Meeting Abstract
Dispersal of diaspores plays a critical role in plant ecology and evolution. For the microscopic pollen or spore to break through the boundary layer, specialized discharging systems have evolved. In this study, we analyzed the high speed videos of sperm discharge in liverwort Conocephalum conicum by fitting the tracked trajectory with fluid dynamic models, and further took kinematic and climate data to estimate the dispersal range. Our results showed that a simple discharge could make sperms shoot at initial velocity of 8.77±3.31 m/s through an opening of 5 μm in width, atomized to droplets of 20 μm in diameter, and reach an average height of 3.1 cm, which was greater than what the ballistics model would predict for a single particle. Constant drag model fit the trajectory well, but underestimated the particle size by 1-2 orders of magnitude, suggesting its aerodynamic efficiency. During the mature season of antheridial disks, the sperms could break through the boundary layer generated by light air or light breeze at 2 m downstream. Light breeze could transport the sperms for over 6 m horizontally, and the dispersal range is affected by the variance of particle radius, discharging height, and wind speed. Compared to the classic discharging plants Sphagnum, C. conicum takes a different strategy by atomizing sperm fluids through a smaller opening, and prolonging discharge duration for the frontal sperm droplets to accelerate the surrounding air, which consequently makes the succeeding ones reach a greater height. This first study on discharge of sperm fluid particles in plants provides new insights into their dispersal mechanics, as well as bio-inspired spray design for various needs.
