Leaf Conductance and Photosynthesis in Four Species of the Oak ...

Leaf Conductanceand Photosynthesis in Four Species of the Oak.Hickory ForestType T. M. HINCKLEY

R. G. ASLIN R. R. AUBUCHON C. L. METCALF

J. E. ROBERTS

ABSTRACT. Forest grown saplingsof sugar maple, northern red oak, white oak, and black

oak were transplantedto a greenhouse.Measurementsof leaf conductance,xylem pressure potential, osmotic potential, photosynthesis, leaf temperature,photosyntheticallyactive radiation, vapor pressuregradient, and soil water potential were recordedon days which representedvarious stagesin a dehydration-rehydrationcycle. Under light sufficient conditions, leaf conductancein sugarmaple, white oak, and northern red oak reactedto changes in turgor pressurewhile stomatain black oak respondedonly to changesin vapor pressure gradient. Photosynthesiswas significantlyrelated to leaf conductancein all species,and photosynthesisdecreasedwith decreasingphotosyntheticallyactive radiation and/or decreasing soil water potential. After reaching a speciesspecific optimum, photosynthesis decreasedwith increasingleaf temperature. Appreciable rates of photosynthesis(between 18 and 33 percent of maximum) were observed at leaf temperatures as high as 40øC. These physiological observationsare discussedin terms of known ecological patterns of behavior for these species. FORESTSCI. 24:73-84. ADDITIONALKEYWORDS. Water relations, Quercusalba, Quercus velutina, Quercus rubra, Acer

saccharum.

THOUGHTHEFOURSPECIES USEDin this studymay simultaneously occupythe overstoryof the oak-hickoryforestin Missouri,they characteristically representdifferent stagesin forestsuccession.Black oak (Quercus velutinaLain.), white oak (Q. alba L.), northernred oak (Q. rubra L.), and sugarmaple (Acer saccharurnMarsh) inhabit a continuumfrom pioneer to climax species.Similar placementof these specieshas been noted in southernIllinois (Chambers 1976) and in southernWisconsin(Curtis 1959). In addition,this rankingrepresentsa shadetoleranceranking with blackoakbeingthe leastshadetolerantand sugarmaplethe most. Leaf conductance-plant-environmental interactionsfor black oak, white oak, northernred oak, and sugarmaple (6 to 8 individualsof each species)growing undera forestcanopyhavebeenanalyzedby Chambers(1976) and by Phelpsand The authorsare, respectively,AssociateProfessorof Forestry, School of Forestry, Fisheries, and Wildlife, University of Missouri, Columbia, MO 65201; Area ExtensionForester, Gardner, Kansas; Forester, USDA Forest Service, Huntsville, Texas; Administrative Assistant, Land

Clearancefor RedevelopmentAuthority, Wellston, Missouri; and ResearchAnalyst, School of Forestry, Fisheries and Wildlife. Missouri Agricultural Experiment Station Journal Series No. 7997. Thanks to Drs. James P. Lassoie, Cornell University, and C. Anthony Federer, USDA Forest Service,Durham, New Hampshire,for critical reviews. Manuscript receivedFebruary 8, 1977.

VOLUME 24, NUMBER 1, 1978 / 73

others(1976). Theseanalyses indicatedthat the moremesicspecies, northernred oak and sugarmaple,respondedto changesin leaf water deficit. In contrast,leaf conductance in morexeric species, blackoak and white oak, reactedto changesin vapor densitygradients. However, these resultswere confoundedby (1) the influenceof an overstory,(2) differentiallevelsof soil moistureand soil depth on eachplot, and (3) species differencesin rootingpatternand, therefore,development of presunrisefoliar water deficits (Chambers 1976). In addition, a concomitant effortto compareratesof photosynthesis withinthreeof thesefour species(9 individualsof each species)was hamperedbecauseof the aforementionedreasonsas well asthe low frequencyof light intensities abovelight saturationfor thesespecies when in the understory(Aslin and others 1975). The purposeof this studywas to use a seriesof greenhouseexperimentsto eliminate someof the problemsthat confoundedfield results. Therefore,it waspossible to compareand contrastmore preciselystomatalreactivityand photosynthetic responsein saplingsof these four speciesto changingsoil moisture,photosyntheticallyactiveradiation,xylem pressurepotential,osmoticpotential,leaf temperature, and vapor pressuredeficit. METHODS

