Effects of salinity, N-nutrition and humidity on photosynthesis and protein metabolism ofChloris gayana Kunth

Abstract

Under high atmospheric humidity, Rhodes grass plants responded favourably to an increase in nitrate fertilization. Under low atmospheric humidity an optimum point was reached at lower N-treatment. Plants' growth was improved by a salinity treatment of up to 100 mM, at high atmospheric humidity. A higher salt concentration cancelled the favourable effect of added nitrate. The rise in yield which follows salt or nitrate treatments is apparently combined with an increase in activity of the key photosynthetic enzymes, Phosphoenol pyruvate carboxylase and Ribulose biphosphate carboxylase. A similar rise in activity is seen in nitrate reductase, a key enzyme in nitrogen metabolism. Evidently, all three enzymatic systems are not damaged in high salt treatments, and the potential photosynthetic capacity remained practically uneffected in all treatments. As no correlation could be found between transpiration and growth curves, it is assumed that the supply of CO2 is also unhampered. Thus, the major negative effect of salinity, seems to be on protein synthesis, which eventually leads to disturbed growth.