Evaluation of the sensitivity of the mineralizable pool of soil organic matter to changes in temperature and moisture

The sensitivity of the potentially mineralizable pool of soil organic matter (C_pm) to changes in temperature and moisture has been assessed from the temperature coefficient (Q10) and the moisture coefficient (W₁₀), which indicate how much the C_pm size changes, when the temperature changes by 10°C and the soil water content changes by 10 wt %, respectively. Samples of gray forest soil, podzolized chernozem, and dark chestnut soil taken from arable plots have been incubated at 8, 18, and 28°C and humidity of 10, 25, and 40 wt %. From the data on the production of C-CO₂ by soil samples during incubation for 150 days, the content of C_pm has been calculated. It has been shown that, on average for the three soils, an increase in temperature accounts for 63% of the rise in the pool of potentially mineralizable organic matter, whereas an increase in moisture accounts for 8% of that rise. The temperature coefficients of the potentially mineralizable pool are 2.71 ± 0.64, 1.27 ± 0.20, and 1.85 ± 0.30 in ranges of 8–18, 18–28, and 8–28°C, respectively; the moisture coefficients are 1.19 ± 0.11, 1.09 ± 0.05, and 1.14 ± 0.06 in ranges of 10–25, 25–40, and 10–40 wt %, respectively. The easily mineralizable fraction (C₁, k₁ > 0.1 days^‑1) of the active pool of soil organic matter is less sensitive to temperature than the hardly mineralizable fraction (C₃, 0.01 > k₃ > 0.001 days^‑1); their Q₁₀ values are 0.91 ± 0.15 and 2.40 ± 0.31, respectively. On the contrary, the easily mineralizable fraction is more sensitive to moistening than the hardly mineralizable fraction: their W₁₀ values are 1.22 ± 0.06 and 1.03 ± 0.08, respectively. The intensification of mineralization with rising temperature and water content during a long-term incubation results in the exhausting of the active pool, which reduces the production of CO₂ by the soils during the repeated incubation under similar conditions nonlimiting mineralization.