Ne w Phytol. (1985 ) 99 , 407-41 6 40 7 DIREC T FOLIA REFFECT S O F SIMULATE D ACI D RAI N II . LEA F SURFAC E CHARACTERISTIC S B Y B . L . HAINES 1 , J . A . JERNSTED T AN D H . S . NEUFELD 2 Botany Department, University of Georgia, Athens, Georgia, 30602, USA (Accepted 13 November

1984) SUMMAR Y Surfac e characteristic s an dwettabilit y o f th e leave s o f

si x plan t specie s hav e bee nexamine di n relatio nt o thei r

susceptibilit y t o damag e fro msimulate daci drain . Th e specie s examine ddiffere d i nth e typ e an dexten t

o f epicuticula r

wa x deposits , surfac e topograph y o f th e cuticle , trichom e typ e an ddistribution , an depiderma l cel l shape . Lea f wettability , a s measure db y eithe r water-holdin g capacit y o r

drople t contac t angle , wa s significantl y differen t amon g species , an d i s highl y correlate dwit hpreviou s report s o f damag e fro msimulate daci drain . Th e leave s o f Platanus occidentalis L . wer e th e mos t wettabl e o f

th e specie s examine dan dar e reporte dt o b e damage dth e mos t

b y repeate dapplication s o f simulate daci drain . Matur e leave s o f Liriodendron tulipifera L. , wit hhig hcontac t angle s an dver y lo w water-holdin g capacity , ar e th e leas t damage d accordin g t o publishe dreports . Lea f water-holdin g capacit y an dsurface-drople t contac t angl e ma y b e usefu l firs t

indicator s o f

resistanc e t o aci drain , an dshoul db e include di nfutur e studie s o f folia r effect s o f aci drain . Ke y words : Aci drain , cuticle , lea f surfaces , wax . INTRODUCTIO N Surfac e characteristic s ar e importan t i n determinin g th e wettabilit y o f leaves , folia r permeabilit y an dpenetration , wate r retention , an drate s o f exchang e o f

wate r an d dissolve dsubstance s betwee n plan t an datmospher e (Fogg , 1947 ; Marti n & Juniper , 1970 ; Halla m& Juniper , 1971 ; Holloway , 1971 ; Norris , 1974 ; Bake r & Hunt , 1981 ; Junipe r

& JefFree , 1983) . Th e increasin g us e i n recen t year s o f folia r applie dherbicides , fungicide s an dspecialize dgrowt hregulator s ha s resulte di n renewe dinteres t

i n leaf surfac e characteristic s suc ha s trichom e distribution , cuticl e thicknes s an dwa x depositio n an dthei r influence s o nefficac y o f folia r applie dcompound s o f

variou s type s (Norris , 1974 ; Bukovac , Flor e & Baker , 1979 ; Bake r & Hunt , 1981) . A nadditiona l are ao f

recen t researc hi nwhic hlea f surfac e characteristic s ma y b e o f particula r

importanc e concern s th e effect s o f aci drai n o n plan t

growt han d survival . Effect s o f

simulate daci drai n o n lea f surfac e perturbation s (Evans , Gmu r & DaCosta , 1977 ; Evans , Gmu r & Kelsch , 1977 ; Paparazz i & Tukey , 1983) , folia r leachin g (Evans , Curr y & Lewin , 1981 ; Haines , Chapma n & Monk , unpublished ) an dphotosyntheti c rate s (Ferenbaugh , 1976 ; Neufeld , Jernsted t & Haines , 1985 ) hav e bee n reported . Sensitivit y t o damag e b y simulate daci drai n ha s bee n reporte d t o var y wit hspecie s (Evan s & Curry , 1979 ; Haines , Stefan i & Hendrix , 1980 ; Evans , Gmu r

& Mancini , 1982) , growt hcondition s (Evan s e t al., 1982 ) an dwit h 1 T o who mcorrespondenc e shoul db e addressed . '

