Grass root litter and soil carbon quality paradoxically control Q10 of labile and recalcitrant carbon pools in a semi-arid Inceptisol

Aim The temperature sensitivity of labile (Q _10L ) and recalcitrant (Q _10R ) pools of soil organic carbon (SOC) decomposition is a critical for predicting soil carbon (C) fluxes under changing climatic conditions. Methods Soils under six grass covers, namely, Cenchrus ciliaris , Chrysopogon fulvus , Panicum maximum , Sehima nervosum , Heteropogon contortus , and Vetiveria zizanioides from semi-arid India were evaluated for Q _10L and Q _10R of bulk soil, macroaggregates, microaggregates, and silt + clay associated SOC. Soil fractions (from 0–20 and 21–40 cm depths) were incubated at 25, 32, and 37°C for 100 days, and cumulative C mineralization was measured. The Q _10L and Q _10R were calculated using a two-pool decay model. The quality of root litter C and SOC was assessed through FTIR spectroscopy. Results Q _10L and Q _10R of microaggregate-C was significantly higher (22–64% and 22–24%, respectively) than macroaggregate-C and silt + clay-C. Among grasses, Q _10L and Q _10R values under C.ciliaris , H.contortus , and S.nervosum were lower than other grasses, indicating their capability to store SOC under global warming scenarios. Q _10L at topsoil layer was correlated with root litter C quality and at the sub-surface soil layer, it was influenced by labile C concentration. The Q _10R was correlated with the recalcitrant C concentration and SOC quality in both soil layers, indicating that quality and availability of recalcitrant SOC had pivotal roles in governing Q _10R in restored land. Conclusions Soil C and litter C quality should be potentially incorporated into the biogeochemical models to better predict SOC dynamics in managed ecosystems in the context of global warming and land use changes.