| Soil is the largest carbon pool in terrestrial ecosystems which contains nearly 1600 Pg carbon,and its carbon content exceeds the sum of the atmosphere and terrestrial vegetation.Therefore,subtle changes in the global SOC pool may greatly change the C balance in terrestrial and atmospheric environments.Soil microorganisms are crucial in the terrestrial carbon cycle because the growth,activity and their interaction with environmental factors largely control the fate of plant-derived carbon input and protected soil organic carbon.Soil carbon storage reflects the balance between the microbial decomposition of organic carbon and the stability of microbial assimilation carbon.Understanding and exploring the degradation mechanism of SOC in eastern China is of great significance in increasing the storage of organic matter in terrestrial ecosystems like farmland,forest and so on,reducing carbon dioxide emissions,and actively responding to future climate changes.The study of dominant phylum.In this experiment,soil samples from three ecosystems of cropland,paddy field,and forest of eight different locations(Hainan Ledong LD 18.69°,Hainan Dongfang DF 19.08°,Guangdong Guangzhou GZ 23.39°,Hunan Qiyang QY 26.76°,Hubei Wuxue WX 30.18°,Shandong Jinan JN 34.97°,Liaoning Shenyang SY 42.05°,Hei Longjiang Hailun HL 47.45°)in eastern China from south to north were used to measure soil respiration,carbon degrading enzyme activity,and carbon degrading functional genes.Combined with high-throughput sequencing technology,we explored the mechanism of carbon degradation mediated by microorganisms in cropland,forest,and paddy fields on a large scale.The sequencing results showed that the dominant bacteria in the soil samples were Actinobacteria,Proteobacteria,Chloroflexi and Acidobacteriota,and the dominant fungi were Ascomycota,Basidiomycota and Mortierellomycota.The results of diversity analysis showed that the diversity of microbial communities was regulated by different locations and different types of land use;the diversity of bacteria was mainly related to the physical and chemical properties of soil,such as p H and MBC,and precipitation also had a significant impact on it.Fungal diversity was significantly affected by climatic factors(temperature,precipitation),and MBC and MOI also significantly affected the diversity.Microbial interactions in paddy fields and forest were more complex than crop filed.The co-occurrence network topology values showed that the microbial interactions of paddy fields and forest were more complex,and the number of nodes and edges was significantly higher than that of cropland ecosystem.The forest interaction network contained 256 nodes and 1965 edges,and the paddy field contained 269 nodes and 1869 edges,while the cropland contained 208 nodes and 630 edges.The clustering coefficients of forest and paddy fields were larger,which were 0.53 and 0.52,respectively,while the clustering coefficient of dry land was 0.44.Analysis of carbon degradation indicators showed that the abundance of functional genes related to starch and lignin degradation in paddy fields was significantly higher than that in cropland and forest.The abundance of genes related to cellulose degradation in dryland was the highest,and that of functional genes in forest was the least;the overall activity of 9 enzymes gradually increased from south to north.Respiration intensity only differed significantly between locations,JN was the highest,followed by SY,and there was no significant difference at the remaining locations.The comprehensive indicators of carbon degradation had significant differences in different habitats(P=0.012),but there were no significant differences between different locations(P=0.153).Microbial diversity and relative abundance of modules had the greatest explanation for the carbon degradation function.Linear regression analysis showed that AP had a significant negative correlation with the Betweenness Centralization of the bacteria-fungi interaction network in different locations from south to north,and AP had a significant positive correlation with soil respiration and carbon degradation functional gene abundances.The VPA analysis shows that the microbial diversity(20%)and the module abundance of the microbial interaction network(17%)contributed the most to the multifunctional indicators of overall carbon degradation.Therefore,AP may affect soil respiration and functional gene abundance by affecting the interaction of microbial communities.Finally,the exploration of carbon degradation models in different ecosystems.Considering the difference of total carbon degradation indicators in different habitats,we applied the structural equation modeling(SEM)analysis to show that in cropland,fungi were the direct influencers of the total carbon degradation function;fungal community composition,precipitation,and AP content directly regulated the total carbon in cropland degradation function.At the same time,climate,soil physicochemical properties,and bacterial community composition also indirectly regulated the total carbon degradation function of cropland by affecting the composition of fungal community.In forest land,the total carbon degradation function was not directly or indirectly regulated by any biological and abiotic factors.The analysis of the specific carbon degradation function showed that the interaction of microorganisms directly regulated the enzyme activity of the forest land.The enzyme activity was also affected by the directly negative regulation of temperature,precipitation,p H,MOI and by directly positive regulation of AP content;respiration was only directly regulated by MBC;the abundances of functional genes were not regulated in any way.The carbon degradation of paddy fields was directly regulated by the most factors,which were directly regulated by biological factors(such as fungal composition,bacterial diversity,microbial interaction)and abiotic factors(such as temperature,AP,MOI,MBC,etc.).Microbial regulation was specifically manifested in that the microbial network module affected soil enzyme activity by changing the abundance of functional genes. |
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