Composition Characteristics Of Soil Organic Matter Functional Groups In Soil Aggregates Of Erosion Landforms

Globally,more than 60% of the land surface is >8°,and the erosion process is extremely active.Soil aggregates are the basic units of soil structure and function,and the influence of erosion process on soil aggregates is obvious.In addition,Soil aggregates are also important sites for mineralization and decomposition of Soil Organic Matter(SOM).Soil erosion significantly affects the carbon cycle in terrestrial ecosystems.SOM composition determines the quality and stability of organic matter.Understanding the composition of organic matter in soil aggregates under the condition of erosion geomorphology can help us to understand the biogeochemical cycle of organic matter.The Loess Plateau is a typical area of soil erosion in China with complex topography and drastic slope changes.Soil samples were collected from three landforms(tableland,slope and gully)of the Loess Plateau.Based on the seperation classification method to aggregate different soil aggregates(>250 ?m,63-250 ?m,<63 ?m)were separated.The content of organic carbon and total nitrogen were determined by the elemental analyzer method,and the functional group composition of SOM was determined by the fourier transform infrared spectroscopy.The following three aspects were studied: 1)the composition of soil aggregates and the variation of SOM content in tablelands,slope and gully;2)Composition characteristics of SOM active functional groups in soil aggregates of tablelands,slope and gully;3)Composition characteristics of SOM inactive functional groups in soil aggregates of tableland,slope and gully.The following main results were obtained:(1)There are significant differences in composition of soil aggregates and SOM content in each grain size aggregates between tableland,slope and gully.The soil aggregates in tableland and slope were mainly concentrated in the 63-250 ?m aggregates,and the gully was concentrated in the <63 ?m aggregates.The content of SOM in tableland and slope were the highest in >250 ?m aggregates,followed by that in 63-250 ?m aggregates.<63 ?m aggregates were the lowest.The SOM content in gully <63 ?m aggregates was the highest,and the lowest in > 250 ?m aggregates.In addition,SOM content in the three aggregates in slope is higher than that in tableland and gully.(2)The spatial distribution characteristics of SOM active functional groups(alcohol C-OH or C-NH,aliphatic C-H)and the decomposability of SOM(CH/COO,CH/C=O)in soil aggregates in tableland,slope and gully showed significant differences.The relative content of active functional groups and decomposability of SOM in >250 ?m,63-250 and<63 ?m aggregates showed the following spatial trends: tableland > slope > gully.(3)The distribution characteristics of inactive SOM functional groups(aromatic C=C or C=N,aromatic amide C=O)and stability of SOM(C=C/C=O,C=C/COO)in soil aggregates vary significantly in tableland,slope and gully.The variation of SOM is opposite to the the relative content of active SOM functional group and decomposability of SOM,gully> slope >tableland.In this study,soil aggregates were used as the research object,and the spatial distribution patterns of each aggregates in tableland,slope and gully were clarified.The variation characteristics of SOM active and inactive functional groups in soil aggregates were revealed,and the mechanism of the differential effect of aggregates on SOM functional group distribution between landforms was clarified.These results provide a theoretical basis for further understanding the biochemical cycle of soil organic matter in erosion landforms.