Evaluating the combined effects of Trichoderma harzianum, Bacillus subtilis, and chemical fertilization on soil fertility, yield, and quality of edible rose

The cultivation of edible rose faces several challenges. Excessive use of chemical fertilizer leads to soil disruptions in microbial community structure and a decline in yield and quality. This study aimed to investigate whether the combination of microbial inoculants with chemical fertilizer could improve the soil environment, enhance both yield and quality of edible rose, and identify the optimal fertilization-inoculant coupling patterns. A two-year field experiment was conducted with a control treatment (CK) of no fertilizer and no microbial inoculant. Three different fertilization rates were tested: low (FL: 500 kg·ha⁻¹), medium (FM: 900 kg·ha⁻¹), and high (FH: 1300 kg·ha⁻¹), combined with two microbial inoculants: Bacillus subtilis (B) and Trichoderma harzianum (T). The results demonstrated that the FM treatment significantly improved soil microbial activity, diversity indices, and carbon source utilization efficiency. Application of Trichoderma harzianum increased microbial carbon source utilization by 5.26 %-288.24 %, while the Shannon and McIntosh indices increased by 28.40 %-43.41 %, respectively. The rose yield, total phenols, and total flavonoid content increased by 20.76 %-36.59 %, 12.01 %-40.99 %, and 34.42 %-65.82 %, respectively. It is noteworthy that Bacillus subtilis increased soil urease and phosphatase activities by 5.36 % and 26.85 %, respectively, concomitantly enhancing photosynthetic performance in edible roses. Compared with CK, the FMT treatment led to an average increase of 426.18 % in soil microbial average well color development (AWCD), 138.74 % in enzyme activity, and 506.29 % in yield. The yield and quality of edible rose were significantly correlated with soil microbial environmental factors, and a random forest model and structural equation modeling revealed that the application of microbial inoculants in conjunction with fertilizer improved the soil microenvironment, thereby promoting an increase in rose yield. Additionally, the FMT treatment provided the highest economic and comprehensive benefits, making it a suitable fertilization-inoculant management strategy for Southwest China. This study provides scientific theoretical support and practical references for the green production of edible rose. Graphical abstract illustrates that graded fertilization combined with microbial inoculants enhances edible rose photosynthesis, yield, and quality by improving soil microbial activity, enzyme activities, and available nutrient content. • Combined application Trichoderma harzianum or Bacillus subtilis with fertilizers improved soil environment. • The integration of Trichoderma harzianum with moderate fertilization achieved optimal comprehensive benefits. • Microbial inoculants with fertilizers enhance photosynthesis for superior edible rose quality and yield.