AND MATERIALS

Six saplings(white oak # 1 and # 2, sugarmaple # 1 and # 2, one northernred oak, and one black oak), each about 1.5 m tall and growingnaturally in close proximity to each other in an oak-hickoryforest locatedin the Ashland Wildlife Area (Garrett and Cox 1973) in southeasternBoone County, Missouri, were trenchedduring late July 1974. Substantialmid-Augustrains then increasedsoil moistureto near field capacity. Each was lifted (between90 and 120 kg of soil) in early January 1975 and placed in a 0.95 x 0.75 x 0.50 m container. Lifting was done by shearingthe soil in a horizontalplane parallel to the surfaceat a depth of 46 cm (within the clay pan of this Weldon silt loam). The saplingsand containerswere then transportedto a greenhouseat the Universityof Missouri. Greenhouseday/night temperatureswere maintainedat 21 ø and 18.5ø - 3.0øC, respectively.Soil moisturewasmaintainednear field capacity. Leavesappearedin early March and the studywas initiated on April 3, 1975. Six studydayswere selectedduringApril (April 3, 4, 10, 15, 16, and 22) and variousmeasurements were taken on all saplingsat 0500 (predawn), 0600, 0700, 0800, 1000, 1200, 1400, 1600, and 1830 hours (post-sunset) true solar time. During this studyperiod, daytimeair temperaturecontrol was eliminatedin order to approximate diurnaltemperature patternsnormallyexperienced in the field. A droughtwasinitiatedon April 2 by withholdingwaterfrom all saplings.White oak # 1, sugarmaple# 1, and the northernred oak saplingwereirrigatedat 1800 hours on April 15 while the threeother saplingswere not irrigateduntil 1800 hourson April 22. The followingsamplingschemewas used at each samplingtime. Photosyntheticallyactiveradiation(PAR) incidentto the uppersurfaceof eachmeasurementleaf was recordedusinga Lambda LI-190S Quantum Sensor (Biggs and others 1971). Leaf temperature(Tx) was determinedby the methoddescribedby Gale and others(1970). Abaxial leaf conductance(klear)to water vapor was estimated with a Lambda diffusiveresistancemeter and horizontal sensor (Kanemasu and others1969) usingtheproceduresdescribedby Morrow and Slatyer(1971). Since all speciesused in this study are hypostomatous (Phelps and others 1976) only abaxialleaf surfacesweremeasured.In addition,photosynthesis (Ps) wasmeasured

74 / FORESTSCIENCE

at two positionson eachleaf usinga •4CO2apparatusmodifiedby Aubuchon • from onereportedby NaylorandTeare (1975). Usinga onecm2 leaf punch,two samplesweretakenfromeachleaf,combined, placedin a microwave ovenfor 30 secto stopenzymaticactivity,processed in a Packard305 Tri-carbOxidizerand counted in a Beckman 100C-->LS-1000Liquid ScintillationSystem. No P8 measurements weretakenat 0600 and0700 hours. Xylem pressure potential(P) of leaf petioles from eachsaplingwasestimatedwith a pressurechamber(Scholanderand others 1965) usingtechniques described by RitchieandHincldey(1975) andMillar and Hansen (1975). After a P measurement, the leaf was frozen in liquid nitrogen, thawedandthe sapwasexpressed usinga hydraulicjack and a stainless steelcontainer,collected,and placedon a discof filter paper,and osmoticpotential(,r) was determined usinga WescorHR-33 Dew-PointHygrometerand a Model C-32 sample chamber.Concurrentmeasurements of P and ,r (on the sameleaf) were then usedto estimatethe averageturgorpressure(TP) of the leaf usingthe following equation (after Turner 1974, Richter 1976): P=•r+

TP.

