Characteristics of isolated Tilia nasczokinii Stepanov (Tiliaceae) populations near Krasnoyarsk

Tilia genus in Siberia is a relict element of flora which grows as isolated plots. Some authors consider Siberian lime as Tilia sibirica Bayer. Two small lime populations near Krasnoyarsk have been described as a separate species Tilia nasczokinii Stepanov. Both T. sibirica and T. nasczokinii retain the ambiguous status in the modern international nomenclature of plants. The facts concerning the presence of a number of relict nemoral species among T. nasczokinii satellites indicate the relict origin of its populations. Recent investigations have ascertained that T. nasczokinii species is essentially genetically removed both from T. cordata and T. sibirica. This confirms the relict origin of the populations. The aim of our investigation is to determine the number of lime plants and their sizes, to find out the ontogenetic structure and reproduction character of relict T. nasczokinii populations and to estimate the vitality of the plants. T. nasczokinii populations are located on different banks of the Yenisei River. The fist population is on the left bank (from 55°57'34''N, 92°28'07''E to 55°57'51''N, 92°30'10''E) and the second one is on the right bank (55°57'26''N, 92°46'41''E) (See Fig. 1). We made a general geobotanical description of phytocenosis. The ontogenetic status was determined for each T. nasczokinii plant. The sizes (height and diameter at 1.3 m) and the vital status were established for virginile and generative plants. In order to assess the contribution of vegetative and seed reproduction, we calculated the index of genotypic richness R (Dorken, Eckert, 2001) and clonal heterogeneity D* (Arnaud-Haond et al., 2007) using the GenClone v2.0 program (Arnaud-Haond and Belkhir, 2007) on the basis of genotype analysis of 11 polymorphic nuclear microsatellite loci (Ekart et al., 2021). Also, we determined the number of unique multy-locus genotypes (MLG) in every population. As a result of our research, 305 T. nasczokinii plants were found in the left bank population (39 of them are large trees, others belong to the undergrowth) and 196 plants (30 from them are rather large) on the right bank. T. nasczokinii is a part of pine and pine-birch forests with Carex macroura Meinsh. and other grasses which have the average closeness of crowns (0.55-0.65). On the right bank, all the lime trees grow on the area of 1.5 ha. On the left bank, they are located on the area of 370 ha as individual trees or as groups up to 7 big trees and 5-96 small plants. The distance between the groups is rather long: from 500 to 1000 m. It is demonstrated that both investigated populations have a similar ontogenetic structure (See Fig. 2). Juvenile and immature plants occupy the biggest part (84% on the left bank and 77% on the right). Not many current year sprouts were found both on the left (2%) and on the right bank (8%). As it is typical for the lime, senile plants were practically absent (only one plant was found on the left bank). The calculated indexes R and D* were rather high (0.731 and 0.987 in general for both populations). We showed that most of the analyzed plants are not the parts of clones but there are some clones with a few ramets. In the left bank population, from 77 analyzed individuals we recognized 61 unique MLG and 10 (16.4%) of them have 2-5 ramets. On the right bank, 32 individuals were analyzed and among 19 MLG there were 3 (15.8%) clones with 2, 5 and 9 ramets. The genotypic diversity of T. nasczokinii is higher than that of T. sibirica in Kemerovo region (R=0.661) but slightly lower than that of T. cordata (R=0.938). The high genotypic diversity demonstrates the significant role of seeds in the self-reproduction of T. nasczokinii populations. The contribution of vegetative reproduction is also considerable (33.8% on the left and 50% on the right banks). It turns out that the sizes of virginile trees in both populations are very close (See Table), the differences in the average values are insignificant at p=0.05. The generative trees in the left bank population are higher than in the right bank population, and they are rather close in diameter. In general, for both populations the virginile trees have the average height of 6.0±0.31 m and trunk diameter of 5.1±0.32 cm, with the generative trees being 13.7±0.71 m and 12.2±0.56 cm, accordingly. Individuals of these groups have the habitus of single-stemmed (56.4% on the left and 73.3% on the right bank) and bush-like trees (See Fig. 3). T. nasczokinii is much smaller than both T. sibirica and T. cordata. The large part (58% on the left bank and 77% on the right) of T. nasczokinii trees has the vitality status “healthy” (See Fig. 4). Thus, both T. nasczokinii populations are characterized by the normal ontogenetic structure with the complete left-handed spectrum. They are able to reproduce both by seeds and by vegetative organs. The existence of unique T. nasczokinii populations is possible only if the natural phytocenosis with its participation is preserved.