Scientists Find Direct Evidence of Thickening Organic Film at Soil-water Micro-interfaces
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Soil organic matter is essential for maintenance of soil fertility, absorption of pollutants and mitigation of global climate change. In the past few decades, the long-term protection mechanism of organic matter in soil and sediment has been extensively studied.

Revealing the intrinsic relationship and nature between microorganisms, organic matter and minerals in the soil microenvironment may be the key to understanding the biogeochemical cycle of soil organic matter.

Soil aggregates are the basic skeleton of soil, and their surface is considered to be the hot spot of microbial-organic matter-mineral interaction.

Prof. WU Jinshui from the Institute of Subtropical Agriculture (ISA) of the Chinese Academy of Sciences and Prof. LIU Bifeng from Huazhong University of Science and Technology applied soilchip technology that overcomes soil micro-heterogeneity at a certain scale. It achieved dynamic continuous monitoring of soil-water micro-interface processes for the first time.

On this basis, they further systematically studied the transformation of organic matter in the typical mollisol soil-water micro-interface and the dynamic coupling process of the solution microenvironment.

Combining X-ray photoelectron spectroscopy and ion sputtering on soil microarrays incubated with a predefined solution (SoilChips), they provided the first direct evidence that a nanoscale organic film with a distinct composition and thickness gradually formed at the soil-water interface (SWI) within 21 days of cultivation.

Although the organic coatings on the soil-water micro-interfaces quickly reached equilibrium within 4 days, the formation of thicker mineral-organic association (MOA, 20-130 nm) and microbial biomass (>130 nm) continued, partially at the cost of the thin MOA (<20 nm).

Consistent with the thickening organic film, the bioavailability of nutrients (dissolved organic carbon and ammonium) decreased gradually over 21 days, which restrained the microbial activities.

Thickening SWIs acted as a biogeochemical gate to regulate the bioavailability of specific organic compounds and determine their preservation or microbial mineralization.

Further, thickening SWIs in the z-axis direction provided direct structural insight to increase carbon sequestration in soil and sediment.

The research was published in Environmental Science: Nano. It was supported by the National Natural Science Foundation of China, the Chinese Academy of Sciences, and China Postdoctoral Fund.

Contact:Huang xizhi

Institute of Subtropical Agriculture, Chinese Academy of Sciences