Daily, seasonal, and interannual variability of airborne pollen of Araucaria angustifolia growing in the subtropical area of Argentina.

Abstract

Araucaria angustifolia is an anemophilous conifer native to Southern America threatenedwith extinction, with a noticeable decrease in itsdistribution area and seed production. To betterunderstand the reproductive dynamics, the aerobiological curves obtained with Hirst methodology wereanalyzed during 7 years in San Antonio (Misiones,Argentina), including productivity, seasonality, start,end, duration, and peak, along with the role ofmeteorological/seasonal climate factors. An alternation between 1 year of high pollen values (1685 pollengrains day m-3, on average), followed by 2 years of aprogressive reduction (456 pollen grains day m-3, onaverage) in productivity, was observed. This patternwas negatively related to temperature during themonth preceding pollination; August minimumtemperature yielded the best fit (r = - 0.9, p \0.01). In only 36 days, includingOctober, 90% of the annual pollen was released. Thedaily pattern showed a curve with higher concentrations between hour 8 and hour 14. The daily maximumat hour 10 suggests pollen inputs from local sources.The eolic transport is limited due to the big size andweight of the grains and the unfavorable atmosphericconditions that prevail in this subtropical forest (highhumidity and low wind speed). The average airbornepollen curve showed a peak during the secondfortnight of October. Rain induced a noticeablereduction in pollen concentration modifying the shapeof the aerobiological curve. Aerobiological analysesprovide reliable information for the design of conservation strategies, such as ex situ planting and selectiveharvesting of seeds.