A PRACTICAL RESEARCH DIGEST FOR TURF MANAGERS

Volume 9, Issue 3 • March 2000 TREND!

AGRONOMY IN THIS ISSUE

• Stomata: The 's Stornata : Port of Entry 1 The Plant's Port of Entry Stomata structure By Dr. Karl Danneberger 's role How antitranspirants work

• Herbicide-resistant hether it is a golf course green, home lawn or athletic field, we often forget that Ttirfgrasses: Panacea or a turf is composed of millions of individual . How each of those plants Problem? ...... 4 Wrespond to environmental and cultural management programs dictates the quality of the turf. When we look at the structure and function of individual turfgrass • Four Zoysia Varieties: Shade Tolerance at a plants, the complexity of life is easily seen. Price 8 In this paper, one small plant structure — stomata — will be discussed. Stomates are rather simple structures that allow for gas exchange and transpiration to occur. However, • Management Forum 11 when you think of survival of turfgrass plants through the necessity to create usable ener- gy from solar radiation via photosynthesis, and the dissipation of heat from the plant via Summer bentgrass decline transpiration, stomata play a critical regulation role. Dry conditions and insects

Gray vs. pink snow mold Stomata structure • Meet Curt Harler. ... 15 The stomatal area of the blade includes the guard cells and the stomatal pore (Esau, 1977). The stomatal pore or opening is where carbon dioxide (C02) enters the plant for photosynthesis and the point of transpiration of water from the leaf. Two cells called the guard cells define the stomatal pore. The guard cells are rather elongated and slightly con- stricted in the middle. When guard cells are turgid they create the open pore. The stomatal area generally accounts for 1% of the total leaf surface. For turfgrass species, the stomatal density is approximately 2% to 3% of the leaf surface (Beard, 1973). The num- ber of stomates can vary depending on the turfgrass species. Green et al. (1990) calculated the stomatal density for ten turfgrass species and found greater stomatal density on the adaxial (upper) leaf side then the abaxial (bottom). Densities ranged on the adaxial side from 68 stom- ata mm-1 for tall fescue to 203 stomata mm-1 for hard fescue. Interestingly, no stomata were found on the abaxial side of hard fescue, sheep fescue, chewings fescue and rough bluegrass. Although we think of all plants having stomata, some plants do not. There are two major groups of astomatous plants (Woodward, 1998). The first group contains plants that never possessed stomates, like the gametophytes of bryophytes and lichens. The second group contains plants that were stomatous at one time, but developed effective astomatous char- acteristics. These types of plants are generally aquatic or parasitic in nature. COLLECTIOBEARDN As previously mentioned, stomates play a role in gas (COz) exchange and transpiration. A question that can be asked is: What did stomates initially evolve to do? The earliest land Visit us at plants were astomatous with a thick cuticle around their arial organ (Edwards et al. 1996). www. landscapegroup. com TURFGRASS TRENDS

Executive Editor Sue Gibson 440/891-2729; 440/891-2675 (fax) sgibson@advanstar. com The absence of stomata along with a thick Thus, if C02 concentrations are high in cuticle reduced any water loss from the the leaf,stomata will close. Conversely, if Managing Editor Curt Harler plant. However, given the extremely low C02 concentrations are low, the stomata 440/238-4556; 440/238-4116 COz diffusion rate into the leaf, a minimal will open. Light also plays a role in stomatal curt@curt-harler. com level of photosynthesis occurred resulting opening. Illumination increases pore open- Senior Science Editor in slow growth and development. These ing by increasing the uptake of potassium Dr. Karl Danneberger early plants probably evolved during peri- and chlorine, along with increased synthesis Consulting Editor of malate, which results in a swelling of the Chris Sarin ods of high C02 concentrations in the atmosphere. guard cells (Raschke, 1975). Croup Editor Vern Henry Later, periods of low COz concentration Within the visible light spectrum, blue drove evolutionary forces toward high stomatal light elicits the greatest response in govern- Production Manager Karen Lenzen density in plants such as horsetails, ferns, ing stomatal opening, although the blue 218/723-9129; 218/723-9576 (fax) conifers and angiosperms (Edwards et al. light effect is enhanced in the presence of [email protected] 1996). Stomata most likely evolved initially for continual red light (Karlsson, 1986). Circulation Manager Frank Christopherson gas exchange followed later as a mechanism to 218/723-9271 regulate water loss (Danneberger, 2000). Transpiration's role Group Publisher Let's look at the effect of stomata on gas John D. Payne exchange and transpiration. 440/891-2786; 440/891-2675 (fax) [email protected] For turfgrasses, transpiration is the major Gas exchange mechanism for dissipating heat from the Corporate & Editorial Office 7500 Old Oak Blvd. Photosynthesis is the process where leaf blade. Favorable conditions for transpi- Cleveland,, OH 44130-3369 plants convert radiant energy from the sun ration are low atmospheric humidity and Mew Subscriptions into usable metabolic energy. The overall high leaf temperature. The major mecha- 888/527-7008 equation for photosynthesis is: nism in regulating transpiration is the open-

Abstracts: 800/466-8443 24HzO + 12 C02 + radiant energy ( ing and closing of stomata. The closure of Reprint: 440/891-2744 1202+C12H24012+ 12H20 stomata reduces transpiration. Permission: 440/891-2742 Single copy or back issues: Where: Although I previously mentioned that, Subscription/Customer Service HzO is equal to water from an evolutionary stand point, stomata 888/527-7008; (fax) 218/723*9437 CO is carbon dioxide as previously evolved initially for CO exchange, the evo- Web site address: z z www.landscapegroup.com mentioned lution of stomatal density most likely Radiant energy is light from the sun allowed for the development for more

02 is oxygen and advanced and taller plants.

