Calypso bulbosa (Orchidaceae) on the northern border of its distribution range (Komi Republic, Russia): population structure, fruit and seed set

Abstract

Orchids form one of the most threatened plant families in the world. For a successful conservation of these species, comprehensive studies of their biology and ecology are necessary, and long-term demographic studies are especially valuable in this regard. This article aimed to present results of long-term observations of two populations of Calypso bulbosa , a rare orchid included in the Red Data Book of the Russian Federation, on the northern border of its range, in the Komi Republic (northeast of European Russia). Seasonal development, ontogenesis, number of individuals and structure of populations, and reproductive success of C. bulbosa were studied. The influence of weather factors on the peculiarities of the small and large life cycles of this species has been revealed. Populations of C. bulbosa located in various habitats differ in a number of characteristics (e.g. number of individuals, spatial placement of plants, their size, the number of generative individuals). The fruit set of C. bulbosa on the northern border of the range is quite low (28.4%). This is compensated by the formation of a large number of tiny (0.68 × 0.11 mm) seeds. The pollination efficiency of the species is affected by the temperature of the beginning of the growing season and precipitation of the second decade of June, as well as by the flowering time. With deterioration of habitat conditions (more northern or shaded habitats), the seed index increases. The seeds become more volatile, which increases chances of reaching favourable sites for seed germination. One capsule of C. bulbosa contains an average of 19 900 seeds. The real seed production is 6500 seeds per plant. The seed production of C. bulbosa varies greatly year by year; it depends on the weather conditions of the first decade of June. In both studied populations, the presence of juvenile individuals (from 3.3% to 41.4%) during all years of the study indicates a successful seed regeneration, which, along with vegetative growth, ensures the stable existence of C. bulbosa populations on the northern border of the range.