Auxins and Water-Retaining Polymer Root Dips Affect Survival and Growth of Newly Transplanted Bare-Rooted European Beech and Silver Birch

Abstract

Abstract The influence of two commercially available auxin products (IBA talc, IBA:NAA solution) in combination with a water-retaining polymer applied to the root system of two transplant-sensitive tree species, silver birch (Betula pendula Roth.) and beech (Fagus sylvatica L.) under field conditions was investigated. The efficacy of the auxins on growth was quantified by recording root and shoot growth and survival rates at week 8 and 20 after bud break. Improvements in tree vitality were assessed by measurement of leaf photosynthetic rates, chlorophyll fluorescence and chlorophyll content. Application of an IBA talc improved growth and vitality of beech but had little beneficial effects on birch. A combination of liquid IBA:NAA (50:1 dilution) and a water-retaining polymer at transplanting proved most effective for root regeneration, growth and tree vitality of both species compared to other treatments. Regardless of species, applications of a water-retaining polymer alone had no significant effect on tree survival rates or tree vitality. However, growth of birch was significantly reduced compared to controls indicating a detrimental effect of polymer application alone on this species. Results show that commercially available auxin products in combination with a water-retaining polymer can be used to reduce transplant losses and improve tree vitality and growth over a growing season in two difficult-to-transplant species. Selection of an appropriate auxin(s), however, is important as effects on growth and vitality can vary between tree species.