The linkage between methane production activity and prokaryotic community structure in the soil within a shale gas field in China.

Soil methane generation mainly driven by soil prokaryotic microbes can be coupled with the degradation of petroleum hydrocarbons (PHCs); however, the relationship between prokaryotic community structure and methane production activity in soil with the potential risk of PHC contamination is seldom reported. In this study, 3 soil samples (CS-1 to CS-3) in the area nearby an exploratory gas well and 5 soil samples (DC-1 to DC-5) in a drill cutting dump area were obtained from the Fuling shale gas field (Chongqing City, China). Then, the prokaryotic community structure was examined by Illumina Miseq sequencing, and the linkage between soil methane production rate (MPR) and prokaryotic community composition was analyzed. The results indicated that 2 samples (DC-4 and DC-5) collected from the drill cutting dump area had significantly higher MPR than the other samples, and a significant and positive relationship (r = 0.44, P < 0.05) was found between soil MPR and soil organic matter (OM) content. The prokaryotic community composition in the sample (DC-5) with the highest MPR was different from those in the other samples, and soil OM and MPR were the major factors significantly correlated with the prokaryotic community structure in this soil. The samples (DC-4 and DC-5) with higher MPR had a higher relative abundance of Archaea and different archaeal community structures from the other samples, and the MPR was the sole factor significantly correlated with the archaeal genus composition in this soil. Therefore, both the prokaryotic and archaeal community structures are essential in the determination of soil MPR, and the bacterial genus of Saccharibacteria and the archaeal genus of Methanolobus might be the key contributors for methane generation in this soil from the shale gas field.

[Influence of Biochar Application on Growth and Antioxidative Responses of Macrophytes in Subsurface Flow Constructed Wetlands].

Constructed wetlands (CWs) have high potential for wastewater treatment in developing countries because of their operational convenience and low maintenance costs. However, rapid accumulation of macrophytes in these wetlands, as a result of plant litter recycling, can lead to lower removal efficiencies. Periodic harvesting is consider to be the effective measure to maintain the wastewater treatment performance, and so a lot of harvested plant waste needs to be properly disposed of. However, in China, plant waste is usually used for agricultural burning and the greenhouse gas emissions bring adverse effects on the atmospheric environment. In the traditional subsurface flow CW, the dissolved oxygen (DO) concentration is low, resulting in long-term anoxic or anaerobic conditions, which will bring damages to plant body, such as membrane lipid peroxidation and protein and DNA damage. Generally, the addition of biochar to CWs is beneficial for aeration, and improves the internal environment of wetlands. Hence, the effects of plant biochar on the pollutant purification efficiencies in CWs were studied, and the role of biochar in macrophyte growth and antioxidative response was investigated. Based on the results of biochar application in agricultural fields, the harvested wetland plant straw was pyrolyzed to biochar at 500 ℃ under a dynamic high-purity nitrogen atmosphere. The wetland plant Acorus calamus L. (AC) was chosen for this study. The impact characteristics of biochar on AC were studied in five independent CWs built in a greenhouse, by combining the analyses of growth and antioxidative responses of plants. Results showed that the removals of ammonium (NH4+-N) and total nitrogen (TN) were significantly enhanced when biochar was added to CWs and that higher long-term nitrogen removal rates were achieved when the biochar application rate was increased. The photosynthetic pigment content in AC increased significantly with increasing biochar application rate. This stimulated photosynthesis and increased the soluble protein (SP) and plant biomass amounts. Further, glutamine synthetase (GS) activity was strengthened with the addition of biochar. This helped enhance the NH4+-N metabolism and increased the relative uptake rate of AC. This study confirmed that long-term anoxic or anaerobic conditions in CWs cause membrane lipid oxidation in plants. However, the activity of the antioxidative response system was promoted with the addition of biochar, significantly decreasing the malonic dialdehyde (MDA) content in the plants.