Elemental stoichiometry and Rock-Eval® thermal stability of organic matter in French topsoils

Abstract. The quality and quantity of soil organic matter (SOM) are key elements that impact health climate regulation by soils. Rock-Eval® thermal analysis technique is becoming more commonly used, as it represents a powerful method for SOM characterization providing insights into bulk chemistry stability. In this study, we applied on large sample set from the first campaign (2000–2009) French Soil Quality Monitoring Network (RMQS – Réseau de mesures la qualité des sols). Based our analyses ca. 2000 composite surface (0–30 cm) samples collected across mainland France, observed significant land cover both stability elemental stoichiometry. Cropland soils had lower mean hydrogen index value (a proxy H/C ratio) higher than grasslands forests. Regarding oxygen O/C ratio), differences among values croplands, grasslands, Positive correlations temperature parameters with clay content pH highlight protective effect well microorganisms' mineralization activity. Surprisingly, found weak effects climatic stoichiometry SOM. Our data suggest topsoil average oxidized biogeochemically stable in croplands. More generally, high number even distribution whole territory allow one to build national interpretative reference these indicators