Effects of Calcium and Magnesium Fertilization on the Rhizosphere Bacterial Community Assembly and Specific Biomarkers in Rainfed Maize

This study investigated the effects of varying levels and combinations of calcium (Ca) and magnesium (Mg) supplementation on the diversity, composition, and species differentiation of the rhizosphere soil bacterial community in rainfed maize, aiming to reveal their regulatory mechanisms on the rhizosphere micro-ecosystem. A field micro-plot experiment was conducted with seven treatments: low Ca (U), high Ca (V), low Mg (W), high Mg (X), low Ca and low Mg (Y), high Ca and high Mg (Z), and a control (K, no supplementation). The bacterial communities were analyzed using high-throughput sequencing of the 16S rRNA gene, and the data were processed using the QIIME2 pipeline, as well as multivariate statistical analyses, and LEfSe. The main results demonstrated that Ca and Mg supplementation significantly altered the rhizosphere bacterial community structure (beta-diversity). Analysis of Similarities (ANOSIM) indicated significant differences between treatments (R > 0.4, <i>p</i> < 0.01). LEfSe analysis successfully identified key biomarkers responsive to different treatments. For instance, high Ca treatment significantly enriched the genus Clostridium within the phylum Firmicutes, whereas high Mg treatment specifically enriched the genus <i>Lysobacter</i>. Furthermore, Ca-Mg interactions exhibited non-additive effects, and the coupled Ca-Mg supplementation treatments (Y, Z) formed unique species assemblages. As key environmental drivers, Ca and Mg supplementation specifically reshaped the rhizosphere bacterial community through "environmental filtering" in rainfed maize. This study provides a theoretical basis for understanding the microbiological pathways through which secondary element fertilizers influence soil health, offering practical implications for precisely managing rhizosphere micro-ecology through Ca and Mg supplementation to promote the sustainable development of dryland farming.