Carbon dioxide efflux from a 550 m3 soil across a range of soil temperatures

Because of scaling problems point measurements of soil CO2 efflux on a small volume of soil may not necessarily reflect an overall community response. The aim of this study was to test this hypothesis in the Biosphere 2 facility and achieve the following broad goals: (1) investigate soil net CO2 exchange-temperature relationship at the community level; (2) compare soil net CO2 exchange at the community level to the traditional sample point estimates Of CO2 efflux scaled up to the community level; (3) evaluate the usefulness of a facility such as Biosphere 2 for conducting community level experiments for studying response to a climatic perturbation under controlled environmental conditions. A 550 m 3 volume of soil with 282, 15 cm tree stumps was enclosed at the Biosphere 2 Center and warmed from 10 to 25 degreesC over a period of 34 days. Net CO2 exchange from this community was measured at various points on the soil surface with 78.5 cm(2) chambers and for the whole community using each of the three bays at Biosphere 2 Center as a closed system. Soil CO2 efflux rates obtained by point measurements showed tremendous variability from location to location. At the community level and with point measurements, net CO2 exchange increased exponentially with increasing soil temperatures. Q(10) values from both the point and community level measurements ranged from 1.7 to 2.5. Scaling of point measurements by soil surface area and time overestimated community rates by 36% revealing some of the limitations of point measurements. This experiment demonstrates how Biosphere 2 facility could be used to study behavior of individual components and measure responses at the community level and test our capacity to scale point in time and space measures of community processes to the community level. (C) 2002 Elsevier Science B.V. All rights reserved.