© 2001 Heron Publishing—Victoria, Canada
Daily and seasonal patterns of carbon and water fluxes above a north Australian savanna
Derek Eamus (1, 2), Lindsay B. Hutley (1) and Anthony P. O'Grady (1)
1. Co-operative Research Centre for Tropical Savannas, Northern Territory University, Darwin NT 0909, Australia / 2. Environmental Sciences, University of Technology, Sydney, P.O. Box 123, Broadway, NSW 2007, Australia / Received August 18, 2000
Summary
Daily and seasonal fluxes of carbon dioxide and water vapor above a north Australian savanna were recorded over a complete
dry season–wet season annual cycle using the eddy covariance technique. Wet season rates of photosynthesis and transpiration
were larger than those measured in the dry season and were dominated by the presence of the grassy understory. As the dry
season progressed and the grass understory died, ecosystem rates of assimilation and water vapor flux declined substantially.
By the end of the dry season, canopy assimilation and evapotranspiration rates were 20–25% of wet season values. Assimilation
was light saturated in the dry season but not in the wet season. Stomatal control of transpiration increased between the wet
and dry season. This was revealed by the decline in the slope of E with increasing leaf-to-air vapor pressure difference (D) between wet and dry seasons, and also by the significant decrease in the ratio of boundary to canopy conductance observed
between the wet and dry seasons. A simple pan-tropical modeling of leaf area index or wet season canopy CO2 flux was undertaken. It was shown that with readily available data for foliar N content and the ratio of rainfall to potential
evaporation, leaf index and wet season canopy CO2 flux can be successfully estimated for a number of tropical ecosystems, including north Australian savannas.
Keywords:
eddy covariance, evapotranspiration, photosynthesis, seasonality.
