Mineralization and temperature sensitivity of soil organic matter pools of contrasting lability

Abstract

Abstract Understanding the temperature sensitivity (Q 10 ) of soil organic matter (SOM) decomposition is crucial to predict CO 2 emissions and carbon (C) stocks under global warming. This study describes the decomposition and Q 10 of four soil C pools: (1) very labile (glucose addition (GLU), representing root exudates), (2) labile (microbial turnover, MT), (3) potentially labile (primed C pool, PE), and (4) resistant (inherent soil C, RES). The soil (loamy Luvisol) was incubated for 4 and 144 days at five temperatures (0, 10, 20, 30, and 40°C) with or without 14 C‐labeled glucose. The dynamics of CO 2 fluxes were measured during short (0–4 days) and long (5–144 days) term incubations. Glucose was mineralized following a two‐pool exponential function. The half‐life of the decomposition of the GLU pool decreased by 3 times as temperature increased from 10 to 40 °C. The flux of unlabeled CO 2 over 4 days reflects a strong contribution to the apparent priming especially at high temperature, which was due to the accelerated microbial biomass turnover. Accordingly, the CO 2 flux increased during short‐term incubation and was dominated by the decomposition of labile SOM and microbial biomass turnover, whereas during the long‐term incubation, the CO 2 was mainly released from the temperature‐stimulated decomposition of RES pool. The short‐term Q 10 of the soil C pools decreased in the order: GLU (2.1) > MT (1.8) > PE (1.3) ≈ RES (1.6) over a few days (0–4 days), but the Q 10 measured over the long‐term period (144 days) was in the range of 1.2 (PE) to 1.8 (RES) and decreased in the order RES > MT > PE > GLU. In conclusion, CO 2 emissions linearly increased with temperature in all pools over short‐ and long‐term incubation, except for the GLU pool during long‐term incubation. The Q 10 strongly depends on the availability of C pools for microorganisms and decreases over time with the exhaustion of available substances in soil. This needs to be considered when estimating temperature effects on CO 2 emissions and C turnover in soil.