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Published in Crop Sci. 44:908-913 (2004).
© 2004 Crop Science Society of America
677 S. Segoe Rd., Madison, WI 53711 USA

TURFGRASS SCIENCE

Total Nonstructural Carbohydrate Assessment in Creeping Bentgrass at Different Mowing Heights

Siddhartha Narra, Thomas W. Fermanian*, John M. Swiader, Thomas B. Voigt and Bruce E. Branham

Dep. of Natural Resources and Environmental Sci., Univ. of Illinois at Urbana–Champaign, 1102 S. Goodwin Ave., Urbana, IL 61801

* Corresponding author (fermo{at}uiuc.edu).


   ABSTRACT
TOP
 NOTES
 ABSTRACT
INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 DISCUSSION
 REFERENCES
 
Any future precision turfgrass management system will benefit from the evaluation of turfgrass stress through indirect measurements of plant components. One such component might be the accumulation dynamics of total nonstructural carbohydrates (TNC). The effects of mowing height (MH) on TNC concentrations were measured in a field experiment. Clippings were collected from eight creeping bentgrass cultivars {Agrostis palustris Huds. [= A. stolonifera var. palustris (Huds.) Farw.]} mowed at three different heights (0.64, 1.27, 1.90 cm) from 1998 through 2001. Clippings were evaluated 29 times by sampling early in the photoperiod before 1200 h. Collected clippings were instantly frozen in liquid nitrogen and freeze-dried before TNC analyses. The TNC levels were predicted with near infrared reflectance spectroscopy (NIRS) after building a predictive equation for each carbohydrate fraction with conventional laboratory values. Seasonal trends in TNC concentrations and differences in TNC accumulation among creeping bentgrass cultivars were also evaluated. Mowing heights showed significant differences in TNC content, with 0.64-cm mowed plots having higher TNC levels than 1.27- and 1.90-cm mowed plots on 13 of the 29 dates of evaluation. No consistent differences were observed in TNC concentrations among different cultivars across different growing seasons. However, there were significant seasonal fluctuations in average TNC content at all MHs. The average TNC content of the clippings during 1999 and 2000 started decreasing in mid-July, showing the lowest TNC content in August. The average TNC content showed an increasing trend in September, exhibiting the highest amount of TNC accumulation in October and November.

Abbreviations: MH, mowing height • NIRS, near infrared reflectance spectroscopy • TNC, total nonstructural carbohydrate


   INTRODUCTION
TOP
 NOTES
 ABSTRACT
 INTRODUCTION
MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 DISCUSSION
 REFERENCES
 
ONE OF THE most important goals in managing golf course fairway turf is maintaining plant health. Any cultural practice directed toward fairway turf will be most efficient when the turf is in a healthy, actively growing state. Since it is usually easier to maintain plant health rather than resurrect it, early detection of plant stress is critical for efficient turfgrass management. If a golf course superintendent had the means to detect levels of general plant stress before symptoms are visually observed, less drastic corrective measures might be needed.

The TNC level of a turf has been considered a potential indirect indicator of the physiological status or the recovery capability of turfgrasses after the stressful effects on turf have been relieved (Beard, 1973; Sheffer et al., 1979; Busso et al., 1990). The effect of various management practices on plant vigor can be measured quantitatively through the quantity of nonstructural carbohydrate content, which represents an energy source (White, 1973). The major TNC found in turfgrass shoots consist of the monosaccharides, glucose and fructose, the disaccharide sucrose, various oligosaccharides of the ß-(2->6)-linked polyfructosylsucrose type, starch, and long-chain fructans (Hull, 1992). Some C-3 grasses accumulate starch (Bender and Smith, 1973) or sucrose (Borland and Farrar, 1985) in their stem bases, but most cool-season turfgrasses concentrate fructans in their vegetative tissues (Chatterton et al., 1989).

The quantification of TNC in turfgrasses has proven valuable in investigations of assimilate translocation in perennial grasses (Hull and Smith, 1974) and the physiological response of turf to environmental and cultural factors (Watschke et al., 1970; Cooper et al., 1988). The TNC content has been measured as an indicator of growth and physiological responses of creeping bentgrass to increasing temperatures and heat-stress conditions (Huang and Gao, 2000; Xu and Huang, 2000). The TNC content has also been useful for evaluating the effects of different cultural practices on disease incidence and severity (Davis and Dernoeden, 1991). These studies indicate that turf TNC content can be influenced by many different factors.

