Effect of water supply on leaf area development, stomatal activity, transpiration, and dry matter production and distribution in young olive trees

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1 CSIRO PUBLISHING AUTHORS PAGE PROOFS: NOT FOR CIRCULATION Austrlin Journl of Agriulturl Reserh, 2, 8, Effet of wter supply on lef re development, stomtl tivity, trnspirtion, nd dry mtter prodution nd distriution in young olive trees Mri Gómez-del-Cmpo Dpto. Produión Vegetl: Fitoteni, Universidd Politéni de Mdrid, Mdrid, Spin. Emil: Astrt. Two-yer-old olive trees v. Cornir, trined in entrl leder form for hedgerow plnting, were grown outdoors in -L weighing lysimeters to evlute the effet of wter supply on growth nd development. Four tretments were estlished nd mintined for dys during spring utumn. Tretment T ws irrigted to mintin the potting medium lose to wter-holding pity y progressive replenishment of onsumption tht ws mesured t weekly intervls y weighing nd reording dringe. Tretments T8, T6, nd T reeived 8, 6, nd %, respetively, of the wter pplied to T. For these tretments, trnspirtion nd lef re were mesured every fortnight. Dry mtter in roots, stems, nd leves ws mesured t the eginning nd end of the experiment. Lef ondutne ws mesured t 9: nd 2: solr time every fortnight nd t. 2-hourly intervls throughout one dy eh month. Over the experimentl period, T produed.2 ±. m 2 lef re, 39.6 ± 6. g dry iomss, nd trnspired. ±. L wter. Wter stress signifintly redued lef re development nd dry mtter prodution (P <.) in T6 nd T, ut not in T8. There ws no effet on dry mtter prtitioning to the vrious orgns of the trees or the roots/eril prt rtio. Lef ondutne ws more sensitive to wter stress thn vegettive growth, with signifint differenes (P <.) estlished mong tretments 3 weeks efore differenes were oserved in trnspirtion. In utumn, trnspirtion nd lef ondutne inresed in ll tretments independently of soil wter sttus. Over the experiment, trnspirtion effiieny (TE, g/l) inresed with redued wter supply, with signifint differene (P <.) etween T nd oth T6 nd T. The study hs estlished tht mximum growth of young olive plnts n e hieved, without effet on the distriution of iomss etween orgns, t wter supply less thn tht required to support mximum trnspirtion. Additionl keywords: Ole europe L., wter reltions, stomtl response, trnspirtion effiieny, drought dpttion. Introdution Hrvesting is the most expensive opertion in Spnish olive ultivtion due to the high ost nd requirement of lour. In the mid-99s the possiility of using mehnil hrvesters ws explored in res where olive trees nd grpevines were oth grown. As result, the first super-high-density olive orhrds were plnted with trees trined to hedgerows, generlly in monoone shpe pruned with entrl leder, nd sped from 3 m y.3 m (26 trees/h) to m y. m (66 trees/h). The mngement of these new plnttions poses hllenge for produers nd reserhers to dpt this typil Mediterrnen rop tht hs een long ultivted using dry-frming methods, wide tree sping ( m y m, trees/h), nd vseshped trining system. In order to rry out rtionl mngement of super-high-density olive orhrds, it is neessry to identify the physiologil responses of olive trees to this new system. The hnge in the trining system inurs n inrese in the lef surfe per unit of ultivted surfe exposed to the sun nd, therefore, n inrese in wter requirements tht in turn demnd greter wter-use effiieny in the olive-growing region where wter is sre nd olive trees ompete with other rops for wter. Olive is rop well dpted to drought onditions y mehnisms tht hve evolved to oth void nd tolerte drought (Connor nd Fereres 2). The olive tree protets internl metolism from wter stress y losing stomt (Fernández nd Moreno 999), whih inevitly dereses photosyntheti rte nd, therefore, growth (Morin et l. 22). Super-high-density olive orhrds ome into ering fter 3 yers while the trees re trined to form ontinuous hedgerow to expose mximum lef surfe to the sun. Optimum irrigtion mngement in this phse seeks to minimise wter pplition without reduing vegettive growth. There is need to e oth effiient in the use of wter nd lso to void risks of noxi nd fungl infetion ssoited with over-wtering. The ojetive of this experiment ws to estlish the growth response of young olive trees to wter vilility, the effet on dry-mtter distriution s determinnt of suitility for plnting, nd to eluidte the response mehnism to wter shortge in terms of lef-re formtion nd stomtl response. For this, olive trees were grown in -L weighing CSIRO 2./AR68-99//

