AN INVESTIGATION OF ROOTING DEPTH OF THE SEMIARID SHRUB RETAMA-SPHAEROCARPA (L) BOISS BY LABELING OF GROUND-WATER WITH A CHEMICAL TRACER

(1) Water containing lithium chloride as a chemical tracer was applied to the bottom of two survey wells 16 and 28 m deep and the concentrat ion of Li+ in young cladodes of Retama sphaerocarpa shrubs growing aro und the wells was monitored for 9 days after the subterranean applicat ion. (2) The mean concentration of Li+ in the young cladodes of the sh rubs increased from a natural background of 1.8 +/- 0.8 mu g Li+ g(-1) dry mass to 91 +/- 18 mu g g(-1) within 24 h of application. (3) The mean concentration of Li+ was significantly higher in shrubs around th e shallower well where a maximum of 184 +/- 52 mu g g(-1) was measured 5 days after application. (4) At the deeper well, mean concentration of Li+ averaged over the 9 day period of observation was positively co rrelated with shrub size.