Comparison of Forest Soil Carbon Dynamics at Five Sites Along a Latitudinal Gradient

Journal Article · Sat Jan 01 04:00:00 EST 2011 · Geoderma

DOI:https://doi.org/10.1016/j.geoderma.2011.08.007· OSTI ID:1033516

Garten, Jr, Charles T ^[1]

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1. ORNL

Carbon stocks, and C:N ratios, were measured in the forest floor, mineral soil, and two mineral soil fractions (particulate and mineral-associated organic matter, POM and MOM, respectively) at five forest sites, ranging from 60 to 100 years old, along a latitudinal gradient in the eastern United States. Sampling at four sites was replicated over two consecutive years. For many measurements (like forest floor carbon stocks, cumulative soil organic carbon stocks to 20 cm, and the fraction of whole soil carbon in POM), there was no significant difference between years at each site despite the use of somewhat different sampling methods. With one exception, forest floor and mineral soil carbon stocks increased from warm, southern, sites (with fine-textured soils) to northern, cool, sites (with more coarse-textured soils). The exception was a northern site, with less than 10% silt-clay content, that had a soil organic carbon stock similar to those measured at southern sites. Soil carbon at each site was partitioned into two pools (labile and stable) on the basis of carbon measured in the forest floor and POM and MOM fractions from the mineral soil. A two-compartment steady-state model, with randomly varying parameter values, was used in probabilistic calculations to estimate the turnover time of labile soil organic carbon (MRTU) and the annual transfer of labile carbon to stable carbon (k2) at each site in two different years. Based on empirical data, the turnover time of stable soil carbon (MRTS) was determined by mean annual temperature and increased from 30 to 100 years from south to north. Moving from south to north, MRTU increased from approximately 5 to 14 years. Consistent with prior studies, 13C enrichment factors ( ) from the Rayleigh equation, that describe the rate of change in 13C through the soil profile, were an indicator of soil carbon turnover times along the latitudinal gradient. Consistent with its role in stabilization of soil organic carbon, silt-clay content along the gradient was positively correlated (r = 0.91; P 0.001) with parameter k2. Mean annual temperature was indicated as the environmental factor most strongly associated with south to north differences in the storage and turnover of labile soil carbon. However, soil texture appeared to override the influence of temperature when there was too little silt-clay content to stabilize labile soil carbon and thereby protect it from decomposition. Irrespective of latitudinal differences in measured soil carbon stocks, each study site had a relatively high proportion of labile soil carbon (approximately 50% of whole soil carbon to a depth of 20 cm). Depending on unknown temperature sensitivities, large labile pools of forest soil carbon are potentially at risk of depletion by decomposition in a warming climate, and losses could be disproportionately higher from coarse textured forest soils.

• Research Organization: Oak Ridge National Laboratory (ORNL); Oak Ridge National Environmental Research Park
• Sponsoring Organization: SC USDOE - Office of Science (SC)
• DOE Contract Number: AC05-00OR22725
• OSTI ID: 1033516
• Journal Information: Geoderma, Journal Name: Geoderma Vol. 167-68; ISSN 0016-7061; ISSN GEDMAB
• Country of Publication: United States
• Language: English

Related Subjects

54 ENVIRONMENTAL SCIENCES
CARBON
FLOORS
FORESTS
ORGANIC MATTER
SAMPLING
SOILS
STABILIZATION
STORAGE
TEXTURE