Visualization and quantification of carbon 'rusty sink' by rice root iron plaque: mechanisms, functions, and global implications

Paddies contain 78% higher organic carbon (C) stocks than adjacent upland soils, and iron (Fe) plaque formation on rice roots is one of the mechanisms that traps C. The process sequence, extent and global relevance of this C stabilization mechanism under oxic/anoxic conditions remains unclear. We quantified and localized the contribution of Fe plaque to C stabilization in a microoxic area (rice rhizosphere) and evaluated the role of this C trap toward global C sequestration in paddy soils. Visualization and localization of pH by imaging with planar optodes, enzyme activities by zymography, and root exudation by 14C imaging, as well as upscale modeling enabled linkage of three groups of rhizosphere processes that are responsible for C stabilization from the micro- (root) to the macro- (ecosystem) level. The 14C activity in soil (reflecting stabilization of rhizodeposits) with Fe2+ addition was 1.4−1.5 times higher than that in the control and phosphate addition soils. Perfect co-localiza...