2 2 Austrlin Journl of Agriulturl Reserh M. Gómez-del-Cmpo lysimeters under vrious irrigtion regimes. The ultivr used ws Cornir, the prinipl ultivr in entrl Spin, eing well dpted to het nd drought in summer nd to old in utumn nd winter. Mterils nd methods This experiment ws rried out in 2 in the open ir t the Universidd Politéni de Mdrid in Spin ( N, 3 8 W; lt. 9 m). Two-yer-old olive trees (v. Cornir) were grown from 2 April to 29 Septemer ( dys) in -L weighing lysimeters overed with plsti film to exlude rinfll nd eliminte diret evportion from the soil. The lysimeters were filled with mixture of pet, orgni soil, nd perlite ( : 32 : 2) over -mm lyer of smll stones to filitte dringe. The sustrte hd porosity of 86% (v/v), esily ville wter ws 36% (v/v), reserve wter % (v/v), nd wter not esily ville ws 3% (v/v) otined ording to the method desried y Griels nd Verdonk (992). The olive trees were stked to height of 2. m nd trined in monoones similr to those in super-high-density hedgerow plnttions using m y. m tree sping. A wether sttion t the study site registered wind speed nd diretion, rinfll, temperture, humidity, nd glol rdition every 3 min nd lulted ETo y the Penmn-Monteith method (Allen et l. 998) from these limti vriles. The experiment used ompletely rndomised design with single tree repetitions of irrigtion tretments tht ommened with ll tretments irrigted to drined wterholding pity. During the experiment, tretment T ws weighed weekly nd irrigted on lternte dys to mintin the potting medium lose to wter-holding pity while tretments T8, T6, nd T reeived 8, 6, nd %, respetively, of the wter pplied to T. Trnspirtion ws determined grvimetrilly t weekly intervls with llownes for dringe in T nd fortnightly for tretments T8, T6, nd T. Dry mtter distriution ws mesured in 2 olive trees, similr to those pled in the lysimeters nd seleted ording to medin trunk dimeter, t the eginning of the experiment. For this, the trees were seprted into roots, stems, nd leves, nd dried to onstnt weight in n oven t 8 C. At the end of the experiment, dry mtter ws mesured similrly in ll experimentl trees, lso seprting stems nd leves formed in the urrent seson from those formed previously. Lef re of eh tree ws determined fortnightly s the produt of totl lef numer per tree nd verge lef size, the ltter estimted monthly for eh tretment y mesuring entrl nerve length of ll leves on one rnh per tree. In this se, there ws no evidene of vrition in lef size distriution etween rnhes of individul trees. At the end of the yle, the reltionship etween entrl nerve length nd lef re ws determined. At the end of the experiment ll leves were removed, ounted, nd mesured with n re meter (Li-3; Li-Cor, Linoln, NE, USA), seprting the leves formed in the urrent from the previous seson. Lef ondutne (g l ) ws mesured fortnightly t 9: nd 2: UTC with stedy-stte porometer (Li-6; Li-Cor, Linoln, NE, USA) on helthy leves exposed to the sun. On 8 Septemer the mesurement t 9: ould not e tken due to loud. On 6 June,, August, nd 22 Septemer, mesurements were mde on osions throughout the dy (:, 9:, :3, 2:, :, 6:3, nd 8:3 UTC, pprox. solr time). On those dys, irrigtion ws delyed until the mesurements were ompleted. Dt were sujeted to nlysis of vrine using MSTAT-C (University of Mihign, USA). Lest signifint differenes (P <. nd P <.) were used to segregte differenes mong tretment mens using Dunn s multiple rnge test. The iomss prtitioning dt were trnsformed efore nlysis of vrine using the r-sin squre-root trnsformtion method to ensure tht the dt were