Effect Of Humic Acid On The Distribution Of Photosynthetic Carbon And Its Rhizosphere Priming Effect In Paddy Soil

Soil organic carbon（SOC）is an important component of the terrestrial carbon pool,and its accumulation and decomposition play an important role in controlling greenhouse gas emissions（CO₂,CH₄）and increasing soil carbon fixation.Humic acid（HA）materials as the most active in paddy soil organic matter,one of the most important polymer quinone polymer,its content height may result in paddy soil physical properties,chemical properties and microbial community structure change,thus affecting rice of photosynthetic carbon in the "rice-soil" system input and turnover.The results provide an effective scientific basis for improving soil fertility,reducing greenhouse gas emissions and sequestration of soil carbon.Therefore,the soil of the long-term location experiment site of Changsha Agricultural Environment Observation and Research Station of Chinese Academy of Sciences in Hunan Province was selected to conduct outdoor simulation test on the rice soil,and humic acid adding group and humic acid adding group were set up.A continuous labeling test was carried out to simulate atmospheric CO₂ by reacting 13CO₂（13C-Na₂CO₃ and Na₂CO₃）with excess H₂SO₄(0.5mol·L^-1)in a CO₂ generator.This study provides a theoretical basis for rice photosynthetic carbon input,turnover and stability under the condition of adding humic acid.The specific results are as follows:（1）Humic acid supplementation significantly affected the input and distribution of rice photosynthetic carbon in"rice-soil”system.Compared with the treatment without humic acid,the addition of humic acid increased the accumulation of dry matter in the underground part of rice by 7.3%,caused the transfer of 8%～33%photosynthetic carbon to the underground part of rice,and significantly increased the root-shoot ratio by 25.4%at the early stage of rice growth.The proportion of 13C in each part of rice photosynthesis changed with the development of rice growth period.The results were as follows:the proportion of 13C in the aboveground increased gradually,which was mainly used for the formation of grain,while the proportion of 13C in the underground part and soil decreased.（2）Humic acid supplementation significantly affected CO₂ and CH₄ emissions in rice fields.with the development of rice growth period,the emission fluxes of CO₂ and CH₄ in paddy soil were significantly different from the decomposition and mineralization of soil organic matter（SOM）under the two fertilization conditions.Compared with the treatment without humic acid,the addition of humic acid promoted the emission of total CO₂ and SOM CO₂,and significantly increased the excitation effect of CO₂ by 37%.However,the emission of CH₄ and CH₄ from SOM was inhibited,and the excitation effect of CH₄ was reduced by 14%.（3）The addition of humic acid significantly affected the C/N/P stoichiometric ratio in soil after the input of photosynthetic carbon,and microorganisms were controlled by the principle of metrology,thus regulating the utilization of C,N and P nutrients.Compared with the treatment without humic acid addition,the contents of microbial organic carbon（MBC）,microbial nitrogen（MBN）and microbial phosphorus MBP were significantly decreased in the treatment with humic acid addition.Correlation analysis showed that there was a significant positive correlation between MBC,MBN and MBP in the soil（P<0.01）.In addition,by analyzing the RPE data of rice,it was found that MBN and NH₄⁺-N jointly affected the carbon dioxide(PE_CO2)and methane（PECH₄）stimulation effects（P<0.01）,The variance decomposition diagram showed that the microbial part mainly affected the PE_CO2,and the rice biomass part mainly affected the PE_CH4.（4）During the process of soil stabilization,the addition of humic acid significantly affected the cumulative amount of photosynthetic carbon in soil.The distribution of aggregate components in soil is as follows:The>microaggregates of clay-silt>were large aggregates,so the absolute content of photosynthetic carbon also changed accordingly,which was mainly the clay-silt component accounted for an absolutely high content in the paddy soil.The humic acid treatment significantly reduced the accumulation of photosynthetic carbon in clay-silt compared with the treatment without humic acid addition.And mineral-bound organic carbon,mainly distributed in small particles,was reduced by 59%.In addition,the correlation analysis between photosynthetic carbon content of different particles and active iron binding carbon and soil enzyme activity showed a certain correlation,indicating that microbial enzyme activity played a certain role in the stabilization process.Above all,humic acid added underground part by promoting rice growth,then increase the rice photosynthetic carbon to the amount of input in the soil,thus changing the C/N/P rice rhizosphere situations stoichiometric ratio,affected the microbial species and amount,further change on the stability of soil organic carbon,which affect the effect of rice rhizosphere excitation and stable photosynthetic carbon in the soil,the result of global greenhouse gas emissions and provide theoretical basis for soil carbon cycle.