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This is an extract from a 2004 jornal research paper on the effects of sugar when used after planting. International Society of Arboriculture 2004 Glynn C. Percival

It has long been accepted that drought-related problems are often responsible for poor growth and deaths of newly planted urban trees (Davies 1998). As little as 5% of a tree’s root system may be moved with a tree following lifting from the nursery bed, in turn significantly reducing the root: shoot ratio and consequently the tree’s ability to uptake sufficient water and nutrients for survival of the newly expanding leaf canopy in spring. This leads to water stress, resulting in “transplant shock” that may be characterized by reduced shoot growth, branch dieback, and, ultimately, tree death. Although tree root systems can be manipulated to reduce the effects of transplant shock by increasing the amount of root to be transplanted by, for example, root pruning, pulling out of the ground (wrenching), or undercutting in the nursery, the effects of these techniques are inconsistent, and a high proportion of the root system may still be lost in the lifting process (Percival and Gerritsen 1998; Davies et al. 2002)

A number of factors have been associated with transplant shock; however, it is now widely believed that survival of newly planted trees is largely dependent on rapid extension of roots that absorb water to replenish transpirational water loss and reduce water stress (Gilbertson and Bradshaw 1990; Watson and Himelick 1997). Ideally an inexpensive, nontoxic, and environmentally friendly compound that can be applied to a tree’s root system postplanting to stimulate root vigor and restore the root:shoot ratio is required.

Trees are planted in urban environments for practical, ecological, and psychological benefits; however, survival, establishment, and reproduction (seed set) are critical for the success of the next tree generation (Percival and Hitchmough 1995). These objectives can be achieved only by the production and expenditure of energy by the tree, which, in turn, is achieved by photosynthesis: 

Previous research has studied alterations to plant growth and development in the presence of high and low concentrations of carbon dioxide, water, and oxygen (Hall and Rao 1999). Surprisingly, the influence of sugar feeding (the end product of photosynthesis) on plant physiological processes has received little scientific investigation. Of the limited literature available, supplementing root systems with sugar in the form of sucrose has been shown to affect root metabolism by significantly increasing lateral root branching and root formation in wheat and barley (Bingham and Stevenson 1993; Bingham et al. 1997; 1998). Work elsewhere (Fuchs 1986) also demonstrated that root regeneration of Rosa multiflora ‘Kanagawa’ was improved more by application of sucrose/auxin combinations compared to auxins alone. This finding indicates that the growth pattern of trees may be altered in favor of enhanced root formation by treating them during or immediately after transplanting with sugar, potentially offering a system for reducing tree mortalities due to transplant shock.

As a prerequisite to larger tree studies, the objectives of this investigation, using small potted trees, were to (1) evaluate the influence of sugar (sucrose) on root and shoot vigor, chlorophyll fluorescence, photosynthesis, and leaf chlorophyll concentrations of four tree species following containerization to simulate transplant conditions; and (2) evaluate three application rates, 25, 50, or 70 g (0.9, 1.8, or 2.7 oz) sugar per liter of water, on those responses.

Download and read the whole paper: Sugar feeding enhances root vigor of young trees following containerisation