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Evidence of Thickening of Organic Matter Layer in Soil Micro-interface Found by Subtropical Ecology Institute
[ Instrument network instrument research and development ] For a long time, the long-term protection mechanism of organic matter in soil and sediment has been extensively studied. However, due to the complexity of soil, scientists mainly conduct soil organic matter research based on traditional component extraction methods and propose different organic matter protection mechanisms. Among these stability mechanisms, there are disputes between the physical and chemical mechanisms of organic matter and the biological preservation mechanisms.
Using biomarker and isotope tracking technology, scientists have found that microorganisms can produce a variety of stable organic matter, which highlights the role of microbial processes in the stability of soil organic matter. However, studies have found that the physical and chemical components of the soil and the environment play a decisive role in the preservation of organic matter, especially long-term stability; soils with different microbial communities and activities after chloroform fumigation treatment have the same final mineralization rate as the blank, Kemmitt et al .(2008) proposed the "regulatory theory" (regulatory theory) to support the physical and chemical control and stability mechanism of organic matter. The focus of the above debate is the biological and non-biological control factors controlling the bioavailability of organic matter. To reconcile the controversy, J. Lehmann and M. Kleber (2015) proposed the "Soil Continuum Model" (Soil Continuum Model, SCM): Soil organic matter is a continuum of organic matter that gradually decomposes, determined by various physics, chemistry and biology. Its preservation or mineralization. Therefore, revealing the internal relationship and nature of microorganisms-organic matter-minerals in the soil microenvironment may be the key to understanding the biogeochemical cycle of soil organic matter.
At present, there are few studies on the biogeochemical process of soil micro-scale in the academic circles, and there is still a lack of research methods for soil microenvironment construction. Soil aggregates are the basic framework of soil, and their surface is considered to be a hotspot of microbe-organic matter-mineral interaction. Under the guidance of Wu Jinshui, a researcher at the Institute of Subtropical Agricultural Ecology, Chinese Academy of Sciences, and Liu Bifeng, a professor at Huazhong University of Science and Technology, Ph.D. graduate Huang Xizhi and Huazhong University of Science and Technology Ph.D. Li Yiwei combined microfluidic patterned microarray technology to construct a soil-microbe interaction feature The soil lattice chip technology that overcomes soil micro-heterogeneity at a certain scale, combined with X-ray photoelectron spectroscopy to achieve dynamic continuous monitoring of the soil-water micro-interface process (Huang, SBB, 2017, Huang, Scientific Report, 2018 ). Researchers studied the transformation of organic matter at the soil-water micro-interface of typical black soil and the dynamic coupling process of the solution micro-environment, and found that during the 21-day cultivation process, the coating of the soil-water interface organic matter on the mineral surface quickly reached saturation (4 days); In the later culture process, the layer-by-layer etching analysis technique of argon ion clusters found that the thickness of microbial biomass carbon (MBC>130nm) and organic-inorganic composites (20nm-130nm) in the Z-axis direction are still gradually increasing. This indicates that the accumulation of soil organic matter is not disordered sedimentation or adsorption and fixation on the mineral interface, but preferentially thickens the existing organic-inorganic composites. With the thickening of the organic layer, the active nutrients (organic carbon and ammonium nitrogen) in the solution decrease, the activity of extracellular enzymes increases, the availability of nutrients and the later microbial metabolic activity (microcalorimeter) decrease.
Based on the continuous observation results of the micro-interface, the researchers proposed the solid-liquid coupling biogeochemical mechanism of soil organic matter stability: the microbial-mediated organic matter conversion process is conducive to the formation of organic-inorganic composite multilayer self-assembled structure; thickened organic matter The layer stores the available nutrients, shields the degradation of the organic matter in the inner layer, limits the metabolism of microorganisms in the solution, and promotes the stability of the organic matter. This mechanism couples physical chemistry and biological control mechanisms to provide evidence for the soil continuum model and provide structural enlightenment for increasing soil carbon fixation on the Z axis. This research result is the third original paper since the soil chip technology (SoilChip) was put forward. The soil chip technology provides a research method to clarify the complex biogeochemical cycle of soil multi-process coupling, and will combine isotope tracer technology and interface in the future. Characterization technology can provide basic knowledge based on micro-nano-scale processes for understanding the fate of other soil elements or pollutants.
Relevant research results were published on Environmental Science: Nano with the title Direct evidence for thickening nanoscale organic films at soil biogeochemical interfaces and its relevance to organic matter preservation. The research work is supported by the National Natural Science Foundation of China, the Natural Science Foundation of China Youth Fund, the Open Fund of the Institute of Subtropical Research, and the China Postdoctoral Fund.