Effects of Different Moisture Content and Freezing Temperature on Organic Carbon Mineralization During Freeze-Thaw Cycles in Black Soil

Abstract

[Objective] Soil respiration occupies an important proportion in the annual total soil respiration during freeze-thaw process. The effects of water content, freezing temperature and freeze-thaw cycles on soil carbon mineralization dynamics during soil freeze-thaw process were studied. [Methods] The study focuses on chernozem soil from the Nenjiang County Heshan Farm Jiusan Soil and Water Experimental Station in Heilongjiang Province, China was used as the research object to carry out an indoor freeze-thaw degree simulation test. Seven freeze-thaw cycles were carried out, and three soil moisture content were set 100% field water holding capacity (100% WHC), 60% field water holding capacity (60% WHC), and 30% field water holding capacity (30% WHC). Additionally, three environmental temperatures were used a constant 10 °C (control), -5 °C (mild freezing) and -15 °C (severe freezing). [Results] The number of freeze-thaw cycles, moisture content and freezing temperature had significant effects on CO2 emissions and the impact degrees were -0.63, 0.21 and 0.14, respectively. The thawing process notably increased soil carbon mineralization. The soil carbon mineralization of 60% WHC in the first three freeze-thaw cycles increased 33.0% and 35.2%, respectively, compared with 100% WHC and 30% WHC in the last 4 freeze-thaw cycles. In the case of severe freezing, the carbon mineralization of 100% WHC soil in the first 2 freeze-thaw cycles increased by 25.2% and 68.0% respectively, compared with 60% WHC and 30% WHC soil in the last 5 freeze-thaw cycles. [Conclusion] The number of freeze-thaw cycles had the greatest effect on soil CO2 emission, followed by moisture content, and the least freezing temperature. The freeze-thaw effect increased the cumulative CO2 emissions of soil with low water content. The cumulative CO2 emission of soil with high water content was reduced. For soils with medium moisture content, mild freezing increased CO2 cumulative emissions, while severe freezing decreased them. The first-order kinetic equation fitted the CO2 emissions from freeze-thaw soil well (R2 > 0.997), both moisture content and freezing temperature significantly influenced the potential for organic carbon mineralization (C0 value).

Keywords

• soil organic carbon mineralization
• soil moisture content
• freeze-thaw cycles
• freezing temperature
• black soil