Characteristics of Particulate Organic Matter Mineralization in Polluted Soils

Particulate organic matter (POM) is a key component of soil organic matter (SOM), which is easily biodegradable and rich in organic carbon (OC) and heavy metals. However, the characteristics of C mineralization and the releases of cadmium (Cd) and zinc (Zn) during POM mineralization are still poorly understood. In the present study, a 90-day incubation experiment was conducted to study the releases of CO₂-C and of Cd/Zn during POM mineralization with and without organic acids amendment. The results showed that 16.6%-26.6% OC, 17.0%-29.1% of Cd and 5.09%-14.3% Zn were stored in 2000–53 µm POM size fractions. Comparing with one-time amendment, frequent organic acids amendment caused 76.4%-83.7% decreases in C priming effects. The total amounts of CO₂-C emissions in POM size fractions were lower in soil with high pollution level than with low pollution level, and lower in 250–53 µm POM size fractions than in 2000–250 µm POM size fractions, respectively. The two-compartment first-order kinetic model can better fit the CO₂-C mineralization process, and organic acids amendment resulting in increase in mean residence time of labile C. After 90-day incubation, 8.58%-26.5% Cd and 10.38%-38.1% Zn in 2000–53 µm POM size fractions discharged into other phrases, and frequent organic acids amendment resulted more Cd/Zn release than that by one-time amendment in soil with high pollution level. Overall, frequent organic acids amendment facilitated C mineralization and Cd/Zn release of POM in comparison with one-time organic acids amendment in soil with high pollution level.