Foliar application of seaweed extracts influences the phytomicrobiome dynamics in tomato and sweet pepper plants

The use of seaweed extracts (SWEs) in crop production is becoming a viable and sustainable agronomic practice due to its multiple benefits to crops and the environment. However, no studies have documented the effect of foliar SWEs applications on the plant microbiota. Here we used foliar applications of Sargassum vulgare, Acanthophora spicifera, and Ascophyllum nodosum extracts in sweet pepper and tomato to study the effects on rhizosphere, phylloplane, and plant endosphere by profiling both bacterial and fungal communities. Microbial community profiling was performed with short amplicon next-generation sequencing utilizing the bacterial 16 s rRNA and fungal ITS regions. Several plant growth parameters were also measured. Foliar SWEs treatments resulted in a significant increase in all plant growth parameters including chlorophyll content, plant height, root length, root and shoot dry weight, flower number, fruit number, and overall fruit yield. Analysis of the metagenomic data indicated significant microbial shifts, with increased alpha and beta diversity metrics and higher proportions of beneficial families in the rhizosphere, phylloplane, and endosphere of SWE-treated plants compared to the controls, for both tomato and sweet pepper. Among the bacterial families, Burkholderiaceae dominated the endosphere and phylloplane, whereas Bacillaceae dominated the rhizosphere samples. Fungi belonging to Nectriaceae dominated the rhizosphere and endosphere, while Pleosporaceae dominated the phylloplane environment. The microbial shifts observed could have aided in the increased plant productivity, either directly or indirectly through the activation of metabolic pathways in SWE-treated plants. The significant shifts in microbial communities achieved with all seaweed species, and in all tissue types, provides evidence for the indirect positive impacts of seaweed extracts on crops.

Automated summary

The use of seaweed extracts as fertilizers in crop production has positive effects on plant growth and microbial community composition. Foliar applications of seaweed extracts can significantly increase plant growth parameters and result in microbial shifts, with increased proportions of beneficial bacteria.