COMPENSATORY ROOT-GROWTH IN WINTER-WHEAT - EFFECTS OF COPPER EXPOSUREON ROOT GEOMETRY AND NUTRIENT DISTRIBUTION

Plants of winter wheat (Triticum aestivum L. cv. Starke II) were grown for seven days in split-root chambers containing nutrient solutions w ith various copper chloride (CuCl2) concentrations [0.5/0.5 (controls) , 0.5/2, 0.5/5, 0.5/7 and 0.5/10 mu M]. At harvest (day 11), shoot dry weights were about the same in the different copper (Cu) treatments. Dry weights of the root parts exposed to 2-10 mu M Cu (Cu-fed) decreas ed while they increased for the control roots. A Cu exposure of 2-10 m u M severely retarded lateral root initiation and average lateral root length. Average seminal root length was also reduced. The control roo ts compensated for the retarded growth of the Cu-fed roots by increasi ng chiefly in lateral root number, but their average length remained s imiliar. Phosphorus (P) concentration decreased gradually in all deter mined plant parts (shoots, Cu-control and Cu-fed roots) with increased external Cu concentration. The potassium (K) concentration in the sho ots was similarly affected, but it did not decrease in the Cu-fed root s until the external Cu concentration reached 10 mu M. The Cu concentr ation in the Cu-fed roots increased proportionally to the external Cu concentration, but Cu was not exported to the other plant parts. The r easons for changes in root geometry and nutrient balance are discussed .