Manure amendment and the rhizosphere of Amaranthus hybridus soil bacterial communities in a semi-arid irrigated agroecosystem

Abstract

Soil biodiversity is fundamental to nutrient cycling and ecosystem functioning in agroecosystems, yet the combined effects of organic amendments and weed rhizospheres on soil bacterial communities remain insufficiently explored in semi-arid irrigated systems. We evaluated soil physicochemical properties and bacterial diversity inferred from 16S rRNA gene amplicon sequencing in three soil treatments: initial bulk soil (T1), bulk soil amended with cattle manure at 20 Mg ha-1 and sampled 11 days after application (T2), and the rhizosphere of Amaranthus hybridus sampled 75 days after manure application (T3). Alpha diversity (Faith's phylogenetic diversity, Shannon diversity, and evenness), beta diversity (Bray–Curtis, weighted UniFrac, and unweighted UniFrac), PERMANOVA, and redundancy analysis (RDA) were used to characterize bacterial communities. Manure amendment increased bacterial richness and alpha diversity, whereas the A. hybridus rhizosphere exhibited intermediate diversity, a distinct taxonomic composition, and higher micronutrient concentrations. Multivariate analyses further demonstrated clear differences in bacterial community composition among treatments and strong associations between dominant bacterial taxa and soil physicochemical gradients. These findings indicate that manure amendment and rhizosphere-associated processes jointly promote heterogeneous bacterial community configurations in semi-arid irrigated agroecosystems.