Abstract The world-wide expansion of urban areas has led to an increase of municipal green waste (MGW) generation. In this study, indole-3-acetic acid (IAA), a known biostimulant, was produced using Trichoderma viride through solid-state fermentation (SSF) of MGW in a tray bioreactor. The production of IAA was optimized under SSF conditions, achieving a maximum yield of 112.6 μg IAA g⁻ 1 dry weight at 28 °C, 65% humidity, and 1% of L-tryptophan supplementation based on total weight. The biostimulant effectiveness was further evaluated in lettuce ( Lactuca sativa L.) germination pot tests, showing significant improvements in growth parameters, photosynthetic pigments and nutrient uptake. Fermented solids with two different IAA concentrations (112.6 and 60.0 μg IAA g⁻ 1 dw) were tested on lettuce plants, resulting in higher biomass, root and shoot length, and overall vigour plant compared to a control without IAA at 7, 14, 21, 28, and 35 days after planting. Additionally, chlorophyll content, carotenoids, and the absorption of key nutrients (K⁺, Ca 2 ⁺, Mg 2 ⁺, P, S) were significantly enhanced. These findings highlight the potential of Trichoderma viride as a biostimulant producer, aligning this strategy to circular economy principles by valorising MGW into agricultural useful bioproducts, thus reducing the dependency on chemical fertilizers, while promoting sustainable agriculture. Graphical Abstract
Solano et al. (Fri,) studied this question.