Twice is better: A new reproductive season in Helianthus annuus as a result of climate change?

Background/Question/Methods

Helianthus annuus is the most common species of sunflower in North America and is commonly found growing and flowering year-round in Corpus Christi, Texas.  In previous studies we found no differences in growth and photosynthetic characteristics between progeny from summer-active and winter-active plants from the Corpus Christi area during each season.  This poster presents results from a winter experiment in which we grew progeny from winter-active Corpus Christi plants and progeny from summer-active plants from San Marcos, Texas.  Plants were grown individually and with 2 or 4 associates from the opposite plant type.  Currently, H. annuus does not grow during the winter in San Marcos.  Our hypothesis is that there is no difference in growth and photosynthetic characteristics between progeny from winter-active Corpus Christi plants and summer-active San Marcos plants during the winter season in Corpus Christi.  If so, in a future warmer climate when winters in San Marcos are more similar to Corpus Christi winters, plants already in the San Marcos area would be able to grow and reproduce during that season.

 Results/Conclusions

In the Corpus Christi winter growing season, progeny from San Marcos summer-active plants are doing just as well as are progeny from winter-active Corpus Christi plants.  An Analysis of Covariance (ANCOVA) of target plant dry weight from an additive design competition experiment shows no significant difference for size between progeny types (P = 0.06) and no significant difference in competitive effect of progeny type (P = 0.94).   We believe that the effect of a single low dry weight Corpus Christi plan is responsible for the P value being 0.06.  We do not believe that there is any indication of a biological difference between the two types of plants. These results, along with our previous results, indicate that H. annuus could extend its growing season in regions farther north of our area if winters become warmer in these areas.