Effects of depth, soil and vegetation types on indicators of soil organic carbon lability in forest soils
Résumé
Soil organic matter is a key property as it influences soil ecosystem services like productivity, water storage, etc. In particular, the labile soil organic carbon (SOC) fraction plays a central role in short- to medium-term nutrient availability and soil structural stability. There is little evidence to differentiate the relative importance of factors influencing the labile SOC fraction in contrasted pedological and vegetation conditions. Soil respiration tests and particulate organic matter (POM) obtained by different fractionation schemes are considered as classical indicators of the labile soil organic carbon (SOC) pool. Thermal analyses, in particular Rock-Eval 6 (RE6) analysis, have also shown promising results in the determination of SOC biogeochemical stability.
Using a large set of samples of French forest soils representing contrasted pedoclimatic conditions we assessed the effects of depth (n = 5; up to 1 m), soil class (entic Podzol; dystric Cambisol; Calcisol) and vegetation types (deciduous; coniferous) on SOC biogeochemical and thermal stability. We explored how respired-C isolated by a 10-week laboratory soil respiration test, POM-C isolated by a physical SOC fractionation scheme (particle-size > 50 μm and d < 1.6 g·cm-3) and four RE6 parameters, correlated to short- or long-term SOC persistence, evolved in a set of 233 soils samples from 53 forest sites. Results showed that depth was the dominant discriminating factor, affecting significantly all parameters. With depth, we observed a decrease of both classical labile SOC indicators and the thermally labile SOC pool and an increase of the thermally stable SOC pool, along with an oxidation and a depletion of hydrogen-rich moieties of the SOC. Soil class and vegetation type had contrasted effects. For instance, entic Podzols and dystric Cambisols had relatively more thermally stable SOC in the deepest layer than Calcisols but more labile SOC in the surface layer than Calcisols. Soils in deciduous stands tend to contain a higher proportion of thermally stable SOC than soils in coniferous stands. This study shows that both vegetation and soil types influenced SOC stability at various depths and thus should be considered when mapping soil climate regulation ecosystem service.
Domaines
Sciences du Vivant [q-bio]
Origine : Fichiers produits par l'(les) auteur(s)
