Photosynthetic Efficiency of Drought-Induced Leaves in Neviusia a

Volume 45 Article 181991 Photosynthetic Efficiency of Drought-Induced Leaves in Neviusia alabamensis Jennifer Martsolf University of Central Arkansas Robert D.. It has been accepted for

Volume 45 Article 18

1991

Photosynthetic Efficiency of Drought-Induced

Leaves in Neviusia alabamensis

Jennifer Martsolf

University of Central Arkansas

Robert D Wright

University of Central Arkansas

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Recommended Citation

Martsolf, Jennifer and Wright, Robert D (1991) "Photosynthetic Efficiency of Drought-Induced Leaves in Neviusia alabamensis,"

Journal of the Arkansas Academy of Science: Vol 45 , Article 18.

Available at:http://scholarworks.uark.edu/jaas/vol45/iss1/18

Proceedings Arkansas Academy of Science, Vol. 45, 1991 61

NEVIUSIAALABAMENSIS

JENNIFER MARTSOLF and ROBERT WRIGHT

Department ofBiology, University of CentralArkansas

Conway,AR72032 ABSTRACT

Plants in one stand of Neviusia alabamensis Gray (Rosaceae), a rare shrub, became drought

deciduous in July,1990, andgrew new leaves following rains inAugust InSeptember the

photosyn-theticefficiency of the new leaves was compared with thatof oldleaves in another stand of the same

population Althoughleaf area fromregrowth wasmuch less than oldleaf area retained,

photosyn-thetic efficiency in new leaves was about3 times higher than in old leaves This response is dis-cussed intermsofcompensation fordrought-induced loss of leaves.

INTRODUCTION

"Neviusia alabamensis Gray (Rosaceae) isaperennial shrub with

numerous slender primary stems and short lateral branches The bright

greenleaves aresimpleandalternating The flowers areodorless and lack

petals;however, thestamens are numerous (usuallyover 100)andshowy,

floweringmay occurbetween March and May" (Long,1983)

N alabamensis is listed as an endangered species in Arkansas,

Alabama and Missouri, and has only recently been discovered in

Tennessee andMississippi The genus seems tobe foundonly above

stream banks ingenerally dry soils Itappears tobecapableof

reproduc-ing only byroot sprouts (Long, 1983)

Thetwo sites atwhich thisstudy tookplacearetheeast andwest ends

of the Conway County, Arkansas population.This population extends

along asoutheast-facing ridge above Cadron Creek between Conway and

Menifee, Arkansas Thepopulationisseparated intotwocolonies by 100

meters of forest (Long, 1989) Theplants atthese two sites arepossibly

allonegenet (Freiley, pers comm.) There are only three other known

populationsin Arkansas

Since N alabamensis ismostly found in dryconditions, thestrategies

todeal withwater stress must beanimportantpartoftheplant'sabilityto

survive InSeptember 1990, plants in sites only 100meters apart were

observed tobe instrikingly different condition followingsummer

drought Plants attheeast Conway County site, site 1,retained the

origi-nal leaves producedinspring while theplantsatthewest Conway County

site, site 2, haddroppedmost of thesematureleaves and,following

sever-al weeks ofrain, hadgrown newleaves

Plants growing in different environments have leaves of characteristic

sizes andshapes AccordingtoTownsend andSolbrig (1980), for

exam-ple,treeleaves in the temperate zone arenormally ofmoderate size with

toothed orserrated margins; evergreen plants from warmsemidesert

regions have smaller leaves, sub-canopy tropicaltrees have verylarge

leaves with entiremargins andpointed apices;andmany treesintropical

andsubtropical savannas havecompound leaves Evenonthesame tree,

leaves exposed tothesuntendtobe smaller than those in the shade

Leaves are the main biochemical factories of theplant, intercepting

light and transforming thatenergy tofixCO2andsynthesize sugars The

leaf needs adequate light, ample rawmaterials, plenty ofwater,and

appropriate temperatures tofunctioneffectively Securing these

condi-tionspresents difficulties totheplant,considering, among other things,

that foreverymolecule of CO2that is fixed,anywhere from 300to1000

molecules of H2O vapor arelost Theadaptive problemtheplantfaces is

towtomaintain adequate waterand nutrients whilemaximizingnet

pho-tosynthesis (Townsend andSolbrig, 1980)

Plant species canmaintain physiological activity duringperiods of

drought through avariety of mechanisms These mechanisms canbe

;rouped as avoidance ortolerance ofdrought One avoidance strategy,

conversion toadormant phase, becomes moreimportant as

cnvironmen-al moisture stress becomes increasingly severe (Chabot and Bunce,

1979)

"Plants growby the progressive accumulation ofrepeated elements:

leaves, buds,intemodes, branches, and flowers"(Maillctte,1985), which

together contribute totheparticular shape ofaplantInmost plants the

number ofelements isnotfixed; itchanges with time because of growth

andsenescence processes Changes in the number ofparts canbe caused

by demographic events,births, and deaths;plants canbe viewedas a pop-ulation ofparts Because leaves photosynthesize, their demography is of

specialinterest (MaiUctie,1985)

