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Abstract Detail

Reproductive Processes

Klahs, Phillip [1], Clark, Lynn [2].

Slower than predicted settling velocity of pollen in the forest grass Diarrhena obovata (Gleason) Brandenburg increases dispersal potential.

The economically and environmentally important flowering plant family Poaceae predominately utilizes wind to transfer pollen during sexual reproduction. Wind pollination (anemophily) relies on environmental conditions which vary across different habitats. The functional morphology of grass reproductive structures, the biomechanical properties of grass pollen, and the timing of anthesis have evolved under these different sets of environmental constraints (i.e., wind speeds, chance of precipitation, temperature cues shaped by seasonality). The settling velocity (Vs) of an object describes the maximum velocity of fall through still air and is determined by the shape, size, and density of the pollen grain, as well as the aerodynamic drag exserted by surface features. Previous studies have directly measured or predicted the Vs of grass pollen grains using drop tower experiments or the Stoke's Law equation respectively, but these studies have only included grass species of open habitat types. To improve our understanding of the biomechanics shaping grass pollination, beyond crops and weedy species of a singular habitat, anthesis of a native forest species of grass, Diarrhena obovata (Gleason) Brandenburg, was documented in its natural habitat through 1) a series of pollen traps in a natural environment; 2) pollen diameter measurements; 3) characterization of the surface ornamentation of the pollen grains using scanning electron microscopy (SEM); 4) prediction of the Vs using the equation; and 5) measurement of Vs with drop tower experiments. D. obovata flowers released pollen for a period of 9 days in July that straddled two days of inclement weather. The ability to regulate anthesis indicates the presence of an arresting mechanism hypothesized to be a required character of anemophilous plants. The pollen of this species is spherical with an average diameter of 38.74 μm which predicts a Vs of 4.48 cm s-1. The measured Vs of 3.77 cm s-1 was a statistically slower rate of fall, and the 15.8% reduction of speed between predicted and measured may be caused by a pollen grain density specific to this species or the surface features observed with SEM. This functional trait increases the dispersal distance of the pollen or, from an alternative biomechanical angle, lowers the necessary wind speeds to establish pollen grains in air currents. Both would be highly desirable for a species of grass living in forests.

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1 - Iowa State University, 251 Bessey Hall, 2200 Osborn Drive, Ames, IA, 50011, United States
2 - Iowa State University, Department Of Ecology, Evolution, And Organismal Biology, 251 Bessey Hall, 2200 Osborn Dr., Ames, IA, 50011, United States


Presentation Type: Oral Paper
Session: RP2, Reproductive Processes 2
Location: /
Date: Thursday, July 22nd, 2021
Time: 1:15 PM(EDT)
Number: RP2004
Abstract ID:226
Candidate for Awards:None

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