Equations for the Motion of Airborne Pollen Grains Near the Ovulate Organs of Wind‐pollinated Plants

Niklas, Karl J.

doi:10.1002/j.1537-2197.1988.tb13457.x

Cited by 6 publications

(6 citation statements)

References 22 publications

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“…The results of both our aggregation and staking experiments confirm Niklas's (1987, 1988) hypothesis that diffuse and compact grass inflorescences rely on contrasting aerodynamic mechanisms to effect pollination. This conclusion is further supported by comparison of the proportion of pollen removed from anthers that reaches stigmas (pollen‐transfer efficiency).…”

Section: Discussionsupporting

confidence: 83%

“…Instead, different architectures must be alternate means of manipulating airflow. For example, Niklas’ (1987; 1988) studies demonstrated that at low airspeeds (10–50 cm s −1 ) a compact panicle ( Setaria geniculata ) captured more pollen by sedimentation than by direct inertial collision, as pollen grains aggregated on the leeward side of the inflorescence, where they recirculated. In contrast, a diffuse panicle ( Agrostis hiemalis ) captured pollen only by direct inertial collision.…”

Section: Introductionmentioning

confidence: 99%

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Inflorescence architecture and wind pollination in six grass species

Friedman

Harder

2004

Functional Ecology

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Summary 1.Inflorescence architecture and floral morphology vary extensively within the Poaceae, but the functional significance of this variation remains largely unknown. As grasses are wind-pollinated, their inflorescence diversity probably reflects alternate solutions to manipulating airstreams to enhance pollen export and import. We tested this hypothesis with two field experiments that contrasted pollen removal and receipt by compact and diffuse inflorescences. 2. In the 'aggregation' experiment, we tied together panicle branches of two species with diffuse inflorescences, creating more compact inflorescences. Aggregation reduced pollen removal from both species, probably by increasing boundary-layer thickness. The effects of inflorescence aggregation differed between the two species in a manner that is consistent with pollen-size differences, which could affect the ability of pollen grains to pass through the thickened boundary layer around stigmas. 3. The 'staking' experiment constrained inflorescence motion and revealed that culm characteristics contribute to the interaction between grass inflorescences and airstreams. In particular, inflorescence oscillation principally serves pollen removal for species with compact inflorescences, but is of primary importance in pollen receipt for species with diffuse architectures. 4. These results suggest that inflorescence architecture interacts with wind in a complex manner to facilitate pollination and supports the hypothesis that the extensive diversity of inflorescence architecture within the Poaceae represents evolutionary solutions to the physical constraints of wind pollination.

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Section: Discussionsupporting

confidence: 83%

Section: Introductionmentioning

confidence: 99%

Inflorescence architecture and wind pollination in six grass species

Friedman

Harder

2004

Functional Ecology

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“…In certain grasses, the large diameter of compact inflorescences appears counter‐adaptive for a structure intended for collecting particles by impaction on its windward surfaces and, therefore, it has been proposed that it functions instead as a recirculatory collector (Niklas 1987; Friedman & Harder 2005). Like previous studies that used stroboscopic photography (Niklas 1987, 1988) and fluid dynamic models (Niklas 1988) to investigate the leeward eddy of grass inflorescences, our study demonstrates leeward recirculation by pollen; in both of the grass species that we investigated, pollen accumulated on wire probes placed in the leeward eddy of a compact inflorescence exposed to oncoming airborne pollen in a wind tunnel and our CFD analyses visualized this leeward recirculation.…”

Section: Discussionsupporting

confidence: 63%

“…The lack of convergence among grasses on a single ideal form for the flowering stem suggests that various combinations of floral and inflorescence traits confer equivalent pollination success (Friedman & Harder 2005). Our study suggests that compact inflorescences, like diffuse inflorescences (Niklas 1988; Friedman & Harder 2005), accumulate pollen by impact collection. Given that the collection efficiency of an object is approximately inversely proportional to its diameter in the size range of grass inflorescences (Paw U & Hotton 1989), how can large and small diameter inflorescences have equivalent performance as pollen receptors?…”

