Three Fertilizer Application Can Alleviate the Damage of Tree Peony (Paeonia × suffruticosa Andr.) under High Temperature in Summer

Tree peony (Paeonia × suffruticosa Andr.), celebrated for its large blooms, diverse morphology, graceful form and enchanting fragrance, thrives in cool and dry environments and holds significant culture value in China. However, climate change-induced high temperatures increasingly threaten cultivation of tree peony in the Jiangnan Region of China. Therefore, developing strategies to mitigate heat stress injury in tree peony has become an urgent horticultural priority. This study investigated the efficacy of three fertilizers (compound fertilizer, CF; water-soluble fertilizer, WSF; soybean cake fertilizer, SCF) in alleviating high temperature stress damage to tree peony. The results showed that all three fertilizer alleviated heat stress in tree peony during summer high temperatures. Key improvements included: (1) Physiological resilience: Reduced heat injure index, elevated SPAD values (indicating chlorophyll retention), and increased relative water content. (2) Metabolic enhancement: Improved photosynthetic efficiency (stable Fv/Fm), upregulation of antioxidant enzymes (e.g., SOD, CAT), and decreased malondialdehyde (MDA) levels (a marker of oxidative stress). (3) Nutrient optimization: Higher soluble protein (SP) content, suggesting better nitrogen assimilation. Moreover, CF treatment demonstrated superior efficacy in alleviating heat stress impacts on tree peony plants. These results indicate that fertilizer supplementation, especially CF, decreased the deleterious effect of high temperature stress in summer on tree peony. These findings develop effective cultivation strategies for improving tree peony yield and quality under abiotic stress conditions.