N alabamensis atsites 1 and 2responded todrought conditions in

twodifferentmanners, whichwereretention, and dropfollowed by regrowth Research has shown that therateofphotosynthesis per unit of leafarea typically increases after leafemergence, reaches anoptimumat

about the time of fullleafexpansion,and then declines (Yamaguchi and Friend, 1979; Catzky and Ticha, 1980; Constable and Rawson, 1980; Bongietal., 1987; and Nilsen,etal., 1988) This investigation of the effect of leafage onphotosynthesis was designed toconsider the

strate-gies of retaining leaves ordropping leaves in N alabamensis

MATERIALSANDMETHODS Usingaportablephotosynthesis system, four of the variables used in thisreport weremeasured in intact leaves ateach site, inSeptember,

1990 At site 1,mostplantsretained original leaves produced in the spring whichhad survived the summer drought For analysis, 130mature

leaves were randomly selected andplacedin the chamber ofaIJ-COR

portablephotosynthesis system (LJ-COR, Inc., Lincoln, NE) After the unit calculated therates oramounts ofnetphotosynthesis, light intensity, leaftemperature, and CO2flow, the leafwasharvested Each leafwas

then traced onto tracing paper and the resulting leaf copy cut out,

weighed, andcompared tothe weight ofaknownareaoftracing paper to

determine leaf areain square centimeters Leafarea data produced the fifthvariable considered in this study and wereentered into the instru-ment's computer toproduce corrected values of the five(Table 1) vari-ables for each leaf

Table J.Analysis of Variance for hypothesis ofnooverall site effect

Variable Silc Mean Standard Deviation

3.20*• 7.19

2

232.16**

731.92 337.06 1

2 leaf temperature 29.94

28.60

1.30 n.s.

2

20.83 1

'2

2 181.97

1.27**

1

Sile 1=ConwayEast, 130 leafnbservaiions. matureleaves

Site 2=Conway West 33 leaf observations, newleaves

** -highly significant,

P < 001

im.-notsignificant

61 Published by Arkansas Academy of Science, 1991

62 Proceedings Arkansas Academy of Science, Vol 45, 1991

Photosynthetlc Efficiency of Drought-Induced Leaves in Nevlusla alabamensis

At site2,the N alabamensis plantsheld virtuallynooriginal leaves

Within three days of the site 1analysis, 33 leaves atsite 2wereanalyzed in

thesame manner.These leaves werereplacements ofthose abscised during

summerdrought

twopatterns as leafarea index increases withgrowth Growthrateeither increased uptoaplateauas morelightwas intercepted ordecreased above

anoptimumleafareaindex

Nilsenetal (1988) studied the changes that occurinleafstructure,

such asaging ofchloroplats,whicheventually causes adecrease in

photo-synthetic efficiencyatsome pointafter leafmaturity He studied Rhododendron maximum L whichisashort flushspeciesproducing one

cohort of leaves each year sothatdemographic patterns would be readily identifiable and differences between same ageleaves wouldnotbe dueto

growthatdifferent times in the season They found that photosynthesis

rates decreased withincreasing leaf age,and decreased more rapidly in light saturated than in low light environments

RESULTS

Mulijvariaicanalysis of variance (MANOVA)for thehypothesis ofno

overall site effect revealed asignificant difference, (P<.0001), between

thetwosites Table 1displays aunivariate analysis for the hypothesis ofno

overall site effect for each variable Theprobabilities exhibitsignificant

difference, (P < 01), between the twosites for all variables except leaf

temperature. Photosynthetic rates ofearly and late leaves ofhoneymesquite were

measured, exhibiting daily maximum photosynthetic rates ofearly leaves to

be significantlygreater than those oflate leaves Thehigherrates ofearly leaves wereassociated withhigher nitrogencontent per unit leafareaanda

thicker leafblade.(Wanand Sosebee, 1990)

Table 2displays astepwise discriminant analysis summary which

shows ahighly significant difference for three of the fivevariables,(P<

.001), and asignificant difference for the other twovariables, (P<.05)

This stepwise analysis wasperformed in order todetermine the rank of

each variable interms ofpredominance Photosynthesis is shown to

explain54% of the variance between site 1and 2 Leafareaand

lightinten-sityatthe time ofanalysis eachaccount for about20%of variance between

sites Carbon dioxide and leaftemperature account forlittleof the variance

Suzukietal.(1987) suggested the influence of leafage on photosynthe-sisratewasduetoassociated changes withthe capacity of the photosynthe-sis cycle through control ofanumber ofenzyme levels He did, however, find similar leafage patterns, reporting, "Therateofphotosynthesis per unit

area in the third leaf of wheatplants reached amaximum onthe seventh day after leafemergence and then declined to1/3of the maximum after 22 days."

