Reproductive phenology and seed development of Gentianella caucasea in different habitats in the Central Caucasus

Abstract

Flowering phenology, seed development and reproductive characteristics influencing seed set were investigated in four populations of Gentianella caucasea, a therophyte growing in different habitats (subalpine meadows, pastures and alpine grassland) along an altitudinal gradient between 1900 and 2700m a.s.l. in the Central Caucasus. During the growing season phenological stages were recorded and samples were collected at short intervals. The embryological stages and the time course of seed formation were determined microscopically using the interference contrast technique.Considerable differences in phenological dates, seed development and seed set were observed between the population growing in the alpine grassland, the population in a hay meadow which is regularly mown during the first decade of August, and the population on an intensively grazed sheep pasture. The extremely low seed set connected with a high percentage of anomalous and abortive ovules as observed in the latter population can be regarded as a criterion for severe stress due to habitat disturbance. Very little variation in reproductive characteristics was found among the population growing in a short-grass vegetation extending from 2200 to 2750m a.s.l. Along such an altitudinal transect the developmental processes would be expected to be retarded in view of the decrease in temperature with increasing altitude. However it appears that, for herbaceous plants, it is not the adiabatic lapse rate which is important, but the specific microclimatic conditions, which on southward slopes are more favourable even at higher altitudes.