Soilsampleswereextractedfrom eachcontainerusinga soil auger,subsampled in orderto excludethe top andbottom5 cm of the soil from the container,weighed, oven-driedat 105øC for 24 hoursand reweighed.Soil moisturewas convertedto energyunitsbasedon soilmoisturereleasecurvestaken from a nearbyfield calibration pit (Chambers 1976). RESULTS AND DISCUSSION

The decreasein soil water potentialbetweenApril 5 and 15 in all speciesand then betweenApril 15 and 22 in black oak, white oak # 1, and sugarmaple # 1 was accompanied by a substantialdecreasein base (predawn) xylempressurepotential (P), photosynthesis (PD, and leaf conductance(k•e•f) (Table 1). The maximum observedreductionin P8occurredin white oak # 1 (83 percent) (Fig. 1) while the leastwas noted in black oak (71 percent). Althoughthe reductionin P8 was relatedto stomatalclosureinducedby decreasingbulk leaf turgot pressure(differencebetweenP and osmoticpotential), it was probablethat leaf temperature(TO and vaporpressuregradient(vpg) both of whichincreasedover this period,were also influencingP• either directlyor indirectlythroughperistomataltranspiration (Fig. 1). Though an obviouscloserelationshipexistsbetweenP• and k•eaf(for white oak, Fig. 1; and for all speciescombined,P,: 1.54 + 11.68 [kleaf],• = 0.71), the environmentaland/or plant factor(s) controllingP• and klearcannotbe easilydeterminedfrom Table 1 or Figure 1. For this reason,the remainderof this paper will be dividedinto three sections: (1) factorscontrollingleaf conductance, (2) factorscontrollingphotosynthesis and (3) an ecophysiological summary. FactorsControllingLeaf Conductance.-•Therelationshipbetweenvariousenvironmentalandplantfactorsand k•e•fwasanalyzedusingboundaryline analysisassuggestedby Webb (1972), Jarvis(1976), andElias (1977). In boundaryline analy-

sis,all valuesfor two variablesareplottedandthena line whichencloses all points is drawn (e.g., the relationshipbetweenP• and PAR, Fig. 2). It is then assumed that all valuesbelow this line are the resultof anotherfactor(s) being limiting. From the boundaryline, one can describethe followingvalues: optimum,thresholds, maximum, and minimum (Table 2). • Aubuchon, R.R.

1976.

Environmental influences on carbon fixation within the crown of

white oak. M.S. Thesis,Univ Missouri-Columbia. 206 p.


TABLE 1. Relationship betweenchanging basexylempressure potential(baseP) and averagedaily (0800, 1000, 1200, 1400, and 1600 hours)photosynthesis (Ps), lea[ conductance (k,e•) and lea[ temperature(TO in white oak, sugarmaple,northern red oak, and blackoak duringpredrought,drought,and recoveryperiods. xtt•o•

Species

Base P

(mg COn

k•e•f

Condition*

(-bars)

White oak

1 & 2** 1 & 2** 1 2

Predrought 12-drought 19-drought recovery

-0.3 -2.8 -8.5 -0.5

1.8 2.1 8.6 1.7

8.7 3.8 1.5 5.5

0.54 .16 .03 .25

27.1 32.8 37.1 37.6

Sugar maple

1 & 2** 1 & 2** 1 2

Predrought 12-drought 19-drought recovery

-0.4 -2.6 -5.1 -0.3

1.7 2.6 6.6 1.8

6.0 3.6 1.1 3.0

.43 .28 .04 .16

28.2 32.4 38.6 39.7

1 1 1

Predrought 12-drought recovery

-0.4 -1.9 -0.6

1.9 2.4 1.4

6.9 2.3 5.0

.56 .11 .28

28.6 35.0 36.6

1 1 1

Predrought 12-drought 19-drought

-0.4 -1.3 -3.5

1.8 1.9 3.9

7.9 3.7 2.3

.49 .29 .09

27.1 34.0 38.8

Northern

red oak

Black oak

(-bars) dm-ehr-:) (cm s-•)

Tx

Sapling#

(øC)

* Predroughtm April 4; 12 day drought: April 15; 19 day drought: April 22; recovery : plants watered on April 15 and measuredon April 22. ** Data averagedas no statisticaldifference between individuals were noted.

