PERFORMANCE OF TEXAS BLUEGRASS HYBRIDS IN THE TRANSITION ZONE KEMIN SU

Transcription

1 PERFORMANCE OF TEXAS BLUEGRASS HYBRIDS IN THE TRANSITION ZONE y KEMIN SU B.S., Beijing Agriculturl University, P. R. Chin, 1991 M.S., Chin Agriculturl University, P.R. Chin, 1997 AN ABSTRACT OF A DISSERTATION sumitted in prtil fulfillment of the requirements for the degree DOCTOR OF PHILOSOPHY Deprtment of Horticulture, Forestry, nd Recretion Resources College of Agriculture KANSAS STATE UNIVERSITY Mnhttn, Knss 2007

2 Astrct High temperture nd drought my reduce qulity in cool seson turfgrsses during summer in the trnsition zone. Texs luegrss hyrids (HBG) re genetic crosses etween ntive Texs luegrss (Po rchnifer Torr.) nd Kentucky luegrss (Po prtensis L.) (KBG) tht resemle KBG ut my hve greter drought nd het resistnce thn other coolseson grsses. The ojectives of four studies were to evlute high temperture, drought, nd lower mowing height effects on HBG compred with KBG ( Apollo ) nd tll fescue (Festuc rundince Schre.)(TF, Dynsty ), compre their rooting chrcteristics, nd investigte their memrne lipid moleculr species compositionl differences. Under high temperture (35/25 C, 14 h light/10 h drkness), HBG ( Therml Blue ) hd greter qulity nd gross photosynthesis (Pg), nd lower electrolyte lekge thn KBG nd TF in growth chmer study. The comintion of high temperture nd drought (60% ET replcement) cused rpid declines in qulity, ut HBG generlly performed etter. In field nd greenhouse studies, TF hd more roots deeper in the profile thn two HBG ( Reveille nd Therml Blue) nd KBG under well wtered conditions. In the field, qulity nd P g were gretest in TF mong turfgrsses. Performnces in qulity nd P g generlly rnked: TF > Reveille >= Therml Blue = KBG. In seprte mowing height nd drought field study, HBG (Therml Blue) generlly hd lower qulity nd P g thn KBG t oth high (7.62 cm) nd low (3.81 cm) heights ut prticulrly t the low height. Drought resistnce nd tolernce to low mowing in Therml Blue ws similr to or poorer thn in KBG. Under supr optimum temperture (35 /25 C nd 40 /30 C, 14 h light/10 h drkness), the rtio of diglctosyldicylglycerol (DGDG) to monoglctosyldicylglycerol (MGDG) ws highest in HBG (Therml Blue) nd lowest in TF. Het tolernce ws lso ssocited with higher phosphtidylethnolmine (PE) content, higher phosphtidylglycerol (PG) content, nd reduced overll unsturtion compred with het sensitive. Results suggest tht 40 memrne lipid molecules re potentil iomrkers for het tolernce nd tht compositionl chnges in lipids in response to het my contriute to differences in het tolernce mong cool seson grsses.

3 Generlly, studies indicted greter het resistnce, ut not drought resistnce, in HBG thn in KBG or TF.

4 PERFORMANCE OF TEXAS BLUEGRASS HYBRIDS IN THE TRANSITION ZONE y KEMIN SU B.S., Beijing Agriculturl University, P. R. Chin, 1991 M.S., Chin Agriculturl University, P.R. Chin, 1997 A DISSERTATION sumitted in prtil fulfillment of the requirements for the degree DOCTOR OF PHILOSOPHY Deprtment of Horticulture, Forestry, nd Recretion Resources College of Agriculture KANSAS STATE UNIVERSITY Mnhttn, Knss 2007 Approved y: Mjor Professor Dle J. Bremer

5 Astrct High temperture nd drought my reduce qulity in cool seson turfgrsses during summer in the trnsition zone. Texs luegrss hyrids (HBG) re genetic crosses etween ntive Texs luegrss (Po rchnifer Torr.) nd Kentucky luegrss (Po prtensis L.) (KBG) tht resemle KBG ut my hve greter drought nd het resistnce thn other coolseson grsses. The ojectives of four studies were to evlute high temperture, drought, nd lower mowing height effects on HBG compred with KBG ( Apollo ) nd tll fescue (Festuc rundince Schre.)(TF, Dynsty ), compre their rooting chrcteristics, nd investigte their memrne lipid moleculr species compositionl differences. Under high temperture (35/25 C, 14 h light/10 h drkness), HBG ( Therml Blue ) hd greter qulity nd gross photosynthesis (Pg), nd lower electrolyte lekge thn KBG nd TF in growth chmer study. The comintion of high temperture nd drought (60% ET replcement) cused rpid declines in qulity, ut HBG generlly performed etter. In field nd greenhouse studies, TF hd more roots deeper in the profile thn two HBG ( Reveille nd Therml Blue) nd KBG under well wtered conditions. In the field, qulity nd P g were gretest in TF mong turfgrsses. Performnces in qulity nd P g generlly rnked: TF > Reveille >= Therml Blue = KBG. In seprte mowing height nd drought field study, HBG (Therml Blue) generlly hd lower qulity nd P g thn KBG t oth high (7.62 cm) nd low (3.81 cm) heights ut prticulrly t the low height. Drought resistnce nd tolernce to low mowing in Therml Blue ws similr to or poorer thn in KBG. Under supr optimum temperture (35 /25 C nd 40 /30 C, 14 h light/10 h drkness), the rtio of diglctosyldicylglycerol (DGDG) to monoglctosyldicylglycerol (MGDG) ws highest in HBG (Therml Blue) nd lowest in TF. Het tolernce ws lso ssocited with higher phosphtidylethnolmine (PE) content, higher phosphtidylglycerol (PG) content, nd reduced overll unsturtion compred with het sensitive. Results suggest tht 40 memrne lipid molecules re potentil iomrkers for het tolernce nd tht compositionl chnges in lipids in response to het my contriute to differences in het tolernce mong cool seson grsses.