Turfgrasses maintained on golf course fairways are subjected to intensive management practices. These harsh conditions may jeopardize carbohydrate availability to the turf during critical growth periods, thus making them vulnerable to other cultural and environmental stresses. In past research, significant differences in TNC concentrations were observed in turfgrasses under different management variables (Sheffer et al., 1979; Han et al., 1998; Xu and Huang, 2000; Richie et al., 2001). Although the effects of MHs have often been discussed in relation to turf quality and other aspects of turf growth (Salaiz et al., 1995; Razmjoo et al., 1996; Bush et al., 2000; Fagerness et al., 2000), no information is available on the effect of MH on carbohydrate status in creeping bentgrass.

An investigation into the effects of MH on TNC levels should give valuable insight into their potential for detecting turfgrasses stress levels. The quantification of individual carbohydrate components may also be valuable (Westhafer et al., 1982; Cooper et al., 1988) to correlate TNC with general turf health or stress. Since TNC is the sum of all individual carbohydrate components there may be an individual component that is more consistently correlated to turf health and will not be masked by the variation contributed from the other components.

Since conventional laboratory methods for analyzing nonstructural carbohydrates are very time consuming, NIRS was selected for the TNC determinations. Near infrared reflectance spectroscopy has been shown to significantly decrease the time and labor involved in measuring TNC in several turfgrasses (Shepard et al., 1990), with an R2 value of 0.86 between laboratory TNC and NIRS predictions in ‘Tifdwarf’ and ‘Tifway’ bermudagrasses [Cynodon dactylon (L.) Pers. x C. transvaalensis Burtt Davy] (Miller and Dickens, 1996). Near infrared reflectance spectroscopy techniques have also been used to predict thatch composition in creeping bentgrass (Couillard et al., 1994). A complete description of the technique adopted in predicting the constituent carbohydrate concentrations is discussed by Narra (2002).

The objectives of this research were to: (i) determine if there was a predictable depression in TNC concentration in creeping bentgrass turf at different MHs; (ii) determine if there were any significant differences in TNC content among different creeping bentgrass cultivars; and (iii) determine seasonal changes in TNC levels under different MHs.


   MATERIALS AND METHODS
TOP
 NOTES
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS AND DISCUSSION
 DISCUSSION
 REFERENCES
 
A field experiment was established at the Landscape Horticulture Research Facility, Urbana, IL, in September 1997. The experimental design was a strip-plot design with three replications. Eight creeping bentgrass cultivars, ‘Penncross’, ‘Penneagle’, ‘Putter’, ‘Seaside II’, ‘G-6’, ‘Southshore’, ‘Crenshaw’, and ‘L-93’ were arranged as whole-plot treatments in a randomized complete block design with three MH treatments as strip-plot factors, each with a dimension of 1.5 by 5.5 m. The plots were seeded on 12 Sept. 1997. Soil at the site is a Flanagan silt loam soil (fine, montmorillonitic, mesic Aquic Argiudoll).

Plots were mowed at bench heights of 0.64, 1.27, or 1.90 cm three times each week with a reel-type walking greens mower (The Toro Co., Minneapolis, MN). Triclopyr {[(3,5,6-trichloro-2-pyridinyl)oxy]acetic acid} + clopyralid [(3,6-dichloro 2-pyridinecarboxylic acid)] was applied at the combined a.i. 1.0 kg ha–1 during 1997 and 0.5 kg ha–1 during 1998 to control the incidence of various broadleaf weeds, principally clover (Trifolium repens L.). During the entire study, chlorothalonil (1,3-benzenedicarbonitrile,2,4,5,6-tetrachloro-chlorothalonil) and propiconazole (1-{[2-(2,4-dichlorophenyl)-4-propyl-1,3-dioxolan-2-y1]methyl}-1H-1,2,4-triazole) were applied as needed to prevent diseases such as dollar spot (Sclerotinia homoeocarpa F.T. Bennett), brown patch (Rhizoctonia solani Kühn), and pythium (Pythium spp.). Turf received N at 106 kg ha–1 yr–1 in 1998, 154 kg ha–1 yr–1 in 1999, 159 kg ha–1 yr–1 in 2000, and 216 kg ha–1 yr–1 in 2001. Rates and timing for individual N applications varied across years. In general, applications were made during the months of April through September four to five times during a growing season. Nitrogen was mainly applied as urea (46-0-0). Surface irrigation was applied as needed to avoid water stress and prevent drying. Plots were spiked in the fall of 2000 with a solid-tine spiker to improve soil aeration and reduce compaction effects on the turf.

