Response of growth and anatomical structure of roots of Tamarix ramosissima seedlings to salinity and water stress

Tamarix ramosissima is a dominate shrub in the lower reaches of the Tarim river. Using a single factor control test with indoor potted plants, five moisture gradients were employed: groups CK, D1, D2, D4, and D5 (flooding), for which soil water contents were 75%, 55%, 35%, 15% field water capacity, and flooding treatment, respectively. For salt stress, the plant were treated with one of five salinity (CK, S1, S2, S3, S4), soil salt contents were 0.02%, 0.2%, 0.5%, 0.8%, 1.5%. We analyzed the effects of water and salt stress on T. ramosissima seedlings by measuring their growth, the roots of microstructure and ultrastructure. The results showed that: 1) under water stress, the flooded D4, promoted the seedling height, crown diameter and biomass accumulation significantly. The relative growth rate of the seedling height and crown width were 1.9 times and 0.9 times of CK, respectively. With the increase of salt concentration, relative growth rates of plant height and crown width increased, and the biomass decreased. In the treatment S3, T. ramosissima seedlings biomass decreased significantly at a rate of 83.42%. 2) Under salt stress, the vessel diameter of the root xylemdecreased, and the diameter of the S3 treatment decreased by 64.5% significantly when compared with that of the control, but vessel densities were higher than that of control group. Opposite trends of the vessel variations were observed under water stress. 3) There were swelling and deformation of starch grains in the root cells under different water and salt stresses, and accompanied by a large number of vesicles secreted. But there was a disintegration phenomenon of organelles under salt stress. Starch grains of the root cell in the leucoplast grew large, the membrane of leucoplast and nucleus disintegrated in the treatment S3. While it was not observed in the disintegration of root organelles under water stress. The results of the experiment proved that salt stress had more influence on T. ramosissima seedlings than water stress.