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 (Cₚₘ) to changes in temperature and moisture has been assessed from the temperature coefficient (Q10) and the moisture coefficient (W ₁₀), which indicate how much the Cₚₘ 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 Cₚₘ 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, k ₁ > 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 > k ₃ > 0.001 days⁻¹); their Q ₁₀ 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 W ₁₀ 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.