normlly distriuted. Results Environmentl onditions The mesurements from the wether sttion re summrised s dily mens in Fig. nd the onditions on the dys of mesurement of lef ondutne re presented in Tle. During the experimentl period, the highest temperture ws reorded on 2 (38 C) nd the lowest on 8 My (2 C). ws the hottest month with men temperture of 2 C while My ws the oldest ( C). Men solr rdition ws 23.8 MJ/m 2 with June hving the highest (. MJ/m 2 ) nd Septemer the lowest (8. MJ/m 2 ). Evportive onditions remined strong throughout the experiment, with umultive ETo of 83 mm. June nd presented the highest vlues (6. mm/dy) nd Septemer the lowest (. mm/dy). The gretest ETo of. mm/dy ourred on June. Tle shows the wether onditions on the dys when diurnl mesurements of lef ondutne were mde. Pek vlues of mximum temperture nd solr rdition ourred t the end of June, within the first month of the experiment. High tempertures were mintined until the end of ut solr rdition delined grdully through the remining period of the experiment. The highest vlues of reltive humidity (t 2: h) oinided with period of rinfll in Septemer. Lef re The sesonl pttern of lef-re development (Fig. 2) is oth determinnt nd onsequene of the sesonl pttern of wter vilility, onsumption (trnspirtion), nd wter stress. At the eginning of the experiment, men tree lef re ws.9 ±. m 2, inresing y the end of the period to.2 ±. m 2 in T. Tretments T8, T6, nd T developed 93, 6, nd 6%, respetively, of the lef re of T. Signifint differenes from the ontrol (T) in lef re were estlished from 2 in T nd from 3 August in T6. At the end of the experiment, tken in pirs, T6 nd T hd 66% of the lef re of T8 nd T. Tle 2 reports the numer, size, nd speifi lef mss (SLM, g/m 2 ) of leves t the end of the experiment. One-yer-old leves were those present t the outset, while urrent-yer leves were produed during the experimentl period. More leves were produed in T nd T8 thn in T. At the end of the experiment, T hd % fewer leves thn T. The trees lost, 3, 2, nd 38% of their -yer-old leves in T, T8, T6, nd T, respetively (dt not presented). In ontrst to the response in lef numer, there ws no signifint

3 Effet of wter supply in young olive trees Austrlin Journl of Agriulturl Reserh Temperture ( C), reltive humidity (%), ETo (mm ) Solr rdition (MJ/m 2 ) ETo x RH Tmx Tmin SRd 2 My 26 My 9 June 23 June Fig.. Dily limti onditions throughout the experimentl period. Mximum nd minimum temperture ( C), men reltive humidity (%), nd umulted solr rdition (MJ/m 2 ) nd ETo (mm/dy). Tle. Dily ETo, mximum nd minimum temperture, solr rdition, nd temperture nd reltive humidity t 2: h solr time on the dys of lef ondutne mesurements 2 June 6 June 3 June 2 8 Sept. 22 Sept. ETo (mm/dy) Tmx ( C) Tmin ( C) Rsol (MJ/m 2 ) Temp. 2: h ( C) RH 2: h (%) Lef re (m 2 ) T T8 T6 T 2 My My June June Ot. Tle 2. Men numer, re (mm 2 ), nd speifi lef mss (SLM, g/m 2 ) of leves formed in urrent-yer nd in -yer-old leves in vrious irrigtion tretments T ws irrigted to mintin the potting medium lose to wter-holding pity; T8, T6, nd T reeived 8, 6, nd % of wter pplied to T. Tretments with the sme letter re not signifintly different y Dunn s test t P <. Tretment Lef numer Lef size SLM Current -yer Current -yer Current -yer T T T T Fig. 2. Development of olive v. Cornir lef re under vrious irrigtion tretments. T ws irrigted to mintin the potting medium lose to wter-holding pity; T8, T6, nd T reeived 8, 6, nd % of wter pplied to T. Tretments with the sme letter re not signifintly different y Dunn s test t P <.. effet of tretment on lef size (men 2 mm 2 ), lthough leves in T were 9% smller thn those in T, nd lef rolling ws oserved in tht tretment. These dt revel tht the formtion of new leves (lef numer) ws more ffeted y tretment thn ws lef expnsion. Speifi lef mss (SLM) of leves inresed signifintly in response to restrited wter vilility, from 22 ± 2 g/m 2 in T to 23 ± g/m 2 in T6 nd T (Tle 2). Leves >-yer old (22 g/m 2 ) hd greter SLM thn leves formed during the experiment (22 23 g/m 2 ). Trnspirtion The sesonl ptterns of trnspirtion per tree nd per lef re, lulted for weekly nd fortnightly periods, re presented, long with ETo, in Fig. 3. Sine tretments were fully wtered

