STATE OF COENOPOPULATIONS OF THYMUS MONGOLICUS (LAMIACEAE) DEPENDING ON ENVIRONMENTAL CONDITIONS

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.