Gao Qiqi, Ma Lixiao, Fang Yunying, Zhang Aiping, Li Guichun, Wang Junjian, Wu Di, Wu Wenliang, Du Zhangliu
College of Resources and Environmental Sciences, China Agricultural University, Beijing 100193, China; Institute of Environment and Sustainable Development in Agriculture, Chinese Academy of Agricultural Sciences, Beijing, 100081, China.
Institute of Environment and Sustainable Development in Agriculture, Chinese Academy of Agricultural Sciences, Beijing, 100081, China.
Sci Total Environ. 2021 Mar 25;762:143116. doi: 10.1016/j.scitotenv.2020.143116. Epub 2020 Oct 20.
Conservation tillage is considered as a potential measure to mitigate climate change by sequestering soil organic matter (SOM), however its stabilization mechanisms remain elusive. In this study, we revealed the molecular composition of SOM in soil profile (~50 cm depth) from a 17-yr tillage experiment in North China. The soils were collected from 0-10, 10-20, 20-30 and 30-50 cm layers under conventional tillage (CT), and conservation tillage such as rotary tillage (RT) and no-tillage (NT). The sequential solvent extraction and CuO oxidation methods were used to quantify free lipids and lignin-derived phenols. The results showed that NT (cf. CT) increased labile compounds (i.e., carbohydrates) and plant-derived SOM (i.e., long-chain (≥C) aliphatic lipids and steroids) in the 0-10 and 30-50 cm layers. The RT (cf. CT) increased the total free lipids by 72-133% in the sublayers (>10 cm). The RT (cf. CT and NT) resulted in higher preservation of plant-derived (≥C aliphatic lipids and steroids) and microbial-derived compounds (<C aliphatic lipids and trehalose) SOM in deep soils (i.e., ≥10 cm). Conservation tillage suppressed lignin degradation, as reflected by 32-137% higher total lignin-derived phenols under RT and NT than CT in the 0-10 and 30-50 cm layers. The NMR revealed higher aliphatic to aromatic C ratio under NT and RT in the whole soil profile, suggesting more aliphatic lipids accumulated. Conservation tillage increased SOC stocks by 10-14% in 0-10 cm layer but not in deeper profiles. These results suggest that conservation tillage have increased plant-derived lipids and lignin accumulation. Our study highlights that conservation tillage (particularly the RT) after 17 years alters SOM molecular compositions and degradation processes in the soil profile. These findings have implications for improving our understanding of C stabilization mechanisms in agroecosystems.
保护性耕作被认为是通过封存土壤有机质（SOM）来缓解气候变化的一种潜在措施，但其稳定机制仍不明确。在本研究中，我们揭示了华北地区一项为期17年的耕作试验土壤剖面（约50厘米深度）中SOM的分子组成。土壤取自常规耕作（CT）以及旋耕（RT）和免耕（NT）等保护性耕作方式下0 - 10厘米、10 - 20厘米、20 - 30厘米和30 - 50厘米土层。采用连续溶剂萃取和CuO氧化方法对游离脂质和木质素衍生酚进行定量分析。结果表明，免耕（与CT相比）增加了0 - 10厘米和3（0 - 50厘米土层中不稳定化合物（即碳水化合物）和植物源SOM（即长链（≥C）脂肪族脂质和类固醇）。旋耕（与CT相比）使亚层（>10厘米）中总游离脂质增加了72% - 133%。旋耕（与CT和NT相比）导致深层土壤（即≥10厘米）中植物源（≥C脂肪族脂质和类固醇）和微生物源化合物（<C脂肪族脂质和海藻糖）SOM的保存率更高。保护性耕作抑制了木质素降解，这体现在0 - 10厘米和30 - 50厘米土层中，旋耕和免耕条件下总木质素衍生酚比常规耕作高32% - 137%。核磁共振显示，在整个土壤剖面中，免耕和旋耕条件下脂肪族与芳香族C比率更高，表明积累了更多脂肪族脂质。保护性耕作使0 - 10厘米土层中土壤有机碳储量增加了10% - 14%，但在更深土层中未增加。这些结果表明，保护性耕作增加了植物源脂质和木质素的积累。我们的研究强调，17年后的保护性耕作（特别是旋耕）改变了土壤剖面中SOM的分子组成和降解过程。这些发现有助于增进我们对农业生态系统中碳稳定机制的理解。
