| Nowadays global warming is a widely concerned issue,which caused changes in temperature and moisture content and it has an effect on soil organic carbon content and soil composition.This paper studied the effects of application and no application corn stalk on the Soil organic carbon and its components(aggregates organic carbon, water-solube organic carbon and Humic substances carbon)and structure characteristic of humic substances,under the condition of different temperature( 10 ℃,30 ℃,50 ℃) and water(30%WHC, 60%WHC,250%WHC).It provides a scientific theoretical basis for the function of farmland ecosystem carbon fixation、mitigation of atmospheric CO2 concentration.The results as below:1. Compared with the treatment without adding corn straws,Application of corn stalk make soil total organic carbon content increased significantly.With the increase of culture temperature,The soil total organic carbon was in the order of 10℃>30℃>50℃,This indicates that high temperature is not conducive to the accumulation of total organic carbon in soil.With the extension of time,the content of soil total organic carbon decreased under application and no application corn stalk.2. Compared with the treatment without adding corn straws,Application of corn stalk make oxidizable organic carbon content increased significantly,With the increase of culture temperature,The oxidizable organic carbon was in the order of 10℃>30℃>50℃,This indicates that high temperature is not conducive to the accumulation of carbon in soil oxidation.3. Compared with the treatment without adding corn straws,application of corn stalk make soil aggregates(2~0.25 mm) content、the mean weight diameter(MWD) and geometric mean diameter(GMD) of aggregates increased significantly and the index of unstable aggregates reduced, This indicates that the addition of corn stalk can increase the stability of soil aggregates.With the increase of culture temperature, The soil aggregates(2~0.25 mm) content、the mean weight diameter(MWD) and geometric mean diameter(GMD) of aggregates is in the order of 10 ℃ >30 ℃ >50 ℃,The index of unstable aggregates(ELT) is in the order of 50℃>30℃>10℃, This indicates that the temperature is not conducive to the formation of soil aggregates, and destroyed the stability of soil aggregates under the condition of adding corn straw and without adding corn straw.With the extension of time,the soil aggregates(2~0.25 mm) content、the mean weight diameter(MWD) and geometric mean diameter(GMD) of aggregates were all increased, the ELT was decreased without adding corn straw at 10℃ and 30℃;but,the soil aggregates(2~0.25 mm grade) content、 the mean weight diameter(MWD) and geometricmean diameter(GMD) of aggregates were all decreased,the ELT was Increased without adding corn straw at 50℃. The soil aggregates(2~0.25 mm grade) content、the mean weight diameter(MWD) and geometric mean diameter(GMD) of aggregates were all decreased,the ELT was Increased with adding corn straw.Compared with the treatment without adding corn straws,application of corn stalk increased the organic carbon of different size aggregates in soil. With the increase of culture temperature, There is a decreasing tendency of the organic carbon in aggregates.4. Compared with the treatment without adding corn straws,application of corn stalk increased the soil organic carbon in soil water soluble substance(WSFC) and humus fractions(HE、HA、FA).With the increase of culture temperature, the WSFC at 50℃ treatment was significantly higher than 10℃ and 30℃ treatment without adding corn straws. The WSFC at 10℃ and 50℃ treatment was significantly higher than 30℃ treatment with adding corn straws.The HEC、HAC、FAC were in the order of 10℃>30℃>50℃, This indicates that high temperature is not conducive to the accumulation of organic carbon in soil humus.With the extension of time,There is a decreasing tendency of HEC、HAC、FAC,but the HAC has a increase trend.At the same time, application of corn stalk increased the CHA/CFA、the logK and E465/E665 of humic acid;With the increase of culture temperature,the CHA/CFA、the log K and E465/E665 of humic acid has an obvious decreasing trend, This indicates that the high temperature cultivation condition accelerates the aging of HA molecular structure,weakens its colloid function and reduces the activity,and simultaneously makes the structure of HA complicated. with the extension of time, the CHA/CFA has a increase trend.5. Compared with the treatment without adding corn straws,After application of corn stalk increased the soil organic carbon in soil water soluble substance(WSFC) and humus fractions(HE、HA、FA).With the increase of culture temperature, the WSFC at 50℃ treatment was significantly higher than 10℃ and 30℃ treatment under the condition of without adding corn straws. The WSFC at 10℃ and 50℃ treatment was significantly higher than 30℃ treatment under the condition of adding corn straws.The HEC、HAC、FAC were in the order of 10℃>30℃>50℃, This indicates that high temperature is not conducive to the accumulation of organic carbon in soil humus.With the extension of time,There is a decreasing tendency of HEC、HAC、FAC;but, the HAC has a trend of increase.At the same time,After application of corn stalk increased the CHA/CFA、the logK and E465/E665 of humic acid;With the increase of culture temperature,the CHA/CFA、the log K and E465/E665 of humic acid has an obvious decreasing trend, This indicates that the high temperaturecultivation condition accelerates the aging of HA molecular structure,weakens its colloid function and reduces the activity,and simultaneously makes the structure of HA complicated. with the extension of time, the CHA/CFA has a trend of increase.6. The results of different water culture experiments show that, the carbon contents of the total soil and corresponding humic fractions generally decreased with increasing soil moisture. A significant difference was observed between the 250% WHC and the two other moisture levels. By contrast, the carbon content of the water soluble fraction significantly increased with increasing soil moisture levels. The solid-state 13 C nuclear magnetic resonance(NMR) spectra showed that the alkyl C/O-alkyl C, aliphatic C/aromatic C, and hydrophobic C/hydrophilic C ratios were in the order of 250% WHC > 30% WHC ≈ 60% WHC, 30% WHC ≈ 60% WHC > 250% WHC and 250% WHC > 60% WHC ≈ 30% WHC for humic acid, and 250% WHC > 30% WHC ≈ 60% WHC, 60% WHC ≈ 250 % WHC > 30% WHC and 30% WHC ≈ 250% WHC > 60% WHC for humin, respectively. These results indicated that a high moisture level was unfavorable to the carbon accumulation of the total soil and humic fractions, whereas it was favorable to the accumulation of water soluble carbon. Although soil moisture levels had a distinct effect on the chemical composition of humic acid and humin, the decomposition degree of the two humic substances components, as indicated by the alkyl C/O-alkyl C ratio, were both higher at a high moisture level than at a low moisture level. Therefore, the lower soil organic carbon content at a high moisture level than at a low moisture level can be ascribed to the higher water soluble carbon content and larger decomposition degree of humic acid and humin in the former. Our results are important for understanding the behavior and mechanisms of humic substances at specific soil moisture conditions. |
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