Temporal and spatial variation of pollen yield in natural populations of Pinus roxburghii

Abstract

Male components of the reproduction process in Pinus roxburghii were investigated for their variation in time and space as well as pollination, viz. flowering phenology, pollen production variability and pollen dispersal, for five successive years at two different locations (at the lower and higher elevations). The study reveals that elevation and the hour of the day are the main determinants of anthesis and microsporangium dehiscence, because both are related to temperature and humidity. The receptivity of ovulate cone strobili or female strobili occurred earlier at the lower elevation than at the higher elevation, with a longer receptivity period in the latter case. The phenology of male and female cones varied significantly between years and elevations. The determinations of pollen yield considered various sources of variability, i.e., the number of pollen strobili per branch, strobili per tree, microsporangia per tree and pollen grains per tree. Each of these parameters revealed significant year-to-year and elevation effects. Year-to-year variation in the production of pollen cone and pollen grains with mass production after a three-year period revealed a three-year cycle of masting in pollen production in P. roxburghii. The pollen dispersal decreased quickly with distance from the pollen source. As a consequence, a distance of 600 m was proposed as a minimum to prevent contamination by pollen in the management of seed orchards. The results ultimately suggest that the ample production of pollen grains per tree along with flowering synchrony and long dispersal of pollen grains results in homogeneity in large populations.