6 Generlly, studies indicted greter het resistnce, ut not drought resistnce, in HBG thn in KBG or TF.

7 Tle of Contents List of Figures... ix List of Tles... xii Acknowledgements... xiii CHAPTER 1 Effects of High Temperture nd Drought on Hyrid Bluegrss Compred with Kentucky Bluegrss nd Tll Fescue...1 Astrct...2 Introduction...4 Mterils nd Methods...5 Results nd Discussion...9 References...16 Figures nd Tles...20 CHAPTER 2 Rooting Chrcteristics nd Responses of Photosynthesis to Irrigtion Deficit of Two Hyrid Bluegrsses, Kentucky Bluegrss, nd Tll Fescue...28 Astrct...29 Introduction...31 Mterils nd Methods...32 Results nd Discussion...37 References...42 Figures nd Tles...45 CHAPTER 3 Mowing Height nd Drought Effects on Texs Bluegrss Hyrid Compred with Kentucky Bluegrss...52 Astrct...53 Introduction...55 Mterils nd Methods...56 Results nd Discussion...60 References...65 Figures nd Tles...68 vii

8 CHAPTER 4 Memrne Lipid Composition nd Het Tolernce in Hyrid Bluegrss Compred with Kentucky Bluegrss nd Tll Fescue...78 Astrct...79 Introduction...81 Mterils nd Methods...82 Results nd Discussion...85 References...91 Figures nd Tles...95 viii

9 List of Figures Figure 1 1 Effects on visul qulity rted on scle of 1 to 9 (1=poorest nd 9=highest) of: high temperture (A), drought (B), high temperture nd drought (C), nd control (D) in KBG, HBG, nd TF. Symols long the sciss of ech grph indicte significnt differences (P=0.05) etween: HBG nd KBG (*); HBG nd TF (+); nd KBG nd TF (Х); on given dy fter tretment initition (Dys of tretment)...20 Figure 1 2 Effects on cumultive Pg of: high temperture, drought, high temperture nd drought, nd control in KBG, HBG, nd TF. Mens with the sme letters were not significntly different (P=0.05)...21 Figure 1 3 Effects on gross photosynthesis (Pg) of high temperture in KBG, HBG, nd TF. Symols long the sciss indicte significnt differences (P=0.05) etween: HBG nd KBG (*); nd HBG nd TF (+); on given dy fter tretment initition (Dys of tretment) Figure 1 4 Effects on electrolyte lekge (EL) of: high temperture (A), drought (B), high temperture nd drought (C), nd control (D) in KBG, HBG, nd TF. Symols long the sciss of ech grph indicte significnt differences (P=0.05) etween: HBG nd KBG (*); nd HBG nd TF (+); on given dy fter tretment initition (Dys of tretment) Figure 1 5 Effects on cumultive dry mtter production of: high temperture, drought, high temperture nd drought, nd control in KBG, HBG, nd TF. Mens with the sme letters were not significntly different (P=0.05)...24 Figure 1 6 Effects on cumultive ET (mm) (A), green LAI (B), nd degree hours (C) t the soil surfce in: high temperture, drought, high temperture nd drought, nd control tretments in KBG, HBG, nd TF. Mens with the sme letters in ech grph were not significntly different (P=0.05) Figure 2 1 Volumetric soil wter content (θ v ) t 5 cm in 2004 (A) nd 2005 (B) in the irrigtiondeficit tretment...45 Figure 2 2 Volumetric soil wter content (θ v ) in the 0 50 cm profile under well wtered (A) nd irrigtion deficit (B) conditions in Mens followed with the sme letter on given dy fter tretment initition (Dys of tretment) re not significntly different (P=0.05)..46 ix

10 Figure 2 3 Mximum root extension (MSE) mong turfgrsses under well wtered conditions in the greenhouse. Mens followed with the sme letter on given dy fter plnting re not significntly different (P=0.05)...47 Figure 2 4 Visul qulity mong turfgrsses under well wtered (A, B) nd irrigtion deficit (C, D) conditions in 2004 nd Mens followed with the sme letter on given dy fter tretment initition (Dys of tretment) re not significntly different (P=0.05)...48 Figure 2 5 Gross photosynthesis (Pg) mong turfgrsses under well wtered (A, B) nd irrigtion deficit (C, D) conditions in 2004 nd Mens followed with the sme letter on given dy fter tretment initition (Dys of tretment) re not significntly different (P=0.05) Figure 3 1 Plots lyout digrm in the field Figure 3 2 Visul qulity in HBG nd KBG in 2004 nd in the lte period of 2005 (3.2A) nd during the interction of species y mowing height in erly nd mid period of 2005 (3.2B). Mens with the sme letters during the sme period were not significntly different (P=0.05) Figure 3 3 The normlized difference vegettion index (NDVI) in HBG nd KBG in 2004 (3.3A) nd 2005 (3.3B). Mens with the sme letters during the sme period were not significntly different (P=0.05) Figure 3 4 Gross photosynthesis (Pg) in HBG nd KBG in 2004 (4A) nd 2005 (4B). Mens with the sme letters during the sme period were not significntly different (P=0.05)...71 Figure 3 5 Volumetric soil wter content (θ V ) t 0 50 cm during the species y mowing height interction in the mid nd lte periods of 2005 (3.5A); nd effects of irrigtion on θ V t 0 50 cm in 2005 (3.5B). Mens with the sme letters during the sme period were not significntly different (P=0.05)...72 Figure 3 6 Volumetric soil wter content (θ v ) t 5cm in KBG nd HBG under 60% evpotrnspirtion (ET) replcement in high mown (3.6A nd 3.6B) nd low mown plots (3.6C nd 3.6D) in 2004 nd Figure 3 7 Effects of mowing height on visul qulity in 2004 nd in the lte period of Mens with the sme letters during the sme period were not significntly different (P=0.05) x

11 Figure 3 8 Effects of mowing height on the normlized difference vegettion index (NDVI) (3.8A nd 3.8B) nd gross photosynthesis (Pg) (3.8C nd 3.8D) in 2004 nd Mens with the sme letters during the sme period were not significntly different (P=0.05)...75 Figure 3 9 Effects of irrigtion level on visul qulity (3.9A nd 3.9B), normlized difference vegettion index (NDVI) (3.9C nd 3.9D), nd gross photosynthesis (Pg) (3.9E nd 3.9F) in 2004 nd Mens with the sme letters during the sme period were not significntly different (P=0.05) Figure 4 1 Electrolyte lekge (EL), indicting cell memrne stility, under optimum nd supr optimum growth tempertures. Mens with the sme letters under the sme temperture tretment (i.e., optimum, supr optimum) were not significntly different (P=0.05) Figure 4 2 The PE moleculr species composition (mol%) of HBG, KBG, nd TF under optiml growth temperture (A) nd supr optiml growth temperture (B). Vlues were the mens + S.E. (n = 4 or 5). Mens with the sme letters in ech PE moleculr species were not significntly different (djusting P = 0.05 y the flse discovery rte method). Mens without letters indicted content <0.1% Figure 4 3 The PG composition (mol%) of HBG, KBG, nd TF under optiml growth temperture (A) nd supr optiml growth temperture (B). Vlues were the mens + S.E. (n = 4 or 5). Mens with the sme letters in ech PG moleculr species were not significntly different (djusting P = 0.05 y the flse discovery rte method). Mens without letters indicted content <0.1 % Figure 4 4 Principl component nlysis (PCA) of 152 lipid moleculr species in hyrid luegrss (HBG), Kentucky luegrss (KBG), nd tll fescue (TF); Principl component (PC)1 nd PC2 ccounted for 39.4 nd 18.0%, respectively, of the vrince of the dtset, for totl of out 57.4% xi

