Effects of Agaricus bisporus SMS-Garden Soil Mixture Ratios on Tomato Growth, Yield, and Quality

The present study evaluated the effects of Agaricus bisporus spent mushroom substrate (SMS) on growth, yield, and quality of tomato (Solanum lycopersicum L. cv. ‘Fenguan 888’) in a pot experiment. Ten treatments (Z1–Z10) were applied using gradient substrate replacement (SMS) ratios, relative to a control (CK) without SMS addition. The results demonstrated that SMS exerted stage-dependent growth promotion. No significant effects were observed at the seedling stage, but gradual enhancements were noted thereafter. Z6 achieved the greatest plant height increase (68.0%), while Z8 achieved the largest stem diameter increase (50.0%) at peak fruiting. Biomass accumulation was significantly enhanced, Z9 increased aboveground fresh weight by 580.7% and root length by 63.9%, while Z8 maximized aboveground dry weight (163.9%) and belowground fresh weight (312.8%). Photosynthetic pigments exhibited differential responses, Z5 maximised chlorophyll a, Z4 optimized chlorophyll b and total chlorophyll, and Z10 achieved the highest carotenoid levels. Yield indicators for Z4 showed a 47.94% increase in individual fruit weight and a 247.02% increase in yield per plant. Z5 increased soluble sugars, vitamin C and flavonoids by 111.4%, 68.9% and 82.0% over CK. Z6 attained peak sugar-acid ratio and anthocyanin, with respective increases of 137.3% and 56.32%. Total phenolics rose by merely 5.7% in Z3. Pearson correlation heatmap and principal component analysis (PCA) revealed significant positive correlations of yield with fruit weight, fruit-set rate and sugar content, whereas the root-to-shoot ratio was significantly negatively correlated with yield traits. The first two principal components, PC1 (growth–yield–quality axis) and PC2 (pigment–metabolism axis), collectively accounted for 64.53% of the total variation. Z4 demonstrated the optimal overall performance, attaining first position in yield per plant and second position on the flavour and quality axis (PC2), and exhibiting a balanced root-to-shoot ratio. Although Z7 achieved the highest score on PC1, this was primarily attributable to excessive vegetative growth and a relatively high root-to-shoot ratio, rather than an increase in reproductive yield.