Stem tissue phosphorus as an index of the phosphorus status of Banksia ericifolia L. f.

The effects of P fertilizer rate on shoot growth and the total P concentrat ion of the whole shoot, new and mature leaves, symptom leaves and stems of Banksia ericifolia L. f., a P-sensitive species, were investigated in a six month greenhouse pot experiment. Shoot dry weight of plants growing in an Australian sedge peat, coarse sand and perlite potting mix (1:1:1) increase d with up to 100 mg P L-1 supplied as a six month controlled release P (0:1 8:0) fertilizer, but was reduced by toxicity at the highest application rat e (200 mg P L-1). Plants receiving this treatment developed chlorotic new a nd mature leaves. Leaf symptoms observed at rates of 60-100 mg P L-1 were c onfined to old leaves and were related to the P concentration of the shoot. Growth was not affected at these rates. The P concentration of stems was s trongly influenced by P supply. This tissue acted as a sink for excess P, h elping to regulate the P concentration of leaves. The approximate range of P concentrations in stem tissue, associated with greater than 90% of maximu m shoot dry weight, was 0.5-1.5 g P kg(-1) tissue dry weight. This was grea ter than that calculated for mature leaves (0.5-0.8 g kg(-1)) or for whole shoots (0.5-1.2 g kg(-1)). This wider range, and the capacity to store P in excess to requirement, makes the stem a better index tissue for plant P st atus than either leaves or whole shoots.