12 List of Tles Tle 1 1 Effects on dry oveground iomss of high temperture, drought, high temperture nd drought, nd control in KBG, HBG, nd TF Tle 1 2 Effects on root mss density of high temperture, drought, high temperture nd drought, nd control in KBG, HBG, nd TF...27 Tle 2 1 Root length density (RLD), dry root weight, verge root dimeter, nd root surfce re in different depths of HBG1 (Therml Blue), HBG2 (Reveille), KBG (Apollo), nd TF (Dynsty) under well wtered conditions in the rinout shelter t Mnhttn, KS, in Tle 2 2 Root length density (RLD), dry root weight, verge root dimeter, nd root surfce re in different depths of HBG1, HBG2, KBG, nd TF under well wtered condition in the greenhouse in Dsh ( ) indictes mounts <0.001 g in dry root weight, <0.01 cm cm 3 in RLD, nd < 1 cm 2 in root surfce re, respectively...51 Tle 3 1 Averge dytime ( CST) ir temperture of ech period during oth yers of the study nd the difference etween yers Tle 4 1 Memrne lipid composition (mol%; percentges of individul species to totl lipid content) of HBG, KBG, nd TF under optimum nd supr optimum growth temperture..99 Tle 4 2 Glycolipid species composition (mol%), DBI, nd the rtios of DGDG to MGDG of HBG, KBG, nd TF under optimum nd supr optimum growth temperture Tle 4 3 Forty memrne lipid moleculr species tht were significntly different in the luegrsses (HBG nd KBG) compred to TF fter exposure of grsses to high tempertures. These lipid moleculr species my e potentil iomrkers for het tolernce in cool seson turfgrsses xii

13 Acknowledgements First thnks goes to my mjor dvisor, Dr. Dle Bremer, nd co dvisor, Dr. Steve Keeley. I m especilly grteful for the opportunity they gve me to pursue this degree nd for their gret support, excellent guidnce nd friendly understnding. I pprecite tht Dr. Bremer spent so much time to improve the qulity of my reserch nd professionl experience. I thnk Dr. Keeley for ringing me into the threshold of turfgrss science. I would sincerely like to thnk my grdute committee memers, Dr. Chnn B. Rjshekr for his guidnce nd letting me use his l fcilities to mesure electrolyte lekge, nd Dr. Mry Beth Kirkhm for her guidnce nd encourgement during my doctorl progrm. I would lso like to thnk Dr. Jck Fry for his counsel; Dr. Ruth Welti, Dr. Jy Hm, nd Dr. Guihu Bi for generously providing their l fcilities; Dr. Aln Zuk for mintining my reserch plots in the field; Mrs Le Westervelt for mintining helthy turfgrss in the greenhouse. My pprecition lso goes to Dr. George Milliken, Dr. Ling Fng, Dr. Leigh Murry, nd Ms. Celeste Yng for their help with sttisticl nlysis; Dr. Richrd Jennotte nd Ms. Mry Roth for their technicl help in lipid study; nd Dr. Jinin Yu for his help in iomrkers. I wnt to cknowledge Qi Zhng, Hyeonju Lee, Derek Settle, Json Lewis, Anthony Goldsy, Rose Ogutu, Shron Knewtson, Jmey Duesterhus, Myung Min Oh, Sin Ae Prk, Sid En nhli, nd ll people working in the Deprtment of Horticulture, Forestry, nd Recretion Resources for their friendship nd ll of the ssistnce they hve offered. My deepest nd specil thnks go to my prents, my wife, Ping Ouyng, nd my sisters nd rothers for their love nd support over the yers. I thnk my son, Owen for his irth for ringing countless hours of joy into my life. xiii

14 CHAPTER 1 Effects of High Temperture nd Drought on Hyrid Bluegrss Compred with Kentucky Bluegrss nd Tll Fescue *This chpter hs een pulished in Crop science :

15 Astrct High temperture nd drought stresses my reduce qulity in cool seson turfgrsses during summer months in the trnsition zone. This growth chmer study ws conducted to evlute effects of high temperture nd drought on physiology nd growth of Apollo Kentucky luegrss (Po prtensis L.) (KBG), Dynsty tll fescue (Festuc rundince Schre.) (TF), nd Therml Blue, hyrid (HBG) etween KBG nd Texs luegrss (Po rchnifer Torr.). Turfgrsses were exposed for 48 dys to supr optiml (high temperture; 35/25 C, 14 h dy/10 h night) nd optiml (control; 22/15 C, 14 h dy/10 h night) tempertures under well wtered (100% evpotrnspirtion [ET] replcement) nd deficit (60% ET replcement) irrigtion. Het resistnce ws greter in HBG, which hd greter visul qulity, gross photosynthesis (Pg), dry mtter production, nd lower electrolyte lekge nd soil surfce tempertures thn KBG nd TF under high temperture. Cumultive Pg during the study ws 16% nd 24% greter in HBG thn in KBG nd TF, respectively. Green lef re index (LAI) in HBG ws not ffected y high temperture, ut LAI ws reduced y 29 % in KBG nd 38% in TF. Differences in drought resistnce were negligile mong species. The comintion of high temperture nd drought cused rpid declines in visul qulity nd dry mtter production, ut HBG generlly performed etter. Results indicted greter het resistnce, ut not drought resistnce, in HBG thn in KBG or TF. 2

16 Arevitions: DOT, dys of tretment; EL, electrolyte lekge; ET, evpotrnspirtion; HBG, hyrid etween Kentucky nd Texs luegrss; KBG, Kentucky luegrss; LAI, lef re index; Pg, gross photosynthesis; TF, tll fescue. 3

