Submitted to: International Grasslands Congress
Publication Type: Proceedings
Publication Acceptance Date: November 28, 2004
Publication Date: June 26, 2005
Citation: Skinner, R.H. 2005. Dormant season carbon fluxes in humid-temperate pastures. International Grasslands Congress. 20:592 Interpretive Summary: An interpretive summary is not required.
Technical Abstract: Because of their vast size, grazing lands have the potential to sequester significant quantities of carbon, slowing the increase in atmospheric CO2 and reducing the risk of global warming. Although C uptake during the growing season can be substantial, losses during winter months can significantly reduce annual sequestration, frequently turning grazing lands into net carbon sources. This research examined dormant-season fluxes and their effect on annual carbon storage. The study was conducted on two pastures near State College, Pennsylvania, USA, dominated by a mixture of cool-season grasses or by alfalfa intermixed with cool-season grasses. Pasture-scale CO2 fluxes were quantified using an eddy covariance CO2 flux system. This report focuses on CO2 fluxes during the winters of 2002-03 and 2003-04. The dormant season was defined as the period beginning when net daily C uptake became negative in the fall and ending when daily uptake became positive again in the spring. The dormant season ranged from 125 to 156 d and was longer in 2003-2004 than in 2002-2003. Some green leaf area was observed in both pastures throughout the winter (Leaf Area Index = 0.03 to 0.50). In the absence of snow cover, photosynthetic uptake occurred at daytime air temperatures below freezing. However, nighttime efflux from the system was greater than daytime uptake so that the pastures remained C sources of approximately 2.0 to 2.5 g CO2 m-2 d-1 throughout the winter. Even though pastures are generally C sources during the winter, there were days at both sites and in both years when light and temperature conditions were conducive to C uptake.