Arboriculture & Urban Forestry 35(2): March 2009 Arboriculture & Urban Forestry 2009. 35(2): 63-67 63 Temporal and Spatial Glucose and Starch Partitioning in Live Oak Tomas Martinez-Trinidad, W. Todd Watson, Michael A. Arnold, and Leonardo Lombardini Abstract. Carbohydrate translocation, which follows anatomical and developmental patterns, is ruled by source-sink rela- tions where energy-containing compounds are moved from sources of production to sinks of utilization. Seasonal carbo- hydrate concentrations in various tree parts were measured and compared in 10 cm (4 in) trunk diameter live oaks (Quercus virginiana P. Miller). Tissue samples from roots, trunks, twigs and leaves were collected from three-year-old field-grown trees on four dates throughout the 2005–2006 seasons. Laboratory analyses of glucose and starch were performed, and values were compared and contrasted according to sample location and time of year. Glucose levels were significantly higher in leaves dur- ing the winter (P ≤ 0.001), while starch concentrations were significantly higher in root and trunk tissues during the spring and winter assessments (P ≤ 0.001). Carbohydrate concentrations varied among tissues sampled within the tree. This study pro- vides valuable information on the spatial and temporal partitioning of energy reserves, glucose and starch, in live oak so that arborists will have a better understanding of tree vitality, and the effects and environmental impacts of arboricultural treatments. Key Words. Carbohydrates; Quercus virginiana; Source-Sink Relations; Sugar. Carbohydrates are the principal products of photosynthetic ac- tivity and serve as the main energy reserve of trees (Tromp 1983). These products are used by organs where they are pro- duced (e.g., leaves) or are translocated to other organs, a phe- nomenon controlled by sink-source relations (Allen et al. 2005). Therefore, carbohydrates can be translocated from organs that produce photosynthates (sources) to organs that produce little or no carbohydrates (sinks) where they can be used or stored (Taiz and Zeiger 2006). These sink-source relationships are influenced by tree vitality, nutritional state, environmen- tal conditions, and the developmental stage of plants or tissues (Tschaplinski and Blake 1994; Grulke et al. 2001; Retzlaff et al. 2001). Understanding carbohydrate activity is critical in stress- ful environments, such as urban forests, where tree health is negatively impacted and environmental stressors are frequent. Research has highlighted the important role of carbohydrate reserves on a tree’s ability to tolerate stressful conditions (Barba- roux et al. 2003). Nonstructural carbohydrates (i.e., starch and sol- uble sugars) influence the capacity in trees for supporting growth, metabolism, and ultimately their survival (Kaelke and Dawson 2005). Most of the research information about reserve transloca- tion in trees has been explained for young plants grown in green- houses or natural environments rather than for older trees where carbohydrate production, translocation, utilization, and storage may differ greatly (Tschaplinski and Blake 1994; Gansert and Sprick 1998; Tognetti and Johnson 1999; Domisch et al. 2002). Additionaly, much of the recent research concerning carbohydrate partitioning has focused on a single season or short period of time (DeLucia et al. 1998; Retzlaff et al. 2001; Barbaroux et al. 2003). Trees vary in the allocation or use of carbohydrates stored in tissues. In deciduous trees, roots and trunk serve as the main stor- age organs during the dormant season, and their reserves are typi- cally depleted shortly before leaves begin to emerge; conversely, evergreen trees store considerable amounts of starch in leaves and branches (Larcher 1980; Grulke et al. 2001; Retzlaff et al. 2001; Newell et al. 2002). Deciduous trees require extensive car- bohydrate storage to maintain the living biomass and cope with stress-inducing factors (Abod and Webster 1991; Gansert and Sprick 1998). For example, white oak (Quercus alba L.) rapidly mobilizes and replaces starch reserves during the critical period of canopy generation in the spring (McLaughlin et al. 1980). Conifers accumulate carbohydrates in needles and twigs prior to bud-break and translocate them during the beginning of shoot growth (Ludovici et al. 2002). Some conifers such as Scots pine (Pinus sylvestris L.) allocate high percentages of sugar in needles as a response to low soil temperatures (Domisch et al. 2002). Trees in urban environments are subjected to numerous envi- ronmental stressors throughout the year that negatively impact car- bohydrate production, utilization, and storage. Live oak (Quercus virginiana) is a common species found in urban environments in the southern United States due to the species’ elegant canopy shape, adaptability to poor sites, low maintenance requirements, disease resistance, and long life span, which make this species suitable as an ornamental for urban environments (Little 1979; Gilman and Watson 1994). Because a live oak’s leaves continue to function throughout the winter until the trees defoliate during budbreak, the species is considered as semi-evergreen. Therefore, research on carbohydrate allocation will help to understand whether the species follows a deciduous or evergreen pattern. Even when un- der urban conditions, carbohydrate allocation can also be affected when tree organs are modified by human activities such as root pruning, canopy pruning or trunk damage (Harris et al. 2004). Carbohydrate reserves help to offset low carbohydrate produc- tion due to stressful conditions or high demand. 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