17 Introduction High temperture nd drought stresses re significnt prolems in cool seson turfgrsses during summer months in the U.S. trnsition zone, which covers 480 to 1120 km north to south etween the northern regions where cool seson grsses re dpted nd the southern regions where wrm seson grsses re dpted (Dunn nd Diesurg, 2004). High temperture nd drought stresses often occur simultneously during summer months nd my limit growth nd cuse severe decline in the visul qulity of cool seson turfgrsses (Perdomo et l., 1996; Bonos nd Murphy, 1999; Jing nd Hung, 2000; Wng nd Hung, 2004). Recent increses in competition for wter hve resulted in restrictions in wter use for irrigtion of turfgrsses (EIFG, 2004), which further excertes the prolem of drought stress in cool seson turfgrsses. Predictions of higher tempertures from glol wrming lso suggest tht het stress in cool seson turfgrsses my ecome more common in some regions, including the trnsition zone (Ntionl Assessment Synthesis Tem, 2000). Hyrid luegrsses (HBG), which re genetic crosses etween ntive Texs luegrss nd KBG, my hve greter het nd drought resistnce thn other cool seson grsses. Hyrid luegrsses hve similr visul qulities to KBG, which is fine textured, cool seson turfgrss commonly used in lwns nd golf courses in the U.S. (Red et l., 1999; Turgeon, 2002). Consequently, new cultivrs of HBG re eing investigted s potentil wter sving, hetresistnt lterntives to current cool seson turfgrsses. Arhm et l. (2004) evluted, in growth chmer study, the drought resistnce of thirty HBG nd their genetic prents nd concluded tht their drought resistnce vried significntly. Those reserchers lso determined tht highly drought resistnt hyrids could e chieved y selecting first genertion hyrids with good drought resistnce nd ckcrossing them with elite drought resistnt genotypes of KBG. In field tests in Colordo, USA, Reveille HBG used significntly less wter while mintining higher qulity thn Bensun s A 34 KBG (Suplick Ploense nd Qin, 2005). Bremer et l. (2006) reported little difference in the generl performnce or drought resistnce mong two HBG (Therml Blue nd Dur Blue ) nd KBG (Apollo) in field study in Knss, USA. Dur Blue HBG nd Apollo KBG were the most desirle mong five cool seson turfgrsses under different nitrogen rte levels in Tennessee, USA (Teuton et l., 2005). Therml Blue nd Dur Blue HBG my e cceptle replcements for KBG in the Upper Midwest, USA ecuse they hd similr qulity nd erlier spring greenup 4

18 thn KBG (Stier et l, 2005). However, little informtion is ville out the effects of oth high temperture nd drought on HBG. The ojectives of this study were to evlute the effects of high temperture nd drought stress on the growth, ppernce, nd physiology of HBG, KBG, nd TF. Mterils nd Methods Preprtion nd mintennce of turfgrsses in lysimeters Lysimeters (10 cm dim. y 60 cm deep) were filled with mixture of snd nd topsoil (1:1, v:v) nd ulk densities inside lysimeters rnged from 1.62 to 1.70 g cm 3. Apollo KBG nd Therml Blue HBG were seeded t 153 kg h 1 nd Dynsty TF ws seeded t 395 kg h 1 in lysimeters. They were kept under mist system fter seeding for out 30 d in greenhouse. The mist system ws utomticlly turned on 4 times per dy for 5 min ech. After 30 d, lysimeters were moved wy from the mist system ut continued to e mintined in the greenhouse. Averge dy/night ir temperture ws 22 C /15 C nd supplementl light ws 12 h/dy. Turfgrsses were well wtered, mowed twice weekly t 6.5 cm, nd fertilized weekly t the rte of 15 kg N h 1 (15N 13P 12K). Totlly, turfgrsses were plnted nd mintined in the greenhouse for out 135 d. Lysimeters were then trnsferred to growth chmers t 22 C /15 C, 14 h dy/10 h night with photosyntheticlly ctive rdition of 580 µmol m 2 s 1 during the dylight period. The turfgrsses were kept well wtered in the growth chmers for 14 d to llow for cclimtion to growth chmers efore tretments. Turfgrsses were mowed nd wtered every 3 d nd fertilized every 6 d with solution supplying 20 kg N h 1 (15N 13P 12K) during the tretments. Tretments nd Experimentl Design Therml Blue HBG, Apollo KBG, nd Dynsty TF were exposed to the following tretments in growth chmers: 1) supr optiml temperture (high temperture; 35 C /25 C, 100% ET); 2) drought (22 C /15 C, 60%ET); 3) high temperture nd drought (35 C /25 C, 60%ET); nd 4) optiml temperture (control; 22 C /15 C, 100%ET). Six whole plots (2 temperture tretments x 3 replictions) nd six suplots per whole plot (3 species x 2 irrigtion tretments), for totl of 36 suplots, were rrnged in split plot 5

19 design. Whole plots were the growth chmers, where the supr optiml nd optiml temperture tretments were pplied in seprte chmers in rndomized complete lock design. Suplots, which were the lysimeters, were rrnged in completely rndomized design within ech whole plot. Becuse only two growth chmers were ville, whole plots could not e replicted concurrently nd hd to e replicted sequentilly in time. The first whole plot repliction ws from Mrch to My 2004, the second repliction from My to July 2004, nd the third from July to Septemer To ensure tht turf ge ws similr in ech repliction, turfgrsses were seeded in lysimeters five months efore tretments were pplied. Therefore, lysimeters for the first, second, nd third replictions (locks) were seeded in Octoer 2003, Decemer 2003, nd Jnury 2004, respectively. Evpotrnspirtion (100%) ws mesured grvimetriclly with the well wtered lysimeters (Bremer, 2003). Using this method, lysimeters were irrigted, llowed to drin until free dringe cesed, seled, nd weighed. Lysimeters were then weighed fter 3 d nd the wter loss ws ttriuted to ET. Lysimeters were irrigted every 3 d ccording to their ET losses. Cumultive ET (mm) for ech tretment ws determined s the sum of ll ET during the study. Turfgrss qulity, photosynthesis, electrolyte lekge, nd cnopy temperture Turf visul qulity ws rted on scle of 1 to 9 (1=poorest qulity, 6=minimlly cceptle, nd 9=highest qulity) ccording to color, texture, density, nd uniformity (Emmons, 2000). Qulity rtings were recorded every 6 d y the sme individul during the entire study. Photosynthesis ws mesured every 6 d t out 8 h into the dily light cycle, with LI 6400 portle gs exchnge system (LI COR Inc., Lincoln, NE) using custom surfce chmer descried y Bremer nd Hm (2005). According to their Equtions 5 nd 6, sunlit chmer mesurements determine Pg (Rc + Rs ) nd shded chmer mesurements determine Rc + Rs, where Pg is gross photosynthesis, Rc is cnopy respirtion, nd Rs is residul soil respirtion in pressurized chmer; ll vlues re positive nd units re µmol m 2 s 1. Shded chmer mesurements were otined y covering the chmer with lck cloth tht completely locked solr rdition from the chmer. Gross photosynthesis ws clculted using eqution 8 in Bremer nd Hm (2005): Pg = sunlit chmer + shded chmer. Cumultive Pg for ech tretment ws clculted y summing the products of men Pg on ech mesurement 6

