Response of Lawn Grasses to Salinity Stress and Protective Potassium Effect

The salinity effects on lawn grasses caused by mine salts (halite and carnallitite) due to road de-icing processes was the aim of this study. Biometric and physiological parameters were evaluated after salt dosage of 50 and 100 g m−2 applied to a lawn surface twice and four times, in weekly intervals. The alleviating effect to the salinity on the grasses from potassium enriched soil was also evaluated. Protective effect of potassium included mostly plasma membrane integrity and an increase in the level of photosynthetic pigments. This probably resulted in more efficient photosynthesis and thus increased lawn growth. Simultaneously, only a slight reduction in relative water content (RWC) was noted, so the recorded increase in proline level may indicate its participation in osmotic adjustment. Our results confirm the importance of proper, and even over-optimal, potassium fertilization of lawn grasses exposed to salinity. Moreover, it is advisable to use other fossil salts instead of halite for the de-icing of near-green areas. The mined salt carnallitite which, besides NaCl, contains about 30% of carnalite (KCl·MgCl2·6H2O) could be such a substance.

Ammonium and potassium effect on nitrate assimilation in cucumber seedlings

The effect of ammonium present in the induction medium toghether with nitrate on the activity of nitrate reductase (NR), nitrite reductase (NiR), glutamic acid dehydrogenase (GDH) and absorption and accumulation of NO₃^- in cucumber seedlings were investigated. Maximum NR and NiR activity in the cotyledons was observed when seedlings were supplied with KNO₃ as the sole source of nitrogen. When plants were supplied with NH₄NO₃ the presence of NH₄⁺ in the induction medium repressed by about 50 per cent the activity of both reductases in the cotyledons. Addition of K⁺ to this medium abolished completely the inhibitory effect of NH₄⁺. The effect of K⁺ cannot be replaced by that Na+ ions. On the other hand, ammonium has no effect on the level of NR activity in roots, while NiR was almost completely repressed. Under the experimental conditions ammonium, in the presence of nitrates, decreased the activity of GDH, but this diminution did not occur when the plants were supplied with K⁺ simultaneously. It has found that NH₄⁺ ions reduced NO₃^- absorption but at the same time, the ratio of NO₃- absorbed to that reduced was increased more than twice. The presumable mechanism of these phenomena is discussed.