Distribution of С4 Plants of the Chenopodiaceae Family According to the Salinization Profile of the Kyzylkum Desert

In the lowlands (0–50 m above sea level), a predominance of C3 halophytes was found, while halophytes with C4 photosynthesis began to predominate at medium elevations (50–200 m above sea level). Above 200 m above sea level, a sharp decline in the contribution of halophilic flora to the biodiversity of native vegetation was detected. Thus, the penetration of halophytes above 200 m is limited by the presence of C4 photosynthesis as an adaptive characteristic to soil desalinization. A decrease in the succulence of leaf morphology in edificatory perennial plants of the Kyzylkum Desert (tamarix, saxaul, and camel thorn) was noted with a decrease in soil salinization. In the summer dry period, C4 photosynthesis provides a competitive advantage over C3 halophytes for survival on desalinated soils of elevated parts of the terrain desiccated during the summer. It was concluded that the acquisition of C4 photosynthesis by halophilic species is an adaptation of the photosynthesis of halophilic flora to seasonal desalinization and drying of the soil of the elevated parts of the Kyzylkum Desert. The morphological structure of the C4 leaf in most cases is characterized by features of the Kranz anatomy, which probably served as the structural basis for the formation of the cooperative mechanism of C4 photosynthesis. The competitive advantage of C4 species is due to the higher production efficiency of C4 photosynthesis under low atmospheric CO2 concentrations and high insolation and temperature due to the use of a special cooperative CO2 concentration mechanism near carboxylation sites. However, some data indicate the limitations of the biochemical hypothesis, which does not explain the species specificity of the correlation of climatic factors with the prevalence of C4 monocotyledonous and dicotyledonous plants. The study aimed to evaluate the effect of landscape-topographic factors on the distribution of C4 photosynthesis in halophytes of the Kyzylkum Desert. The evaluation was performed based on the analysis of anatomical changes of leaves of plants representing the main edificatory floristic groups of the Kyzylkum Desert using the natural soil salinity profile and the distribution of the C4 species of the Chenopodiaceae family in the biodiversity of the local plant communities. The study was conducted in the desert territory of the Kyzylkum Desert, which extends between the two largest rivers of Central Asia: Syr Darya in the east and Amu Darya in the south and southwest. The relief of the terrain decreases from the piedmont plains in the southeast to the coast of the Aral Sea in the northwest. The study used a botanical-geographical map of the Kyzylkum Desert, topographic maps of the area, navigator, and GPS altimeter to reconstruct the prevalence of Chenopodiaceae species. The characteristics of the sampling sites of soil and plant material are presented in Table 1. The study focused on the morphological structure of the leaf and photosynthetic shoots of the species representing the main edificatory groups: halophilic and xerophilous flora of the Kyzylkum.