Arboriculture & Urban Forestry 35(3): May 2009 Photosynthesis measurements are also important for providing additional information about tree vitality and treatment effects. Carbohydrate injections could affect photosynthetic processes considering that sugars and water are incorporated into the vas- cular system and moved up through the canopy (Tattar and Tattar 1999; Percival and Fraser 2005). The effect may be less evident if sugars are mainly translocated to storage organs such as trunk or roots. Therefore, tracking carbohydrate content in twigs and roots can help to determine the effect of exogenous applications. Sugars extracted from C3 isotope ratios δ13C (Fotelli et al. 2003) and when sugar from a C4 plant (e.g., Zea mays L.) is applied to a C3 and C4 plants differ in their carbon plant (e.g., Q. vir- giniana), the fate of the applied sugar can potentially be traced within the plant by comparing carbon isotope ratios of treated and nontreated plants. This information would be useful for determin- ing the fate and impact of carbohydrate supplementation in trees. Information about the effects of introducing exoge- nous carbohydrates as a source of energy might provide ar- borists with a potential technique to improve the health of ur- ban trees. The main goals of this investigation were to study the effects of trunk injections of carbohydrates on growth and vitality of live oak and to assess the potential for trac- ing exogenous carbohydrates using carbon isotope ratios. MATERIALS AND METHODS Thirty-six established, field-grown live oaks [16–20 cm (6.3– 7.8 in) dbh] grown under similar conditions were used. Similar trees were selected from a group of nonirrigated trees planted with 6 m (19.6 ft) spacing in an urban forest near College Sta- tion, TX in Burleson County (30°33’14.71”N, 96°25’33.61”W). Trees were growing in a Weswood silty clay loam soil. The site has an annual mean temperature of 20.3°C (68.5°F), [-1.6°C (29°F) minimum and 37.7°C (100°F) maximum], and annual precipitation varies between 762 and 1016 mm (30 and 40 in). Trunk injections using corn-derived glucose, sucrose, or a 50:50 mixture of glucose and sucrose by weight in three dif- ferent concentrations [40, 80, and 120 g/L (5.3, 10.6, 16.0 oz/ gal)] were used. Nine trees served as a water-only control, and three trees were injected for each concentration and type of carbohydrate. The concentrations were determined accord- ing to previous research on carbohydrate applications on plants (McLaughlin et al. 1980; Abdin et al. 1998; Iglesias et al. 2003). Approximately 10 L (2.6 gal) of solution were injected into the buttress roots using injection protocols established for inject- ing trees for oak wilt (Appel 2001; Eggers et al. 2005). Trees were injected during January 2005 and again in January 2006. Trunk diameters were measured at 30 cm (12 in) aboveg- round using a diameter tape (Forestry Suppliers Inc.; Jackson, MS) and recorded three times during the year throughout the ex- periment. To avoid possible effects of varying trunk sizes among trees, a growth index was calculated per year by dividing the ab- solute increase in trunk diameter in a year by the initial trunk measurement at the beginning of the experiment (Arnold et al. 2007). Growth index values were used for the statistical analysis. Four soil holes [15 cm (6 in) deep x 6 cm (2.3 in) diameter] were dug 1.5 m (4.9 ft) from the trunk and refilled with sandy loam soil to evaluate root growth. Core samples were extracted using a core sampler one year after treatment application. An herbicide (glyphosate) was applied periodically throughout the experiment 143 Table 1. P values from the ANOVA table for diameter growth index, twig glucose content, root starch content, and chlorophyll fluo- rescence Fv/Fm for live oaks injected with three sugars (glucose, sucrose, and a 50:50 mixture) and four concentrations (0, 40, 80, and 120 g/L-1). Factors Concentration Carbohydrate Time Concentration x carbohydrate Concentration x time Carbohydrate x time Conc. x carb. x time Diameter Twig growth index 0.159 0.049 0.001 0.532 0.334 0.133 0.160 Root glucose content 0.036 0.941 0.001 0.404 0.469 0.531 0.974 starch 0.881 0.001 0.152 0.002 0.627 0.209 Chlorophyll fluorescence content Fv/Fm 0.001 0.001 0.104 0.001 0.216 0.064 0.141 0.767 to control weeds. Root lengths and average root diameters were measured using the Winrhizo software® (Regent Instruments Inc., Québec, Canada). Soil samples were collected annually in the same location to evaluate new root growth among treatments. Twig samples were collected three times each year (January, April, and August) for carbohydrate analysis. Samples were tak- en from the lowest third of the canopy in all trees. Glucose and starch content were determined for each sample using Sigma® GAGO-20 reagents (Sigma®, St. Louis, MO). Glucose was ex- tracted from tissue in methanol:chloroform:water (MCW, 12:5:3, v/v/v) solution after centrifugation at 2800 rpm. A 0.5 mL (0.016 fl oz) aliquot of the extract and the glucose standards were mixed with 5 mL (0.16 fl oz) of anthrone reagent (Jaenicke and Thiong’o 1999). Starch content was determined by enzymatic conversion of starch to glucose using amyloglucosidase enzyme in the remain- ing pellet after glucose extraction. Absorbance of samples and standards were read within 30 minutes with a spectrophotometer (Spectronic 20, Baush & Lomb, Rochester, NY) set at 625 nm for glucose and 540 nm for starch (Haissig and Dickson 1979; Renaud and Mauffette 1991; Martinez-Trinidad et al. 2009a). Net carbon assimilation was measured in each treatment using a portable photosynthesis closed system LI-6200 (Li- Cor®, Lincoln, NE). Carbon assimilation was measured in the morning on sunny days on the southern side of the canopy. Three leaves from the lowest third of the canopy were selected. Chlorophyll fluorescence was measured using a HandyPEA® portable fluorescence spectrometer (Hansatech Instruments Ltd, King’s Lynn, UK). Ten leaves from the lower two-thirds of the canopy were adapted to darkness for 25 minutes. After the dark- ness period, the fluorescence response was induced by a red light of 1500µmol/m2 /Hz photosynthetically active radiation intensity provided by an array of 6 light-emitting diodes, with a data acqui- sition rate of 10 µs for the first 2 ms and 12-bit resolution. The ratio Fv/Fm was used to estimate tree vitality (Percival and Fraser 2001). Chlorophyll fluorescence data was taken at January, April, and August 2005, and January, April, August 2006, and January 2007. The translocation of carbohydrates was evaluated by deter- mining carbon isotope compositions. Twigs one-year-old and buttress roots samples [4 mm (0.15 in) x 100 mm (3.93 in)] were collected from controls, glucose [40 and 120 g/L (5.3 and 16.0 oz/gal)], and sucrose [40 and 120 g/L (5.3 and 16.0 oz/gal)] treat- ments 12 months after the first treatment. Samples were submit- ted for analysis to the Stable Isotope Facility at University of Cal- ifornia, Davis. The isotope composition was expressed to PeeDee Belemnite (PDB) carbonate standard (Peterson and Fry 1987). ©2009 International Society of Arboriculture
May 2009
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