- Biolog y Department , Ne w Mexic o Stat e University , La s Cruces , Ne w Mexico , 88003 , USA . 0028-646X/85/03040 7 + 1 0 $03.00/ 0 © 198 5 Th e Ne w Phytologis t40 8 B . L . HAINE S e t al. ag e o f leave s (Evan s & Lewin , 1981) , al l o f whic har e factor s influencin g lea f surfac e feature s (Juniper , 1959 ; Hull , Morto n & Wharrie , 1975 ; Cutter , 1978) . A little-studie daspec t o f aci drai n effect s o n cro p an dfores t specie s i s tha t

o f lea f wettability . Th e wor k o f Keeve r & Jacobso n (1983a , b ) wit hGlycine max indicate s tha t

th e greate r

lea f wettabilit y o f

aglabrou s soybea n isolin e ma y b e a facto r i n it s increase dsusceptibilit y t o folia r injur y an dleachin g b y simulate daci d rai ncompare dwit hplant s o f apubescen t

isoline . However , i t

appear s tha t

cuticl e thicknes s an dfor man depicuticula r wa x distributio n hav e no t ye t bee n considere d a s factor s influencin g th e magnitud e o f effect s o f

aci drain . Becaus e o f

th e possibilit y tha t

lea f wettabilit y ma y b e relate dt o damag e b y aci d rai ni n othe r

species , an dbecaus e surfac e feature s suc ha s trichom e numbe r an d distribution , cuticl e thicknes s an dpatter n an dwa x distributio n determine , a t leas t i n part , lea f

wettability , thes e aspect s o f lea f structur e an dfunctio n wer e investi

gated . Th e objective s o f th e presen t

stud y wer e t o compar e (1 ) lea f surfac e characteristics , especiall y epicuticula r wa x deposits , (2 ) lea f

wate r holdin g capacity , an d(3 ) lea f

surface-wate r

drople t contac t angle s o f

severa l specie s whic hhav e bee n subject s o f

previou s studie s o f

effect s o f

simulate daci drain . Th e result s ar e discusse di n term s o f

specie s susceptibilit y t o an dexten t o f damag e resultin g fro m simulate daci drain . MATERIAL S AN D METHOD S Plant material Plant s o f

Liquidambar

styraciflua L . (sweetgum) , Platanus occidentalis L . (sycamore ) an dRobinia pseudo-acacia L . (blac k locust ) wer e grow n fro msee di n 4 litr e pot s i n agreenhouse . Whe n th e seedling s wer e 3 t o 6 c mtal l the y wer e thinne dt o on e pe r

po t fo r atota l o f

6 0 seedling s pe r

species . Individual s o f Liriodendron tulipifera L . (tuli p poplar ) an dQuercus prinus L . (chestnu t oak ) wer e obtaine da s establishe dseedling s fro mfiel dpopulation s i n northeaster n Georgi a an dsouther n Nort hCarolina , respectively , transplante dint o 4 litr e pots , an d maintaine di n agreenhouse , unde r whic hcondition s mos t o f th e foliag e an d approx . 90 % o f

th e tota l biomas s developed . Stratifie dseed s o f Erechtites hieracifolia Raf . (fir e weed ) wer e germinate dan dgrow n t o maturit y i n agreenhouse . A loam y san dmixtur e wa s use dfo r th e pottin g soil . Plant s wer e kep t well-watere d an dfertilize dweekl y wit hhalf-strengt hHoagland' s nutrien t solution . Leaf surface structure Sample s o f

fres hlea f

materia l o f

al l si x specie s wer e mounte do n aluminu m stub s wit heithe r

silve r conductiv e pain t

o r double-side dtape . Specimen s wer e examine ddirectl y wit haCambridg e Stereosca n (Cambridg e Instrument s Ltd. , Cambridge , England ) scannin g electro n microscop e o r afte r sputter-coatin g wit h gold-palladium . Water-holding capacity Wate r holdin g capacitie s wer e determine di n th e laborator y fo r fiv e tre e species , Liquidambar, Liriodendron, Platanus, Quercus, an dRobinia, an dth e herb , Erechtites. Individual s o f eac hspecie s wer e selecte dan dth e fourt ho r fift hlea f fro m th e ape x spraye dfro mabov e wit hdistille dwate r fo r 2 0 s fro madistanc e o f 3 0 cm , usin g ahan dsprayer . Drople t siz e frequenc y distributio n wa s determine db y th e flou r metho do f

