Yang Yang, Gunina Anna, Cheng Huan, Liu Liangxu, Wang Baorong, Dou Yanxing, Wang Yunqiang, Liang Chao, An Shaoshan, Chang Scott X
State Key Laboratory of Loess Science, Institute of Earth Environment, Chinese Academy of Sciences, Xi'an, China.
National Observation and Research Station of Earth Critical Zone on the Loess Plateau, Xi'an, Shaanxi, China.
Glob Chang Biol. 2025 Jan;31(1):e70033. doi: 10.1111/gcb.70033.
Soil microorganisms transform plant-derived C (carbon) into particulate organic C (POC) and mineral-associated C (MAOC) pools. While microbial carbon use efficiency (CUE) is widely recognized in current biogeochemical models as a key predictor of soil organic carbon (SOC) storage, large-scale empirical evidence is limited. In this study, we proposed and experimentally tested two predictors of POC and MAOC pool formation: microbial necromass (using amino sugars as a proxy) and CUE (by O-HO approach). Soil sampling (0-10 and 10-20 cm depth) was conducted along a climatic transect of 900 km on the Loess Plateau, including cropland, grassland, shrubland, and forest ecosystems, to ensure the homogeneous soil parent material. We found the highest POC and MAOC accumulation occurred in zones of MAT between 5°C and 10°C or MAP between 300 and 500 mm. Microbial necromass C was more positively related to POC than MAOC (p < 0.05), suggesting that microbial residues may improve POC pool more strongly compared to MAOC pool. Random forest and linear regression analyses showed that POC increased with fungal necromass C, whereas bacterial necromass C drove MAOC. Microbial CUE was coupled with MAOC (p < 0.05) but decoupled with POC and SOC (p > 0.05). The POC have faster turnover rate due to the lack of clay protection, which may lead to the rapid turnover of microbial necromass and thus their decoupling from the CUE. In this sense, the SOC accumulation is driven by microbial necromass, whereas CUE explains MAOC dynamics. Our findings highlight the insufficiency of relying solely on microbial carbon use efficiency (CUE) to predict bulk SOC storage. Instead, we propose that CUE and microbial necromass should be used together to explain SOC dynamics, each influencing distinct C pools.
土壤微生物将植物源碳（C）转化为颗粒有机碳（POC）和矿物结合碳（MAOC）库。虽然微生物碳利用效率（CUE）在当前生物地球化学模型中被广泛认为是土壤有机碳（SOC）储存的关键预测指标，但大规模的实证证据有限。在本研究中，我们提出并通过实验测试了POC和MAOC库形成的两个预测指标：微生物坏死物质（以氨基糖为代理）和CUE（通过O-HO方法）。在黄土高原900公里的气候样带上进行土壤采样（深度为0-10厘米和10-20厘米），包括农田、草地、灌丛和森林生态系统，以确保土壤母质均匀。我们发现，POC和MAOC的最高积累发生在年均气温（MAT）为5°C至10°C或年均降水量（MAP）为300至500毫米的区域。微生物坏死物质碳与POC的正相关性比与MAOC更强（p<0.05），这表明与MAOC库相比，微生物残体对POC库的改善作用可能更强。随机森林和线性回归分析表明，POC随真菌坏死物质碳增加，而细菌坏死物质碳驱动MAOC。微生物CUE与MAOC相关（p<0.05），但与POC和SOC解耦（p>0.05）。由于缺乏黏土保护，POC的周转速度更快，这可能导致微生物坏死物质的快速周转，从而使其与CUE解耦。从这个意义上说，SOC积累由微生物坏死物质驱动，而CUE解释MAOC动态。我们的研究结果突出了仅依靠微生物碳利用效率（CUE）来预测土壤总有机碳储存的不足。相反，我们建议应将CUE和微生物坏死物质一起用于解释SOC动态，它们各自影响不同的碳库。
