Effects of water and salt for groundwater-soil systems on root growth and architecture of Tamarix chinensis in the Yellow River Delta, China

To test the patterns of the root morphology and architecture indexes of Tamarix chinensis in response to water and salt changes in the two media of the groundwater and soil, three-year-old T. chinensis seedlings were chosen as the research object. Groundwater with four salinity levels was created, and three groundwater level (GL) were applied for each salinity treatment to measure the root growth and architecture indexes. In the fresh water and brackish water treatments, the topological index (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-like branching pattern. Under different GLs and 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. The treatment with fresh water and a GL of 1.5 m was the most suitable for T. chinensis root growth, while the root growth of T. chinensis was the worst in the treatment with saline water and a GL of 0.3 m. T. chinensis can adapt to the changes in soil water and salt by regulating the growth and morphological characteristics of the root system. T. chinensis can adapt to high-salt environments by reducing its root branching and to water deficiencies by expanding the distribution and absorption area of the root system.