Evidence for a freezing tolerance growth rate trade-off in the live oaks (Quercus series Virentes) across the tropical temperate divide

Transcription

1 Reserh Evidene for freezing tolerne growth rte trde-off in the live oks (Querus series Virentes) ross the tropil temperte divide Kri Koehler, lyson Center nd Jennine Cvender-res Deprtment of Eology, Evolution nd ehvior, University of Minnesot, 987 Upper uford Cirle, Sint Pul, MN 558, US uthor for orrespondene: Jennine Cvender-res Tel: Emil: vender@umn.edu Reeived: 2 ugust 2 epted: 26 Otoer 2 doi:./j x Key words: freezing tolerne, growth rte, live oks, Querus series Virentes, trde-off, tropil temperte divide. Summry It hs long een hypothesized tht speies re limited to the north y minimum temperture nd to the south y ompetition, resulting in trde-off etween freezing tolerne nd growth rte. We investigted the extent to whih the limti origins of popultions from four live ok speies (Querus series Virentes) were ssoited with freezing tolerne nd growth rte, nd whether speies fitted model of lolly dpted popultions, eh with nrrow limti tolernes, or of rodly dpted popultions with wide limti tolernes. orns from popultions of four speies ross tropil temperte grdient were grown under ommon tropil nd temperte onditions. Growth rte, seed mss, nd lef nd stem freezing trits were ompred with soure minimum tempertures. Mximum growth rtes under tropil onditions were negtively orrelted with freezing tolerne under temperte onditions. The minimum soure temperture predited the freezing tolerne of popultions under temperte onditions. The tropil speies Q. oleoides ws differentited from the three temperte speies, nd vrition mong speies ws greter thn mong popultions. The trde-off etween freezing tolerne nd growth rte supports the rnge limit hypothesis. Limited vrition within speies indites tht the distriutions of speies my e driven more strongly y rod limti ftors thn y highly lol onditions. Introdution entrl issue in eology is to understnd the mehnisms tht underlie the distriutions of speies. Climte is known to e ritil ftor ontrolling the rod-sle distriution of orgnisms (Huthinson, 98; Mrthur, 972; Gre, 987; Iverson & Prsd, 998; Rehfeldt et l., 999, 26; Cvender-res, 25; Chuine, 2), ut often the physiologil sis for limti nihe onstrints is unknown. Linking the physiologil tolernes of speies to their limti distriutions is importnt in prediting future distriutions of speies under hnging limti onditions (Morin et l., 27). In prtiulr, the freezing tolerne of speies often orresponds to the minimum tempertures in their limte of origin (Ski & Weiser, 973; Woodwrd, 99; izen & Woodok, 996), nd the ility of different speies to void or tolerte freezing stress through vrious mehnisms goes long wy to explin the geogrphi distriutions of speies (Prker, 963; George et l., 974; Lthm & Riklefs, 993). It hs long een hypothesized tht the distriutions of speies re limited y freezing tolerne in the north (in the Northern Hemisphere) nd y ompetition in the south (M- rthur, 972). potentil mehnism underlying this hypothesis is trde-off etween growth rte nd freezing tolerne (Woodwrd, 987; Shenk, 996; Loehle, 998; itken & Hnnerz, 2). In the north, the quisition of trits for old limtion nd freezing tolerne hs een hypothesized to impose ost in terms of resoure llotion tht results in lower growth rtes (Levitt, 98; ek, 988; Körner & Lrher, 988; Woodwrd, 99; Howe et l., 23); lk of freezing tolerne t the southern edge of the speies distriution thus permits higher growth rtes nd inresed ompetitive ility (Woodwrd & Pigott, 975; Woodwrd, 987). More generlly, inresed tolerne to ioti stress is elieved to trde off ginst growth nd ompetitive ilities in plnts (Tilmn, 988) s result of resoure limittions tht drive the evolution of llotion strtegies. In ddition to growth rte, seed mss is onsidered to e ritil life history ttriute ssoited with seson length tht my limit southern distriutions (Morin & Chuine, 26). Seed mss ontriutes diretly to solute growth rtes (Cvender- res et l., 24) nd is linked to inresed survivl nd ompetitive ility (Kitjim & Fenner, 2; Fenner & Thompson, 25; Turnull et l., 28). Towrds the tropis, higher seed mss my e fvored y longer seson length, whih llows longer time for ron umultion, nd my provide

2 2 Reserh New Phytologist ompetitive dvntge in highly diverse tropil ommunities in whih ompetitive intertions my dominte ssemly proesses. y ontrst, seed mss my e onstrined diretly y seson length t northern ltitudes (Moles & Westoy, 23; Chuine, 2), or my e limited y resoure investment in freezing tolerne, nd lrge seeds my e less dvntgeous t northern ltitudes where freezing stress is dominnt filter in ommunity ssemly. From historil iogeogrphi perspetive, if speies evolve in tropil regions with no freezing tolerne nd then expnd into the temperte zone, freezing tolerne my e quired simultneously with the evolution of slower growth during unfvorle periods, s oth re thought to e dvntgeous in sesonlly old limtes (Lrher & uer, 98; Körner & Lrher, 988; Kozlowski & Pllrdy, 997). Therefore, negtive reltionship etween freezing tolerne nd growth rte ould rise s result of differentil llotion of limited resoures or of orrelted evolution during rnge expnsion from the tropis to the temperte zone, or oth. For similr resons, negtive reltionship etween freezing tolerne nd seed size my lso e expeted. Vrition in freezing tolerne, s well s oth growth rtes nd seed size, mong speies ould ontriute to n explntion of rnge limits. Within speies, evidene of deline in growth rte t more northern ltitudes nd older tempertures is onsistent ross studies oth in situ (Roerds et l., 99; Mtys & Yetmn, 992; Rehfeldt et l., 999, 2) nd in ommon grdens (Smitherg & Weiser, 968; Li et l., 998; Oleksyn et l., 998). In ddition, severl studies hve shown similr reltionship ross speies (Rehfeldt, 997; Ymhir & Conover, 22; Green, 27; Svge, 2). ross speies, seed size in forest speies hs een shown to inrese towrds the tropis nd derese t high ltitudes (Moles & Westoy, 23; Morin & Chuine, 26). still deted question is whether popultions within speies show onservtism in their limti tolernes, perspetive used to defend limti nihe modeling pprohes (Wiens & Grhm, 25; Permn et l., 28). For exmple, freezing tolerne my hve evolved onservtively, suh tht ll popultions within speies (or linege) hve the sme resistne to freezing. Under this view, rodly distriuted speies exposed to rnge of tempertures my e dpted to tolerte wide rnge of limti onditions with little lol dpttion (Lrher, 25). Mny tree speies n survive muh older freezing tempertures thn our in their urrent rnge (Fuhigmi et l., 97; Ski & Weiser, 973; itken & dms, 996), suggesting tht freezing tolerne my not e ostly to mintin in speies with rod distriutions. Woody speies re known to hve rod eologil distriutions in omprison with hereous speies, whih hve more speilized nihes (Riklefs & Lthm, 992). If speies hve rod nd onserved limti tolernes, little vrition in limti tolernes would e expeted mong popultions. Within speies rnges, however, there is evidene tht the distriutions of plnt speies onsist of popultions