Subpollen particle release from different species of the invasive allergenic genus Ambrosia: the effect of rainwater composition and wind speed

Allergen-containing subpollen particles (SPPs) are micrometric or sub-micrometric particles (0.12–5 µm) released from pollen. They are able to reach the lower airways, causing allergenic reactions. SPP release occurs through the pore of intact grains or by rupture of the whole grain. In this paper the results of two laboratory experiments investigating the dynamics of SPP release for three alien species of Ambrosia genus are shown. Rainwater composition and wind speed were considered, by simulating different conditions, in accordance with a fully orthogonal experimental design. The principle response variable was the total percentage of SPPs-releasing pollen grains; also the percentage of intact grains releasing SPPs through the pore and of broken SPPs-releasing grains were considered. Both osmotic and mechanical shock caused the discharge of SPPs but different results were observed. The highest number of releasing grains was recorded in case of acid solution and 20 knots wind speed. Moreover, wind and rainfalls caused SPPs release through different mechanisms. Wind mainly provoked a mechanical shock leading to grain rupture, whereas rainfall caused mainly SPPs release through the pore of intact grains. Comparing species, the effect of wind and at least in some cases also that of rainwater appeared to be less relevant for Ambrosia trifida than for Ambrosia psilostachya and Ambrosia artemisiifolia. The obtained results suggest a species-specific response of Ambrosia species to wind speed and rainwater that lead to a different release of SPPs and then to a species-specific impact on allergy according to the characteristics of their growth environment.