The Influence of Groundwater Salinity on the Growth and Architecture of Tamarix chinensis Root System

To explore the response patterns of the root morphology and architecture indexes of Tamarix chinensis to changes in groundwater salinity. Taking three-year-old T. chinensis seedlings as the research object. Under the condition of 1.8 m groundwater level, 4 salinity levels of fresh water (0 g/L), brackish water (3 g/L), saline water (8 g/L), and salt water (20 g/L) were created. To measure the root growth and architecture indexes, such as root diameter, root length, root biomass, root-shoot ratio, topological index, and link length. The results showed that the groundwater salinity has no significant effect on the soil water content, but has a significant effect on the soil salt content and the absolute soil solution content, thus affecting the growth and architecture of root system of T. chinensis. With the increase of groundwater salinity, T. chinensis root diameter, root length, lateral root number, main root, and lateral root biomass all show a trend of first increasing and then decreasing, reaching the maximum under brackish water salinity. In the fresh water and brackish water treatments, the TI of the T. chinensis roots was close to 0.5, and the root architecture was close to a dichotomous branching pattern. In the saline water and saltwater treatments, the TI of the T. chinensis roots was large and close to 1.0, and the root architecture was close to a herringbone branching pattern. Under different groundwater salinities, the total root length was significantly greater than the internal link length, the external link length was greater than the internal link length, and the root system showed an outward expansion strategy. There were differences and similarities in the morphology and architecture characteristics of the root system of T. chinensis, exhibiting different adaptation characteristics to different soil water and salt conditions. Appropriately, increasing the groundwater salinity to brackish water can promote the root growth of T. chinensis, while higher salinity than brackish water will inhibit the root growth.