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Translocation of total nonstructural carbohydrates (TNC) in mature honey mesquite (Prosopis glandulosa var. glandulosa) trees was studied by photosynthetically incorporating 14CO2 on eight dates during the summer of 1975. Several plant parts were analyzed for TNC and relative total activity (RTA) to determine direction of translocation and sink strength. Stem and twig TNC fluctuated more than basal bud TNC in response to phenological development. Pods were generally the strongest TNC sink except during initial pod formation (June 23, when bidirectional translocation occurred and all plant parts sampled contained equal concentrations of the l4C label. A RTA/TNC ratio used in conjunction with RTA and TNC suggested that increased TNC concentrations in the pods and stems may not always be due to increased import of TNC but caused by a reduction in growth with constant importation. Greatest translocation of TNC to the basal buds occurred between the phenological stages of green flower spikes (June 10) and pod formation (June 25) and during pod maturation (August 4 to August 19). Honey mesquite (Prosopis glandulosa var. glandulosa) is the most widely spread “pest” plant in Texas and now occupies more than 22.7 million ha of grassland. The distribution of honey mesquite increased by 506,000 ha between 1948 and 1963 (Smith and Rechenthin 1964). Many mechanical and chemical control methods are beneficial, but none prevent reestablishment of honey mesquite. Dormant buds, located in the crown area of the underground stem, allow honey mesquite to resprout and become reestablished. Any foliar applied herbicide must be translocated to the crown area and accumulate at toxic levels in order to kill honey mesquite. Translocation of organic food materials from the leaves to other plant parts has been associated with the movement of 2,4-D (2,4dichlorophenoxyacetic acid) (Mitchell and Brown 1946). Greatest translocation of 2,4,5-T (2,4,5trichlorophenoxyacetic acid) occurred when there was a moderate to rapid movement of sugars to the roots of honey mesquite (Fisher et al. 1956). Thus, carbohydrate translocation can be studied to determine the probable distribution of foliar applied systemic herbicides indirectly. Previous studies have examined root and stem carbohydrates in relation to season of the year (Fisher et al. 1956) and total available carbohydrates in honey mesquite roots in relation to phenological development and reproductive potential (Wilson et al. 1975). These studies used carbohydrate concentrations as an indication of direction of translocation. This study examined total nonstructural carbohydrates (TNC) in several parts of honey mesquite during the growing season and the distribution of radioactive labeled Authors are graduate research assistant and professor, Department of Range and Wildlife Management, Texas Tech University, Lubbock. W. FickS present address is assistant professor (range management), Department of Agronomy, Kansas State University, Manhattan, Kansas 66506. This report is a contribution of the College of Agricultural Sciences, Texas Tech University No. T-9-225. Manuscript received November 13, 1979. JOURNAL OF RANGE MANAGEMENT 34(3), May 1981 TNC. Specific objectives of the study were to determine nonstructural carbohydrate sinks and better establish direction of translocation as affected by phenological development. Experimental Procedures The site for this study was on the Texas Tech University campus in Lubbock, Level topography characterizes the area and the soil is an Amarillo fine sandy loam (an Alfisol). Blue grama (Bouteloua gracilis) and buffalograss (Buchloe dactyloides) are the dominant grasses. Major forb species are horseweed (Conyza canadensis), kochia (Kochia scoparia), and broom snakeweed (Xanthocephalum sarothrae), whereas honey mesquite is the dominant shrub. Radioactive carbon dioxide was generated in the field by mixing a 10% HCl solution with aqueous sodium bicarbonate (NaHi4C03) solution. The generation occurred in a closed system into which ~~CCIJ was pumped and circulated for 10 min. The system consisted of a plexiglass chamber placed on the terminal branch of the mesquite tree. A total of 32 trees were randomly selected and exposed to 2 PC of the V-label on eight treatment dates between May 20 and September 8, 1975. Samples collected 1 week after tagging included the tagged leaves, tagged twig, stem below the tagged twig, a portion of the basal bud zone, and pods. Tagged tissues refer to those actually exposed to Y&. The below-ground sample was collected by mechanically removing the soil around a tree to a depth of 0.6 m and cutting the taproot approximately 0.3 m below the crown buds. A hatchet was used to chip an adequate sample (5 to 10 g) from the bud zone. Once collected, all samples were immediately placed under dry ice to stop enzyme activity. Samples were dried in a forced-air oven at 55” C for a minimum of 48 hr and ground in a Wiley Mill to pass a 0.5-mm screen. Phenological development was described on each sampling date. All samples were analyzed for TNC by extracting a 500 mg sample of plant material using acid (0.2N HCl) hydrolysis as described by Smith et al. (1964). Carbohydrate concentration was determined using anthrone reagent and spectrophotometry (Murphy 1958) with glucose as the standard. Once extracted, a 2-ml aliquot of the aqueous solution was added to 10 ml of a dioxane based counting solution which was prepared by adding 4g PPO (2,5-diphenyloxazole), 300 mg POPOP (p-bis[2-(5phenyloxazolyl)]-benzene), and 100 g naphthalene to 1,000 ml 1,6dioxane. The amount of radioactivity in a sample was determined using a liquid scintillation counter. Results are reported as relative total activity (RTA) which is the disintegrations per minute (dpm) in a plant fraction divided by the total dpm recovered from the entire plant multiplied by 100. Within a treatment date, TNC, RTA, and RTA/TNC data were analyzed using a nested classification. A completely randomized design with subsampling was used to analyze across treatment dates and within a plant part. Means were separated by Duncan’s multiple range test.

Translocation and Storage of 14 C-Labled Total Nonstructural Carbohydrates in Honey Mesquite