Importance of periphytic biofilms for carbon cycling in paddy fields: A review

Paddy fields play an important role in global carbon (C) cycling and are an important source of methane (CH₄) emissions. Insights into the processes influencing the dynamics of soil organic C (SOC) in paddy fields are essential for maintaining global soil C stocks and mitigating climate change. Periphytic biofilms composed of microalgae, bacteria, and other microorganisms are ubiquitous in paddy fields, where they directly mediate the transfer of elements at the soil-water interface. However, their contributions to C turnover and exchange have been largely neglected. Periphytic biofilms affect and participate in soil C dynamics by altering both abiotic (e.g., pH and redox potential) and biotic conditions (e.g., microbial community composition and metabolism). This review summarizes the contributions of periphytic biofilms to soil C cycling processes, including carbon dioxide fixation, SOC mineralization, and CH₄ emissions. Future research should be focused on: i) the mechanisms underlying periphytic biofilm-induced C fixation and turnover and ii) quantifying the contributions of periphytic biofilms to soil C uptake, stabilization, and sequestration in paddy fields.