Phosphorus Nutrition of Lodgepole Pine and Sitka Spruce Stands as indicated by a Root Bioassay

A bioassay for determining P-deficiency, based on the rate ofuptake of ³²P-labelled phosphorus by roots from a standard solutionand developed on pot grown tree seedlings, has been appliedto roots from 10–18 year old lodgepole pine and Sitkaspruce stands in field fertilizer trials on peat. Rates of ³²-phosphorusuptake by roots were negatively related to quantities of P fertilizerpreviously given and to tree heights. The P content of firstwhorl needle samples were generally high but were not significantlydifferent between fertilizer treatments nor related to treeheights. There was, however, a general relationship between rates of³²P uptake by roots and P content of needles over all sitesand tree species. The bioassy, however, rapidly detects changesin internal P status of the tree which takes time to manifestitself in a change of needle P content. Preliminary work suggests that the bioassay detects a P-statusin trees, not identifiable from needle analyses. A number offactors which might influence the results of the bioassay andtherefore the field applicability of the method are discussed.