| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
|
|
|
|||||||
|
|||||||||
a Dep. of Horticulture, Clemson Univ., Clemson, SC 29634-0375
b Dep. of Experimental Statistics, Clemson Univ., Clemson, SC 29634-0375
* Corresponding author (toddb{at}sepro.com)
 |
ABSTRACT |
|---|
 TOPNOTES ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
|---|
Abbreviations: DLI, daily light integral • DMSO, dimethyl sulfoxide • GA, gibberellic acid • +N, additional nitrogen • PGR, plant growth retardant • PPF, photosynthetic photon flux • RG, regrowth • RLE, reduced light environment • TE, trinexapac-ethyl • TNC, total nonstructural carbohydrates • TQ, turf quality • WAS, weeks after shade initiation
|
INTRODUCTION |
|---|
|
TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
|---|
Limited research exists on shade effects to dwarf-type bermudagrass grown in a golf green or fairway condition where trees are positioned to the north, south, east, or west, and rarely directly above. Therefore, these turf areas receive direct sunlight at intervals surrounding solar noon rather than continuous reduced irradiance. The inherent lack of shade tolerance of bermudagrasses makes growing quality turfgrass stands in a RLE challenging. Cultural practices can potentially be used to improve bermudagrass performance and appearance in a RLE. A greenhouse study evaluated four dwarf-type hybrid bermudagrasses [C. dactylon (L.) Pers. x C. transvaalensis Burtt-Davy] (‘Tifdwarf’, ‘Champion’, ‘FloraDwarf’, and TifEagle) at two mowing heights of 3 and 4 mm at various levels of continuous shade application. Increasing mowing heights from 3 to 4 mm improved net photosynthesis and overall turfgrass performance in shade (Miller and Edenfield, 2002). Benefits of raised mowing heights include increased total leaf area for maximum light absorption, increased root density and depth, and improved turfgrass density (Dudeck and Peacock, 1992).
Nitrogen fertilization has been well documented to increase shoot growth of hybrid bermudagrass (Trenholm et al., 1998). Low plant N concentrations can depress photosynthesis and lower the carbohydrate supply (Bowman, 1991). Often, turf managers will increase N fertility in an attempt to stimulate bermudagrass growth and photosynthesis in shaded environments. However, excessive application of N increases tissue succulence and potential damage from stresses such as extreme shade or limited sunlight (Dudeck and Peacock, 1992). Burton et al. (1959) found high N fertility decreased common bermudagrass (C. dactylon L.) density and leaf area and protein production by 26% and decreased carbohydrates by 30% in a RLE. Additional work on Tifgreen bermudagrass grown in a RLE determined N utilization was inhibited and carbohydrates decreased with excessive N application (Schmidt, 1969). In response to a RLE, the applied N is utilized for protein production rather than carbohydrate production to maintain a nontoxic level of ammonia N from building in the plant (Burton et al., 1959). The reduced quantity of carbohydrate reserves is not adequate for plant growth, hence decreasing plant density and leaf area (Burton et al., 1959).
Increased shoot elongation and internode length in plants under a RLE is a shade avoidance response due to increased GA synthesis (Endo et al., 1989; Lange, 1998). Gibberellins are a class of plant hormones responsible for cell division and elongation. Synthesis of Gibberellin A1 (GA1), the physiologically active form, increased 45% in Kentucky bluegrass (Poa pratensis L.) under RLEs (Tan and Qian, 2003). When GA3 is applied to Tifdwarf bermudagrass, turfgrass color appears yellow–green (Dudeck and Peacock, 1985). Application of antigibberellin plant growth retardants (PGRs) can slow the synthesis of active gibberellins in plants. Trinexapac-ethyl is a commonly used antigibberellin PGR in turf which inhibits the enzyme 3β-hydroxylase, responsible for the conversion of physiologically inactive GA20 to GA1 (Adams et al., 1992). Application of TE on Kentucky bluegrass reduced GA1 by 47% and increased GA20 by 146% (Tan and Qian, 2003). By inhibiting GA1 synthesis in shade, shoot elongation can be reduced, thus reducing mowing frequency and slow possible carbohydrate allocation to shoots. ‘Meyer’ (Zoysia japonica Steud.) and ‘Diamond’ [Z. matrella (L.) Merr.] zoysiagrass maintained acceptable TQ with monthly and bimonthly applications of TE at 0.048 to 0.096 kg a.i. ha–1 under heavy continuous shade (77 to 88%) applications (Ervin et al., 2002; Qian and Engelke, 1999a).
