USDA Forest Service, Northern Research Station, Houghton, MI 49931.
Department of Forest Resources and Environmental Conservation, Virginia Tech, Blacksburg, VA 24061.
Proc Natl Acad Sci U S A. 2023 Feb 14;120(7):e2210044120. doi: 10.1073/pnas.2210044120. Epub 2023 Feb 6.
Mineral stabilization of soil organic matter is an important regulator of the global carbon (C) cycle. However, the vulnerability of mineral-stabilized organic matter (OM) to climate change is currently unknown. We examined soil profiles from 34 sites across the conterminous USA to investigate how the abundance and persistence of mineral-associated organic C varied with climate at the continental scale. Using a novel combination of radiocarbon and molecular composition measurements, we show that the relationship between the abundance and persistence of mineral-associated organic matter (MAOM) appears to be driven by moisture availability. In wetter climates where precipitation exceeds evapotranspiration, excess moisture leads to deeper and more prolonged periods of wetness, creating conditions which favor greater root abundance and also allow for greater diffusion and interaction of inputs with MAOM. In these humid soils, mineral-associated soil organic C concentration and persistence are strongly linked, whereas this relationship is absent in drier climates. In arid soils, root abundance is lower, and interaction of inputs with mineral surfaces is limited by shallower and briefer periods of moisture, resulting in a disconnect between concentration and persistence. Data suggest a tipping point in the cycling of mineral-associated C at a climate threshold where precipitation equals evaporation. As climate patterns shift, our findings emphasize that divergence in the mechanisms of OM persistence associated with historical climate legacies need to be considered in process-based models.
土壤有机质的矿物稳定化是全球碳（C）循环的一个重要调节因素。然而，目前尚不清楚矿物稳定的有机物质（OM）对气候变化的脆弱性。我们研究了美国大陆 34 个地点的土壤剖面，以调查在大陆尺度上，与气候相关的矿物结合有机碳的丰度和持久性如何变化。通过结合使用放射性碳和分子组成测量的新方法，我们表明，矿物结合有机质（MAOM）的丰度和持久性之间的关系似乎是由水分可用性驱动的。在降水超过蒸散量的湿润气候下，多余的水分会导致更深和更长时间的湿润，创造有利于更多根系的条件，同时也允许更多的输入与 MAOM 扩散和相互作用。在这些潮湿的土壤中，矿物结合土壤有机碳的浓度和持久性密切相关，而在干燥的气候中则不存在这种关系。在干旱的土壤中，根系丰度较低，输入与矿物表面的相互作用受到较浅和短暂的水分期的限制，导致浓度和持久性之间的脱节。数据表明，在降水等于蒸发的气候阈值处，矿物结合碳的循环存在一个转折点。随着气候模式的转变，我们的研究结果强调，在基于过程的模型中，需要考虑与历史气候遗产相关的 OM 持久性机制的差异。
