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Soil injections of sucrose may offer significant aid to trees suffering transplant or root damage problems
by Art Drysdale
by Art Drysdale

email: art@artdrysdale.com

Art Drysdale, a life-long resident of Toronto and a horticulturist well known all across Canada, is now a resident of Parksville, British Columbia on Vancouver Island, just north of Nanaimo. He has reno-vated an old home and has a new garden there. His radio gardening vignettes are heard in south-western Ontario over radio station Easy 101 FM out of Tillsonburg at 2 PM weekdays.

Art also has his own website at http://www.artdrysdale.com


September 24, 2017





Above, One of our prolific Daphne odoro in bloom around the base of our water-side deck; This nice Hydrangea has yellow-variegated foliage all season; and this blue Hydrangea (H. serrata ‘Bluebird’) is lovely when in bloom. Below, Lilium x Robina is now producing a massive number of flowers; two Yucca filamentosa in the small bed along our seawall; and our pink Camellia along our neighbour’s fence.
Author photos.







 


 



 

My thanks this week to Pat Coutts, the event director of the Four Oaks Horticultural Trade Show held near Lower Withington, in Cheshire, U.K. Here are some of the things she said about this year’s show.

“In urban and suburban landscapes, trees frequently grow in close proximity to buildings and infrastructure. Consequently, the process of developing land for buildings and infrastructure can be devastating to root systems of established trees. Likewise, soil deoxygenation as a result of excess water application, impeded drainage, mechanical compaction or impermeable surface coverings is an almost ubiquitous factor post construction that results in physical impedance to root growth and reduced levels of aeration. Further damage during construction such as trenching is also a major factor implicated in the death of urban trees due to severe root loss. Root damage reduces the root:shoot ratio and consequently the tree's ability to uptake sufficient water and nutrients for survival. This leads to water stress that may be characterized by reduced shoot growth, branch dieback and ultimately tree death.

“It is now recognised that the survival of trees following root damage or severance is largely dependent on the rapid extension of roots to absorb water, replenish transpirational water loss and reduce drought related water stress symptoms . Consequently, plant growth regulators such as auxins, commercially available root biostimulants and mycorrhiza have all been tested for their root promoting abilities.

“While many of these products have proved to possess useful root promoting properties a number of problems have been encountered. These include, expense, environmental impact and most importantly marked growth responses between different tree species. Ideally an inexpensive, non-toxic and environmentally friendly compound that can be applied to tree root systems post construction to stimulate root growth and restore the root:shoot ratio is required. Carbohydrates such as sucrose, glucose and fructose form the end products of photosynthesis. Supplementing root systems with carbohydrates effected root metabolism by significantly increasing lateral root branching and root formation i.e. root growth compared with controls. Likewise, application of the carbohydrates sucrose, glucose and fructose applied as a soil drench to containerised and field planted four year old trees has been shown to improve significantly root dry weights compared to water treated controls. This raises the possibility that the growth pattern of trees may be altered in favour of enhanced root formation by treating them during or immediately after construction damage with carbohydrates such as sucrose.

“Objectives of this investigation were to determine if soil injections with sucrose at a range of concentrations would improve the density or development of fine roots on established trees growing in urban environments. Sucrose was chosen as a test carbohydrate as this form of carbohydrate is the major photoassimilate transported from source to sink tissues in most tree species.

“Plots consisted of two mature oaks (Quercus robur), six wild cherry (Prunus avium) two horse chestnut (Aesculus hippocastanum) and four silver birch (Betula pendula) located at the University of Reading campus (oak, horsechestnut) and University of Reading Shinfield experimental field site (cherry, silver birch). All trees were surrounded by grass. Soil pH was determined using a soil pH electrode at a depth of 20cm.

“Sucrose (sugar) was obtained from a local supermarket. Quadrants beneath the dripline of each tree were randomly assigned to each treatment. Root lngrowth Cores (RlCs) were installed April 26th, 2003 to monitor new root development. RlCs are 7.6 cm (3 in.) diameter by 20 cm (8 in.) deep plastic screen cages which allow ingrowth of roots.

“Soil injections of sucrose increased fine root growth of all four test species five months after application compared to water only controls. In some cases, however, such increases were not significant i.e. applications of sucrose at 25g L of water, where root dry weight was higher, but not significantly so, than controls. This indicates soil of injections >25g L of water are required to significantly increase fine root growth of established Aesculus Hippocastanum, Q. robur, P. avium and B. pendula.

“Applications of sucrose ?50g L of water significantly increased (P<0.05) root dry weight of A. hippocastnum, Q. robur and B. pendula. Reasons for improved root growth following sucrose application include the fact that the process of recovery following root severance is dependent on the ability of a tree to manufacture abundant photosynthetic products i.e. carbohydrates such as sucrose. As carbohydrates function as a direct substrate for growth then an abundance of photosynthetic products at and around the root zone is available for immediate use. Use of sucrose as a direct substrate for root growth coupled with alterations in gene expression and microbial-plant interactions may account for increased root growth recorded in this investigation. This is an area worthy of consideration given the fact that sugars are water soluble, non-toxic, environmentally safe and inexpensive to purchase.

“While many of these products have proved to possess useful root promoting properties a number of problems have been encountered. These include, expense, environmental impact and most importantly marked growth responses between different tree species. Ideally an inexpensive, non-toxic and environmentally friendly compound that can be applied to tree root systems post construction to stimulate root growth and restore the root:shoot ratio is required. Carbohydrates such as sucrose, glucose and fructose form the end products of photosynthesis. Supplementing root systems with carbohydrates effected root metabolism by significantly increasing lateral root branching and root formation i.e. root growth compared with controls. Likewise, application of the carbohydrates sucrose, glucose and fructose applied as a soil drench to containerised and field planted four year old trees has been shown to improve significantly root dry weights compared to water treated controls .

“Objectives of this investigation were to determine if soil injections with sucrose at a range of concentrations could improve the density or development of fine roots on established trees growing in urban environments. Sucrose was chosen as a test carbohydrate as this form of carbohydrate is the major photoassimilate transported from source to sink tissues in most tree species. Sucrose (sugar) was obtained from a local supermarket. Quadrants beneath the dripline of each tree were randomly assigned to each treatment.

“Soil injections of sucrose increased fine root growth of all four test species five months after application compared to water only controls.

“Applications of sucrose ?50g L of water significantly increased (P<0.05) root dry weight of A. hippocastanum, Q. robur and B. pendula. Reasons for improved root growth following sucrose application include the fact that the process of recovery following root severance is dependent on the ability of a tree to manufacture abundant photosynthetic products i.e. carbohydrates such as sucrose. As carbohydrates function as a direct substrate for growth then an abundance of photosynthetic products at and around the root zone is available for immediate use. In addition, work has shown that in plants, carbohydrates such as sucrose affect sugar sensing-systems that initiate changes in gene expression and subsequent plant growth.

“Sucrose is the major photoassimilate transported from source to sink tissues in birch, oak and horse chestnut that is hydrolysed into glucose and fructose to provide energy via respiration. In the case of P.avium, sorbital is the major photoassimilate used for respiration. Differing photoassimilates between species may account for the non significant effects on root dry weight recorded in P.avium.

“In conclusion results indicate applications of sucrose via a soil injection system should be considered to stimulate fine root development of established trees which in turn should improve water and nutrient absorption following construction damage and aid in their recovery. This is an area worthy of consideration given the fact that sugars are water soluble, non-toxic, environmentally safe and inexpensive to purchase.”

   

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