C]2H24012 is carbohydrate molecules If we look at water movement through ADVANSTAR where the usable energy for metabolic the plant xylem (the plants' water transport COMMUNICATIONS processes is stored. system), the tension of the water increases

Chairman and The presence of atmospheric C02 is when transpiration increases and soil mois- Chief Executive Officer critical for photosynthesis. For C02 to ture decreases. If this water tension increases Robert L. Krakoff enter the photosynthetic process, it must to a point where the column of water breaks Vice Chairman have an entrance point in the leaf. The port in the plant, air enters the xylem, disrupting James M. Alic of entry for COz is through stomata. The water flow. VP-Finance, CFO & Secretary David W. Montgomery opening and closing of stomates follows a This process is called xylem cavitation. It circadian rhythm in many plants. is postulated that increased stomatal density Executive Vice President, Business Development During daylight when photosynthesis is enhanced the evolutionary process of plants Skip Färber active, the stomata open to allow for C02 by preventing xylem cavitation, thus allowing Executive Vice Presidente diffusion, while at night when photosyn- for longer xylem pathways to develop for William J. Cooke thesis is not active, closure occurs. The taller plants (Woodward, 1998). Alexander S. DeBarr Morris R. Levitt exceptions are CAM plants (ex. desert Only 1% to 3% of the water absorbed by a Daniel M. Pjiillips plants). The trigger for stomatal opening is plant is actually used for metabolic processes.

Vice President & General the C02 concentration in the intercellular The vast majority of absorbed water is used for Counsel Eric I. Lisman spaces and not at the leaf surface or in the transpiration, with 90% of that water escaping stomatal pore (Mott, 1988). through stomata (Beard, 1973). Thus, stom- Treasurer and Controller Adele D. Hartwick atal opening or closure can have a drastic effect synthesis and cool itself through transpira- on the cooling of a turfgrass plant. tion. A major regulating mechanism for A field study at Rutgers University these processes are stomata. Although looked at the effect of summer stress on the small and relatively insignificant when performance of two Kentucky bluegrass compared to the entire leaf surface, - cultivars (Perdomo et al.; 1996). They ta play a critical role in turfgrass health. found that the cultivar that gave the best LITERATURE CITED quality during summer stress (drought and high temperature) had more open stomata Beard, J.B. 1973. Turfgrass: Science and Culture. during conditions of decreasing leaf water. Prentice-Hall, Inc. Englewood Cliffs, NJ. The more open stomata on the higher Danneberger,T.K. 2000. Humidity effects on plant quality cultivar allowed for greater cooling. growth. Plant Environmental Interaction. Marcel- Structurally, stomata that are under mois- Dekker, Inc. (in press) ture stress are smaller and have less turgor than stomata from well-watered plants. Edwards, D., G.D. Abbott, and J.A. Raven. Cuticles Related to water loss but not necessary of early land plants: a palaeoecophysiological eval- stomata action, mowing can add to summer uation. In: G. Kersteins, ed. Plant cuticles: An inte- stress. Increased transpiration has been grated Functional Approach. Oxford: Bios:1 -31. detected immediately following mowing Esau, K. 1977. Anatomy of Seed Plants. John due to injury to leaf cells and the cut ends Wiley and Sons, New York, pp. 88-99. (Hull, 2000; Kneebone et al., 1992). This is significant on frequently mowed Green, R.L., J.B. Beard, and D.M. Casnoff. 1990. turfs (Hull, 2000). During summer stress Leaf blade stomatal characterizations and évapo- times, mowing with a sharp blade versus a transpiration rates of 12 cool-season perennial dull blade (causes more damage to the leaf) grasses. HortScience 25:760-761. would be an important factor in water loss. Hull, R.J. 2000. Mowing: Its impact on turfgrasses. Turfgrass Trends 9(1): 1-8. How antitranspirants work Karlsson, P.E. 1986. Blue light regulation of stomata in wheat. I. Influence of red background illumination and initial conductance level. In some cases, it would make logical sense Physiological Plant 66:202-206. if you could limit transpiration — by restricting water loss, you could conserve Kneebone, W.R., D.W. Kopec, and C.F. Mancino. plant moisture. You could argue, however, 1992. Water requirements and irrigation. In (eds.) that a turfgrass plant undergoing water Waddington, D.V., R.N Carrow, and R.C. Sherman. stress would close stomata on its own. Turfgrass. Agronomy Monograph No. 32. ASA, Wl. There are two major types of antitran- Martin, E.S., M.E. Donkin, and R.E. Stevens. spirants. The first is stomata inhibitors — Stomata. In: E Arnold, ed. Studies in Biology synthetic compounds that induce stomata 155:48-53. closure by affecting the stomatal mecha- nism. They include certain plant growth reg- Mott, K.A. 1988. Do stomata respond to C02 ulators, herbicides and fungicides. concentrations other than intercellular? Plant The second type of antitranspirant are Physiology 86: 200-203. film-forming products. Film forming prod- Perdomo, P., J.A. Murphy, and G.A. Berkowitz. ucts coat the leaf, acting as a physical barrier 1996. Physiological changes associated with per- to water loss. Unfortunately, these products formance of Kentucky bluegrass cultivars during tend to cause a greater reduction in photosyn- summer stress. HortScience 31:1182-1186. thesis than transpiration (Martin et al. 1983). Raschke, K. 1975. Stomatal action. Annual Review Plant Physiology 26:309-340.

Conclusion Woodward, F.I. 1998. Do plants really need stomata? Journal Experimental 49:471- Turfgrass health depends on the ability to 480. capture and store energy through photo-