Conservation agriculture boosts topsoil organic matter by restoring free lipids and lignin phenols biomarkers in distinct fractions

Abstract

Conservation-based practices may differentially regulate the pathways of soil organic carbon (SOC) formation and stabilization. Yet, we lack the knowledge regarding alternative farming on the quantity and composition of distinct C pools within soil matrix. To fill the knowledge gap, we sampled soils down to 0–20 cm layer from three tillage practices, i.e., conventional tillage (CT), rotary tillage (RT), and no-tillage (NT) in a 17-year trial in Northern China. We quantified the targeted SOC molecular fingerprints (i.e., free lipids and lignin phenols, lability and origins) in three functional fractions: particulate organic matter (POM, > 53 μm), coarse (cMAOM, 2–53 μm) and fine mineral-associated organic matter (fMAOM, < 2 μm). Our results showed that NT (cf. CT) increased SOC amounts by 33 % in POM and by 61 % in fMAOM in the 0–10 cm layer. Compared with CT, NT increased the plant-derived lipids (i.e., ≥ C₂₀ and steroids) by 19 % in POM and by 45 % in cMAOM, selectively preserving the structural plant-derived compounds; RT augmented microbial-derived lipids (i.e., < C₂₀ and simple sugars) by 18 % in POM and plant-derived lipids by 64 % in cMAOM in this topsoil. In contrast, conservation-based practices (i.e., RT and NT) decreased the plant-derived lipids by 37–40 % and microbial-derived lipids by 20–40 % relative to CT in lower 10–20 cm layer. Besides, RT and NT (cf. CT) enhanced lignin phenols in both POM (26–35 %) and fMAOM fractions (42–58 %) in topsoil, but RT decreased these lignin phenols by 36 % in POM in deep layer. Partial Least Squares – Path Modeling revealed the increased topsoil organic C under conservation practices via restoring free lipids and lignin phenols in POM and fMAOM fractions. Collectively, our study highlights that conservation agriculture alters the SOC amounts and biogeochemistry in soil functional fractions, which could provide some mechanistic insights into soil C accrual pathways and persistence in temperate agroecosystems.