4 Austrlin Journl of Agriulturl Reserh M. Gómez-del-Cmpo Trnspirtion (L/dy) Trnspirtion (L/m 2.dy) T T8 T6 T ETo 2 My 26 My 9 23 June June 2 d 8 () () Fig. 3. Dily trnspirtion of olive trees v. Cornir in vrious irrigted tretments: () trnspirtion per tree; () trnspirtion per unit lef re. T ws irrigted to mintin the potting medium lose to wter-holding pity; T8, T6, nd T reeived 8, 6, nd % of wter pplied to T. Tretments with the sme letter re not signifintly different y Dunn s test t P <.. t the eginning of the experiment, no signifint differenes in trnspirtion were oserved in the stress tretments until the esily ville wter (6.2 L) hd een onsumed. Thus, tretment effets on tree trnspirtion (Fig. 3) ppered suessively: first in T on, followed y T6 on 2, nd finlly y T8 on 8 August. Trnspirtion then deresed until 29 Septemer when shrp inrese ws oserved in ll tretments. Mximum trnspirtion per tree (..8 L/dy) ws oserved in nd August responding to inresing lef re (Fig. 2) rther thn oiniding with mximum vlues of ETo (6. 6. mm/dy). In ontrst, when evluted ginst lef re (Fig. 3), mximum trnspirtion ws rehed etween mid-june nd mid-, erlier thn for tree trnspirtion (Fig. 3), nd oiniding with mximum ETo. There were no differenes mong tretments to tht time. T hieved the gretest trnspirtion, nerly 3. ±. L/m 2.dy, t the eginning of nd mintined higher rte thn the other tretments lmost to the end of the experiment when trnspirtion inresed suddenly in ll tretments. Signifint differenes in trnspirtion were reorded mong tretments on 3 August, 8 August, nd Septemer, when trnspirtion ws signifintly greter in T thn in T6 nd T. Cumultive tree trnspirtion over the experimentl period ws signifintly different mong tretments (Tle 3) ETo (mm/dy) Tle 3. Effet of wter supply on trnspirtion per tree (L) over the experimentl period, the men trnspirtion per unit lef re (L/m 2.dy) lulted from progressive mesurements of trnspirtion nd tree lef re, nd trnspirtion effiieny (g iomss/l) in prodution of iomss T ws irrigted to mintin the potting medium lose to wter-holding pity; T8, T6, nd T reeived 8, 6, nd % of wter pplied to T. Tretments with the sme letter re not signifintly different y Dunn s test t P <. Tretment Tree Men trnsp./ Trnspirtion trnspirtion lef re effiieny T T T T.d.6.66 Tretment T onsumed. ±. L, while T8, T6, nd T onsumed 8%, 69%, nd 3% of T, respetively. On the sis of lef re, signifint differene ws estlished only etween extreme tretments, T nd T, this refleting the vrition in lef re within tretments. Men dily trnspirtion for T ws 2. ±.3 L/m 2.dy, flling to. ±.2 L/m 2.dy in T. Biomss nd prtitioning At ommenement of the experiment in April the trees hd ± 6 g dry iomss tht y Septemer hd inresed to ± 6. g in T (Tle ). In April, 2 ± g,9± g, nd 2 ± 3 g ws in roots, leves, nd stems, repetively. By the end of the experiment, tree iomss ws signifintly redued from the ontrol (T) in T6 nd T ut not in T8. Biomss in T6 nd T ws nd 63%, respetively, of T. Signifint differenes in the distriution of iomss in omponent orgns of roots, stems, nd leves were oserved mong tretments (Tle ). The gretest proportion of iomss oth t the eginning (3% in April) nd t the end of the seson (% in Septemer) ws in stems. In Septemer, 66% of eril dry mtter ws found in stems of whih % ws in stems formed efore the strt of the experiment. Dry mtter ontent in these stems inresed from 2. g in April to. g in Septemer, while dry mtter ontent of new stems ws.3 g in Septemer. Dry mtter ontent in stems ws signifintly different mong irrigtion tretments. Lef mss ws signifintly greter in T nd T8 thn in T6 nd T, while root mss ws signifintly greter in T nd T8 thn in T. In ll tretments, leves were the orgns tht showed the gretest inrese in iomss. Over ll tretments, iomss in leves, stems, nd roots inresed 9,, nd 3 times, respetively. Root/eril dry mtter rtio (Tle ) nd iomss prtitioning mong orgns (dt not presented) were not signifintly ffeted y irrigtion tretments. Lef ondutne Two sets of mesurements re ville to evlute the sesonl nd diurnl responses of stomt, respetively. The first set, presented in Fig., reords the lef ondutne (g l ) t 9: nd 2: h t fortnightly intervls during the experiment. These dt revel ommon trend of deline during the summer months

