Ecological and Biological Features of Mertensia sibirica during Introduction in the South of Western Siberia

The objects of scientific interest include endemic, sub-endemic and relict species found among rare and endangered species of the Siberian flora, which are often used as valuable ornamental, medicinal, and honey plants. Mertensia sibirica (L.) G. Don fil. (Boraginaceae) is an East Siberian endemic species, a relict Pleistocene species, listed in the Red Books of Irkutsk Oblast, the Republic of Buryatia, and the Trans-Baikal Territory. The biology and ecology of M. sibirica are still poorly studied. The aim of this work was to study the ecological and biological features of Mertensia sibirica during its introduction in the Siberian Botanical Garden. The plants for the study were collected in 2010 in natural habitats in Chita Oblast (Chikoy Range) and were then planted in the introduction site of the Siberian Botanical Garden (Tomsk) located in the subzone of the southern taiga of Western Siberia. The experimental work and observations were done within the period from 2016 to 2021. The antecological studies were carried out; seasonal rhythms of development and the reproductive biology were studied in accordance with the commonly used methodological guidelines; seed viability, pollen fertility and viability were determined; stigma receptivity to accept pollen was assessed; the morphology of pollen grains was studied. When introduced in the subzone of the south of Western Siberia, M. sibirica exhibits a stable spring-summer green seasonal rhythm of development, typically grows in the second half of April and blooms from late May to June for 20-28 days. The study revealed the adaptation of M. sibirica flowers to entomophilic pollination, which is evidenced by the presence of primary (nectar, pollen) and secondary visual attractants (color, size of flowers collected in inflorescences), a long bloom period, and a number of morphological and dynamic adaptations that prevent autogamy (proterandry, hercogamy, etc.). The pollen grains of M. sibirica are single, 6(8)-furrowed-3(4)-po-rous, small. The fertility of pollen grains averaged 86%. The highest rate of viability of pollen grains (34.4%) was observed during germination on culture media supplemented with 15% sucrose. Seed and vegetative reproduction (by dividing the rhizome with renewal buds) and regular fruiting were observed. Self-seeding was not found. The number of flowers in the inflorescence varies from 8 to 52. Hemimericarps ripen at the end of July - the first half of August. Over the study years, the period from the beginning of blooming to the beginning of seed maturation averages 43-44 days. The percentage of fruit formation in different years ranges from 38.0 to 58.2% (with the average of 48%). The productivity index varies from 16.3 to 24.0%. M. sibirica exhibits an average of 19.2% of its potential for seed reproduction, which is due to an insufficient activity of pollinators when plants grow in a semi-shady area, a small number of normally developed hemimericarps, disturbance of embryogenesis, etc. To reduce seed yield losses caused by fruit shedding, the ripened hemimericarps should be regularly harvested. Seeds exhibit physiological dormancy, which can be terminated by cold stratification at +4 ... 5 °C for 1-1.5 months, followed by germination in the light. This increased the laboratory seed germination to 60.5% versus 10% in the control. The species is resistant to abiotic and biotic factors and recommended for introduction into culture in the south of Western Siberia. The article contains 4 Figures, 31 References The Authors declare no conflict of interest.

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