Microbial Degradation of Phytotoxic Root Exudates in Portable Ebb-and-Flow Hydroponic Systems as a Factor of Environmental Sustainability in Urban Farming

Abstract

This study evaluated the effectiveness of consortium-based microbial preparations (EM (Effective Microorganisms), EM-1, EM Agro and EM Bioactive) in degrading phenolic compounds and regenerating nutrient solution in portable ebb-and-flow hydroponic systems during sweet pepper (Capsicum annuum L.) cultivation under controlled conditions, using vertical portable hydroponic units. Microbial preparations were applied to the nutrient solution every 14 days. Total phenolic content, biometric parameters, chlorophyll content (SPAD index, Soil and Plant Analysis Development), nutrient solution parameters and phytotoxicity were assessed. Without regeneration, phenolic compounds accumulated to 458.6 ± 31.4 mg L⁻¹ over 90 days, reducing plant productivity by 51.1 %. A strong significant negative correlation using Spearman’s rank correlation coefficient with perfect rank-order reversal, rs = -1.0, p = 0.017 was found between phenolic compound concentration and productivity. All microbial preparations effectively degraded phytotoxic exudates, with EM Bioactive showing the highest efficiency (89.4 %). This treatment increased plant productivity compared with complete nutrient solution replacement, while reducing water and fertilizer consumption and lowering solution phytotoxicity to a low-toxicity level. The findings indicate that microbial degradation of root exudates is an effective strategy for nutrient solution regeneration, improving environmental sustainability, and resource efficiency of closed portable hydroponic systems for sweet pepper cultivation. As the study was limited to a single crop and a single 90-day cultivation cycle, these conclusions regarding the ecological sustainability of urban farming and closed hydroponic systems more broadly should be regarded as preliminary, pending validation on other vegetable crops (e.g., tomato, cucumber, lettuce) and over multiple nutrient-solution reuse cycles.