5 Effet of wter supply in young olive trees Austrlin Journl of Agriulturl Reserh Tle. Dry mtter ontents (g) in trees t the end of the experiment nd its distriution in roots, stems, nd leves, together with the reltionship etween root/eril dry mtter ontent (g/g) in vrious irrigtion tretments T ws irrigted to mintin the potting medium lose to wter-holding pity; T8, T6, nd T reeived 8, 6, nd % of wter pplied to T. Tretments with the sme letter re not signifintly different y Dunn s test t P <. Roots Stems Leves Totl iomss Root/eril dry mtter T T T T 3..d Stomtl ondutne (mmol/m 2.s) My My June T T8 T6 T 9: hours 2: hours Ot. Fig.. Lef ondutne t 9: nd 2: h in olive trees v. Cornir in vrious irrigtion tretments. T ws irrigted to mintin the potting medium lose to wter-holding pity; T8, T6, nd T reeived 8, 6, nd % of wter pplied to T. Tretments with the sme letter re not signifintly different y Dunn s test t P <.. tht is more mrked t 2: thn t 9: h. They lso show tht tretment differenes were estlished 3 weeks erlier thn were differenes in lef re (Fig. 2). Signifint differenes were oserved mong tretments fter t 9: nd fter 9 June t 2: h. After these dtes, g l ws signifintly greter in T thn in T. Signifint differenes in g l were only found etween T6 nd T on t 2: h nd etween T8 nd T6 on t 9: h. Mximum vlues of g l were round 39 mmol/m 2.s, flling to mmol/m 2.s in T towrds the end of the summer. Men g l t 9: h throughout the seson ws 29 ± 2, 26 ± 8, ±, nd 98 ± 3 mmol/m 2.s in T, T8, T6, nd T, respetively, while t 2: h the orresponding vlues were 2 ± 3, 29 ±, 88 ± 9, nd 6 ± 23 mmol/m 2.s. Comining oth times of mesurement, men g l ws 8, 3, nd 66% of T in T8, T6, nd T, respetively. A signifint feture of these dt is the reupertion of g l in ll tretments t the end of the seson. Lef ondutne rose then to mmol/m 2.s in T, its highest vlue reorded in this experiment. Temperture nd evportive demnd (ETo) were less thn during the previous mesurements so the dt suggest some internl plnt response ontrolling this spet of ehviour. The diurnl mesurements of g l presented in Fig. onfirm spets of the fortnightly dt. The diurnl trends show the sme pttern of erly development of stress in T, followed y grdully inresing stress in the other tretments s the seson progressed. Differenes in g l eme greter etween tretments s the seson progressed. On 6 June, g l in T ws signifintly greter thn in T t 2:, 6:3, nd 8:3 h. On, signifint differenes were oserved mong tretments throughout the dy exept t 9: h. Signifintly greter g l ws oserved in T thn in T. After :3 h, g l in T8 ws not signifintly different from tht in T6, while fter 2: h, g l in T ws signifintly smller thn in the rest of the tretments, exept t the end of the dy. On August, g l in T ws signifintly greter thn in T from 9: h nd signifintly greter thn in T6 from 2: h onwrds. After 2: h, no signifint differenes were found mong T8, T6, nd T. On 22 Septemer, the gretest g l ws registered nd the gretest differenes were found mong tretments. Lef ondutne ws signifintly greter in T thn in T6 nd T t ll times of mesurement. The dt lso showed nother spet of stomtl response of olive to wter stress nd environment in the form of ommon diurnl trend tht persisted throughout the seson in ll tretments. Even when wter ws redily ville nd trnspirtion demnd ws low due to smll lef re (e.g. 8 June), g l ttined mximum vlues in the morning with delining vlues in the fternoon. As the stress developed, the pttern ws mintined ut the time of pek g l ourred erlier in stressed tretments. Thus ll tretments ttined mximum g l t : : h t the strt of the seson, ut y August, mximum g l for T6 nd T ws