Comprehensive evaluation of the effects of different composite substrates on the growth of tree peony

This study evaluated the effects of various composite substrates, including forestry and agricultural waste, on the growth, photosynthesis, and carbon–nitrogen allocation of potted peonies (Paeonia suffruticosa Andrews). The substrates were composed of peat, vermiculite, perlite, and different proportions of agricultural waste (rice husks, pine needles, straw). Key growth and photosynthetic parameters were measured, and comprehensive evaluation was conducted using principal component analysis (PCA). The results showed that Substrate I (peat:perlite:vermiculite:rice husks = 3:1:1:1) was the most effective, followed by Substrate A (peat:perlite:vermiculite = 6:2:2), which served as the control and was the least effective among traditional substrates. Substrate E (peat:perlite:vermiculite:straw = 3:1:1:1), representing new forestry and agricultural waste, showed the poorest performance overall. Substrate I significantly improved plant height, new shoot length, and leaf number, enhancing morphology and photosynthetic efficiency. Growth was closely related to substrate porosity and nitrogen content. Carbon and nitrogen allocation analysis revealed that Substrate I promoted efficient carbon transport and higher nitrogen uptake, supporting both vegetative and reproductive growth. In contrast, Substrate E demonstrated inefficient nutrient distribution, limiting growth. Integrating agricultural waste into substrates in an optimal manner effectively promoted the growth and photosynthesis of peonies, supporting sustainable cultivation practices. This study provides a basis for incorporating agricultural waste into substrate formulations and selecting optimal substrates for peony cultivation.