Section: Discussionmentioning

confidence: 66%

The aerodynamics and efficiency of wind pollination in grasses

et al. 2010

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Summary1. Under natural selection for sexual success, the reproductive organs of plants should evolve to become highly effective pollen receptors. Among wind-pollinated plants, larger reproductive structures appear counter-adapted to accumulate pollen by impaction on their windward surfaces, because airborne particles are less able to penetrate the thicker boundary layer of larger targets. Therefore, it has been proposed that wind-pollinated plants with pollen receptors on relatively large structures, like some grasses (family Poaceae), are architecturally adapted to create downstream vortices in which airborne pollen recirculates before accumulating on leeward surfaces. From this basis, the striking diversity among the grasses in the architecture of their flowering stems has been attributed in part to the existence of these contrasting mechanisms for effecting pollen receipt, namely impact collection and recirculatory collection. 2. We investigated the relative importance of impact and recirculatory collection in grasses by analysing a model system in silico using Computational Fluid Dynamics and by conducting in vivo experiments, both in a wind tunnel and outdoors, using two grass species with compact inflorescences, Alopecurus pratensis and Anthoxanthum odoratum. 3. Irrespective of the experimental approach, we found that although pollen recirculated in the leeward eddies of inflorescences, over 95% of the accumulated pollen was collected by windward surfaces. 4. In A. pratensis, the collection efficiency (proportion of oncoming pollen collected) was between 5% and 20%, depending on wind speed in the range 0AE5-1AE9 m s )1 and these levels conform to those predicted by a mechanistic model of impact collection.5. Our results demonstrate that grass species with larger inflorescences are, like those with smaller inflorescences, primarily impact collectors of airborne pollen, which suggests that dissimilar reproductive morphology among species cannot be attributed to differentiation in the mode of pollen capture and, instead, requires reference to other factors, such as the need to produce, protect and disperse seeds of different sizes in different environments.

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“…Tall species expose their anthers to the faster airspeeds needed to remove large grains, because windspeed increases with elevation above the ground (Campbell, 1977). The tendency of large stigmas to deflect more air would be less disadvantageous for species with large pollen, both because the higher momentum of large grains makes them more likely to break free of deflected airstreams and collide with a stigma and because the higher settling velocity of large grains increases their sedimentation in eddies on the downstream side of stigmas (see Niklas, 1988). However, the positive relation between pollen size and both the number and total volume of pollen per floret indicates that species with large pollen invest more in pollen than species with small pollen (recall that all grasses produce one ovule per ovary).…”

Section: Possible Functional Differences Between Floret Size-infloresmentioning

confidence: 99%

Functional associations of floret and inflorescence traits among grass species

Friedman

Harder

2005

American J of Botany

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The aerodynamics of wind pollination selects for an intimate relation between form and function in anemophilous plants. Inflorescence architecture and floral morphology vary extensively within the Poaceae, but the functional implication of this variation remains largely unknown. Here we quantify associations between floret, culm, and inflorescence characteristics for 25 grass species in Kananaskis, Alberta, Canada, and consider whether different architectures may implement unique mechanisms to aid pollination. The species cluster into four categories defined by all combinations of floret size (small vs. large) and inflorescence architecture (compact vs. diffuse). Species differed significantly for all 18 traits that we measured, with 12 traits differing only between floret-size classes, three differing only between inflorescence types, and three differing among both (independently or by an interaction). Based on these morphological associations, we discuss the aerodynamic and functional consequences of each category for wind pollination. The independence of inflorescence and floral traits has probably allowed exploration of all possible combinations of inflorescence architecture and floret size during the evolution of the Poaceae.

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Equations for the Motion of Airborne Pollen Grains Near the Ovulate Organs of Wind‐pollinated Plants

Cited by 6 publications

References 22 publications

Inflorescence architecture and wind pollination in six grass species

Inflorescence architecture and wind pollination in six grass species

The aerodynamics and efficiency of wind pollination in grasses

Functional associations of floret and inflorescence traits among grass species

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