Ecological, Floristic, Physiological, and Biochemical Characteristics of Calcicoles of the Zhiguli Mountains

Abstract The ecological, floristic, physiological, and biochemical characteristics of plants growing on carbonate outcrops of the Zhiguli Mountains, one of the unique botanical-geographic regions of Russia, have been investigated. All species are confined to the petrophytic steppe coenoses in two distinct biotopes but differed in their geographic distribution: five of them represent Middle/Lower Volga and South Ural species, three are endemic to the Zhiguli mountains, two represent Southeast European species; East European-Asian group, South European, Middle- and Central Asian groups, and European-Asian group are represented by one species each. The studied calcicoles exhibit diverse life forms, including perennial herbs, dwarf-shrubs, and shrubs. Regarding the soil substrate, these species are classified as obligate and facultative calcicoles. The leaf biomass and architecture, pigment content, membrane complex parameters, and components of the antioxidant systems were determined as parameters characterizing the structural, physiological, and biochemical properties of calcicoles. The analysis of the combination of these traits revealed differentiation among plant groups depending on the soil substrate (facultative/obligate species), zonal-geographic element, and life form. To elucidate the reasons of these differences, the variability of individual variables across different ecological groups has been analyzed. The calciphilous flora of the Zhiguli mountains represented by various taxa and ecological groups, has been found to be capable of using complementary strategies for adaptation to carbonate substrates. The confinement of obligate calcicoles to the specific growing conditions of this region is realized through the lower leaf density, lower susceptibility to oxidative processes, and more effective antioxidant defense. These traits are particularly maifested in the case of Zhiguli endemics. The more active involvement of phenolic compounds, sugars, and proline in protection against oxidative stress can be considered as one of the possible reasons for the endemics’ thriving in specific local biotopes.