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

Ma, Hongyuan, Yang, Haoyu, Lü, Xiaotao, Pan, Yuepeng, Wu, Haitao, Liang, Zhengwei, Ooi, Mark K. J.
Plant and soil 2015 v.394 no.1-2 pp. 35-43
Leymus chinensis, alkaline soils, alkalinity, buffers, case studies, ions, pH, seed germination, seeds, sodium bicarbonate, sodium carbonate, sodium chloride, sodium sulfate
BACKGROUND AND AIMS: 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. METHODS: 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. RESULTS: 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. CONCLUSIONS: 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.