Comparative Contribution of СО2/Н2О Exchange Components to the Process of Adaptation to Drought in Xero-Halophytes from the Family Chenopodiaceae with Different Types of Photosynthesis

Abstract

Components of СО2/Н2О exchange (rates of apparent photosynthesis, transpiration, and dark respiration), as well as efficiency of photosystem I, growth rate, and proline content, were investigated in plants of the С3 species (Atriplex verrucifera M. Bieb), two populations of the С4 species (A. tatarica L.), and two populations of the intermediate С3–С4 species (Sedobassia sedoides (Pall.) Freitag & G. Kadereit), family Chenopodiaceae, in the course of adaptation to PEG-induced moderate osmotic stress (–0.4…–0.5 MPa). Two taken СО2 concentrations (400 and 200 ppm) enabled the examination of stomatal and metabolic contribution to the formation of the mechanisms of drought tolerance and estimate sensitivity of stomata. Under moderate water deficit, the С3 species showed drought tolerance and succulence and was notable for insensitive stomata. Examination of growth characteristics made it possible to reveal differences in productivity and tolerance between populations of the С4 and С3–С4 species. In spite of a different nature of carbon-concentrating mechanism (aspartate in С4 and photorespiratory in С3–С4), populations tolerant to water deficiency shared common features: less sensitive stomata and operation of the mechanism stabilizing water balance of the leaf cells probably due to proline and cyclic transport of electrons. Realization of such a strategy maintains coordination among parameters of СО2/Н2О exchange, which ensures a lower variability of dark respiration and a greater tolerance of plants to moderate osmotic stress. In nontolerant populations, adaptation mainly depends on stomatal closure, which probably results in upsetting the balance among parameters of СО2/Н2О exchange.