Studies On The Changes Of Functional Groups Of Soil Organic Carbon During The Process Of Different Vegetation Restoration On The Hilly Region Loess Plateau

Revegetation is one of the most effective methods for increasing soil organic carbon(SOC), improving the stability of soil aggregates, and changing the composition of organiccarbon on the Loess plateau in China. During the process of vegetation restoration,understanding the composition of the SOC functional groups, which is important to deepenour understanding of SOC learning stability mechanism. This study directly measured thedistributions and composition of SOC functional groups from different revegetation waysusing XANES and SR-FTIR Spectroscopy. This study provides the first detailed investigationof changes in SOC functional groups composition in different size aggregates duringvegetation restoration process on the Loess Plateau. This may provide fresh insights into theeffects of natural vegetation restoration on the chemical stability of SOC. The main resultsand conclusions were presented as follows:1. Vegetation restoration in semi-arid nature grassland changed the content of functionalgroup and distribution of SOC in different soil layers, and prompted structural stability ofSOC in the process of the grassland recovery. Peak intensity of aliphatic-C from fallowinggrasslands significantly increased with increasing years of fallowing. Results obtained bySR-FTIR technique were analyzed which showed that compared with slop farmland, relativecontent of functional groups from fallowing grasslands SOC were increased, the growing rateof aliphatic-C, alcohols-C in0-5cm,10-20cm soil horizon was greater than growing ratearomatic-C. Results obtained by soft X-ray technique are consistent with SR-FTIR, andrelative content of the same functional groups(aliphatic-C, aromatic-C) gained by twodetermination methods were T-test, which was not significant (P>0.05), indicated that usingSynchrotron radiation soft X-ray for the determination of SOC structural change of fallowinggrasslands is feasible.2. Planting alfalfa for long time increased SOC, improved stability of aggregates, changed the distribution and content of SOC functional groups in soil and different size aggregates.The improvement effect was in8years. Percentage of>0.25mm aggregates increased withthe increasing of planting years. Relative content of saturated alkyl increased, and which werefixed mainly in0.25-1mm aggregates. Relative content of aliphatic-C and alcohol-Cdecreased with increasing of aggregate sizes. The increasing of the aliphatic-C and alcohol-Cexisted major in macro-aggregates, while, aromatic-C distributed in <0.25mm aggregates.The change content of functional groups in macro-aggregates were more clear than <0.25mmaggregates, which showed that organic carbon stability of micro-aggregates was higher thanmacro-aggregates, increasing of labile functional groups (aliphatic-C, alcohol-C) of SOCwere easier than aromatic-C in the process of plating. Percentage ratio of aliphatic-C,alcohol-C, and saturated alkyl of SOC are main, and the change of those are most active, sothat increasing of aliphatic-C, alcohol-C and saturated alkyl contributed immense to theincreasing of SOC.3. Plant succession improved chemical stability of SOC, which indicated that revegetationcan promote increases in aliphatic-C and ketone-C contents in both the0-5cm and20-40cmsoil layers, and this effect gradually increased with plant succession. Labile oxidationfunctional groups of SOC (alcohol-C, polysaccharide-C, telescopic vibration aliphatic-C)increased significantly, recalcitrant ones (deformation vibration aliphatic-C, and aromatic-C)also increased during plant succession promoting SOC increase process. Especially,functional groups of SOC increased obviously in Sophora viciifolia, Quercus liaotungensisstages, the vegetation restoration improve the chemical stability of SOC. Plant successioneffected more the change of SOC from0-5cm soil layer than20-40cm layer.4. The result showed that polysaccharide-C was the most abundant in the0.5-0.25mmaggregate, while carbonyl-C was found mainly in the <0.25mm aggregate. High levels ofaliphatic-C, carboxylic-C and alcohol-C were found mainly in the5-2mm,0.5-0.25mm, and<0.25mm aggregations, respectively. In forest aromatic-C was mainly in <0.5mm aggregate,and absolute content of aromatic-C from forest increased obviously in different aggregates.5. The type of functional groups of SOC(polysaccharide-C, aliphatic-C, aromatic-C,alcohol-C) from semi-arid nature grassland and semi-humid grassland grassland was the same,moreover, which from planting alfalfa land included-COOH, alkane.In three grassland, theresult showed that aliphatic-C, alcohols-C, polysaccharide-C increased significantly during the vegetation restoration process,aromatic-C perform the trend of increasing. Resultsobtained by SR-FTIR technique were semiquantitative analyzed which showed that the rateincreasing of aromatic-C from the yunwu mountains grassland>Ziwuling grassland> alfalfaland. It illustrated that structural stability of SOC enhance more in yunwu mountainsgrassland than Ziwuling grassland and alfalfa land.