Phenotypes of plants that received different soil treatments in greenhouse, pot, and field experiments (a). Plant height (b), stem diameter (c), aboveground fresh weight (d), aboveground dry weight (e), root surface area (f), root volume (g), aboveground fresh weight (h), and belowground dry weight (i) of M. hupehensis Rehd seedlings in the greenhouse experiment. Plant height (j) and stem diameter (k) of M. hupehensis Rehd grown in pots from July to September 2021. Plant height (l), stem diameter (m), branch number (n), and branch length (o) of young apple trees in the field experiment in October 2021. GR, control replant soil in the greenhouse experiment; GC, replant soil with blank carrier in the greenhouse experiment; GT, replant soil with 6S-2 fertilizer in the greenhouse experiment; PR, control replant soil in the pot experiment; PC, replant soil with blank carrier in the pot experiment; PT, replant soil with 6S-2 fertilizer in the pot experiment; LR, control replant soil in Laizhou; LC, replant soil with blank carrier in Laizhou; LT, replant soil with 6S-2 fertilizer in Laizhou; QR, control replant soil in Qixia; QC, replant soil with blank carrier in Qixia; QT, replant soil with 6S-2 fertilizer in Qixia; YR, control replant soil in Yiyuan; YC, replant soil with blank carrier in Yiyuan; YT, replant soil with 6S-2 fertilizer in Yiyuan. The displayed data were presented as mean ± SE (standard error). Different lowercase letters in the same column indicate a significant difference at p ≤ 0.05 level by Duncan’s new multiple range test. The same treatment names and statistical tests were used in subsequent figures.