Root distribution characteristics of green roof Sedum plants and their effects on saturated hydraulic conductivity

In order to enrich the research on the distribution characteristics of the root system of Sedum plants in green roofs in China, and to explore the relationship between the root characteristic parameters and the saturated hydraulic conductivity of the green roof matrix layer, Sedum sarmentosum and Sedum lineare were planted in perlite substrate with a depth of 6, 10, and 14 cm. The plants were cultivated in a uniform watering system in accordance with the characteristics of rainfall in Wuhan. The root length density, root surface area density, root volume density were selected to describe the root morphology, and the saturated hydraulic conductivity of each group was measured. The group without plants was used as a control to quantitatively compare the root distribution characteristics of Sedum plants and the variation of saturated hydraulic conductivity under different substrate depths. The results showed that: 1) The root length density, root surface area density, and root volume density of Sedum plants were significantly affected by the depth of the perlite substrate. Under the same conditions, the root diameter of plants in the 6 cm substrate ranged from 0 to 0.8 mm, and the total root length density was the highest, which was mainly related to the roots with a diameter of 0.2 to 0.4 mm. The root diameter of plants in the 14 cm substrate ranged from 0 to 2 mm. The total root surface area density and root volume density were the largest, and their values were mainly related to the roots with a diameter of 1 to 2 mm. 2) Compared with the group without plants, the addition of Sedum roots changed the saturated hydraulic conductivity of the perlite substrate by −98.95% to −95.15%, and the saturated hydraulic conductivity of the plant group was much lower than that of the non-plant group. For the plant group, the saturated hydraulic conductivity had a significant positive correlation with the root length density (P=0.050, R²=0.786), root surface area density (P=0.047, R²=0.818), and root volume density (P=0.044, R²=0.824) of Sedum plants with a diameter of 0.2-0.4 mm. 3) The roots of Sedum plants significantly changed the saturated hydraulic conductivity of perlite substrate.