genetilly suited to lol limtes (Morgenstern, 996; itken & Hnnerz, 2; Rehfeldt et l., 2; Lrher, 25; Cvender-res, 27), nd often show linl vrition in the limti tolernes of speies s result of dptive differentition (Endler, 977; Dvis & Shw, 2; Rehfeldt et l., 2; Howe et l., 23). Clinl vrition in freezing tolerne hs een demonstrted in severl tree speies, suggesting high levels of lol dpttion (Rehfeldt et l., 2; Li et l., 22; rnd et l., 25; Morin et l., 27; Friedmn et l., 28). In this study, we exmine growth, old limtion nd freezing tolerne within nd etween four speies in the live ok group (Querus setion Virentes) Q. virginin, Q. oleoides, Q. fusiformis nd Q. gemint in ommon grden experiment. The live oks re smll monophyleti linege ontining speies in the southern US nd Centrl meri. They re useful group in whih to exmine the mehnisms underlying geogrphi distriutions, euse they spn the tropil temperte divide, with severl speies overing lrge ltitudinl grdients. Previous studies hve estlished geneti nd morphologil differentition etween Q. gemint nd Q. virginin (Cvender-res & Phlih, 29) nd Q. virginin nd Q. oleoides (Cvender-res, 27; Cvender-res et l., 2), nd there is evidene tht the group originted in the tropis of Centrl meri nd susequently expnded into the temperte zone (Cvender-res et l., 2). Our gols were to estlish the extent to whih the distriutions of live ok speies rnges were ssoited with old limtion, freezing tolerne nd growth, onsistent with the hypothesis tht they re limited t the northern rnge y minimum temperture nd t the southern rnge y ompetitive ility (growth rte), nd whether live ok popultions fit model of lol dpttion with nrrow limti tolernes, or of rod limti tolernes with little vrition mong popultions. We speifilly tested, first, whether there ws popultion- nd or speies-level vrition in the ility to old limte. If more northern popultions nd or speies inresed their freezing tolerne signifintly under temperte onditions, ut more southern popultions did not, this provides evidene for the evolution of old hrdening in response to old temperture ues. Seond, we tested whether there ws trde-off etween freezing tolerne nd growth rte (oth solute nd reltive growth rtes). negtive reltionship, suh tht mternl lines with slower growth rtes exhiit greter freezing tolerne, would provide evidene for this trde-off. We lso exmined the reltionship etween freezing tolerne nd seed mss, euse seed mss n influene ompetitive ility nd hs een predited to vry with limti distriution (Morin & Chuine, 26). We note tht shde tolerne n drive ompetitive outomes in lte suessionl forests (zzz, 979; Grime, 979), ut we did not exmine it here, euse ll of the live oks n e hrterized s midsuessionl svnnh speies tht regenerte under similr (modertely high) light regimes (Kurz & Godfrey, 962; Spetor & Putz, 26; Klemens et l., 2). Finlly, we tested the extent to whih minimum tempertures t the popultion soure predited freezing tolerne nd growth rte. Clinl vrition in old limtion, freezing tolerne nd growth rtes mong popultions within speies would provide evidene for lol dpttion. lterntively, lrge differenes in freezing tolerne, growth rtes nd or limtion potentil etween speies, ut limited

3 New Phytologist Reserh 3 vrition mong popultions within rodly distriuted speies, would indite tht speies hve onserved limti nihes nd rod limti tolernes. Mterils nd Methods Study speies nd experimentl design The live oks (Querus series Virentes Nixon) onsist of seven speies of interfertile ostl oks tht spn the tropil temperte divide through the southern US, Mexio nd Centrl meri (Muller, 96; Nixon, 985; Nixon & Muller, 997). Live oks re evergreen to revi-deiduous (mintin leves in mild tempertures, ut my drop leves in response to old stress) trees hrterized y rhizomtous lonl growth, nd often our in shru form in the juvenile stge in response to low-nutrient soil onditions nd sesonl drought. We exmined four live ok speies (Fig. ): Querus virginin Miller (southern live ok), evergreen to revi-deiduous, ours in xeri snds to mesi sites from ostl est Texs to Virgini; Q. gemint Smll, evergreen to revi-deiduous (snd live ok), ours in xeri snds to mesi sites from Louisin to North Crolin; Q. fusiformis Smll (Texs live ok), evergreen to revi-deiduous, ours in xeri sites nd open woodlnds from Texs to Oklhom (Nixon & Muller, 997); nd Q. oleoides Shltdl. & Chm., tropil evergreen shru, ours in tropil dry forest from the north Pifi ost of Cost Ri to northern Mexio (ouher, 983; Nixon, 985). orns were olleted from one to five popultions within eh of four live ok speies: Q. virginin (North Crolin, northern Florid, southern Florid, Louisin nd Texs); Q. gemint (northern Florid nd North Crolin); Q. fusiformis (Texs); nd Q. oleoides (Mexio, elize nd Cost Ri) (Fig., Supporting Informtion Tle S). Coordintes for eh tree were reorded (Tle S) nd olletion permits, export import permits nd phytosnitry ertifites were otined (ville on request). Eh geogrphilly determined popultion inluded five to nine mternl fmilies nd. 5 individuls in eh fmily. Seeds were olleted from rndom trees within eh popultion; however, the numer of mternl fmilies per popultion ws reltively low nd these fmilies my not dequtely represent the entire popultion. Moreover, germintion mong fmilies ws unequl, nd some fmilies hd low numers. The length nd width of eh orn were mesured nd the orns were stored t 4 C until synhronous plnting in glsshouse filities t the University of Minnesot in Novemer 25. fter yr of growth in onstnt temperture nd wtering regime (tropil onditions), two replited limte tretments were implemented during the winter months of 26 (mid- Novemer to Mrh): tropil tretment, in whih dytime temperture ws mintined etween 3 nd 35 C, nd nighttime tempertures were etween 22 nd 26 C; nd temperte tretment, in whih winter growth tempertures rehed minimum night-time temperture of 4 C with dytime temperture of 5 C, simulting the monthly verge tempertures in Lieri, Cost Ri (southern rnge limit) nd Wilmington, North Crolin (northern rnge limit). Eh limte regime ws replited in two independently ontrolled glsshouse rooms. The photoperiod ws extended to 2 h during the winter, similr to Cost Ri (southern rnge limit). Summer photoperiods were left t nturl levels with mximum of 5.5 h, whih ws up to h longer thn in North Crolin (northern rnge limit) nd 3 h longer thn in Cost Ri. The photoperiod ws not limiting ftor in this experiment; however, the derese from 5.5 to 2 h my hve provided some ues for dormny. These limte tretments were repeted every yer for three susequent yers. Growth rte nd seed mss We ompred oth the solute growth rte (GR) nd reltive growth rte (RGR) in the growth rte freezing tolerne trdeoff. GR is the mount of iomss tht umultes in yer nd RGR is the mximum intrinsi growth rte. Plnts t () () Querus virginin Querus gemint Querus fusiformis Querus oleoides Fig. () Rnge mps for the four live ok speies: Querus virginin, Q. gemint, Q. fusiformis nd Q. oleoides, showing herrium reords nd olletion sites from Cvender-res et l. (2). () Lotion of seed soures (lrge shpes) for eh popultion, using the sme symols s in ().

