Effect Of Shallow Flooding On Mineralization Of Organic Carbon In Paddy Soil And Its Restrictive Factors

Soil organic carbon(SOC)mineralization is an important process of organic carbon pool cycle in terrestrial ecosystem,and plays an important role in the global carbon cycle,which connects the whole ecosystem.Soil organic carbon mineralization plays an important role in soil functions,including the production of greenhouse gases,the stability of soil structure,the maintenance of soil quality and the support of biodiversity.Therefore,in this paper,paddy soil was used as the test soil to study the influence of water on the mineralization mechanism of soil organic carbon.There are three incubation experiments in this study.According to the relevant test data measured in the cultivation process,analyze the mineralization characteristics and temperature sensitivity of farmland soil organic carbon under the periodic temperature change environment and the difference with constant temperature cultivation;set different water gradients at the same time,compare the mineralization strength of farmland soil organic carbon under different flooding environment;and set different organic material content,which is better under the gas and flooding environment.The mineralization intensity of soil organic carbon is expected to provide a reference for a comprehensive understanding of the water effect of soil organic carbon mineralization in purple hilly area.In addition,by changing the depth of flooding and the addition of exogenous organic carbon,we can change the strength of SOC mineralization in farmland and play a guiding role in agricultural production.The results are as follows:(1)It can be concluded from the three experiments that SOC mineralization rates of paddy soil all show a trend of sharp decline in the early stage of culture and gradually slow in the later stage.Under the condition of good qi,the decrease of paddy soil was relatively large,while under the flooded condition,the decrease of paddy soil was relatively small after the increase of paddy soil.At the 29 th day of culture,the SOC mineralization rate was basically stable.The time for SOC mineralization rate to reach a stable state in flooded condition lags behind that in haoqi condition.Under the same water condition,the SOC mineralization rate of each thermostatic culture in the early stage of culture was arranged in the order of the culture temperature from high to low,and there was a significant difference.At different flooded depths,the SOC mineralization rate of haoqi culture fluctuated between the flooded rate of 1.5cm to 10 cm 2 days before the removal of culture.Under the same water condition,the mineralization rate of paddy soil increased gradually with the increase of organic materials,and the average growth rate of paddy soil mineralization rate in aerobic culture was much higher than that in submerged culture.With the extension of culture time,the SOC mineralization rate of paddy soil also decreased gradually,but the SOC mineralization rate of paddy soil fluctuated greatly under the submerged culture.(2)Under the same water condition,the order of SOC accumulation mineralization amount and mineralization intensity of rice soil cultivated at each constant temperature was 25°C >,20°C >,15°C.The higher the temperature,the greater the effect of SOC mineralization on rice soil.In addition,the cumulative mineralization amount of paddy soil with periodic temperature change of 15/25°C was always between a constant temperature of 15°C and a constant temperature of 25°C in both flooded and aerobic culture,and there was no significant difference between the cumulative mineralization amount and mineralization intensity of organic carbon in paddy soil and a constant temperature of 20°C.The change of temperature is not the main factor affecting SOC accumulation mineralization of paddy soil,but the change of accumulated temperature is.In addition,under the same temperature condition,the SOC accumulation mineralization amount and mineralization intensity of paddy soil were higher in the flooded condition than in the aerobic condition,and the flooded condition was more conducive to the SOC mineralization of paddy soil.SOC accumulation mineralization amount of paddy soil is significantly affected by temperature and water,and the change of temperature amplitude does not affect the effect of water on SOC accumulation mineralization amount.Under different submergence depths,SOC accumulation mineralization of paddy soil showed a significant trend of decreasing with the deepening of submergence depth,that is,the deeper the submergence depth,the smaller the accumulation mineralization.However,there was no significant difference between the cumulative mineralization amount of haoqi(70%WHC)culture and that of submergence of 3cm and 5cm.This indicates that at the shallow level of flooding(1.5cm),water has no inhibition or even a strengthening effect on SOC mineralization.However,with the increasing depth of flooding,the inhibition effect of water on SOC mineralization is gradually strengthened.With the increase of organic materials,SOC accumulation mineralization of paddy soil showed an obvious increasing trend.Moreover,with the increase of organic materials,SOC accumulation mineralization in paddy soil increased at a higher rate than that in submerged culture,which can be seen from the mineralization intensity.Under the same amount of organic material addition,when the input was > 0.2g,the SOC accumulation mineralization amount of paddy soil in the aerobic culture was significantly higher than that in the flooded culture.At a low level(straw input was 0.1~ 0.2g),there was no significant difference in SOC accumulation mineralization between aerobic culture and submerged culture.(3)The change of soluble organic carbon content of paddy soil with culture time was inconsistent under different submergence depth.The DOC content of M2 and M3 showed a trend of rising first and then stable,while that of M4 and M5 showed a trend of decreasing first and then slowly rising.The sequence of DOC content in each water treatment was more complicated when the first and fifth days were cultured.At the end of the 10 th day of culture,the content of DOC in each water treatment M2 was significantly higher than that in other treatments,followed by M3,while there was no significant difference in the content of DOC between M4 and M5 treatments.When organic materials with different contents were added into the paddy soil,the change trend of DOC content in each treatment of paddy soil was not consistent with the culture time under the same water condition.Under the two kinds of water conditions,there was a trend that the submerged culture was significantly higher than the haoqi culture in different cultivation periods,and the overall performance was that the treatment with high amount of straw addition and high DOC content.In general,in each culture period,under the same straw content treatment,the paddy soil DOC of submerged culture was higher than that of haoqi culture.There was not a significant correlation between DOC content and SOC mineralization rate in paddy soil.(4)The change of MBC content in paddy soil under various hydrothermal conditions showed a trend of increasing first and then decreasing,then increasing and then decreasing.There was no significant correlation between MBC content and SOC mineralization rate under various hydrothermal conditions,which indicated that MBC content of paddy soil could not effectively reflect the difference of SOC mineralization process between different hydrothermal conditions.On the 1st day of culture,the effects of temperature and water on microorganisms had a delayed effect,and the microbial communities had not yet reached equilibrium,so the effect of temperature on microbial biomass carbon content was not obvious.The influence of temperature on MBC content of paddy soil under favorable gas condition was greater than that under flooded condition.The MBC content of rice soil under each flooded treatment decreased rapidly in the early stage and continued to drop after reaching the peak on the 10 th day.On the 10 th day of culture,the MBC content of paddy soil reached the peak under different flooded conditions.In the same culture time,the MBC content of rice soil did not vary greatly under different water conditions,which indicated that the depth of flooding had no significant effect on the MBC content of rice soil.The variation trend of MBC content in the tested soil in each treatment was more complicated with no obvious regularity.The average MBC value of submerged culture was higher than that of haoqi culture,and the lowest and highest MBC content of submerged culture were significantly higher than that of haoqi culture.The three experiments showed that there was no significant correlation between MBC content of paddy soil and SOC mineralization rate at each culture stage,and water could not affect SOC mineralization process by changing soil MBC content.(5)Microbiological indexUnder the same water condition,there was no significant difference in gene copy number between the constant temperature of rice soil at 20°C and 15/25°C.However,under the same temperature,the number of gene copies in the cultivated rice was higher than that in the submerged culture,but the difference was not significant.Under the same water condition,the community types were more similar,and the species abundance varied greatly between the submerged culture and the aerobic culture.