The Microbial Community Structure In Liaohe Delta Wetlands And Its Environmental Significances

The global warming potential（GWP） of CH4 is ²5 times greater than that of CO2 on a 100 year time scale and high emissions of CH4 can therefore have disproportionately adverse effects on the climate. Wetlands contribute to about 24% of global CH4 emissions from all sources, and are the largest natural source of CH4. Due to the increasing concern of greenhouse gas emissions and global warming, it is important to gain more knowledge about the factors affecting CH4 emissions in different wetland systems from molecular level, presumably because the rates of CH4 emissions have closely related to methanogenus and methanotrophs. This study would give scientists new insights into the mechanism on CH4 emissions, and provide effect service to mitigation strategy.This work studied microbial communities and related physical and chemical parameters at 4 wetland sites colonized by Asian rice（Oryza sativa L.）, reed（Phragmites australis（Cav.） Trin. Ex Steud） and seablite（Suaeda salsa（L.） Pall., III） in the west of the Liaohe Delta（LHD）. The principle techniques involved in this study were sediment core sampling, microcosm incubation, High–throughput sequencing, and R program for data analysis. The major findings were shown as follows:（1） The p H values were within the range of 7–8, accumulated with high organic matter on the surface of the wetland soils. The concentrations of ions Na+、Cl–、SO₄^2– were generally high, presumably response to the coastal environment.（2） Sulfate–reducing bacteria, SRB, which likely functioned as electron acceptance, and reduced the available substrate for methanogenus, and consequently inhibited CH4 emissions. The implication being that the coastal wetlands are more valuable for regulating climate than fresh water weltands, where generally absent the ion of SO₄^2–.（3） The relative abundance of methanogen varied within a given habitat and cross different wetlands. The methanogen relative abundance normalized to dry weight peaked at the depth of 30 cm for reed wetland due to reduction environment, while there was no detectable methanogen in the upper 10 cm for aged wetlands as the aerobic zone generally created when there is no water cover its surface. However, I found there were very low methanogen enrichments beneath 10 cm for aged reed wetlands and below surface for rice wetlands, the most likely explanation is that the both P. autralis and rice have well–developed aerenchyma in roots, rhizomes and stems, which provides them with a high ability to transport gasses between the soil and the atmosphere through the plant tissue and brought a plenty air to the deeper soils, which does not favor the colonization of methanogens. The dominant methanogens was methanobacterium for aged reed wetlands and rice paddy, methanosarcina for newly created reed wetlands near coasts. There were no detectable methanogens in seablite wetlands due to most of those wetlands distributed along the coasts and derived a plenty of SO₄^2– from sea waters, which could function as oxidizing material.（4） The depth variations of methanotrophs and methanogens showed near mirror images of one another. The relative abundance of methanotrophs in soils peaked at 30 cm for aged reed wetlands, 20–25 cm for rice paddy and 10 cm for newly created reed, respectively, Compared to methanogens, the methanotroph distribution showed no limitation by depths, and dominant methanotrophs were methylomonas, methylobacter, methylomicrobium and methylosarcina.