Seasonal and inter-annual variation in carbon dioxide exchange and carbon balance in a mixed grassland

Abstract

Seasonal and inter-annual variation in carbon dioxide exchange and carbon balance in a mixed grassland by Peter Carlson Chairperson of the Supervisory Committee: Professor Lawrence Flanagan Department of Biological Science Eddy covariance measurements were carried out to document the seasonal and inter-annual variation in CO2 flux in a mixed prairie grassland. There was very different net ecosystem carbon exchange between the two years of study. In 1998 the maximum net ecosystem carbon exchange was 4.95 g C m-2d-1, compared to 2.50 g C m-2d-1 in 1999. The most important environment control on CO2 uptake was volumetric soil moisture content through its affect on leaf area index. There was evidence of stomatal limitation of CO2 uptake, during periods of atmospheric drought. The total seasonal net ecosystem carbon gain for 1998 was 190.0 g C m-2, compared with 46.8 g C m-2 in 1999. This grassland is a large carbon sink in a growing season of above normal precipitation. In a year of normal summer precipitation, this grassland is a small carbon sink, replacing slightly more carbon than is lost through winter respiration.