4 4 Reserh New Phytologist northern ltitudes my grow more rpidly in erly spring, nd thus hve higher RGR, ut, y the end of the yer, my hve umulted less totl iomss (GR) euse of shorter growing seson. Therefore, in studies with sesonl vrition in growth, the GR of speies under ommon onditions is the ritil ftor to ompre mong popultions. eginning in erly Mrh 27, 3 months fter the strt of the winter limte tretment, ll individuls were monitored for mximum height (root ollr to pex of tllest stem), numer of leves (totl leves on ll stems) nd stem dimeter (mesured t the root ollr). llometri equtions used to estimte the iomss for eh speies were developed from dt in previous experiments (Cvender-res et l., 24). ove-ground iomss ws estimted using the mximum height, totl numer of leves nd stem dimeter. The sme eqution ws used for Q. virginin nd Q. fusiformis, euse of lk of iomss dt for Q. fusiformis. orn mss ws estimted using the orn volume. GR (g yr ) ) ws lulted s GR = (M finl ) M initil ) (T finl ) T initil ), where M finl is the iomss estimte from growth mesurements mde in Mrh 27, M initil is the estimted orn mss, T finl is the pproximte dte on whih plnts were mesured in Mrh 27 nd T initil is the dte of seedling emergene. RGR (g g ) yr ) ) ws lulted s RGR = log e (M finl ) ) log e (M initil ) (T finl ) T initil ). Seed mss ws mesured s the seed volume (V) t the time of plnting sed on the height (h) nd dimeter (d) of eh orn, ssuming n ellipsoid: V =4 3 (d 2) 2 (h 2). Fresh seed mss ws lulted on the sis of the empiril reltionship etween volume nd fresh mss with the seed ot removed sed on seed vrition for 48 orns for 6 speies of ok: M = 363V ).23 (R 2 =.97; Cvender-res et l., 24). Lef freezing tolerne In Ferury 29, freezing mnipultions were onduted to determine differenes in lef freezing sensitivity within nd etween the four speies grown in oth temperture tretments. Drk-limted hlorophyll fluoresene (F v F m ) ws mesured in situ to determine the mximum photosyntheti quntum yield for one lef. rnhlets with t lest five leves, inluding the mesured lef, were susequently ut under wter, pled in wter-filled rose tues in the drk nd frozen in tempertureontrolled freezer ox overnight t minimum temperture of ) C. Overnight freezing events were simulted using ustom-designed freezer ox (Perivl LT-5HID; Perivl Sientifi, In., Perry, Iow, US) following previously desried methods (Cvender-res & Holrook, 2; Cvender-res et l., 25; Cvender-res, 27) (Methods S). To llow reovery, frozen smples were pled in drk hmer t room temperture (25 C) efore the re-mesurement of drk-dpted F v F m following oorse et l. (998). Smples were mesured.5, 6, 2, 24 nd 48 h fter the freezing yle hd ended. pproximtely nine individuls were mesured in eh popultion nd limte tretment. The rnk order of vlues for speies remined onstnt ross these time points (Fig. S2); for revity, only vlues 6 h fter freezing re reported further. The deline in F v F m ws lulted s F v F m efore freezing minus F v F m fter freezing. Lef freezing tolerne ws lulted s one minus the deline in F v F m. Lef old limtion ility ws lulted s the differene etween the tropil nd temperte tretment divided y the tropil tretment for deline in F v F m fter freezing t ) C. Lef loss Lef loss or the development of winter deiduous strtegy is one dpttion to old tempertures y whih some speies void freezing dmge. lthough live oks often mintin their leves during the winter months, oth field nd experimentl dt indite tht senesene is indued y hilling nd vries mong popultions (Cvender-res & Holrook, 2; Cvender- res, 27). In Mrh 29, 4 months fter the strt of the winter limte tretment, lef loss ws quntified. The perentge of lef loss for eh plnt ws estimted on the sis of fllen leves in the pot nd lef srs, nd ws otined t the end of the tretment yle to pture ll sesonl loss. Stem freezing tolerne In Ferury 2, eletrolyte lekge ws mesured to determine stem freezing sensitivity. The eletrolyte lekge method uses hnges in eletril ondutivity to predit ell lysis in response to freezing (Flint et l., 967; Friedmn et l., 28). Stem segments (. 2.2 mm in dimeter) were exised from eh seedling, the leves were removed, stems were ut into five -m piees nd eh piee ws pled in seprte test-tue with ml of deionized wter. One tue ws stored t 4 C s nonfrozen ontrol nd the other tues were susequently frozen t four freezing tempertures () 5, ), ) 5 nd ) 2 C) in progrmmle freezing hmer (Cole-Prmer Instrument Co., Vernon Hills, IL, US) following the methods of Friedmn et l. (28) (Methods S). n verge of 2 individuls per popultion in eh limte tretment ws mesured. The index of injury t eh temperture (I t ) ws lulted s the perentge of ell lysis t eh freezing temperture (Flint et l., 967). The index of injury dt were rsin trnsformed for sttistil nlyses. Stem old limtion ility ws lulted s the differene etween the tropil nd temperte tretments divided y the tropil tretment for index of injury fter freezing t ) 5 C. Stem freezing tolerne ws lulted s minus the index of injury t eh freezing temperture. lthough the rnk order of vlues for stem freezing injury remined reltively onstnt t the speies level t ), ) 5 nd ) 2 C, vlues t ) 5 C showed slightly higher differentition mong speies (Fig. S2); for revity, only this mesurement is reported further. Dt nlysis Climte dt were ompiled from WorldClim (Hijmns et l., 25), using herrium speimen ourrene lolities (GIF Dt Portl, to determine limte rnges for ll four speies. The 9 ioclim limti prmeters nd ourrene lolities were used in the MXENT modeling

5 New Phytologist Reserh 5 progrm to predit speies rnges nd to determine whih limte prmeters hd the gretest preditive vlue. The Mxent limte model predited speies distriutions very lose to tul distriutions (Fig. S); of the 9 ioclim vriles, the minimum temperture of the oldest month ontriuted the most to rnge preditions for ll four speies. Therefore, the minimum temperture of the oldest month is used s the limti vrile in ll susequent nlyses. Physiologil nd growth dt for individuls were verged ross mternl fmilies, nd mternl fmilies were grouped into popultions on the sis of lotion nd speies. NOVs for ll physiologil, growth rte nd minimum temperture dt were onduted with popultion nested within speies to determine speies- nd popultion-level differentition nd intertions with limte tretment. Student s t-test differentition ws used to determine speies nd popultion differenes within eh tretment. Liner regressions were used to test trde-offs etween growth rte, freezing tolerne, orn mss, old limtion nd minimum temperture of the oldest month ross mternl fmilies. We lso used NCOV to test whether growth