase. Currently, little is known of the annual dynamics or magnitude of CO2 flux on many native and agricultural ecosystems. Remoteness of many ecosystems has limited our ability to measure CO2 flux on undisturbed vegetation. Today, many ecologists have portable photosynthesis measurement equipped with leaf cuvettes. Utility of this equipment would be enhanced if canopy-level CO2 flux could be determined as well. We designed a portable, 1-m3 chamber for use in measuring CO2 exchange in shrub dominated communities having widely varied canopy structure. The chamber was tested on an Artemisia tridentata ssp. wyomingensis / Stipa thurberiana community using 10 plots equally divided among shrub and interspace. Results show that the technique can be used to characterize CO2 fluxes with good precision (+-0.001 umol/m2/s). Net CO2 uptake was greatest May 25, on sagebrush-grass plots (7.6 umol/m2/s); whereas net CO2 uptake on grass-only plots was 3.1 umol/m2/s on that date. On sagebrush plots chamber and leaf temperature increase averaged 0.5 and 1.2 degrees C, respectively.