Law s & Parson s (1943) . Th e spraye r produce ddroplet s suc htha tFoliar effects o

f simulated

acid rain II . 4° 9 6 8 % (s o 8-54 , n = 3 ) o f th e mas s wa s betwee n 0-5 9 an d1- 0 m mdiamete r an dth e remainde r

o f th e mas s wa s betwee n 1- 0 an d2- 0 m mdiameter . Fo r Robinia, th e compoun dlea f

wa s detache dfirs t

an dplace do n ahorizonta l surfac e becaus e o f difficult y i n sprayin g whe n stil l attache dt o th e stem . Leave s o f al l othe r

specie s remaine dattache dt o th e plant , i n thei r natura l orientations . Sprayin g too k plac e i nth e laboratory , i n th e absenc e o f ai r current s whic hwoul dcaus e lea f motion . Sprayin g wa s sufficien t t o saturat e th e leaves . Wate r whic hremaine do n th e adaxia l surfac e wa s soake du p wit habsorben t tissu e pape r

an dweighed . Lea f

area s wer e determine dfo r

eac hlea f

wit haLi-Co r

(Li-Co r

Inc. , Lincoln , Nebraska ) are a meter . Wate r

holdin g capacit y wa s expresse da s m g H 2 O cm~ 2 projecte dlea f area . Leaf contact angles Contac t angle s wer e measure do n adaxia l surface s o f detache dleave s o f

al l si x species . Angle s wer e characterize do n bot hrapidl y expandin g an drecentl y mature dleaves . T o determin e firs t i f p H influence dth e contac t angle , 1 0 /A drop s o f eithe r deionize d(p H = 5-8 ) o r acidifie dwate r

(p H = 2-0 ) wer e place do n horizonta l piece s o f

commercia l waxe dpape r usin g a n autopipette . Dro p outline s wer e projecte dont o awal l usin g amodifie d35-m mslid e projecto r an dtrace do n paper . Contac t

angle s wer e calculate dfro mth e tracing s a s describe db y Fog g (1947) . Drop s o f

deionize dwate r

(10/tl ) wer e the n place do n adaxia l surface s o f freshl y detache dlea f

pieces , th e outline s projecte dan dtraced , an dcontac t angle s calculate daccordin g t o Fog g (1947) . Dat awer e analyze dusin g ANOV A program s i n SA S (SAS , 1982 ) after , wher e appropriate , transformatio n (Zar , 1974) . Additiona l statistica l calculation s wer e performe do n a n HP-100 0 mini-compute r followin g procedure s i n Za r (1974) . RESULT S Leaf fine structure Scannin g electro n micrograph s o f th e lea f surface s ar e show n i n Figure s 1 an d2 . Th e specie s examine ddiffere di n typ e an dexten t o f epicuticula r

wa x de

posits , cuticl e surfac e topography , trichom e typ e an ddistribution , an depiderma l cel l shape . Adaxia l lea f surface s o

f Robinia pseudo-acacia wer e characterize db y th e presenc e o f

uniseriat e coverin g trichomes , flattene depiderma l cell s an dadens e coverin g o f

crystallin e surfac e wa x deposit s overlayin g a n apparentl y smoot h cuticl e [Fig . l(a) , (b)] . Leave s o f Liriodendron tulipifera wer e glabrous . Cell s o f th e adaxia l epidermi s wer e onl y slightl y convex , wit hadens e coverin g o f granula r surfac e wa x deposite do n a n unornamente dcuticl e [Fig . l(c) , (d)] . Leave s o f Platanus occidentalis bor e branche dcoverin g trichome s o n bot hsurfaces . Th e trichome s wer e locate dpredominantl y ove r th e vein s an doccurre di n extremel y lo w frequenc y o n th e adaxia l surface . Adaxia l epiderma l cell s wer e conve x an d marke dwit hdistinc t

cuticula r

striations . Epicuticula r wa x wa s absen t

fro mth e adaxia l lea f

surfac e [Fig . l(e) , (f)] . Leave s o f Liquidambar

styraciflua wer e glabrous . Cell s o f th e adaxia l epidermi s wer e conve x wit hasmoot hcuticl e an ddevoi do f visibl e (crystalline ) surfac e wa x deposit s [Fig . 2(a)] . Adaxia l surface s o f Erechtites hieracifolia leave s wer e glabrou s an dwaxless ; epiderma l cell s wer e fla t wit ha smoot hcuticl e [Fig . 2(b)] . Quercusprinus leave s bor e uniseriat e coverin g trichomes , usuall y alon g th e veins . Adaxia l epiderma l cell s wer e conve x wit hasmoot hcuticle , an dcovere db y arelativel y spars e laye r o f granula r

surfac e wa x [Fig . 2(c) , (d)] .41 0 B . L . HAINE S e t al. ( a

Fig . 1 . Scannin g electro nmicrograph s o f adaxia l lea f

surfaces , (a ) Uniseriat e trichom e an d wax-covere depiderma l cell s o f Robinia pseudo-acacia', scal eba r —2 0 //m . (b ) Crystallin esurfac e wa x deposit s coverin g R . pseudo-acacia epidermis ; scal eba r = 2 /*m . (c ) Slightl y conve x epiderma l cell s o f Liriodendron tulipifera covere dwit hgranula r wa x deposit ; scal eba r

