Elevated CO₂ increases soil redox potential by promoting root radial oxygen loss in paddy field

Soil redox potential (Eh) plays an important role in the biogeochemical cycling of soil nutrients. Whereas its effect soil process and nutrients' availability under elevated atmospheric CO₂ concentration and warming has seldom been investigated. Thus, in this study, a field experiment was used to elucidate the effect of elevated CO₂ concentration and warming on soil Eh, redox-sensitive elements and root radial oxygen loss (ROL). We hypothesized elevated CO₂ and warming could alter soil Eh by promoting or inhibiting ROL. We found that soil Eh in the rhizosphere was significantly higher than that of non-rhizosphere. Elevated CO₂ enhanced soil Eh by 11.5%, which corresponded to a significant decrease in soil Fe²⁺ and Mn²⁺concentration. Under elevated CO₂, the concentration of Fe²⁺ and Mn²⁺ decreased by 14.7% and 13.7%, respectively. We also found that elevated CO₂ altered rice root aerenchyma structure and promoted rice root ROL. Under elevated CO₂, rice root ROL increased by 79.5% and 112.2% for Yangdao 6 and Changyou 5, respectively. Warming had no effect on soil Eh and rice root ROL. While warming increased the concentration of Mn²⁺ and SO₄^2- by 4.9% and 19.3%, respectively. There was a significant interaction between elevated CO₂ and warming on Fe²⁺ and Mn²⁺. Under elevated CO₂, warming had no effect on the concentration of Fe²⁺ but decreased Mn²⁺ concentration significantly. Our study demonstrated that elevated atmospheric CO₂ in the future could increase soil Eh by promoting rice root ROL, which will alter some soil nutrients' availability, such as Fe²⁺ and Mn²⁺.