reorded on the first osion of mesurement (: h). Trnspirtion effiieny (TE) The reltionship etween iomss prodution nd totl trnspirtion defines TE over the experimentl period (Tle 3). The vlue of this reltionship revels grdul inrese in TE with restrited wter supply, with signifint differenes estlished (P <.) etween T nd extreme tretments T6 nd T. Disussion The oservtions of growth nd trnspirtion revel tht mximum growth of olive v. Cornir n e hieved t wter supply less thn required to support mximum trnspirtion. The trnspirtion of trees grown without wter stress (T) during dys from spring to summer mounted to. ±. L, whih is low ompred with ETo nd the re (6 m 2 ) lloted to eh tree. Irrigtion t T8 tht sustined totl sesonl trnspirtion of 6. L/tree mintined the sme

6 6 Austrlin Journl of Agriulturl Reserh M. Gómez-del-Cmpo Stomtl ondutne (mmol/m 2.s) June August 22 Septemer T T8 T6 T : :8 9:36 :2 9:2 : Fig.. Lef ondutne throughout the dy on 9 June,, August, nd 22 Septemer in olive trees v. Cornir in vrious irrigtion tretments. T ws irrigted to mintin the potting medium lose to wter-holding pity; T8, T6, nd T reeived 8, 6, nd % of wter pplied to T. Tretments with the sme letter re not signifintly different y Dunn s test t P <.. lef re (Fig. 2) nd umulted the sme finl iomss (Tle ) s T. Finl lef re (.2 ±. m 2 ) (Fig. 2) nd finl dry mtter in T (369.6 ± 6. g) (Tle ) re omprle with those of similr ged trees of other ultivrs oserved in the field y Nuzzo et l. (99) nd Mrisl et l. (2). It is n importnt finding of this work tht wter supply limited to 8% of potentil trnspirtion n lso mintin mximum growth in young tively growing trees with dominne of new leves well exposed to the sun. Mngement n use this informtion to void over-wtering during this formtion phse euse tht introdues risks of poor growth under neroi onditions nd of estlishing diseses suh s Vertiillium in plnting stok. The dt lso define the ost in terms of growth t suoptiml wter supply. Irrigtion t T6 redued trnspirtion to 69% ut growth to %. At T, the orresponding vlues were 3% nd 63%, respetively. Olive hs rnge of voidne nd tolerne mehnisms to ssist produtivity nd survivl in low-wter environments (Connor nd Fereres 2). Although the lssi prtitioning response of greter root/shoot rtio tht improves wter lne (Kozlowski nd Pllrdy 99) ws not oserved in this experiment, importnt responses in rte of lef formtion, lef morphology, nd lef ondutne led to shifts in the reltionship etween trnspirtion nd growth. Lef size nd SLM reorded in this study with men vlues of 2 ± 3 mm 2 nd 23 ± 2 g/m 2 re onsistent with mny other oservtions in the olive literture, ering in mind tht oth prmeters exhiit vrition mong ultivrs nd responses to growing onditions (Boslidis nd Kofidis 22; Hgidimitriou nd Pontikis 2). Under extreme stress, lef size is known to deline, SLM to inrese (Adel-Rzik 989; Fernández nd Moreno 999), nd finlly leves to url nd fll. In this experiment, with its ontrolled development of stress, lef size did not vry mong tretments, SLM ws greter in T6 nd T thn in the ontrol (Tle 2), nd while lef fll of -yerold leves did inrese with wter shortge, the effet ws smll so the development of lef re ws dominted y the prodution nd expnsion of new leves during the experiment. The regulr mesurements of stomtl ondutne (g l ) tht were mde throughout the experiment revel importnt spets of the drought resistne of olive (Figs nd ). First, the usul levels of g l (rnge mmol/m 2.s) in well wtered olive re low y omprison with other hortiulturl tree speies (Connor nd Fereres 2) ut lso with the high vlues t 9: UTC (3 mmol/m 2.s) tht were oserved in utumn (see elow). Seond, stomtl losure ws the first response to wter shortge oserved in this experiment. Redution in g l ws oserved 3 weeks efore effets on lef re development were reorded. Lef ondutne t noon fell grdully from 2 to 2 mmol/m 2.s in T6 nd T, s the stress deepened. Third, the dily ehviour of stomt, more open in the morning thn in the fternoon, is onsistent with the optimistion theory of stomtl ontrol tht