Clipping Collection for Total Nonstructural Carbohydrate Analysis
Clippings were collected for TNC analysis three times in 1998, 12 times in 1999, nine times in 2000, and five times in 2001. The turf was mowed 4 to 6 d before each clipping collection, depending on the growth rate to collect an adequate volume of tissue. In previous research, significant variations of measured TNC were reported (Sheffer et al., 1979) because of diurnal fluctuations. Hence, diurnal variations were minimized by harvesting consistently early in the photoperiod (before 1200 h).

Collected clippings were immediately frozen in the field in liquid nitrogen, placed in plastic zip-closure bags, held in a dry ice chamber, and then stored at –20°C. In a separate research study conducted by Narra (2002), significant differences in TNC levels of creeping bentgrass clippings were measured between samples that were air dried and samples that were frozen in liquid N. Before analysis, samples were freeze dried in a general-purpose freeze-drier (The Virtis Company, Inc., Gardiner, NY). All samples were ground with a cyclone sample mill (Udy Corp., Fort Collins, CO) to pass a 1.0-mm screen. All 2088 samples were scanned in a near infrared spectrometer (NIRS Systems 5000, Silver Springs, MD) to determine a representative population of samples (112 samples) to develop lab values for calibration by chemical analysis by the method of Westhafer et al. (1982). Briefly, 60-mg tissue samples were extracted in 0.1 M phosphate buffer (pH 5.5) overnight (about 12 h). Glucose, fructose, sucrose, and fructans were quantified by glucose oxidase and invertase enzymes. Reducing sugars (glucose and fructose) and sucrose were determined by absorbance at 540 nm with a Shimadzu double-beam UV-visible spectrophotometer (Scientific Instrument Corp., Inc., Columbia, MD). Fructan absorbance was determined at 490 nm.

Data Analyses
The effects of MHs and cultivars and their interactions on TNC and its component concentrations were determined by ANOVA according to the general linear model procedure of the Statistical Analysis System (SAS Institute, Inc., Cary, NC). Fisher's protected least significance difference procedure was used to separate means when appropriate. The mixed procedure of SAS was used to estimate the parameters in building regression curves to model TNC concentrations across time. The earliest date of data collection in 1999 was 22 June, while data were first collected in 2000 on 2 May. Therefore, the y-intercept of the equations in regression curves is set to 1 January instead of the first data collection date. We used the "mmddyy8." SAS date format and made necessary conversions to get the numeric date values for the regression analyses and used the same date format and values for the trend lines in Fig. 1 and 2 . The main effects and treatment interactions were considered significant at P ≤ 0.05. Since the original data were not normally distributed, a square root transformation was applied to the data before statistical analyses. Following transformation, data did not significantly differ from normality (Shapiro-Wilks test).



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  		Fig. 1. Seasonal changes in creeping bentgrass total nonstructural carbohydrate (TNC) concentrations at (A) 0.64-, (B) 1.27-, and (C) 1.90-cm mowing heights during 1999. Curves represent predicted TNC values by a quadratic regression of TNC.

 


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  		Fig. 2. Seasonal changes in creeping bentgrass total nonstructural carbohydrate (TNC) concentrations at (A) 0.64-, (B) 1.27-, and (C) 1.90-cm mowing heights during 2000. Curves represent predicted TNC values by a quadratic regression of TNC.

