Accumulation,distribution, and physiological contribution of oxalic acid and other solutes in an alkali‐resistant forage plant,Kochia sieversiana,during adaptation to saline and alkaline conditions

Kochia sieversiana (Pall.) C. A. Mey is a forage plant in the family Chenopodiaceae, which can grow in extremely alkalinized grasslands at pH levels of 10 or higher. Kochia sieversiana often contains a large amount of oxalic acid. In the present study, seedlings of K. sieversiana were exposed to the following conditions: nonstress, salt stress (molar ratio of NaCl : Na₂SO₄ = 1:1, salinity: 200 mM), and alkali stress (molar ratio of NaHCO₃ : Na₂CO₃ = 1:1, salinity: 200 mM). By determining and analyzing various physiological factors such as the concentrations and distribution of different organic acids (including oxalic acid) in various parts of K. sieversiana, the concentrations of inorganic ions (K⁺, Na⁺, Cl^–, SO$ _4^{2-} $ , etc.), the organic solutes (proline, betaine, and soluble sugar) in shoots, and the accumulation and distribution of oxalic acid in K. sieversiana, the physiological contribution of oxalic acid to K. sieversiana adaptability to saline and alkaline conditions was investigated. Results show that oxalic acid mainly accumulated in shoots, and that its concentration was highest in mature functional leaves where photosynthesis productivity was based and lowest in old stems and roots, regardless of plant treatment (nonstress, salt, or alkali conditions). Under nonstress, salt, and alkali conditions, the concentrations of oxalic acid in mature leaves were 8%, 10%, and 12% of their dry weights, respectively, and were 1%, 0.7%, and 0.6% of dry weights, respectively, in roots. There were varying effects of salt and alkali conditions on oxalic acid concentrations in different parts of K. sieversiana. Oxalic acid concentration increased in leaves, did not change significantly in young stems, and decreased in old stems and roots. The present analysis shows that oxalic acid exists as an organic anion in K. sieversiana. Consequently, oxalic acid not only plays a crucial role in osmoregulation and pH adjustment, but it also is the dominant contributor of negative charge, playing a key role in maintaining ionic balance in vivo. Oxalic acid in K. sieversiana shoots is a key substance on which the adaptation to saline and alkaline conditions is based.