Study On The Effect Of Soil Composition,sterilization And Inoculation On Soil Organic Carbon Mineralization And Their Mechanisms

Soil is the largest carbon?C?pool in the terrestrial ecosystem.About two thirds of terrestrial C is stored in soil,and 60% of this is organic C.Soil organic carbon?SOC? has significant agricultural and ecological functions,and is an important source and sink of greenhouse gases including CO₂.Research into the SOC mineralization is therefor of great importance for greenhouse gas mitigation and soil fertility maintenance.SOC mineralization can be affected by many factors.Among them,soil biotic factors are popularly studied in many researchs,while abiotic ones are somewhat neglected and underestimated.The significance,mechanisms and key factor of certain abiotic and biotic factors were mainly studied in this reseach using technique including Fourier Transform Infrared Spectroscopy?FTIR?,DNA Miseq sequencing,network analysis,structural equation model,etc.Abiotic factors of soil particle compostion,oxidizing mineral on SOC mineralization were studied by adding quartz sand/kaoline and cryptomelane??-MnO₂? into soil.Biotic factor of gradient bacteria community on SOC mineralization was studied by perfusing and inoculating a previously sterilizated soil by chloroform fumigation.The main results include:?1?The influence of particle composition on SOC mineralization in fumigated and non-fumiagted soils was studied by mixing a loam soil with quartz sand and/or kaoline clay.Particle composition didn't significantly influence the SOC mineralization and soil dissolved organic C?DOC?concentration in non-fumigated soils during the incubation.In the fumigated soils,the amended kaoline significantly adsorbed the necromass,decreased DOC and the cumulative CO₂ evolution,but had little influence on the respiration rate in the late incubation.Thus,soil particle composition would not significantly influence the SOC mineralization rate in an equilibrium state without any exogenous substrates or disturbances.However,clay mineral?kaoline?would significantly retard the SOC mineralization by adsorbing more organic C?OC?including the necromass,changing the OC existing form and decreasing its bioavailabilty,when the substrate supply and microbial demand were approaching an equilibrium.?2?The influence of cryptomelane??-MnO₂? on SOC mineralization was studied in soils of different p H.0.5% ?-MnO₂ addition caused little toxicity to the soil microorganisms.?-MnO₂ increased SOC mineralization in the acid soil by about 13%,which was much more than that in the neutral or alkaline soil.In the acid soil,?-MnO₂ could participate the SOC mineralization as an electron acceptor,and significantly increase the extracellular mineralization rate of SOC,resulting in an increase in Mn???concentration.While in the neutral and alkaline soil,?-MnO₂ had lower oxidizability and tended to adsorb and condense certain organic matter containing functional groups as carboxyl,oxhydryl,etc.500 ppm HgCl₂ significantly decreased the microbial biomass and activity by about 90%,but only the SOC mineralization curve of the sterilized alkaline soil showed the same pattern as in CHCl₃ fumigated soil.The necromass might be adsorbed in the HgCl₂ sterzlized acid and neutral soil,thus not available to the survived or recolonized microorganisms.?3?The biochemical properties,SOC mineralization and DOC generation rate and characteristics were studied in a sterilazied soil with biomass depleted by repeated CHCl₃ fumigation-incubation?FI?.Repeat FI significantly reduced soil microbial biomass,destroyed microbial community composition and diversity,while it had little influence on the soil respiration rate,potential enzyme activity or the generation rate and organic composition of leached DOC in the late perfusion.Both DOC in the fresh soil or FI treated soil were gengerated at a slow but constant rate(6-8?g C g^-1 soil)after 40-day perfusion,and comprised the same organic functional groups,mainly the carboxyl,alkyl and carbohydrates.This result indicated SOC mineralization rate was not regulated by the microbial biomass or community,but related to the soil DOC generation or potential enzyme activities.?4?The bacteria recolonization and the influence of grediant bacterial community on SOC mineralization was studied by inoculating a FI sterilazied soil with increasing fresh inocula.Gradient inocula effectively promoted the recovery of microbial biomass,activity and community composition in the steralized soil.And the recovery extents were positively correlated with the inoculation rates.DOC in the inoculated soil was negative correlated to both the inoculation rates and the relative abundance of the core bacteria classes,indicating the recolonized microorganisms utilized DOC as substrate.The DOC increase in the non-inoculated FI soil by the end of incubation indicated microorganisms could act as a DOC sink to facilitate its turnover in soil.The gradient inocula did not cause significant differences in the cumulative CO₂ evolutions between the inoculated soils and the fresh soil,or in the respiration rates among treatments in the late incubation.Our results indicated that the SOC mineralization rate in the inoculated soils was not affected by soil microbial biomass or community composition,however,it depended on the microbial available and accessible DOC.