Temperature responses of growth and photosynthetic CO2 exchange rates in coastal and desert races of Atriplex lentiformis.

Comparative measurements of CO2 exchange and growth rates were made on Atriplex lentiformis (Torr.) Wats. plants from populations native to coastal as well as desert habitats in southern California. While both had similar CO2 exchange rates at moderate growth temperatures, the desert plants had a substantially greater capacity to acclimate to high growth temperatures indicating that clear ecotypic differences in acclimation capacity are present in this species. This large capacity for photosynthetic acclimation resulted in nearly equal CO2 exchange rates of the desert plants under the different day temperatures characteristic of the desert habitat during the summer and winter months. In contrast, the photosynthetic CO2 exchange rates of the coastal plants was markedly reduced by high growth temperatures. The large acclimation capacity of the desert plants may function to maintain high productivities during both the winter and summer months but would not be required in the coastal plants because of the moderate temperatures throughout the year in their native habitat.Relative growth rates (RGR) of the coastal and desert plants were similar at 23°C day/18°C night and 33°C day/25°C night growth temperatures. At 43°C day/30°C night temperatures, however, the RGR of the desert plants was higher than that of the coastal plants. Thus, the larger acclimation capacity of the desert plants is related to a greater ability to maintain high growth rates over a wide range of temperatures as compared to the coastal plants. Small differences in allocation patterns could account for differences in the comparative photosynthetic responses and growth rates in each temperature regime.