Experimental design: scaling up in time and space, and its statistical considerations

Abstract

INTRODUCTION Accurate measurement of the soil CO 2 efflux is critical for the assessment of the carbon budget of terrestrial ecosystems, since it is the main pathway for assimilated carbon to return to the atmosphere, and only small changes in the soil CO 2 efflux rate might have important implications on the net ecosystem carbon balance. Due to this central role in the terrestrial carbon cycle, soil CO 2 efflux has been measured throughout all biomes, and covering all principal vegetation types. Using simplified regressions of soil CO 2 efflux measurements reported in the scientific literature, the total amount of carbon emitted as CO 2 by soils worldwide has been estimated at approximately 68–80 Pg (1995; Raich et al ., 2002), representing the second largest carbon flux between ecosystems and the atmosphere. This amount is more than ten times the current rate of fossil fuel combustion and indicates that each year around 10% of the atmosphere's CO 2 cycles through the soil (Prentice et al ., 2001). Thus, even a small change in soil respiration could significantly intensify, or mitigate, current atmospheric increases of CO 2 , with potential feedbacks to climate change. In fact, soils store more than twice as much carbon globally than the atmosphere (Bolin, 2000) and consequently contain a large long-term potential for the carbon cycle climate feedback. Applying results from small-scale experiments to larger areas is necessary in order to understand the potential role of soils in sequestering or releasing carbon under changed climatic conditions, and to inform management and policy makers about likely consequences of land-use changes on carbon fluxes and stocks in specific regions.