 

   RESULTS AND DISCUSSION
TOP
 NOTES
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
DISCUSSION
 REFERENCES
 
Overall Analysis of Variance
At the P ≤ 0.05 level of probability, the analysis of all 4 yr of data showed significant main effects for MH on all TNC fractions (Table 1). When the 4 yr of data were analyzed together to examine the potential for by-date interactions, significant interactions were observed for all by-date factors. A further analysis for each growing season showed significant MH x date interactions during 1999 and 2000, while they were not significant during 1998 and 2001. Hence, seasonal trends in TNC concentrations are reported for only 1999 and 2000. Although the by-date interactions were significant with MH, cultivars, and their interaction during 1999, they were not consistent during the other growing seasons. The main effect of cultivar treatment was not significant in any growing season. The TNC levels averaged across the four growing seasons for eight cultivars are: Penncross (74.24 mg g–1), Penneagle (78.47 mg g–1), Putter (81.06 mg g–1), Seaside II (75.10 mg g–1), G-6 (77.96 mg g–1), Southshore (77.66 mg g–1), Crenshaw (78.61 mg g–1), and L-93 (79.34 mg g–1).


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  		Table 1. Analysis of variance of nonstructural carbohydrate fractions and total nonstructural carbohydrate (TNC) concentrations of eight creeping bentgrass cultivars mowed at three cutting heights from 1998 to 2001.

 
Seasonal Changes in Nonstructural Carbohydrates at Different Mowing Heights
Quadratic regression models were developed for 1999 (Fig. 1) and 2000 (Fig. 2) data to describe the relationship of TNC concentrations with sample date for each of the MH treatments. Average TNC content of the clippings during 1999 and 2000 greatly decreased in the middle of July, reaching the lowest TNC content in August. The TNC concentrations began to increase in September, exhibiting highest TNC accumulation in October and/or November. The above trend was consistent for the three MHs.

Analysis of Individual Nonstructural Carbohydrate Components
There was a yearly increase in average TNC concentrations when averaged across all dates within a growing season. Average TNC content of creeping bentgrass clippings on dry weight basis was 56.95 mg g–1 in 1998, 67.36 mg g–1 in 1999, 78.88 mg g–1 in 2000, and 113.44 mg g–1 in 2001. On all sampling dates and MHs, the major nonstructural carbohydrate in creeping bentgrass was fructan, followed by fructose. The fructan content in clippings ranged from 22.08 mg g–1 in 1998 to 56.33 mg g–1, which was about 50% of TNC concentration in 2001. The other soluble carbohydrates, glucose and sucrose, were relatively low in concentration.

Since fructans are the major nonstructural carbohydrates found in cool season grasses (Westhafer et al., 1982), the effect of MH on TNC in creeping bentgrass followed the general patterns established by fructans. An analysis of fructan and TNC concentrations across all dates showed a high degree of correlation (r = 0.96). Mowing heights had highly significant effect on the level of fructans throughout the experiment. The level of fructan content of 0.64-cm mowed plants was significantly (P ≤ 0.05) higher than 1.27- or 1.90-cm mowed plants on 11 of the 29 dates, while 1.27-cm mowed plots had the highest fructan concentration on only 1 d, and 1.90-cm on none (Table 2). Mowing heights showed similar trends in fructan content as they showed in TNC content on 27 of the 29 d during which clippings were collected. Trends of reducing sugars were most similar to TNC trends at different MHs (r > 0.96), while sucrose was least similar (r = 0.86).


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  		Table 2. Number of significant dates for comparisons among nonstructural carbohydrate fractions of creeping bentgrass clippings at three mowing heights collected from 1998 to 2001.

 
Effect of Mowing Height on Nonstructural Carbohydrate Concentration
Although overall means during each year showed significant differences in TNC concentration at different MHs, mean differences were not consistent throughout the study. In 1998, plots mowed at 0.64 cm had the highest sucrose, fructan, and TNC concentrations, followed by 1.27-cm plots and 1.90-cm plots, while there were no significant differences (P ≤ 0.05) in reducing sugar concentrations between 0.64-cm and 1.27-cm plots; however, both 0.64-cm and 1.27-cm mowed plots had higher concentrations than 1.90-cm mowed plots. In 1999, the average TNC concentration of 0.64-cm mowed plots was 16.82 and 22.43% higher than 1.27-cm and 1.90-cm mowed plots, respectively, while in 2000 it was 20.6 and 26.5% higher. The trend was similar even in 2001, with 0.64-cm mowed plots showing 18.75 and 20.66% higher concentrations than 1.27- and 1.90-cm mowed plots, respectively. The average TNC concentrations were significantly different (P ≤ 0.05) between 1.27- and 1.90-cm mowed plots in 1998, while no differences were observed from 1999 through 2001. A summary of comparisons of MHs with concentrations of nonstructural carbohydrate fractions is presented in Table 2.


