Temperature, nitrogen and light effects on hybrid bermudagrass growth and development.
Temperature, photoperiod, and light levels influence bermudagrass growth and development. New shoot production and stolon elongation occurred for 'U-3' bermudagrass (Cynodon dactylon L. Pers) when day temperatures were greater than or equal to 15.5[degrees]C and night temperatures were greater than or equal to 4.4[degrees]C (Youngner, 1959). Longer internodes and less stolon and rhizome branching were observed in bermudagrass grown at 20% of full sunlight than when grown in full sun (Dong and de Kroon, 1994). Orthotropic shoots (elongated stems) are common to bermudagrass and other grasses grown in shade or low light conditions.
Growth (herbage yield) of bermudagrass was affected more by photoperiod at 21.1/15.5[degrees]C than at 32.2/26.7[degrees]C day/night temperatures (Lovvorn, 1945).
Developmental morphology is an important consideration in the management of perennial grasses used for turf and forage (Moore and Moser, 1995). Leaf development and appearance rates (phyllochron) expressed in either chronological days or degree days are useful for determining mowing height and frequency, growth regulator and pesticide application, and future growth potential (Waller et al., 1985; Parsons, 1988; Moore et al., 1991; Frank et al., 1993; Moore and Moser, 1995; Bonhomme, 2000). Plant shoots develop by sequentially forming a series of building blocks called phytomers at each axis meristem (Madison, 1971; Rickman and Klepper, 1995). A phytomer consists of a leaf and leaf sheath, node, internode, and the associated axillary bud below the point of sheath attachment (Moore and Moser, 1995).
To date limited research has been conducted comparing the combined effects of temperature and light on Tifdwarf growth and development. Such research is needed to further our understanding of how turfgrass responds to its environment so that turf managers can adjust their practices as needed to compensate for environmental conditions. The objectives of the present study were to assess the influence of temperature, nitrogen, and light on the developmental morphology of Tifdwarf bermudagrass.
MATERIALS AND METHODS
Sprigs consisting of three to four distinguishable nodes were harvested from stock plant material maintained in a greenhouse. Sprigs were surface sterilized by soaking in a 10% (v/v) bleach solution for 2 min to eliminate potential funsal pathogens, rinsed three times with distilled water, and planted in 12.7-cm diameter pots containing a sand:peat (6:1 v/v) root zone mix. Each pot received three sprigs and rooting occurred within 3 d in a dew chamber. Misting nozzles in the dew chamber activated for 0.75 min every 2.75 min and the average temperature was 29[degrees]C. After rooting, plants were maintained in a greenhouse before treatment initiation, where greenhouse temperature fluctuated between 25 and 35[degrees]C. Plants were watered as needed to prevent water stress and nutrients were supplied at 8.1 kg N [ha.sup.-1] [wk.sup.-1] as 20-8-16 (N:[P.sub.2][O.sub.5]:[K.sub.2]O) dissolved in 60 mL of water. The grass canopy was maintained at a height of 5 cm by weekly hand clipping.
Experiment #1--Effects of Temperature and Nutrients
A total of 108 pots were arranged in a completely random design with factors of temperature and nutrient rate at three levels and 12 replications. Temperature regime treatments were established in three separate growth chambers (Model Q 2936, Environmental Growth Chambers, Chagrin Falls, OH). Temperature regimes were day/night temperatures of 35/27[degrees]C, 27/19[degrees]C, and 19/11[degrees]C, each with a 14-h photoperiod. The high and low temperatures of each growth chamber were recorded daily utilizing a maximum/minimum thermometer. Plants were allowed to acclimate to the growth chamber conditions for a 10-d period immediately followed by a 25-d data collection period. Each chamber was illuminated by 30 243.8 cm fluorescent lamps, six 121.9 cm fluorescent lamps, and 15 incandescent lamps providing a total photosynthetic photon flux density (PPFD) of 525 [micro]mol [m.sup.-2] [s.sup.-1] (approximately 25% of full sun) at the plant canopy. PPFD was measured using a Li-Cor Model LI-185 Quantum Radiometer/Photometer (Lincoln, NE). After completion of all tests and measurements, the entire experiment was repeated with a new set of plants, but the same equipment and procedures. Assignment of treatments to growth chambers was random for both the experiment and its repetition.
