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Sangwook Han, Thomas W. Fermanian, John A Juvik, and Louis A. Spomer

Total nonstructural carbohydrates (TNC) are important for summer recuperation from injury for cool-season turfgrass. The objectives of this study were to determine if trinexapac-ethyl (TE) [4-(cyclopropyl-a-hydroxy-methylene)-3,5-dioxo-cyclohexane-carboxylic acid ethyl ester] affects TNC content and turf quality of a creeping bentgrass at various application frequencies and rates and to investigate any interactions between the effects of TE and traffic treatments on TNC content. Field experiments were conducted in 1995 and 1996 on a mature stand of `Pennlinks' creeping bentgrass grown on a Flanagan silt loam soil maintained at a height of 1.9 cm. Treatments included a single application (0.28 kg·ha-1) or repeat applications at 2 (0.06 kg·ha-1) or 4 (one at 0.28 kg·ha-1 and one at 0.09 kg·ha-1) week intervals during the first 8 weeks of each experiment. Treatments were arranged in a strip-plot design with TE applications as whole plots and traffic treatments as strip plots. Traffic treatments began at 2 weeks and 2 days after initial applications in 1995 and 1996, respectively and continued until the last evaluation date. Traffic treatments consisted of 4 passes of a 102.2 kg smooth roller, 2 days·week-1 in 1995 and 8 passes daily in 1996. A single aqueous extraction method was used for quantification of glucose, fructose, sucrose, and fructan. TNC was the total of all analyzed fractions. Single applications of TE at 0.28 kg·ha-1 significantly reduced turf quality for 4 weeks in both experiments. Sequential applications of TE at 0.06 kg·ha-1 exhibited reduced quality compared to the control at 4 and 8 weeks in 1995 and 2 weeks in 1996. When TE was applied once at 0.28 kg·ha-1, there was a significant reduction in TNC from 4 to 8 weeks after treatment. In 1996 when TE applications were repeated at 2 and 4 week intervals at 0.06 and 0.09 kg·ha-1, a reduction of TNC from week 4 to week 14 was observed. After 14 weeks the TNC content showed incremental increases. There was no interaction effect between traffic treatments and TE applications in the verdure TNC in either year. In 1996, verdure TNC content was 6% to 17% lower in plots receiving traffic from weeks 4 to 18. These results suggest that high rates of TE, either sequential or single applications, might reduce turf quality or carbohydrate content. While this study has not examined if this is detrimental, multiple TE applications at low rates may minimize any TNC reduction while providing effective growth suppression for extended periods.

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W.E. Richie, R.L. Green, and F. Merino

Turfgrass growth regulators (TGRs) are an effective means of reducing vertical shoot growth and the production of clippings of tall fescue (Festuca arundinacea Schreb.). Recently, using TGRs has been suggested as a way to acclimate or precondition turfgrass to stress conditions, possibly through total nonstructural carbohydrate (TNC) accumulations and altered TNC partitioning. The TNC may accumulate in response to growth suppression associated with the TGR application. The objective of this study on tall fescue was to determine the effect of a single trinexapac-ethyl (TE) application on tissue weight and on TNC concentration and weight in leaves, crowns, and roots when sampled 6 to 7 weeks following TE application. This sampling time was chosen to coincide with the 28- to 56-day callback schedule that professional lawn care personnel follow when working with tall fescue. In 1995, a high level of turfgrass maintenance was used, consisting of N applications at 49 kg·ha-1 per month and two mowings per week, while in 1996 a moderate level was used, consisting of N applications at 24 kg·ha-1 per month and one mowing per week. Though TE provided reasonable inhibition of clipping growth for a 4-week period during both years, we observed no increase in tissue weight or in TNC concentration or weight in leaves, crowns, and roots when sampled 6 to 7 weeks after treatment. Chemical name used: [4(cyclopropyl-α-hydroxy-methylene)-3,5-dioxocyclohexanecarboxylic acid ethyl ester] (trinexapac-ethyl).