rte nd minimum temperture, treted s ovrites, predited stem nd lef freezing tolerne when speies, popultion nd limte tretment were inluded in the model s fixed ftors. We otined restrited mximum likelihood (REML) vrine omponent estimtes to determine the perentge of totl vrition tht ould e ttriuted to speies nd to popultions. ll nlyses were onduted in JMP 7. (SS, Cry, NC, US). Results Climti distriutions The rnge of minimum tempertures for the three temperte speies (Q. virginin, Q. gemint nd Q. fusiformis) overlpped, ut ws distint for Q. oleoides (Fig. 2). The minimum tempertures of the oldest month t the highest proility of presene were s follows: Q. virginin (5 C), Q. gemint (8 C), Q. fusiformis (7 C) nd Q. oleoides (6 C). oth Q. virginin nd Q. fusiformis were distriuted ross rod rnge of minimum tempertures, wheres Q. gemint hd nrrower limti rnge (Fig. 2). hierrhil NOV, with popultion nested within speies, showed signifint vrition in the minimum temperture of the oldest month (P <.;Tle)etweenpopultionlotions. The northern popultions of North Crolin (Q. virginin) nd Texs (Q. fusiformis) experiened lower minimum tempertures (Fig. 2). However, Louisin, Texs nd northern Florid popultions were not signifintly different with regrd to the minimum temperture of the oldest month (Fig. 2). In North Crolin nd northern Florid, Q. gemint nd Q. virginin o-ourred nd were exposed to similr minimum tempertures. y ontrst, Q. virginin nd Q. fusiformis in Texs experiened signifintly different minimum tempertures (Fig. 2). Querus oleoides popultions ourred in lotions with higher minimum tempertures thn ll popultions of Q. virginin, Q. fusiformis nd Q. gemint (Fig. 2). () () Lef loss Cost Ri elize Mexio S Florid N Florid Louisin Texs N Crolin (Q. gemint) Texs (Q. fusiformis) Fig. 2 () Climti distriutions for four live ok speies sed on the perentges of herrium reord ourrenes for the minimum temperture in the oldest month ( C). The rnge of minimum tempertures for the three temperte speies (Querus virginin (VI); Q. gemint (GE); Q. fusiformis (FUS)) is overlpping, ut is distint for the tropil speies Q. oleoides (OL). () Minimum monthly tempertures for popultions within speies verged ross mternl fmily soure lotions (dt from WorldClim; Hijmns et l., 25): Q. virginin, squres; Q. gemint, rosses; Q. fusiformis, irles; Q. oleoides, tringles. For the North Crolin nd northern Florid popultions of Q. virginin nd Q. geminte, the lines re nerly identil nd only one is shown. Popultions nested within speies re signifintly differentited (). There ws lmost no lef loss under tropil onditions for popultions or speies (Fig. 3). However, Q. virginin nd Q. fusiformis exhiited signifint lef loss under temperte onditions (P <.; Tle ; Fig. 3). Within Q. virginin, Louisin nd Texs popultions exhiited greter lef loss thn southern Florid popultions (Fig. 3). Interestingly, Q. gemint ourred in the sme region s Q. virginin in North Crolin nd northern Florid, ut did not drop its leves in response to old tempertures (Fig. 3). There ws lrge mount of vrition within Q. fusiformis, used y individuls tht either lost very few or lmost ll of their leves. Under temperte onditions, 55% of vrition ws ttriuted to speies-level differenes nd 2% to popultion-level differenes (Tle S2). Cold limtion hierrhil NOV showed signifint vrition mong speies for oth lef nd stem old limtion ility (P =.2;

6 6 Reserh New Phytologist Tle NOV for lef nd stem freezing tolerne, perent lef loss, solute growth rte (GR), reltive growth rte (RGR), minimum temperture of the oldest month from popultion soures, lef nd stem freezing limtion Effet DF SS F rtio P vlue Lef freezing tolerne Speies <. Popultion (Speies) Growth temperture <. tretment Speies tretment <. Popultion (Speies) tretment Stem freezing tolerne Speies <. Popultion (Speies) Growth temperture <. tretment Speies tretment <. Popultion (Speies) tretment Lef loss Speies <. Popultion (Speies) Growth temperture <. tretment Speies tretment <. Popultion (Speies) tretment GR (g yr ) ) Speies <. Popultion (Speies) <. Growth temperture <. tretment Speies tretment Popultion (Speies) tretment RGR (g g ) yr ) ) Speies <. Popultion (Speies) <. Growth temperture tretment Speies tretment Popultion (Speies) tretment Minimum temperture C Speies <. Popultion (Speies) <. Lef freezing limtion Speies Popultion (Speies) Stem freezing limtion Speies Popultion (Speies) Signifint vlues (P <.5) re shown in old nd mrginlly signifint vlues (P <.) re shown in itlis. SS, sum of squres. P =.75), ut popultions nested within speies were not differentited signifintly (Tle ). For lef old limtion, 35% of the vrition ws found t the speies level nd % t the popultion level. For stem old limtion, 5% of vrition ws ttriuted to speies-level differenes nd 3% to popultion-level differenes (Tle S2). Lef freezing tolerne hierrhil NOV showed signifint intertion with limte tretment for oth speies (P <.) nd popultion nested within speies (P =.493; Tle ). Plnts grown under tropil onditions ll showed less lef freezing tolerne thn plnts limted to old tempertures, nd showed no signifint differentition in response to freezing t either the popultion or speies level (Fig. 3,d). Cold-limted plnts showed differentition in lef-level freezing tolerne t the speies level: the temperte speies Q. gemint, Q. virginn nd Q. fusiformis ll showed greter freezing tolerne thn the tropil speies Q. oleoides (Fig. 3). Under temperte onditions, within Q. virginin, the North Crolin popultion showed greter freezing tolerne thn the northern nd southern Florid popultions, exhiiting some popultion-level vrition (Fig. 3d). However, there were no differenes etween the northern Florid nd North Crolin popultions of Q. gemint with regrd to lef freezing tolerne. Querus oleoides showed the lowest stem freezing tolerne. Under temperte onditions, 69% of the vrition ws ttriuted to speies-level differenes nd 5% to popultion-level differenes (Tle S2). Stem freezing tolerne hierrhil NOV showed signifint intertion with limte tretment for speies (P <.), nd popultion nested within speies ws mrginlly signifint (P =.594, Tle ). Cold-limted plnts showed speies-level vrition fter freezing t ) 5 C (Fig. 3e). Querus oleoides showed the lowest freezing tolerne ross oth limte tretments (Fig. 3e). In the temperte tretment, Q. gemint showed less freezing tolerne thn Q. virginin or Q. fusiformis. Within Q. oleoides, there ws limited popultion-level differenes. However, the Mexin popultion exhiited greter stem freezing tolerne thn the Cost Rin or elizen popultions (Fig. 3f), orresponding to lower minimum temperture in Mexio (Fig. 2); the sme pttern ws not seen in lef freezing tolerne, however (Fig. 3d). Under temperte onditions, within Q. virginin, the North Crolin popultion showed less stem freezing dmge thn the northern nd southern Florid popultions, exhiiting some popultion-level vrition orresponding to ltitude (Fig. 3f). However, there were no differenes etween the northern Florid nd North Crolin popultions of Q. gemint. Under temperte onditions, 82% of the vrition in stem freezing tolerne ws ttriuted to speies nd 5% to popultion differenes(tle S2). Growth rte hierrhil NOV showed signifint vrition etween speies (P <.) nd popultion nested within speies (P <.; Tle ). However, intertions with limte tretment were not signifintly different. In generl, GR nd RGR showed similr ptterns in speies-level response (Fig. 3g,i). Growth rtes were redued in response to the temperte tretment

