TY - JOUR

T1 - Carbon mineralization in soil

T2 - Impact of wetting-drying, aggregation and water repellency

AU - Lamparter, A.

AU - Bachmann, J.

AU - Goebel, M. O.

AU - Woche, S. K.

N1 - Copyright: Copyright 2009 Elsevier B.V., All rights reserved.

PY - 2009/5/15

Y1 - 2009/5/15

N2 - Carbon sequestration in soil is influenced by chemical and physical soil properties. Physical soil properties such as soil structure, wettability, or soil moisture content are strongly scale-dependent. Therefore, we examined the influence of physical and chemical parameters on carbon sequestration in the laboratory on a scale termed here as "mesoscale". Carbon mineralization was measured in undisturbed and homogenized soil cores originating from three loess sites similar in texture but different in important physical and chemical properties due to the actual land-use (i.e., arable land, grassland, and forest). We related physical factors like wettability (measured in terms of contact angle), wetting history, apparent oxygen diffusion coefficient, as well as chemical factors like pH and C/N ratio, to the evolution of CO2 from disturbed and undisturbed core samples equilibrated at different matric potentials. The influence of the wetting history could be shown by drying and rewetting the samples. To simulate natural conditions, some samples were treated with a dissolved organic matter (DOM) solution instead of water to evaluate the carbon sequestrating effect when a liquid with lower surface tension than water containing additional carbon is used for rewetting. Results show that carbon sequestration is moisture-dependent. Carbon mineralization decreases with decreasing pH and increasing C/N ratio with the same significance. A close correlation between soil water repellency, measured on air-dried samples as potential contact angle (CA), and chemical parameters like pH and C/N ratio could be found, indicating that these basic chemical parameters are also closely correlated with wettability. Water repellency of natural soil is known to diminish with time when the material is wetted and re-establishes as the soil dries. Consequently, after rewetting the dried samples, a physical impact of water repellency on the CO2 release rate could be measured that was not observed during drying conditions. This could also be observed for the samples wetted with a DOM solution with easily accessible carbon and a lower liquid surface tension than pure water, simulating natural conditions. Chemical parameters seem to describe sufficiently the relation between chemical quality of the soil organic matter (SOM) and its bio-availability under drying conditions, whereas the impact of wettability on carbon mineralization rate is apparently smaller than the impact of chemical parameters. Soil structure had a significant influence on the samples' respiration rate. Whereas aggregated samples at pF 1.8 showed a higher respiration rate compared to the homogenized samples, the opposite was found for aggregated samples at pF 2.5 and no difference could be found at pF 3.2. Therefore, a carbon sequestrating effect of aggregation could only be observed at pF 2.5. We conclude that not only chemical soil properties but also physical soil properties, like aggregation and wettability as well as the wetting dynamics, are important to understand specific differences in the dynamics of carbon mineralization in soils.

AB - Carbon sequestration in soil is influenced by chemical and physical soil properties. Physical soil properties such as soil structure, wettability, or soil moisture content are strongly scale-dependent. Therefore, we examined the influence of physical and chemical parameters on carbon sequestration in the laboratory on a scale termed here as "mesoscale". Carbon mineralization was measured in undisturbed and homogenized soil cores originating from three loess sites similar in texture but different in important physical and chemical properties due to the actual land-use (i.e., arable land, grassland, and forest). We related physical factors like wettability (measured in terms of contact angle), wetting history, apparent oxygen diffusion coefficient, as well as chemical factors like pH and C/N ratio, to the evolution of CO2 from disturbed and undisturbed core samples equilibrated at different matric potentials. The influence of the wetting history could be shown by drying and rewetting the samples. To simulate natural conditions, some samples were treated with a dissolved organic matter (DOM) solution instead of water to evaluate the carbon sequestrating effect when a liquid with lower surface tension than water containing additional carbon is used for rewetting. Results show that carbon sequestration is moisture-dependent. Carbon mineralization decreases with decreasing pH and increasing C/N ratio with the same significance. A close correlation between soil water repellency, measured on air-dried samples as potential contact angle (CA), and chemical parameters like pH and C/N ratio could be found, indicating that these basic chemical parameters are also closely correlated with wettability. Water repellency of natural soil is known to diminish with time when the material is wetted and re-establishes as the soil dries. Consequently, after rewetting the dried samples, a physical impact of water repellency on the CO2 release rate could be measured that was not observed during drying conditions. This could also be observed for the samples wetted with a DOM solution with easily accessible carbon and a lower liquid surface tension than pure water, simulating natural conditions. Chemical parameters seem to describe sufficiently the relation between chemical quality of the soil organic matter (SOM) and its bio-availability under drying conditions, whereas the impact of wettability on carbon mineralization rate is apparently smaller than the impact of chemical parameters. Soil structure had a significant influence on the samples' respiration rate. Whereas aggregated samples at pF 1.8 showed a higher respiration rate compared to the homogenized samples, the opposite was found for aggregated samples at pF 2.5 and no difference could be found at pF 3.2. Therefore, a carbon sequestrating effect of aggregation could only be observed at pF 2.5. We conclude that not only chemical soil properties but also physical soil properties, like aggregation and wettability as well as the wetting dynamics, are important to understand specific differences in the dynamics of carbon mineralization in soils.

KW - Carbon sequestration

KW - Contact angle

KW - Hysteresis

KW - Soil respiration

KW - Soil structure

KW - Water repellency

UR - http://www.scopus.com/inward/record.url?scp=64549116276&partnerID=8YFLogxK

U2 - 10.1016/j.geoderma.2009.02.014

DO - 10.1016/j.geoderma.2009.02.014

M3 - Article

AN - SCOPUS:64549116276

VL - 150

SP - 324

EP - 333

JO - GEODERMA

JF - GEODERMA

SN - 0016-7061

IS - 3-4

ER -