| Moso bamboo is a unique bamboo species and an important forest type in China,which has more carbon sequestration potential than other tree species.Bamboo has been planted in China for thousands of years.Under the conventional management of bamboo forest with no or little external fertilizer input,the total soil organic carbon in the soil remains at a certain level despite the long-term harvesting and artificial disturbance.Bamboo forest can grow well in the soil environment developed by different parent rocks.There is no soil degradation after continuous planting,which reflects that it has better resistance,recovery and balance to the interference that does not exceed the ecological threshold.At present,there are few studies on the formation and stabilization mechanism of soil organic carbon in Moso bamboo plantation.The change of organic carbon is driven by microorganisms,and the complexity of its composition and structure may lead to different microbial mechanisms of decomposition,transformation and fixation.Coupling organic carbon composition,structure and microbial community to study the special biochemical characteristics of SOC accumulation in bamboo forest is very important for us to deeply understand the bamboo soil carbon sequestration mechanism.This study adopts the space-time substitution method,and selects the bamboo forests with different management types(intensive management,extensive management,no operation)and different planting histories(19,37,64a)as the research objects,respectively,with adjacent secondary evergreen broadleaves.forest(>60a)and secondary deciduous broad-leaved forest(37a)were used as controls to study changes in ecosystem carbon storage,understory vegetation diversity and root morphological characteristics during long-term planting of bamboo,using chemical,aggregate,density,particle size and the grouping method of biological analysis of organic carbon accumulation and stability,Fourier infrared spectroscopy,solid nuclear magnetic resonance,fluorescence quantitative PCR and high-throughput sequencing were used to analyze the change characteristics and internalrelationship between organic carbon structure and microbial community structure and functional activity.The main results are presented in the paper as follows:(1)The carbon storage and distribution pattern of bamboo forest ecosystem were significantly affected by different planting years.Long-term planting of Moso bamboo significantly increased the soil organic carbon pool and its distribution ratio,which led to the increase of total carbon reserves of the ecosystem with the increase of planting years.Shrub layer vegetation diversity,bamboo fine root biomass and specific root length and root length density of ? 0.5mm diameter fine roots were significantly positively correlated with soil carbon reserves,indicating that the composition of vegetation under bamboo stands,and the biomass and morphological characteristics of fine roots affected the formation process of organic carbon.(2)The content and storage of organic carbon in bamboo soil increased significantly with the extensive management of bamboo planting time.The contents of active carbon components such as hot water soluble organic carbon,easily oxidized carbon,free particle organic carbon and closed storage particle organic carbon,and stable organic carbon components including mineral bound organic carbon and humus carbon were significantly increased.The distribution ratio of SOC in Moso bamboo forests was highest in MOC(52.12-73.3%),followed by o POC(11.51-20.73%)and f POC(7.98-12.76%),and then MBC(1.46-6.62%),ROC(1.82-4.45%)and DOC(1.43-1.68%).The stability of soil aggregates and amorphous iron oxide content increased with the increase of bamboo planting years,and there was a significant positive correlation between amorphous iron oxide and agglomerate stability and organic carbon content.The above results indicate that soil minerals play a major role in the stabilization of organic carbon in the soil of bamboo plantation.The physical protection of organic carbon by soil aggregates gradually increases with the increase of planting years.The results of solid-state NMR showed that the soil organic carbon in the bamboo forest was dominated by alkoxy carbon and aromatic carbon,and the proportion of carbonyl carbon and alkyl carbon was small.Alkyl carbon,alkyl carbon/alkoxy carbon and hydrophobic carbon/hydrophilic carbon gradually increase with the increase of planting years in 0-20 cm soillayer;aromatic carbon and aromaticity are planted in 20-40 cm soil layer.The increase of years indicates that the chemical structure stability of soil organic carbon in long-term planting of bamboo forest is improved.(3)Peroxidase activity decreased during long-term planting of bamboo,and polyphenol oxidase,acid phosphatase and protease activities were increased.As the number of years of bamboo planting increases,the number of soil bacteria and fungi gradually decreases,and bacterial diversity decreases.The soil bacteria are mainly composed of Proteobacteria,and the proportion increases with the increase of planting years.The relative abundance of Acidobacteria and Chloroflexi,which mainly decomposes refractory carbon,is gradually reduced.(4)Compared with the control secondary forest,total organic carbon(TOC)content in the soil,as well as free particulate organic carbon(f POC),soluble organic carbon(DOC),and mineral-associated organic carbon(MOC)in the undisturbed and extensively managed Moso bamboo plantations significantly increased.Although the ratio of f POC to TOC in the undisturbed Moso bamboo plantation increased significantly,mineral-associated organic carbon MOC stored the most soil organic carbon(67.6 %).Intensive management resulted in the loss of soil organic carbon,total nitrogen storage,and the contents of each component,but significantly increased the DOC/TOC ratio and microbial quotient(MBC / TOC).Therefore,human disturbance accelerated C cycles and worsened the stability of organic carbon.Management measures also had significant effects on the chemical structure of SOC.Compared with the control,the relative intensities of phenolic and alcoholic–OH,aliphatic methyl and methylene,aromatic C=C,and carbonyl C=O absorption were higher in the SOC of undisturbed and extensively managed Moso bamboo plantations,with soil hydrophobicity also increasing.The increased hydrophobicity of organic carbon was mainly manifested in the mineral-associated organic carbon of the three physical fractions.Therefore,lower forest disturbance enhances the accumulation of aliphatic and aromatic groups in components with small particle size.Correlation analysis showed that soil hydrophobicity and the content of aliphatic and aromatic groups were negatively correlated with MBC,MBC/TOC and Cmineralization,but positively correlated with TOC content.Therefore,the chemical structure of organic compounds largely controls the extent of decomposer activity and the rate of degradation.Reduced human disturbance could increase the input of organic matter residues(such as litter and roots),leading to the relative accumulation of chemical resistance compounds,which significantly enhance the chemical stability of soil organic carbon.Soil mineral clay contributed towards preserving soil carbon through the formation of mineral-organic compounds,making it conducive to the storage of soil carbon..(5)The transformation of secondary broad-leaved forest to bamboo plantation and its subsequent management practices significantly changed soil properties,main nutrient content and bacterial community structure,but did not reduce the Shannon diversity index.As the intensity of bamboo forest management increases,bacterial diversity increases.Non-operating and extensive management mainly increased the relative abundance of ?,? Proteobacteria and Bacteroidetes,and this type of bacteria mainly has a strong effect on easily decomposable organic substances.The relationship between soil physical and chemical properties and bacterial community showed that the difference of soil p H and carbon and nitrogen content may be important factors in determining the structure of bacterial community.At the same time,the multiple regression analysis of SOC structure and bacterial community composition showed that aliphalia-CH and aromatic C=C were important functional groups to distinguish the difference of bacterial community composition between bamboo plantations with different management measures... |
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