Daily growing degree days (GDD) were calculated as GDD ([degrees]C) = [(daily maximum air temperature + daily minimum temperature)/2] - base temperature of 5[degrees]C. Daily GDD based on actual temperature measurements for the first experimental period were 22, 18.5, and 11 for the 35/27[degrees]C, 27/19[degrees]C, and 19/11[degrees]C temperature regimes, respectively, and 23.5, 19, and 9.5 for the second experimental period. Daily GDD for the 35/27[degrees]C treatment were slightly lower than predicted because of the inability of the growth chambers to maintain a constant 35[degrees]C.
Nutrient treatments consisted of 24.4, 16.3, and 8.1 kg N [ha.sup.-1] [wk.sup.-1] applied as 20-8-16 (N:[P.sub.2][O.sub.5]:[K.sub.2]O) dissolved in 60 mL [H.sub.2]O. Plants were watered as needed to prevent water stress. The nature of the measurement parameters prevented clipping the grass during the data collection period. Treatment effects over the 35-d period in the growth chamber were determined as follows. Internode length, leaf length, and shoot weight measurements were made at the conclusion of the experiment. Internode length was determined as the distance between the first and second most recently formed phytomers. Leaf length was determined by measuring the youngest leaf of the second most recently formed phytomer. Shoot weight was measured by harvesting all the vegetative plant material above the root/ shoot interface. Samples were frozen by submersion in liquid nitrogen and kept in liquid nitrogen until they could be transferred to a freeze drier for a 48 h drying cycle after which they were weighed to determine total dry weight. The phyllochron was quantified by marking expanding leaves on a shoot tip and recording accumulated GDD and leaves produced each 24 h for 10 consecutive days following the 10-d acclimation period. Calculations were done by the following equation:
 [P.sub.GDD] = [summation] GDD/[summation] LT
where [P.sub.GDD] = pyllochron in units of growing degree days [leaf.sup.-1], [summation] GDD = sum of the growing degree days from Day 1 through Day 10, [summation] LT = sum of the leaves produced from Day 1 through Day 10.
A viable axillary bud was defined as consisting of three or more leaves produced from the phytomer of origin. The GDD required for the production of a viable axillary bud were calculated by counting the number of leaves from the stolon tip to and including leaves at the node of attachment of the most recently formed viable axillary bud and multiplying by the corresponding phyllochron. This can be expressed mathematically by the following equation:
 BA = L x P
where BA = axillary bud appearance in units of GDD, L = number of leaves from the stolon tip to the node of attachment, and P = phyllochron in units of GDD [leaf.sup.-1].
The entire data set was statistically evaluated by ANOVA and showed no significant difference between experiment or any experiment by treatment interactions. Therefore, all data for the experiment and its repetition were pooled and subjected to analysis of variance. When a significant F statistic occurred for a treatment effect, Tukey's multiple range test was used for mean comparison (Zar, 1996).
Experiment #2--Effects of Light and Temperature
Treatments including three levels of PPFD and two day/ night temperature regimes were arranged in a completely randomized design with six replications. The different light treatments were achieved by varying the distance between the light source and the turf canopy. The light treatments used in the experiment were PPFD levels of 975,575, and 300 [micro]mol [m.sup.-2] [s.sup.-1] at the plant canopy. Plants were maintained at these PPFD levels in the growth chambers for 28 d before recording leaf length and internode length. Temperature treatments were 35/27[degrees]C and 27/19[degrees]C. Nutrients were applied at 16.3 kg N [ha.sup.-1] [wk.sup.-1] as 20-8-16 (N:[P.sub.2][O.sub.5]:[K.sub.2]O) dissolved in 60 mL [H.sub.2]O. Leaf length and internode length were determined as previously described. After completion of all tests and measurements, the entire experiment was repeated using a new set of plants. Temperature treatments were randomly assigned to two growth chambers.
The entire data set was statistically evaluated by ANOVA and showed no significant difference between experiment or any experiment x treatment interactions. Therefore, all data for the light and temperature experiment and its repetition were pooled.