= 2 0 /<om . (d ) Granula r surfac ewa x o nL . tulipifera leaf ; scal eba r —2 //.m . (e ) Conve x epiderma l cell s an dsunke n stom ao f Platanus occidentalismscal eba r —20//m . (f) Cuticula r

striation s o nepiderma l cell s o f P. occidentalismscal eba r

—5 //m . Water-holding capacity Lea f water-holdin g capacity , i n m g H 2 O cm^ 2 projecte dlea f are a(Tabl e 1 ) showe dsignifican t

difference s amon g species . Water-holdin g capacit y wa s greates t i nPlatanus, Quercus, an dErechtites, an dleas t i n Liriodendron, wit hLiquidambar an dRobinia intermediat e i n wettabilit y a s determine db y thi s method .Foliar effects of

simulated

acid rain II. 41 1

Fig . 2 . Scannin g electro nmicrograph s o f adaxia l lea f

surfaces , (a ) Conve x epiderma l cell s wit h smoot hcuticl ean dn o surfac ewax , Liquidambar styraciftua; scal eba r

—20//m . (b ) Flattened , waxles s epiderma l cell s o f

Erechtites hieracifolia; scal eba r = 2 0 /(.m . (c ) Uniseriat etrichom ean d spars ewa x coverin g o f

Quercus prinus leaf ; scal eba r = 5 0 /;m . (d ) Spars elaye r

o f granula r surface

wa x o f O. prinus leaf ; scal eba r

—20//m . Tabl e 1 . Mean contact angles an d

mean water-holding capacities (m g H 2 O c m '') of adaxial leaf surface^ Specie s Robinia pseudo-acacia Liriodendron tulipifera* Quercus prinus* Liquidambar

styraciflua Platanus occidentatis Erechtites hieracifolia Wa x pape r p H 2 J (acidifie dH..O ) Wa x pape r p H 5' 8 (deionize dH.,O ) Contac t angl e ff+SE 131- 6 + 2-2 a 124-8±l-6 a 10O 9 + 6-2 b 97-8±4-7 b 80- 7 + 8-5 c 70-l+2-7 c 1 1 9- 7 + 2-6 a 116-( ) + 2-2 a n

5 5 3 3 3 5 3 3 Wate r

holdin g X±S E 15- 4 + 3-2 b 3- 9 + (>8 a 29- 5 + 3-7 f 19-7±(>8b, c 25- 0 + 1 -9 c 24- 9 + 3 -6 c

— capacit y

n 5 5 3 3 3 5

* Transplante da s seedling s t o th e greenhouse , unde r whic hcondition s al l th e foliag euse di nthi s stud y an dapprox . 9 0 % o f

th e tota l biomas s developed . f No t include di nDuncan' s multipl e rang etes t becaus eo f insufficien t plants . %Mean s fo r

th ewa x pape r

compariso nwer eanalyze dusin g aStudent' s /-tes t (Soka l & Rohlf , 1981) . § Mean s no t

followe db y th e sam e lette r diffe r a t th e P< O'O S level , a s determine db y aDuncan' s multipl erang etes t

(SAS , 1982) .41 2 B . L . HAINE S e t al.

Fig . 3 . Sid e view s o f

1 0 /i.l droplet s o f deionize dwate r

place do nadaxia l leaf

surfaces ; contac t

angle s increasin g fro m(a ) t o (d) . (a ) P/atanus occidental!*, 0= 82-2° . (b ) Liquidambar styraciflua, 0= 88-9° . (c ) Liriodendron tu/ipifera, 0— 118'6° . (d ) Robinia pseudo-acacia, 0= 126-3° . Leaf contact angles Leaf-wate r

drople t contac t angl e measurement s an dth e effec t o f p H o n contac t angl e ar e show n i n Tabl e 1 . Th e mea n contac t angle s o f

droplet s o f deionize dwate r

(p H 5-8 ) an dacidifie dwate r (p H 2-0 ) place do n commercia l wa x pape r wer e no t

significantl y differen t

( P< 0 - 05) . Mea n contac t angle s o f

deionize d wate r o n youn g an dmatur e leave s o f al l specie s examine dwer e no t significantl y differen t an dwer e poole dfo r

analysis . Mea n contac t angle s fo r

adaxia l surface s o f Platanus an dErechtites leave s wer e les s tha n 90 ° an dth e lo w spreadin g droplet s covere dacomparativel y larg e are ao f th e lea f surfac e [Fig . 3(a)] . Mea n contac t angle s fo r

