| The natural decomposition process of forest surface fuel is slow.Maoer Mountain area is located in the middle temperate zone,and the winter is cold and long,so the decomposition of surface fuel is more restricted,which increases the fuel load and causes forest fire hazard when the climate is dry.Forest fire managers usually use methods such as mechanical elimination,prescribed burning,and biological fire prevention to reduce the forest fuel load.Mechanical elimination has a direct effect on reducing fuel load,but the potential impact on vegetation,soil,wildlife and the possibility of smoldering need to be considered.Prescribed burning can reduce the hidden danger of fire,and the use of low-intensity fire can effectively reduce the accumulation of forest fuel,but there is a risk of fire escape,which may cause unexpected fire losses.Biological fire prevention can enhance the fire resistance and fire resistance capacity of forest by using the differences of biological and ecological characteristics of plants,animals and microorganisms,combined with forestry production measures.Therefore,biological fire prevention methods have no negative effects and risks after treatment and can reduce the fuel load without pollution.Cellulose is the main component of forest fuel,which controls the decomposition process of forest fuel to a great extent.Fungi can decompose macromolecular compounds such as cellulose that other microorganisms cannot decompose into simple small molecule compounds through their own secreted enzymes,thus accelerating the decomposition process of forest surface fuel.Screening and applying of high-efficiency cellulose-degrading fungi to decompose the cellulose components which are not easily decomposed in the surface fuel can reduce the forest fuel load and achieve the purpose of reducing forest fire risk levels.In this study,fuel materials were collected from Larix gmelinii,Juglans mandshurica,Fraxinus mandshurica and Picea asperata Mast.plantations in Maoer Mountain Experimental Forest Farm of Northeast Forestry University.Fungi were isolated and cultured with Rose Bengal chloramphenicol medium.After that,congo red staining method was used to screen the cellulose-degrading fungi,and highly active cellulase strains were selected according to the cellulose decomposition index.Molecular identification and genetic relationship analysis were carried out.Taking fuel fragments of Juglans mandshurica,Larix gmelinii and their mix as decomposition substrates,the fungal suspensions were prepared by highly active cellulase strains and cultured in an artificial incubator for inoculated degradation test.The content of holo-cellulose was determined by regular sampling,and the cellulose decomposition process in the laboratory was analyzed.The cellulose-degrading fungi with high efficiency were screened out,which was verified by scanning electron microscopy.Single and mixed microbial agent were prepared by the screened efficient cellulose-degrading fungi,and sprayed them on Juglans mandshurica,Larix gmelinii and their mixed fuel substrates in different doses in the field.Samples were taken regularly every month and the holo-cellulose content was determined.By comparing and analyzing the field degradation effects of different microbial agents and different doses,the cellulose-degrading microbial agent suitable for field degradation was obtained.The correlation analysis between the mass reduction of the fuel substrate and the holo-cellulose degradation rate was carried out,and a one-variable linear regression prediction model was established,and the prediction accuracy of the model was evaluated according to MAE and RMSE.Dissolved organic carbon(DOC)in forest surface fuel substrates was extracted to analyze the dynamic change of DOC content in fuel substrates,and the humification process and mode of fuel substrates treated with different microbial agents were compared.The main results are as follows:(1)Among fifteen fungi selected by RBC medium,eight had high cellulase activity,according to the distinct hydrolytic circles they produced on CMC-Na medium.Strain B2 showed the highest cellulolytic index,followed by strain A4.Strain A2 was identified as Peniophora incarnate,strain A3 was Pleosporales sp.,strain A4 was Sarocladium strictum,strain B2 was Cladosporium ramotenellum,strain B4 was Aspergillus foetidus,strain C2 was Dothideomycetes sp.,strain D2 was Fungal sp.and strain D3 was Penicillium griseofulvum.(2)During the indoor degradation,strain A4 was found to be most capable of degrading holo-cellulose in Juglans mandshurica,Larix gmelinii and the mixed substrate.At the end of the degradation,the mass fraction of holo-cellulose decreased by 25.7%,30.3%and 27.1%respectively compared with the control.For strain A2,the mass fraction of holo-cellulose decreased by 24.4%,30.0%and 26.3%respectively compared with the control,and the degradation ability was second only to strain A4.The cellulolytic index of strain B2 was significantly greater than that of other strains,but its ability to degrade natural cellulose was relatively weak,indicating that strains with strong cellulase activity was not necessarily strong in decomposing surface fuels.The scanning electron micrographs indicated that the mycelia of strain A4 could adhere to the leaf surface and invade the leaf tissue to degrade holo-cellulose in leaves by secreting cellulolytic enzymes.(3)During the field degradation,the degradation rates of holo-cellulose in Juglans mandshurica,Larix gmelinii and the mixed substrate increased with time.The degradation rates of holo-cellulose in the three fuel substrates with microbial agents application was as follows:microbial agent C>microbial agent B>microbial agent A,that is,the degradation effect of mixed microbial agent was better than that of single microbial agent made by strain A4 and strain A2.At the end of the degradation,the degradation rates of holo-cellulose in the three fuel substrates increased by 22.47%,16.66%and 17.63%respectively compared with the control.No matter what the dose was,the degradation effect of holo-cellulose in three kinds of fuel substrates with microbial agent was better than that of the control group,and the degradation effect was in the order of large dose>medium dose>small dose.With the increase of degradation time,the degradation rate of holo-cellulose in fuels gradually slowed down.(4)During the field degradation,the dynamic changes of mass loss of Juglans mandshurica,Larix gmelinii and the mixed substrate were significantly positively correlated with holo-cellulose degradation rate,and the correlation coefficients were 0.93252,0.97853 and 0.95376,respectively.There was a single linear correlation between the mass loss and the holocellulose degradation rate of Juglans mandshurica,Larix gmelinii and the mixed substrate.The goodness of fit of regression model was 86.96%,95.75%and 90.97%,respectively.The Larix gmelinii substrate model has the highest accuracy,with RMSE and MAE of 14.19%and 11.93%,respectively;followed by mixed substrate,with RMSE and MAE of 15.63%and 12.25%,respectively;and the least accurate was Juglans mandshurica substrate,with RMSE and MAE of 28.71%and 25.04%,respectively.(5)During the field degradation,the dissolved organic carbon content of Juglans mandshurica,Larix gmelinii and the mixed substrate decreased with time,and the decreasing range was mixed>Juglans mandshurica>Larix gmelinii.Under the same degradation time,the DOC content of Juglans mandshurica substrate treated with microbial agent C was significantly lower than that treated with microbial agent A and B.The content of DOC in Larix gmelinii substrate treated with microbial agent C was significantly lower than that treated with microbial agent B,and the content of DOC in mixed substrate treated with microbial agent C was significantly lower than that treated with microbial agent A.There was a significant positive correlation between the two treatments in the four groups(P<0.01).The Juglans mandshurica substrate treated with microbial agent A and C,B and C,the Larix gmelinii substrate treated with microbial agent B and C,and the mixed substrate treated with microbial agent A and C had the same humification pattern. |
PDF Full Text Request