Conservation tillage for 17 years alters the molecular composition of organic matter in soil profile

Qiqi Gao; Lixiao Ma; Yunying Fang; Aiping Zhang; Guichun Li; Junjian Wang; Di Wu; Wenliang Wu; Zhangliu Du

doi:10.1016/j.scitotenv.2020.143116

Conservation tillage for 17 years alters the molecular composition of organic matter in soil profile

Sci Total Environ. 2021 Mar 25:762:143116. doi: 10.1016/j.scitotenv.2020.143116. Epub 2020 Oct 20.

Authors

Qiqi Gao¹, Lixiao Ma², Yunying Fang³, Aiping Zhang², Guichun Li², Junjian Wang⁴, Di Wu⁵, Wenliang Wu⁵, Zhangliu Du⁶

Affiliations

¹ 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.
² Institute of Environment and Sustainable Development in Agriculture, Chinese Academy of Agricultural Sciences, Beijing, 100081, China.
³ NSW Department of Primary Industries, Elizabeth Macarthur Agricultural Institute, Menangle, NSW 2568, Australia.
⁴ Guangdong Provincial Key Laboratory of Soil and Groundwater Pollution Control, School of Environmental Science and Engineering, Southern University of Science and Technology, Shenzhen 518055, Guangdong, China.
⁵ College of Resources and Environmental Sciences, China Agricultural University, Beijing 100193, China.
⁶ College of Resources and Environmental Sciences, China Agricultural University, Beijing 100193, China. Electronic address: dzl@cau.edu.cn.

PMID: 33158522
DOI: 10.1016/j.scitotenv.2020.143116

Abstract

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 (≥C₂₀) 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 (≥C₂₀ aliphatic lipids and steroids) and microbial-derived compounds (<C₂₀ 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.

Keywords: Biomarkers; Conservation tillage; Lignin; Lipids; No-tillage; Nuclear magnetic resonance (NMR).