Journal
BIOGEOSCIENCES
Volume 13, Issue 11, Pages 3427-3439Publisher
COPERNICUS GESELLSCHAFT MBH
DOI: 10.5194/bg-13-3427-2016
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Funding
- Swiss National Science Foundation (SNF)
- National Research Plan 68 Sustainable use of soils as a resource (NRP68) [SNF 406840_143023/11.1.13-31.12.15]
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Soil organic matter (SOM) forms the largest terrestrial pool of carbon outside of sedimentary rocks. Radiocarbon is a powerful tool for assessing soil organic matter dynamics. However, due to the nature of the measurement, extensive C-14 studies of soil systems remain relatively rare. In particular, information on the extent of spatial and temporal variability in C-14 contents of soils is limited, yet this information is crucial for establishing the range of baseline properties and for detecting potential modifications to the SOM pool. This study describes a comprehensive approach to explore heterogeneity in bulk SOM C-14 in Swiss forest soils that encompass diverse landscapes and climates. We examine spatial variability in soil organic carbon (SOC) C-14, SOC content and C : N ratios over both regional climatic and geologic gradients, on the watershed-and plot-scale and within soil profiles. Results reveal (1) a relatively uniform radiocarbon signal across climatic and geologic gradients in Swiss forest topsoils (0-5 cm, Delta C-14 = 130 +/- 28.6, n = 12 sites), (2) similar radiocarbon trends with soil depth despite dissimilar environmental conditions, and (3) micro-topography dependent, plot-scale variability that is similar in magnitude to regional-scale variability (e.g., Gleysol, 0-5 cm, Delta C-14 126 +/- 35.2, n = 8 adjacent plots of 10 x 10 m). Statistical analyses have additionally shown that Delta C-14 signature in the topsoil is not significantly correlated to climatic parameters (precipitation, elevation, primary production) except mean annual temperature at 0-5 cm. These observations have important consequences for SOM carbon stability modelling assumptions, as well as for the understanding of controls on past and current soil carbon dynamics.
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