Methanogenesis and Methanotrophy in Soil: A Review

Global warming,as a result of an increase in the mean temperature of the planet,might lead to catastrophic events for humanity.This temperature increase is mainly the result of an increase in the atmospheric greenhouse gases(GHG)concentration.Water vapor,carbon dioxide(CO2),methane(CH4)and nitrous oxide(N2O)are the most important GHG,and human activities,such as industry,livestock and agriculture,contribute to the production of these gases.Methane,at an atmospheric concentration of 1.7μmol mol-1currently,is responsible for 16%of the global warming due to its relatively high global warming potential.Soils play an important role in the CH4cycle as methanotrophy(oxidation of CH4)and methanogenesis(production of CH4)take place in them.Understanding methanogenesis and methanotrophy is essential to establish new agriculture techniques and industrial processes that contribute to a better balance of GHG.The current knowledge of methanogenesis and methanotrophy in soils,anaerobic CH4 oxidation and methanotrophy in extreme environments is also discussed.

Anthracene Removal and Mineral N Dynamics in a Surfactant-Amended Soil

Surfactants, such as non-ionic Surfynol485(ethoxylated 2,4,7,9-tetramethyl-5-decyne-4,7-diol), have been applied to accelerate removal of polycyclic aromatic hydrocarbons from soil. This study investigated the dissipation of anthracene, and carbon(C) and nitrogen(N) mineralization in soil amended with non-ionic Surfynol485 at different rates. Soil samples of a Typic Fragiudept taken from Otumba, Mexico were spiked with anthracene at a final concentration of 520 mg kg-1dry soil using acetone as solvent, amended with 0.0, 24.9, 49.8 or 124.4 g kg-1soil of the surfactant and incubated in the laboratory. The soil not amended with anthracene,acetone and the surfactant was used as a control. Dynamics of C and N and the concentration of anthracene were monitored for 56 d. After 56 d of incubation, 38% of the anthracene was removed from the unamended soil, and 47%, 55% and 66% of the anthracene were removed when 24.9, 49.8 and 124.4 g kg-1of the surfactant were applied, respectively. Application of acetone, anthracene or surfactant increased the emission of CO2, but decreased the mineral N compared to the unamended control. Applying the surfactant to the acetone or anthracene-amended soil reduced emission of CO2, but increased the mineral N at the lower application rates of the surfactant. It was found that the application of the non-ionic surfactant increased the bioavailability of anthracene and thus its removal from soil, increased C mineralization, but decreased N mineralization. Consequently, the application of non-ionic surfactant could be easily used to accelerate the removal of pollutants from hydrocarbon-contaminated soils, but mineral N in the soil would decrease, which might inhibit plant growth.