Impact of phyllosilicate mineralogy on organic carbon stabilization in soils: incomplete knowledge and exciting prospects

Soil mineral phases strongly influence soil organic carbon (SOC) dynamics. Clay-size particles have been recognized as protecting SOC from microbial decomposition. Among clay-size minerals, phyllosilicates (clay minerals) have been shown to efficiently protect SOC. There is an important variety of phyllosilicate types present in soils which have contrasting surface properties (specific surface area, charge density). Although these differing surface properties should influence their ability in protecting SOC, this has not been clearly established yet. Publications comparing the ability of the different phyllosilicates to protect SOC are reviewed in this study. Relatively few studies dealing with the link between phyllosilicate mineralogy and SOC protection exist. The few existing studies have followed different methodologies and are based on various analytical techniques, such that direct comparisons among them are difficult. More problematic, they provide different conclusions. Indeed, if experiments conducted in suspension using pure clay phases and recent meta-analyses suggest that phyllosilicate mineralogy has a significant importance for SOC stabilization and SOC stock response to land-use change, these results are not clearly corroborated by studies conducted on a reduced number of soils. The recent technical developments which allow improving both quantitative and qualitative descriptions of the soil clay mineral assemblages, together with nanoscale investigations of phyllosilicate/OM interactions, offer exciting perspectives for determining more accurately the efficiency of the different phyllosilicate types in SOC protection. Such information may provide a much clearer understanding of the impact of phyllosilicate mineralogy on SOC dynamics in the coming years.