Robinia an dLiriodendron exceede d120 ° an donl y asmal l are ao f th e adaxia l surfac e wa s covere db y thes e rounde ddroplet s [Fig . 3(c) , (d)] . Quercus an d Liquidambar

lea f contac t angle s wer e o f

intermediat e magnitudes ; drople t shap e an dcoverag e wer e als o intermediat e [Fig . 3(b)] . DISCUSSIO N Th e degre e o f

damag e whic htree s an dherb s suffe r whe n expose dt o aci drai n varie s widel y amon g specie s (Woo d& Bormann , 1974 , 197 5 ; Evan s & Curry , 1979 ; Le e & Weber , 1979 ; Haine s e t al., 1980 ; Neufel de t al., 1985) , bu t

th e underlyin g mechanism s ar e poorl y understoo da t present . Lea f

wettabilit y ma y b e a n importan t

determinan t

o f folia r damag e b y aci drain , an dphysica l an dchemica l characteristic s o f

th e lea f surfac e determin e th e wettabilit y o f mos t leave s (Marti n & Juniper , 1970 ; Evans , 1982 ; Shriner , 1983) . A n estimat e o f th e potentia l wettabilit y o f

alea f surfac e ca nb e obtaine db y measurin g th e angl e o f contac t betwee n awate r

dro p an dth e surfac e o n whic hi t rest s (Fogg , 1947) . Th e highe r th e contac t

angle , th e mor e hydrophobi c th e leaf , whil e th e lowe r th e angle , th e mor e wettabl e i t

is . Wate r

holdin g capacit y o f

leaves , whil e influence db y suc h factor s a s lea f

motio n an dorientation , i s als o generall y indicativ e o f wettability , wit hmor e wettabl e leave s retainin g mor e moistur e tha n mor e hydrophobi c leaves . I n th e presen t

stud y th e contac t

angle s o f

lea f surface-wate r

droplet s an d laborator y estimate s o f water-holdin g capacit y wer e somewha t positivel y correlated . O f th e tre e specie s examined , matur e leave s o f Platanus retaine dth e mos t wate r an dha dth e lowes t

contac t angles . A t

th e othe r

extreme , th e leave s o

f Liriodendron ha dth e lowes t

water-holdin g capacit y an dhig hcontac t angles . Althoug hRobinia leave s ha dth e highes t contac t angles , the y wer e intermediat e i n water-holdin g capacity , whil e leave s o f Liquidambar

wer e intermediat e i n bothmeasure s o f wettability . Th e relativel y hig hwater-holdin g capacit y o f Robinia ma y hav e bee nFoliar effects o

f simulated

acid rain II. 41 3 becaus e thes e leave s wer e no t spraye di n situ. Difference s i n contac t angle s amon g tre e specie s coul db e du e t o th e distributio n an dnatur e o f waxe s overlyin g th e cuticle . Bothth e chemica l compositio n an dorientatio n an dpatter n o f surfac e waxe s o n th e cuticl e ar e importan t determinant s o f

lea f wettabilit y (Holloway , 1969a , b ; Leece , 1978) . I n additio n t o th e effect s o f superficia l waxes , contac t angle s ma y b e altere db y surfac e roughnes s (Wenzel , 1936 ; Gray , 1965) . Th e presence o f hair s may decreas e contac t angle s (Boize , Gudi n & Purdue , 1976) , bu t thi s ca n b e dependen t o n th e basi c contac t

angle . I f

th e angl e i s originall y les s tha n 90° , increase dsurfac e roughnes s furthe r

lower s th e angle , bu t

i f i t i s greate r

tha n 90° , the n i t

raise s th e angl e (Wenzel , 1936 ; Fogg , 1947) . Surfac e roughnes s ma y partiall y explai n th e lo w contac t angle s observe dfo r

