Xylem sap analysis for determining the nutrient status and growth of Pinusponderosa

Abstract

Natural variation in the ion concentration of the xylem sap of ponderosa pine (Pinusponderosa Laws.) in Montana was studied relative to tree height, crown aspect, age, time of day and year, species, tree to tree (within-stand variation), soil chemistry, and growth prediction. Xylem sap was extracted from branches at 2.4–2.7 MPa. The sap was analyzed chemically for 13 ions and total nitrogen. Extraction and analysis are fast and inexpensive. The top third of the crowns of P. ponderosa normally had higher ion concentrations in the sap for all but four ions. Crown aspect has little effect on the ion concentrations in sap. Age is a significant factor in xylem sap ion concentrations. Trees to be compared should be within 10 years in age. Time of day causes significant changes in ion concentration in the sap, but two stands can be compared over the same 2 to 8 sunlight hours. Xylem sap can be collected easily in the winter from frozen branches or in the summer when transpiration should be measured as well. Most ions decrease in concentration in the sap from the time of flush through hardening off. Douglas-fir (Pseudotsugamenziesii (Mirb.) Franco) sap has higher Ca than P. ponderosa sap. Slowly growing P. ponderosa had low Ca, Mn, K, P, and N, but high Mg and Si in the sap, compared with more rapidly growing trees. Xylem sap shows promise as a means of simultaneously evaluating the water, nutrient, and energy stress of trees and may be useful as a rapid means of predicting various parameters of tree growth.