Effects of global warming on soil organic carbon (C) can be investigated by comparing sites experiencing different temperatures. However, observations can be affected by covariance of temperature with other environmental properties. Here, we studied a thermal gradient in forest soils derived from volcanic materials on Mount Taranaki (New Zealand) to disentangle the effects of temperature and reactive minerals on soil organic C quantity and composition. We collected soils at four depths and four elevations with mean annual temperatures ranging from 7.3 to 10.5 °C. Soil C stocks were not significantly different across sites (average 162 MgC ha⁻¹ to 85 cm depth, P > .05). Neither aluminium (Al)-complexed C, nor mineral-associated C changed significantly (P > .05) with temperature. The molecular characterisation of soil organic matter showed that plant-derived C declined with increasing temperature, while microbial-processed C increased. Accompanying these changes, soil short-range order (SRO) constituents (including allophane) generally increased with temperature. Results from structural equation modelling revealed that, although a warmer temperature tended to accelerate soil organic C decomposition as inferred from molecular fingerprints, it also exerted a positive effect on soil total C presumably by enhancing plant C input. Despite a close linkage between mineral-associated C and soil organic C, the increased abundance of reactive minerals at 30–85 cm depth with temperature did not increase soil organic C concentration at that depth. We therefore propose that fresh C inputs, rather than reactive minerals, mediate soil C responses to temperature across the thermal gradient of volcanic soils under humid-temperate climatic conditions.

全球变暖对土壤有机碳 (C) 的影响可以通过比较经历不同温度的地点来研究。然而，观测结果可能会受到温度与其他环境特性的协方差的影响。在这里，我们研究了塔拉纳基山（新西兰）火山物质衍生的森林土壤的温度梯度，以阐明温度和活性矿物质对土壤有机碳数量和组成的影响。我们收集了四个深度和四个海拔的土壤，年平均气温在 7.3 至 10.5 °C 之间。不同地点的土壤碳储量没有显着差异（平均 162 MgC ha ^-1至 85 cm 深度，P  > .05）。铝 (Al) 络合碳和矿物缔合碳均不随温度发生显着变化 ( P  > .05)。土壤有机质的分子特征表明，植物来源的碳随着温度的升高而下降，而微生物处理的碳则增加。伴随这些变化，土壤短程有序（SRO）成分（包括水铝英石）通常随着温度的升高而增加。结构方程模型的结果表明，虽然从分子指纹推断，较高的温度往往会加速土壤有机碳的分解，但它也可能通过增加植物碳输入而对土壤总碳产生积极影响。尽管矿物相关碳和土壤有机碳之间存在密切联系，但 30-85 厘米深度的活性矿物质丰度随温度的增加并没有增加该深度的土壤有机碳浓度。因此，我们建议，在湿温带气候条件下，新鲜的碳输入，而不是活性矿物质，可以介导土壤碳对跨越火山土壤热梯度的温度的响应。