BOWKER, G.B.: The role of electrostatic forces in wind pollination

Electrostatic forces are found throughout the terrestrial environment. Even when the weather is clear, a 100 Volt per meter (V/m) electric field is present between the atmosphere and ground. Consequently, organisms in electrical contact with the ground have negative charge induced on their surfaces. The surface charge is concentrated at points – such as on stigmas and the edges of leaves. The electric field around these points is magnified and reaches values of many hundreds of thousand volts per meter. When charged airborne objects such as pollen grains encounter these large electric fields they experience large electrostatic forces. The electrostatic force on the pollen is the product of its charge multiplied by the ambient electric field at its position. Thus, even moderately charged pollen experiences large electrostatic forces in the electric fields surrounding plants. The charge on pollen varies between 0 and 100 fempto-Coulombs (fC). The electrostatic field around the plants can generate a force on the pollen grains producing velocities comparable to the gravitational settling velocity (0.02 to 0.06 m/s). Typically, each species has some positively charged pollen grains as well as some negatively charged pollen grains. Negatively charged pollen grains are repelled from the plant, while positively charge pollen grains are attracted to the plant. Thus, electrostatic forces may play a role in pollen capture.