| At present,the environmental problems,such as global warming caused by the increase of CO2 concentration,carbon emission reduction have attracted attentions of scientists in all over the world.Biochar is a carbon-rich material produced by theanaerobic or anaerobic pyrolysis of biomass.It can remain in the natural environment for hundreds and thousands of years as its high biological and chemical stability,therefore,the addition of biochar to soil is generally considered to be a low-risk and low-cost method of soil carbon sink.Cunninghamia lanceolata is an important fast-growing tree species for timber production in southern China.A large amount of deforested residue is produced in the process of logging and production.if the deforested residue is prepared into biochar and returned to the soil,it can not only avoid the waste of resources and environmental pollution,the biochar with high carbon and stable properties can also increase the soil carbon stock in artificial forests after being mixed into the soil.The effect of biochar on the soil carbon stability of Chinese fir has directly determined the potential of carbon sequestration from biochar.In this paper,some tests were carried out by means of element determination,Fourier transform infrared spectroscopy,scanning electron microscopy,boehm titration and phospholipid fatty acids.The biochar prepared from the residues of several common C.lanceolata was used to analyze the effects of different feedstocks of C.lanceolata and pyrolysis temperature on the physicochemical characteristics of biochar,and to reveal the characteristics of biochar under different preparation conditions.And the stability and carbon sequestration potential of biochar were predicted and evaluated by the established mathematical model to discover the mechanism of the stability of biochar itself.Through the comparison of soil CO2 mineralization,the carbon and nitrogen composition,microbial community structure and enzyme activity,the effects of biochar addition on SOC mineralization and its intrinsic association and influence were explored.And by studying the stability of soil aggregates and the relationship between carbon storage in soil aggregates and soil microbial communities,the formation mechanism of soil aggregates on the physical protection of exogenous organic carbon in the presence of biochar was elucidated.The results are as follows:(1)Temperature and feedstocks have a significant effect on the properties of biochar.With the increase of pyrolysis temperature,the yield of biochar in different parts of C.lanceolata gradually declined,pH increased,ash content increased,volatile component decreased and fixed carbon content increased.The carbon content increased,while the content of hydrogen and oxygen was reduced.The number of surface functional groups declined,but the aromaticity and stability were enhanced,and the polarity was weakened.The content of DOC,cellulose carbon,hemicellulose carbon decreased.Therefore,the biochar produced in the high temperature condition is more stable,containing higher carbon content,which is more beneficial to carbon sequestration.Because the bark contains lower cellulose and hemicellulose content,when the pyrolysis temperature reached 300?,500? and 700?,the biochar yield of barks was the highest,while that of trunks was the lowest.Because of the high lignin content of the branches,branch biochar has higher C content and C yield.And the DOC content,CEC content,pH and nutrient content of leaf biochar was significantly higher than that of the other three parts of C.lanceolata at the same pyrolysis temperature(p<0.05).Therefore,leaf biochar is beneficial to improve soil fertility and alleviate soil acidification after entering the soil.Wood biochar has low carbonate content and strong aromaticity.As well as the larger specific surface area,it is of great significance in the application of carbon sequestration.(2)By using alkali liquor absorption method to determine the CO2 release rate of biochar in abiotic and biotic incubation in order to characterize its degradation rate in 390 days,The half-life of biochar was calculated by using the prediction model.the cumulative mineralization of biochar and carbon loss decreased with the increase of pyrolysis temperature,but the stability increased.In the early stage of degradation,biochar was mainly degraded by the abiotic oxidation process.But with the increase of pyrolysis temperature,the difference of cumulative mineralization between biotic and abiotic degradation of biochar is gradually reduced.The first order kinetic model and the double exponential kinetic model were applied to predict the cumulative mineralization of biochar.The results showed that under the same pyrolysis conditions,the half-life of trunk biochar was the highest,while that in leaf biochar was the lowest.The cumulative mineralization showed a significant negative correlation with the specific surface area of biochar,C elements,fixed carbon content,but a significant positive correlation with DOC content,H%,H/C,O/C,(O+N)/C,volatile component,cellulose and hemicellulose content and acidic functional groups.In addition,the total acidic functional groups of biochar increased in varying degrees,both in biological and abiotic incubations.(3)In order to explore the effect of Chinese fir biochar on the soil mineralization of Chinese fir forest after being added to the soil.A 90-day indoor incubation was carried out to monitor the effects of adding branch biochar from C.lanceolata on the changes of soil carbon component and microbial community structure.The results showed that biochar rapidly reduced the DOC content by adsorption after only entering into the soil,and the significantly decreasing of DOC forced the microbial community structure to change,which increased the efficiency of carbon utilization and SOC stability,and reduced the mineralization of SOC.When there was litter in the soil,the addition of biochar decreased the total mineralization of SOC and litter.It promoted litter degradation while it reduced the mineralization of SOC,which indicated that whether at the presence or absence of litter,the addition of biochar to soil would reduce the total mineralization of SOC and carbon loss,and increase the SOC content in soil and its stability.In this process,the adsorption of biochar to DOC has important effect on reducing soil organic carbon mineralization and increasing soil carbon stability.A series of DOC adsorption experiments were carried out by using the trunk biochar and branch biochar with large difference in properties.The results showed that no matter where the source of DOC was from,soil or litter,Biochar has obvious selectivity for the adsorption of DOC,which means it is easier to adsorb the small molecules of fat that are easy to be used by microorganisms in DOC solution,leading to the increase of the proportion of relatively stable aromatic substances in the remaining DOC solution,and the increase of molecular weight.This selective adsorption may be closely related to the specific surface area of biochar.(4)In order to understand the effects of Chinese fir biochar on the soil aggregates stability and the distribution of organic carbon in Chinese fir plantations.Two different textures of plantations soil(siltstone clay soil and granite sandy soil)were used to carry out a 180-day indoor incubation with the addition of leaf biochar and trunk biochar at 300?,500? and 700 ?,respectively.The results showed that the addition of biochar significantly increased the structure of water stable aggregate and stability of aggregate on siltstone clay loam,but had no significant effect on granite sandy loam.Among which,the leaf biochar can better stimulate the formation of soil aggregates compared with that in trunks,and the biochar at low temperature can greater stimulate the stability of soil aggregates.Nevertheless,after the addition of biochar into two different textures of soil,more carbon existed in large and medium aggregates.Moreover,the addition of biochar changed the microbial community structure in soil,and influenced some soil characteristics such as soil pH,electrical conductivity and organic carbon composition.And the influence of biochar on these factors may affect the microbial community and aggregate of soil by various mechanisms,or it can affect the stability of soil aggregates by affecting the microbial community structure.The stability of biochar is beneficial to the stability of soil carbon in the process of carbon sequestration.Biochar could become a part of soil organic carbon after entering the soil,improving the stability of biochar itself is also beneficial to the stability of soil carbon.Meanwhile,in the case of avoiding DOC being utilized by microbes,the adsorption of DOC by biochar forces the change of microbial community structure to increase the utilization efficiency of carbon and reduce the release of CO2.In addition,the selective adsorption of biochar to DOC is also important for the stability of SOC,which is more obvious in the biochar treatment at high temperature.But the leaf biochar can stimulate the formation of soil aggregates and increase its stability,compared with that in trunk biochar.This indicates that the dominant mechanisms of the influence of biochar on soil carbon stability after entering the soil are different due to its different properties. |
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