Does soil organic carbon quality or quantity govern relative temperature sensitivity in soil aggregates?

Abstract

Soil aggregates govern soil organic carbon (SOC) sequestration. But, sparse understanding about the process leads to inaccuracy in predicting potential of soil to stabilize C in warming world. We appraised effects of 43 years of fertilization on relative temperature sensitivity of SOC decomposition (Q10) in soil aggregates to know whether SOC quality or quantity governs Q10. Treatments were: fallow, control, 100% recommended dose of nitrogen (N), N and phosphorus (NP), N, P and potassium (NPK), and NPK + farmyard manure (FYM) (NPK + FYM). Macroaggregates, microaggregates and silt + clay (s + c) fractions were incubated for 16 weeks at 25, 35 and 45 °C, SOC quality (R0) and Q10 were computed. SOC mineralization from macro- and micro- aggregates were 34 and 28% higher than s + c across the treatments. The s + c fraction of NPK + FYM had ~ 41, 40 and 24% higher C decay rate than NPK plots at 25, 35 and 45 °C, respectively. For s + c fraction Q10 increased over other aggregates. Mean Q10 of s + c fraction was ~ 18.3 and 17.5% higher than macro and micro-aggregate-C, respectively. R0 was the lowest for NPK + FYM, suggesting long-term manuring with balanced NPK significantly enhance recalcitrance of C. We observed Q10 of macroaggregates and s + c fraction is controlled by C quality but C quantity governs Q10 of microaggregates in Vertisol. Specifically, microaggregates of NPK + FYM were more temperature sensitive, and could be vulnerable to C loss. Hence, practices facilitating microaggregate formation should be avoided. Thus, we recommend manure application for facilitating C sequestration.