ARS | Publication request: Spectroscopic characteristics and biodegradability of cold and hot water extractable soil organic matter under different land uses in subarctic Alaska

Submitted to: Chemosphere
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 6, 2013
Publication Date: N/A

Interpretive Summary: The release and turnover of water extractable organic matter (WEOM) play an important role in soil carbon and nitrogen cycling. WEOM can be extracted by water at ambient (20°C) temperature (cold WEOM), and at temperature of 70 or 80°C (hot WEOM). The aim of this study was to comparatively assess chemical characteristics and biodegradability of water extractable organic matter (WEOM) at 22 and 80oC in 14 subarctic Alaskan soils under different land uses. Sequentially extracted cold and hot WEOM were characterized by ultraviolet and fluorescence spectroscopies. Biodegradability was assessed in a 21-d solution incubation by measuring the loss of water extractable organic C (WEOC) and N (WEON). Both cold and hot WEOM possessed three similar fluorophore components, but the percentages differed. The protein-like fluorophore component in hot WEOM was tyrosine-relevant, whereas the protein-like fluorophore in cold WEOM was tryptophan-relevant. Analysis of other spectral features showed that hot WEOM contained more protein-like fluorophore, and less humified and aromatic aromatic small molecular weight compounds than did cold WEOM. Furthermore, the biodegradability of both cold and hot WEOC was correlated to changes of these spectral properties. Information derived from this work contributed to better understanding of subarctic soil WEOM properties and their biodegradability.

Technical Abstract: Cold (22 degrees C) and hot water (80 degrees C) extractions have been used to estimate labile organic C and N in soils. The aim of this study was to comparatively assess chemical characteristics and biodegradability of water extractable organic matter (WEOM) at 22 and 80 degrees C in 14 Alaskan soils under different land uses. Sequentially extracted cold and hot WEOM were characterized by ultraviolet and fluorescence spectroscopies. Biodegradability was assessed in a 21-d solution incubation by measuring the loss of water extractable organic C (WEOC) and N (WEON). In all soils, the concentrations of WEOC and WEON were significantly (p<0.05) higher in hot than in cold water extractions. The cold and hot WEOM consisted of three fluorescence components including humic-like, fulvic-like, and protein-like fluorophores. However, for protein components in the extractions, tryptophan-like component was dominated in cold WEOM, while tyrosine-like component was predominant hot WEOM. Compared to cold WEOM, the UV absorptivity at 254 nm (SUVA254) and Fluorescence index (FIX) were significantly (p<0.05) decreased in hot WEOM of all soils, but the Feff, humic-like, and proportion of protein-like components were significantly (p<0.05) increased. The biodegradability of hot WEOC and WEON was significantly (p<0.05) higher than that of cold WEOC and WEON in all soils. The biodegradability of cold or hot WEOC was significantly correlated (r=0.78, p<0.01) with the protein-like component, indicating that a protein-like fluorophore is a labile fraction in both cold and hot WEOM pools. Information derived from this work contributed to better understanding of subarctic soil WEOM properties and their biodegradability.