Ma. Leck et al., GERMINATION ECOLOGY OF BIDENS-LAEVIS (ASTERACEAE) FROM A TIDAL FRESH-WATER WETLAND, Bulletin of the Torrey Botanical Club, 121(3), 1994, pp. 230-239
Eight or more weeks of cold stratification (5-degrees-C) were required
to break dormancy in achenes of Bidens laevis (L.) BSP from a tidal f
reshwater wetland. When achenes began to come out of dormancy, they ge
rminated to 50% first at 35/20-degrees-C, and then with additional str
atification the minimum temperature for 50% germination decreased to 1
5/6-degrees-C. Germination of stratified achenes was inhibited by dark
ness and was completely prevented by hypoxia (inundation in closed jar
s). Seeds inundated in open jars and those in Petri dishes, however, g
erminated to > 80%. Germination declined sharply with depth of burial
(0, 1, and 5 cm). Moisture regime (drained, saturated, and inundated)
also significantly affected germination, but afterripening condition (
cold greenhouse or 5-degrees-C) altered the effect. Interaction betwee
n depth of burial and moisture regime was significant (P less-than-or-
equal-to 0.05). At the end of the period of burial, nongerminated ache
nes transferred to the soil surface were capable of germinating over a
19 mo period. Storage conditions (approximately 0, 20, 50, and 100% r
elative humidity) of fresh achenes for 1 wk to 4 mo followed by at lea
st 16 wk stratification at 5-degrees-C had no effect on total germinat
ion. However, storage at approximately 0% RH for 4 mo reduced the rate
of germination. Light and oxygen requirements are reflected in the re
sponses to burial and inundation. These, in turn, provide a mechanism
for maintenance of a persistent seed bank (> 1 yr) following winter af
terripening of achenes in the field.