Adding dissolved organic carbon to simulate freeze-thaw related N2O emissions from soil

• Published in: Journal of plant nutrition and soil science 2004-08, Vol.167 (4), p.471-478
• Main Authors: Sehy, U, Dyckmans, J, Ruser, R, Munch, J.C
• Format: Article
• Language: English
• Subjects: Agronomy. Soil science and plant productions; arable soils; ATP; available carbon; biological activity in soil; Biological and medical sciences; carbon; carbon dioxide; DOC; emissions; equations; freeze-thaw cycles; freezing and thawing; Fundamental and applied biological sciences. Psychology; General agronomy. Plant production; mathematical models; nitrification; nitrous oxide; organic compounds; soil microorganisms; soil nutrient balance; soil respiration; Soil science; soil temperature; Soil-plant relationships. Soil fertility; Soil-plant relationships. Soil fertility. Fertilization. Amendments
• ISSN: 1436-8730; 1522-2624
• DOI: 10.1002/jpln.200421393

It has been assumed that high winter N2O emissions from soils are the result of increased amounts of microbially available organic C liberated during freezing and metabolized during subsequent thawing. In a laboratory experiment, we attempted to simulate freeze‐thaw events by adding dissolved organic C (DOC) to sieved soil of high water content (95% water‐filled pore space). In a full factorial design, CO2 and N2O emissions of a) soil samples provided with DOC extracted from frozen soil and b) soil samples frozen for 46 days and thawed were compared. Additionally, NO$_3^-$, DOC and microbial ATP contents of all treatments were repeatedly analyzed during the experiment. The addition of DOC to unfrozen soil (–F+C) resulted in a substantial (22‐fold) increase in N2O emissions as compared to the control (–F–C). However, following thawing, the increase in N2O emissions was much larger (828‐fold in +F–C and 1243‐fold in +F+C). Freezing, but not the addition of DOC led to increased CO2 emissions. Neither treatment affected microbial adenylate content. By adding 15N‐labeled nitrate to the soil samples, the main process leading to elevated N2O flux rates after both DOC addition and freeze‐thaw treatment was identified as denitrification. We conclude that the availability of C substrate plays an important role for freeze‐thaw‐related N2O emissions. However, the fact that the simulated treatment and the freeze‐thaw treatment yielded significantly different amounts of N2O suggests that both quantity and quality of available C differed between the treatments. The localization of the liberated substrate, i.e., the availability in situ, seems to be of major importance for the amount of N2O produced. Die Zugabe gelöster organischer Substanz zur Simulation von durch Frost und Auftauen induzierten N2O‐Freisetzungen aus Böden Die vorgestellten Untersuchungen basieren auf der Annahme, dass hohe N2O‐Emissionsraten im Winter auf durch Frostwirkung erhöhte Mengen an mikrobiell verfügbarem organischem C zurückzuführen sind. In einem Laborexperiment sollten daher Frost‐Auftau‐Ereignisse durch die Zugabe von gelöstem organischem C (DOC) zu gesiebtem Boden mit einem hohen Wassergehalt (95 % wassergefülltes Porenvolumen) simuliert werden. In einer vollständigen Faktorenanalyse wurden die CO2‐ und N2O‐Emissionen von a) Bodenproben, die mit DOC, der aus gefrorenem Boden gewonnen wurde, beaufschlagt wurden, und b) Bodenproben, die über 46 Tage gefroren waren und aufgetaut wurden, vergli