Soil Carbon Components And Enzyme Activities In Aggregate Under Different Plant Communties On The Hilly-gully Region Of Loess Plateau

Vegetation recovery is an important measure of manage and recover the ecologicalenvironment in Loess Plateau. The composition of the soil organic carbon is different for thedifference of the plant residues and root exudates. In this paper we researched nine kinds oftypical plants in the Yan River basin in loess hilly region, we measured>5mm,5-2mm,2-0.25mm,<0.25mm size aggregates with the wet sieving method and theircontent of total organic carbon, active organic carbon and humus carbon, we also determinedthe soil organic carbon functional groups using the XANES method, We analyzed the activityof sucrose, cellulose, polyphenol oxidase, peroxidase of β-glucosidase enzyme and urease insoil aggregates, we also discussed the carbon component, the distribution of the functionalgroups of organic carbon in soil aggregates, and the relationship between the organic carbonand the enzyme activity. These studies can provide a basis to improve the soil structure andrecover the ecological environment, and also provide guidance for evaluating soil qualityafter revegetation. The main conclusions are as follows:（1） The soil organic carbon content at forest zone was obviously higher than sylvosteppeand Steppe zone at study area, the order of the soil organic carbon content among differentvegetation communities was: Quercus liaotungensis (19.87g·kg^-1)> Robinia pseudoacacia(7.70g·kg^-1)> Thymus mongolicus+Hippophae rhamnoides (6.62g·kg^-1)> Hippophaerhamnoides+Artemisia giraldii (5.51g·kg^-1)> Sophora viciifolia (3.37g·kg^-1)> Artemisiagiraldii+Artemisia sacrorum (3.33g·kg^-1)> Lespedeza davurica+Stipa grandis (2.76g·kg^-1)> Phragmites australis+Artemisia sacrorum (2.51g·kg^-1)> Artemisiasacrorum+Bothriochloa ischaemun(2.46g·kg^-1)，the soil organic carbon content of Quercusliaotungensis was obviously higher than any other plant communities with its Largevariability, we can easily draw a concludion that Artificial vegetation restoration is conduciveto accumulation of soil organic carbon because of both of the Robinia pseudoacacia andHippophae rhamnoides community had a high content of soil organic carbon. （2） Under different vegetation community,the proportion of active organic carbon tototal organic carbon in each grade aggregate range between24%-46%，the proportion ofhumus to total organic carbon range between14%-34%,the proportion of active organiccarbon to total organic carbon and humus to total organic carbon were both no significantdifference among different aggregate,the proportion of active to total organic carbon wasgreater than that of humus to total organic carbon under each vegetation community. Thereare little organic matter input to soil at a short time vegetation restoration and most of whichexist as a relatively active form which was provided to plant as nutrient. The lowaccumulation rate leaded to a low humus content.（3） Aromatic-C, carboxyl-C and alkoxy-C presented in each communities, while onlyfew aliphatic-C exited in some of the communities that was: Quercus liaotungensis、Platycladus orientalis、Lespedeza davurica、Stipa bungeana. Carboxyl-C had the highestcontent, followed by aromatic-C, minimum levels of alkoxy-C at each soil sample. The soilorganic carbon relative content of functional groups showed differences between the varioussize aggregates at forest zone while which didn’t have significant differences at sylvosteppeand Steppe zone.（4） For Quercus liaotungensis, high organic carbon content and a high level of enzymeactive contributed positive impact on its soil fertility and soil structure; Artificial Robiniapseudoacacia had a high activity of sucrase, cellulase and beta-D glucosidase while had a lowactivity of polyphenol oxidase and peroxidase, leading to its active organic carbon was muchhigher than the humus. Sylvosteppe and Sophora viciifolia community had a low activity ofsucrose, cellulose and beta-D glucosidase while had a high activity of polyphenol oxidase andperoxidase, there were no significant difference of soil organic carbon and enzyme activityamong different aggregates, a small quantity of soil organic carbon and lower enzyme activitywere not conducive to vegetation growth and the stability of the soil structure. Thymusmongolicus+Hippophae rhamnoides community had higher organic carbon content andsucrose、cellulose、and beta-D glucosidase enzyme activity which made its soil organiccarbon decomposition conversion and humification smoothly, is conducive to theimprovement of the soil environment.（5） The pattern of the various forms of organic matter in the soil particles suggestedinitial increase in organic carbon, followed by decrease or flat curve with increasingaggregate size, a large proportion of soil organic carbon existed in2⁰.25mm and <0.25mmaggregates. The <0.25mm aggregates had the highest humus content which indicate thatorganic carbon is accumulated largely in micro-aggregates in the form of humus. The sucrose,cellulose, and beta-D glycosidase activity among soil aggregates expressed as:|<0.25mm|>| 2-0.25mm|>|5-2mm|>|>5mm|, enzyme activity increased as the aggregate size decreased.A high activity of hydrolytic enzyme in micro-aggregates was positive to the activation oforganic carbon and improvement of soil fertility; polyphenol oxidase and peroxidase activitywere no significant differences between the various fractions of aggregates.