7 New Phytologist Reserh 7 () () de e de de d () (d) d d d d d d C C C C C C C C C Fig. 3 Speies (left olumn) nd popultion (right olumn) mens (± SE) under ontrolled tropil (gry) nd temperte (lk) limti onditions for lef loss (,), lef ( ) deline in F v F m fter freezing t ) C) (,d) nd stem ( ) index of injury fter freezing t ) 5 C) (e,f) freezing tolerne nd solute (GR) (g,h) nd reltive (RGR) (i,j) growth rtes. Speies: Querus virginin, VI, squres; Q. gemint, GE, rosses; Q. fusiformis, FUS, irles; Q. oleoides, OL, tringles. Popultions: Querus oleoides, CR_OL, Cost Ri; Z_OL, elize; MX_OL, Mexio; Q. virginn, FLS_VI, southern Florid; FLN_VI, northern Florid; L_VI, Louisin; TX_VI, Texs; NC_VI, North Crolin; Q. gemint, FLN_GE, northern Florid; NC_GE, North Crolin; Q. fusiformis, TX_FUS, Texs. Different letters indite signifint Student s t-test speies- nd popultion-level differentition (P <.5) within the tropil nd temperte tretments. (e) (g) (i) C C d C C (f) de e de d e d C E E E DE E CDE DE CD (h) C C CD CD DE E E E d de de de e de e (j) C C C CD CD DE F F d d EF de def ef f ef reltive to the tropil tretment for ll speies (Fig. 3g,i). Cold-limted plnts showed speies-level vrition (Fig. 3g,i). Querus oleoides showed redued GR in the temperte tretment, ut mintined higher growth rte thn ny of the temperte speies (Fig. 3d). In ddition, Q. fusiformis nd Q. gemint hd lower growth rtes thn Q. virginin. Within Q. virginin, old-limted plnts in the Louisin popultion hd higher growth rte (GR nd RGR) thn other Q. virginin popultions, similr to some popultions of Q. oleoides (Fig. 3h,i). For GR, 7% of the vrition ws ttriuted to speies-level differenes nd 3% to popultion-level differenes. For RGR, 54% of the vrition ws ttriuted to speies-level differenes nd 7% to popultion-level differenes (Tle S2). Seed mss differed signifintly mong speies, ut not mong popultions within speies (Fig. S2). Seed mss ws wekly orrelted with GR (R 2 =.92, P =.9, Fig. 5f), reltionship driven lrgely y speies; reltively little of the vrition in GR mong fmilies ws explined y seed mss. Seed mss ws not orrelted with RGR (Fig. S4). Trde-offs etween freezing tolerne, growth nd seed mss ross the tropil temperte grdient We found evidene for trde-off etween growth nd freezing tolerne ross four live ok speies (Fig. 4 ). The most pproprite test for trde-off etween growth nd freezing tolerne is etween growth rtes under nonstressed (tropil) onditions nd freezing tolerne under old-limted (temperte) onditions. This omprison ws possile, given tht seeds from the sme mother tree were plnted in oth tretments nd fmily men vlues for nonstressed growth nd old-limted freezing ould e ompred diretly. Fmilies with higher GRs hd lower freezing tolerne in oth stems nd leves (Fig. 4,). The sme ws true for RGR nd stem freezing tolerne, ut there ws no reltionship etween RGR nd lef freezing tolerne. oth lef nd stem freezing tolerne were negtively orrelted with seed mss (Fig. 4e,f), lthough the reltionship with stem freezing tolerne ws stronger. Cold limtion ility in oth leves (Fig. 4g) nd stems (Fig. 4h) ws negtively

8 8 Reserh New Phytologist () Stem freezing tolerne (Temperte) () Lef freezing tolerne (Temperte) (e) Lef freezing tolerne (Temperte) (g) Lef old limtion (i) Lef old limtion R 2 = GR (g yr ) (Tropil) R 2 =.95 P = GR (g yr ) (Tropil) R 2 =.23 P = orn mss (g) R 2 =.62 P = GR (g yr ) (Tropil) R 2 =.9 P = RGR (g g yr ) (Tropil) () Stem freezing tolerne (Temperte) (d) Lef freezing tolerne (Temperte) (f) Stem freezing tolerne (Temperte) (h) Stem old limtion (j) Stem old limtion R 2 =.96 P = RGR (g g yr ) (Tropil) R 2 =.6 P = RGR (g g yr ) (Tropil) R 2 = orn mss (g) R 2 = GR (g yr ) (Tropil) R 2 = RGR (g g yr ) (Tropil) Fig. 4 Trde-offs etween growth rte in nonstressed tropil onditions nd freezing tolerne fter old limtion in temperte onditions ross mternl fmilies from four live ok speies: Querus virginin (squres), Q. gemint (rosses), Q. fusiformis (irles) nd Q. oleoides (tringles). Points represent fmily mens. Reltionships re shown for: temperte stem freezing tolerne ( ) index of injury fter freezing t ) 5 C) nd tropil solute growth rte (GR) (); temperte stem freezing tolerne nd tropil reltive growth rte (RGR) (); temperte lef freezing tolerne ( ) deline in F v F m fter freezing t ) C) nd tropil GR (); temperte lef freezing tolerne nd tropil RGR (d); temperte lef freezing tolerne nd orn mss (e); temperte stem freezing tolerne nd orn mss (f); lef old limtion ility ((tropil ) temperte) tropil for deline in F v F m fter freezing t ) C) nd GR under tropil onditions (g); stem old limtion ility ((tropil ) temperte) tropil for index of injury fter freezing t ) 5 C) nd GR under tropil onditions (h); lef old limtion ility nd RGR under tropil onditions (i); nd stem old limtion ility nd RGR under tropil onditions (j). Lest squres fitted lines re shown for signifint reltionships (P <.5); the dshed line (g) indites mrginl signifine. Corretions re not mde for multiple tests. orrelted with GR. Cold limtion ility of stems (Fig. 4j), ut not leves (Fig. 4i), ws negtively orrelted with RGR. The minimum temperture of the oldest month of the soure popultions predited freezing tolerne, growth nd old limtion (Fig. 5 h). In NCOV, GR signifintly predited stem freezing tolerne (P =.2,Tle2)whentkingintoount popultion- nd speies-level vritions, nd minimum temperture signifintly predited lef freezing tolerne when tking into ount speies- nd popultion-level vritions (P =.36, Tle 2). Minimum tempertures in the oldest month lso predited seed mss (Fig. 5e), reltionship driven lrgely y the ft tht the tropil speies, Q. oleoides, hd lrger seeds thn the speies tht ourred in temperte regions. Given tht seeds were olleted in the field, we nnot eliminte n environmentl influene on seed mss. However, vrition in seed mss ws greter etween thn within speies, despite steep environmentl grdients within speies rnges, suggesting tht seed mss my e genetilly onstrined t the speies level, s onluded in erlier studies (skin et l., 998; Morin & Chuine, 26). Disussion We provide evidene for trde-off etween growth rte nd freezing tolerne ross mternl fmilies from four speies of live ok (Querus series Virentes) tht spn the tropil temperte divide ross North nd Centrl meri. Mternl fmilies with

