There has been little consideration of possible influence of the substrates used for seed germination in experiments examining the effect of stresses, such as salinity, on germination and early seedling growth. The effect of salinity on the early seedling growth of soybean (Glycine max L.) cv. Williams was therefore studied using a range of NaCl concentrations (0-161 mMolal NaCl) using both a paper towel and a hydroponic method. Seeds were initially germinated in paper towels at different salinities (0-161 mMolal NaCl) and subsequent growth was examined using either a new paper towel or a hydroponic method at the same salinity. Seedlings were harvested 10d after transfer and both fresh and dry weight assessed. The concentrations of Na+, K+ and Ca2+ in the seedling and in the solution extracted from paper towels were determined by Flame Photometry and Atomic Absorption Spectrophotometry. Seedling growth was reduced with increased salinity, but the effects were markedly less when experiments were conducted in paper towels. Seedlings were able to grow in paper towels at an external NaCl concentration of 161mMolal NaCl, when a Na+ concentration 2.3mg g-1 FW was recorded in the roots. However, in the hydroponic method, seedlings failed to grow even at an external NaCl concentration as low as 12 mMolal, when the Na+ concentration in the root was 1.6mg g-1 FW. Analysis of the solutions soaking the paper towels revealed that 4.25 mMolal Ca2+ was available to the seeds in the paper towel method in saline conditions. Addition of 4.25 mMolal Ca2+ in the hydroponic method at 30 mMolal NaCl resulted in enhanced seedling growth. This suggests that paper towels may influence the response of soybean seedlings to NaCl due to the release of other ions from the paper towels into the solution soaking the towels. The role of Ca2+ in reducing Na+ uptake or protecting the seedling against the toxic effects of Na+ is discussed.

Keywords