The informationin Table 2 would suggestthe following: (1) light saturation occursfirst in sugarmaple,thenin northernred oak, thenin whiteoak, andfinally in black oak, (2) k•e in white oak had the broadesttemperatureoptimum,k•e•rin sugarmapleandnorthernred oak the least,(3) temperaturemaximumsappearsimilar in all species,(4) the k•f-vpg thresholdin sugarmaple was the lowestwhile it was the highestin white oak, (5) P thresholdsfor initiation of stomatalclosure varied from -21.5 bars in black oak to -15.5 bars in sugarmaple, and (6) the highestcoefficientsof determination(r s between TP and k•f were observedin sugarmaple and white oak, the lowestin black oak (Fig. 3). The relationshipfoundbetweenk•f and PAR is similarto that shownin Figure2 and hasalsobeenobservedin thesefour speciesunderfield conditions(Phelpsand others1976), in Juglansnigra (Doughertyand others1976), in Picea sitchensis (Jarvis 1976), and in Quercuspetracea (Elias 1977). Under field conditions, Phelpsandothers(1976) andChambers(1976) did not find asbroadtemperature optimums(k•f-leaf temperature),but they did note an identicalorderingof the species.Again,highervpgthresholds, but the samespecies order,werenotedin this greenhousestudy in comparisonwith the field studiesconductedby Chambers (1976). Xylem pressurepotentialthresholdsaveragedfrom 2.5 to 3.0 barsmore negativein eachof the species underfield conditions(Chambers1976, Phelpsand others1976) than in the greenhouse. Droughthistoryplaysan importantrole in shiftingenvironmentaland plant variable thresholds,even within the sameindividual,so thesedifferencescould be anticipated(Thompsonand Hinckley 1977). Thompsonand Hinckley (1977) have noted3 to 4 bar shiftsin P thresholds in a maturewhiteoak treefrom earlyJuneto late August. They suggested the possibilityof osmoticadjustments.Indeed, osmotic

76 / Fo•t•s•

SCmNC•

t/Jsoi I :-0.3

•oit =-8.5

•oit =-0.5

WO#1:4-4

WO#1:22-4

WO#2:22-4

T, (øC), , , , , 38

PAR (/•E m -2 S -1)

30

22 •

1400 1200 800 400 0

Rs mg 002 dm-2 hr •)

P or •' (-bars)

Iø -

•TO•O_O_.O •0•0

16

- 24

k,• (cm s-)

5

9

13

17

7

11

15

19

9

13

17

True Solar Time (hours) FiOURE1. Relationshipbetweenday and photosyntheticallyactive radiation (PAR), leaf temperature (Tx), photosynthesis(P,), xylem pressurepotential (P), osmoticpotential (•-), and leaf conductance(kte•t) in two white oak saplings. April 4: predrought, April 22: drought (whi• oak • 1) and recovery (white oak • 2). White oak • 2 had been irrigated on April 15.

adjustments(z- more negativefor a givenP value) after irrigationwere observedin whiteoak sapling# 2 in this study(Fig. 1). The responsebetweenturgot pressureand k•eafwas anticipatedto be highly correlatedin all species, but wasnot, especially in blackoak (Fig. 3). The poor relationshipsbetweenturgot pressureand k]e•fin black oak was in contrastwith the


Ps (mg CO2dm-2 hr -4)

k•eaf(cm s-1)

12

White

0 •

I

I

200

I

I

600

I

Oak

I

1000

I 1400 .8

8

o

oß

ß

.•

ß

ee-ß.•Oak

.4

4

o Northern I

I

200

I

I

600

. .,

Red Oak I

12

I

1000

Northern , 8

4

0

1400

.8

ß

IBlackOak ee'--•• ß

Black

I

I

200

I

I

600

I

V

' .

o1.,

T&,.

12

8

' ' 'e[•

Oak

I

1000

I 1400

,

', 4

0

.8

.4

ee ß ß

I

200

I

I

!

600

I

1000

I

I

1400

PAR (/•E rn 2 s •)

e•

ßß

Sugar Maple e_ eeee•

Sugar Maple

0

, 12

,

. 8

.

,

e,

&•

4

0

Turgor Pressure (bars) FmURE 2. Boundary line relationship between photosynthetically active radiation (PAR) and photosynthesis (P,) in white oak, northern red oak, black oak, and sugar maple saplings under both field (open circles) and greenhouse (solid circles) conditions. Only data near maximums were plotted.