The negative morphological and physiological responses of a TifEagle bermudagrass golf green to shade may be altered through the application of growth materials and the change in mowing height to improve turfgrass performance. Therefore, the objective of this study was to investigate the growth response of TifEagle bermudagrass to various growth promoters/inhibitors at two mowing heights under various hours of sunlight.
|
MATERIALS AND METHODS |
|---|
|
TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
|---|
Three durations of sunlight hours were utilized to simulate differing shade canopies surrounding golf greens. Sunlight treatment durations were 12, 8, and 4 h. Sunlight hours were applied at equal times before and after solar noon, designated at 1400 h in Clemson, SC. Therefore, 12-h treatments received sunlight from 0800 to 2000 h, 8-h treatments received sunlight from 1000 to 1800 h, and 4-h treatments received sunlight from 1200 to 1600 h. A neutral density shade cloth (92% shade) (6 by 8 m) was applied for nonsunlight hours (International Greenhouse, model no. SC-BL90, Sidel, IL). Shade cloth was supported and held with 4-mm steel cable wire. Shade cloth grommets were connected to cable wire with zip ties. The cable wire was supported by using 15-cm aluminum caps designed to fit over ground installed removable rebar. Shade cloth was pulled tight to maintain a height of 1 m above ground to facilitate air movement below the shade canopy. Vertically hanging shade curtains (92%) were adjoined to the east and west sides of shade tents in morning and afternoon hours, respectively, to prevent penetration of low angle incidence radiation. Shade was removed during sunlight hours. Percentage shade was determined by comparing photosynthetic photon flux (PPF) under shade cloths at the turf canopy to sunlight measurements with a hand-held quantum sensor (LiCor LI-190SA; Lincoln, NE). Measurements were taken twice yearly on a clear, cloud free day before shade cloth removal and after shade cloth application.
Treatments applied to investigate their effects on TifEagle bermudagrass visual quality and growth characteristics included: TE at 0.0393 kg a.i. ha–1 every 3 wk, 0.062 kg GA3 ha–1 every 2 wk, +N application of 24.5 kg N ha–1 every 2 wk using NH4SO4 (21–0–0 N–P–K), and an untreated check. A biweekly application of 24.5 kg N ha–1 was made over all plots using a 18–4–15 N–P–K fertilizer (Scotts Co., Marysville, OH).
Two mowing heights, 3.2 and 4.7 mm, were maintained throughout the study. Plots were mowed six times weekly with a walking greens unit between 1200 and 1600 h when all shade tents were removed from plots. Fiberglass whips were used below shade tents to remove heavy dew during morning hours.
Measurements
Hourly light integrals were recorded in a datalogger (LiCor LI-1000; Lincoln, NE) fitted with a quantum sensor (LiCor; LI-190SA Lincoln, NE) programmed to collect readings every minute. Daily light integrals for shade treatments (12, 8, and 4 h) were calculated by taking 8% of PPF for the shade period. Daily light integrals (mol m–2 d–1) were averaged across the growing season for both years. Standard errors were calculated for DLI yearly and 2-yr averages for each sunlight treatment.
Turf quality was rated weekly by assessing color, density, uniformity, and aesthetic appeal on a 1-to-9 scale with 9 = best TQ. Unacceptable TQ was deemed <7.
Percentage lateral RG was evaluated by removing 10.8-cm-diam. TifEagle bermudagrass plugs at the initiation of each study from each replicate. Holes were backfilled with golf green media sand. A wire mesh grid was constructed equal to the dimension of the original hole. The grid contained 230 square holes, 0.4-cm2 in area. A green shoot present in a 0.4-cm2 square denoted a point. Percentage lateral RG was calculated weekly by [green shoot points/total squares (230)]. Weekly percentage lateral RG and TQ data were averaged to yield overall RG and TQ ratings during the 8-wk shade application.
Total shoot chlorophyll concentration (mg g–1) was measured 4 and 8 weeks after shade initiation (WAS) for both years. Fresh clippings were harvested and collected during mowing from individual replicates and chlorophyll extracted using dimethyl sulfoxide (DMSO) (Hiscox and Israelstam, 1979). The DMSO technique extracts chlorophyll from shoot tissue without grinding or maceration (Hiscox and Israelstam, 1979). A spectrophotometer (Beckman DU-64, Beckman Instrument, Inc., Fullerton, CA) determined absorbance values at 645 and 663 nm, which were used in the equation proposed by Arnon (1949) to determine total shoot chlorophyll.
