Interactive effects of various salt and alkali stresses on growth, organic solutes, and cation accumulation in a halophyte Spartina alterniflora (Poaceae)

Abstract Soil salinization and alkalinization frequently co-occur in nature, but very few studies focus on the interactive effects of various salt and alkali stresses on plants. A study quantifying the effects of various salt and alkali stresses on growth, organic solutes, and cation accumulation in a halophyte Spartina alterniflora was conducted. The experiment consisted of six levels of salinity (100, 200, 300, 400, 500, and 600 mM) in each of six pH levels: A (pH 7.1 ± 0.02), B (pH 8.1 ± 0.17), C (pH 8.8 ± 0.14), D (pH 9.8 ± 0.14), E (pH 10.4 ± 0.08), and F (pH 10.8 ± 0.10). Survival rate, relative growth rate (RGR), tiller rate, rhizome number, leaf chlorophyll content, root activity, electrolyte leakage rate (ELR), and content of proline, soluble carbohydrates, Na + , and K + were determined. The results showed that S. alterniflora was capable of surviving all treatments under low pH (pH ≤8.30) regardless of the levels of salinity. However, high pH in conjunction with salinity sharply reduced survival rate. As expected, the interactive effects of salinity and high pH on RGR, tiller rate, rhizome number, leaf chlorophyll content, and relative root activity were additive. Moreover, ELR and Na + /K + ratio increased with increasing salinity and pH. The content of Na + increased, while K + decreased with increasing salinity and pH, suggesting competitive inhibition between absorptions of Na + and K + . The content of proline and soluble carbohydrates both increased with increasing salinity and pH, suggesting that alkali stress may also cause accumulation of these organic solutes. The deleterious effects of high pH or salinity alone were significantly less than those of combined high pH and salinity. For salt–alkali mixed stress, it is concluded that reciprocal enhancement between salt and alkali stress is a characteristic feature. We also constructed models to elucidate this feature of mixed salt–alkali stress. Multiple linear regressions found strong correlations between all physiological indices and the three stress factors. However, the effects of the three stress factors on the physiological indices were different in magnitude. Overall, salinity is the dominant factor, while pH and buffer capacity are secondary. The combined action of salinity, pH, and buffer capacity should be considered when evaluating the strengths of salt–alkali mixed stress.