Constructing Periphytic Biofilms at the Soil–Water Interface for In Situ Control of Agricultural Surplus Phosphorus Pollution

Farmland drainages are a hotspot for agricultural phosphorus (P) pollution. Periphytic biofilms (PBs) are easy to grow on waterlogged solid surfaces in farmland ecosystems, such as paddy soils and ditches, and greatly impact P biogeochemical cycles. However, the substantial benefits of the in situ removal of surplus P in farmland areas by PBs remain overlooked. We conducted a field investigation in paddy fields in various regions of China and found that polyphosphate-accumulating organisms (PAOs) and microalgae are key contributors to P entrapment by PBs. We subsequently used PAOs (Pseudomonas putidaand Flavobacterium johnsoniae) and microalgae (Chlamydomonas sajao and Chlorococcum humicola) as initial colonizers and constructed functional PBs de novo. Functional PBs at the soil-water interface reduced approximately 92% of surplus P in water and increased the soil P availability. PAO as initial colonizers promoted extracellular polymeric substances production by increasing amino acid metabolism and improving P entrapment by PBs. PAOs introduced P solubilization genes into the PB, releasing phosphate from residual P and organic P in the topsoil. Microalgae, as initial colonizers, enhanced vitamin B6 metabolism and synergized with bacteria in PBs to promote P entrapment. The results offer a promising way to in situ control of surplus P pollution in farmland ecosystems and highlight the potential of microbial tools for advancing sustainable agriculture.