78 / FOREST SCIENCE

FretroE 3. Boundary line relationship between turgor pressure (difference between xylem pressure potential and osmotic potential) and leaf conductance (kleaf) in white oak, northern red oak, black oak, and sugar maple saplingsunder greenhouseconditions. All data were plotted.

A

A

A

A

A

A

A

A

V

V

V

V


TABLE 3. Effect of variablephotosyntheticallyactive radiation (PAR), leaf temperature(TD and vapor pressuregradient(vpg) on leaf conductance(kz,at),xylem pressurepotential(P) and photosynthesis (Ps) in black oak (BO) and white oak sapling # 2 (WO) on April 10, 1975. Ps

Time

PAR (t•E m-• s-x)

(hours) BO WO

T• (øC)

BO WO'

vpg (mb)

k•eaf (cm s-x)

BO WO 'BO WO

P (-bars)

BO WO

0500

0

0

26.2

25.0

15.1

13.6

.02

.02

1.9

2.1

0600

30

32

26.8

26.9

22.4

22.7

.19

.13

3.6

4.8

(mg CO• dm-ahr-• )

BO WO

0700

200

170

27.7

27.5

23.5

23.1

.50

.40

12.5

12.1

0800

250

200

28.8

26.2

24.3

20.7

.56

.48

16.6

20.2

7.0

1000

1800

1550

36.4

38.0

48.4

53.6

.05

.12

11.7

21.0

0.4

3.3

1200

350

280

31.5

30.5

34.2

29.6

.50

.13

20.7

20.3

7.1

3.4

1400

1880

1650

41.3

36.6

63.3

45.7

.02

.15

12.1

19.7

0.1

3.5

1600

500

300

31.8

32.5

33.9

35.8

.35

.13

17.6

18.6

4.1

3.0

1900

0

0

27.7

27.5

26.8

26.2

.02

.02

3.1

5.2

6.5

excellent relationship notedin whiteoak (Figure3, Tables2 and3). The datapresentedin Table 3 were collectedon April 10, a day whenBP was-1.9 and -2.1 barsin the blackoak and white oak, respectively, and a day of widelyfluctuating light intensitiesand, therefore,fluctuatingvpg. Initially under conditionsof low vpg,stomatawereopenin bothspecies.From 0800 to 1000 hoursaslightintensity, leaf temperature,andvpgincreased,stomataclosedin both species.Xylem pressure potentialrecoveredin blackoak, but P did not recoverin whiteoak. Then between 1000 and 1200 hours, tight intensityand vpg dropped; however, stomataonly openedin blackoak. Again, light intensityincreasedand the 0800 to 1000 hour patternwasrepeated.The consequences of thisresponse in whiteoak and black oak were that there was a closerelationshipbetweenTP and k•eafin white oak, but not in blackoak (Table 2, Fig. 3 ) and therewasa highlysignificantcorrelationbetween vpgandk•e• in blackoak (re = 0.80 for all datawhenlightwasnot limiting) and a lesssignificantrelationshipin white oak (r 2 = 0.41 ). Metcalf and others (1975) also found a poor statisticalrelationshipbetween estimates of plant water statusand k•eafmeasuredin six black oak saplingsfrom three sitesat the AshlandWildlife Area. They observedthat k•o•fwas not significantly correlatedwith P, but was with vpg. Stomatalapertureis controlledby differences in turgorpressure between theguardcellandthe surrounding epidermal cellsandobviously, the estimates of bulkleaf waterstatususedin thisstudymayor maynot reflectthisdifference.Data from Piceasitchensis (Jarvis1976) andfrom Juglansnigra (Doughertyand others1976) alsoindicatethat bulk foliar water statusis not alwaysa sensitive indicatorof guardcell waterstatus.The importance

of peristomatal transpiration hasbeenofferedas an explanation whensignificant relationships betweenvpg and k•oafare observed(Hall and others 1976, Jarvis 1976). In addition,the possibilityof petiolewaterpotentialbeingas muchas 180ø out-of-phase with that of the guardcell hasbeenproposedby Barrs (1971). Certainly the rapid out-of-phaseoscillationsin both P and k•oafound in black oak wouldtendto supportthis (Table 3). FactorsControllingPhotosynthesis.-•Ithas beenpreviouslymentionedthat a significantcorrelationwasobserved betweenk•eafandphotosynthesis (PD in all species under all conditions;however,decreasing P, may just as effectivelycontrol k•eafas

