Changes Of Organic Carbon Functional Groups And Fractions During The Quercus Liaotungensis Litter Decomposition

Soil organic carbon is an important part of the soil carbon pool,and its change is closely related to global climate change.In forest ecosystems,litter is the main source of soil organic carbon.Studying the changes of soil organic carbon fractions and functional groups during litter decomposition and exploring the chemical mechanism of soil organic carbon sequestration are great significance for understanding soil organic carbon sequestration and sources.In this study,Ziwuling forest vegetation area in Fu County,Shaanxi was selected.Through the indoor cultivation experiment to study the changes of soil organic carbon functional groups during the decomposition of litter under different quality and quantity of Quercus liaotungensis litter and different soil organic carbon content.In order to explain the mechanism of soil organic carbon sequestration during the decomposition process of Quercus liaotungensis litter at the molecular structure level.And through the study of the characteristics of soil nutrients,microbial biomass and their eco-stoichiometry with longitude in the forest belt of the Loess Plateau to discuss the feasibility of using infrared spectroscopy to determine the organic carbon functional groups Hope to provide a theoretical basis for the soil organic carbon sequestration mechanism in the Loess Plateau.The main research conclusions are as follows:(1)With the decomposition of litter,the main functional groups of soil organic carbon did not change significantly.The initial soil organic carbon content and litter type had no significant effect on the change of soil organic carbon functional group types during litter decomposition.The soil infrared spectra of different litter types and different soil organic carbon contents had similar spectral shapes and the same absorption peak positions at different cultivation periods,Absorption peaks appeared at 3622,3412,2512,1795,1628,1434 and 1025 cm-1.Under different treatments,the soil had alcohols,phenols,ketones,esters and aldehydes,aliphatic,aromatic,and polysaccharide organic carbon functional groups in different periods of litter decomposition.(2)During the decomposition of litter,the relative percentage of organic carbon functional groups changed continuously with the decomposition time,but there was no obvious rule.The relative percentages of alcohols,phenols,aromatic and aliphatic were all affected by the initial organic carbon content of the soil and the amount of litter added,and the relative percentages of polysaccharides were only affected by the initial organic carbon content of the soil.During the decomposition of Quercus liaotungensis,the relative percentages of alcohols,phenolic and aromatic in different initial organic carbon content soil were as follows: high organic carbon content soil> medium and low organic carbon content soil,and under the different amount of litter added were as follows 2% and 3% soil > soil without litter.The relative percentage content of aliphatic in soils with different initial organic carbon content was as follows: medium> low> high,and in soils with different litter addition amounts was as follows: not added> added 1%,2%> added 3%.During the decomposition of Quercus liaotungensis,the relative percentage of polysaccharides in the soil with different initial organic carbon content was as follows: high> low> medium.(3)During the decomposition of litter,soil organic carbon,soil dissolved organic carbon and soil microbial biomass carbon content changed continuously with the time of litter decomposition but there were no significant rule,and they were all affected by the amount of litter added.At the same time,soil dissolved organic carbon was also affected by the type of litter addition,and soil organic carbon was also affected by the initial organic carbon content of the soil.The content of soil organic carbon in the soil with different initial organic carbon content was as follows: high> low> medium,and in the soil with different added amount of litter was as follows: the added amount 3%> the added amount 2%> the added amount 1%> not added.The content of soil dissolved organic carbon in soil with different types of litter addition was as follows: adding leaf> adding branches,and in soil with different litter addition amounts was as follows: addition amount 3%> addition amount 2%> addition amount 1% > not added.The microbial biomass carbon content was as follows: soil with litter added> soil without litter added,litter promotes the increase of soil microbial biomass carbon.(4)Polysaccharides had only extremely significant correlation with aliphatic,the aromatic,alcohols,phenolic,soil dissolved organic carbon,soil organic carbon and soil microbial biomass carbon showed extremely significant correlations.Polysaccharides were only significantly negatively correlated with aliphatic compounds(P <0.01).There was a very significant negative correlation between aliphatic compounds and aromatic compounds,alcohols,phenolic compounds,soil dissolved organic carbon,soil organic carbon and soil microbial biomass carbon(P <0.01).Aromatic compounds,alcohols,phenolic compounds,soil dissolved organic carbon,soil organic carbon and soil microbial biomass carbon all showed extremely significant positive correlation(P <0.01).(5)The soil organic carbon and total nitrogen in the forest belt from east to west of the Loess Plateau have regional characteristics,and generally decrease first and then increase with the change of longitude.In theory,Fourier infrared spectroscopy can be promoted The soil organic carbon content in the forest belt from the east to the west of the Loess Plateau is 7.12 ~ 42.99 g / kg,which is within the range of soil organic carbon of the tested functional groups.to the identification of soil organic carbon functional groups in this area.There were extremely significant correlation between soil organic carbon and total nitrogen,carbon to phosphorus ratio,and nitrogen to phosphorus ratio(P <0.01),and a significant correlation between soil organic carbon and total phosphorus,the ratio of microbial biomass carbon to nitrogen,and the ratio of microbial biomass carbon to phosphorus(P <0.05).There were extremely significant correlation between soil microbial biomass carbon and microbial biomass nitrogen(P <0.01),and a significant correlation between soil microbial biomass carbon and microbial biomass phosphorus,total nitrogen,and the ratio of nitrogen to phosphorus(P <0.05).The overall change trend of soil microbial biomass carbon,nitrogen and phosphorus were similar to that of soil organic carbon and total nitrogen.The total soil phosphorus content varied from 0.24 to 0.66 g/kg,the coefficient of variation was 22.92%,and the spatial distribution was relatively stable.