Total nonstructural carbohydrates of below ground tissue, including roots and rhizomes which are the primary carbohydrate storage organs for bermudagrasses, were measured at the end of the study (8 WAS) for both years (Shepard, 1991). Below ground tissues were harvested using a 5-cm-diam. plugger to a depth of 6.5 cm. Two samples were taken per individual replicate before sunrise to minimize diurnal fluctuations in carbohydrates (Westhafer et al., 1982). Invertase (Sigma I-4753, 433 units mg–1) and amyloglucosidase (Sigma A-7255, 23000 units g–1) were added to convert sucrose to glucose and fructose moieties and starch to glucose, respectively. Total nonstructural carbohydrates were measured by using Nelson's Assay, which quantifies the reducing sugars, glucose and fructose, in plants (Nelson, 1944; Somogyi, 1945).
Statistical Design and Analysis
The three study factors of sunlight hours, growth factors, and mowing heights were arranged in a factorial treatment design. The experiment design was a split-plot. The sunlight hours factor was arranged in a RCB design with two replicates (years), and the growth factor and mowing height factors were applied within the sunlight treatments, resulting in the split-plot design. Plot size of sunlight blocks were 4 by 6 m and contained three subplots of size 1 by 1 m for the split factors.
An ANOVA testing the interactions and main effects of all three experimental factors on the four measured variables (TQ, RG, shoot chlorophyll, and TNC) is shown in Table 1. Both main effect means and individual treatment means are presented in the following tables to allow meaningful evaluation of the factor effects when interaction is present or when interaction is not present. When variable interactions occur, main effects means are still discussed and should be interpreted with caution. Mean separations were performed with all data using Fisher's LSD.
|
level of 0.05 was used for all tests of significance. |
RESULTS AND DISCUSSION |
|---|
|
TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
|---|
|
|
Within the 4-h sunlight treatments, TifEagle with TE treatments and mowed at 4.7 mm maintained an acceptable TQ rating of 7.5, which did not differ from untreated and +N plots with the 8-h sunlight treatments (Table 3). When mowed at 3.2 mm, TifEagle receiving 4 h of sunlight and TE, maintained a TQ rating of 6.8. These results are similar to the findings of Ervin et al. (2002) and Qian et al. (1998), who report that TE improves TQ of Meyer and Diamond zoysiagrass.
Growth factor main effect means showed highest TQ ratings across all mowing heights and sunlight treatments with TE, +N, and untreated plots with ratings of 7.6, 7.1, and 7.0, respectively (Table 4). An unacceptable TQ rating of 5.4 followed GA applications.
|
TifEagle receiving 12 (41.1 mol m–2 d–1) and 8 h (35.5 mol m–2 d–1) of sunlight maintained acceptable TQ ratings of 7.7 and 7.3, respectively (Table 4). In contrast, the 4-h sunlight treatments, receiving 22.1 mol m–2 d–1, had an unacceptable TQ rating of 5.2.
Percentage Lateral Regrowth
Percentage lateral RG measured horizontal growth or recovery of TifEagle bermudagrass. Highest percentage lateral RG of 78 and 72% were achieved in plots receiving +N applications and 12-h sunlight and mowed at 3.2 and 4.7 mm, respectively (Table 3). Gibberellic acid and untreated plots receiving 12 h of sunlight at both mowing heights maintained 66 and 62% lateral RG, respectively. Trinexapac-ethyl treated TifEagle receiving 12 h of sunlight had 10 to 20% less RG compared with other growth factors.
Similar trends continued with plots receiving 8 h of sunlight. As sunlight decreased from 12 to 8 h, percentage lateral RG of +N and untreated plots at both mowing heights did not decline (Table 3). Therefore, in this study the 8-h sunlight application did not inhibit the horizontal growth of TifEagle bermudagrass. Trinexapacethyl applications and the low mowing height of GA plots maintained lowest percentage lateral RG at 8 h of sunlight. Percentage lateral RG of TE plots remained constant at approximately 59% when receiving either 12 or 8 h of sunlight. By inhibiting cell and stem elongation, TE may slow horizontal growth of TifEagle bermudagrass.
