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

Abstract

AbstractUnderstanding the temperature sensitivity (Q10) of soil organic matter (SOM) decomposition is crucial to predict CO2 emissions and carbon (C) stocks under global warming. This study describes the decomposition and Q10 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 14C‐labeled glucose. The dynamics of CO2 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 CO2 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 CO2 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 CO2 was mainly released from the temperature‐stimulated decomposition of RES pool. The short‐term Q10 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 Q10 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, CO2 emissions linearly increased with temperature in all pools over short‐ and long‐term incubation, except for the GLU pool during long‐term incubation. The Q10 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 CO2 emissions and C turnover in soil.