Microbial nutrient limitations and chemical composition of soil organic carbon regulate the organic carbon mineralization and temperature sensitivity in forest and grassland soils

Background and aim

Soil organic carbon (SOC) mineralization which relates to SOC stability and sequestration, predicating the SOC stocks under climate change, is affected by land use and exogenous carbon addition. However, how SOC chemical composition and soil enzymes regulate SOC mineralization of grassland and forest soils receiving exogenous C addition is still not well understood.

Methods

Forest and grassland soils were incubated without or with two levels of ¹³C-enriched glucose, simulating labile C inputs, at 15 and 25 ℃ for 28 days. The priming effect, temperature sensitivity (Q₁₀), enzyme activities and chemical composition of SOC were determined.

Results

Increasing labile C addition and higher temperature accelerated native SOC mineralization in forest and grassland soil. Changes of enzyme C:N and N:P ratio contributed to the differences in CO₂ production in forest and grassland soil. In grassland soil, the relationship between soil-derived CO₂ production and relative peak areas of SOC at 1420 cm⁻¹ by Fourier-Transform infrared spectroscopy was significant. The temperature sensitivity of the native SOC mineralization in the forest soil amended with 0.8 g glucose-C kg⁻¹ dry soil application was greater than that with 0.4 g glucose-C kg⁻¹ dry soil application, but in the grassland soil, the Q₁₀ of glucose derived CO₂ emission was lower after the higher glucose application.

Conclusion

Soil enzyme nutrient ratios and chemical composition of SOC together play an important role in regulating the mineralization of SOC and the Q₁₀ value of external C addition mineralization in forest and grassland soil.