Diurnal changes of COn net assimilation rate and related parameters in Pistacia vera L.

8/12/2019 Diurnal changes of COn net assimilation rate and related parameters in Pistacia vera L.

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Diurnal changes of COnnet assimilation rate and relatedparameters in Pistacia ver L.V. Novello

Istituto di Coltivazioni Arboree, University f Bari,Via Amendola 165/a, 170126 Bari, Italy

SUMMARY - In Pistacia vera L., the average diurnal patterns of net O2 ssimilation, stomatal conductance andtranspiration rates were assessed at the eaf surface during a clear summer day, with reference to the diurnalfluctuations of eaf temperature and photosynthetic photon flux. The rate of eaf gas exchange was highest at9:OO. The subsequent decline in net carbon assimilation did not appear to be related to changes in stomatalconductance (gs). The latter seemed to be primarily limited y vapour pressure deficit (VPD) of 3.8 Pa and leaftemperature (T,)of 36C. urther, stomatal conductance declined at3:00, at a time when VPD slightly increasedto 4.2 kPa and T, reached38C. he partialg recovery, two hours later, did not seem to be related to changesntheambientconditions.Themiddayranspiration atedidnotshowanysignificantdecline,henceeaftemperature did not change markedly. The photosynthetic efficiency declined at eaf temperatures higher than31C.Key words: Leaf gas exchange, leaf temperature, photosynthetic photon flux, pistachio, vapour pressure deficit.

RESUME - Changements diurnes du taux d'assimilation nette de CO, et paramtres associs chezistacia veraL. . Chez Pistacia veraL., les tendances moyennes diurnes pour l'assimilation nette de CO,, pour les taux deconductance stomatale et de transpiration, ont t valus la surface de la feuille pendant une claire journed't, avec rfrence aux luctuations diurnes de a emprature de a euille et du lux photosynthtique dephotons. Le taux d'change foliaire de gaz tait le plus lev 9.00. La baisse subsquente d'assimiliation nettedu carbone ne semblait pas tre lie aux changements de conductance stomatale gs). Cette dernire semblaittre limite premirement par le dficit de pression de vapeur de 3,8 kPa et la temprature de la feuilleT,) de36C. En outre, a conductance stomatale a baiss 13.00, un moment o le dficit de pression de vapeuraugmentait lgrement jusqu'4,2 kPa et T,atteignait 38C. La rcupration partielle de g,, deux heures plustard, ne semblait pas tre lie des changements des conditions du milieu. Le taux de transpiration vers la mi-journe ne montrait aucune diminution significative, car la temprature de la feuille ne changeait pas de faFonnotable. L'efficacit photosynthtique baissait avec une temprature de la feuille suprieure31C.Mots-cls change foliaire de gaz, temprature de la feuille, flux photosynthtique de photons, pistache, dficitde pression de la vapeur.

IntroductionThe net photosynthetic activity s subjected to seasonal changes and to diurnal changes whichre

mainly influenced by the stage of shoot development, the leaf ageing, the accumulation of hormonesand of carbohydrates in the leaves, as well as heby the luctuationsof light intensity,eaftemperature,air emperatureandhumidity Lakso,1985;Downton et al., 1987;FloreandSams,1986).

Within Pistacia genus, some investigations have beenarried out to evaluate seasonal changesfnet carbonassimilation and chlorophyllcontent and toassess ates of net carbonassimilation,stomatal conductance, ranspiration and related parameters in P. vera L. (Vemmos, 1994; Novelloand de Palma, 1995; de Palma and Novello, 1996); moreover, the diurnal pattern of changes in netCOp leaf uptakeand leaf conductance havebeen compared among several species (Lin t al. 1984).However, he diurnal pattern of photosynthetic changes related to fluctuations of vapour pressuredeficit, leaf transpirationand leaf temperature havenot been nvestigated.

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The aim of the presentwork was to study the diurnal changes of net carbon assimilation, stomatalconductance and transpiration ateson leaves of P. vera in relation to leaf emperature,vapourpressure deficit and photosynthetic photon lux at leaf surface.

Materials and methodsThe trial was carried out at a private orchard in the Apulia region (Bari province) on four seedlings,

six year old, originated rom CV. Bianca open pollination. Five leaves were randomly selected oneach seedling for diurnal leaf gas exchange measurements.The leaf chamber was oriented to obtainmaximum light interception, to get light saturated readings.

