Carbon mineralization and temperature sensitivity of particulate versus mineral associated organic matter in a 56-year long-term no-till Vertisol

Abstract

Temperature sensitivity (Q 10 ) of soil organic carbon (SOC) mineralization is crucial for understanding dynamics of soil C-climate feedback and SOC sequestration. Differentiating between SOC fractions, such as particulate organic matter (POM) and mineral-associated organic matter (MAOM), can enhance our understanding of C dynamics under global change. However, studies focusing on these processes, especially in high-clay Vertisol agroecosystems remain limited. To address this gap, we leveraged a 56-year long-term experiment examining the impacts of different management practices on SOC mineralization and Q 10 of these fractions. The treatments included tillage (no-till, NT vs. conventional tillage, CT), residue management (residue retention, RR vs. residue burned, RB), and fertilization (0, N0 and 90 kg N ha −1 , N90) in a randomized complete block design. A 63-day incubation was conducted at 15°C and 25°C for the bulk soil, POM and MAOM to assess how these treatments influence SOC mineralization and Q 10 dynamics. We found that SOC mineralization rates followed the order: POM > bulk soil > MAOM. In the bulk soil, Q 10 was significantly higher in RR than RB, but remained significantly lower than that of POM and MAOM. Q 10 of POM was significantly reduced under NT during the early stage (first 21 days), and N90 in the late stage (21–63 days) of incubation. Correlation analysis and structural equation modeling showed that the C:N ratio and pH mediated management effects on mineralization. Substrate availability strongly affected Q 10 of MAOM (and the bulk soil, which contained 96.7 % MAOM in total soil mass), while C quality (C:N ratio) was the primary driver for Q 10 of POM in this high-clay Vertisol. This study highlights the importance of considering not only bulk SOC but also SOC fractions when evaluating mineralization and Q 10 dynamics. Our findings suggest that focusing on specific SOC fractions and management practices can improve long-term C sequestration under different agricultural regimes. • Novel exploration of Q 10 across soil fractions in agroecosystems. • Mineralization amount followed the order: POM > bulk soil > MAOM. • In bulk soil, residue retention increased Q 10, but lower than that in POM and MAOM. • Distinct Q 10 treatment effects observed at different incubation stages. • C:N ratio and substrate availability were primary Q 10 regulators.

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