Growth and Development of Five Populations of Themeda australis in Response to Temperature

Abstract

Five populations of the widespread indigenous grass Themeda australis were selected from sites in south-eastern Australia with different temperature regimes. Differences between populations in some morphological characters are reported for plants grown in a uniform environment.

In one experiment shoot and root temperatures were varied together: in a second, root tempera- ture only was varied and shoot temperature kept constant. Results of both experiments show that there were few significant differences between populations in the number of tillers per plant formed at the various temperatures. Deniliquin plants had the greatest leaf area of all populations. Time to anthesis differed between some populations and these differences could be related to the temperature regimes of the sites of origin. Plants from Tantangara, the coldest site, flowered first and uniformly at low temperatures, and plants from Deniliquin, where the summer (flowering) temperatures are highest, flowered last at low temperatures but first and uniformly at high temperatures.

There were no differences between populations when mature post-flowering plants were subjected to low temperatures as radiation frosts but, when seedlings were frosted, the Adelaide Hills popula- tion from the most frost-free site was more frost-sensitive at - 6°C than all other populations.

It is concluded that genetic differentiation of ecological significance within the taxon T. australis has occurred not only for the photoperiodic response reported previously but also for a temperature response to flowering. While no differentiation has been shown for growth at medium and high temperatures, a difference is reported in the ability of one population to withstand a minimal temperature of - 6° as frost.