Xylem sap analysis for determining nutritional status of trees: Pseudotsugamenziesii

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Abstract
Xylem sap extraction of branches as a new field problem-solving technique in forestry, environmental pollution, and botany is described. The influence of extraction pressure, crown aspect, height into the crown, tree age, time of year and day and soil chemistry on the ion concentrations in xylem sap are discussed. Xylem sap extraction with a pressure chamber provides a good indication of the nutrient status of a species if the trees are of similar age, and if they are sampled at the same aspect, crown height, time of day, time of year, and on the same soils. P. menziesii (Mirb.) Franco (Douglas-fir), growing on nutrient-poor acid soils and moderately fertile alkaline soils showed significant differences in growth rate and in concentrations in the xylem sap and soil. Trees on the faster growth site (< 12 rings/2.54 cm) had significantly more Ca, K, Mn, P and N in the xylem sap. Trees on the poor growth site had high levels of Mg in the sap. Trees growing on the poor site which was also K deficient transpired more rapidly than those with faster growth. It is hypothesized that insufficient plant K could reduce the ability of the guard cells to control water loss. The stem water potential was slightly, but not significantly, higher on the poor growth site. Although there is no proof that the deficient ions are the cause of poor growth, they are suspect, given the similar water availability on the 2 sites. The concept of nutrient supplying potential of a tree, or its ability to supply its needles and meristems with water and nutrients is discussed. Distilled water soil extracts and foliar analyses would not have reflected the same ion relationships (deficiencies of excesses) that are evident in the xylem sap. Evidence for the factors controlling growth in these stands is being sought through fertilizer tests.