142 Martínez-Trinidad et al.: Carbohydrate Injections for Live Oaks Arboriculture & Urban Forestry 2009. 35(3): 142–147 Carbohydrate Injections as a Potential Option to Improve Growth and Vitality of Live Oaks Tomás Martínez-Trinidad, W. Todd Watson, Michael A. Arnold, Leonardo Lombardini, and David N. Appel Abstract. This study evaluates the effects of carbohydrate injections on the growth and vitality of live oak (Quercus virginiana P. Miller). Glucose, sucrose, or a 50:50 mixture of both carbohydrates at increasing concentrations [0, 40, 80, and 120 g/L (0, 5.3, 10.6, and 16.0 oz/gal)] were injected into live oaks. Trunk and root growth, net photosynthesis, root and twig carbohydrate concen- tration, and chlorophyll fluorescence were monitored. Isotope composition of twig and root samples was measured as an indicator of injected carbohydrate distribution. There were significant differences (P < 0.05) in trunk growth among types of carbohydrates, but no significant differences for carbohydrate concentrations. The mixtures of sucrose and glucose had the largest effect on growth compared to either sugar alone, suggesting that glucose and sucrose alone were used in processes other than trunk growth. 50:50 mixtures caused a greater effect on overall mean growth indices than either sugar alone. Glucose content in twigs and starch in roots were significantly different (P < 0.05) among overall means for concentrations with increased levels found in trees treated with the greatest concentrations. Chlorophyll fluorescence Fv/Fm revealed highly significant differences (P < 0.001) among overall concentrations. Carbon isotope values did not reveal a definite trend that corroborated the exogenous carbohydrate distribution. Results from this experiment suggest that carbohydrate trunk injections can have an impact on growth and vitality of live oak. Key Words. Glucose; Quercus virginiana; Sucrose; Sugars; Tree Vitality. Photosynthesis in leaves and other chlorophyll-containing tissues produces carbohydrates, which are converted into energy by res- piration (Pallardy 2008). Carbohydrates can be used in situ, or be transported to organs where they are needed or stored for fu- ture use (Taiz and Zeiger 2006). Trees allocate carbohydrates for maintenance, reproduction, growth, and/or defense based on en- vironmental factors and growth stage (Pallardy 2008). Research has shown that tree growth and vitality depend on carbohydrate content in tree organs (Wargo et al. 1972; Kolosa et al. 2001). When trees are affected by stress-inducing factors, carbohydrate levels can be decreased or depleted, which can have negative re- percussions on growth and vitality (Gregory and Wargo 1985). Urban trees are commonly subjected to stressful conditions that can negatively impact tree vitality. Previous research has shown that improvement in tree vitality is directly affected by the en- ergy level in trees (Wargo 1975; Carroll et al. 1983; Percival and Smiley 2002). Use of inexpensive, nontoxic, and environmentally friendly products such as sugars could help improve growth and vitality of trees (Percival 2004; Martínez-Trinidad et al. 2009b). Trunk injections have been useful for introducing various com- pounds into trees. The most common types of injections on trees include bark banding, trunk infusion, and pressurized trunk injec- tions (Sachs et al. 1977; Sanchez and Fernandez 2004). Trunk injections are classified as micro- or macroinjections according to the amount of material injected (Costonis 1981). Macroinfu- sion is a trunk injection system that has been used for applying high amounts of solutions into trees while producing minimal damage (Appel 2001; Eggers et al. 2005). This method makes it easier to control the amount of sugars injected when using great- er volumes of solution compared with microinjection systems. ©2009 International Society of Arboriculture The increase of plant carbohydrate levels as a result of injec- tions can have an effect on growth and vitality (Abdin et al. 1998; Iglesias et al. 2001). For sucrose microinjections in fruit trees, re- search has shown quite variable and unpredictable supplementa- tion of sucrose into the tree by the microinjection system (Iglesias et al. 2001). Anecdotal reports of sucrose macroinjections in the trunk of a large, historic live oak (Quercus virginiana P. Miller) showed some apparent vitality improvement after being treated (Giedraitis 1990). Unfortunately, there are no scientific research studies on macroinjections of carbohydrates in urban trees. Tree growth is one of the most common indicators used for studying the effect of environmental factors or treatments on tree vitality (Dobbertin 2005). The application of carbo- hydrates through trunk injections may increase the energy pool and generate greater growth rates (Giedraitis 1990). In- jected solutions may move up through the xylem, or they may be stored or translocated to storage tissues (Sachs et al. 1977; Tattar and Tattar 1999). Considering that exogenous carbohy- drates can be translocated to different parts of the tree, vari- ables in addition to growth should be measured to assess tree vitality and effects caused by carbohydrate supplementation. Various tools have been suggested for determining tree vi- tality in the field. The chlorophyll fluorescence parameter Fv/ Fm is often used for measuring the photochemical efficiency of photosystem II, which indicates the energy level absorbed by chlorophyll and damage by excess light (Maxwell and Johnson 2000). The Fv/Fm parameter has been suggested as one mea- surement of tree stress tolerance and tree vitality (Percival and Sheriffs 2002; Percival and Fraser 2005). An advantage of us- ing chlorophyll fluorescence measurements is the ease and speed of collecting data using a portable fluorescence spectrometer.
May 2009
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