Effects of Different Ratios of Coal Gangue and to Garden Soil Composite Substrates on the Growth and Physiology of Rhododendron Delavayi Franch. Seedlings

Rhododendron delavayi Franch. is often used as home cultivation because of its high ornamental value, however, the commonly used cultivation substrate can led to yellowing of leaves. Coal gangue is widely present in the soil of its native habitat, and its leaves are not yellowing. Thus, the purpose of this study is to investigate whether the addition of coal gangue to the commonly used substrate is helpful to solving the problem of leaf yellowing during home cultivation. A pot experiment was conducted to test the effects of coal gangue and garden soil treatments on morphological, photosynthetic and biochemical characteristics of R. delavayi cultivation, and substrate properties in six different ratio (9:1, 8:2, 7:3, 6:4, 5:5 and 0:10 by volume). Compared with the control, the soil pH in the coal gangue substrate can be reduced to a minimum of 5.35, the organic matter content can be increased to a maximum of 169.04 (g kg^{− 1}), the plant phosphorus content can be reduced to a minimum of 45 (mg kg^{− 1}), and the effective iron in the substrate can be increased to a maximum of 5.35 (mg kg^{− 1}). It is worth noting that the relative chlorophyll content, net photosynthetic rate, stomatal conductance, transpiration rate, intercellular carbon dioxide concentration, water use efficiency, plant height, stem thickness, plant nitrogen, potassium, active iron content and matrix effective nitrogen and effective potassium content of composite substrate with gangue to garden soil ratio of 7:3 were the highest significantly higher than that of control by 21.70%, 87.21%, 103.27 35.56%, 21.32%, 38.10%, 16.03%, 14.16%, 77.72%, 73.68%, 223.87%, 55.90% and 250.60% respectively. The composite substrate with a 7:3 ratio improved the photosynthetic capacity of R. delavayi leaves by enhancing the physicochemical properties of the substrate and effectively solved the problem of leave yellowing.