Effect of defoliation on root growth of some arid zone perennial plants

Abstract

The effect of defoliation on the extension, longevity and branching of roots was studied with use of root observation boxes. Three perennial species commonly found in the southern portion of the Australian arid zone—wallaby grass (Danthonia caespitosa), old man saltbush (Atriplex nummularia) and bladder saltbush (A. vesicaria)&,dash;were investigated and compared with lucerne (Medicago sativa). The rate of root extension of theAtriplex spp. was about double that of M. sativa and D. caespitosa and for all species was proportionately reduced with the severity of defoliation. Root mortality increased and branching of roots decreased with increasing severity of defoliation. Time-lapse photography showed that extension of the roots of D. caespitosa began to slow down about an hour after complete defoliation whereas extension of the roots of A. nummularia and M. sativa did not begin to slow down until 12–24 hr after defoliation.