Changes in the photosynthetic characteristics of Plantago major plants caused by soil drought stress

Changes in net photosynthetic rate (P-N), stomatal conductance (g(s)), intercellular CO2 concentrations (C-i), transpiration rate (E) and water use efficiency (WUE) were measured in Plantago major L. plants grown under sufficient soil water supply or under soil water stress conditions. The plants had high P-N in a wide range of soil water potential and temperature regimes. Soil water had little effect on P-N under ambient CO2 concentrations, which was explained by a high carboxylation rate, but increased the dark respiration rate. Carboxylation activity at low C-i depended on RuBP regeneration, whereas at high C-i it depended on the phosphate regeneration rate. The g(s) and E values were low in plants under stress as compared to the controls that resulted in an increase of WUE. The results obtained show that Plantago major plants have different ways of adaptation to soil water deficit conditions.