Effects of Various Mixed Salt-Alkaline Stress Conditions on Seed Germination and Early Seedling Growth of Leymus chinensis from Songnen Grassland of China

Ryegrass has a relatively high salt tolerance and is considered to be a promising species for both foraging and turf purposes in salt-affected soils in China. While annual ryegrass and perennial ryegrass are two different species, they have similar genomes. However, little is known about their physiological and molecular response mechanisms to salinity stress. Here, biomass, chlorophyll fluorescence, and inorganic ion and organic solute content were measured. 2-DE-based proteomic technology was then used to identify the differentially expressed proteins in the salt-treated seedlings. The results showed that salt stress reduced growth and photosynthesis in the seedlings of both species, but much more so in annual ryegrass. With increasing salinity, the Na⁺ concentration increased while the K⁺ concentration decreased in both species, and the sugars and proline increased as the primary organic solutes used to cope with osmotic stress. Additionally, proteomic analysis revealed 33 and 37 differentially expressed proteins in annual and perennial ryegrass, respectively. Most of the identified proteins were involved in carbohydrate and energy metabolism, photosynthesis, genetic information processes, amino acid metabolism, stress defense, and protein synthesis and folding. The results suggest that the two-ryegrass species had different physiological and proteomic responses. These findings can provide new insights into physiological mechanisms by which ryegrass species respond to salt stress.

Two neutral salts (NaCl and Na₂SO₄) and alkaline salts (NaHCO₃ and Na₂CO₃) were both mixed in 2:1 ratio, and the effects of saline and alkaline stresses on growth and physiological changes in oat seedlings were explored. Result showed that biomass, water content and chlorophyll content decreased while cell membrane permeability significantly increased under alkaline stress. Saline stress did not have obvious effect on pH value in tissue fluids of shoot and root, but alkaline stress increased pH value in root tissue fluid. The contents of Na⁺, Na⁺/K⁺, SO₄^2- increased more, and K⁺, NO₃^-,H₂PO₄^- decreased more under alkaline stress, the Cl^- content increased obviously under saline stress but had little change under alkaline stress. The increments of proline and organic acid were both greater under alkaline stress, but organic acid content kept the same level under saline stress. Alkaline stress caused more harmful effects on growth and physiological changes in oat seedlings especially broke the pH stability in root tissue fluid. Physiological adaptive mechanisms of oat seedlings under saline stress and alkaline stress were different, which mainly took the way of accumulating organic acid under alkali stress but accumulating Cl^- under saline stress.

The oat (Avena sativa) is a kind of cereal grain, which has high saline-alkali tolerance. This experiment was carried out to investigate and compare the growth and physiological changes of oat seedling. Oat was grown under five concentrations of NaCl stress (48, 72, 96, 120 and 144 mmolL^-1). The results showed that NaCl stress had no effect on the survival rate and organic acids. With the increasing of the NaCl concentration, tiller number, the chlorophyll, K⁺, Ca²⁺, NO^3-, H²PO^4- contents, shoot length, the shoot biomass, and shoot water content were decreased significantly. However, the Cl^-, Na⁺, Na⁺/K⁺, SO₄^2- and proline contents were extremely increased. K⁺, Ca²⁺, dry weight, and water content of shoots changed greater than that of roots. While Na⁺ and Na⁺/K⁺ of shoots changed less than that of roots. When NaCl concentration was less than 96 mmolL^-1, the length, dry weight, and water content of roots had no significant changes. Based on this investigation, it can be concluded that oat seedlings accumulated more proline, Cl^- and SO₄^2- to maintaining osmotic and ion balance. In addition, NaCl stress had no significant effect on the growth of roots, and the roots can play the interceptive and protective role with a stronger salt tolerance. The roots can change the distribution of Na⁺, then it decreased the harm on the shoots and increased the tolerance of oat seedling.