| Litter and roots are the exogenous substances of forest ecosystems,and changes in their quantity can change the underground biogeochemical process.Forest soil is considered as a huge carbon and nitrogen pool,and its slight variations will have a profound impact on the soil carbon and nitrogen balance and greenhouse gas emissions.Soil microorganisms are the crucial drivers of the carbon(C)and nitrogen(N)cycles and dynamics at the plant-soil interface and play a vital role in nutrient cycle of forest soil.Tianshan Mountain is located in arid areas with fragile habitats and more sensitive to climate change.Schrenk's spruce(Picea schrenkiana)is the dominant species in the Tianshan forest ecosystem and plays a vital role in fixing nitrogen,releasing oxygen,regulating the climate,and maintain ecological safety.We analyzed the response of soil carbon,nitrogen,and biological characteristics of Schrenk's spruce forest in the Tianshan Mountain to litter and root changes and explored the driving mechanism of soil carbon and nitrogen.These can provide a scientific basis for the exploration of soil protection and soil carbon sequestration measures for mountain forest ecosystems in arid areas,and provide small-scale and accurate data for the evaluation of global forest soil carbon and nitrogen cycles and "source-sink effect".This study is based on the experiment of adding and removing plant residues in the spruce forest area of Tianshan Mountains to analyze the change characteristics of soil microenvironment,carbon and nitrogen components,enzyme activities,microbial community structure and functional genes under different treatments.Compare the changes in soil C,N and biology under different carbon input treatments.We also discussed the relationship between soil C,N and soil environmental factors and biological characteristics.Clarify the biological and non-biological mechanisms that drive changes in soil carbon and nitrogen.(1)Under double litter treatment,soil moisture increased,soil temperature and pH value decreased.Plant residue removal(remove litter,cut roots,cut roots and remove litter)treatments of each soil layer reduced moisture,soil temperature and pH value increased.The temperature,moisture,and pH of the upper soil under different carbon input treatments changed significantly.The rate of change of soil water-heat factor and pH value under the treatment of root cutting and removing litter was greater than that of other treatments.(2)The content of soil organic carbon and carbon components under different carbon input methods has a surface accumulation phenomenon.The total organic carbon content of the soil under double litter does not increase significantly.The soluble organic carbon and microbial biomass carbon content were significantly higher than the control.Plant residue removal treatment reduced the total organic carbon and carbon content of the soil.Among them,the reduction of root cutting and root cutting with litter remove was greater than other treatments.The soil respiration rate under different carbon treatments showed a single-peak curve,and the double litter treatment promoted the soil respiration rate,while removing the litter,cutting the root,root cutting with litter remove the litter had an inhibitory effect on it.The contribution rates of litter respiration,root respiration and mineral soil respiration to total respiration were3.78%?15.47%,37.88%?48%,and 45.77%?60.84%,respectively.The contribution of mineral soil respiration was the largest.(3)The contents of organic nitrogen,inorganic nitrogen,and microbial biomass nitrogen in the upper soil under different carbon source treatments are greater than those in the deep soil.The soil microbial biomass nitrogen and ammonium nitrogen in 0-20 cm soil increased significantly under the double litter treatment.The treatments of removal of litter,root cutting,root cutting with litter remove reduced the total nitrogen,microbial biomass nitrogen and ammonium nitrogen content of the soil,while the soil nitrate nitrogen content increased.Root cutting with remove litter had more negative effects on soil nitrogen than other treatments.(4)Double litter treatment significantly increased the activities of cellulase,phosphatase,and peroxidase of 0-10 cm soil.In addition to the peroxidase activity,the activities of cellulase,?-N-Acetylglucosaminidase and phosphatase were significantly reduced under the treatments of removing litter,cutting roots,cutting roots with remove litter.The soil enzyme activity decreased the most under the treatments of root cutting and root cutting with remove litter.(5)The double litter treatment increased the content of soil biological groups.Removal of litter(treatment of removing litter,cutting roots,cutting roots with remove litter)reduced the soil microbial content and the diversity index of bacteria and fungi(AEC,Shannon and Chao1).The Proteobacteria,Acidobacteria,and Actinobacteria in the soil bacterial community of the Schrenk's spruce forest were the dominant phyla;the Basidiomycota,Ascomycota and Mortierella in the fungal community were the dominant phyla.The relative abundance of Basidiomycota increased under double litter treatment.The relative abundance of soil Proteobacteria,Acidobacteria and Ascomycota decreased under the treatment of litter removal and root cutting.Litter and root treatment changed the abundance of genes related to metabolism,environmental adaptation,and cell growth and death in bacteria.The genes related to ectomycorrhizal,ectomycorrhizal-orchid-mycorrhizal-root-associated organisms and soil saprophytic fungi in fungi also showed differences with different treatments.(6)Soil total nitrogen,microbial biomass nitrogen,ammonium nitrogen,nitrate nitrogen had a significant or very significant positive correlation with?-N-Acetylglucosaminidase,cellulase activity,soil moisture,Basidiomycota,and Glomus phylum,and there was a very significant negative correlation with the Blastomonas phylum.Soil microbial biomass nitrogen and ammonium nitrogen had a significant positive correlation with the metabolism of coenzymes and vitamins.Soil total nitrogen,ammonium nitrogen and microbial biomass nitrogen showed significant or extremely significant positive correlation with ectomycorrhizal,ectomycorrhizal-orchid-mycorrhizal-root-associated growth.Among the factors that drive soil carbon and nitrogen dynamics,soil moisture and pH had positive and negative indirect effects on soil carbon and nitrogen,respectively,and enzyme activity and microorganisms had direct effects. |
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