INVESTIGATION INTO THE USE OF DEUTERIUM AS A TRACER FOR MEASURING TRANSPIRATION FROM EUCALYPTS

A study into the use of deuterium oxide as a tracer for measuring transpiration rates from trees was carried out on three year old Eucalyptus teretecornis trees growing in a plantation in southern India. Two trees, with diameters equal to that of the mean of the plantation, were injected at their bases with 3. 0 and 1. 5 ml of D//2O, respectively. Four samples of transpired water were collected per tree as condensate in plastic bags which enclosed branches in the top and bottom of the canopy. Transpiration rates were calculated as 0. 86 plus or minus 0. 05 and 0. 85 plus or minus 0. 07 mm per day from the two trees. The internal consistency of the results suggest that the method is well suited to transpiration studies from young eucalypts; on safety and economic considerations deuterium is to be preferred to tritium as a tracer.