20 dy nd the numer of hours etween smples when lights were turned on (i.e., 14 h dily period when plnts were photosynthesizing). Lef electrolyte lekge (EL) ws determined y the method of Blum nd Eercon (1981) nd Mrcum (1998) with modifictions. Five living leves out the sme ge were collected from ech lysimeter t 0, 3, 15, 27, 39, nd 45 dys of tretment (DOT). Ech lef ws cut into two to three 2 cm segments nd rinsed 3 times with distilled deionized wter. All rinsed lef segments from ech lysimeter were plced in test tue contining 20 ml deionized wter. Test tues were shken on shker tle t 120 RPM (L Line Instruments Inc., Melrose Prk, Illinois) for 24 h to dissolve electrolytes tht hd leked from cells (e.g., due to memrnes dmged y het or drought stress tretments). After mesuring conductivity (C 1 ) with conductivity meter (Model 32, Yellow Spring Instrumentl Inc., Yellow Spring, Ohio), the test tues with lef smples were plced in n utoclve t 140 o C for 20 min to destroy ll cell memrnes, shken for 24 h to extrct ll electrolytes from the cells, nd then the conductivity (C 2 ) ws mesured gin. The percentge of the totl electrolytes tht hd leked from cells during tretments ws clculted s (C 1 / C 2 )*100. Lower EL indicted greter resistnce to stresses. Cnopy temperture ws mesured every 6 d with three infrred thermometers (model IRTP5, Apogee, Logn, UT). The infrred thermometers were positioned t 0.2 m ove the turf cnopy. Mesurements were utomticlly logged every 5 sec nd verged nd recorded every 30 min with micrologger (CR10x, Cmpell Scientific, Logn, UT). Mesurements for ech lysimeter were conducted for out 1.5 to 2.5 h. Dry mtter production, soil surfce temperture, nd volumetric soil wter content Turfgrsses were mowed every 3 d, nd ll clippings were collected. Clippings were dried in forced ir oven for 48 h t 70 o C nd then weighed. Cumultive dry mtter production for ech tretment ws determined y summing the dry weights of ll clippings during the 48 d study. Dily dry mtter production ws clculted s the clipping weight t ech mowing divided y the numer of dys since the previous mowing. Soil surfce temperture ws mesured with soil encpsulted thermocouples using the method of Hm nd Senock (1992). To evlute potentil cumultive het effects mong tretments during the most stressful periods, het units (degree hours) were clculted s the sum 7

21 of soil surfce tempertures during the finl 8 h of ech dily light cycle. Our dt indicted tht this ws the period of mximum soil surfce tempertures, which my hve hd importnt physiologicl impcts on the turfgrsses (e.g., on meristemtic ctivity in the crowns). Volumetric soil wter content (θ v ) nd temperture inside the lysimeters t 5, 25, nd 45 cm were mesured utomticlly using the dul proe het pulse technique (Cmpell et l., 1991; Trr nd Hm, 1997; Song et l., 1998). Sensors were fricted in the lortory s descried y Bsinger et l. (2003) nd Bremer (2003). Mesurements of θ v were logged twice dily t 0800 nd 2000 CST nd soil tempertures were logged every 60 min. All dt cquisition nd control were ccomplished with micrologger nd ccessories (CR10x, two AM16/32 s, nd one AM25T, Cmpell Scientific, Logn, UT). Green LAI, oveground iomss, nd root mss density At the end of ech 48 d repliction, oveground iomss ws hrvested from ech lysimeter nd seprted into living nd ded components. Green leves were seprted from green shoots nd the re of the leves ws mesured with n re meter (LI 3100, LI COR, Lincoln, NE). All green nd ded tissue ws then dried in forced ir oven for 48 h t 70 o C nd weighed seprtely. Green LAI ws clculted s the rtio of the green lef re to ground surfce, nd totl oveground iomss for ech tretment ws clculted s the sum of the dry weights of ll living nd ded tissue. After oveground iomss ws hrvested, lysimeters were lid horizontlly nd cut into three sections (0 to 15, 15 to 35, nd 35 to 57.5 cm). The soil ws wshed from the roots in ech section nd roots were dried in forced ir oven for 48 h t 70 o C nd then weighed. Root mss density of ech section ws clculted s dry root mss divided y the volume of soil inside ech respective section of lysimeter. All dt were nlyzed with the mixed procedure of SAS (SAS Institute Inc., Cry, NC). Vrition ws prtitioned into grss species, temperture tretment, nd irrigtion level. Interctions mong species, temperture, nd irrigtion level were not significntly different on given dy fter tretment initition (Dys of tretment). Therefore, the comprison of species under temperture nd / or drought tretments ws sttisticlly nlyzed. Differences etween mens were seprted y the lest significnce difference (LSD) test t P=

22 Results nd Discussion Visul qulity In the high temperture tretment, HBG consistently hd the highest visul qulity of ll three species, lwys greter thn or equl to reltive qulity rting of six (Fig. 1 1A). Visul qulity of HBG ws significntly greter thn TF nd KBG strting on 24 nd 42 DOT, respectively, nd differences remined significnt therefter. Visul qulity of KBG ws lso significntly greter thn TF during the lst week of the study (i.e., 42 nd 48 DOT). Under drought stress t optiml tempertures, visul qulity of ll turfgrsses egn to decline fter out two weeks (Fig. 1 1B). Although the qulity of HBG ws greter thn TF on 6 nd 12 DOT, this ws consistent with the control, in which HBG ws lso higher thn TF on those dtes under well wtered conditions (Fig. 1 1D). As the severity of drought effects intensified, differences in qulity etween HBG nd TF diminished. Visul qulity ws similr mong species fter 12 DOT, which indictes no differences in drought resistnce mong species. These results contrdict Supplick Ploense nd Qin (2005), who found greter drought resistnce in HBG (Reveille) ecuse of its greter root length density nd root mss. Our results lso contrdict Bremer et l. (2006), who reported tht TF hd greter drought resistnce thn HBG in the field. In contrst to the previous studies in which soils were deep, the development of roots in our study ws proly more restricted ecuse of limited soil volumes nd soil wter reservoirs inside lysimeters. Thus, our results my e more comprle to turfgrsses grown in shllow or poor soils such s is typicl of home lwns, where soils re often distured, lyered, nd compcted during home construction (Hmilton nd Wddington, 1999). The comintion of high temperture nd drought stresses cused more rpid decline in visul qulity mong species thn individul tretments of high temperture or drought (Figs. 1 1A, 1 1B, nd 1 1C). For exmple, visul qulity of TF fell elow six y 6 DOT, nd HBG nd KBG fell elow six y 18 DOT. Nevertheless, the visul qulity of HBG ws consistently higher mong species lte in the study (i.e., fter 18 DOT), leit significntly higher only thn TF. In the control, visul qulity ws consistently higher in HBG nd KBG thn in TF lthough differences were not lwys significnt; visul qulities were similr etween HBG nd KBG (Fig. 1 1D). Tll fescue hd lower visul qulity thn HBG nd KBG in the control primrily ecuse of its corser texture. 9

