Biology of Thymus dmitrieva Gamajun. (Lamiaceae) in the protected area (Aksu-Dzhabagly Reserve)

Abstract

The aim of our work was to study the architecture and morphogenesis of Ihymus dmitrievae Gamajun. (Lamiaceae Lindl.) growing in the Tien-Shan mountains to identify morphological mechanisms of its adaptation to growing conditions. The main habitat of the species is steppe communities in forest, subalpine and alpine zones of the mountains. According to AP Gamayunova and AA Dmitrieva (1964), T. dmitrievae in different habitats is characterized by the density of head inflorescence, leaf size, calyx teeth shape and its pubescence. Information about the biology of this species is absent in literature. We conducted our study on the territory of the Aksu-Zhabagly Reserve (Western part of the Talas Alatau): 1) the Kshi-Kaindy upriver (42°22'31"N, 70°34'37"E, altitude of 2206 m above sea level), the upper limit of the juniper belt, forb-fescue high-mountain steppe, dark brown soil among the outcrops of stones; 2) middle reaches of the Kshi-Kaindy river, (42°24'25"N, 70°34'42"E, altitude of 1808 m above sea level), the belt of junipers, bushy forb-feather-grass mountain steppe, soils are leached and covered with cobbles. The life form of T. dmitrieva was specified using ecological-morphological classification of life forms by IG Serebryakov (1962). The biomorph type was established in accordance with OV Smirnova et al.’s (2002) phytocoenotic classification developed on the features of spatial distribution of shoots, buds and roots of plants. The morphogenesis phases of T. dmitrieva were selected according to the characteristics given by OV Smirnova and supplemented by NP Savinykh and VA Cheryomushkina (2015). In 25 individuals of each ontogenetic state, we calculated the number of vegetative and generative shoots in the bush structure, their length, the number of compound skeletal axes and partial bushes, and the bush diameter. The data for each feature are presented as an arithmetic mean with a standard error. When describing the shoot system of T. dmitrievae, we used the architectural approach (Caraglio and Edelin, 1990; Barthelemy and Caraglio, 2007; Millan et al., 2019), according to which an architectural unit consisting of the main (or maternal n-order) composite skeletal axis, the composite skeletal axis of the 1st (or n+1) order, single shoots of the 1st order formation, branching shoots and ephemeral shoots was distinguished. The analysis of shoot formation, the pattern of death of shoots and the method of their growth showed that T. dmitrievae was characterized by the life form of the dwarf shrub. Depending on the characteristics of the substrate, we revealed polyvariance of individuals. In the areas of substrate free from stony-gravelly outcrops, the morphogenesis of individuals is characterized by a variety of phases (in genets: primary shoot, primary bush, clump; in ramets: partial bush, the system of partial bushes), the clump phase being the longest of them (until 16 years) (See Fig. 1). The structure of individuals is formed by repeating three architectural units: orthotropic-plagiotropic, plagiotropic and orthotropic (See Fig. 3). The presence of an individual of simultaneously three architectural units in the structure ensures the seizure of the territory and leads to the compaction of the bush. In this case, several centers of consolidation form in the structure of the bush (See Table). In individuals growing on a soil and stony substrate, morphogenesis consists of two phases that take place in genets: primary shoot and primary bush. The phase of the primary bush is the longest. It occurs in the immature state and continues until the death of the individual in the old generative state (until 22 years) (See Fig. 2). The structure of individuals is formed by multiple repeating of two architectural units: plagiotropic and orthotropic (See Fig. 3), which leads to intensive growth of the bush. The paper contains 3 Figures, 1 Table and 31 References.