The measurement and simulation of CO₂ efflux in a Florida slash pine plantation

• Main Author: Fang, Changming
• Published: University of Edinburgh 1997
• Subjects: 577.27
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.650484

Accurately measuring CO<SUB>2</SUB> efflux from the soil surface and adequately simulating the processes of CO<SUB>2</SUB> production and transport in the soil are crucial to enhance our understanding of carbon cycling in an ecosystem and at the global scale. However, significant uncertainty remains in both measurement and simulation of the efflux. An open-top, dynamic chamber technique was developed for <I>in situ</I> CO<SUB>2</SUB> efflux measurement. The pressure difference between inside and outside the chamber was found to be a dominant factor controlling the measured CO<SUB>2</SUB> efflux from the soil surface with dynamics chamber methods as a change of a few tenths of a Pa in the pressure difference will cause a several fold variation in the measured CO<SUB>2</SUB> efflux. This influence is negligible in this new open-top chamber. A flow rate up to 8 dm<SUP>3</SUP> min<SUP>-1</SUP> has no influence on the measured CO<SUB>2</SUB> efflux. The mean carbon dioxide efflux, measured in a mature Florida slash pine (<I>Pinus elliottii </I>Engelm. var. <I>elliottii</I>) plantation in 1995-1996, was 0.217 mg CO<SUB>2</SUB> m<SUP>-2</SUP> s<SUP>-1</SUP> (varying from 0.179 to 0.253) in October 1995 and 0.087 mg CO<SUB>2</SUB> m<SUP>-2</SUP> s<SUP>-1</SUP> (varying from 0.031 to 0.146) in January 1996. Soil temperature, which accounts for about 90% of the variability in CO<SUB>2</SUB> efflux, is by far the most influential factor controlling the CO<SUB>2</SUB> efflux from the soil surface. The Q<SUB>10</SUB> value for total soil CO<SUB>2</SUB> efflux in relation to soil temperature measured at 5 cm is 2.5 and the activation energy of soil respiration has a value of 56.9 kJ mol<SUP>-1</SUP>. Soil respiration in the slash pine plantation is highly and spatially variable, and generally increases with increase in fine root biomass, litter and humus amount on the forest floor but is inversely related to the amount of organic matter in the mineral soil. The spatial heterogeneity of CO<SUB>2</SUB> efflux in the plantation is mainly caused by the uneven distribution of palmetto plants and can be well explained by a simple model incorporating live and dead biomass and soil total porosity as predictor variables. CO<SUB>2</SUB> concentration in the soil gas increases with depth, with ranges of 0.25% to 1% by volume at a depth of 60cm and 600-760 cm<SUP>3</SUP> m<SUP>-3</SUP> at 2 cm depth during October and January in the slash pine plantation.