Rice hull biochar improved the growth of tree peony (Paeonia suffruticosa Andr.) by altering plant physiology and rhizosphere microbial communities

High temperatures due to global warming threaten agricultural production. The application of biochar may enhance plant growth and soil fertility, but whether it exerts an influence on plants under high-temperature stress has not been confirmed. In this study, the effects of biochar on physiological and biochemical indices of high-temperature tolerance were evaluated in the tree peony. It was found that biochar application reduced temperature-induced injury, especially 50% biochar, which was significantly better than 100% biochar in terms of phenotypic changes, stress physiological index and rhizosphere microbial abundance. First, biochar application prevented the decreases in chlorophyll content, and restrained the increases in relative electrical conductivity, malondialdehyde content and reactive oxygen species. Moreover, four antioxidant enzymes showed increased activation in response to biochar application. Furthermore, biochar application enhanced photosynthesis and maintained intact anatomical structures. Additionally, the related physicochemical properties and soil enzyme activities, together with nitrogen, phosphorus and kalium content of cultivation substrate were improved in response to biochar application, while the rhizosphere microbial abundance was increased, which promoted the root of tree peony to grow. These results revealed that biochar could improve high-temperature tolerance of plants, suggesting that the use of biochar is feasible for enhancing plant growth under high-temperature stress.