RESULTS AND DISCUSSION
Analysis of the entire data set showed no effect because of experiment or any experiment x treatment interactions (Table 1). The results showed temperature to have a significant effect on all seven measured plant responses. In addition, nitrogen level had a significant effect on four plant responses. The only significant interaction effect was for a temperature regime x nitrogen interaction effect on shoot weight. Therefore, except for shoot weight, only main effects of treatments will be discussed.
Effects of Temperature
Temperature regimes had significant effects on phyllochron, axillary bud appearance, internode length, leaf length, and shoot weight (Table 1). When averaged over all nutrient levels, phyllochron, expressed as GDD leaf 1, increased when the temperature regime was increased from the 19/11[degrees]C regime to the 27/19[degrees]C regime. Phyllochron at the 35/27[degrees]C regime was similar to that at the 27/19[degrees]C regime. Fewer GDD [leaf.sup.-1] measured on plants grown in the 19/11[degrees]C regime suggested more efficient utilization of heat units as compared with plants grown in the 27/19[degrees]C and 35/27[degrees]C regimes.
The phyllochron for corn (Zea mays L.) grown between 25 and 32[degrees]C was three to six times greater than that measured in the present study for Tifdwarf bermudagrass (Cutforth et al., 1992). Phyllochron values reported for winter rye (Secale cereale L.) during the prevernalization and vernalization stages were three to seven times greater, respectively, than the values measured for Tifdwarf bermudagrass (Gan and McLeod, 1997). Compared with the present study, Frank et al. (1985) measured phyllochron values for reed canarygrass (Pharlaris arundinacea L.), crested wheatgrass [Agropyron desertorum (Fisch. Ex Link) Schult.], intermediate wheatgrass [Elytrigia intermedia (Host) Nevsk.], and western wheatgrass [Pascopyrum smithii (Rhdb.) Love] that were four, five, six, and seven times greater, respectively. The Tifdwarf bermudagrass phyllochron measured in this study was much less than many other annual crop species and may be related to its rapid growth rate and small leaf size, both of which are desirable characteristics for closely mowed turfgrass.
The phyllochron, when expressed in chronological days, exhibited a significant decrease with each increase in temperature (Table 1) and was two fold greater at 19/11[degrees]C than at 35/27[degrees]C. Some of this decrease was due to the increased number of GDD per chronological day at the higher temperatures. In addition, Tifdwarf bermudagrass is a warm-season grass and 30[degrees]C is a near optimal temperature for its metabolism (Beard, 1973).
The number of GDD required for axillary bud appearance was lower for plants grown in the 19/11[degrees]C temperature regime compared with those in the warmer 27/19[degrees] and 35/27[degrees]C regimes. This suggests a higher GDD efficiency at the lower temperature. The chronological days required for appearance of axillary buds was least for the plants in the 35/27[degrees]C temperature regime and increased significantly with each decrease in temperature regime to 19/11[degrees]C. Although axillary bud formation was most rapid at the 35/27[degrees]C temperature regime, more energy input per bud was probably required because of increased respiration rates at the higher temperature. This indicates that growing turf at high temperatures to achieve the fastest possible growth rate in terms of buds per day may not be in the best long-term interest of plant health and may actually reduce carbohydrate reserves.
Internode length increased from 18 to 24 mm with an increase in temperature from the 19/11 to 27/19[degrees]C regime but then showed a large decrease to 7 mm at the 35/27[degrees]C regime (Table 1). Internode length at the 35/27[degrees]C regime was similar to that observed for Tifdwarf bermudagrass maintained on putting greens during the summer months in the southern portion of the USA when temperatures are high, while that at the 19/11[degrees]C and 27/19[degrees]C regimes was much longer (Fig. 1).
[FIGURE 1 OMITTED]
Leaf lengths increased from 9.2 to 11.5 mm with an increase in temperature regime from 19/11 to 27/19[degrees]C (Table 1). Leaf lengths then decreased to 7.1 at the 35/ 27[degrees]C regime. The short leaf length of 7.1 mm at the 35/ 27[degrees]C regime is also similar to that observed for Tifdwarf bermudagrass maintained on putting greens during the summer months in the southern portion of the USA when temperatures are high. Leaf width was measured (data not presented) but was similar among regimes.
