Osmotic and saline effect on growth, water relations, and ion uptake and translocation in Phlomis purpurea plants

Abstract

The effect of different levels of water deficit and saline stress on physiological and morphological parameters in Phlomis purpurea plants was studied to evaluate their adaptability to such conditions. P. purpurea plants, grown under greenhouse conditions, were subjected to four irrigation treatments lasting 26 weeks: control (C, 1dSm−1, 100% water holding capacity), moderate water deficit (MWD, 1dSm−1, 60% of the control level of irrigation water), severe water deficit (SWD, 1dSm−1, 40% of the control level of irrigation water) and saline (S, 4dSm−1, nutrient solution containing 44mM NaCl). Aerial dry weight decreased in all three treatments, although this response was more marked in the water deficit treatments, especially SWD. Stem diameter, leaf number and leaf area were similarly reduced in both water deficit treatments, while only leaf area decreased in saline treated plants. Throughout the experiment, plant height remained similar in both control and saline treated plants but was inhibited 10 weeks after the beginning of the deficit irrigation. At the end of the experiment there were significant differences in plant height between the control and saline treatment. The control treatment produced a higher number of plants with flowers. Plants irrigated with saline water had higher Na+ concentrations in their leaves than in their roots and shoots, while the increase in the Cl− concentrations were similar in leaves and roots, suggesting some resistance to the movement of the latter ions from root to shoots. There was a negative relationship between leaf growth and Na+ concentration in the saline treated plants, in which the accumulation of salt in leaves was associated with osmotic adjustment, which was responsible for maintaining predawn and midday leaf turgor. However, no osmotic adjustment was observed in plants submitted to water stress. Root hydraulic resistance increased in SWD plants, in which the lowest leaf water potential values were recorded. In water stressed plants, in general the decrease of photosynthesis rate was mainly related with stomata factors, although the reductions observed in saline-stressed plants suggest that non-stomatal limitations to photosynthesis could also have been operating.