Temperature sensitivity of decomposition of soil organic matter fractions increases with their turnover time

Abstract

© 2019 John Wiley & Sons, Ltd. Soil organic carbon (SOC) is an indicator of soil fertility. Global warming accelerates SOC decomposition, consequently, resulting in land degradation. Characterization of the response of SOC decomposition to temperature is important for predicting land development. A simulation model based on temperature sensitivity (Q10) of SOC decomposition has been used to predict SOC response to climate warming. However, uncertain Q10 leads to substantial uncertainties in the predictions. A major uncertainty comes from the interference of rainfall. To minimize this interference, we sampled surface (0–5 cm) soils along an isohyet across a temperature gradient in the Qinghai–Tibetan Plateau. The Q10 of bulk soil and the four soil fractions, such as light fraction (LightF), particulate organic matter (POM), hydrolyzable fraction (HydrolysF), and recalcitrant fraction (RecalcitF), were studied by 14C dating. Turnover time follows the order: LightF < POM < bulk soil < HydrolysF < RecalcitF. The Q10 follows the order: LightF (1.0) = POM (1.0) < HydrolysF (3.63) < bulk soil (5.93) < RecalcitF (7.46). This indicates that stable fractions are much more sensitive to temperature than labile fractions. We also suggest that protection mechanisms rather than molecular composition regulate SOC turnover. A new concept 'protection sensitivity' of SOC decomposition was proposed. Protection sensitivity relates to protection type and primarily controls Q10 variation. A simulation model based on the Q10 of individual fractions predicted SOC change and land development in the Qinghai–Tibetan Plateau in the next 100 years much effectively as compared to simulations based on one-pool model (Q10 = 2) or bulk soil (Q10 = 5.93).