Study On Humus In Pure Culture And Microbial Formation In Soil

Humic substances (HS) are the most widespread and ubiquitous natural nonliving organicmaterials in terrestrial and aquatic environments and they represent the major fraction of soilorganic matter. HS are extremely important environmentally due to their crucial role inreductive and oxidative reactions, sorption, complexation and transport of pollutants, mineralsand trace elements, sustaining plant growth, soil structure and control of the biogeochemistry oforganic carbon in the global ecosystem.HS are formed by secondary synthesis reactions (humification) during the decay processand transformation of biomolecules originating from plants and other dead organisms.Microorganisms are the driving force behind the formation, transformation, degradation andmineralization of humic substances. Although bacteria dominate the environment and participatein turnover of humic substances, their ability to degrade stable macromolecules such as humicacid（HA）and lignin is limited. Bacteria probably have their effect via the utilization oflow-MW compounds such as FA and HA metabolites. Fungi, on the other hand, are the mostefficient HS degraders which carried out mainly via secondary or cometabolic processes.Although bacteria and ascomycetes are common soil inhabitants, their utilization of humicsubstances has been studied to a lesser extent than that of white rot and litter decomposing fungi,leaving many open questions. Their ability to degrade stable compounds such as HA is limitedcompared to white rot and litter decomposing fungi.. However, their relative abundance and roleduring turnover of humic substances are still unclear, the details of the processes and the role offungi are far from being understood, there is still a gap in our knowledge of their actual diversityand function in OM decomposition. Thus, elucidating the role of microorganisms in thetransformation and degradation of these compounds is crucial to an understanding of thetransformation of HA in soil. This study was therefore undertaken with the aim of investigatingthe role of soil microbial communities in changing the structure of soil humic acid and tohighlight problems, unsolved questions and hypotheses. We hypothesized that bacteria and fungiplay different role in the formation and transformation of soil humic acid and also heavilyinfluences their structure, bioavailability and hence their biodegradability.I The results of the humus from microbial residues in pure culture conditions 1Both prokaryotic microbial cells and eukaryotic microbial cells can be extracted intohumus when they have been broken. But with the time of culture prolonged, the amount ofwhich shows a decreasing trend.2The biomass carbon of prokaryotic microorganisms and eukaryotic micro-organisms which in humic fractions follows the same pattern, and the main of them are in FA.The biomass carbon from death cells under aerobic conditions shows that:there are27%allocation in HE, the7.9%of biomass carbon allocation in HA at begin,19.2%of biomasscarbon allocation in FA; under anaerobic conditions: The intracellular soluble in microbialcells(dead body), there are26.9%in HE,9%in HA,17.7%in FA.3In the liquid culture conditions, humus formed from microbial residues shown acontinuous degradation trend. Under aerobic conditions, the degradation rate of humic acid islarger than that of fulvic acid, while it is on the contrary in anaerobic conditions.4Photochemical properties of HA, FA from prokaryotic microbial and eukaryotic microbialshown a similar tendency. With the culture time prolonging, Δ LogK and E4/E6values werereduced show that, the degree of oxidation and aromatization is rising. A stabilization directionof molecular structure is developing.5The nitrogen content of HA and FA which from prokaryotic microorganisms are a littlehigh. What’s more, the nitrogen content in eukaryotic microorganisms in HA is below than it’sFA.6There are the same obvious peaks in HA and FA’s IR waveform between prokaryoticbacteria and eukaryotic microorganisms. What differences from prokaryotic bacteria is that,eukaryotic microorganisms has C=O. In another, C=C appears both of them. The content offunctional groups in eukaryotic microorganisms(fungi)is higher than that one.7In the liquid culture conditions, humus shows more about the characteristic of degradationproducts. And it has not been combined in the whole process. In another word, humus will becompletely mineralized to carbon dioxide and water sooner or later without carbon source whichis used by microorganism.II The results of the humus from microbial degradation of non aromatic carbon sourceand microbial residues in pure culture conditions1Streptomyces “cell” yield increased significantly with the culture time prolonging. And itarrives at7.29%in60days.2It has a big difference to the real soil humus, which “Bacteria” is formed bystreptomyces and cellulose. Especially it shows a relatively low condensation degree,crystallinity, aromatic, carbonyl and methylene content. 