Large reductions in TifEagle percentage lateral RG occurred when it only received 4 h of sunlight. Highest percentage lateral RG values within the 4-h sunlight treatments were 55 to 58% with the 4.7-mm mowing height of +N, TE, and untreated plots (Table 3). All other treatment combinations fell below 50% lateral RG. Lowest percentage lateral RG of 30% followed GA plots maintained at 3.2 mm. Percentage lateral RG decreased only 4% on TE-applied TifEagle maintained at 4.7 mm receiving 4 h of sunlight compared with the 12-h sunlight treatments.
Growth factor main effects showed highest percentage lateral RG ratings of 65 and 58% following +N applications and untreated plots, respectively (Table 4). The TE- and GA-applied plots significantly reduced TifEagle percentage lateral RG value by approximately 10% compared with +N plots. The increased shoot growth associated with hybrid bermudagrasses with N applications promoted greater lateral spread and horizontal growth (Trenholm et al., 1998).
The main effect of mowing height and sunlight hours influenced percentage lateral RG of TifEagle bermudagrass. Percentage lateral RG increased 5% when raising mowing height to 4.7 mm (Table 4). Also, when sunlight hours were reduced from 12 or 8 h to 4 h, percentage lateral RG decreased 18% (Table 4).
Total Shoot Chlorophyll
At 4 WAS, all treatment combinations influenced total shoot chlorophyll concentration. Highest shoot chlorophyll concentration of 3.95 and 3.57 g kg–1 followed TE-applied TifEagle mowed at 4.7 mm and receiving 12 and 8 h of sunlight, respectively (Table 5). Previous work on Poa pratensis L. and P. supina L. also found increased shoot chlorophyll following TE applications (Stier and Rogers, 2001). Generally, chlorophyll concentration decreased with less sunlight and lower mowing heights. However, TE-applied plots mowed at 4.7 mm receiving 4 h of sunlight maintained similar chlorophyll concentration as untreated and +N plots receiving 12 h of sunlight at both mowing heights (Table 5). In the 4-h sunlight treatments, TE-applied TifEagle mowed at 4.7 mm maintained highest total shoot chlorophyll by 22 to 25% compared with the untreated, +N, and GA plots maintained to the exact standards.
|
Growth factors influenced the total shoot chlorophyll concentration of TifEagle bermudagrass. At 4 WAS, TE increased chlorophyll by approximately 19 and 42% compared with other growth factors (Table 4). At 8 WAS, growth factor means were highest with TE, untreated, and +N-applied TifEagle. However, only TE significantly improved chlorophyll compared with GA-applied plots by 40% (Table 4). The TE applications improved overall chlorophyll concentration on a gram-per-kilogram fresh-weight basis. The plant growth regulating effects of TE include the inhibition of active GA formation and a decrease in cell and shoot elongation (Adams et al., 1992). Through cell and shoot elongation inhibition, plant morphology changes to create shorter stems and leaves. The morphology change might be responsible for the increased chlorophyll concentration due to a more compact leaf, rather than actually an increase in chlorophyll synthesis. Further research is necessary to determine if TE applications increase chlorophyll molecules or change shoot/leaf morphology to increase shoot chlorophyll concentration.
At both 4 and 8 WAS, the 4.7-mm mowing height significantly improved TifEagle chlorophyll concentration. At 4 WAS, 4.7 mm mowed TifEagle increased chlorophyll by 24% compared with 3.2-mm plots (Table 4). As the study progressed in time and increased low light stress was induced, the 4.7-mm mowing height increased chlorophyll by 45% at 8 WAS. By increasing mowing height of TifEagle bermudagrass, total leaf area and net photosynthesis are increased, therefore increasing chlorophyll concentration (Miller and Edenfield, 2002; Dudeck and Peacock, 1992).
Sunlight hours influenced total shoot chlorophyll concentration of TifEagle bermudagrass. At 4 WAS, the 12-h sunlight treatments increased chlorophyll concentration by 7 and 42% compared with 8- and 4-h sunlight treatments, respectively (Table 4). At 8 WAS, the 12- and 8-h sunlight treatments increased chlorophyll concentration by approximately 45% compared with the 4-h sunlight treatments.
