Influence of annual fluctuations in environmental conditions on chasmogamous flower production in Viola striata

摘要

The ecological factors affecting chasmogamous flower production by Viola striata, a perennial herb widely distributed in temperate forests of the northern and eastern United States and southern Canada, were studied in a natural setting. Forty semi-permanent quadrats were established at two sites in southern Ohio where populations of V. striata are abundant. Investigations were conducted from April to mid-June in 2002 and 2003. The number of chasmogamous flowers produced per individual per quadrat wasrecorded and the percentage of flowers becoming fruits per plant was measured as an indication of reproductive success. For each quadrat, canopy openness and soil properties (N, K, P, Ca, Mg, pH, and moisture) were documented and their effects on chasmogamous flower production were evaluated. Chasmogamous flower production was correlated in some, but not in all cases with light availability one to two weeks before the population reached the peak of blooming. Multiple correlations showed that phosphorusand calcium were important in all significant cases while light, magnesium, nitrogen and pH were important in some cases. Chasmogamous flower success was highly variable ranging from 1 to 100 % of success in fruit set possibly due to differential pollinator activity.