L'influenza delle placche di ferro e della morfologia radicale sul ciclo del carbonio organico nella detritosfera delle radici di riso

Paddy soils are characterized by a high content of soil organic carbon (SOC). There is considerable uncertainty regarding the contribution of root-derived C inputs and their fate in these soils as a function of water management practices. The aim of this work was to provide new insights into the effects of water management on shoot and root C input, root traits and iron plaque and how these aspects influence the decomposition and mineralization of root-derived and native soil-derived organic matter as well as their contribution to stable SOC. To do this we sampled rice plants from different paddy fields, separated fine and coarse roots that were characterised and treated to remove iron plaque from a portion of roots. The different rice plant materials (C3 plant) were then incubated in soil under long-term maize cropping (C4 plant), and changes in microbial respiration and biomass were measured. The contribution of soil and residue-derived C to the total CO2 emissions were distinguished thanks to δ13C analysis and the contribution of rice residues to different functional SOM pools were quantified by coupling δ13C analysis with density fractionation. Water management did not influence the amount of above and belowground C inputs that can be incorporated in soil with tillage, but did affect the root traits. These differences in root traits and iron plaque contents did not however result in significant changes in C stabilization and mineralization as expected. Only minor differences were observed between fine and coarse root types but it was not possible to clearly attribute these differences in biochemical composition or presence of Fe plaque on the different root types. Nonetheless, the rapid mineralization and the enhanced SOC priming effect with the addition of rice straw with respect to roots, suggest that increasing belowground C inputs could contribute to enhancing stable SOC pools in rice paddies.