mximises TE (Cown 982) during the diurnl yle. Olive, with low internl ondutne to CO 2 due to lef ntomy, is good ndidte for greter TE with stomtl losure. The effet is seen in these dt s TE inresed grdully with wter restrition nd ws signifintly different (P <.) etween extreme tretments (Tle 3). The onsequene is the potentil for wter sving without growth penlty in ommeril prtie. The fortnightly oservtions lso deteted n unexpeted mrked inrese in g l in utumn (August Septemer) (Fig. ). Tht response, inferred from greter trnspirtion rte t the lef level, ws lso evident in the plnt trnspirtion dt shown in Fig. 3. Hgidimitriou nd Pontikis (2) hve reently reported similr response in g l in ll Greek ultivrs of

7 Effet of wter supply in young olive trees Austrlin Journl of Agriulturl Reserh olive they studied, lso grown outdoors in pots. In tht se, ll plnts were well wtered, wheres in the present experiment, the response ws lso evident, without re-wtering, in the lowwter-supply tretments. There is no ovious explntion for this response, whih tkes g l in olive, in oth studies, to the highest vlues (. mmol/m 2.s in the Greek study) reported in the literture. The response nnot e redily ssoited with hnges in temperture or humidity ut rther seems to e due to modifition in tree physiology, perhps to inresed wter uptke due to root tivity or greter xylem ondutivity within the plnt. This stomtl response is pprently distint from tht reported y Morin et l. (23) in field orhrd in utumn. There, mrked inrese in g l ould e explined s response to sudden resumption of soil wter supply when sustntil rinfll terminted n extended dry summer utumn period. The response oserved here nd in the Hgidimitriou nd Pontikis (2) study wrrnts further investigtion. Aknowledgments I express my grtitude to Prof. Dvid J. Connor for suggestions on the mnusript nd to José Rmón Lissrrgue for lending some reserh equipment. I grtefully thnk Betriz Surez, Pilr Tejel, nd Frnois Cmsusou for field dt olletion. This projet ws supported y Universidd Politéni de Mdrid (Projet A9). Referenes Adel-Rzik M (989) A model of the produtivity of olive trees under optionl wter nd nutrient supply in desert onditions. Eologil Modelling, 9 2. doi:.6/3-38(89)98- Allen RG, Pereir LS, Res D, Smith M (998) Crop evpotrnspirtion. Guidelines for omputing rop wter requirements. FAO Irrigtion nd Dringe Pper 6. (FAO: Rome) Boslidis AM, Kofidis G (22) Comprtive effets of drought stress on lef ntomy of two olive ultivrs. Plnt Siene 63, doi:.6/s68-92(2)3-8 Connor D, Fereres E (2) The physiology of dpttion nd yield expression in olive. Hortiulturl Reviews 3. Cown IR (982) Wter-use nd optimiztion of ron ssimiltion. In Enylopedi of plnt physiology. New series, Vol. 2B. (Eds OL Lnge, PS Noel, CB Osmond, H Ziegler) pp (Springer-Verlg: New York) Fernández JE, Moreno F (999) Wter use y the olive tree. Journl of Crop Prodution 2, 62. doi:.3/jv2n2 Griels R, Verdonk O (992) Referene method for the determintion of physil properties of plnt sustrtes. At Hortiulture 32, Hgidimitriou M, Pontikis CA (2) Sesonl hnges in CO 2 ssimiltion in leves of five mjor Greek olive ultivrs. Sienti Hortiulture, 2. doi:.6/j.sient.2.. Kozlowski TT, Pllrdy SG (99) Physiology of woody plnts. (Ademi Press: New York) Mrisl MJ, Orgz F, Villloos FJ (2) Rdition-use effiieny nd dry mtter prtitioning of young olive (Ole europe) orhrd. Tree Physiology 2, 6 2. Morin A, Orgz F, Pstor M, Fereres E (23) Yield responses of mture olive orhrd to wter defiits. Journl of the Amerin Soiety for Hortiulturl Siene, 2 3. Morin A, Villloos FJ, Fereres E (22) Stomtl nd photosyntheti responses of olive (Ole europe L.) leves to wter defiits. Plnt, Cell & Environment 2, 39. doi:.6/j x Nuzzo V, Xiloynnis C, Dihio B, Montnro G, Celno G (99) Growth nd yield in irrigted nd non-irrigted olive trees ultivr Cortin over four yers fter plnting. In 2nd Interntionl Symposium on Irrigtion of Hortiulturl Crops. Vols nd 2. pp. 82. (Interntionl Soiety Hortiulturl Siene: Louvin, Belgium) Mnusript reeived 3 My 26, epted 8 Mrh 2