BOWKER, G.E.; Furman University: A mathematical evaluation of wind, gravitational, and electrostatic forces in pollen capture.

Under typical pollination conditions (clear skies), plants carry a net negative charge. This charge is located on the skyward distal parts of the plants, and is concentrated at points (e.g. the edges of leaves, the tips of needles, and around spiky stigmas). Consequently, electric fields are present around plants ranging from 100 V/m to 3 million V/m with the largest electric fields localized around the points. The possible role of these electric fields in the capture of wind-dispersed pollen remains unexplored. The electric force acting on a pollen grain is the product of the pollen�s charge and the electric field. Using direct measurements of pollen grain charge (10 to -10 fC) and size (5 to 20 mm radius), the movement of wind-dispersed pollen grains around charged �plants� was mathematically modeled. Plants were modeled as charged spheres 1m above the ground in a 100 V/m ambient electric field. In the absence of wind, electrostatic forces influence the capture of pollen and were often larger or equal in magnitude to gravitational forces. In some cases, for particularly light and charged pollen, plants were able to capture positively charged pollen millimeters away from small stigmas (radius 1 mm). When simple wind forces were introduced (as a position independent horizontal velocity ranging between 1 and 10 m/s), the importance of electrostatic forces decreased. Electrostatic forces were able to influence the capture of pollen found tens to hundreds of microns from the plant�s surface. In essence, the wind limited the time the pollen grains were present in high field regions. While the model is extremely simple, it highlights the fact that the electric force is localized and only important in pollen capture when pollen is close (100�s of mm to 1 mm) to the plant�s stigma.