Analysis Of Mixed Effects Of Leaf Litter Decomposition And Its Main Affecting Factors Of Dominant Tree Species In Yaoxiang Forest Farm

Litter decomposition is one of the main sources of organic matter and nutrients in forest soil,which plays an important role in maintaining soil fertility and promoting the normal biological circulation and nutrient balance of forest ecosystem.Leaf litter is the main component of forest litters,covering about 70% of the forest litters.Although there has been a great deal of research on the decomposition of litters in forest ecosystem,there are still insufficient resea rches on the mixed effects and main influencing factors of leaf litter decomposition.In this study,the leaf litter of Robinia pseucdoacacia(RP),Quercus acutissima(QA),Pinus densiflora(PD),and Pinus tabulaeformis(PT),the four dominant tree species in the Yaoxiang forest farm,were used as the study object.To determine the effects of litter initialization properties,microenvironmental conditions,and microbial and enzyme activities on the decom position rate of mixed litters,using the Nylon litterbag method and combined with two kinds of micro-environmental conditions in the wild(placed on the soil surface and placed in the soil)for the monitoring of microbial community structure,enzyme activity and nutrient content of component litter during decomposition.At the same time,grasp the role of the component litter in the decomposition in the mixture.The results show that:1.Mixing effects and effects of component litterThe mixing effect is closely related to the type of component litter,and the mixing effects of different litter types are different.After two years,the mixed decomposition of RP×PD was the fastest,while PT×PD was the slowest.The mixture of RP,PT,PT and PD had the highest effect intensity but showed inhibition of decomposition,while the mixture of RP × PD had the lowest effect intensity and showed promotion of decomposition.However,all mixed treatments developed towards positive mixing effect with the change of time.PR promotes the litters decomposition of other three species when mixed with other three species,but its decom position is inhibited,which shows that the decomposition rate is the fastest when it is decomp osed alone.QA is the opposite of RP.Mixing with the other three species will promote its own decomposition.The mixing of PT with three other species inhibited the decomposition of PT and other species.2.Effects of chemical composition on litter decompositionThe initial chemical contents of the four selected species were significantly different,and the decomposition rate was negatively correlated with the initial C/N ratio,Ccontent,P conte nt and lignin /N ratio,while positively correlated with the initial N content and N/P ratio.The C and N residues of litters show a significant positive correlation with the dry weight residual rate,regardless of single decomposition or mixed decomposition.C,N and lignin residues are more correlated with tree species(P<0.01).Among them,C residues are positively correlated with initial C content of litters and P content(P<0.05).The lignin residual rate was negatively correlated with the N/P ratio(P<0.05).3.Effect of enzyme activity on litter decompositionThe activities of cellulase and polyphenol oxidase were negatively correlated with the mass remaining,C remaining and N remaining(P<0.01).Cellulase activity peaked in 1.25 year,while polyphenol oxidase activity continued to rise.4.Effects of microorganisms on litter decompositionThe litter mixture changed the composition and richness of the bacterial community.After two years,the richness index(number of observed species,Chao1 and Ace),diversity index(Shannon)and phylogenetic diversity index were higher than that of mixed decomposition.The results of NMDS analysis of the bacterial community also showed that decomposed separ ately and mixed in the bacterial community structure in the four species were significant diffe rent.The RDA results between the bacterial community structure and the initial chemical properties showed that the initial N/P ratio,P content and C:N ratio had greater influence on the bacterial community structure.The bacterial community structure in RP had the greatest correl ation with N/P ratio,and that of QA had the greatest correlation with C:N ratio,and that of PT had the greatest correlation with C content and P content.Advantage bacteria were Proteobac teria(59.1%),Acidobacteria(10.9%),Bacteroidetes(6.8%),Actinobacteria(6.4%),Planctom ycetes(5.8%),When litters were decomposed separately,the relative abundance of Proteobact eria and Bacteroidetes was higher than that of mixed decomposition,while Acidobacteria was the opposite.The initial C and P contents and N/P ratio had greater influence on the communi ty structure of dominant bacteria.Advantage bacteria genera were Bradyrhizobium(4.7%),Sp hingomonas(3.8%),Acidipila(2.2%),and nidentified-Burkholderiaceae(2.1%),Acidibacter(2.1%).The relative abundance of Sphingomonas was higher when litters were decomposed separately than when litters were mixed,while that of Acidibacter was oppositely.Cellulase activity had the greatest influence on the community structure of dominant bacteria,followed by initial lignin content and polyphenol oxidase activity.In addition,rhizobia and dry weight residual rate was correlated greatly.5.Effects of environmental conditions on litter decompositionThe decomposition rate of most treated leaf litters was faster underground than on the surface,but the mixture of QA × PT was opposite,and some treatments showed no significant difference(P>0.05).Compared with the place where litters are placed,litters have a greater effect on decomposition.The mass remaining of litters was significantly negatively correlated with soil enzyme activity and various climatic factors(P<0.01).In summary,the decomposition is affected by the initial properties of litter,enzymeactiv ity,microorganisms,and environmental conditions(such as soil temperature,soil moisture,and precipitation),from the perspective of environmental conditions,precipitation and soil temp erature have the greatest influence on the litter decomposition rate.However,the nature of initialization has a greater impact on the decomposition when the environment is consistent,it can affect decomposition by affecting enzyme activity and microbial groups.The litter mixture decomposition process is different from the separate decomposition process,but some also show an additive effect.The mixing effect is affected by the type of litter.In this experiment,through the study of decomposition of mixed litter,in order to create a reasonable mixed forest in the warm temperate zone and select excellent tree species.To provide a theoretical basis for the healthy management of mixed forests in the region and increase the carbon sink capacity of forests.