Distribution Characteristics Of Microorganisms In The Soil Of Unearthed Wooden Relics And Their Corrosion Mechanism

In China's long history,there have been a large number of wooden art treasures with high artistic and historical value,which provide information for the study of ancient history and culture,living standards,etc.,and can not be copied.As a kind of biological material,wooden cultural relics will inevitably suffer from microbial damage,reduce its value,and even be completely destroyed.In this paper,we take the burial soil of an ancient tomb of the Warring States period in Baoji and the burial soil of a coffin in the wohuwan cemetery group in Yulin as the research object,and study the Physicochemical properties of the soil and the wooden cultural relic samples and the distribution characteristics of the microorganism in them,and use the isolated microorganism to study the corrosion mechanism of the wood,designed to provide a reference for the protection and preservation of wooden cultural relics.The main conclusions are as follows:1.Physicochemical properties of buried soil:the p H of chariot pit soil is 8.56-9.46,which is alkaline and easy to cause hydrolysis and corrosion of wood fiber components;the p H of coffin soil sample is 7.01-7.29,which is basically neutral and will not cause excessive damage to wood cultural relics.The soil moisture content of chariot pit and coffin is less than5%and the organic matter content is less than 6%.It belongs to arid and barren soil.The main anions are SO₄^2-,F^-,Cl^-,NO₃^-,PO₄^-,and the main cations are Na⁺,Ca²⁺,NH₄⁺,K⁺,Mg²⁺,of which the content of SO₄^2-,Na⁺,Ca²⁺is the highest,which can form salt crystal to cause the surface of wood ware to pan alkali and crisp and catalyze the cellulose decomposition in cultural relics.The soil of chariot pit pit is compact silty soil,which to a certain extent blocks the moisture.The soil of coffin is sandy soil,with less clay particles,which is not easy to absorb microorganisms.Therefore,both of them have a certain positive effect on the protection of woodenrelics.2.Distribution characteristics of buried soil microorganisms:(1)the concentration range of bacteria in each sampling point of chariot pit is 1.24×10⁶?6.26×10⁶CFU/g,and eight kinds of bacteria are isolated,among which,there are more aurebacterrumand bacillus,and the distribution of aurebacterrumis uniform in each soil sample,while bacillus is mainly concentrated in the internal sampling point of tomb(TC-6?TC-9),which decomposes cellulose and lignin in wooden relics through oxidation;the concentration of actinomycetes is 1.102×10⁵?9.5×10⁵CFU/g,and 5 kinds of actinomycetes were isolated,among which the distribution of cellulomonas was more;the number of fungi is 2.13×10⁴?5.79×10⁴CFU/g,and 11 kinds of fungi were isolated;the internal sampling points(TC-6?TC-9)of the tombs were mainly wood decomposing fungi such as pythium,aspergillus and mucor,the edge sampling points(TC-1?TC-5)of the tombs,and the common fungi in the soil such as rhizopus were more;the preference for fungi was more.the number of halophilic archaea is 1×10³?6.6×10³CFU/g,and three kinds of halophilic bacteria were isolated,among them,halophilic bacteria distributed more,and they are concentrated in the soil samples(TC-7,TC-8),which will not damage the wooden cultural relics alone.There are a lot of bacteria in the soil samples of chariot pit,which can degrade the wooden cultural relics by adsorbing them on the surface of cultural relics.(2)Five kinds of bacteria were isolated from each sampling point of coffin with the concentration of1.16×10⁶?8.8×10⁶CFU/g.among which Bacillus and Brevibacterium were the most distributed,and Brevibacterium had strong ability to decompose amorphous cellulose.The concentration of actinomycetes was 1.7×10⁵?4.56×10⁵CFU/g,four kinds of actinomycetes were isolated,among which Streptomyces was the most distributed,and degraded wood cultural relics through alkaline cellulase production;the number of fungi was4.06×10⁴?8.13×10⁴CFU/g,and 6 kinds of fungi were isolated.Among them,Paecilomyces and Pythium were the most distributed fungi,which degraded the lignin in the wooden relics by oxidation.The number of halophilic archaea was 1×10³?8×10³CFU/g,and 2 kinds of halophilic bacteria were isolated,among which halophilic coccus was the most distributed.The microbes in the coffin among which the fungi accounted for a large proportion.They were decomposed and destroyed by secreting extracellular enzymes and hyphae attached to the surface of cultural relics.3.Physicochemical properties and microbial distribution characteristics of lignocellulosic materials:taking the wooden relics in the coffin as a representative,the sample pH 6.76,water content 15.3%,density 0.46g/cm³,pH and water content are equivalent to those of the uncorroded wood,and the density is about 3/4 of that of the healthy wood.The water is 2.01%,which shows that the content of inorganic matter and soluble sugar in the sample is greatly reduced.The cellulose content is 27.62%,hemicellulose content is 8.25%,lignin content is 16.04%;the wood component is about 1/2?1/3 of the healthy wood.The decrease of the wood component content weakens the protective effect on the internal fiber of the wood and causes the corrosion gradually.Theconcentration of bacteria in woody relics is 2.69×10⁶CFU/g,four kinds of bacteria are isolated,among which Arthrobacter is the most distributed,adsorbed on the surface of amorphous cellulose,swelled and then decomposed.The concentration of actinomycetes was 2.21×10⁵CFU/g,and two kinds of actinomycetes were isolated.Among them,Streptomyces albicans distributed more and degraded wood fiber through two ways of continuous hydrolysis and oxidation.Six species of fungi were isolated at a concentration of 7.01×10⁵CFU/g,among which Penicillium and Trichoderma were distributed more frequently.The wood relics were cut through mycelium and enzymolysis was carried out.Two kinds of halophilic cocci were isolated at the concentration of 7×10³CFU/g,among which halophilic cocci distributed most.Penicillium is the most active microorganism of cellulase and trichoderma is the most active microorganism of lignin peroxidase(LIP).There are many fungi and high enzyme activity in woody relics,and there is synergism among them,which is destructive to cultural relics.4.Through the orthogonal experiment of bacteria,actinomycetes,fungi and halophilic archaea,the mechanism of microbial corrosion was studied:fungi in wood cultural relics corrode for 100 days under the temperature of 30?,the external C/N of 0.5/1,and the soil water content of 15%.Under these conditions,the weight loss rate is 2.305%,hemicellulose loss rate is 3.406%,cellulose loss rate is 2.033%,and lignin loss rate is 1.574%,which indicates that under 30?and 15%water content,microorganisms have strong corrosion on wooden cultural relics,and the environment should be kept dry and the temperature should be lower than 30?.