The influence of iron plaque and root traits on organic carbon turnover in the rice root detritusphere

Rice roots represent an important contributor to belowground organic carbon (C) inputs in paddy soils. They have characteristic traits specifically linked to their growth in predominantly anoxic soils, such as the presence of iron plaque (IP) on the roots surfaces and the development of apoplastic barriers through the lignification/suberization of cell wall exteriors. Nevertheless, evidence on how these traits influence microbial decomposition and root C turnover in the detritusphere is still lacking. In this work we evaluated how water management practices, involving rice cropping under continuous flooding (CF) and alternate wetting and drying (AWD), affect coarse and fine root C inputs, their biochemical quality and IP contents. Moreover, by harnessing the difference in natural abundance 13C between C3 rice plant residues added to a C4 maize-cropped soil, we elucidated how these traits affect microbial decomposition, soil organic C (SOC) priming and the contribution of root C to different functional SOC pools over a 90-d microcosm incubation under aerobic conditions. The main findings suggest that growing rice under CF resulted in a lower abundance of fine roots and favoured the accumulation of root-associated IP compared to AWD. This, together with their greater content of aromatic and alkyl C moieties, was mainly responsible for the slower turnover of fine compared to coarse roots, and their slightly greater contribution to mineral-associated OC pools, without considerably affecting native SOC priming. We conclude that evaluating the effects of water management practices, among other parameters, on belowground C inputs and rice root traits may help decipher the root C turnover and contribution to stable SOC in rice paddies.