By means of aportable nfrared gas analyser (ADC,LCA-4, Analytical Development Company Ltd,Hoddesdon, UK , the following parameters were assessed per unit eaf area: net assimilation (Pn,pm01 m S ), stamatal conductance (gs, mol m- S- , ranspiration E, mmol mm2 - , photosyntheticphoton flux PPF, pmol m S ), quantum yield (Q, Pn:PPF ratio), leaf temperature (T,, %) and vapourpressure deficit VPD, kPa).

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Measurements were performedon one cloudless day in he last week of July 1995and 1996:datawere collected every two hours from 6:OO to 18:OO (standard time) with a final measurement taken at19:oo.Data were analysed for the mean standard errors using SAS software (SAS Institute, Cary-NC,USA).

ResultsAt the leaf surface, he photosynthetic photon lux was 290 pmol mm2- at 6:00 increased o 1 l 90

pmol m- S- at 8:OO and was 1,770 and 1,940 pmol mm2- at 1O:OO and 12:OO respectively (Fig. 1 .Values of light intensity in the afternoon were found to be similar to those in the morning hours. Leaftemperature was 25OC at 6:00 then it increased to 30Cat 8:OO and 36Cat 1O:OO. Small eaftemperature fluctuations were observed from midday onwards, ranging between 350C at 12:OO and37C at 18:OO. T, was 28C at 19:OO.The vapour pressure deficit was found to be about 2.10 kPa at6:OO and 19:OO;a maximum value of 4.2 kPa was obtained at14:OO.

1435iI

25I20 -

15

10I

PDP P FT

L 5-----0 -

I , ,6 :OO 8 :O O 1O:OO 12:OO 14:OO 16:OO 18:OO 20:OO

Time

Fig. 1. Average diurnal patterns of photosyntheticphoton flux at eafsurface, eaf emperatureand pressure apour deficit.

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At a PPF of 290 pmol me2 -l at the leaf surface, the average leaf net CO2 uptake was1.07 pmolm-2S-' of CO2. The maximum net carbon uptake was 17.59 pmol m-2S-' at 1O:OO, then it slowlydecreased to 11.O0pmol m-' S-' at 18:OO (Fig. 2), at a time when the PPF was still above 1,000 molm-' S- , One hour later, both PPF and Pn dropped to the sameevel observed at 6:OO.

T Q 5- P n

6 6:OO:OO 1O:OO 12:OO 14:OO 16:OO 18:OO 20:OOTime

Fig. 2. Average diurnal pattern of stomatalonductance, et ssimilation ndranspirationrates.

The stomatal conductance was lowest at about dawn and dusk, with values of 0.025 and 0.050mol m-' S-', respectively. Its maximum value was 1.150 mol m S at aboutmidday.After a slightdecline at 14:00, g recovered hereafter andhada value of 1 .O00 mol m" S-' at 18100.Thetranspiration rate was 0.25 mmol mQsP1 t 6:OO and 19:OO;however over the central part of the day(10:OO-18:OO) t maintained a value of about 3.8 mmol m" S-'.

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Quantum yield B)ncreased with leaf temperature until 31C and then declined. D gave similarvaluesoreafemperature at about 26 and 38C (Fig. 3).

DiscussionThe ratesof eafgasexchange showed the highest intensity at 9:00 solar time; since the

subsequent decline in net carbon assimilation did not appear to be related to changes in stomatalconductance, it might have been nfluenced by a eedback effect of carbohydrate accumulation n theleaves rather than by a limiting effect of stomatal opening (Herold,1980;Azcon-Bieto, 1983;Bica andNovello, 1995).

The rate of stomatal conductance seemed to be limited by the leaf exposure to high VPD and T,for a long time: in this trial, g declined when VPD and T, slightly exceeded the threshold of 3.8 kPaand 38 , respectively. Under hese ambient conditions, resulting in high evaporative demand, apartial closure of stomata may help to avoid a critical leaf water potential (Jones, 1985; Lakso, 1985).The partial g recovery, occurring two hours later, does not seem o be related with changes inambient conditions thus it might be due to an increase in leaf water potential determined by osmoticadjustment (Jones, 1983; Dring, 1984; Novello et al., 1990). This could explain the relatively hightranspiration rate of pistachio leaves under midday conditions. Because of the isolateral structure ofpistachio leaflets and their random orientation (Lin et al., 1984),and because of he low densityof the

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tree canopy, pistachio leaves are naturally exposed to intense solar radiation, thus the maintaining ofa relatively high transpiration ratemighthavean mportant role in limiting the increment of leaftemperature hat could cause damages to the photosynthetic apparatus nd to the eaf tissues.