9 New Phytologist Reserh 9 Fig. 5 Minimum temperture of the oldest month in the limte of origin predits lef () nd stem () freezing tolerne nd reltive growth rte (RGR) () nd solute growth rte (d) under oth tropil (gry) nd temperte (lk) growth onditions in mternl fmilies from four live ok speies. Minimum temperture of the oldest month lso predits orn mss (e), nd orn mss is orrelted with GR under tropil (nonstressed) onditions (f). Minimum temperture of the oldest month further predits lef old limtion ility ((tropil ) temperte) tropil for deline in F v F m fter freezing t ) C) (g) nd stem old limtion ility ((tropil ) temperte) tropil for index of injury fter freezing t ) 5 C) (h). Points represent fmily mens. Querus virginin, squres; Q. gemint, rosses; Q. fusiformis, irles; Q. oleoides, tringles. Lest squres fitted lines re shown for tropil (lk) nd temperte (gry) tretments. The dshed gry line () indites mrginl signifine. Corretions re not mde for multiple tests. () Lef freezing tolerne () 6 RGR (g g yr ) (e) orn mss (g) (g).2 Lef old limtion Minimum temperture of oldest month ( C) Minimum temperture of oldest month ( C) Minimum temperture of oldest month ( C) R 2 =.37 R 2 =.568 R 2 =.36 R 2 =.26 R 2 =.6 P =.64 R 2 = Minimum temperture of oldest month ( C) () (d) (f) (h) Stem freezingtolerne GR (g yr ) GR (g yr ) (Tropil) Stem old limtion Minimum temperture of oldest month ( C) R 2 =.58 R 2 =.54 R 2 = 7 R 2 = Minimum temperture of oldest month ( C) R 2 =.92 P = orn mss (g) R 2 = Minimum temperture of oldest month ( C) higher freezing tolerne under temperte (old-limting) onditions hd slower growth rtes under tropil (nonstressed) onditions. These reltionships were strongest etween stem freezing tolerne () 5 C) nd oth GR nd RGR, ut were lso supported for lef freezing tolerne () C) nd GR (Fig. 4 d). Unlike mternl fmilies from Q. oleoides, fmilies from temperte ltitudes (from Q. virginin, Q. gemint nd Q. fusiformis) demonstrted the ility to inrese freezing tolerne in response to hilling growth tempertures. The ility to old limte nd express higher freezing tolerne under temperte onditions thn under tropil onditions ws ssoited with less ompetitive growth rtes under tropil (nonstressed) growth onditions (Figs 4g j, S3). Lower GRs in live oks from more northern ltitudes were driven y oth lower RGR (Fig. S4) nd redued seed mss (Fig. 5f). Seed mss delined with lower minimum tempertures (Fig. 5e) nd my e limited y the length of the growing seson euse of energy onstrints (Morin et l., 27; Chuine, 2). Our results indite tht, t more northern ltitudes, live oks hve een seleted to invest in freezing tolerne nd old limtion ility, rther thn higher growth rtes nd lrger seed sizes, whih my enfore speies oundries ross the tropil temperte divide. This trde-off supports the lssi hypothesis tht the distriutions of speies re limited y freezing tolerne in the north nd y ompetition in the south (Mrthur, 972; Woodwrd, 987; Shenk, 996; Gross & Prie, 2). Climte of origin predits growth rtes, seed mss, freezing tolerne nd old limtion ility Live ok speies showed signifint differentition in their sensitivity to freezing, s expeted from their limti distriutions (Fig. 2,). Under oth tropil nd temperte growth onditions, minimum tempertures in the limte of origin strongly predited freezing tolerne, growth rtes, seed mss nd old limtion ility of mternl fmilies (Fig. 5). Mternl fmilies from limtes with older winters hd slower growth rtes nd greter freezing tolerne thn those from milder limtes. Minimum temperture ws signifint ovrite prediting lef freezing tolerne when speies, popultion nd tretment were

10 Reserh New Phytologist Tle 2 NCOV inditing tht the solute growth rte (GR), reltive growth rte (RGR) nd minimum temperture re importnt ftors prediting lef nd stem freezing tolerne within nd mong four live ok (Querus series Virentes) speies Lef freezing tolerne Stem freezing tolerne Soure df SS F rtio P vlue df SS F rtio P vlue Speies < <. Popultion (speies) Growth temperture tretment < <. Speies tretment < Popultion (speies) tretment GR (g yr ) ) Speies < <. Popultion (speies) Growth temperture tretment < <. Speies tretment < <. Popultion (speies) tretment RGR (g g ) yr ) ) Speies <. Popultion (speies) Growth temperture tretment < <. Speies tretment < <. Popultion (speies) tretment Minimum temperture Signifint vlues (P <.5) re shown in old nd mrginlly signifint vlues (P <.) re shown in itli. SS, sum of squres. inluded in the model (Tle 2). Within Q. virginin, the speies with the gretest minimum temperture rnge, signifint vrition mong popultions ws deteted in stem nd lef freezing tolerne, s well s in GR nd RGR (Fig. 3 j), suggesting the lol dpttion of popultions to ltitudinl vrition in limte. Within Q. oleoides, the Mexin popultion lso showed greter freezing tolerne nd ility to old limte thn popultions from elize or Cost Ri (Fig. 3f). The Mexin soure popultions enounter mild freezing tempertures in the winter months, wheres the rest of the rnge of Q. oleoides does not. Fewer olletion sites for Q. gemint nd Q. fusiformis limited our ility to detet popultion-level vrition in these speies. The minimum temperture of the soure popultion lso strongly predited old limtion ility ross mternl fmilies in linl pttern (Fig. 5e,f). Under tropil growth onditions with no old limtion, there ws lower tolerne of stem nd lef freezing ross ll speies nd popultions, lthough it ws lowest in the tropil speies Q. oleoides (Fig. 3 f). The most northern fmilies (from North Crolin) showed the highest old tolerne nd old limtion ility. n inrese in old limtion ility t more northern ltitudes (Fig. 5e,f) provides evidene for dptive plstiity in response to the onset of winter tempertures. However, the vrition in freezing tolerne nd old limtion within speies ws low reltive to the vrition mong speies, suggesting tht the distriutions of speies my e more strongly driven y rod limti tolernes thn y lol dpttion. Seed mss lso inresed with minimum temperture of the oldest month (Fig. 5e). Minimum temperture is strongly ssoited with seson length nd the totl energy ville for photosynthesis during the growing seson. oth reprodutive