Effects of seed age, germination substrate, gibberelic acid, light, and temperature on seed germination in Flourensia cernua (Asteraceae), a Chihuahuan Desert shrub

摘要

Flourensia cernua seeds have far lower germination than the average recorded for arid land shrubs of the family Asteraceae. In this study, we investigated whether low germination was due to dormancy effects of embryonic immaturity, the absence of hormones (i.e., gibberelic acid), moisture conditions provided by the germination substrate, or specific conditions of light and temperature. Percent germination increased for seeds between 5 and 8 months and decreased for older seed ages. We observed no increase in germination when gibberelic acid was applied to seeds. Germination was higher on an agar substrate (33.47%) than on a substrate of filter paper with cotton (7.73%), suggesting the advantage of a constant moisture condition. The highest germination percentages were obtained with white and red light, indicating that germination might be favored under conditions of exposed seed or conditions of minimal canopy and litter cover. The highest germination followed a combined pretreatment of heat and cold. These pre-treatments probably reproduced thermic conditions encountered by F. cernua seeds under field conditions. Specifically, in nature, these seeds are dispersed during cold, winter months, but germinate later, after passing through the heat of the summer. Percent germination in our experiments rarely surpassed 30%, but is still considered low compared to those reported for other desert species of Asteraceae. We suggest that a dormancy mechanism, other than those considered in this study, accounted for low germination rates in F. cernua; alternatively, reduced germination might have been caused by endogamic depression.