Shoot weight was greatest at the 27/19[degrees]C temperature regime (Table 1). This may be a result of the low phyllochron (days [leaf.sup.-1]), the long internode length, and the long leaf length at the 27/19[degrees]C temperature regime. Measured shoot weights at the 19/11 and 35/27[degrees]C regimes were lower than that at the 27/19[degrees]C regime but because of the significant temperature by nitrogen interaction effect for shoot weight these differences can only be considered trends.
Effects of Nutrients
Nutrient regime significantly affected the GDD for axillary bud appearance, internode length, and leaf length (Table 1). In contrast, nutrient regimes had no significant effect on phyllochron, leaf width, or shoot dry weight.
An overall trend was seen in which an increase in nitrogen increased the internode length; however, internode lengths at the lower two N levels were statistically similar (Table 2). Plants fertilized at the greatest N rate had the longest internode length.
Plants fertilized with 8.1 kg N [ha.sup.-1] [wk.sup.-1] had shorter leaf lengths than plants fertilized with either 16.3 or 24.4 kg N [ha.sup.-1] [wk.sup.-1]. Total shoot dry weight increased with each increase in N fertilization. The combination of increased leaf length and internode length in response to N fertilization resulted in an increase in total above ground dry matter. Thus, at day/night temperatures ranging from 19/11[degrees]C to 35/27[degrees]C increasing the N fertilization from 8.1 kg [ha.sup.-1] [wk.sup.-1] up to as much as 24.4 kg [ha.sup.-1] [wk.sup.-1] will result in increased dry matter production.
Effects of Light Quantity
Reduced light can alter plant development and form within 4 to 7 d (Langham, 1941; and McBee, 1969). Internode lengths observed for Tifdwarf bermudagrass in the present experiment increased with decreasing PPFD from 975 to 300 [micro]mol [m.sup.-2] [s.sup.-1] (Fig. 2). Similar increases in internode length in response to decreased light quantity were observed in plants grown at both temperature regimes; however, the internode lengths for plants grown in the 27/19[degrees]C temperature regime were consistently twofold greater (Fig. 2) than those in the 35/27[degrees]C temperature regime. This indicates that both high temperature and light intensity have regulating effects on internode length.
[FIGURE 2 OMITTED]
Leaf length responded in a similar fashion (Fig. 3). Reductions in PPFD from 975 to 300 [micro]mol [m.sup.-2] [s.sup.-1], resulted in a three- to four-fold increase in leaf lengths. A reduction in temperature from 35/27 to 27/19[degrees]C resulted, on average, in a doubling of leaf length at a given light quantity. This indicates that both high temperature and light intensity also have regulating effects on leaf length.
[FIGURE 3 OMITTED]
The results of these experiments suggested that both light levels and growth temperature play pivotal roles in the growth and development of Tifdwarf bermudagrass and regulate expression of the dwarf phenotype. The data also suggest that establishment of Tifdwarf bermudagrass from sprigs, and recovery from disruptive cultivation practices such as core aerification and dethatching, may be slower during periods of high temperature (>30[degrees]C) and light (>1000 [micro]mol [m.sup.-2] [s.sup.-1]) characteristic of late-June through early September in the southern USA. Thus, turf managers may be able to take advantage of the morphological changes in Tifdwarf bermudagrass to achieve more rapid turf cover following establishment or cultivation by judiciously timing these activities on the basis of average monthly diurnal temperatures.
Abbreviations: GDD, growing degree days; MSD, minimum significant difference; PPFD, photosynthetic photon flux density.
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R. L. Stanford, R. H. White, J. P. Krausz, J. C. Thomas, * P. Colbaugh, and S. D. Abernathy
R.H. White, R.L. Stanford, J.C. Thomas, and S.D. Abernathy, Soil and Crop Sciences Dep., Texas A&M Univ., 2474 TAMU, College Station, TX 77843-2474; J.P. Krausz, Plant Pathology and Microbiology Dep., Texas A&M Univ., 2132 TAMU, College Station, TX 77843-2132; P. Colbaugh, Texas A&M Dallas, 17360 Coit Road, Dallas, TX 75252-6599. Received 24 Jan. 2005. * Corresponding author (email@example.com).
