Effects of seed morphology and orientation on secondary seed dispersal by wind

Abstract

Aims Understanding how diaspore (hereafter “seed”) morphology and orientation affect secondary seed dispersal by wind is important to link seed dispersal and post-dispersal processes, such as seed lodging, predation and germination. This study aims to describe the effects of seed morphology and orientation on secondary seed dispersal by wind via mechanistic modelling. Methods We extend the mechanistic model of Schurr et al. (2005) in order to describe how secondary seed dispersal by wind is affected by wind conditions, ground surface, seed morphology and orientation. The model simulates the initial landing orientations, dispersal distances and stopping orientations of individual seeds. To parameterise the model, we measured orientation-specific vertical seed projection and seed lift-off velocity (the wind speed at which a seed starts moving on the ground) of the asymmetric seeds of heterocarpous Zygophyllum xanthoxylon, and determined orientation-specific model parameters that depend on properties of seeds and/or the environment. To validate the model, we conducted wind-channel experiments in which we released seeds of Z. xanthoxylon onto a sand-coated tar paper, and recorded the initial landing orientations, dispersal distances and stopping orientations of the seeds. Important findings The extended model could precisely predict secondary dispersal distance, and explain up to 99% of variation in the observed proportions of seeds which stopped in various orientations. The model predicts that secondary dispersal distance increases with wind speed and decreases with aerodynamic roughness length, and that there might be a positive correlation between dispersal distance and germination success.

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“…We used seed height and seed surface area as proxies for seed dispersal syndrome, because these dimensions influence primary wind dispersal (a seed departure from mother plant, (Sheldon and Burrows 1973; Jongejans and Telenius 2001) and secondary wind dispersal (a seed lifts off ground by wind power, (van Tooren 1988; Schurr et al . 2005; Zhu et al . 2022).…”

“…Secondary dispersal distance strongly depends on the lift-off velocity, which is influenced by seed height and the planform area of a seed exposed to airflow (van Tooren 1988; Schurr et al . 2005; Zhu et al . 2022).…”

“…Primary dispersal is mainly related to dispersal height and terminal falling velocity, which is influenced by seed morphology (Sheldon and Burrows 1973;Jongejans and Telenius 2001). Secondary dispersal distance strongly depends on the lift-off velocity, which is influenced by seed height and the planform area of a seed exposed to airflow (van Tooren 1988;Schurr et al 2005;Zhu et al 2022). Classicially, seed shape seed shape was measured by the roundness or closeness of a seed to specific shape, such as ellipse or cardioid (Cervantes et al 2016) and linked with seed persistence in soil seed bank (Moles et al 2000;Laughlin 2014).…”

“…We used seed height and seed surface area as proxies for seed dispersal syndrome, because these dimensions influence primary wind dispersal (a seed departure from mother plant, (Sheldon and Burrows 1973;Jongejans and Telenius 2001) and secondary wind dispersal (a seed lifts off ground by wind power, (van Tooren 1988;Schurr et al 2005;Zhu et al 2022). Primary dispersal is mainly related to dispersal height and terminal falling velocity, which is influenced by seed morphology (Sheldon and Burrows 1973;Jongejans and Telenius 2001).…”

“…Primary dispersal is mainly driven by dispersal height and terminal falling velocity, which are influenced by seed morphology (Sheldon and Burrows 1973;Jongejans and Telenius 2001). Secondary dispersal distance strongly depends on the lift-off velocity, which is influenced by seed seed height and the seed surface area (van Tooren 1988;Schurr et al 2005;Zhu et al 2022). There are many other seed physiological traits associated with seed germination that are not commonly tested, such as base water potential, cardinal temperature, thermal time and hydrothermal time for germination (Bradford 2002;Hardegree et al 2013).…”