Fujii, K., Morioka, K., Hangs, R., Funakawa, S., Kosaki, and Anderson, D. W. 2013. Rapid turnover of organic acids in a Dystric Brunisol under a spruce-lichen forest in northern Saskatchewan, Canada. Can. J. Soil Sci. 93: 295-304. Organic acids released by lichen play an important role in mineral weathering and podzolization in the Boreal-Tundra transition zone of Canada; however, importance of low-molecular-weight organic acids in the soil carbon (C) cycle in the black spruce-lichen forests remains unclear. We examined soil solution composition and mineralization kinetics of 14C-radiolabelled oxalate and citrate to quantify the C fluxes from organic acid mineralization in a Dystric Brunisol under a spruce-lichen forest in northern Saskatchewan. Oxalate concentration in soil solution was greatest in the lichen layer, while the high levels of citrate were observed in the lichen and organic (O) layers to the Ae horizon with the lowest sorption capacity. Oxalate and citrate were rapidly mineralized within the lichen and O layers and had short mean residence times (0.5 to 2.7 h). Substantial C fluxes due to citrate mineralization were observed both within the lichen and O layers, but oxalate mineralization led to C flux in the lichen layer only. The contribution of citrate and oxalate to microbial respiration was large (up to 57%) in the surface soil layers. Citrate was the dominant substrate for microbial respiration of the surface soil; however, it appears that oxalate could also be an important microbial substrate within the lichen layer, at least in summer months. We conclude that the exudation of low-molecular-weight organic acids by lichenous fungi, followed by their rapid mineralization, could play an important role in the C cycles of the sandy soils under spruce-lichen forest.
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Vol. 93 • No. 3