Molecular dynamics of soil humeome as a function of conventional tillage

Soil organic carbon (SOC) mineralization signifies reduction in soil fertility and release of greenhouse gases. An effective technology for soil carbon stabilization requires an extended knowledge of SOC turnover dynamics at a molecular level. To reach this goal, we applied the novel humeomics methodology on a maize-cropped soil after 1 and 3 years of conventional tillage and characterized the molecular development of soil humeome. Humeomics solvated organo- and hydro- soluble SOC fractions, including humin, and used advanced analytical techniques, such as ESI-Orbitrap- and GC-MS, to identify the molecules comprised in the supramolecular SOC structure. While % SOC remained similar despite crop litter addition over time, SOC losses during humeomics fractionation rose from 0.1 (1st year) to 11% (3rd year), mainly represented by newly formed N-rich hydrosoluble compounds. Such increase of hydrosoluble material with tillage cycles was also revealed by the larger hydrosoluble/organosoluble ratio in the 3rd year soil humeome than for the 1st year. Amides, amines, heterocyclic nitrogen compounds, fatty acids, phenolic esters and sugars were the identified compounds. Some of these molecules were lost, some remained the same and some were anew in the 3rd year. High-resolution ESI-Orbitrap-MS revealed several specific molecules with high affinity to Fe in soil oxides, especially those which were constant in soil despite tillage, thereby implying an important sequestration mechanism. As compared to the capacity of humeomics to distinguish SOC molecules upon soil changes, the traditional SOM alkaline extraction did not reveal equal variations in molecular distribution. Our findings show that molecular identification of soil humeome by humeomics represents a sensitive, reproducible and rapid method to follow molecular dynamics of SOC compounds with changes in soil managements and functions.