A comparison of the phosphorus nutrition of Australian heath plants and introduced economic plants

Abstract

Dry weight and phosphorus fractionation data are presented for seven species grown over a range of phosphorus levels from 0.Wi to 10.0 p.p.m. in 2 iitres of water culture. As the phosphorus level was established at the beginning of the experiment and not afterwards adjusted, the maximum available phosphorus for each species (six plants per pot) was within the range of 0.3 to 3000 μg, plus seed phosphorus, per plant. The species were representative of two groups: species indigenous to the heath formation (Eucalyptus baxteri, Casuarina pusilla, Acacia suaveolens, and Banksia ornata) and introduced economic species now being grown with fertilizer on the same soils (Pinus radiata, Avena sativa, and Trifolium subterraneum).

Results showed that at least one of the economic species, T. subterraneum, was able to absorb phosphorus from nutrient solutions to the same extent as the native species.

No difference in growth, as measured by total dry weight, was observed in any species in the nutrient cultures containing less than 30 μg P per plant. 300 μg P per plant produced extra growth in all species except P. radiata, which responded only at 3000 μg P per plant. Nutrient imbalance temporarily decreased growth in all cultures containing 3000 μg P per plant.

An important factor in the growth of perennial heath species at low levels of substrate phosphorus is considered to be an increase in the percentage of orthophosphate in the plant at a time of the year when active growth is being made.

Other factors, such as the low death-rate of leaves and an efficient means of redistribution of nutrients from senescing leaves, may also be important.

The significance of these findings in relation to the growth of the indigenous species in the field is discussed. Species which possess all these characteristics have a decided advantage for survival in low phosphorus environments.