Root contributions to long-term storage of soil organic carbon: theories, mechanisms and gaps

The depth to which plants locate their roots has important but yet poorly understood implications with regard to the profile distribution and dynamics of soil organic carbon (SOC). We compared the profile distribution of fine root biomass (FRB) with depth distribution of SOC, based on data recalculated from published literature. Mechanisms through which roots might contribute to long-term storage of SOC were reviewed. There was general agreement across previous studies that over 60% of SOC were in the top 0.3 m of soil, where FRB was concentrated. However, studies in which depth distribution of SOC was simultaneously compared to profile distribution of RB were not readily available, suggesting that this area of research has received limited attention. There is a paucity of empirical evidence to lend support to theorised mechanisms through which roots stabilise SOC. The relationship between profile distribution of roots and depth distribution of SOC must be evaluated on-site for defined landuses. A standardised format for presenting results must be developed and agreed upon to ease interpretation of the results. National Soil Science Societies may have a significant role in this process and this 19th World Congress of Soil Science will be an opportune assembly for dialogue.