Evaluation of salinity tolerance in four suitable tree species in urban forestry

The saplings of four well known urban trees, namely: Acer negundo, Fraxinus angustifolia, Robinia pseudoacacia and Thuja orientalis were regularly watered by 0, 40, 80, 120 and 160 milimole per liter NaCl, during a three-month period in growing season and some of their quantitative and physiological characteristics of growth and development were measured, immediately after pot-planting in greenhouse conditions. In general, saplings of Robinia demonstrated better survival characteristics, as the results indicated. It was the same story for increasing in diameter growth and weight of stem: a decline in these factors for Acer (from 120 and 40 mMol/l) and Fraxinus (from 40 mMol/l), respectively and no change in Robinia. Significant decrease in leaf sodium and increase in leaf potassium contents were recorded only in Robinia. Other results were rather different or controversial. As salt become more accumulated, for example, the least height increasing was observed in Acer, along with Thuja, or the ratio of Na+/K+ raised from 120 and 40 mMol/l for Fraxinus and Thuja, respectively. The leaf calcium content was increased only in Acer (from 80 mMol/l), and no change was observed in leaf magnesium content. In general, for all broadleaved species, saltier water was associated with more leaf decoloration, as expected.