23 Photosynthesis High temperture reduced cumultive Pg y 21% in HBG, 30% in KBG, nd 27% in TF, compred with the control (Fig. 1 2). In the high temperture tretment, however, cumultive Pg of HBG ws 16% greter thn KBG nd 24% greter thn TF. During the study, high temperture cused generl decline in dily Pg mong species lthough Pg ws consistently higher in HBG thn in TF nd KBG lte in the study (Fig. 1 3). Dily Pg ws significntly higher in HBG thn in TF from 24 through 42 DOT, nd higher in HBG thn in KBG on 42 DOT. These dt indicte greter resistnce to het in HBG thn in TF nd KBG. Drought stress reduced cumultive Pg y 36% in HBG, 33% in KBG, nd 29% in TF, compred with the control (Fig. 1 2). Lte in the study, the deleterious effects of sustined drought on dily Pg surpssed tht of well wtered turfgrsses experiencing only high temperture stress (dt not shown). Cumultive Pg under drought stress ws similr mong species, however, indicting no differences in drought resistnce mong the three species s relted to photosynthetic cpcity. Under comined high temperture nd drought stress, cumultive Pg of HBG, KBG, nd TF ws reduced y 51%, 56%, nd 60%, respectively, compred with the control (Fig. 1 2). The comintion of high temperture nd drought stresses reduced cumultive Pg more thn individul tretments of high temperture or drought. This result is similr to other reports where the comined stresses of het nd drought cused photosynthesis to decline in Kentucky luegrss (Jing nd Hung, 2000) nd in tll fescue (Jing nd Hung, 2001). Wng nd Hung (2004) reported tht the comintion of high temperture nd drought stresses decresed lef photochemicl efficiency nd chlorophyll content of two Kentucky luegrss cultivrs ( Midnight nd Brillint ) nd hd detrimentl effect on the photosynthesis system for Kentucky luegrss. Cumultive Pg in this study ws greter in HBG thn in TF under the comined stresses of high temperture nd drought. Electrolyte lekge (EL) High temperture hd no effect on EL in well wtered HBG, ut EL incresed in wellwtered KBG on 27 DOT, nd remined higher thn HBG therefter (Fig. 1 4A). Men EL lso incresed in TF on 27 DOT nd remined higher thn HBG therefter, ut differences were significnt only on 39 DOT. Drought stress under optiml tempertures hd no significnt effect 10

24 on EL mong species, lthough men EL ws consistently higher in TF mong species eginning on 15 DOT (Fig. 1 4B). The comintion of high temperture nd drought cused EL to increse in ll species (Fig. 1 4C). Interestingly, EL decresed in HBG fter 27 DOT nd ws significntly lower thn in KBG nd TF therefter. In the control, EL remined consistently low nd ws similr mong the three turfgrsses throughout the study (Fig. 1 4D). The EL results from our study gree with Wng nd Hung (2004), who reported tht EL incresed rpidly during the comined stresses of het nd drought in Kentucky luegrss. Hldimnn nd Feller (2005) reported tht improved therml stility of thylkoid memrnes preserved the functionl potentil of the photosynthetic pprtus t high temperture nd significntly minimized the effect of het stress in pe (Pisum stivum L.) leves. Our results suggest tht cell memrne stility is higher in HBG thn in KBG nd TF under high temperture stress. Dry mtter production In ll tretments nd the control, cumultive dry mtter production ws greter in HBG thn in KBG nd TF (leit not significntly in the comintion high temperture nd drought tretment) nd similr etween KBG nd TF (Fig. 1 5). Within ech species, however, cumultive dry mtter production ws significntly reduced y high temperture, drought, nd the comintion of high temperture nd drought. High temperture reduced cumultive dry mtter production in KBG, HBG, nd TF y 88%, 74%, nd 91% respectively, which ws greter thn the reduction under drought; drought reduced cumultive dry mtter production in KB, HBG, nd TF y 49%, 48%, nd 52% respectively. Lower cumultive dry mtter production in high temperture thn in drought ws result, in prt, of drmtic decrese in clippings fter the initil three dys of tretments compred with the more grdul decline in dily dry mtter production under drought s soils dried (dt not shown). The comintion of high temperture nd drought reduced cumultive dry mtter production in KBG, HBG, nd TF y 95%, 86%, nd 93% respectively. Within ech species, the comintion of het nd drought hd no dditionl effect on cumultive dry mtter production compred to high het only. 11

25 Evpotrnspirtion nd green lef re index High temperture incresed cumultive ET during the study y 57, 67, nd 37% in KBG, HBG, nd TF, respectively, compred with the control (Fig. 1 6A). Interestingly, ET lso incresed in HBG when exposed to high temperture nd drought (i.e., despite reduced irrigtion) compred with the control. Presumly, higher vpor pressure deficits contriuted to increses in ET in the well wtered, high temperture tretment nd to incresed ET in HBG or sustined ET in KBG nd TF in high temperture comined with drought. Within the high temperture tretment, cumultive ET in HBG ws 13% greter thn in KBG nd 22% greter thn in TF (Fig. 1 6A). Within the drought nd high temperture tretment, cumultive ET ws 20% greter in HBG thn in TF ut ws similr etween HBG nd KBG. In oth of the ltter tretments, greter ET in HBG my hve een cused, in prt, y its greter memrne integrity in trnspiring leves thn in KBG nd TF, s indicted y the lower EL in HBG in those tretments (Figs. 1 4A nd 1 4C). Greter dry mtter production (i.e., clippings) in HBG (Fig. 1 5) my lso hve contriuted to its greter ET compred with KBG nd TF. For exmple, during the study HBG consistently grew fster nd ws visily tller thn KBG nd TF etween mowing. Greter mounts of new growth etween mowing indicte greter surfce re of young, ctively trnspiring leves in HBG. Green LAI hrvested from lysimeters t the end of the study ws lso higher in HBG thn in TF under high temperture (Fig. 1 6B) indicting greter surfce re of green, trnspiring leves in HBG compred with TF. Drought lone reduced ET compred with the control, ut similr ET mong species indicted no differences in drought resistnces (Fig. 1 6A). Similrly, no differences in ET were oserved mong species in the well wtered, optiml temperture of the control. Our results contrdict those of Suplick Ploense nd Qin (2005), who found tht HBG (Reveille) used less wter nd exhiited greter drought resistnce in the field thn KBG (Bensun s A 34). Our results lso differ from Minner nd Butler (1985), who found tht tll fescue used significntly more wter thn Kentucky luegrss y using lysimeters filled with snd to mesure ET under field conditions. High vriility in wter use mong individul HBG nd cultivrs of KBG nd TF my prtilly explin the contrsts etween results from those studies nd ours; the specific hyrids nd cultivrs used in their studies were different from those used in ours. Reserch y others hs indicted significnt vriility in wter use mong individul cultivrs of KBG nd 12

