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Priming of soil organic carbon (SOC) is a crucial factor in ecosystem carbon balance. Despite its increasing importance in the changing global climate, the extent of influence of temperature and soil properties on the priming effect remains unclear. Here, soil priming was investigated using 13C labeled wheat residues in two cultivated, subtropical (Vertisol) and semi-arid (Luvisol), soils of Australia at four incubation temperatures (13, 23, 33 and 43 °C). The priming effect was computed from respired CO 2 and associated δ13C, which were measured periodically over the 52-day incubation period. Wheat residue addition resulted in greater priming effect in the Luvisol (1.17 to 2.37% of SOC) than the Vertisol (0.02 to 1.56% of SOC). The priming of SOC was the highest at 23 °C in the Luvisol, and at 43 °C in the Vertsiol, which indicates a variable positive priming effect of temperature in different soil types. Wheat residue addition significantly increased the temperature sensitivity (Q 10) of SOC mineralization in the Vertisol at temperature ranges below 33 °C (i.e., 13–23 and 23–33 °C) and had no significant effect in the Luvisol. A negative correlation was observed between temperature and the Q 10 values. Across soils, the Q 10 of residue C was lower than SOC suggesting that soil C is more vulnerable to climatic warming. This work demonstrates that the magnitude of SOC priming by wheat residue and Q 10 of SOC mineralization varied significantly with soil type (Luvsiol > Vertisol) and incubation conditions (temperature and time). Given the current trend towards increasing atmospheric temperatures, future studies should evaluate temperature effects on the priming of different pools of SOC induced by crop residue in different agro-ecosystems. • The wheat residue addition caused greater SOC priming in the sandy clay loam than clayey soil. • Temperature significantly influenced SOC priming but this differed by soil type. • The difference in SOC priming between sandy clay loam and clayey soil was greater at ≤23 °C temperatures. • Wheat residue significantly increased the Q 10 of SOC mineralization but only in clayey soil below 33 °C. [ABSTRACT FROM AUTHOR]

[Display omitted] • FTIR spectroscopy of clay is sensitive to temperature during bushfires. • Boron leached from combusted bark decreases d11B of clays. • No direct influence of combustion temperature on d11B of clays. • Clays have higher d11B after experiencing a high severity fire. • Both FTIR spectroscopy and B isotope could be viable fire proxies. Bushfire occurrences will likely be exacerbated by climate change, thus requiring a model to forecast and manage their impacts. However, a robust bushfire model requires new proxies that can infer fire severity responses to past climate variability. A key test to the viability of new fire proxies is whether they record fire severity in the affected soil. We address this by testing Attenuated Total Reflectance- Fourier Transform Infrared (ATR-FTIR) spectroscopy and boron (B) isotopes in soil clay fractions from Yengo National Park, southeastern Australia, as proxies for bushfire severity. The isotopic results were also compared to that of clays that reacted with experimentally combusted bark. ATR-FTIR spectroscopy constrains the soil temperature to between 225 and 500 °C during high severity fires, based on the lack of dehydroxylation peak characteristics and the increased aromatic to aliphatic organic peak ratios in clays, compared to that of low severity sites. The isotope composition of the non-exchangeable B fraction in clays is lighter after reacting with leaching solutions of bark combusted at higher temperatures. Combustion temperature does not affect the B isotope fractionation during B adsorption onto clays. Changes to the B isotope composition of clays could instead be justified by the varying B concentration and B isotope compositions of the leaching solutions. In Yengo soil clay fractions, sites that experienced a high severity fire show higher δ 11B values by about 1.5 ‰, compared to low severity sites- at odds with observations from our experiment using combusted bark. The combustion of leaves from tree crowns in high severity fires could account for the increase in δ 11B of clays post-fire. In summary, FTIR spectroscopy of clays could be useful for constraining soil temperature during bushfires, while the B isotope composition of clays appears as a promising proxy for fire severity. [ABSTRACT FROM AUTHOR]