Objective It plays an important role in terrestrial ecosystem carbon cycle and global climate change to study soil organic carbon (SOC) mineralization. Laboratory incubation experiment is an important method to study SOC mineralization. The mineralization intensity of SOC decreases gradually with time under constant temperature and humidity incubation environment. Will the dry-wet cycles and periodic disturbance (man-made crushing and air-drying under sun) during incubation experiment change this trend? There is a lack of attention to this problem. Therefore, the dynamic characteristics of SOC mineralization in multiple dry-wet cycles were analyzed, and impacts of man-made crushing and air-drying under sun on SOC mineralization during dry-wet cycles were discussed, in order to provide reference and scientific basis for the accurate setting of laboratory incubation experiment and the standardized storage of air-dried soil samples.
Method Farmland paddy soil was selected as the sampled soil. The method of combination of pumping, air drying and temperature control was used to simulate the process of dry-wet cycles soil in the dark. Two dry-wet cycles were carried out, each cycle included 14 d shallow flooding period (soil water mass ratio 1∶2) and 14 d drainage-drying period (100% water holding capacity - natural drying). The specific disturbance measures were that after the first dry-wet cycle, the soil was moved to the glass greenhouse for air drying under sun and man-made crushing (grinding and sieving), and then enter the second cycle. At the same time, continuous shallow flooding and aerobic treatments were carried out as reference. Double reservoir first-order kinetic equation was used to fit and evaluate the different carbon pools and mineralization rate constants of soil in shallow flooding period and drainage-drying period of dry-wet cycles.
Result The average mineralization rate of shallow flooding treatment was significantly higher than that of aerobic treatment. Compared with the continuous shallow flooding and aerobic treatments, the conventional dry-wet cycles treatment had significant priming effects on SOC mineralization after each re-watering and drainage. The priming effects gradually weakened with the increase of the times of dry-wet cycles. And the cumulative mineralization amounts of SOC from two soils increased by 72.09% and 128.48% in the end of incubation experiment. Compared with air-drying without sun treatment, the peak value of SOC mineralization rate and cumulative SOC mineralization amount of air-drying under sun treatment were increased by 26.29% and 16.15%, while the SOC mineralization characteristics of man-made crushing treatment had no significant impact. The fitting of mineralization kinetic equation showed that the proportion of non-labile organic carbon mineralization in each period increased gradually with the times of dry-wet cycles.
Conclusion The multiple dry-wet cycles does not change the periodic attenuation trend of mineralization intensity over time, but the attenuation extent slows down significantly. The periodic disturbance of air-drying under sun further slows down the attenuation trend during dry-wet cycles. It is suggested that the soil samples collected for SOC mineralization incubation experiment should be kept away from sun as far as possible during air-drying and preservation.
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