K. Bishop et E. Dambrine, LOCALIZATION OF TREE WATER-UPTAKE IN SCOTS PINE AND NORWAY SPRUCE WITH HYDROLOGICAL TRACERS, Canadian journal of forest research, 25(2), 1995, pp. 286-297
This study explores the potential of hydrological tracers for determin
ing the proportion of water uptake by Scots pine (Pinus sylvestris L.)
and Norway spruce (Picea abies (L.) Karst.) from different layers in
the upper 3 dm of podzolized forest soil. To improve the resolution of
the tracer technique, a pair of tracers was employed. One tracer was
the naturally occurring vertical gradient in the oxygen isotope ratio,
delta(18)O, of soil solution. The second tracer was a H-3 solution pl
aced in the mor layer. A three-component mixing model of water uptake
was used to simulate the content of these two tracers in the xylem sap
. Each component in the mixing model represented a horizontal layer of
soil with a characteristic composition of delta(18)O and H-3. Two sta
nds were investigated. In both stands, the volume-weighted water uptak
e by Scots pine occurred at a depth of 8-17 cm in the upper B horizon.
This was below the concentration of fine roots in the mor layer and t
he upper few centimeters of mineral soil. In one of the two study stan
ds, Norway spruce was present. It had mean uptake depths ranging from
within the mor layer to 5 cm below the mor-mineral soil contact. An un
certainty in the water uptake depth for each tree of +/-1-2 cm was est
imated from a Monte Carlo analysis of uncertainties in the model input
s. In addition to these specific results, the study demonstrated that
isotopic tracers provide a simple and effective method for determining
the vertical distribution of water uptake.