Subarctic regions are particularly affected by global warming. As vegetation periods lengthen, boreal forests could gradually be converted into agricultural land. How land use alters the susceptibility of soil organic matter decomposition to rising temperatures or how changes in nutrient availability, such as nitrogen (N) fertilisation, affect carbon (C) cycling is unknown. Microbial carbon use efficiency (CUE) defines how much of the decomposed soil organic carbon is directed to growth or lost to the atmosphere. Here, we investigated the response of CUE (24 h) and soil organic matter decomposition (50 days) to + 10 °C warming and N addition in three subarctic soils derived from paired plots (forest, grassland, cropland) in the Yukon, Canada. Contrary to our literature-based expectations, boreal forest soils did not demonstrate the most sensitive response to warming and N addition. Temperature sensitivity was not affected by land-use type. In contrast to a generally assumed decline, short-term warming increased CUE by + 30%, which was positively correlated with microbial growth. N addition reduced overall CUE by − 7%, in contrast to the expectation that CUE would rise due to the alleviation of nutrient limitations. The response to N addition was negatively correlated with the ratio of fungi to bacteria, and presumably depended on the prevailing N-fertilisation regime. The temperature sensitivity of microbial metabolism was driven by site-specific parameters rather than by land-use type. Our results indicate that it may not be necessary to consider land use-specific temperature sensitivities when modelling soil organic carbon dynamics under future climate conditions.

亚北极地区尤其受到全球变暖的影响。随着植被期的延长，北方森林可以逐渐转变为农田。土地利用如何改变土壤有机质分解对温度升高的敏感性，或者养分有效性的变化，如氮 (N) 施肥，如何影响碳 (C) 循环，目前尚不清楚。微生物碳利用效率 (CUE) 定义了有多少分解的土壤有机碳直接用于生长或流失到大气中。在这里，我们研究了来自加拿大育空地区配对地块（森林、草地、农田）的三个亚北极土壤中 CUE（24 小时）和土壤有机质分解（50 天）对 + 10 °C 升温和 N 添加的响应. 与我们基于文学的期望相反，北方森林土壤没有表现出对变暖和氮添加最敏感的反应。温度敏感性不受土地利用类型的影响。与普遍假设的下降相反，短期变暖使 CUE 增加了 + 30%，这与微生物生长呈正相关。N 添加使整体 CUE 降低了 - 7%，这与预期 CUE 会由于营养限制的缓解而上升形成对比。对 N 添加的反应与真菌与细菌的比例呈负相关，并且可能取决于普遍的 N 施肥方案。微生物代谢的温度敏感性是由特定地点的参数而不是土地利用类型驱动的。