Effects of soil moisture and light intensity on the chasmogamous and cleistogamous components of reproductive effort of Dichanthelium clandestinum populations

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Abstract
Plants from six New Jersey populations of Dichanthelium clandestinum, a perennial grass with chasmogamous and cleistogamous flowers on the same individual, showed significant differences in their responses to decreasing light and soil moisture, but chasmogamous reproductive effort was always less than cleistogamous. In an experiment with three light treatments, populations were significantly different in biomass allocation to chasmogamous and cleistogamous reproduction and varied as to which light treatment produced the most significant difference between chasmogamous and cleistogamous allocation. In an experiment using soil moisture gradient boxes, chasmogamous reproductive effort remained relatively constant over the moisture gradient for all six populations; however, for five populations, percentage biomass allocation to cleistogamous reproduction was significantly lower at low soil moistures. The population responses formed a continuum from no difference in allocation to cleistogamy along the moisture gradient to a sharp drop in cleistogamous allocation at the lower end of the gradient to a relatively steady decrease in cleistogamous allocation with decreasing soil moisture. These results indicate genetically based differences in phenotypic plasticity and underscore the need to use more than one population of a species when research is conducted on variation in relative allocation to chasmogamous and cleistogamous reproduction along environmental gradients.