The influence of plant growth regulators on root and shoot growth of containerized trees following root removal

Abstract

SummaryThree plant growth regulators (indole-3-acetic acid (IAA), indolebutyric acid (IBA) and naphthaleneacetic acid (NAA)) singly and in combination, were incorporated as a drench into the growing medium of containerized Alnus rubra, Sorbus aucuparia, Tilia × europea and Quercus robur following removal of half of the root system. Unpruned trees drenched with distilled water were used as controls. Irrespective of species, applications of auxin solutions at 10 g 1–1 was associated with 100% mortality by week 16. In all cases leaf chlorophyll fluorescence values and necrosis of unpruned trees (controls) remained relatively constant. Root removal and application of distilled water reduced leaf chlorophyll fluorescence and increased necrosis regardless of species. Minimal leaf necrosis and high chlorophyll fluorescence were recorded following application of IAA, IBA, IAA + IBA and IAA + IBA (1 g 1–1) to Q. robur, T. × europea, S. aucuparia, and A. rubra, respectively. Generally treatments of NAA alone or in combination with IAA or IBA had no significant effect or increased leaf necrosis and reduced chlorophyll fluorescence. By week 8 applications of PGRs had no significant effect upon shoot dry weight; however root dry weights and root: shoot ratio were significantly reduced in the majority of trees tested. By week 25 applications of IAA, IBA, IAA + IBA, IAA + NAA + IBA significantly increased root weight and root:shoot ratio (P<0.01) of all species tested compared with controls; no significant effects upon shoot dry weight were recorded. Applications of NAA singly or in combination with IAA or IBA generally had no significant effect upon root dry weight of S. aucuparia, increased root dry weight of Q. robur and T. × europea but decreased root dry weight of A. rubra. A species-specific response to individual and combinations of auxins was demonstrated.