Pipe material governs biofilm development and microbial communities more than organic suspended solids in drip...

Biofilm development in pressurized drip irrigation systems impairs emitter performance and irrigation uniformity, increasing production risks in greenhouse systems where small substrate volumes limit moisture buffering capacity. The present study evaluated the effects of pipe material and peat-derived organic total suspended solids (TSS), representative of recirculated greenhouse irrigation water, on biofilm accumulation, microbial community composition, and emitter performance. Polyvinyl chloride (PVC; main lines) and polyethylene (PE; lateral lines) were tested using nutrient solutions containing 0, 30, 60, and 120 mg L⁻¹ organic TSS (<150 µm). The system incorporated pressure-compensated drip emitters with anti-drain mechanisms and operated under short-pulse irrigation typical of greenhouse production (twice daily for 2 min over 8 weeks). Biofilm accumulation was quantified by dry mass and heterotrophic plate counts, and microbial communities were characterized using 16S rRNA and ITS2 sequencing. Surface hydrophobicity and roughness were evaluated before and after biofilm exposure. PVC pipes accumulated more biofilm than PE pipes and exhibited greater changes in surface properties. Pipe material explained more variation in bacterial community composition than organic TSS. No emitters fully clogged; however, organic TSS ≥ 60 mg L⁻¹ increased emitter discharge, indicating early-stage performance drift in anti-drain emitters. These findings highlight the importance of pipe material selection and organic TSS management for maintaining irrigation performance in greenhouse systems.