Plant canopy may promote seed dispersal by wind

Abstract

Seed dispersal has received much research attention. The plant canopy can intercept diaspores, but the effect of the plant canopy (the aboveground portion of a plant consisting of branches and leaves) on dispersal distance has not been explored empirically. To determine the effect of plant canopy on seed dispersal distance, a comparison of diaspores falling through open air and through plant canopy was made in a wind tunnel using three wind speeds and diaspores with various traits. Compared with diaspores falling through open air, the dispersal distance of diaspores falling through plant canopy was decreased or increased, depending on wind speed and diaspore traits. When falling through a plant canopy, dispersal distance of diaspores with thorns or those without appendages was promoted at low wind speed (2 m s^-1), while that of diaspores with low wing loading (0.5 mg mm^-2) and terminal velocity (2.5 m s^-1) was promoted by relatively high (6 m s^-1) wind speed. A plant canopy could increase seed dispersal distance, which may be due to the complicated updraft generated by canopy. The effect of maternal plants on seed dispersal regulates the distribution pattern and the species composition of the community.

Figure 1

Diagram of wind tunnel used in the study. (a) 1, Pitot tube; 2, differential pressure transmitter; 3, diaspore release device (seed release point was 90 cm above the ground, and placed 10 cm in the center of the canopy); 4, leafy plant (plant height was 1 m); 5, experiment section; 6, diaspore-blocking net; 7, switch; 8, steel tube; 9, bottom flap. (b) Inside view of the wind tunnel showing position of the plant. (c) Inside view of the wind tunnel without the plant. (d) Close-up view of plant inside the wind tunnel showing position of diaspore release device. The photograph in this figure was taken by Xuanping Qin.

Figure 2

Dispersal distance of diaspores of the 29 species that passed through plant canopy or through open air at three wind speeds. (a–c) wind speed was 2, 4, and 6 m s⁻¹, respectively. * (P < 0.05) and ** (P < 0.01) indicate significant differences between dispersal distance after passing through plant versus open air.

Figure 3

The effect of plant canopy on the dispersal distance of different diaspores. (a, b) Wind speed 2 and 6 m s⁻¹. Squares represent diaspores for which plant canopy decreased dispersal distance, and star represent diaspores for which plant canopy increased dispersal distance. Colors represent diaspore with different appendage: black without appendage; blue, a samara; violet, with wing; green, with thorn; red, with hair; pink, with balloon.