Interactive effects of biochar types and Bacillus velezensis inoculation on soil properties, microbial communities and wheat performance under greenhouse conditions

Abstract

Agricultural intensification has led to soil degradation, reducing fertility and microbialdiversity, compromising long-term productivity. Biochar and plant growth-promotingrhizobacteria (PGPR) are proposed as sustainable soil amendments, but their combined effects in agricultural semi-arid soils are poorly understood. This study assessedthe interactive effects of poultry manure-derived biochars produced at 500C(BC500) and 700C (BC700), with and without Bacillus velezensis inoculation, on soilchemical properties, enzymatic activities, microbial communities and wheat (Triticumaestivum) performance under greenhouse conditions. The effects of biochar were thedominant drivers across all variables analysed, whereas those of PGPR inoculationwere less evident. Biochar addition significantly altered soil chemistry, increasing pH,cation exchange capacity and nutrient availability. Enzymatic activities related to C, Nand P cycling were also stimulated, with BC500 enhancing β-glucosidase activity andBC700 promoting phosphomonoesterase and xylosidase activities. High-throughputsequencing revealed that biochar and PGPR modulated microbial community structure and diversity. The BC500 treatments were associated with Planctomycetota,whereas the BC700 enriched Actinobacteriota, Proteobacteria and Firmicutes. PGPRinoculation increased Shannon diversity and evenness, suggesting an enhancedmicrobial balance, although its persistence appeared to be limited. Wheat responsesdiffered according to biochar type: BC500 did not significantly affect performancecompared with the control, whereas BC700 reduced shoot and root biomass, graindry weight and grain number. B. velezensis inoculation modestly improved rootgrowth and grain biomass, particularly in the absence of biochar, but did not consistently interact synergistically with biochar amendments. Finally, multivariate analysessuggest that the chemical changes induced in the soil by biochar addition are likelythe main drivers of wheat performance in these environments. In addition, the resultsindicate that the effects of biochar depend strongly on pyrolysis temperature, withmoderate-temperature biochars preserving soil functionality while maintaining cropproductivity comparable to the control. The limited effects of B. velezensis highlightthe need for improved inoculation strategies to ensure long-term persistence. Thesefindings emphasise the importance of tailoring biochar properties and microbial applications to local soil conditions for sustainable crop management.