Oral Session #4: Plant Ecology: Gas Exchange. Presiding: J. Pereira.
Monday, August 6, 2001. 8:00 AM to 12:00 PM. Hall of Ideas P&Q.

Effect of increasing soil temperature on below ground CO2 efflux: A large scale controlled system perspective.

Murthy, Ramesh1, Griffin, Kevin2, Zarnoch, Stanley 3, Dougherty, Phillip4, Watson, Barbara5, Van Haren, Joost5, Patterson, Lane 5, Mahato, Tilak5, Osmond, Barry1, 1 2 3 4 5

ABSTRACT- It has long been a goal in ecological research to make integrative measurements that can be used to scale up and down to assess large system responses in the environment in terms of detailed understanding of the component parts Until now, scaling up in complex biomes tends to have been limited to profiling a few representative species with hundreds of spot measurements (Osmond 1989). Models scaling soil respiration to a biome or landscape level has essentially utilized Q10 rates for various component parts of soil activity and then integrated the various parts. However, results obtained from spot measurements either in the field or in the laboratory have tremendous variability. This is due to inherent difficulties in the method of measurement or due to the artificiality imposed on the medium either in the laboratory or in the field. In this study we demonstrate the usefulness of a large scale facility such as the Biosphere2 Center using response of the soil to temperature increases as the model. Soil contained in three separate large enclosed parcels of land (500 square meters) were heated from 10C to 28C over a period of 42 days. This was achieved by raising the air temperature. Since each parcel of land is enclosed in a glass shell (approximate volume of 11600 cubic meters) we were able to make measurements of the whole system carbon dynamics. As there were no trees during this period of time whole system carbon dynamics was essentially whole system below ground CO2 efflux in response to increasing temperature. During this period we also took several spot measurements with a gas exchange instrument. Curves were fit to the data using the Arrhenius function and Q10 values were also derived. This was obtained for both the system level data and for the spot measurements. We further tried to scale CO2 efflux from spot level measurements to arrive at whole system CO2 efflux. Results obtained from this modeling exercise will be presented to demonstrate the usefulness of large systems in arriving at whole system carbon balances.

KEY WORDS: below ground CO2 efflux, soil respiration, system level measurements