Objectives Phenolic acid stress is one of the primary factors limiting continuous cropping of tomato. The impact and mechanism of biochar-calcium peroxide composite particles as soil conditioners in relieving tomato phenolic acid stress were studied.

Methods Pot experiments were carried out with ‘millennium cherry’ tomatoes and latosolic red soil. There were 5 treatments in total, including conventional cultivation (CK), phenolic acid stress treatment (T1), and exogenous phenolic acid together with biochar-calcium peroxide composite particles (T2), biochar particles (T3), and calcium peroxide particles (T4), respectively. The phenolic acid stress content in soil was 140 μg/g. The tomato growth and physiological indicators were examined at 30 and 120 days after transplanting tomato. At the harvest period, fruit production and quality, and rhizosphere soil physicochemical parameters were determined. High-throughput sequencing was employed to investigate the microbial diversity and community structure of in rhizosphere soil of tomato .

Results Compared with T1, T2 treatment enhanced tomato root vigor and promoted plant growth, thus increased the yield, fruit weight and sugar-acid ratio of tomato by 13.8%, 20.1%, and 52.6%, respectively; decreased the total residual phenolic acid content and electrical conductivity (EC) in rhizosphere soil by 44.6% and 17.7%, increased pH by 0.77 units, and enhanced organic matter content by 77.4%. T2 treatment also enriched the microbial community structure, increased bacterial community diversity, reduced fungal community diversity, and effectively restored microbial community balance. According to the Spearman correlation heatmap and redundancy analysis, tomato yield and fruit sugar-acid ratio were negatively related with soil residual total phenolic acid and EC, but positively correlated with soil pH and organic matter content. Other than the reduced soil phenolic acids and EC as well as increased soil pH and organic matter content, the biochar-calcium peroxide composite soil conditioner selectively promoted the relative abundance of Bacteroidetes and Chytridiomycota, which are positively correlated with tomato yield and quality, and suppressed the relative abundance of Acidobacteria and Ascomycota, which are negatively correlated with tomato yield and quality.

Conclusions The key environmental parameters driving the fluctuation of tomato rhizospheric microbial community are the residual total phenolic acid in soil, pH, organic matter content, and EC, which are all strongly related with tomato yield and quality. Through the dual regulation of soil physicochemical properties and microbial communities, biochar-calcium peroxide composite particles improves the micro-ecological environment of tomato rhizosphere, thereby effectively alleviating the allelopathic stress impact of phenolic acids on tomato growth and promoting fruit yield and quality.