output nd seed mss hve een predited to inrese with seson length (Chuine, 2), nd empiril evidene in forest trees indites tht seed mss dereses with ltitude (Morin et l., 27). Seed mss ws positively ssoited with GRs (Fig. 5f) nd proly ontriutes to ompetitive ility. Previous studies hve shown similr pttern of old nd freezing tolerne vrying with ltitude. Liner regressions for freezing nd minimum temperture for popultions of three ok speies, Q. ilex, Q. rour nd Q. puesens, were signifint t oth the inter- nd intrspeifi levels (Morin et l., 27). In etul pendul, the northern-most eotype ws more responsive thn the southern eotype to old limtion nd freezing tolerne (Li et l., 22). In Cornus stolonifer, more northern popultions showed greter limtion ility nd old resistne (Smitherg & Weiser, 968). Tmrix nd Populus popultions showed ltitudinl vrition for old hrdiness nd survivl (Friedmn et l., 28). Hereous speies, suh s ridopsis, lso exhiit linl vrition in freezing tolerne (Zhen & Ungerer, 28). Previous studies hve lso shown tht minimum temperture predits growth rte (Li et l., 998, 22; Rehfeldt et l., 2; Green, 27; Gimeno et l., 29; Svge, 2). In Mediterrnen evergreen ok speies, Q. ilex, grown under ommon onditions, individuls from more northern ltitudes hd lower growth rtes, nd linl vrition ourred etween popultions (Gimeno et l., 29). Contrsting freezing tolerne strtegies We sw severl different freezing tolerne strtegies in the temperte speies, whih hve overlpping limte distriutions (Fig. 2). In rod-lef evergreen trees tht reple leves on n nnul sis (lef exhngers, sensu Givnish, 22), erly

11 New Phytologist Reserh senesene nd lef sission in response to hilling represent strtegy to void freezing dmge. lterntively, leves n e mintined for longer, ut hve higher freezing tolerne. We found evidene of evolution towrds erly lef sission in oth Q. virginn nd Q. fusiformis, with elerted lef loss fter old exposure in temperte onditions reltive to lef loss in tropil onditions. y ontrst, Q. gemint mintined its leves throughout the durtion of the winter period under temperte onditions (Fig. 3), ut hd higher lef freezing tolerne (Fig. 3). Querus gemint nd Q. virginin o-our from North Crolin to entrl Florid, where they experiene similr winter tempertures in their lol environments. Querus virginin pprently shows greter investment thn Q. gemint in proteting its stem tissue from freezing dmge, wheres the ltter mintins its leves under old onditions nd shows greter investment in proteting them from freezing dmge. The vrition in response to freezing my e explined y the eologil nihe differentition oserved in Q. virginin nd Q. gemint (Nixon, 985; Cvender-res & Phlih, 29). These symptri speies show nihe differentition ross soil types, with Q. virginn found in moister, nutrient-rih soils nd Q. gemint found in drier, nutrient-poor sites (Cvender-res et l., 24). Morphologil dt support the differentition etween the speies, s Q. virginin llotes greter proportion of its resoures to shoots nd hs lrger nd thinner leves, wheres Q. gemint invests less in shoots nd hs smller nd denser leves (Cvender-res & Phlih, 29). lthough denser leves my hve dpted in response to dry hitt onditions, dense leves re lso n importnt ttriute in old-tolernt plnts (Loehle, 998). Explining trde-offs etween growth nd freezing tolerne In order for trde-off to e iologilly importnt, fitness dvntge in one environment would result in lower fitness in ontrsting environment, nd vie vers. Greter stem nd lef freezing tolerne fter old limtion presumly provides fitness dvntge in sesonl limtes tht inur winter freezing. Greter umulted iomss under yer-round wrm onditions presumly provides fitness dvntge in the tropis. There is no seletive dvntge to investing in high freezing tolerne in the sene of freezing stress, nd tively growing tissues re inherently vulnerle to freezing (Howe et l., 23; Li et l., 23). s freezing tempertures eome more severe nd the durtion of winter inreses t higher ltitudes, nturl seletion would e expeted to use n inrese in freezing tolerne in plnts nd the ility to old limte. Explining the redued growth in older limtes is somewht more omplited, nd there re likely to e multiple ontriuting ftors. In prtiulr, two explntions re supported y the urrent study. The first is tht resoure llotion to freezing tolerne limits llotion to growth. numer of iohemil hnges our during old limtion tht onfer freezing tolerne, inluding n inrese in sturted lipids, the umultion of wter-solule solutes nd onformtionl hnges in ell memrnes (Levitt, 98; ek, 988). In ddition, struturl investments, suh s the development of thiker leves, re importnt for old limtion (Chot & Hiks, 982; Körner & Lrher, 988). Resoure investment in physiologil nd struturl trits for old nd freezing tolerne is thus hypothesized to use more onservtive growth. The lower growth rtes (RGR nd GR) in soure lotions with older winters, even under nonstressed, tropil onditions (Fig. 5,d), nd in mternl fmilies with higher freezing tolerne nd old limtion ility, support this explntion. seond potentil ontriuting ftor to slower growth is tht shorter seson length t northern ltitudes limits reprodutive output nd seed size s there is less time for ron umultion (Morin & Chuine, 26; Chuine, 2). Redued seed size my then drive lower GRs. Consistent with this explntion, seed mss is redued in limtes with older winters (Fig. 5e), where the growing seson is presumly shorter, nd seed size is orrelted with GR (Fig. 5f). The ltter reltionship is signifint, lthough the vrition explined is low: R 2 =.92, P =.9. Therefore, seed mss my e ontriuting diretly to the trdeoff etween GR nd freezing tolerne. However, redued seed mss nnot explin the negtive reltionship etween stem freezing tolerne nd RGR (R 2 =.29,, Fig. 4j), euse seed mss is not orrelted with RGR (Fig. S4). The strongest reltionships etween freezing tolerne nd growth re found when GR is the mesure of growth (Fig. 4; Tle 2). However, RGR nd GR re strongly positively orrelted (R 2 = 9, P =., Fig. S4). oth RGR nd seed mss, whih re oth positively orrelted with GR nd minimum tempertures, ut negtively orrelted with stem freezing tolerne, thus ontriute to the trde-off etween freezing tolerne nd GR. It is interesting to note tht lef freezing tolerne is negtively ssoited with seed mss nd GR, ut not with RGR (Fig. 4 e). RGR my e less likely thn GR to trde off with freezing tolerne, euse rpid growth rtes my e required in short growing sesons. lterntively, slower growth in old limtes my e dptive, if more onservtive growth strtegy limits the risk of tissue dmge (Guy, 99). Given the limits to ron umultion with shorter seson length, seson length my drive seletion for oth lower seed mss nd lower GR; however, the smller seed, slower growth strtegy my lso e onsequene of resoure llotion to old tolerne (Lmers et l., 28). Life history strtegies nd limits to rnge expnsion Low tempertures re mjor limittion to northern rnge expnsion in mny speies tht lk freezing tolerne (Ski & Weiser, 973; Riklefs et l., 999). The lk of old limtion ility nd freezing tolerne exhiited y Q. oleoides indites physiologil rrier tht proly prevents expnsion eyond its northern rnge limit. The extremely limited migrtion of Q. oleoides northwrds over the lst 2 million yr is supported y moleulr evidene (Cvender-res et l., 2). If growth rte is n inditor of reltive fitness nd ompetitive ility (Lmers et l., 28; Moles et l., 29), the growth rte freezing tolerne trde-off lso implies tht southern expnsion of the