Platanus. Numerou s cuticula r striation s covere dth e adaxia l surfac e o f

Platanus leaves , an dbranche dcoverin g trichome s an dsunke n stomat aoccurre da s well , al l o f whic hmigh t

ac t collectivel y t o lowe r

th e contac t angle . Robinia leave s showe dth e highes t contac t angles , a s migh t

b e expecte dfro m th e presenc e o f

trichome s an dadens e coverin g o f crystallin e wa x deposit s o n adaxia l surfaces , althoug hth e flattene depiderma l cell s an dabundan t trichome s ma y hav e als o contribute dt o th e intermediat e water-holdin g capacity . N o attemp t wa s mad e i n th e presen t stud y t o estimat e th e relativ e contribution s t o th e determinatio n o f

lea f contac t angle s mad e b y epicuticula r wa x chemistr y an d distributio n an dlea f

surfac e feature s suc ha s trichom e type , numbe r an dpositio n o r stomata l position . Nonetheless , i t i s probabl e tha t

ther e ar e primar y an d secondar y effect s o f

eac ho n lea f

contac t angles , an dtha t

th e relativ e importanc e o f th e variou s feature s varie s wit hth e species . Fou r o f th e tre e specie s o f

thi s stud y ar e subject s o f apreviou s repor t

o n th e effect s o f

simulate daci drai n o n lea f damage , growt han dga s exchang e (Neufel d e t al., 1985) . Althoug hsampl e siz e i s small , percen t damag e amon g specie s i s highl y correlate dwit hbot hth e water-holdin g capacit y o f th e leave s an dwit hcontac t angles . Platanus leaves , th e mos t wettabl e b y ou r

presen t determinations , wer e damage dth e mos t

b y repeate dapplication s o f simulate daci drain . Matur e leave s o f Liriodendron, wit hhig hcontac t angle s an dver y lo w water-holdin g capacity , wer e th e leas t damaged , i n term s o f

percen t necroti c lea f

area , wrinklin g an dabscissio n (Neufel de t

al., 1985) . Liquidambar, whic hshowe dintermediat e wettabilit y i n th e presen t study , als o showe dintermediat e degree s o f damage . Robinia show s a somewha t

anomalou s response . Althoug hi t ha dth e highes t

contac t angles , i n orde r o f damag e i t

wa s secon damon g thes e specie s (Neufel de t al., 1985) . Thi s ma y hav e bee n du e t o th e metho db y whic hdamag e wa s assessed . Fo r Robinia, entir e rachise s an dleaflet s ofte nabscis e afte r exposur e t o th e aci drains , eve n thoug hleaflet s themselve s appeare dgree n an dhealthy . Los s o f arachi s wa s score da s 100 % lea f loss . Actua l damag e t o leafle t lamina e wa s quit e low , whic hwoul dcorrelat e wit h th e hig hcontac t

angle s measure dfo r

thi s species . I t doe s no t

appea r tha t lea f wettabilit y i s correlate dwit hth e susceptibilit y threshol do f

tre e leave s t o aci drai n a s muc ha s wit hpercen t damag e tha t

occurs . Accordin g t o Neufel de t al . (1985) , th e fou r

hardwoo dspecie s exhibite ddamag e a t approximatel y th e sam e p H leve l (les s tha n p H 3-0) . I n Keeve r & Jacobson' s studie s (1983a , b ) contac t angle s wer e als o mor e closel y relate dt o th e degre e o f damag e tha n t o th e threshol dfo r damage . I t

mus t therefor e b e conclude dtha t th e susceptibilit y threshol dan dresistanc e t o damag e ar e no t necessaril y linked . I n th e presen t

study , contac t

angle s o f

youn g an dmatur e leave s o f Platanus, Liquidambar, Liriodendron an dRobinia wer e no t significantl y differen t

an dconse -4 J 4 B . L . HAINE S e t al. quentl y wer e poole dfo r subsequen t

analysis . However , i n othe r studies , specie s specifi c difference s i nlea f wettabilit y occurre ddurin g maturation , resultin g fro m change s i nwa x an dcuticl e developmen t (Juniper , 1959 ; Marti n& Juniper , 1970 ; Bake r & Hunt , 1981) . Fo r

