Comparative ecophysiology of the chromosome races in Viola adunca J.E. Smith.

Comparisons of net CO2 assimilation, dark respiration, leaf resistance, and leaf water potential were made between diploid and polyploid races of Viola adunca from the Cypress Hills, Alberta, Canada. The mean maximum net CO2 assimilation rate, at 20 C and 500 μE m-2 s-1 (phAR) was 26 mg CO2 g-1 h-1 (12 mg CO2 dm-2 h-1) for polyploids, and 23 mg CO2 g-1 h-1 (11 mg dm-2 h-1) for diploids. The difference is not statistically significant. Net CO2 assimilation rates at low (0° C) and high (40° C) temperatures were virtually the same for diploids and polyploids. There were no statistically significant differences between the chromosome races in light compensation or light saturation over the 0° to 40° C temperature range studied. Average dark respiration of the polyploid race at 20 C was 2.2 mg CO2 g-1 h-1 (1.0 mg CO2 dm-2 h-1) compared with 2.0 mg CO2 g-1 h-1 (0.95 mg CO2 dm-2 h-1) for the diploid race. The mean maximum leaf water potential of well watered plants was-7.9 bars for both ploidy levels. Minimum leaf resistance was ca. 3.6 s cm-1 for both ploidy levels. Maximum net CO2 assimilation rates in both ploidy levels occurred at-9 bars leaf water potential. Based upon the plant responses studied, there are no differences between chromosome races collected from the same general area, and the polyploids do not respond more favorably to extremes of temperature and water potential. Ploidy per se does not affect the response of Viola adunca to its environment in this particular case.