Soil C quantification and CO2  efflux in the Boreal forest, James Bay, Québec, Canada

Jessica Lagacé-Banville, Michelle Garneau
GEOTOP-UQAM-McGill and Department of Geography,
Université du Québec à Montréal

David Paré
Natural Ressources Canada, Canadian Forest Services,
Laurentian Forestry Centre

The Boreal forest contains about 50% of the total organic carbon stored in forest ecosystems. These types of forest cover nearly 3 million km2 and consequently (it) influence(s) significantly the global carbon cycle (Kurz et al. 2002). Forest ecosystems take up atmospheric CO2 by converting it into organic C through photosynthesis. Carbon losses in the boreal forest are insignificant compared to the carbon sink (s) it represents, especially in soils where low temperatures promote net accumulation of organic C (Dioumaeva et al. 2003). Various physico-chemical and microbial properties of boreal forest soils regulating soil organic C (SOC) accumulation and decomposition are poorly understood. In this study, we present data on the quantity and quality of SOC in five different boreal forest types, in northern Quebec.

The aims of our research are to (1) determine the role of several site-specific variables influencing carbon storage such as forest stand age, soil pH, litter accumulation and its quality, C:N ratio and sand/clay content; and (2) determine labile vs recalcitrant fraction of the SOC carbon by quantification of C mineralization rates. Results show that litterfall, soil drainage classes, and clay contents correlate significantly with the SOC contents in different forest types. Forest stand age and litterfall have a bearing on SOC accumulation rates. Forest types do not seem to affect SOC accumulation. Moreover, results suggest that wetter soil conditions result in accumulating more SOC than aerated soils through its influence on organic C decomposition rates.

This project is still underway and we are currently measuring SOC mineralization rates under variable soil temperatures (2, 14 and 29 oC) in vitro to determine site specific difference in SOC quality and reactivity to temperature across forest stand types. 
 

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