Table 1. Effects of air temperature regime and applied nitrogen on phyllochron, axillary bud appearance, internode length, leaf length, and shoot weight of 'Tifdwarf' bermudagrass over a 35-d period with a 14-h photoperiod. Temperature regime Nitrogen Phyllochron day/night ([degrees]C) kg [ha.sup.-1] [wk.sup.-1] GDD ([dagger]) 19/11 8.1 20 19/11 16.3 18 19/11 24.4 21 Mean 20 27/19 8.1 22 27/19 16.3 22 27/19 24.4 20 Mean 21 35/27 8.1 27 35/27 16.3 23 35/27 24.4 23 Mean 24 MSD([dagger])[sub.0.05]T 2 Source of variation df Experiment (E) 1 NS ([section]) Replication 5 NS Temperature regime (T) 2 <0.001 Nitrogen (N) 2 NS EXT 2 NS EXN 2 NS TXN 4 NS EXTXN 4 NS Auxillary bud Internode Temperature regime Phyllochron appearance length day/night ([degrees]C) d GDD d mm 19/11 2.0 82 8.2 16 19/11 1.8 72 7.2 18 19/11 2.1 78 7.8 19 2.0 77 7.7 18 27/19 1.2 66 3.7 23 27/19 1.2 67 3.7 23 27/19 1.1 64 3.5 27 1.2 66 3.6 24 35/27 1.0 96 3.7 6 35/27 0.9 79 3.0 7 35/27 0.9 79 3.1 8 0.9 85 3.2 7 MSD([dagger])[sub.0.05]T 0.2 8 0.6 2 Source of variation P > F Experiment (E) NS NS NS NS Replication NS NS NS NS Temperature regime (T) <0.001 <0.001 <0.001 <0.001 Nitrogen (N) NS 0.02 NS 0.01 EXT NS NS NS NS EXN NS NS NS NS TXN NS NS NS NS EXTXN NS NS NS NS Leaf Shoot Temperature regime length weight day/night ([degrees]C) mm g [pot.sup.-1] 19/11 8.0 0.87 19/11 9.8 1.59 19/11 10.0 2.03 9.2 1.50 27/19 10.3 1.40 27/19 13.0 2.70 27/19 11.2 3.61 11.5 2.57 35/27 6.3 0.57 35/27 7.5 0.84 35/27 7.5 1.16 7.1 0.85 MSD([dagger])[sub.0.05]T 1.2 -- Source of variation Experiment (E) NS NS Replication NS NS Temperature regime (T) <0.001 <0.001 Nitrogen (N) 0.01 <0.001 EXT NS NS EXN NS NS TXN NS <0.002 EXTXN NS NS ([dagger]) GDD = growing degree days. ([double dagger]) MSD = minimum significant difference. ([section]) NS = nonsignificant. Table 2. Effects of nitrogen fertility on phyllochron, axillary bud appearance, internode length, and leaf length of 'Tifdwarf' bermudagrass. N-Fertilization regime Phyllochron Phyllochron kg [ha.sup.-1] [wk.sup.-1] GDD ([dagger]) [leaf.sup.-1] days [leaf.sup.-1] 8.1 23 a ([double dagger]) 1.4 a 16.3 21a 1.3 a 24.4 21a 1.4 a N-Fertilization Axillary bud Axillary bud regime appearance appearance kg [ha.sup.-1] [wk.sup.-1] GDD [bud.sup.-1] days [bud.sup.-1] 8.1 81.3 a 5.2 a 16.3 72.7 b 4.6 a 24.4 73.7 b 4.8 a N-Fertilization Internode Leaf regime length length kg [ha.sup.-1] [wk.sup.-1] mm 8.1 15.2 b 8.2 b 16.3 16.4 b 10.1 a 24.4 17.9 a 9.6 a ([dagger]) GDD = growing degree days. ([double dagger]) Numbers in a given column followed by the same letter do not differ at p = 0.05.
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|Author:||Stanford, R.L.; White, R.H.; Krausz, J.P.; Colbaugh, P.; Abernathy, S.D.|
|Date:||Nov 1, 2005|
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