Effects of biochar as a peat-based substrate component on morphological, photosynthetic and biochemical characteristics of Rhododendron delavayi Franch.

Abstract

Biochar could be a promising peat substitute for horticultural plant production. We evaluated the feasibility of rice husk biochar (RHB) and wood chip biochar (WCB) as a peat-based substrate component for the cultivation of Rhododendron delavayi Franch., that is an ornamental dwarf tree species. A pot experiment was conducted to test the effects of RHB and WCB treatments at five application rates ( 0, 10, 20, 30, and 40% by volume) on morphological, photosynthetic and biochemical characteristics of R. delavayi. The substrate properties, plant growth, root traits, photosynthetic and biochemical parameters were analyzed. The addition of 20% WCB or 30-40% RHB enhanced the growth and photosynthetic activity of R. delavayi seedling, including increased plant height, numbers of leaves, leaf area, root surface area and root tip numbers, as well as improved total chlorophylls content and net photosynthetic rate. The addition of 40% RHB significantly increased the contents of carotenoids, polyphenols and anthocyans, indicating an enhanced antioxidant activity of R. delavayi seedlings. The mixed substrates (20% WCB, 30% RHB and 40% RHB) all have balanced aeration porosity and water holding porosity, suitable pH and electrical conductivity, and increased plant nutrient supply (especially K, Fe and Mn). However, the 40% WCB substrate depressed seedlings growth and reduced total chlorophylls content and net photosynthetic rate. The negative effects were linked to its low water holding porosity, high alkalinity and salinity, as well as high content of phytotoxic compounds, such as polycyclic aromatic hydrocarbons and volatile matter. In conclusion, a peat-based substrate containing 20% WCB or 30–40% RHB is a more favorable growth media for obtaining high-quality R. delavayi seedlings, while achieving sustainable horticulture production.