Exploring the Role of Intercropping and Mulching on Modulating Lettuce Biomass and Rhizosphere Microbiome

ABSTRACT Modern agriculture faces the dual challenge of maintaining high yields while minimising environmental impact, all under increasingly difficult climatic conditions. Practices such as intercropping and mulching have demonstrated potential to improve resource use efficiency, but their effects on crop performance and soil microbial communities remain insufficiently understood. We examined how both factors affect lettuce ( Lactuca sativa cv. Grazer Krauthäuptel) growth performance, soil conditions, and the rhizosphere microbiome for three cropping cycles over a growing season in Styria, Austria. Four production systems were compared: unmulched monoculture, mulched monoculture, and two intercropping with either bush bean or broccoli, sweet corn, and wildflower strips. Intercropping increased lettuce fresh weight at early and late stages in comparison to monoculture, while mulching consistently enhanced biomass. However, increased yield losses were observed in the mulched systems under extreme weather conditions. The regulating effect of mulching and intercropping was reflected in the main soil parameters. Rhizosphere microbial communities profiled using 16S rRNA gene fragments and ITS region amplicon sequencing revealed contrasting effects for bacteria and fungi. Bacterial alpha diversity was significantly higher in intercropped systems, particularly at the last cropping cycle, with community structure most strongly driven by timepoint and further shaped by production system and mulching. Enriched genera under intercropping included Pseudomonas and Bacillus , both potential plant growth‐promoting bacteria. Interestingly, fungal diversity was generally reduced by mulching and intercropping, with unmulched monoculture showing the highest fungal diversity later in the season. Saprotrophic genera were associated with intercropping and mulching, whereas unmulched monocultures were linked to several potential plant or animal pathogens. The results demonstrate that intercropping and mulching can enhance lettuce yield and bacterial diversity, while modulating soil moisture and microclimate. Selecting appropriate companion crops and implementing optimised mulch management is key to enhancing productivity and resilience amid increasing climate variability.