Impact of Weather Conditions on the Population Dynamics and Reproductive Success of Platanthera bifolia (L.) Rich. in the Komi Republic

Abstract

The results of an 8-year study of the Platanthera bifolia (L.) Rich. (Orchidaceae) population on the northern border of its range (the Komi Republic, northeast of the European part of Russia) are presented. A negative correlation is found between the size of the leaves of this species and precipitation at the beginning of the current growing season. The number of flowers and their sizes are influenced by the weather conditions of August of the previous growing season. There are no significant differences in plant height or inflorescence length over the years. The number of the population is high for this species (400 plants); it is negatively affected by a lack of moisture in the previous year. Observations of mapped individuals reveal the duration of the presence of plants in different phases of ontogenesis. The ontogenetic spectra of the studied population correspond to the basic spectrum of the species; in some years, the dominance of juvenile specimens is observed, which is associated with the renewal waves characteristic of the species. Pollination efficiency is not affected by the number of flowers in the inflorescence or their size; it is related to the level of moisture availability of the territory. Seeds of P. bifolia (0.60 × 0.13 mm) in the studied area are smaller than in the southern parts of the range of this species. Significant differences in the size of seeds in different years of the study are revealed; the main influence on them is the weather conditions of July. A tendency to an increase in the volume of air space in the seed in wetter years has been found, which contributes to their better distribution under adverse weather conditions. Real seed productivity of P. bifolia varies by year from 25 400 to 40 800 seeds; this indicator is associated with the level of moisture availability of the current growing season. The presence of juvenile individuals (18.3–51.8%) in all years of study indicates successful seed renewal in this population. The number of juvenile individuals correlates with the moisture level of the previous growing season.