example , youn g leave s o f on e isolin e o f

Glycine ma x

ha d lowe r contac t angle s tha nolde r

leaves , an dthi s wa s correlate dwit hgreate r damag e t o younge r

leave s b y aci drai n(Keeve r & Jacobson , 1983b) . A s emphasize db y Keeve r & Jacobso n(1983b) , rapidl y expandin g leave s ma y hav e lo w rate s o f wa x productio nan dthereb y develo p discontinuitie s i nth e coverag e o f waxe s ove r

th e lea f surfac e (Bake r

& Hunt , 1981) . Sinc e th e cuticl e i s mor e hydrophili c tha nth e surfac e waxes , thi s result s i nlowe r contac t angle s (Holloway , 1969a) . Furthermore , rainfal l acidit y i s ofte nhighe r i nsprin g an dsumme r (Hornbeck , Liken s & Eaton , 1977) , aperio dcoincidin g wit hrapi dlea f expansion , an dth e potentia l fo r folia r damag e woul dtherefor e b e greates t a t thi s tim e o f

th e year . Th e leachin g o f

nutrient s an dothe r

substance s fro mleave s i n respons e t o aci d rai nha s receive dattentio nrecentl y (Evan s e t al., 1981 ; Keeve r

& Jacobson , 1983) . Becaus e th e wa x componen t o f th e cuticl e i s though t

t o b e responsibl e fo r

reductio n o f nutrien t

losse s b y leachin g (Marti n& Juniper , 1970) , lea f surface s an d wettabilit y wer e examine do ntw o specie s fo r whic hrate s o f

minera l elemen t leachin g i n respons e t o simulate daci drai nhav e bee ndocumented . Haines , Chapma n& Mon k

(unpublished ) showe dtha t th e highes t

leachin g rate s occurre d i nth e herb s Erechtites hieracifolia an dErigeron canadensis. Ou r result s sho w tha t Erecht.it.es leave s ha dth e lowes t mea ncontac t

angl e ( 0 = 70-1° ) o f

th e si x specie s examined . Adaxia l lea f surface s o f

Erechtites ar e glabrou s an dwaxless , an d compose do f

flattene depiderma l cell s wit hasmoot hcuticle . Th e resultin g highl y wettabl e leave s o f

Erechtites see mt o b e mor e subjec t t o leachin g tha nanothe r specie s examined , Ouercus pnnus. Haine s et . al . (unpublished ) reporte d1 0 t o 100-fol ddifference s i nleachin g rate s betwee nErechtites an dQuercus, whic hi s consisten t

wit hexpectation s base do nlea f surfac e characteristics . Leave s o f Ouercus ha damea ncontac t angl e o f

101-5° , an dadaxia l surface s ar e covere dwit h aspars e bu t

distinc t laye r o f wa x granules , indicatin g alowe r degre e o f

wettabilit y tha nErechtites leaves . Keeve r & Jacobso n(1983a ) wer e abl e t o correlat e folia r damag e o f

soybean s fro msimulate daci drai nwit hfolia r leachin g an dlea f

contac t angles . The y observe dtha t thei r glabrou s isolin e o f

Glycine max, whic hha dmor e wettabl e leave s tha nth e pubescen t isoline , showe dmor e damag e t o aci drai nan d wa s mor e pron e t o folia r leachin g o f

8 "Rb . The y sugges t

tha t th e greate r

wettabilit y o f th e glabrou s isoline , a s indicate db y lowe r mea ncontac t

angles , ma y hav e bee n afacto r i nth e observe ddifference s i nfolia r sensitivity . Beside s ou r

ow nresearc han dtha t o f Keeve r & Jacobso n(1983a , b) , w e kno w o f n o othe r

studie s relatin g eithe r lea f water-holdin g capacit y o r contac t angl e t o damag e b y aci drain . Th e effect s o f increase dretentio ntim e o f aci dprecipitatio n o nwettabl e leave s (i.e . water-holdin g capacity ) an dexten t o f surfac e are acovere d b y rai ndroplet s (i.e . lea f contac t angle ) o nsusceptibilit y t o damag e b y aci drai n ma y provid e insigh t

int o th e mechanis mo f folia r damag e b y aci drain . On e o r bot h o f thes e characteristic s shoul db e quantifie di nfutur e studie s becaus e o f th e possibilit y tha t

thes e simpl e measurement s ma y b e usefu l firs t indicator s o f

th e resistanc e o f

plant s t o aci drain .

ACKNOWLEDGEMENT S Suppor t fo r thi s researc hwa s provide di npar t b y aUniversit y o f

Georgi aFacult y Researc hgran t

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