Changing Characteristics And Influencing Factors Of The Soil Microbial Community During Litter Decomposition In The Mixed Quercus Acutissima Carruth. And Robinia Pseudoacacia L.Forest

The Huangqian watershed of Tai'an city in Shandong Province was selected as the study area,which is a typical area in the rocky mountainous area of northern China.Mixed Quercus acutissima Carruth.and Robinia pseudoacacia L.forest(QR)and pure Quercus acutissima Carruth.forest(QAC)are important tree species for ecological afforestation in this area,which have an important ecological protection function.The soil microorganisms are the main driving force for the litter decomposition,the study on the change characteristics of soil microbial community and its response to the litter decomposition has attracted much attention.In order to study the changes of soil microbial community and influencing factors in litter decomposition,this study took QR and QAC as the research objects,using a combination of spot sampling in the field,indoor quantitative analysis and high-throughput sequencing technology to analyze the litter decomposition dynamics,ecological stoichiometric characteristics,and the composition,diversity and influencing factors of soil bacteria and fungi community during the litter decomposition of two forest stands.This research aims to provide a scientific basis for in-depth exploration of the microbiological mechanism of litter decomposition in a mixed forest,and to provide basic data support for the selection of tree species in the process of ecological restoration and the quantitative evaluation of ecological service functions in this area.The results of this research were as follows:(1)The decomposition rate of litter in QR was higher than that in QAC,and the litter decomposition law conforms to Olson negative index model.During the litter decomposition(the observation period of 360 days),the monthly mass loss of litter showed a trend of increasing-decreasing-increasing,the maximum values were 1.33 g and 1.13 g,and the minimum values were 0.15 g and 0.28 g.The cumulative mass loss after litter decomposition for 360 days were 6.83 g and 6.24 g.According to the Olson negative index model,the decomposition coefficient of litter in QR is 0.58,the time to decompose 50% is 1.07 a,and the time to decompose 95% is 5.04 a.The decomposition coefficient of forest of litter in QAC is0.53,the time to decompose 50% is 1.21 a,and the time to decompose 95% is 5.54 a.This shows that the QR can accelerate the decomposition of litter and promote the material circulation of the ecosystem compared with the QR.(2)The total organic carbon(TOC),total nitrogen(TN),total phosphorus(TP)content and ecological stoichiometric ratio of litter in the QR and QAC changed significantly.After 360 days of litter decomposition,TOC content,TP content,and C: N decreased significantly,while TN content,C: P,and N: P increased significantly.In the litter decomposition,the TOC content of QR was lower than that of QAC,a net release process occurred,and the release rates were 51.3% and 50.5%.The TN content of litter in QR was higher than that of QAC,a net release process occurred,and the release rates were 29.4% and26.7%.The TP content of litter in QR was higher than that of QAC.During the decomposition process,the content of TP showed an increase-decrease trend,an accumulation-release process occurred,and the release rates were 59.2% and 50.4%.(3)The dominant groups of soil bacteria in the litter decomposition of QR and QAC were the same,but the community richness index(Chao1 index and ACE index)and community diversity index(Shannon index and Simpson index)has changed significantly.In the process of litter decomposition of the two forests,soil bacteria had 36 phyla,49 classes,112 orders,203 families and 394 genera.At the phylum level,Acidobacteria,Proteobacteria and Actinobacteria were dominant groups.At the class level,Acidobacteriia,Alphaproteobacteria and Gammaproteobacteria were the dominant groups.At the genus level,Bryobacter,Acidibacter and unidentified?Alphaproteobacteria were the dominant groups.The Chao1,ACE,Shannon and Simpson index of two forests showed a trend of increasing,decreasing and then increasing,the range of changes in QR was smaller than that of QAC.(4)The dominant groups of soil fungi in the litter decomposition of QR and QAC were the same,but the community richness index and community diversity index has changed significantly.In the litter decomposition,soil fungi had 13 phyla,42 classes,94 orders,198 families and 339 genera.At the phylum level,Basidiomycota,Ascomycota and Mortieromycota had were the dominant groups.At the class level,Agaricomycetes,Leotiomycetes,and Sordariomycetes were the dominant groups.At the genus level,Amanita,Gyroporus,and Leotia were the dominant group.The Chao1,ACE,Shannon and Simpson index of soil fungi in the two forests showed a trend of decreasing then increasing,the range of changes in QR was smaller than that of QAC.(5)During the litter decomposition of QR and QAC,the soil microbial community changed significantly,the litter carbon and nitrogen content and its ecological stoichiometric ratio,as well as the soil temperature and moisture were the main influencing factors.The composition of the bacterial community was significantly different at different decomposition periods of the litter,and the fungal community composition was significantly different between different vegetation types.Redundancy analysis(db RDA)found that TOC,TN,C: P,N: P,soil moisture(SM),soil temperature(ST)and soil p H are important factors affecting the structure of soil microbial community,indicating that the change of soil microbial community structure is the result of the combination of many factors such as the nature of litter and the soil environment.