   DISCUSSION
TOP
 NOTES
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 DISCUSSION
REFERENCES
 
The effect of MH on TNC concentration presented the same general trend in each of the four seasons, but at different degrees of intensity. Turf mowed at the lowest cutting height (0.64 cm) generally accumulated the most TNC, which was in direct contrast to our original hypothesis. Although it is not clear why the lowest-cut turf accumulated the most TNC, previous studies have shown partitioning of TNC in turfgrass plants (Hull, 1987). The TNC is mobilized from leaf blades to sheath, crown, and rhizome tissues during dark periods (Hull, 1981, 1987) and leaf carbohydrate levels return to their concentrations of the previous morning (Sicher et al., 1984). Clippings collected from the lowest MH probably contained more sheath and stem portions of the plant than plots mowed at higher heights, thus resulting in higher TNC concentrations. Previous research has shown reduced turf quality and growth of creeping bentgrass at low MH, especially during summer (Salaiz et al., 1995; Carrow, 1996; Huang et al., 1998), but treatments used in all these studies were at putting green height. However, in this study, no reduction in turf quality or growth for any mowing treatments, which were maintained at fairway heights, was measured in any season.

Since diurnal variations in TNC content of turfgrasses were reported in past research (Sheffer et al., 1979), the TNC concentrations of the clippings could well have been a snapshot of the accumulated TNC at the time of sample collection. Therefore, a measurement of TNC levels at different times during each sample date is warranted for a consistent estimation of TNC levels in creeping bentgrass.

On the basis of nonsignificant cultivar effects, it is found that the eight cultivars evaluated in this study produced and utilized the measured sugar components similarly. Though there were some differences in individual TNC fractions among different cultivars on some of the sample dates, the levels of observed differences did not have a practical impact on turf health. These results are consistent with previous studies where Sweeney et al. (2001) reported very few differences in TNC levels among 15 creeping bentgrass cultivars, while Xu and Huang (2003) reported inconsistent cultivar differences between carbohydrate fractions at different times of the year. Lack of differences among different cultivars with respect to carbohydrate allocation is critical for blended fairways or turfs of unknown cultivar composition. These results should be particularly useful in developing future precision turfgrass management of areas with mixed cultivar composition.

In this study, significant differences were observed in the TNC concentrations of creeping bentgrass across a season with the highest accumulation of TNC during the late-fall period. This observed trend was similar to the one seen by Zanoni et al. (1969), where carbohydrate reserves in Kentucky bluegrass increased from spring to midsummer followed by a prominent depression in late summer, before the concentrations increased again in the fall. This was during a period of cool temperatures with little vertical turf growth. This situation of relatively high photosynthetic activity with little growth allows for the continuing accumulation of TNC in blade tissue with very little utilization. Others have also reported decreases in TNC content during summer for creeping bentgrass (Sweeney et al., 2001) and other cool-season turfgrasses (Youngner et al., 1978; Xu and Huang, 2003).

In summary, the accumulated TNC in creeping bentgrass was not correlated with mowing stress. Ideally, it would be best to predict plant stress through a single, nondestructive measurement. Additional research is needed to determine how TNC is concentrated within turf tissue above the mowing height.


   ACKNOWLEDGMENTS
 
The authors wish to thank Karsten Turf Analysis, The Toro Company, and the Illinois Turfgrass Foundation for supporting this study.


   NOTES
TOP
 NOTES
ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 DISCUSSION
 REFERENCES
 
Contribution from the Illinois Agric. Exp. Stn. Study supported in part by the Illinois Turfgrass Foundation.

Received for publication May 4, 2003.


   REFERENCES
TOP
 NOTES
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 DISCUSSION
 REFERENCES
 




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