Exploring links in the root trait - soil organic matter continuum

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Soils represent the largest terrestrial pool of stored carbon (C); this pool is important both as a potential source and also sink for atmospheric C. The future potential to sequester excess atmospheric C is greatest in soils which have previously lost organic matter (and C) through intensive use or degradation; these degraded soils represent an enormous land area on a global basis. For example, recent syntheses have suggested that on average, agricultural soils worldwide could sequester a supplemental 50 t ha-1. However, to effectively exploit this sequestration potential, we need to have a better understanding of the fate and paths of above and belowground plant litter (especially root litter) in relation to the different known mechanisms of stabilization in the soil (recalcitrance; protection in soil aggregates; chemical reactions with mineral surfaces). The current series of studies will focus on how diversity (specific and functional) and «effect» functional traits (morphological characters of plants) may influence soil C storage via the leaves, but especially root systems (root tissue chemistry; root soil exploitation traits; rooting depth etc), in both forest ecosystems and in grassland systems (collaboration with France). In current experiments with grassland soils planted with monocultures, we measured species and root trait effects on soil aggregation, pointing to the possibility of identifying specific root traits that may promote protection of soil C. This observation will be verified along gradients of tree diversity, with the hypothesis that increasing diversity (richness or functional) will be related to increasing both soil aggregation and chemical protection of C. We will also explore the feedback of traits on microbial community structure and function; indirect effects of traits on soil processes may be mediated by this compartment. In sub-boreal forest communities we will measure traits of eight understory plants, and decomposition rate in relation to traits will be tested by measuring mass loss of a common substrate in the rooting zone. This series of studies will increase our understanding of biodiversity effects on ecosystem function (several ecosystems) and the role of specific root characters (effect traits) on processes related to soil carbon stabilization. Land managers have the capacity to identify the situations (site, soil, chemistry) where the potential for soil C storage is greatest, that is, where the soils are further from carbon saturation. If studies such as proposed here can also begin to identify the combination of root traits that can maximize long term C storage in different soil types and ecosystems, we can propose management systems that could sequester C on a much larger scale, across both forest and agro-ecosystems. This progress is critical to reducing the potential impacts of global change and to maintaining and restoring productive ecosystems.