26 TF, respectively (Shermn, 1986; Bowmn nd Mculy, 1991). Furthermore, considerle vriility in reltive wter content nd drought resistnce, which suggests vriility in wter use, ws found mong 30 HBG, nd some HBG exhiited less drought resistnce thn KBG (Arhm et l., 2004). Green LAI in HBG ws not ffected y high temperture compred with the control, ut LAI in HBG ws reduced (i.e., 56 to 64%) y drought nd y the comintion of high temperture nd drought (Fig. 1 6B). High temperture reduced green LAI in KBG compred with the control, nd high temperture comined with drought cused further reductions in LAI in KBG compred with high temperture only. Green LAI in KBG ws 29%, 55%, nd 61% lower in high temperture, drought, nd comined high temperture nd drought tretments, respectively, thn in the control. Green LAI in TF ws reduced y 38 to 68% mong tretments compred with the control, ut differences in green LAI in TF were not significnt mong stress tretments. Green LAI ws similr mong ll three species in the control. Cnopy nd soil surfce temperture nd volumetric soil wter content In the drought nd the comintion drought nd high temperture tretments, cnopy temperture incresed stedily y 4.1 to 4.8 o C during the study (dt not shown). Presumly, decresing trnspirtion s the soils dried cused corresponding decrese in evportive cooling of leves nd incresed drought stress on lef tissue (Sifers nd Berd, 1993). Within ech tretment, cnopy temperture ws generlly similr mong species (dt not shown). In the high temperture tretment, men soil surfce temperture ws consistently cooler in HBG thn in KBG nd TF, y out 1 o C (dt not shown). Cumultive het (degree hours) t the soil surfce ws significntly lower in HBG thn in KBG nd TF under high temperture (Fig. 1 6C), which suggests tht long term het impcts on meristemtic ctivity my hve een reduced in HBG compred with KBG nd TF. Under comined high temperture nd drought stress, the soil surfce lso ws consistently cooler in HBG thn in KBG nd TF on dily sis (dt not shown). Cumultive het t the soil surfce ws lower in HBG thn in TF, ut ws sttisticlly similr to KBG. Cooler soil surfce temperture in HBG exposed to high temperture my hve resulted from greter shding of the soil surfce, cused y fster growth in HBG etween mowing s discussed erlier. Fster growth etween mowing my hve incresed trnspirtion of the cnopy nd thus, cooled the ir ove the soil surfce in HBG 13

27 (Bonos nd Murphy, 1999). Under drought lone, there ws no difference in soil surfce temperture mong species, which ws similr to the control. Volumetric soil wter content inside the lysimeters ws similr mong species under ll tretments nd the control (dt not shown). At lower depths (i.e., 25 nd 45 cm) under the comintion of high temperture nd drought, however, volumetric soil wter content ws consistently lower in TF nd HBG thn in KBG, which indicted tht TF nd HBG were using wter from deeper in the profile thn KBG. Aoveground iomss nd root iomss density In ll tretments nd the control, totl oveground iomss t the end of the study ws gretest in TF, except under high temperture, lthough more thn hlf ws ded (Tle 1 1). In ll tretments nd the control, ded oveground iomss ws greter in TF thn in HBG. Conversely, in HBG, the living iomss s percentge of the totl ws greter thn in TF under high temperture, indicting tht HBG hs greter resistnce to het thn TF. High temperture nd high temperture comined with drought reduced totl root iomss compred with the control nd drought tretments (Tle 1 2). These results re similr to other studies where root iomss production ws reduced y high temperture (Howrd nd Wtschke, 1991; Hung et l., 1997; Hung et l, 1998; Xu nd Hung 2000,; Hung nd Liu, 2003). In our drought tretment, totl root iomss density ws not different mong species from the control, indicting drought lone did not reduce totl root iomss production of HBG, KBG, or TF. This is contrry to reports y other reserchers who oserved declines in totl root iomss production under drought (Howrd nd Wtschke, 1991; Hung et l., 1997). In our study, 60% ET replcement (drought tretment) my hve stimulted root growth during the erly periods of tretment efore inhiiting root growth s severity of the drought effects intensified. Thus, forty eight dys my e not long enough to show the decline in totl root iomss production under drought (60%ET replcement). In the lower profile (i.e., 35 to 57.5 cm), root mss density ws greter in TF thn in HBG nd KBG under ll tretments (Tle 1 2), which indictes TF my e le to extrct soil wter from deeper depths thn HBG nd KBG. A deep extensive root system, which is n importnt drought voidnce mechnism, hs een oserved in TF in other studies (White et l., 1993; Crrow, 1996; Qin et l., 1997, Jing nd Hung, 2001). In growth chmer study, 14

28 however, the mount of extrctle wter y turfgrss roots is limited to the ville reservoir inside the lysimeters, wheres in field soils the roots my extrct wter from lower in the profile. Therefore, TF ws proly not le to enefit sustntilly from its deeper root system in our study. At shllower depths (i.e., 0 to 15 nd 15 to 35 cm), root iomss ws generlly similr mong species within ech tretment (Tle 1 2). Root iomss ws greter in TF thn in KBG, however, in the middle profile (15 35 cm) of the control nd under the comintion of high temperture nd drought. Conversely, root iomss ws greter in KBG thn in TF in the surfce lyer under the comintion of high temperture nd drought. Totl root iomss t ll depths ws similr mong species within ech tretment with the exception of the control, where totl root iomss ws greter in TF thn in KBG. Conclusions In the high temperture tretment, HBG generlly exhiited higher visul qulity, cumultive Pg, dry mtter production, green LAI, nd cumultive ET nd lower EL nd soilsurfce temperture thn KBG nd TF (P=0.05). High temperture did not ffect green LAI in HBG ut reduced green LAI in KBG nd TF y 29 nd 38%, respectively. Under drought stress, the performnce of ll species declined nd differences mong species were negligile. The only exception ws in cumultive dry mtter production, which ws higher in HBG thn in KBG nd TF under drought. The comintion of high temperture nd drought cused reductions in visul qulity, cumultive Pg, cumultive dry mtter production, nd living oveground iomss mong species lthough men vlues were generlly greter in HBG lte in the study. High temperture nd drought comined cused EL nd ded oveground iomss to increse mong species lthough EL ws significntly higher in KBG nd TF thn in HBG lte in the study. In this growth chmer study, HBG exhiited higher resistnce to het thn KBG nd TF, which suggests tht HBG my e etter suited for res where frequent high temperture my dmge other cool seson turfgrsses. Differences in drought resistnce were negligile mong HBG, KBG, nd TF, however, indicting no dvntge of this HBG over KBG nd TF under dry conditions. Field studies re needed to further investigte the het nd drought resistnce of HBG, including dditionl cultivrs of HBG, under the ctul dynmic nd stressful environments where turfgrsses re grown. 15

