Microbial Actvity and¹³C/¹²C Ratio as Evidence of N-Hexadecane and N-Hexadecanoic Acid Biodegradation in Agricultural and Forest Soils

Abstract

The dynamics of microbial degradation of exogenous contaminants, n-hexadecane and its primary microbial oxidized metabolite, n-hexadecanoic (palmitic) acid, was studied for topsoils, under agricultural management and beech forest on the basis the changes in O 2 uptake, CO 2 evolution and its associated microbial and non-microbial carbon isotopic signature, the respiratory quotient (RQ) and the priming effect (PE) of substrates. Soil microbial communities in agricultural soil responded to the n-hexadecane addition more rapidly compared to those of forest soil, with lagperiods of about 23 ± 10 and 68 ± 13 hours, respectively. Insignificant difference in the lag-period duration was detected for agricultural (t lag = 30 ± 13 h) and forest (t lag = 30 ± 14 h) soils treated with n-hexadecanoic (palmitic) acid. These results demonstrate that the soil microbiota differed in metabolic activities for using n-hexadecane as a reductive hydrocarbon and n-hexadecanoic acid as a partly oxidized hydrocarbon. The corresponding δ 13 C of respired CO 2 after the addition of the hydrocarbon contaminants to soils indicates a shift in microbial activity towards the consumption of exogenous substrates with a more complete degradation of n-hexadecane in the agricultural soil, for which some initial contents of hydrocarbons are inherent. It was reflected in the carbon isotope signature of microbial biomass. It is supposed that the observed deviation of RQ from theoretically calculated value under microbial substrate mineralization is determined by difference in the time ( t i ) of registration of CO 2 production and O 2 consumption. Positive priming effect (PE) of n-hexadecane and negative PE of n-hexadecanoic (palmitic) acid were detected in agricultural and forest soils. It is suggested that positive PE of n-hexadecane is conditioned by the induction of microbial enzymes that perform hydroxylation/oxygenation of stable SOM compounds mineralized by soil microbiota to CO 2 . The microbial metabolism coupled with oxidative decarboxylation of n-hexadecanoic acid is considered as one of the most probable causes of the revealed negative PE value.

The Waste Oil Resulting from Crude Oil Microbial Biodegradation in Soil

“…However, PE became negligible in both experiments during 6-8 day exposure; it is possibly the mineralization time of aliphatic hydrocarbons or their partially oxidized products. The negative PE has been demonstrated previously in the processes of the microbial mineralization of n-hexadecanoic acid introduced into soil (Zyakun et al 2011). At the next period of the exposure, the PE values demonstrate the positive values of 300 % in experiment 1 and about 400 % in experiment 2.…”

“…Acceleration of SOM degradation (positive PE) was also observed in case of addition of an aliphatic hydrocarbon (n-hexadecane) to the soil. Introduction into soil of n-hexadecanoic acid, the product of n-hexadecane oxidation, resulted in the lower rate of SOM mineralization compared to native soil (negative PE) (Zyakun et al 2011). In the light of brief presentation of methods characterizing biodegradation and transformation of exogenous organic products entering the soil, the fate of crude oil in soils may be defined by the following parameters: (a) the rate of CO 2 production as result of mineralization of crude oil and SOM; (b) activation of mineralization of native soil organic matter by introduced substrate (priming effect); c) the ratio of the quantities of biomass of the microorganisms growing on oil hydrocarbons as a substrate and quantities of SOM mineralized into CO 2 .…”

“…(Blagodatskaya et al 2007;Blagodatskaya and Kuzyakov 2008). Obviously, unambiguous determination of PE by CO 2 production calls for an exogenous substrate different from SOM in carbon isotopes (Zyakun et al 2003;Dilly and Zyakun 2008;Zyakun et al 2011). It has been shown that addition to the soil of a substrate easily accessible for microorganisms (e.g., glucose, amino acids, etc.)…”

Microbial Activity and Decomposition of Soil Organic Matter in Roadside Soils Contaminated With Petroleum Hydrocarbons

“…Due to the unique metabolic system with extracellular enzymes the microbial community utilizes PHs for growth‐supporting carbon and energy, however they are toxic in high concentrations and thus the degradation of PHs requires adaptations and resource trade‐offs . The quantitative and qualitative transformation of PHs by microbial communities depends on the PHs characteristics (amount, nature, and age), environmental conditions (oxygen diffusion, temperature, physical and chemical PHs dispersion, nutrient availability) and composition of autochthonous microbial community .…”

“…The estimation of PHs biodegradation intensity and microbial activity in soils can be determined by monitoring the PHs contamination and related metabolites; one of the most universal is CO 2 efflux as indicator of biologically processed carbon by respiration . It has been demonstrated that addition of exogenous organic substrate (e.g., glucose, cellulose, amino acids, etc.)…”