3Cellulose degradation by streptomyces takes a good advantage forthe formation of“insoluble fractions of alkali and acid”(equivalent to the class of humic acid).III The results of the effects on the soil humus formation of microbial residues1Under aerobic conditions, the precursors of humus polymerization were synthesized inmicrobial cells, which promotes the formation of humus soil. In another, intracellular solublematerial increased HA and FA to a extremely significant level. Therefore, it is certain scientificto the theory of the polyphenol from microbial synthesis by humus’ formation, but whether itis “polyphenols” will be proved in the future.2Synthesis of humus’ polymeric precursor is microbial’s universal common. Therefore, wecan know that, the formation of humus is the interaction result of microorganisms.3In aerobic conditions, the newly formed humus shown a degradable trend. Combinedwith the previous research findings, soil humus is likely to be a degradation product.And itsformation occurs in the microbial cell soluble substances material getting into the soil, namely:polymerization occurs before the cell residues’decomposition.4Humus promote polymeric material’s formation by microorganism were widely spread inmicrobial cells.And from the quantity of “new carbon (soil organic matter fibrinogendegradation products)”which binged the original soil humus, with “trace, efficient”characteristics--they have beyond their own quality hundreds of times.5In anaerobic conditions, the formation of humus is unstable and undulant, and it existstwo processes which named degradation and “together again”. Therefore, it would be exist moremechanisms about mutual transformation of redox and HA-FA than that in aerobic conditions.Combined with LovleyD R,（1998），which confirms that the quinone group humus is the mainelectron acceptor site by Electron spin resonance spectroscopy (ESR) and nuclear magneticresonance (NMR).We presume that the promotion of soil humus polymeric substances is likelyquinones. Especially ubiquinone and methyl naphthoquinone which as the microbial respiratoryelectron acceptor. On one hand, the quinone can transfer and accept electrons, and it makes thesame as Lovley D R research results. On the other hand, they are the most widely ones inmicrobial cells as electron acceptors. In addition, the isoprene side has a different unit(active-C=C-double bonds),as a microbial respiratory electron acceptor ubiquinone and methylnaphthoquinone, which can produce a variety of polymerization.Polyphenol oxidation toquinones as a key step in quinone ammonia from the formation of the humus polymerizationtheory. And it also emphasizes the role of quinone. Therefore, what we hypothesized is likely tobe right.IV The results of Population change and metabolic activity of soil prokaryotic and eukaryotic microorganisms on the formation of soil humus1Bacteria, fungi and Whole-cell used in the process of the development can promote theformation of humus, but in varying degrees. Among them, bacteria, fungi and Whole-cell havethe faster formation speed than decomposition speed in the pre-training, but in late trainingactinomyces is the main HE producer.2The absolute and relative content of humic acid (HA) showed an upward trend in thewhole process, showed that each species promot the formation of HA in varying degrees,whole-cell has the strongest promoting role,followed by bacteria, fungi again, actinomyces isthe smallest.3Bacteria can promot the formation of HA.4FA is easier than HA in the process of complexity and agingin.In addition, the ΔLogKand E4/E6of FA are higher than HA, show that the molecular structure of FA is Simpler thanHA, and the aromatic and oxidation of FA is low.5There are the same IR waveform between the different humic acid (HA) and differentfulvic acid (FA), but the chemical shift of the absorption peaks are significant differences instrength,HA、FA has a similar structure of C respectively. The molecular structure of HA has acommon fungus in different training, in addition, the phthalocyanine amine C=O of fungusincreased,others are weakened; and in the molecular structure of the FA, the phthalocyanineamine C=O of whole-cell enhanced,show that fungi and whole-cell can play an important role ofthe source of nitrogen in the humus.In addition,in the molecular structure of HA, onlyactinomycosis occurres the extend of aromatic C=C;and there always have no aromatic C=C inFA.In one word, under pure culture conditions,the cell debris of prokaryotic and eukaryoticmicrobes with their degradation products, the non aromatic carbon source used bymicrobial(cellulose) and microbial residues, the alkali extract of soil microbial residues and theproducts of microbial degradation’s corn straw in burn clay have the same alkali solubilitycharacteristics to soil humus. In addition it has a big difference on it’s elemental compositionand structure. According to the modern definition of humus, the alkali extracts are a new class ofhumus. What’s more, the humus formed by microbial residues and its degradation products cansignificantly promote the formation of soil HA.