Vol 108, No 1 (2023)

The application of the concept of population organization of ecosystems is an integral part in assessing the state of plant populations, as well as in modeling the response of vegetation to climate change. In this regard, it is especially important to focus on the plant species which are widespread in different habitat conditions, the study of their populations will reveal the range of adaptive capabilities of the species at different levels of organization (organismic, populational). One of such species is Thymus mongolicus (Ronn.) Ronn., an implicitly polycentric dwarf shrub, widely distributed in different environmental conditions of Tuva. The aim of the work is to study the features of the development and ontogenetic structure of T. mongolicus coenopopulations in different environmental conditions of Tuva.

Three coenopopulations (CP) were studied: in a sandy steppe on a plain (51°34'55.6"N, 94°21'25.5"E), in a steppified meadow along the river bank (51°18'26.4"N, 95°50'45.7"E), in a petrophytic high-altitude steppe on a talus slope (50°31'55.6"N, 91°07'25.5"E). The polyvariance of individual development, the ontogenetic structure of CP, the type of the ontogenetic spectrum of CP, the type of CP, the ecological and average density of CP, demographic parameters (recovery index, aging index, efficiency and age indexes, the rate of population development) were analyzed (Uranov, 1975; Tsenopopulatsii…, 1976, 1988; Zhukova, 1995; Zhivotovsky, 2001). The variability of population traits in different years of the study (2012 and 2021) was analyzed in the CP in the sandy steppe. Spearman’s correlogram was used to study the interrelationships between the traits of coenopopulations and environmental conditions.

In this research we revealed that a bimodal type of the ontogenetic spectrum with an absolute maximum on individuals of the young generative state (44.1%) is formed in the CP located in the sandy steppe. According to the peculiarities of the T. mongolicus development in the conditions of sandy steppes, the accumulation of individuals of a young generative state is associated with intensive vegetative reproduction. It was also revealed that their number increases with an increase in the amount of precipitation during the growing season, the height of the snow cover and the projective cover of the herbage. Due to increased competition for environmental resources, later on there is a rapid transition of young generative individuals to the old generative state, a second maximum is formed in the right part of the spectrum. The bimodal type of the ontogenetic spectrum is also formed in the CP located in the conditions of a petrophytic community on a steep slope (angle 40°) with a mobile rocky substrate. Virginal and young generative individuals accumulate in almost equal numbers (26.3% and 25.4%, respectively). Statistical analysis shows a relationship between the slope steepness and a high proportion of individuals of vegetative origin, and on the contrary, the number of individuals of seed origin is in inverse relation to the slope steepness. Ramets are characterized by low viability, they quickly pass into a subsenile state. In the CP in the conditions of a steppified meadow community, a left-sided type of the ontogenetic spectrum is formed. The maximum in the spectrum is accounted for young generative individuals. A strong positive relationship was revealed between the number of young individuals and such factors as the amount of precipitation during the growing season, leveled relief, static soil substrate, snow cover height, total projective cover of the herbage.

It is established that fluctuations occurring in different years in the CP located in the sandy steppe are expressed in the alternation of the processes of aging (in 2012) and rejuvenation (in 2021). The rejuvenation of the CP in 2021 occurs due to intensive particulation in young and mature generative states and coincides with a more favorable humidification regime. In addition, there is a decrease in ecological and average density due to a decrease in the proportion of old individuals over the past 10 years.

The revealed changes in the characteristics of coenopopulations due to the peculiarities of the development of individuals in specific habitat conditions should be considered as organismic and populational adaptation mechanisms that support the stable state of T. mongolicus coenopopulations in Tuva.

Scanning electron microscopy (cryoSEM) was used to study the micromorphology of the leaf epidermis surface of species of 6 genera: Sorbus L., Aronia Medik., Amelanchier Medik., Cydonia Mill., Cotoneaster Medik., Crataegus L. (Rosaceae). The surface of the leaves of the studied plants has two types of cuticular folding. In C. melanocarpus and S. aucuparia, larger and sometimes branched single cuticular strands, usually located on one cell, were observed. In other species, the folding has the form of numerous smaller parallel microstrands running along the long axis of the cell. Different degree of manifestation of both types of cuticular folding was observed on the surface of main epidermal cells on one or both sides of the leaf blades. In addition, the stomata and trichomes were surrounded by radial striations. Microstrands in A. spicata and S. aucuparia were also present on papillae in the area of stomata. All the studied species show stomatal dimorphism. Larger primary stomata with more pronounced cuticular strands are located at some distance or in the center of a group of several smaller secondary stomata. The proportion of primary stomata ranged from 5 to 17%. In the studied species, there is a negative correlation between the stomata length and stomata density, which is close to such correlation in other taxa.

The aim of this study was to assess the influence of unfavorable conditions of the mud volcano on the morphological features of pollen. Using light, scanning and transmission electron microscopes, the morphology of pollen of 20 species from 14 families of dicotyledonous plants growing on the Gyzmeidan mud volcano (Shamakhi) in the Republic of Azerbaijan has been studied. According to the aperture patterns of the pollen grains in the studied species, there are 5 pollen types: 3-colpate (Brassicaceae, Convolvulaceae, Fabaceae (Hedysarum sericeum), Lamiaceae, Linaceae), 3-colporate (Asteraceae, Cistaceae, Clusiaceae, Euphorbiaceae, Fabaceae, Rosaceae), stepanocolporate (Polygalaceae), heteroaperturate (Boraginaceae), pantoporate (Ranunculaceae).

No significant deviations of the main morphological features of pollen (shape, outline, size of pollen grains, type and number of apertures, exine sculpture, thickness and ultrastructure of the sporoderm) were found. Most of the studied species have a low percentage of deformed, underdeveloped, morphologically sterile, and atypical pollen grains. The number of deformed pollen grains differs between taxa. It can vary from single grains (most of the studied samples) to 56% in Potentilla pedata. However, its plants from the mud volcano produce less deformed pollen than the control ones (88%). This is most likely a feature of the taxon, rather than the influence of growing conditions.

The III All-Russian Conference with the international participation “Problems of studying and preserving the plant world of Eurasia”, dedicated to the memory of Doctor of Biological Sciences, Professor, Honoured Scientist of the Russian Federation, Leonid Vladimirovich Bardunov (1932−2008) was held on August 29 − September 3, 2022. It was housed by the Irkutsk Scientific Center of the SB RAS (Irkutsk) and the Baikal Museum of the SB RAS (Listvyanka township). The Conference was attended by colleagues from 24 cities and other settlements of Russia and from 4 cities of 4 foreign countries, representing 48 scientific, scientific-research, educational, environment-oriented domestic organizations as well as 5 foreign ones. Six plenary lectures, 52 sectional ones and 4 poster sessions on various problems of modern botany were presented at the Conference.