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Daniel S. Kirschbaum, Kirk D. Larson, Steven A. Weinbaum, and Theodore M. DeJong

The pattern of total nonstructural carbohydrate [starch and soluble sugars (TNC)] accumulation in strawberry (Fragaria ×ananassa Duch.) nursery runner plants, cv. Camarosa, was determined for three growing seasons. A similar study was conducted on `Selva', but for only one year. Growth, development and fruit production patterns of plants transplanted to growth chambers (GC) or fruiting fields were also evaluated. The experiments were carried out on plants propagated in high latitude (41°50' N) nurseries in California (Siskiyou County). Plants were sampled beginning late summer through early autumn and analyzed for dry mass (DM) and TNC. Plants from different digging dates were established in GC or fruit evaluation plots in Irvine, Calif. (33°39'N). Initial TNC concentration in storage tissues at the time of nursery digging increased steadily from the second week of September to the third week of October. Crown and root TNC concentration and content were correlated positively with the accumulation of chilling units (CU = hours ≤7.2 °C) in the nursery. Root TNC concentration consistently increased from 6% to 10% DM in `Camarosa' (a short-day cultivar), and from ∼4% to 14% DM in `Selva' (a day-neutral cultivar) from mid-September to the first week of October. The root TNC content increased ∼2.5 times in `Camarosa' and ∼3.7 times in `Selva' during the same period. Transplant growth, development, and fruiting pattern were affected by digging date. Root TNC concentration and content were more sensitive to CU accumulation than crown TNC concentration and content. Therefore, root sampling appeared to be more appropriate than crown sampling for assessing the carbohydrate status and optimal digging dates of strawberry nursery runner plants early in the fall.

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Frank B. Matta, Crofton Sloan, and Shakeel Khan

Apple leaves from current seasons' growth at mid-season (July) and during dormancy (December) were used to determine the influence of various apple scion/rootstock combination on total non-structural carbohydrates (TNC). `Empire' and `Royal Gala' had higher foliar TNC at mid-season compared to `Ultra Gold' on MM.106. `Empire' had higher foliar TNC on Mark than on MM.111, M.7A and M.26. `Blushing Golden' had higher foliar TNC on MM.111 than on the remaining rootstock% There was no significant interaction between cultivar and rootstock. Foliar TNC During Dormancy: `Blushing Golden' had the highest and lowest foliar TNC on MM.111 and M.7A, respectively. Cultivar differences did not exist with any rootstock. Foliar TNC results of this study indicated that there was a higher foliar TNC percentage in leaves at mid-season compared to leaves during dormancy. Data indicated cultivar influences on foliar TNC only at the mid-season. It seems that cultivar differences in TNC might be due to an increase in TNC formation, which during dormancy was stabilized. Rootstock influenced foliar TNC both at mid-season and during dormancy.

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Muntubani D.S. Nzima, George C. Martin, and Chic Nishijima

The objective of this investigation was to determine the dynamics of carbohydrate use as revealed by soluble sugar and starch concentration in leaves, inflorescence buds, rachises, nuts, current and 1-year-old wood, and primary and tertiary scaffold branches and roots (≤10 mm in diameter) of alternate-bearing `Kerman' pistachio (Pistachia vera L.) trees that were in their natural bearing cycles. Two hypotheses were tested. First, carbohydrate concentration is greater early in the growing season in organs examined from heavily cropping (“on”) than light cropping (“off”) trees. This hypothesis was affirmed as judged by soluble sugar and starch concentration in leaves, inflorescence buds, rachises, nuts, current and 1-year-old wood, and primary and tertiary branches and roots of “on” compared to “off” trees. Second, carbohydrate concentration remains high in “on” tree organs as the first wave of inflorescence bud and nut abscission occurs early in the growing season. This hypothesis was also affirmed. In fact, soluble sugars and starch remained high in “on” trees through full bloom FB + 60 days (FB + 60) as inflorescence bud and nut abscission occurred. In the persisting “on” tree inflorescence buds, sharp decreases in soluble sugars and starch were evident by the final sample date when “off” tree inflorescence buds contained a 13 times greater concentration of soluble sugars and starch than “on” tree buds. At that time, “off” tree inflorescence buds contained 50% more dry mass than “on” tree inflorescence buds. After FB + 60, “on” tree soluble sugars and starch declined in all organs as nut growth occurred. During the same time period, organs of “off” trees began to accumulate greater concentrations of soluble sugars and starch and exceeded concentrations measured in organs of “on” trees.

