Environmental and physiological effects on pistillate flower production in Silene noctiflora L. (Caryophyllaceae)

Environmental and physiological elements influencing pistillate flower production are described for the gynomonoecious annual Silene noctiflora L. (Caryophyllaceae). We tested two environmental (temperature/physical disturbance) and two hormonal (gibberellin/ethylene) factors in greenhouse experiments. The effect of ethylene on rosette-stage seedlings was also tested in the field. A 6 degrees C increase in average greenhouse temperature (19 degrees/25 degrees C) caused a significant increase in the production of pistillate flowers, whereas the removal of buds, flowers, or branches did not cause any significant changes. There was a trend, however, for increased pistillate flower production as more biomass was rec moved. Of the two hormones tested, only ethylene caused a significant increase in pistillate flower production. This effect was more prominent when applications were given to rosette-stage seedlings in the field, compared with newly emerging buds in the greenhouse, probably because sex determination occurs early in bud development. The results of this study show that plasticity in pistillate flower production in S. noctiflora is influenced by changes in temperature and ethylene. Such temperature-related plasticity may represent an adaptive mechanism to increase outcrossing when conditions are more favorable for pollinator activity.