30hmm0

25

205i

15-10

vO

24 268 30 32 34 36 38 40TI ( C)

Fig. 3. Relationshipbetweenphotosynthetic efficiency a) nd leaf emperature.On the whole, the diurnal pattern of changes in CO2 net assimilation and related parameters

seemed to indicate that non-stomatal mechanisms of photosynthetic limitation can be relevant forf vera leaves,while fluctuations of stomatalconductance could be supposed more related tochanges in leaf water potential, and finally, the transpiration rate seemed to play a central role in leafthermoregulation.

Moreover, the diurnal average leaf net CO2 uptake pointed up a decline in quantum yield at leaftemperature higher han 31%: in the warmest hours of the day, when either external or internalfactors can limit the COp uptake, a more rapid increment of the respiration than of the assimilationrate could be supposed (Jones, 1983). The influence of the leaf temperature on the photosyntheticefficiency was found higher han in a previous trial (de Palma and Novello, 1996) where leaf gasexchange was taken over summer in the central hours of the day: in that trial, the vsTl relationshipwas consistent with a mean seasonal response while, n thepresent study, the same relationship wasconsistent with a short term fluctuation of the quantum yield in pistachio leaves.

AcknowledgementResearch support provided by the University of Bari R.S. 60 funds).

ReferencesAzcon-Bieto, J. (1983). Inhibition of photosynthesis by carbohydrates in wheat leaves. Plant Physiol.,

73: 681-686.Bica, D. and Novellg, V. 1995). Photosynthetic activity in grafted and ownrooted Erbaluce grapevinestrained to four trellis systems. Vjtjs,34(3): 141 144.

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de Palma, L. and Novello, V. 1996). Caratteristiche dell'attivit fotosinteticadi mandorlo e pistacchio.Frutticoltura,58(1): 55-56.

Downtown, W.J.S., Grant, W.J.R. and Loveys, B.R. (1987). Diurnal changes in the photosynthesis offield-grown grapevines. New Phytol., 105: 71-80.

Dring, H. (1 984). Evidence for osmotic adjustments to droughtn grapevine. Vitis,23: 1-1O.Flore, J.A. and Sams, C.E. (1986). Does photosynthesis imit yield of sour cherry (Prunus cerasus)

'Montmorency'? ln: Regulation of Photosynthesis in Fruit Trees, Lakso, A.N. and Lentz, F. (eds).Symp. Proc. Publ. NY State Agr. Exp. Sta., Geneva, New York, pp. 105-110.Herold, A. (1980).Regulation of photosynthesis by sinkactivity- hemissing ink. New Phytol.,

86: 131144.Jones, H.G. (1983).Plants and Microclimate.Cambridge University Press, Cambridge.Jones, H.G. (1985).Physiologicalmechanismnvolved in the control of the leafwaterstatus:

Implications for the estimationf the tree water status.Acta Hort., 171:291-296.Lakso, A.N. (1985). The effects of water potential on physiological process in fruit crops. Acta Hort.,

171 275-290.Lin, T.S., Crane, J.C., Ryugo, K., Polito, V.S. nd DeJong, T.M. (1 984). Comparative study of eafmorphology, photosynthesis, and eaf conductance in selected Pistacia species. J. Amer. Soc.

Horf Sci., 109(3): 325-330.Novello, V., Boschi, A. and Bo, G. (1990). Influenza di cinque portinnesti e di due modalit d'innesto

in campo su alcuni parametriisiologici in viti CV. 'Arneis'. Rv. Vit. no/., 43(2): 3-22.Novello, V. and de Palma, L. (1995). Observations on he pistachio photosynthetic activity n SouthernItaly. Acta Hod., 419: 97-1 02.Vemmos, S.N. (1 994). Net photosynthesis, stomatal conductance, chlorophyll content and specific

leaf weight ofpistachio rees (CV. 'Aegenes') s influenced by fruiting. J . Hort. Sci. 69: 775-782.

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Diurnal changes of COn net assimilation rate and related parameters in Pistacia vera L.

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