Soil organic matter (SOM) is the largest terrestrial pool of organic carbon, and potential carbon-climate feedbacks involving SOM decomposition could exacerbate anthropogenic climate change. However, our understanding of the controls on SOM mineralization is still incomplete, and as such, our ability to predict carbon-climate feedbacks is limited. To improve our understanding of controls on SOM decomposition, A and upper B horizon soil samples from 26 National Ecological Observatory Network (NEON) sites spanning the conterminous U.S. were incubated for 52 weeks under conditions representing site-specific mean summer temperature and sample-specific field capacity (−33 kPa) water potential. Cumulative carbon dioxide respired was periodically measured and normalized by soil organic C content to calculate cumulative specific respiration (CSR), a metric of SOM vulnerability to mineralization. The Boruta algorithm, a feature selection algorithm, was used to select important predictors of CSR from 159 variables. A diverse suite of predictors was selected (12 for A horizons, 7 for B horizons) with predictors falling into three categories corresponding to SOM chemistry, reactive Fe and Al phases, and site moisture availability. The relationship between SOM chemistry predictors and CSR was complex, while sites that had greater concentrations of reactive Fe and Al phases or were wetter had lower CSR. Only three predictors were selected for both horizon types, suggesting dominant controls on SOM decomposition differ by horizon. Our findings contribute to the emerging consensus that a broad array of controls regulates SOM decomposition at large scales and highlight the need to consider changing controls with depth.

土壤有机质 (SOM) 是最大的陆地有机碳库，涉及 SOM 分解的潜在碳气候反馈可能会加剧人为气候变化。然而，我们对 SOM 矿化控制的理解仍然不完整，因此，我们预测碳气候反馈的能力是有限的。为了提高我们对 SOM 分解控制的理解，来自美国本土 26 个国家生态观测网络 (NEON) 站点的 A 和上层 B 层土壤样本在代表站点特定夏季平均温度和特定样本场的条件下孵育 52 周容量 (-33 kPa) 水势。定期测量呼吸的累积二氧化碳，并通过土壤有机碳含量归一化，以计算累积比呼吸 (CSR)，SOM 对矿化的脆弱性的度量。Boruta 算法是一种特征选择算法，用于从 159 个变量中选择重要的 CSR 预测变量。选择了一套多样化的预测因子（A 层为 12 个，B 层为 7 个），预测器分为三类，对应于 SOM 化学、反应性 Fe 和 Al 相以及场地水分可用性。SOM 化学预测因子与 CSR 之间的关系是复杂的，而活性 Fe 和 Al 相浓度较高或较湿的位点具有较低的 CSR。两种层位类型只选择了三个预测变量，表明对 SOM 分解的主要控制因层而异。