Print PageHelianthus annuus and H. argophyllus are the most common species of sunflowers in Nueces County, Texas. In previous studies, we found H. argophyllus was restricted to sandy soil sites, while H. annuus was nearly restricted to clay soil sites. While H. argophyllus senesces in October, it is not uncommon to see H. annuus growing and flowering during every month of the year. Data from a related study indicates that there are different cohorts of H. annuus throughout the year. In a first attempt to understand the differences between summer and winter active plants we examined photosynthetic rates of H. annuus in July and January. Ultimately, we would like to determine if progeny from winter-active and summer-active plants do equally well in both growing seasons and if H. annuus could extend its growing season in regions farther north of our area if winters become warmer in these areas.
Results/Conclusions
An ANVOA indicates photosynthetic rates for summer-active plants are significantly higher than are photosynthetic rates for winter-active plants (P < 0.0001). However, the rates for winter-active plants are not low for most plant species. Temperature and to a lesser extent light level may be partly responsible for these differences. However, other factors such as water availability may be more favorable during the winter season. We hope to determine if differences in photosynthetic rates between plants growing during different seasons are due to differences in photosynthetic characteristics between these populations or are due to different environmental conditions during these seasons.