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J.M. Goatley Jr., V.L. Maddox, and K.L. Hensler

Bermudagrass turfs in the southern United States often receive late growing season applications of nitrogen (N) in order to sustain turfgrass color prior to dormancy, even though such applications might increase winterkill potential. Yearly research trials were initiated in the last week of Sept. 1989 to 1991 at Mississippi State Univ. to evaluate fall and spring color responses and rhizome levels of total nonstructural carbohydrates (TNC) of `Tiflawn' and Arizona (AZ) Common bermudagrass [Cynodon dactylon L. (Pers.)] treated with various N sources delivering N at 98 kg·ha-1 in a single application. The fertilizers were ammonium nitrate (AN), sulfur-coated urea (SCU), a natural organic (`Milorganite', NO), isobutylidene diurea (IBDU), ureaformaldehyde (UF), and methylene urea (MU). Color responses from N fertilization were most prominent in the fall except when there was an early frost event in Oct. 1990. The most rapid greening response and highest color ratings were consistently observed for the water-soluble AN. Of the slow-release sources, SCU, MU, and IBDU provided color responses as long as temperatures remained warm enough to promote bermudagrass growth. The NO source provided an unexpected, significant greening response in Oct. 1989 and 1991 on `Tiflawn', but not on AZ Common. The UF consistently provided the lowest color ratings. There were virtually no differences in TNC levels between N treatments for either grass. At no time was there any indication that N fertilization increased bermudagrass winterkill potential; to the contrary, the predominant responses were better fall and spring color than the nontreated control.

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Michelle DaCosta and Bingru Huang

Efficient carbon distribution and utilization may enhance drought survival and recovery ability for perennial grasses. The objectives of this study were to examine changes in carbon partitioning and carbohydrate accumulation patterns in shoots and roots of colonial bentgrass (Agrostis capillaris L.), creeping bentgrass (A. stolonifera L.), and velvet bentgrass (A. canina L.) in response to drought and re-watering following drought, and to determine whether species variation in drought tolerance and recuperative potential is related to differences in the patterns of carbon partitioning and accumulation. The experiment consisted of three treatments: 1) well-watered control; 2) drought, irrigation completely withheld for 18 days; and 3) drought recovery, a group of drought-stressed plants were re-watered at the end of the drought treatment (18 days). Drought tolerance and recuperative ability of three species was evaluated by measuring turf quality and leaf relative water content. These parameters indicated that velvet bentgrass was most drought tolerant while colonial bentgrass had highest recuperative ability among the three species. Plants were labeled with 14CO2 to determine carbon partitioning to shoots and roots. Carbohydrate accumulation was assessed by total nonstructural carbohydrate (TNC) content. The proportion of newly photosynthesized 14C partitioned to roots increased at 12 days of drought compared to the pre-stress level, to a greater extent for velvet bentgrass (45%) than for colonial bentgrass (35%) and creeping bentgrass (30%). In general, the proportion of 14C was highest in roots, intermediate in stems, and lowest in leaves at 12 days of drought treatment for all three bentgrass species. As drought duration and severity increased (18 days), 14C partitioning increased more in leaves and stems relative to that in roots for all three species. Stem TNC content was significantly greater for drought-stressed plants of colonial bentgrass and velvet bentgrass compared to their respective well-watered control plants, whereas no differences in stem TNC content were observed between drought-stressed and well-watered creeping bentgrass. Our results suggest that increased carbon partitioning to roots during initial drought stress represented an adaptive response of bentgrass species to short-term drought stress, and increased carbon partitioning and carbohydrate accumulation in stems during prolonged period of drought stress could be beneficial for rapid recovery of turf growth and water status upon re-watering.

