Effects Of Winter Fire On Soil Microbial Characteristics And Vegetation Growth In Wugong Mountain Meadow Under Nitrogen Addition

The vertical mountain and unique climatic and hydrological conditions of Wugong Mountain make a large area of mountain meadow above 1550 m above sea level.It is a rare low-altitude mountain meadow area at the same latitude,which is of great research value.Meanwhile,local departments also conduct"mountain refining"on the meadow from time to time.As an important factor of grassland ecosystem,fire has certain influence on the material circulation of meadow soil and vegetation growth.In this study,a sample plot located at an altitude of 1600 m in the mountain meadow of Wugong Mountain was selected as the research object.The randomized block test was used to set up five block groups,and three treatments CK control（not burned）,burning and burning+nitrogen（N）)were set in each block group,a total of 15 quadrats.The changes of soil material circulation and microbial properties and the effects on the growth and development of meadow vegetation in Wugong Mountain were studied by artificial burning and nitrogen application after burning.At the same time,whether the addition of nitrogen after fire can reduce the effect of burning on soil and vegetation of meadow was investigated.The aim is to provide scientific guidance for the restoration and correct management of meadow after burning and theoretical support for the development of ecological economy and sustainable management.Specific research results are as follows:1.The soil water holding capacity of the Wugong Mountain meadow decreased after burning,and the soil water holding capacity of the 0-10 cm soil layer was greater than that of the 10-20 cm soil layer.The contents of soil total nitrogen,organic matter,available potassium and available phosphorus decreased after burning.The content of p H and ammonium nitrogen increased.In the topsoil,the organic matter content of CK was 23.35%and 23.51%higher than that of burning and burning+N,respectively.The content of organic matter in upper layer and lower layer treated by burning+N was 16.86 g·kg^-1and 24.72%higher.The results showed that nitrogen application after burning mitigated the effect of fire on organic matter to a certain extent.2、The activities of sucrase and acid phosphatase in the soil of Wugong Mountain meadow decreased after burning,and the urease activity of burning+nitrogen treatment in September after burning was higher than that of burning only.It shows that fire reduces soil enzyme activity,while burning+nitrogen can increase urease activity after burning to a certain extent.There was a very significant positive correlation between organic matter,available potassium and urease and sucrase;soil alkaline phosphatase and ammonium nitrogen content had a very significant positive correlation.3、In a short period of time,burning and burning+N treatment could increase the number and abundance of fungal community,but with time,the number and richness of OTU of fungal community in meadow soil decreased correspondingly after burning.In September,the proportion of fungal community was more uniform under burning and burning+nitrogen treatment,and the proportion of Chordata in the soil under burning+nitrogen treatment was significantly increased.Ascomycota and Basidiomycota can exist as the dominant phylum in many soil types.Ascomycota and Basidiomycota can exist as dominant phylum in many soil types.The abundance of Platyhelminthes was the lowest in the measured fungal community,accounting for 0.09%to 1.71%.The available potassium,organic matter and sucrase were positively correlated with Streptophyta and Chytridiomycota,but negatively correlated with other fungi.4、In a short period of time,burning and burning+N treatment could increase the number and abundance of fungal community,but with time,the number and richness of OTU of fungal community in meadow soil decreased correspondingly after burning.There was a significant difference in the number of OTU between the upper and lower layers of meadow soil nine months after burning.The highest proportion of Proteobacteria in the meadow soil bacterial community was 29.1%-40.5%,followed by the abundance of Acidobacteria was 28.4%-35.6%.Available potassium,organic matter,sucrase and urease were positively correlated with Planctomycetes,Verrucomicrobia and Firmicutes,but negatively correlated with other categories.5、After burning,the growth height of plants in wugong Mountain meadow was generally reduced,but after burning+N,the plant height was increased compared with that after burning alone.Senecio latouchei was only found in burning and burning+N plots,indicating that the species of Senecio latouchei had strong resistance to burning However,Hypericum monogynum was only found in CK plots.The main reason was that it was a shrub,and the burning of branches during burning indirectly enhanced the burning intensity,so that the branches were seriously damaged and could not be recovered within a short time after burning.The proportion of awn and wild millet grass in all kinds of land is greater than other species,occupy the absolute dominance.In conclusion,soil organic matter decreased,p H increased,and available nutrients changed with different growth seasons and treatments after wugong Meadow burning.Burning and burning+N increased the number and activity of bacteria and fungi in a short period of time,but with the increase of time,the diversity of bacteria and fungi community decreased.After burning,vegetation species and plant growth height and aboveground biomass also decreased.However,nitrogen application after fire could significantly improve the adverse effects of burning on meadow vegetation growth and increase plant growth height and aboveground biomass.Therefore,in the actual management,it is necessary to treat the winter fire reasonably.Although the winter fire can kill the overwintering eggs and reduce the pests and diseases of the meadow in the following year,it will also reduce the soil organic matter and adversely affect the vegetation growth.Nitrogen will be beneficial to the renewal of organic matter and some nutrients in the meadow after fire,and increase the plant height and biomass of vegetation.