Impacts Of Polyploidy And Subsequent Natural Selection On The Ecophysiology Of Solidago Altissima

The evolutionary importance of polyploidy in plants is still a subject of much research. Polyploidy could be an evolutionary dead end, or it could lead to reproductive isolation and creation of new species. Goldenrod (Solidago altissima) is a North American herbaceous perennial with diploid, tetraploid, and hexaploid populations: diploids (MWD) and tetraploids are restricted to the Midwest while hexaploids occur in both the Midwest (MWH) and East (EH). Plants were grown in a common outdoor garden at Appalachian State University, and aspects of their morphology measured. EH had larger and more vertically oriented leaves than MWD and MWH, but MWH leaves had a higher specific leaf mass. Stomatal guard cells were larger in both hexaploids, but abaxial densities were not different between MWD and MWH, and were lowest in EH. Hydraulic flow rates were potentially higher in the hexaploids. A split-plot greenhouse drought experiment was performed. Photosynthetic rates (A) were initially highest in MWH, followed by MWD, and lowest in EH. A and stomatal conductance (gs) declined with time in both treatments, but more so in droughted plants after cessation of watering. MWD stomata displayed a threshold response to drought before closing whereas MWH did not EH was intermediate. MWH had the lowest water use efficiency, while during peak drought it was highest for EH. By the end of the experiment, cytotype differences for A, gs, and water potential were absent in both treatments. Results show substantial morphological and physiological differences among the hexaploids, indicating significant natural selection following polyploidization