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Biogeochemical processes in frozen soils

unfrozen water in frozen soils and factors regulating carbon mineralization at low temperatures

Harrysson Drotz, Stina (2010). Biogeochemical processes in frozen soils. Diss. (sammanfattning/summary) Umeå : Sveriges lantbruksuniv., Acta Universitatis Agriculturae Sueciae, 1652-6880 ; 2010:32
ISBN 978-91-576-7509-5
[Doctoral thesis]

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High latitude ecosystems are important for global carbon (C) balances and are among the most sensitive ecosystems to climate change. Microbial CO2 production in soil is known to proceed at temperatures < 0ºC in these regions and winter CO2 emissions can significantly affect annual C balances. However, the low-temperature processes involved were poorly understood. In frozen soils, the microbial activity must be confined to small pools of liquid water present in the bulk soil. Therefore, in laboratory incubation and NMR experiments I have investigated: the distribution of unfrozen water in frozen boreal forest soils; its implications for the mineralization of soil organic matter (SOM) and microbial substrate utilization under frozen conditions; factors controlling these phenomena and their temperature responses. The results show that the osmotic potential of unfrozen water contributes 20-69% of the total water potential in frozen soil, in contrast to unfrozen soil where its contribution is generally negligible. They also show that recalcitrant SOM components, such as aromatics and alkyl C, have positive effects on unfrozen water contents, and thus on CO2 production in frozen soils. Further, temperature responses of CO2 production in frozen soils are controlled by unfrozen water, and estimated biochemical Q10-values were consistent with thermodynamic theory after factoring out the effects of water availability. In addition, both catabolic and anabolic processes can proceed at -4ºC and no clear differences in C allocation patterns of metabolised substrates were observed across the -4°C to +9°C temperature range. However, at < 0ºC the soil microbes required longer times to adapt and utilise substrates maximally than at > 0ºC. At -4ºC, this adaptation was associated with increased cell membrane fluidity, and resulted in significant increases in CO2 production. The findings contribute to the general understanding of low temperature microbial processes; indicating that the hierarchy of controlling factors changes as soil freezes, but microbial metabolism is similar in frozen and unfrozen soil. The results have important implications for the conceptualization of processes related to soil C dynamics.

Authors/Creators:Harrysson Drotz, Stina
Title:Biogeochemical processes in frozen soils
Subtitle:unfrozen water in frozen soils and factors regulating carbon mineralization at low temperatures
Series Name/Journal:Acta Universitatis Agriculturae Sueciae
Year of publishing :2010
Number of Pages:61
ALLI Harrysson Drotz S., Tilston E. L., Sparrman T., Schleucher J., Nilsson M., and Oquist M. G. (2009) Contributions of matric and osmotic potentials to the unfrozen water content of frozen soils. Geoderma 148(3-4), 392-398. II Harrysson Drotz S., Sparrman T., Schleucher J., Nilsson M., and Oquist M. G. (2010) Effects of soil organic matter composition on unfrozen water content and heterotrophic CO₂ production of frozen soils. Geochimica et Cosmochimica Acta 74(8), 2281-2290. III Oquist, M.G., Sparrman, T., Klemedtsson, L., Harrysson Drotz, S., Grip, H., Schleucher, J., Nilsson, M. (2009). Water availability controls microbial temperature responses in frozen soil CO₂ production. Global Change Biology 15(11), 2715-2722. IV Harrysson Drotz S., Sparrman T., Schleucher J., Nilsson M., and Oquist M. G. Microbial activity in frozen boreal forest soils – potentials for catabolic and anabolic processes under frozen conditions. Manuscript.
Place of Publication:Umeå
ISBN for printed version:978-91-576-7509-5
Publication Type:Doctoral thesis
Full Text Status:Public
Agrovoc terms:soil, frost, soil organic matter, carbon, carbon dioxide, soil water, soil temperature, catabolism, anabolism, carbon cycle, mineralization
Keywords:frozen soil, unfrozen water, NMR, water potential, soil organic matter, CO2, carbon, temperature response, boreal, catabolism, anabolism, microbial activity, C mineralization.
Permanent URL:
ID Code:2270
Department:(S) > Dept. of Forest Ecology and Management
Deposited By: Stina Harrysson Drotz
Deposited On:14 Apr 2010 00:00
Metadata Last Modified:02 Dec 2014 10:17

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