80 / FoaEs• SCIENCE

Ps (mg C02 dm-2 hr •) 12

18

26

34

42

'18

26

34

42

Black Oak ßßß•ee•e ,•ooß

Sugar Maple ,. ,

26

,

, ..;,0%

34

42

Ti (øC) FmURE 4. Boundary line relationship between leaf temperature (Tx) and photosynthesis(PD in white oak, northern red oak, black oak, and sugar maple saplingsgrown under field (open circles) and greenhouse(solid circles) conditions. Only data near maximums were plotted.

k•e•f affects P8 (Meidner and Mansfield 1968). The relationshipsbetween PAR

andP8 (Fig. 2) and T• andP• (Fig. 4) wereinvestigated usingboundaryline analysis. In addition,field data on 9 saplingsof eachspecies(three saplingsfrom eachof three diversesites,black oak not examined) were included to illustrate that trans-


plantedand field saplingsbehavedsimilarlyand to expandthe data set. The PAR valuewhichproduces50 percentof maximumP8 (170, 125, 120, 80/xE m-2 s-x for black, white, northernred oak, and sugarmaple, respectively)and the estimated light compensation point (P8= 0: 30, 32, 28, and 20/xE m-2 s-x, respectively) suggestedthe followingranking of species(from most to least efficient at low light intensities): sugarmaple•> northernred oak > white oak •> black oak. Maximum ratesof P• were9.5, 12.0, 9.3, and 7.5 mg CO,dm 2 hr-• for black, white,northern red oak, and sugarmaple, respectively. Leaf temperaturecan influence P, both through its effects on k•eaf (through changingvpg) and its influenceon enzymaticactivity (Black 1973). In both white oak and sugarmaple, a rather broad plateauof high P8 rateswas noted (Fig. 4). In all species,ratesof P8were still highat 40øC (33.3, 30.0, 17.9, and 28.0 percent of maximumin white oak, northernred oak, black oak, and sugarmaple, respectively). It was estimatedthat Ps would reach zero as Tx approached44øC in all species. Leaf temperature under field conditionsduring the summer of 1974 rangedfrom 8.5 ø to 45.7øC (Metcalf and others 1975). Consequently,optimum and maximum Tx valuescited by Black (1973) for C-3 speciesseem low when comparedto valuesdescribedherein. Usingan air-conditionedcuvette,Lassoieand Chambers(1976) found that the net carbonexchangerate approachedzero (respiration = photosynthesis) at 37.5øC in a northernred oak sapling.However,they alsoobservedthat stomatawere still partially open (klear/• 0.1 cm S4) at 44øC.

Eco-physiological Summary.--Three generalconclusions appearappropriate: (1) black oak stomatawere more sensitiveto vpg than to turgor pressurewhile the oppositewastrue in white oak, sugarmaple,and northernred oak; (2) patternsof stomatalclosureto either vpg or xylem pressurepotentialor both suggested the followingdroughtavoidance ranking: sugarmaple> northernred oak > whiteoak > black oak; and (3) basedon P8 data, sugarmaple was the most shadetolerant while black oak was the least. Similar results have been observed under field condi-

tionsby Aslin and others(1975), Chambers(1976), Metcalf and others(1975), and Phelpsand others(1976). Wuenscherand Kozlowski(1971) alsonotedthat stomataof black oak seedlings were more sensitiveto leaf temperature(and hence vpg) thanthoseof whiteoak andsugarmaple. The data from this studywould suggestthat, of thesefour species,sugarmaple might best conservewater throughstomatalclosure,best conductphotosynthesis under low light conditions,and hencedo well in both low and high light environments. Unfortunately,this conclusionis too simplisticas stomatalclosureis only one of several means of drought avoidance (e.g., rooting distribution, cuticular thickness,and xylem morphology). Indeed, roots of sugar maple seem to be

