MINERALIZATION OF SELENIUM-CONTAINING AMINO ACIDS IN TWO CALIFORNIA SOILS

Authors: MARTENS, DEAN - UCR, RIVERSIDE, CA; Suarez, Donald

Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/10/1996
Publication Date: N/A
Citation: N/A

Interpretive Summary: The cycling of selenium (Se) in natural systems is very complex, yet this knowledge is needed for predicting the transport and fate of Se in agricultural environments. Plants are suggested to play a role in the Se cycle due to assimilation of soluble Se from soil into plant tissues. Upon decomposition of the plant residue in soil, the assimilated Se is believed to be released back into soil solution, but little to no information is available on the release and form of Se upon decomposition. Plants are known to assimilate Se as amino acids similar to the sulfur amino acids. This manuscript reports the mineralization of the selenoamino acids and compares the mineralization rates and resulting products to the mineralization rates and decomposition products of the corresponding sulfur amino acids.

Technical Abstract: To determine the mineralization rate of selenoamino acids in soil, 5, 25 or 50 mg Se kg-1 soil as SeMet and 5, 10, 25 mg Se kg-1 soil as SeCys were added to samples of a Panoche or a Panhill series soil and aerobically incubated at 22oC for times up to 144 h. Independent of rate of addition, SeMet and Met were rendered nonextractable by phosphate buffer within 96 h in both soils. Met additions resulted in adsorption or direct assimilation and deviated from first-order reaction kinetics, but SeMet additions more closely followed first-order reaction kinetics. The calculated half-life (t0.5) of SeMet in the Panhill and Panoche soils was 23.5 and 3.2 h (5 mg Se kg-1), 35.1 and 14.7 h (25 mg Se kg-1), and 42.0 and 24.8 h (50 mg Se kg-1), respectively. The majority of the SeMet and Met additions were recovered as volatile species (50 to 80%) with minor accumulation of inorganic forms suggesting that SeMet and Met are mineralized by the same microbial methylation pathway. In contrast to SeMet, SeCys was rapidly nonextractable (< 6 h) from both soils used with little to no volatile Se detected. The released SeCys-Se was initially recovered as phosphate-soluble selenite and selenide after 6 h of incubation. Increased incubation time to 48 h resulted in an increased conversion to less soluble Se forms. These results suggest that SeMet-Se present in organic Se residues as will not accumulate in soil due to extensive volatilization. Additions of seleniferous plant residues rich in SeCys will result in organic Se mineralization to inorganic Se forms in soil as a result of microbial pathways that lack volatilization mechanisms.