Winter soil frost conditions in boreal forests control growing season soil CO₂ concentration and its atmospheric exchange

• Published in: Global change biology Vol. 14; no. 12; pp. 2839 - 2847
• Main Authors: ÖQUIST, M.G, LAUDON, H
• Format: Journal Article
• Language: English
• Published: Oxford, UK Oxford, UK : Blackwell Publishing Ltd 01.12.2008; Blackwell Publishing Ltd; Wiley-Blackwell
• Subjects: Animal and plant ecology; Animal, plant and microbial ecology; Biological and medical sciences; boreal forest soil; Carbon dioxide; Ecosystem studies; Forest soils; Forestry; frozen soils; Fundamental and applied biological sciences. Psychology; General aspects; General forest ecology; Generalities. Production, biomass. Quality of wood and forest products. General forest ecology; Ice; Plant growth; soil frost; soil respiration; Winter; Norway; Boreal forest; Forest stand; boreal forest soil; Carbon dioxide; Growing season; frozen soils; soil respiration; Forest soil; Exchange; Concentration measurement; Gymnospermae; soil frost; Frozen ground; Coniferales; Spermatophyta; Respiration; Picea abies
• ISSN: 1354-1013; 1365-2486
• DOI: 10.1111/j.1365-2486.2008.01669.x

The impact of changes in winter soil frost regime on soil CO₂ concentration and its atmospheric exchange in a boreal Norway spruce forest was investigated using a field-scale soil frost manipulation experiment. The experiment comprised three treatments: deep soil frost, shallow soil frost and control plots (n= 3). Winter soil temperatures and soil frost distribution were significantly altered by the different treatments. The average soil CO₂ concentrations during the growing season were significantly lower in plots with deep soil frost than in plots with shallow soil frost. The average CO₂ soil-atmosphere exchange rate exhibited the same pattern, and differences in soil respiration rates among the treatments were statistically significant. Both the variation in soil CO₂ concentration and the CO₂ soil-atmosphere exchange rate could statistically be explained by the differences in the maximum soil frost depth during the previous winter. A response model for growing season soil respiration rates suggests that every 1 cm change in winter soil frost depth will change the emission rates by ca. 0.01 g CO₂ m⁻² day⁻¹, corresponding to 0.2-0.5% of the estimated net ecosystem productivity (NEP). This suggests that the soil frost regime has a significant influence on the C balance of the system, because interannual variations in soil frost up to 60 cm have been recorded at the site. We conclude that winter climate conditions can be important in controlling C balances in northern terrestrial ecosystems, and also that indirect effects of the winter season must be taken into account, because these can affect the prevailing conditions during the growing season.