Diurnal cycles of pollen dispersal are an important aspect of gene flow between wind-pollinated plants. Previous attempts to correlate these cycles with variation in meteorological factors have had little success. In Ambrosia artemisiifolia (common ragweed) and other species which produce aeroallergenic pollen, these cycles also present a major burden to public health. In a large field dominated by A. artemisiifolia, we collected measurements of low-atmosphere pollen concentration and pollen release from individual A. artemisiifolia flowers. We then constructed a relatively simple model that relates early morning variations in relative humidity to the probability distribution of anther dehiscence initiation timing and incorporates quantitative data on the progression of diurnal pollen release from individual male flowers. The model successfully predicts normalized pollen concentration above the field. We suggest that the extension of a tiny floral organ unique to this genus and some closely related taxa explains a ubiquitous, but previously overlooked, large-scale feature in patterns of A. artemisiifolia pollen dispersal. Our study shows that pollen release at the flower scale is a physiological characteristic that is intrinsically bimodal, but highly asynchronous anther rupture caused by variations in relative humidity sometimes obscures this effect and determines the overall pattern of pollen release at the scale of the entire field. We suggest that future attempts to predict diurnal pollen dispersal cycles should consider direct observations of species-specific floral development and morphology.
All Science Journal Classification (ASJC) codes
- Global and Planetary Change
- Agronomy and Crop Science
- Atmospheric Science