restrictedto soil horizonsaboveregionsof high bulk densitiessuch as clay pans (Teskeyand Hinckley,unpublished data). In addition,early stomatalclosurein a typicallyxeric environmentwould reducephotosynthate productionsignificantly. Hinckleyandothers(1977) estimatedthat duringa severedroughtat the Ashland Wildlife Area in 1976, completestomatalclosureencompassed 52, 28, 23, and 18 percentof the matureleaf season(May 25 throughOctober16, 1976) for sugar maple,northernred oak, whiteoak, andblackoak, respectively.Underconditions of a prolongeddroughtsuchas that in 1976, the oakswouldpotentiallyfix more carbon than the sugarmaple. In thisstudy,all species, with the possibleexceptionof blackoak, seemedto be ableto developoptimumratesof photosynthesis overa broadrangeof temperatures.

82 / FORESTSCIENCE

Even with leaf temperaturesof 40øC, appreciablerates of photosynthesis were found. Under cool, moist, soil conditions,all specieswould be able to maintain maximumratesof photosynthesis. Reducinglevelsof lightwouldfavor sugarmaple and northernred oak while reducingsoil water potentialunder conditionsof low atmosphericevaporativedemandwould favor black oak. LITERATURE

CITED

ASLIN, R. G., J. L. CHAMBERS,C. L. METCALF,J. E. ROVERTS,T. M. I-IINCKLEY,and G. S. Cox.

1975. Photosyntheticpatternsof three tree speciesas related to environmentaland plant factors. Bull Ecol Soc Am 56(2) :62.

BARRS, H.D.

1971. Cyclic variation in stomatalaperture,transpiration,and leaf water poten-

tial under constant environmental conditions. Ann Rev Plant Physiol 22:223-236.

BIca3s,W. W., A. R. EDISON,J. D. EASTIN,K. W. BaowN, J. W. MAR•VILLE, and M.D. CLEO_a3.1971. Photosynthesis light sensorand meter. Ecology 52:125-131. BLACK,C. C., JR. 1973. Photosyntheticcarbonfixation in relation to net CO2 uptake. Ann Rev Plant Physiol 24:223-286. CHAMBERS, J.L. 1976. Patterns of leaf conductanceand plant water statusfor several hardwood speciesin relation to selectedenvironmental factors. Ph.D. dissertation,Univ Missouri-Columbia. 174 p. Univ Microfilm No. 77-15,498. CURTIS,J.T. 1959. The vegetation of Wisconsin. Univ Wisconsin Press, Madison. 657 p. DOUGHERTY,P.M., J.P. LASSOIL,and T. M. I'-IINCKLEY. 1976. Leaf conductance to water vapor transfer from leavesof a black walnut sapling. In Proc 1st Central Hardwood For Conf, Southern Illinois Univ-Carbondale (Fralish, J. S., G. T. Weaver, and R. C. Schlesinger, eds.), p 259-268. ELIAS, P. 1977. Photosynthesisand water regime of woody plants. In Proc Symp Dendrophysiology Modra-Piesky, Czechoslovakia,April 12-14, p 84-91.

GXLe, J., A. M.•d•ES,and A. POLJAKOFF-MAYBER. 1970. A rapidly equilibrating thermocouple contact thermometer for measurementof leaf surface temperature. Ecology 51: 521-525.

GARRETr,H. E., and G. S. Cox. 1973. Carbon dioxide evolution from the floor of an oakhickory forest. Soil Sci Soc Am Proc 37:641-644. HALL, A. E., E. D. SCHULZE,and O. L. LANGE. 1976. Current perspectivesof steady-state stomatal responsesto environment. In Water and Plant Life (Lange, O. L., L. Kappen, and E. D. Schulze,eds.). Ecological Studies 19:169-188. Springer-Verlag, Berlin. HINCICLe¾,T. M., J.P. LsssoIE, and S. W. RUNNING. 1977. Tree water deficits: cellular to community level implications. Bull Ecol Soc Am 58(2): 10. JARmS,P.G. 1976. The interpretationof the variations in leaf water potential and stomatal conductancefound in canopiesin the field. Phil Trans R Soc Lond B 273:593-610. KANEMASU, E. r., G. W. THURTELL,and C. B. TANNER. 1969. The design,calibration and field use of stomatal diffusion porometer. Plant Physiol 44:881-885. L•ssom, J.P., and J. L. CHAMBERS. 1976. The effect of an extreme drought on tree water statusand net assimilationrates of transplantednorthern red oak under greenhouseconditions. In Proc 1st Central Hardwood For Conf, SouthernIllinois Univ-Carbondale (Fralish, J. S., G. T. Weaver, and R. C. Schlesinger,eds.), p 269-283. MEn)NeR, M., and T. A. MANSFIELD. 1968. Physiology of stomata. McGraw-Hill, England. 179 p.

