| The boreal forest is one of the largest biological communities on the earth,which plays a variety of ecological services,such as acting as a carbon sink,protecting biodiversity,maintaining soil and water,and regulating climate.The soil nitrogen mainly exists in the form of organic nitrogen in the boreal forest,and the nitrogen mineralization rate is low.The growth of trees is limited due to nitrogen deficiency.Biochar is considered to improve soil fertility and is also a possible means of mitigating climate change through carbon sequestration.The biochar application has been shown to increase the rate of net nitrogen mineralization and nitrification,which is particularly important in nitrogen-deficient boreal forest soils.Forest soil is one of the most diverse microbial habitats,including bacteria,fungi,archaea,viruses,and protozoa.Microorganisms that exist in the soil in the form of communities are an important part of terrestrial ecosystems.They play an important role in nutrient cycling,organic matter decomposition,soil structure formation,promoting plant growth,organic pollutant degradation,and pest inhibition.Therefore,studying the response of soil microbial community and function to the biochar application in the boreal forest will help us to better understand the effects of biochar application as a soil amendment the forest ecosystem.In this study,two biochar pyrolysis temperatures（500℃and 650℃）and two biochar application amounts(0.5kg·m-2 and 1.0kg·m-2)were selected and the biochar was applied to a boreal pine forest in Finland.Soil samples were collected after two-and three-year of application,respectively.By using Illumina Nova Seq sequencing,the bacterial 16s r DNA V3-V4 and fungal ITS2 regions were sequenced respectively,combined with Functional Annotation of Prokaryotic Taxa（FAPROTAX）and Prediction and Analysis of Fungi functional structure（FUNGuild）techniques,the study aims to analyze the changes in soil microbial community and functional structure,soil physical and chemical properties,and soil extracellular enzyme activities involved in nutrient cycling,and to clarify the dynamic effects of different biochar treatments on soil microbial community in a boreal pine forest.The main results as follow:1.Biochar application had no significant effect on soil water content,soil organic matter,and soil total nitrogen in boreal forest（P>0.05）.After two-and three-year of biochar application,the 500℃/1.0kg·m-2 biochar treatment showed a marked increase in soil p H（P<0.05）,and of the other treatments the rises were not significant compared with the control（P>0.05）.This may probably be due to the application method and lower amount of application used in the study.2.Three-year after biochar application,the activity ofβ-glucosidase,β-cellobisidase,andβ-xylosidase in the 500℃/0.5 kg·m-2 treatments were far more higher than those of 1.0 kg·m-2treatments（P<0.05）.The activity of N-Acetyl-glucosamidase,Phosphatase,and Sulfatase in biochar treatments did not show difference compared with the control（P>0.05）.The interaction of the biochar pyrolysis temperature,applying amount,and the time after application impacted the activity ofβ-cellobisidase greatly（P<0.05）.3.The bacterial species richness in the 0.5kg·m-2 treatment was significantly higher than that of 1.0kg·m-2 treatment（P<0.05）.Along the time after application,the bacterial community species richness decreased（P>0.05）.The interaction between the biochar pyrolysis temperature and biochar applying amount had a significant effect on the bacterial community species richness（P<0.05）.4.Proteobacteria（33.79%,relative abundance）,Acidobacteria（26.74%）,and Actinobacteria（24.68%）were the most abundant phyla in the soil,while Mycobacterium（6.89%）,Acidobacterium（6.07%）,and Acidothermus（4.50%）were the most abundant genera.Two-year after biochar application,the relative abundance of Verrucomicrobia in the 500℃biochar treatments and 0.5kg·m-2 biochar treatments were significantly lower than that of the control（P<0.05）,and the relative abundance of Opitutus was lower in 650℃biochar treatments and 1.0kg·m-2 biochar treatments compared with the control（P<0.05）,respectively.Three-year after the biochar application,the relative abundance of Actinobacteria was lower in the 500°C biochar treatments than that of the control（P<0.05）.The relative abundance of Acidocella and Phenylobacterium in the 650℃biochar treatments was significantly lower than that of the control（P<0.05）.In the 650℃biochar treatment,the relative abundance of Cyanobacteria and Firmicutes in 1.0kg·m-2 treatment was significantly lower than that of 0.5kg·m-2treatment（P<0.05）,while the relative abundance of Chlorobi in 1.0kg·m-2 treatment was significantly higher than that of 0.5kg·m-2treatment（P<0.05）.1.0kg·m-2 biochar treatment significantly decreased the relative abundance of Edaphobacter,Conexibacter,and Nevskia,respectively（P<0.05）.5.Functionally,3 012 OTUs were divided into 39 functional groups,in which chemoheterotrophy（67.71%）was the main functional group.Two-year after biochar application,the relative abundance of nitrate reduction and fermentation of the 650℃(0.5kg·m-2 and 1.0kg·m-2)treatments was lower than that of the control（P<0.05）.In the 650°C biochar treatment,the relative abundance of chitin decomposition functional group of 0.5kg·m-2 treatment was significantly lower than that of 1.0kg·m-2 treatment（P<0.05）.In three-year samples,1.0kg·m-2 biochar application,the abundance of aromatic compound degradation functional group in 650℃biochar treatment was significantly higher than that in biochar at 500℃（P<0.05）.With the increase of time after biochar application and pyrolysis temperature,the relative abundance of the functional groups on degradation of aromatic compounds increased.6.Different soil bacterial community structures and functional structures were formed at different times after biochar application,while no difference was observed among biochar treatments with different pyrolysis temperatures and different applying amounts.In conclusion,the application of biochar in the boreal pine forests minimally affected soil physical and chemical properties,and the interaction of biochar pyrolysis temperature and applying amount had a significant effect on bacterial species richness.The relative abundance of specific bacterial groups altered for different applying amounts or produced temperatures of biochar.Different biochar application times resulted in different soil bacterial communities and functional structures,which indicating that the time played a crucial role in influencing soil microbial community structure.Biochar is generally stable with the potential to exist in the soil for a long period of time.And the biochar we spread on the soil vegetation surface in boreal pine forest takes time to integrate into the soil.Therefore,it is necessary to establish longer-term monitoring and research,to better understand the dynamic effects of biochar application on soil microbial community in boreal pine forests. |
