The effects of long-term climate warming on soil respiration and its drivers remain unclear in forests, which store approximately 40% of global soil carbon. Here we conducted a climate change experiment for 13 years in forest plots planted with tree juveniles at two southern boreal forest sites. Treatments included simultaneous above- and below-ground warming (ambient, +1.7 °C and +3.3 °C) under different rainfall scenarios (100% and 60% of summer rainfall) and contrasting overstory canopy openness (open and closed). Soil respiration increased by 7% and 17% under +1.7 °C and +3.3 °C warming, respectively, averaged across all sites, treatments and years. These increases in respiration were higher than impacts per degree warming of the only two prior long-term, but soil-only, forest warming experiments. Moreover, warming effects on soil respiration varied significantly over time. Under almost all conditions, moist soil exhibited a greater increase in respiration in response to warming than dry soil. Our results suggest that a realistic range of anticipated conditions, including both above- and below-ground temperature and moisture, should be accounted for when predicting warming effects on soil respiration.

长期气候变暖对森林土壤呼吸的影响及其驱动因素仍不清楚，森林储存了全球约 40% 的土壤碳。在这里，我们在南部北方森林的两个地点种植了幼树的林地中进行了为期 13 年的气候变化实验。处理方法包括在不同降雨情景（夏季降雨量的 100% 和 60%）下同时进行地上和地下变暖（环境温度+1.7°C 和+3.3°C）以及对比上层树冠开放度（开放和封闭）。所有地点、处理和年份的平均值在+1.7°C 和+3.3°C 变暖的情况下，土壤呼吸分别增加了 7% 和 17%。这些呼吸作用的增加高于之前仅有的两次长期但仅限土壤的森林变暖实验中每升高一度的影响。此外，变暖对土壤呼吸的影响随时间变化显着。几乎在所有条件下，潮湿的土壤都比干燥的土壤表现出更大的响应变暖的呼吸作用。我们的结果表明，在预测变暖对土壤呼吸的影响时，应考虑实际的预期条件范围，包括地上和地下温度和湿度。