Total Nonstructural Carbohydrates
Highest TifEagle TNC concentration, ranging from 41.81 to 34.79 mg g–1, followed all treatments receiving 12 h of sunlight at both mowing heights and 8 h of sunlight mowed at 3.2 mm. The 4.7-mm mowing height within 8-h sunlight treatments had lower TNC concentrations compared with the corresponding growth factor maintained at 3.2 mm (Table 5). The TNC was increased by 42, 53, 65, and 72% when lowering the mowing height from 4.7 to 3.2 mm in untreated, TE, GA, and +N plots, respectively, in 8-h sunlight treatments (Table 5). Similar increases in TNC also occurred in the 4-h sunlight treatments with untreated and TE plots. The lower mowing height of 3.2 mm possibly created a smaller carbohydrate sink and allocation requirement due to the lesser quantity of shoot tissue present. A California study found higher TNC concentration in perennial ryegrass (Lolium perenne L.) mowed at lower heights (Mahady et al., 1979).
In 4-h sunlight treatments, +N application decreased TifEagle TNC by 39% compared with TE plots when maintained at 3.2 mm (Table 5). This supports research by Burton et al. (1959) showing a 30% TNC reduction in common bermudagrass under heavy shade with +N fertility.
Mowing height influenced carbohydrate storage of TifEagle bermudagrass. Plots mowed at 3.2 mm had 19% greater TNC compared with the 4.7-mm mowing height (Table 4). These results were influenced by higher TNC concentration found in TifEagle mowed at 3.2 mm compared with 4.7 mm in the 8- and 4-h sunlight treatments. Sunlight main effect TNC means did not differ significantly; however, numerical differences show a downward trend in carbohydrate storage as sunlight hours decreased.
|
CONCLUSIONS |
|---|
|
TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
|---|
A growth-promoting application of +N had positive impact on percentage lateral RG. In 12- and 8-h sunlight treatments, biweekly applications of 49 kg N ha–1 increased percentage lateral RG compared with other treatments. However, in a RLE (4-h sunlight), percentage lateral RG ratings of +N, TE, and untreated plots did not differ.
Trinexapac-ethyl applications significantly improved TifEagle total shoot chlorophyll concentration in all sunlight treatments. The increased chlorophyll concentration associated with TE is probably from morphological changes due to reduced cell and shoot elongation. Chlorophyll becomes more densely packed in shorter, more compact leaves. This also might explain the increased TQ with TE plots in 4-h sunlight treatments. Trinexapac-ethyl increased chlorophyll by 22 to 25% compared with untreated, GA, and +N plots, respectively, in TifEagle receiving 4 h of sunlight and mowed at 4.7 mm. However, the increased chlorophyll with TE-applied TifEagle did not equate to greater reserve TNC concentration.
|
NOTES |
|---|
|
TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
|---|
Received for publication January 7, 2004.
|
REFERENCES |
|---|
|
TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
|---|
This article has been cited by other articles:
|
|
 |
|
  C. M. Baldwin, H. Liu, L. B. McCarty, H. Luo, C. E. Wells, and J. E. Toler Impacts of Altered Light Spectral Quality on Warm Season Turfgrass Growth under Greenhouse Conditions Crop Sci., June 26, 2009; 49(4): 1444 - 1453. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 C. M. Baldwin, H. Liu, L. B. McCarty, H. Luo, and J. E. Toler Nitrogen and Plant Growth Regulator Influence on 'Champion' Bermudagrass Putting Green under Reduced Sunlight Agron. J., January 8, 2009; 101(1): 75 - 81. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
P. E. McCullough, H. Liu, L. B. McCarty, and J. E. Toler Trinexapac-Ethyl Application Regimens Influence Growth, Quality, and Performance of Bermuda Grass and Creeping Bentgrass Putting Greens Crop Sci., September 1, 2007; 47(5): 2138 - 2144. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
E. A. Guertal and D. L. Evans Nitrogen Rate and Mowing Height Effects on TifEagle Bermudagrass Establishment Crop Sci., June 20, 2006; 46(4): 1772 - 1778. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
P. E. McCullough, H. Liu, L. B. McCarty, T. Whitwell, and J. E. Toler Bermudagrass Putting Green Growth, Color, and Nutrient Partitioning Influenced by Nitrogen and Trinexapac-Ethyl Crop Sci., May 18, 2006; 46(4): 1515 - 1525. [Abstract] [Full Text] [PDF]
|
|
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
| The SCI Journals | Agronomy Journal | Vadose Zone Journal | |||
| Journal of Natural Resources and Life Sciences Education |
Soil Science Society of America Journal | ||||
| Journal of Plant Registrations | Journal of Environmental Quality |
The Plant Genome | |||
