Sodium (Na+) and silicon (Si) coexistence promotes growth and enhances drought resistance of the succulent xerophyte Haloxylon ammodendron

Abstract

Abstract: Haloxylon ammodendron (C. A. Mey), a C4 perennial woody species of the desert areas of northwest China, is a succulent xerophyte that has excellent adaptability to adverse arid environments. Our previous investigations showed that sodium (Na+) has a positive effect on the growth and drought resistance of Haloxylon ammodendron under drought conditions, which was closely related to high Na+ accumulation in photosynthesizing stems (PS). In this study, we further investigated the effect of Na (as sodium chloride, NaCl), Si (as silicic acid, H2SiO3) and Na and Si coexistence (NaCl + H2SiO3) on the growth and drought resistance of Haloxylon ammodendron under water deficit (30% of field water capacity) in a pot culture experiment. The results indicate that 0.3 g kg−1 NaCl, 0.2 g kg−1 H2SiO3 and Na and Si coexistence (0.3 g kg−1 NaCl + 0.1 g kg−1 H2SiO3) could effectively mitigate deleterious impacts of drought stress on the growth of Haloxylon ammodendron, and the coexistence of 0.3 g kg−1 NaCl + 0.1 g kg−1 H2SiO3 could more effectively mitigate deleterious impacts of drought stress on the growth of Haloxylon ammodendron than the 0.3 g kg−1 NaCl or 0.2 g kg−1 H2SiO3. The coexistence of 0.3 g kg−1 NaCl + 0.1 g kg−1 H2SiO3 encourages plant height, crown diameter, biomass and main root length and, concomitantly, accumulates a higher concentration of Na+ and Si (SiO2) than Potassium (K+) to adapt to arid environments. In comparison with the 0.3 g kg−1 NaCl or 0.2 g kg−1 H2SiO3, a significant increase in total Na+ concentrations by 18.4% and 135.3%, and a significant increase in total Si (SiO2) concentrations by 92.6% and 15.6% (compared with 0.3 g kg−1 NaCl or 0.1 g kg−1 H2SiO3) were observed in plants grown in the presence of the coexistence of 0.3 g kg−1 NaCl + 0.1 g kg−1 H2SiO3. These findings suggest that the positive roles of Na and Si coexistence in the drought resistance of Haloxylon ammodendron might be due to the ability of the plants to accumulate a high concentration of Na+ as an important physiological osmoregulator, while still absorbing and accumulating a large amount of Si (SiO2) to cope with drought stress. However, the physiological mechanisms underlying how Si, Na, and Si and Na coexistence promote growth and enhance drought resistance of Haloxylon ammodendron need further research.