12 2 Reserh New Phytologist temperte speies, Q. virginin, Q. gemint nd Q. fusiformis, my e limited y their inferior ompetitive ility reltive to the tropil speies, Q. oleoides, or reltive to other speies t or elow their southern rnge limits. Speies generlly hve mximum growth rtes t their southern rnge limit, ut do not inrese their growth rtes when grown further south or under optiml onditions (Lnglet, 97; Ski & Lrher, 987; Roerds et l., 99; Loehle, 998). This is true for the temperte speies Q. fusiformis nd Q. gemint, ut ws more vrile for Q. virginin. Under yer-round tropil onditions, popultions of the temperte speies Q. gemint nd Q. fusiformis mintined lower growth rtes nd were unle to inrese growth rtes to level omprle with tht of tropil Q. oleoides (Fig. 3g,i). However, some mternl fmilies nd one popultion of Q. virginn (Louisin) hd GRs similr to tht of Q. oleoides under tropil onditions (Fig. 3h,j). This suggests tht, lthough Q. gemint nd Q. fusiformis my hve limited ility to inrese their growth rtes under tropil onditions, some Q. virginin popultions my hieve ompetitive growth rtes. There ws muh greter overlp in RGR thn in GR vlues, suh tht regressions with RGR s the preditor of freezing tolerne were less signifint (Fig. 4 d). The totl iomss hieved y plnt within given period of time (GR) my ultimtely e the est preditor of fitness nd or ompetitive ility. Seed mss is lso ssoited with ompetitive ility nd ontriutes diretly to GR. However, other ftors not investigted, inluding suseptiility to ioti pthogens nd pests (Reder, 992; lexnder & Holt, 998; Meiners & Hndel, 2; Fine et l., 24), re thought to ply n importnt role in mediting ompetition nd limiting speies rnges. Sesonl drought tht ours throughout the rnge of Q. oleoides in Centrl meri my lso intert with temperture to medite speies rnges. symmetril gene flow etween Q. oleoides nd Q. virginin, with higher rtes southwrds thn northwrds (Cvender-res et l., 2), suggests tht lk of freezing tolerne my present more formidle rrier to northwrd expnsion thn does the lk of ompetitive ility to southwrd expnsion. Lol dpttion or rod limti tolernes? ross the ltitudinl grdient of the live ok group, we found limited vrition mong popultions, suggesting onserved speies-level limti tolernes. In Q. virginin, the northern-most popultion of North Crolin exhiited greter lef nd stem freezing tolerne thn the Florid popultions, nd men vlues of the popultions suggested linl vrition long the ltitudinl grdient (Fig. 3d,f). previous ut more limited study with Q. virginin found similr differentition etween the North Crolin nd Florid popultions for lef freezing tolerne, inditing tht the popultion-level differenes re repetle, even ross different experimentl onditions nd olletion lotions (Cvender-res, 27). Minimum temperture is good preditor for freezing tolerne ross mternl fmilies (Fig. 4e,f), reltionship driven y oth the vrition mong speies nd within Q. virginin nd, to lesser extent, within Q. oleoides. Within the rodly distriuted speies, Q. virginin nd Q. oleoides, vrition mong mternl fmilies followed ltitudinl trjetory, showing deresed freezing tolerne with inresed growth rte (Fig. 3d,f,h,j). These results suggest some degree of lol dpttion to freezing, prtiulrly within Q. virginin. Lol dpttion within Q. virginin must hve ourred sine the Pleistoene, when Q. virginin nd Q. oleoides re thought to hve diverged from ommon nestor (Cvender-res et l., 2). study with Querus suer found popultion-level differentition under winter onditions sed on the nnul temperture of the popultion soure (rnd et l., 25). Other studies support the lol dpttion hypothesis nd show popultion-level vrition in old sensitivity orresponding to hitt of origin (Rehfeldt et l., 22). Clinl vrition in freezing tolerne hs een demonstrted in severl tree speies, inditing lol dpttion (Duousso et l., 996; Rehfeldt et l., 2; rnd et l., 25; Cvender-res, 27; Morin et l., 27). Nevertheless, the trde-off ourred lrgely ross speies (Fig. 4 d; Tle ), suh tht temperte speies exhiited slower growth rtes nd higher levels of freezing tolerne, wheres the tropil speies mintined higher growth rtes nd exhiited greter lef nd stem dmge in response to freezing. The limited vrition mong popultions, ompred with the vrition mong speies, in freezing tolerne (Tle ) indites onservtism in the limti nihes of speies. This finding is onsistent with limited lol dpttion in popultions of Mediterrnen holm ok (Gimeno et l., 29). Conserved limti nihes nd rod limti tolernes my thus e more importnt thn the lol dpttion of popultions in determining speies rnges. ross the temperte nd tropil divide, we see distint rek, s evidened y the redued ility of Q. oleoides to old limte nd void freezing dmge. This orresponds with the nrrow rnge of minimum tempertures of Q. oleoides when ompred with the three more temperte speies exhiiting overlpping temperture rnges (Fig. 2). oth Q. virginin nd Q. fusiformis hve firly rod rnge of minimum temperture limti tolernes (Fig. 2). Temperte speies tht enounter high limti vriility throughout the yer my e dpted to tolerte wide rnge of limti onditions nd thus oupy rod ltitudinl nd limti distriutions with limited lol dpttion (Jnzen, 967; Lrher, 25; Morin & Chuine, 26). Conlusions The trde-off etween freezing tolerne nd growth rte supports the lssi rnge limit hypothesis, whih posits tht the distriutions of speies re limited y freezing tolerne in the north nd y ompetition in the south (Mrthur, 972; Woodwrd, 987; 988; Shenk, 996; Gross & Prie, 2). Speies nd popultions from older limtes hve greter ility to enhne their freezing tolerne fter exposure to old tempertures thn those from more tropil ltitudes, providing evidene for dptive plstiity. Freezing tolerne, old limtion ility nd diminution of growth rtes hve proly