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

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Abstract
A bioassay for determining P-deficiency, based on the rate of uptake of 32 P-labelled phosphorus by roots from a standard solution and developed on pot grown tree seedlings, has been applied to roots from 10–18 year old lodgepole pine and Sitka spruce stands in field fertilizer trials on peat. Rates of 32 -phosphorus uptake by roots were negatively related to quantities of P fertilizer previously given and to tree heights. The P content of first whorl needle samples were generally high but were not significantly different between fertilizer treatments nor related to tree heights. There was, however, a general relationship between rates of 32 P uptake by roots and P content of needles over all sites and tree species. The bioassy, however, rapidly detects changes in internal P status of the tree which takes time to manifest itself in a change of needle P content. Preliminary work suggests that the bioassay detects a P-status in trees, not identifiable from needle analyses. A number of factors which might influence the results of the bioassay and therefore the field applicability of the method are discussed.
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