| Researches on the role of biochar in carbon sequestration in soil have been widely reported Substrate is an important "new carbon" to the soil,but still remained unclear on its mineralization in biochar-containing soil and its interaction with soil organic matter mineralization.How biochar determines the mineralization of exogenous substrates by affecting the physio-chemical properties of soil,and microbial community structure remains unclear.To solve these scientific questions on carbon process(substrate mineralization,priming effect)and involved mechanisms in biochar-containing soil,we collected forest burned soil after fire(including residual biochar)in the north and south regions of China with different ecosystems and spatial and temporal scales,or soils containing man-made biochar,and carry out indoor incubation experiments,to investigate the effects of substrate type and soil properties on substrate mineralization in biochar-contaiining soil.By combining high-throughput sequencing with X-ray CT scanning,we analyzed the changes of soil pore structure and microbial community structure by biochar,and comprehensively explore the physio-biological mechanisms of substrate mineralization in biochar-containing soil.The main conclusions obtained are as following:(1)By analyzing the correlation between soil physio-chemical properties and substrate mineralization in different ecosystems,it was found that the C:N was significantly negatively correlated with the cumulative mineralization(days 14)of the substrate in the soil.Therefore,the C:N of the soil could be an important factor for determining the mineralization of substrates in biochar-containing soil.(2)We aimed to investigate the mineralization of substrates in the soils with different depth under different fire history.The cumulative mineralization of the sucrose in the forest soil after fire of 12 years is significantly higher than that of the soil with fire for 28 years.As the soil depth increases,the cumulative amount of substrate-derived mineralization in the soil is gradually reduced.The substrate caused the largest primed CO2 of SOC(3362 mg C kg-1soil)with the rate at 387.8μg C g-1 soil d-1 in the humus layer.Furthermore,through high-throughput sequencing,it was found that the forest soil with a fire age of 28 years had higher abundance of the proteobacteria and a lower cumulative mineralization of the substrate.Therefore,combined high-throughput sequencing with correlation analysis,we found that Proteobacteria may be a key microbial type of substrate with increased mineralization in biochar-containing soil.(3)X-ray CT scanning technology was adopted to explore the mineralization of substrates and involved physical mechanisms in the long-term biochar amended soils.Biochar significantly changed the pore in the long-term biochar amended soils.The application of biochar in the three different proportions of low,medium and high increased the pore connectivity of the soil,and the connectivity showed BM>BH>BL trend;the cumulative mineralization of substrate in soil also showed a trend of BM>BH>BL.Therefore,there is a good correlation between the amount of mineralization of the substrate in the soil treated by biochar and the connectivity of the soil pores(r<-0.7,P<0.01).The change of soil pore connectivity may be one of the main mechanisms for the mineralization difference of substrate in biochar-containing soil.(4)X-ray CT scanning and high-throughput sequencing techniques were combined to explore the differences in mineralization of different gradient substrates in burned soils.It was found that biochar addition increased the mineralization of three gradient substrates of sucrose,maize powder and maize straw in the soil.Also,we found biochar by increasing the proportion of spiracle(>80 μm)in the soil,decreased the abundance of Firmicutes(r=-0.777,P<0.001)and Actinobacteria(r=-0.782,P<0.001)and increased the relative abundance of Chloroflexi(r=0.444,P<0.001).In addition,the mineralization of the three gradient substrates has a certain correlation with the microbial type,for example,sucrose(correlation with Actinobacteria:r=-0.567,P<0.05)maize powder(correlation with Actinobacteria:r=-0.924,P<0.001;Chloroflexi:r=0.230,P<0.001)and maize straw(correlation with Actinobacteria;r=-0.863,P<0.001;Firmicutes:r=-0.944,P<0.001),there are some differences between the key microbial types indicating different substrate mineralization.Thus,it was confirmed that biochar may affect the mineralization process of the substrate in biochar-containing soil by changing the physical structure of the soil and the community composition of the soil microbes. |
