Effects of carbohydrate applications on growth and vitality of live oak (Quercus virginiana)

Urban forests grow in stressful environments that can have negativerepercussions on tree energy reserves. The goal of this research was to evaluate theimpact of exogenously applied carbohydrates on growth and vitality of live oaks(Quercus virginiana P. Miller). An initial study focused on carbohydrate partitioningrevealed that annual mean glucose concentration in leaf tissues (49.55 mg?g-1 DW) wasalmost double that in twigs, trunks, or roots. Starch concentrations in roots and trunks(38.98 and 38.22 mg?g-1 DW of glucose, respectively) were higher during the dormantseason and approximately three times the concentrations found in other tissues. Aninvestigation of the effects of exogenous soil applications of glucose and starch on soilmicrobial activity revealed no significant differences using recoverable viable microbes.However, soil respiration was significantly increased (P<0.05) by glucose a week afterapplication, while higher starch concentrations (120 g?L-1) significantly increased(P<0.05) soil respiration after the fourth week. Although tree soil drenched withcarbohydrates in a different study showed significantly (P<0.05) greener leaf color, higher chlorophyll fluorescence, and increased soil respiration at higher concentrationsof starch (120 g?L-1), no significant differences were observed in photosynthesis or trunk,canopy, or root growth. Analysis of 13C signatures was unable to detect uptake ofexogenous carbohydrates. For trunk-injected trees with glucose and sucrose, trunkgrowth was significantly (P<0.05) increased by carbohydrate supplementation.Differences were also found in twig glucose content, root starch content, and chlorophyllfluorescence among overall concentration means. A study to compare field diagnostictools with carbohydrate laboratory analysis established that a portable blood glucosemeter can be used to measure glucose content in trees. However, ohmmeter,refractometer, chlorophyll fluorescence spectrometer, and iodine staining results did notcorrelate well with laboratory analysis of carbohydrate concentrations. Results fromthese studies reveal that soil applied carbohydrates can greatly increase soil microbialactivity, provide evidence that trunk-injected carbohydrates may improve growth andvitality of live oaks, and provide a new field diagnostic tool to increase the efficiency ofmeasuring carbohydrates in trees.