Integrative multi-omics elucidates the impact of microalgae on growth, quality, phytohormones, and rhizosphere microbiome of Angelica sinensis.

Microalgae have recently been recognized as sustainable biofertilizers that improve soil fertility while enhancing crop performance. However, their roles in regulating medicinal plant growth and quality, as well as the underlying ecological mechanisms, remain poorly understood. In this study, we systematically assessed the effects of three representative microalgae-Anabaena cylindrica (AC), Phormidium tenue (PT), and Chlorella vulgaris (CV)-on the growth, quality, hormonal regulation, soil nutrient dynamics, and rhizosphere microbiome of Angelica sinensis. Field inoculation trials demonstrated that all three microalgae significantly promoted biomass accumulation and increased antioxidant capacity. AC and CV further enhanced the accumulation of ferulic acid and flavonoids, which are two key quality determinants. Microalgal inoculation significantly altered rhizosphere soil properties by increasing total organic carbon and alkali-hydrolyzable nitrogen, with AC uniquely elevating available phosphorus and iron. Metagenomic analysis revealed that AC and PT stimulated nitrification while suppressing denitrification, thereby reducing nitrogen loss and stabilizing the soil nitrogen pools. Distinct microbial taxa, including Rhodanobacter, Streptomyces, and Pseudomonas, were identified as the major contributors to carbon and nitrogen cycling. Hormone metabolomics showed that microalgal inoculation reprogrammed A. sinensis phytohormone profiles in a species-specific manner. Partial least squares path modeling suggested that AC and CV promote ferulic acid biosynthesis through distinct mechanisms, with AC associated with reduced investment in C-mineralization processes and CV associated with lower salicylic acid levels, whereas PT enhances biomass accumulation mainly by stimulating N-cycle processes. Collectively, this study provides integrated evidence linking microalgae-mediated nutrient cycling, rhizosphere microbiome shifts and hormonal regulation to enhanced quality formation in A. sinensis.