Does high pH give a reliable assessment of the effect of alkaline soil on seed germination? A case study with Leymus chinensis (Poaceae)

Alkaline soils, characterized by high pH, are representative of degraded regions throughout the world. Studying germination in relation to alkalinity can contribute to understanding how species cope with such conditions. Although the effects of pH have been widely studied, it is unknown whether germination response to pH gradients created with buffer solutions is representative of the conditions experienced in alkaline soils. Our aims were to (1) determine if high pH gives an accurate assessment of the effects of alkaline soils on germination, and (2) identify the inhibitory factors for germination in alkaline soils. Using Leymus chinensis seeds, germination was tested over a gradient of pH solutions prepared using Tris (50 mM and 100 mM) and H2O buffers and eight germination media prepared from non-alkaline and alkaline soils with different pH and electrical conductivities (EC). Additionally, solutions of 10-100 mM NaCl, Na2SO4, Na2CO3 and NaHCO3 were used to determine the main ions inhibiting seed germination. H2O-buffered pH had no effect on seed germination, and seed germination was much lower at all pH levels in 50 mM Tris-HCl solutions (pH 7.0-10.35) than in the H2O control (pH 7.05). No seeds germinated in 100 mM Tris-HCl buffers irrespective of the pH. In alkaline germination media (pH 10.04-10.61), high germination was obtained only at low EC. The rank order of the inhibitory effect of salts was Na2CO3 > NaHCO3 > NaCl > Na2SO4. Buffer solutions used to simulate alkaline environments did not provide a reliable indicator of the effects of alkaline soils on seed germination. High pH of alkaline soil had no negative effects, and results suggest that salt composition and concentration, especially CO3 (2-) and HCO3 (-), are key inhibitors.