Achene heteromorphism in Bidens pilosa (Asteraceae): differences in germination and possible adaptive significance.

Keliang Zhang,Linjun Yao,Jun Tao,Yin Zhang

doi:10.1093/aobpla/plz026

Abstract

Bidens pilosa (Asteraceae), a noxious weed in many ecosystems worldwide, produces large amounts of heteromorphic (central and peripheral) achenes. The primary aims of the present study were to compare the morphological, dormancy/germination characteristics of dimorphic achenes. Temperatures simulating those in the natural habitat of B. pilosa were used to test for primary dormancy and germination behaviour of fresh central and peripheral achenes. The effects of cold stratification, gibberellic acid (GA3) and dry storage on breaking dormancy were tested and the germination percentage of dimorphic achenes in response to osmotic stress was measured. Cold stratification, GA3 and dry storage significantly increased the germination percentage, suggesting both types of achenes had non-deep physiological dormancy. Variously pretreated central achenes had significantly higher germination percentages than peripheral achenes. Central achenes were more osmotically tolerant than peripheral achenes with a high germination percentage in high polyethylene glycol concentrations. These above differences among dimorphic achenes of B. pilosa increased the species’ fitness to adapt to heterogeneous habitats creating an ecological adaptive strategy that may allow B. pilosa to successfully thrive in stressful habitats.

Highlights

Environmental heterogeneity creates a natural selection pressure that increases the complexity of plant growth and reproduction (Gutterman 2002)
The number (t = 15.875, P < 0.001), mass (t = 7.702, P < 0.001) and length (t = 7.805, P < 0.001) of central achenes were significantly larger than peripheral achenes (Table 1), while the width (t = 8.016, P = 0.739) and height (t = 1.169, P = 0.709) were not significantly different
Central achenes imbibed water quickly, and achene mass increased by 51.21 ± 1.64 % in 0.5 h and by 59.28 ± 1.16 % in 1.5 h, at which time water imbibition had reached its maximum

Summary

Introduction

Environmental heterogeneity creates a natural selection pressure that increases the complexity of plant growth and reproduction (Gutterman 2002). Do the diaspores of heteromorphic species look different, but they may differ in numerous other ways, including size/mass (Ellner and Shmida 1984; Venable and Levin 1985; Rocha 1996; Liyanage et al 2016); dispersal ability (Venable 1985; Rocha 1996; Mandák and Pyšek 2001; Zhang et al 2015); dormancy and germination (Corkidi et al 1991; Wang et al 2008; Baskin and Baskin 2014; Zhang et al 2015; Liu et al 2018); and the reproductive allocation of plants grown from heteromorphic seeds (Cheplick and Quinn 1988; Liyanage et al 2016; Zhang et al 2017).

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Conclusion