Effects Of Different Addition Rates Of Chinese Fir Litter And Its Biochar On Soil Organic Carbon Mineralization And Microbial Community Structure

Soil organic carbon?SOC?mineralization is one of the important processes of carbon cycle and has an important influence on the greenhouse effect and global climate change.Studies had shown that global climate change and forest management measures will lead to changes in the amount of input litter,which in turn affects soil SOC mineralization and microbial community structure.However,there are few studies on the effects of higher addition rate on soil CO2 emissions and microbes.Biochar?BC?is a soil amendment that has received extensive attention in recent years.In the process of managing Chinese fir forest,if the litter is prepared into BC,it can not only avoid the environmental pollution caused by fire,but also increase soil carbon retention and enhance soil fertility.Litter as a kind of easily decomposable carbon source,BC is a hard-to-decompose carbon source.How does they affect the soil SOC mineralization and microorganisms when they are added to the soil in the short term?What is the response to different addition rate?Based on the above questions,In this experiment,the subtropical Chinese fir plantation soil was used as the research object.The ¹³C-labeled Chinese fir litter and its biocahr?BC,350°C pyrolysis?were used as exogenous carbon,and the28-day indoor culture test was combined with stability.Sex isotope technique was used to study the effects of exogenous carbon types and additions rates?0,1,2,3,4,5%soil mass fraction?on soil basic properties,SOC mineralization and microbial community structure of Chinese fir plantations.The main findings are as follows:Litter and BC addition significantly increased soil total carbon?TC?,total nitrogen?TN?content and C/N ratio?except for 1%addition of litter?in the short term.Litter treatment had no significant effect on pH?except for 5%litter treatment?,while BC addition significantly increased soil pH.Both litter and BC addition increased the total PLFA content of soil microbes in different degrees,and the response of various microorganisms in the soil to their addition was also very different.There was a significant positive correlation between the total PLFA,bacterial and fungal PLFA contents in the litter treatment,and the soil microbial activity increased in the range of the addition rates of the study.However,the BC treatment was different,the soil microbial total PLFA and the PLFA content of all kinds of microorganisms reached the maximum at 3%,showing a parabolic relationship with the opening downward,the addition amount further increased,and the microbial activity decreased.Both litter and BC addition significantly changed the soil microbial community structure,and the effect of litter was more obvious,while the addition rates had less effect on it.The study also showed that soil TN and C/N ratios are the key factors affecting the changes of microbial community structure in litter and BC treatment,respectively.Litter and BC addition significantly increased the cumulative amount of CO2,and the promotion of litter is more obvious.Using the short-term test combined with the isotope ¹³C tracer technique,it was found that the promotion effect of litter or BC alone on the native SOC mineralization increased with the increase of the addition rates,compared with the control soil,litter treatment is 6.50 to 13.74 times of S treatment,while BC treatment is 2.08 to 3.98 times of S treatment.and the influence of the litter treatment was more obvious.There is a linear relationship between the decomposition rate of the native SOC and the addition rate.There is a linear relationship between the litter carbon decomposition rate and its addition rates,but the BC-C decomposition rate does not show this trend,and reaches the maximum when the addition rate is 1%.Compared with litter,the decomposition of BC in the short term is less affected by microbial activity,lower in bioavailability,and more stable in soil.The relevant microbiological mechanism needs further study.The types and addition rates of exogenous carbon had essential influence on soil basic properties,microbial community structure and SOC mineralization.This study provides a scientific basis on soil organic matter management and efficient utilization of biochar resources in subtropical plantations.