Graduate School of Global Environmental Studies, Kyoto University, Kyoto 606-8501, Japan.
Graduate School of Global Environmental Studies, Kyoto University, Kyoto 606-8501, Japan; Graduate School of Agriculture, Kyoto University, Kyoto 606-8502, Japan.
Sci Total Environ. 2021 May 15;769:144842. doi: 10.1016/j.scitotenv.2020.144842. Epub 2021 Feb 2.
Soil organic carbon (SOC) in the subsoil may not be so resistant to decomposition as previously assumed, while the mechanisms controlling C dynamics in subsoils are not yet known. This study aimed to (1) identify the factors that control SOC pools in subsoil and (2) compare the differences in SOC pools and controlling factors between the subsoil and topsoil. Subsoils (20-40 cm) were sampled along elevational gradients from two volcanic regions with less-disturbed vegetation each from Tanzania (11 sites) and Indonesia (12 sites). The sizes and mean residence times of labile, intermediate, and stable SOC pools were estimated by fractionation and model fitting to CO release during long-term incubation. The controlling factors of each SOC pool were determined by accompanying partial correlation and path analyses. In subsoil, the intermediate SOC pool predominantly controlled the SOC stability within decades. Climatic, geochemical, and biotic factors controlled different SOC pools. Temperature negatively affected the sizes of all three pools. The nanocrystalline minerals contents predominantly and positively controlled the sizes of intermediate and stable SOC pools, and the mean residence time of intermediate SOC pool. Biotic and climatic factors (i.e., microbial biomass, available N for microbes, and excess precipitation) controlled the labile SOC pool. Compared with topsoil, stabilized organic matters were more in the intermediate rather than in the stable SOC pool, and the temperature had a more significant effect on the stable SOC pool in subsoil than in topsoil. Available N for microbes partially controlled the labile and intermediate SOC pools in subsoil (more limited available N for microbes), but not in topsoil. Thus, subsoil SOC would be more sensitive to climate change than topsoil SOC. This study helped to understand the SOC stabilization mechanism and emphasized the high climate- and mineral-dependence of SOC in subsoil of tropical volcanic regions.
土壤有机碳（SOC）在亚表层可能不像之前假设的那样具有抗分解性，而控制亚表层 C 动态的机制尚不清楚。本研究旨在：（1）确定控制亚表层 SOC 库的因素；（2）比较亚表层和表土之间 SOC 库和控制因素的差异。从坦桑尼亚（11 个地点）和印度尼西亚（12 个地点）两个受干扰较小植被的火山地区，沿海拔梯度采集了 20-40 厘米深的亚表层土壤。通过分馏和模型拟合 CO 在长期培养期间的释放来估计易变、中间和稳定 SOC 库的大小和平均停留时间。通过伴随的偏相关和路径分析确定每个 SOC 库的控制因素。在亚表层，中间 SOC 库主要在几十年内控制 SOC 的稳定性。气候、地球化学和生物因素控制着不同的 SOC 库。温度对所有三个库的大小都有负面影响。纳米晶体矿物含量主要和积极地控制了中间和稳定 SOC 库以及中间 SOC 库的平均停留时间。生物和气候因素（即微生物生物量、微生物可用 N 和过量降水）控制着易变 SOC 库。与表土相比，稳定的有机物质更多地存在于中间 SOC 库而不是稳定 SOC 库中，温度对亚表层稳定 SOC 库的影响大于表土。微生物可用 N 部分控制了亚表层易变和中间 SOC 库（微生物可用 N 更有限），但在表土中则不然。因此，与表土 SOC 相比，亚表层 SOC 对气候变化更为敏感。本研究有助于了解 SOC 稳定机制，并强调了热带火山地区亚表层 SOC 的高气候和高矿物依赖性。