Table 2.Stepwise Discriminant Analysis Summary

For all leafages of Rosa Hybrida L.ev.Samantha, Bozarth etal (1982) found maximum photosynthetic rates were reached atirradiance levels of 450-500 microeinsteins* 2sec1.These rates werehighest in the

youngest leaves studied and lowest in the oldest Photorespirationwas

shownnot tobeamajor factor inthis trend

1 photosynthesis

leafarea

.54**

.195"

.04*

Tschaplinskietal (1989) studied the physiological basis ofrcinvigora-tion after shootdecapitation "Reinvigoration refers tothe renewed vigor of growth andnet photosynthesis followingdecapitation Defoliation and shootdecapitationare known toincrease netphotosynthetic rates in the remaining leaves oftreeand cropspecies." Waring et al (1968) and Meidner (1969) also found that anincrease innetphotosynthesis usually

occurs three tofourdays following shootdecapitation Partial defoliation which results inanenhancement ofphotosynthetic rates in the remaining leaves mayalsooccurinrose (MorandHalevy, 1979) These studies sug-gest thatnot only is N alabamensis displaying typical leafage photosyn-thetic efficiencies, but itmay also bedisplaying post defoliation reinvigoration

3 light intensity

CO2flow 4

?*-P<.01

•

-P < 05

Most of the studies chartingarise, plateau, and decline

inphotosynthet-icefficiency of leaves astheyage aredealing withsenescence duetoleaf

age Water deficit is also a cause of decline Vu and Yelenosky (1988) found thatwaterdeficit reduced the photosynthetic CO2 assimilation rateas

wellasthecarboxylation reaction, and the soluble proteincontent in leaves ofcitrustrees. Aikinand Hanan(1975) found thenetphotosynthesis ratein

"Forever Yours"rosetoincrease for the first 8-36days, and decrease until the leaf is 40-68 days, when the leafdrops.However,internalplant water potentialinfluenced the CO2uptakeby reducing itateach increase of radia-tionenergy,resulting in lowernetphotosynthesis with lowerwater poten-tial

DISCUSSION Netphotosynthetic ratefor the youngleaves at site 2 is significantly

higherthan thenet rate atsite 1 which iscomposed ofplants withmature

leaves Thelight during the times ofdata collection was different, being

moreintense whenmeasurements weretakenatsite 1,sotheefficiency of

photosynthesis innewleaves was accomplished evenatsignificantly lower

levels of irradiance Thishigher efficiency is probably afactor of the leaf

age.Catzky and Ticha (1980) and Constable and Rawson (1980) foundnet

photosynthesis rates tobe low inyoung,unfolding leaves, increasing

rapid-lyasleaves expanded andgradually declining thereafter, reaching low

values at senescence Pasian and Iieth(1989) foundnoclearpattern in

photosynthetic efficiency associated withleafage,possibly because the

study they conducted examined leaves of 10, 20, 30 and 40 days ofage

Their study suggested that 10 day -oldroseleaves haveanalmost

com-pletely developedphotosynthetic mechanism, whilesenescence does not

jegin untilroseleaves areolder than 40days AccordingtoBongi (1987),

the effect ofleafage on apparent photosynthesis was shown graphicallyto

increase the first 6 months and remain atalevelplateaufor about 12

months, declining the last 6 monthspriortosenescence, inolive leaves

Therefore itseems thatatacertain minimum waterpotential,N alaba-mensis plantsatsite 2droppedtheir leaves When rainbroughtmorewater

inearly fall, theplants wereabletosprout newleaves, which exhibited the high photosynthetic efficiency characteristic of theiryoung age as wellas

reinvigoration following defoliation

Ifthe populationof N alabamensis isasinglegenet, the differences exhibited in leafholdingmaybe duetodiffering soilwaterholding

capaci-ties between sites Also,it wouldbe interesting toobserve overtime ifthe

same twostrategies of holdingversus dropping leaves arepredictable after

adrysummer and how this affects rate ofgrowthas evidenced byplant

biomass between thetwosites

InFlaveria trinervia,aC4dicot, photosynthesis wasfoundtovary

con-siderably during leafexpansion.Inpartiallyexpanded leaves (20% of full

size), 10-12% ofatmospheric CO2is assimilated directly by the C3

path-waywhile with further leafexpansion,this bypass ofthe C4cycle

decreas-esuntil the C4cycle is fullyoperational atleafmaturity (Moore and

Edwards,1988)

Further study isnecessary tomakeanyconclusions as tothelong term success ofreinvigoration ofleavesas a strategy tocope withwater stress, in

termsofnetcost/benefits totheplant.However,regrowth of photosyntheti-cally efficient leaves does extend the growingseason forNeviusia alaba-mensis

Bunce(1989)attempted toexplainthe response ofgrowthrateper unit

ofground area,by creatingaleafareaindex He found crop growthtoshow

62 http://scholarworks.uark.edu/jaas/vol45/iss1/18

Proceedings Arkansas Academy of Science, Vol 45, 1991 63

Jennifer Martsolf and Robert Wright

ACKNOWLEDGMENT The authors would liketothank Mr and Mrs Alan

Stallings for providing safe harbor for the Conway County

populationofNeviusiaalabamensis.

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63 Published by Arkansas Academy of Science, 1991