Canadian Forest Service Publications

Topographically regulated traps of dissolved organic carbon create hotspots of soil carbon dioxide efflux in forests. Topographically regulated traps of dissolved organic carbon create hotspots of soil carbon dioxide efflux in forests. 2013. Creed, I.F.; Webster, K.L.; Braun, G.L.; Bourbonnière, R.A.; Beall, F.D. Biogeochemistry 112:149-164.

Year: 2013

Issued by: Great Lakes Forestry Centre

Catalog ID: 35535

Language: English

Availability: PDF (request by e-mail)

Available from the Journal's Web site.
DOI: 10.1007/s10533-012-9713-4

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Abstract

Soil carbon pools are an essential but poorly understood factor in heterotrophic soil respiration on forested landscapes. We hypothesized that the topographically regulated distribution of dissolved organic carbon (DOC) is the dominant factor contributing to soil CO2 efflux. We tested this hypothesis by monitoring soil CO2 efflux and sampling particulate and dissolved substrates (both mobile DOC in soil solution and DOC potentially sorbed onto Fe and Al oxyhydroxides) in surface (freshly fallen leaves (FFL) and forest floor) and near-surface (A-horizon or top 10 cm of peat) soils along three hillslope transects (15°, 25° and 35° slopes) that included upland (crest, shoulder, backslope, footslope, and toeslope) and wetland (periphery and central) topographic features during the snowfree season within a sugar maple forest. We observed that median snowfree season soil CO2 efflux ranged from <1 to >5 μmol CO2 m−2 s−1. Substrates in the near-surface mineral soil were most strongly related to median soil CO2 efflux, and when combined mobile DOC and sorbed DOC together explained 78% of the heterogeneity in median soil CO2 efflux (p < 0.001). When the carbon pool in FFL (an important source of DOC to the forest soils) was included, the explanation of variance increased to 81% (p < 0.001). Topographically regulated processes created high concentrations of mobile DOC at the footslope, and high concentrations of sorbed DOC further downslope at the toeslope, forming distinct traps of DOC that can become hotspots for soil CO2 production. A reduction in the uncertainty of forest carbon budgets can be achieved by taking into consideration the topographic regulation of the substrates contributing to soil CO2 efflux.

Plain Language Summary

Oil carbon pools are an essential part of soil respiration in forests. Carbon budget estimates could be improved by obtaining more accurate estimates of carbon in forest soils. Some locations in the forest contain much higher amounts of carbon due to their position on a slope or the type of soil. We tested the hypothesis that topography has the greatest influence on the amount of dissolved organic carbon in surface soils and is the most important factor in release of soil carbon dioxide. We sampled surface and near-surface soils from various topographic positions within a sugar maple forest and measured carbon dioxide release. Substrates in the near-surface mineral soil had the biggest effect on release of carbon dioxide from the soil.