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Xiaozhong Liu and Bingru Huang

Understanding physiological factors that may confer heat tolerance would facilitate breeding for improvement of summer turf quality. The objective of this study was to investigate whether carbohydrate availability contributes to changes in turf quality and root mortality during heat stress in two creeping bentgrass [Agrostis stolonifera L. var. palustris (Huds.) Farw. (syn. A. palustris Huds.)] cultivars, `L-93' and `Penncross', that contrast in heat tolerance. Grasses were grown at 14-hour days and 11-hour nights of 22/16 °C (control) and 35/25 °C (heat stress) for 56 days in growth chambers. Turf quality decreased while root mortality increased under heat-stress conditions for both cultivars, but to a greater extent for `Penncross' than `L-93'. The concentrations of total nonstructural carbohydrate (TNC), fructans, starch, glucose, and sucrose in shoots (leaves and stems) and roots decreased at 35/25 °C. The reduction in carbohydrate concentrations of shoots was more pronounced than that of roots. Shoot glucose and sucrose concentrations were more sensitive to heat stress than other carbohydrates. `L-93' maintained significantly higher carbohydrate concentrations, especially glucose and sucrose, than `Penncross' at 35/25 °C. Results suggest that high carbohydrate availability, particularly glucose and sucrose, during heat stress was an important physiological trait associated with heat-stress tolerance in creeping bentgrass.

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Guohai Xia and Lailiang Cheng

One-year-old `Concord' grapevines (Vitis labruscana Bailey) were fertigated with 0, 5, 10, 15, or 20 mm N in a modified Hoagland's solution for 8 weeks during summer. Half of the vines fertigated at each N concentration were sprayed with 3% foliar urea twice in late September while the rest served as controls. Four vines from each treatment combination were destructively sampled during dormancy to determine the levels and forms of N and carbohydrates. Nitrogen fertigation during the summer did not significantly alter vine N concentration whereas foliar urea application in the fall significantly increased vine N concentration. In response to foliar urea application, concentrations of both free amino acid-N and protein-N increased, but the ratio of protein-N to free amino acid-N decreased. Arginine was the most abundant amino acid in free amino acids and proteins, and its concentration was linearly correlated with vine N concentration. Concentrations of total nonstructural carbohydrates (TNC) decreased slightly in response to N supply from fertigation. Foliar urea application in the fall significantly decreased TNC concentration at each N fertigation level. Starch, glucose, and fructose decreased in response to foliar urea applications, but sucrose concentration remained unaffected. Approximately 60% of the carbon decrease in TNC caused by foliar urea application was recovered in proteins and free amino acids. We conclude that free amino acids account for a larger proportion of the N in vines sprayed with foliar urea compared with the unsprayed vines, but proteins remain as the main form of N storage. In response to foliar urea application, part of the carbon from TNC is incorporated into proteins and free amino acids, leading to a decrease in the carbon stored in TNC and an increase in the carbon stored in proteins and free amino acids.

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Lailiang Cheng, Guohai Xia, and Terry Bates

One-year-old `Concord' grapevines (Vitis labruscana Bailey) were fertigated with 0, 5, 10, 15, or 20 mm nitrogen by using a modified Hoagland's solution for 8 weeks during active vine growth in summer. Half of the vines at each N concentration were sprayed with 3% foliar urea twice in late September while the rest served as controls. After natural leaf fall, all the vines were overwintered in a cold room (2 to 4 °C). Four vines from each treatment were destructively sampled before budbreak for reserve N and carbohydrate analysis. The remaining vines were supplied with either no N or sufficient N (10 mm N) from 2 weeks before bloom to 1 month after bloom. All the vines were destructively harvested at 1 month after bloom. Total amount of N in dormant vines increased with increasing N fertigation concentration. Total nonstructural carbohydrates (TNC) increased with increasing N fertigation concentration from 0 to 10 mm, and then leveled off with further rises in N supply. Foliar urea application increased total N but decreased TNC of dormant vines at each given N fertigation level. When no N was provided during the regrowth period, vine total leaf area, fruit yield, and total dry weight increased with increasing N supply from fertigation the previous year. Vines sprayed with foliar urea the previous fall produced a larger total leaf area, a higher yield, and a higher total vine dry weight at each given N fertigation concentration. Providing vines with sufficient N during the regrowth period significantly increased total leaf area, fruit yield, and vine total dry weight across the previous N fertigation concentrations, but vines sprayed with foliar urea still had a larger leaf area, a higher yield, and a higher total vine dry weight at each given N fertigation concentration. Therefore, we conclude that both vegetative growth and fruiting of young `Concord' vines are largely determined by reserve nitrogen, not by reserve carbohydrates, and that current-season N supply plays a very important role in sustaining vine growth and development, especially fruit growth.