Allometric relationships in young seedlings of faba bean (Vicia faba L.) following removal of certain root types

Sink-source relationships and allometric ratios were studied in young seedl ings of faba bean (Vicia faba L.) following pruning of some root types. The plants were grown in an aeroponic system allowing an easy access to each p art of the root system, throughout the experiment, without disturbing the o thers. Root, leaf and stem growth as well as their mineral content were det ermined in one group of undisturbed plants (CTRL) and in four groups of pla nts treated as follows: TAP - the distal-free portion of the taproot was re moved; HALF - half the laterals were removed; ALL - all lateral roots were removed, and TAP+HALF - both the distal part of the taproot and half of the laterals were removed. Removal of all the lateral roots (ALL) induced the development of a longer taproot but severely arrested shoot growth. Phospho rus, potassium and calcium contents were lower in the plants of the ALL tre atment. However, the content of Mg was practically unaffected. The effect o f the HALF treatment was hardly noticeable but the effects of TAP+HALF trea tment were cumulative. The allometric relationships between the surface are a of the roots and that of the leaves were restored within the experimental period, apparently due to reduction in shoot growth. Removal of the distal parts of the taproot did not cause an increase in shoot growth. This indic ates that the strength of the sinks (mostly of lateral roots) rather than t hat of the source determines these relationships.