von Fromm Sophie F, Olson Connor I, Monroe Matthew D, Sierra Carlos A, Driscoll Charles T, Groffman Peter M, Johnson Chris E, Raymond Peter A, Pries Caitlin Hicks
Department of Biological Sciences, Dartmouth College, Hanover, New Hampshire, USA.
The Neukom Institute for Computational Science, Dartmouth College, Hanover, New Hampshire, USA.
Glob Chang Biol. 2025 May;31(5):e70250. doi: 10.1111/gcb.70250.
The timescales over which soil carbon responds to global change are a major uncertainty in the terrestrial carbon cycle. Radiocarbon measurements on archived soil samples are an important tool for addressing this uncertainty. We present time series (1969-2023) of radiocarbon measurements for litter (Oi/Oe and Oa/A) and mineral (0-10 cm) soils from the Hubbard Brook Experimental Forest, a predominantly hardwood forest in the northeastern USA. To estimate soil carbon cycling rates, we built different autonomous linear compartmental models. We found that soil litter carbon cycles on decadal timescales (Oi/Oe: 7 years), whereas carbon at the organic-mineral interface (Oa/A), and mineral soil (0-10 cm) carbon cycles on centennial timescales (104 and 302 years, respectively). At the watershed-level, the soil system appears to be at steady-state, with no observed changes in carbon stocks or cycling rates over the study period, despite increases in precipitation, temperature, and soil pH. However, at the site-level, the Oi/Oe is losing carbon (-15 g C m year since 1998). The observed decline in carbon stocks can be detected when the Oi and Oe layers are modeled separately. This pattern suggests that the rapidly cycling litter layer at the smaller scale is responding to recent environmental changes. Our results highlight the importance of litter carbon as an "early-warning system" for soil responses to environmental change, as well as the challenges of detecting gradual environmental change across spatial scales in natural forest ecosystems.
土壤碳对全球变化做出响应的时间尺度是陆地碳循环中的一个主要不确定因素。对存档土壤样本进行放射性碳测量是解决这一不确定性的重要工具。我们展示了美国东北部主要为阔叶林的哈伯德布鲁克实验森林凋落物（Oi/Oe和Oa/A）以及矿质土壤（0 - 10厘米）的放射性碳测量时间序列（1969 - 2023年）。为了估算土壤碳循环速率，我们构建了不同的自主线性隔室模型。我们发现土壤凋落物碳在十年时间尺度上循环（Oi/Oe：约7年），而有机 - 矿质界面（Oa/A）的碳以及矿质土壤（0 - 10厘米）碳在百年时间尺度上循环（分别约为104年和302年）。在流域尺度上，土壤系统似乎处于稳态，尽管降水量、温度和土壤pH值有所增加，但在研究期间未观察到碳储量或循环速率的变化。然而，在站点尺度上，Oi/Oe正在失去碳（自1998年以来为 - 15克碳/平方米·年）。当分别对Oi层和Oe层进行建模时，可以检测到观测到的碳储量下降。这种模式表明，较小尺度上快速循环的凋落物层正在对近期环境变化做出响应。我们的结果强调了凋落物碳作为土壤对环境变化响应的“早期预警系统”的重要性，以及在天然森林生态系统中跨空间尺度检测渐进环境变化的挑战。