29 References Arhm, E.M., B. Hung, S.A. Bonos, nd W.A. Meyer Evlution of drought resistnce for Texs luegrss, Kentucky luegrss, nd their hyrids. Crop Sci. 44: Bsinger, J.M., G.J. Kluitenerg, J.M. Hm, J.M. Frnk, P.L. Brnes, nd M.B. Kirkhm Lortory evlution of the dul proe het pulse method for mesuring soil wter content. Vdose Zone J. 2: Blum, A., nd A. Eercon Cell memrne stility s mesurement of drought nd het tolernce in whet. Crop Sci. 21: Bonos, S., A. nd J. A. Murphy Growth responses nd performnce of Kentucky luegrss under summer stress. Crop Sci. 39: Bowmn, D.C., nd L. Mculy Comprtive evpotrnspirtion rtes of tll fescue cultivrs. HortScience 26: Bremer, D.J Evlution of microlysimeters used in turfgrss evpotrnspirton studies using the dul proe het pulse technique. Agron. J. 95: Bremer, D.J. nd J.M. Hm Mesurement nd prtitioning of in situ cron dioxide fluxes in turfgrsses using pressurized chmer. Agron. J. 97: [errt: 98:1375]. Bremer, D.J., K. Su, S.J. Keeley, nd J.D. Fry Performnce in the trnsition zone of two hyrid luegrsses compred with Kentucky luegrss nd tll fescue. Applied Turfgrss Sci. [Online]. Aville t (Pulished 8 Aug. 2006; Verified 23 Oct. 2006). Cmpell, G.S., C. Clissendorff, nd J.H. Willims Proe for mesuring soil specific het using the het pulse method. Soil Sci. Soc. Am. J. 55: Crrow, R.N Drought voidnce chrcteristics of diverse tll fescue cultivrs. Crop Sci. 36: Dunn, J.H. nd K. Diesurg Turf mngement in the trnsition zone. Hooken, NJ. EIFG, Environmentl Institute for Golf [Online]. Aville t (verified 31 My 2006). Emmons, R.D Turfgrss science nd mngement. 3 rd ed. Delmr, Alny, NY. 16

30 Hldimnn P. nd U. Feller Growth t modertely elevted temperture lters the physiologicl response of the photosynthetic pprtus to het stress in pe (Pisum stivum L.) leves. Plnt, Cell nd Enviroment. 28: Hm, J.M. nd R.S. Senock On the mesurement of soil surfce temperture. Soil Sci. Soc. Am. J. 56: Hmilton, G.W., nd D.V. Wddington Infiltrtion rtes on residentil lwns in centrl Pennsylvni. J. Soil Wter Conserv. 54: Howrd, H.F., nd T.L. Wtschke Vrile high temperture tolernce mong Kentucky luegrss cultivrs. Agron J. 83: Hung, B., R.R. Duncn, nd R.N. Crrow Drought resistnce mechnisms of seven wrm seson turfgrsses under surfce soil drying: II. Root spects. Crop Sci. 37: Hung, B., nd X. Liu Summer root decline: Production nd mortlity for four cultivrs of creeping entgrss. Crop Sci. 43: Hung, B., X. Liu, nd J.D. Fry Effects of high temperture nd poor soil ertion on root growth nd viility of creeping entgrss. Crop Sci. 38: Jing, Y., nd B. Hung Physiologicl responses to het stress lone or in comintion with drought: A comprison etween tll fescue nd perennil ryegrss. HortScience 36(4): Jing, Y. nd B. Hung Effects of drought or het stress lone nd in comintion on Kentucky luegrss. Crop Sci. 40: Mrcum, K.B Cell memrne thermostility nd whole plnt het tolernce of Kentucky luegrss. Crop Sci. 38: Minner, D.D., nd J.D. Butler Cool seson turfgrss qulity s relted to evpotrnspirtion. p In 1985 Agronomy strcts, ASA. Mdison, WI. Ntionl Assessment Synthesis Tem Climte chnge impcts on the United Sttes: The potentil consequences of climtic vriility nd chnge. US Glol Chnge Reserch Progrm. Wshington, DC. Perdomo, P., J.A. Murphy, nd G.A. Berkowitz Physiology chnges ssocited with performnce of Kentucky luegrss cultivrs during summer stress. HortScience 31(7):

31 Qin, Y.L., J.D. Fry, nd W.S. Uphm Rooting nd drought voidnce of wrm seson turfgrsses nd tll fescue in Knss. Crop Sci. 37: Red, J.C., J.A. Reinert, P.F. Colugh, nd W.E. Knoop Registrtion of Reveille hyrid luegrss. Crop Sci. 39:590. SAS Insititue Inc Version 9.1 for Windows. SAS Inst., Cry, NC. Shermn, R.C Kentucky luegrss cultivr evpotrnspirtion rtes. HortScience 21: Sifers, S.I. nd J.B. Berd Comprtive inter nd intr specific lef firing resistnce to suproptiml ir nd soil temps in cool seson turfgrss genotypes. Intl. Turf. Soc. Res. J. 7: Song, Y., J.M. Hm, M.B. Kirkhm, nd G.J. Kluitenerg Mesuring soil wter content under turfgrss using the dul proe het pulse technique. J. Am. Soc. Hortic. Sci. 123: Stier, J., E. Koeritz, nd J. Frelich Fertility nd mowing response of het tolernt luegrss nd tll fescue in the upper midwest. p.1. In 2005 Agronomy strcts, ASA. Mdison, WI. Supplick Ploense, M.R., nd Y. Qin Evpotrnspirtion, rooting chrcteristics, nd dehydrtion voidnce: Comprisons etween hyrid luegrss nd Kentucky luegrss. Int. Turf. Soc. Res. J. 10: Trr, J.M., nd J.M. Hm Evlution of dul proe het cpcity sensors for mesuring soil wter content in the lortory nd in the field. Agron. J. 89: Teuton, T.C., J.C. Sorochn, S. J. McElroy, C. L. Min, nd T. C. Mueller Are het tolernt Kentucky luegrsses etter suited for the trnsition zone? p.1. In 2005 Agronomy strcts, ASA.Mdison, WI. Turgeon, A.J. Turfgrss Mngement th ed. Prentice Hll, Englewood Cliffs. NJ. Wng, Z. nd B. Hung Physiologicl recovery of Kentucky luegrss from simultneous drought nd het stress. Crop Sci. 44: White, R.H., A.H. Bruneu, nd T.J. Cowett Drought resistnce of diverse tll fescue cultivrs. Intl. Turf. Soc. Res. J. 7: Xu, Q. nd B. Hung Growth nd physiologicl responses of creeping entgrss to chnges in ir nd soil tempertures. Crop Sci. 40: