Genetic differentiation of Black Saxaul,Haloxylon aphyllum (Chenopodiaceae), along a soil salinity gradient in the Kyzylkum Desert
The Kyzylkum Desert lies in the Turan Lowland, Central Asia. Its landscape is a plain crossed by sets of aligned low hills and closed depressions. The vegeta tion has a complex spatial structure, which is condi tioned by micro and mesotopographic heterogeneity of the environment and associated processes, such as salinization and desalinization, changes in groundwa ter table depth, etc. (Akzhigitova et al., 2003). Species with the С4 type of photosynthesis are an essential component of halophyte–xerophyte plant communi ties indicative of salinization–desalinization processes in Kyzylkum soils (Akzhigitova et al., 2003; Toderich et al., 2009).
Among these plants, a special place belongs to the black saxaul, Haloxylon aphyllum (Minkw.) Iljin (Che nopodiaceae), a major edificator species that also plays a very important role as a soilstabilizing and for age plant and a source of firewood for local residents (Nikitin, 1966; Gintzburger et al., 2003). This treelike shrub (1–9 m tall) with succulent photosynthesizing shoots can grow in topographic depressions on sandy, solonchak, or gypsum soils, forming large populations extending over tens of kilometers (Nikitin, 1966; Gintzburger et al., 2003). Natural populations have a certain optimum of genetic diversity established in the course of evolution, and disturbances in the genetic balance of a population system lead to its degradation, which has consequences for the state of the species and ecosystem as a whole (Altukhov, 2003). To gain an insight into such microevolutionary processes, it is necessary to identify ecological factors responsible for local genetic differentiation of populations, which takes place in response to heterogeneity of the environment (e.g., differences in moisture or nutrient supply) manifested even within distances of no more than several hundreds of meters (Nevo, Krugman, and Beiles, 1994; Mitton, Grant, and Yoshino, 1998; Prentice et al., 2000).
The effect of soil salinity on local genetic differentiation of populations has not been studied sufficiently. Therefore, the purpose of this study was to analyze the role of this factor in the genetic diversity and differentiation of H. aphyllum populations.