METCALF,C. L., J. L. CHAMBERS, R. G. ASLIN, G. S. Cox, and T. M. HINCKLEY. 1975. Patterns of water stressin contrastingmicroenvironmentswithin a mid-Missouri oak-hickory forest. Bull Ecol Soc Am 56(2) :62.

MILLAR, B. D., and G. K. HANSEN. 1975. Exclusion errors in pressurechamber estimatesof leaf water potential. Ann Bot 39:915-920. MORROW,P. A., and R. O. SEATIER. 1971. Leaf resistancemeasurementswith diffusion porometers;Precautionsin calibration and use. Agric Meteorol 8:223-233. N•YLOR, D.G., and I.D. TEARE. 1975. An improved, rapid, field method to measure photo-

synthesis with •'CO2. Agron J 67:404-406.


PHELPS,J. E., J. L. CHAMBERS, and T. M. HINCKLEY. 1976. Some morphological,ecological and physiologicaltraits of four Ozark forest species. In Proc 1st Central Hardwood For Conf, Southern Illinois Univ-Carbondale (Fralish, J. S., G. T. Weaver, and R. C. Schlesinger, eds.), p 231-243. RICHTER, H. 1976. The water status in the plant--Experimental evidence. In Water and Plant Life (Lange, O. L., L. Kappen, E. D. Schulze, eds.), Ecological Studies 19:42-58. Springer-Verlag, Berlin. RITCHIE, G. A., and T. M. HINCKLEY. 1975. The pressure chamber as an instrument for ecologicalresearch. In Advancesin Ecological Research (A. Macfadyen, ed.), 9:165-254. Academic Press, New York. SCHOLANDER, P. F., H. T. HAMMEL, E. D. BRADSTREET, and E. A. HEMMINGSEN. 1965. pressurein vascular plants. Science 143: 339-346. THOMPSON, D. R., and T. M. HINCKLEY.

1977.

Sap

A simulation of water relations of white oak

based on soil moisture and atmosphericevaporative demand. Can J For Res 7:400-409. TURNER•N. C. 1974. Stomatal behavior and water status of maize, sorghum and tobacco under field conditions. II. At low soil water potential. Plant Physiol 53:360-365. WEBB,R.A. 1972. Use of the boundary line in the analysis of biological data. J Hort Sci 47:309-319.

WUENSCHER, J. E., and T. T. KOZLOWSKI. 1971. The responseof transpiration resistanceto leaf temperatureas a desiccationresistancemechanismin tree seedlings.Physiol Plant 24: 254-259.

Call for Papers: National Symposiumon Systemic Chemical

Treatments

in Tree Culture

The National Symposiumon SystemicChemical Treatments in Tree Culture will be held October 10-11, 1978, at Michigan State University, East Lansing. Cosponsors are Michigan State University, United States Forest Service State and Private Forestry, and leading systemic chemical producers and suppliers. Purposesare: to present current researchon direct trunk application of systemicchemicals; to serve as a "state of the art" reference for this important aspect of tree culture; and to. consider the advantages and disadvantages of trunk, stem, or root treatments.

Invitedpaperswill be presentedat concurrenttechnicalsessions whichwill coverphysiological processes;plant nutrients and growth regulators;Dutch elm disease;and specific antibiotics,

fungicides,and insecticides.An additionalsessionis plannedfor contributedpaperscovering the above or closely related topics.

Personswishing to submit a paper for considerationmust provide a 150-word abstract no later than June 1, 1978. Sendto Dr. JamesKielbaso, Department of Forestry, Michigan State University, East Lansing, Michigan 48824.

84 / FOREST SCIENCE