growth Effect of nitro gen source on response to salinity stress wheat

In maIze and

By O. A. M. LEWIS*, E. O. LEJ DI AND S. H. LIPS

P lant A daptatioll R esearch U llit , Th e Jacob Blausteill Institut e for D esert R esearch, Ben C llrion U lli'L'ersity 01 the Nege'L', S ede Boqer Campus, Israel 8-1993

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' rh e e fleel 0 1' HmnlOnium 'lIld nitra te nutri t io n on mai zc and \\"h cat g ro\Vn hyd ro [)o ni eall) ' a nd sa linity st ressed II'<I S

8ssessed fro m men surem ents of gro\\"th rate and gas exch a nge. In both m a ize and wheat the Hmmonium- g ro \\"n p lants lI'ere mu c h more scns itin' 10 s, Jlinit y toxi c ity than nitTate-gro\\"n plants parti c ularly \\"h e n ex p osed to

6 ()- RO m ~ 1 sa linitv, Shoot gr()\nh \\"as reta rd e d to ¡¡ far g reate r ex ten t than root g ro \\"th in sa linit\' - st rcssed [)Ian ts 0 1' b o rh \\"h eat 'Ind mai ze \\'ith e ith e r nirrogen so urce,

There \\"as no s ig nili ca nt decrease o f photos\' n theti c ra te in salinity-s tressed pl a nl's 01' e ith e r s pee ies fed nitral t' o r alllmonium, exee pt in seH'rch' \\"ilt ed [)I a n ts o f both s pec ies fed nitrare 0 1' ammoniu1l1 el( th e hi g h es t (XO 1ll ~ 1 )

s alinit\, concentnnion , The same \\"a s tTu e 1'0 1' s tomaral condu c ta nee , transpiration rale 3nd transp iration ratio

(\\'a te r use e Hi c ie ncv), In nitnll'e- fe d ",hca t, mi s in g th e ea lcium concc nrrari o n fro m 2 t'o 12 nHI in the [)resenee of 6 () m~1 sa linity [)rodueecl nn II " c, inc rease in g ro\\,th, Thi s eHect is nsc ribecl to illlprn\'ed nitrate u[)tak e due lO

c alciulll [)rotect ion o f th e nitrate tran sporte r and \Vas not e l'ident in ammonium- g ro\\'n ",heat, Poss ibl e reasons for t h e dille re ntial cHec ts o f amlll o niulll ancl nitral'e nutr i¡i o n are c1iscussccl,

I-"':' ey words: Salini ty t()xi city , nitrate nutritiun, anll110tÚUIll nutritio J1, c a1ciulll nutri tiun, photosy nth es is. Illai ze.

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I NT H O D lIC TI ON

Two major e tlec ts h ave been id entified as th e probable causes 01' sa linit y toxi c ity in va riou s plants: th e iuni c e lfec t and th e usmotic effect. Th e ioni c e fi'ec ts inc lude inte rfe rence with nitrogen uptake, dis locat ion 01' nitrogen assim il a tion and pro te in asse lllbly, inte rfe ren ce \Vith the tran sport 01' essenti a l ion s within th e pl ant and a lowering of n et photo­synthet ic rates in the affec ted plants , Thc oSll1otic e flects are assoc iated wirh lack of ce ll wall exren s ion a nd ce11ul a r expans ion lead in g to cessa tion of g ro"'th, A range 01' upiniuns exist as ro whic h uf thcse facto rs i s chieA y operat ive in th e m anifes tation 01' salinity tox ic ity in various plant spec ies , Rawson (1 986), for

examp1e, reports a sa linity- indu ced d ec rease III

p hotosynth et ic rate in wh ea t and barl ey , wh il e wa te r u se e Hi c iency is onl y marg ina11y afFected, Downton ( 1977) al so reports a dec rease 01' photosynthe ti c rate in salinity-stressed g rapevines with an acculllu lation 01' intermediates 01' the g lyco lyti c pathway , T e rry &

" But <ln y Dcp<lrlm enl , U ni\'ersill' ofC"pc To\\'n, H.unclcbosch , 7700, Suulh Arríe",

\"' aldron ( 1986) , h owevc r, obsen'ed no etfect on the rate 0 1' photosynthes is in s uga rbeet 01' sa linit ), leve ls 01' up to 250 m ;V1 in the feedin g medium, the toxi c it), e f-Tec ts b e ing brought about b y sa linity- induced changes in leal' wate r sta tu s which co uld b e alm os t completely oA'set by inc reases in relati,'e hUlllidity, HuHaker & Rains ( 1986) repo rt an in c reased activity 01' th e nitrate transporte r b y th e addition 0 1' ca lc ium to sa linity-stressed ba rl ey, this inc reas ing the rate 01' nitrate ass imilat ion and seedl ing g ro\\,th in these plants , H e la l & lVIenge l (1979) repon an imprm'e­Ill en t 01' growth and nitrogcn utili za tion in yo ung, sa lini zed barley plants b y the addition of potassiulll to th e sa line nutri ent Ill edium, T e rlllaat & lVIunn s ( 1986) hm'e shown that both osmot ic and ioni c effects are operative in sa linity toxi c ity induction in barl ey, wh ea t and c love r, th e ioni c e tTec ts be ing asc ribed to a poss ib1e d ec rease in th e rate o f transport to th e shoot of an essenti a l nutri ent,

In the work to b e described h ere furth e r fa cto rs which co uld b e ill\'o h-ed in th e response 01' p lants ro sa linity stress ha ve been itwest iga ted: th e etrect 0 1' rh e foml in which nitrogen is fed to th e plant

(am m o nium o r ni trate) and the p h otosyn th e ti c path way (C3 o r C4) w hi ch th e p lan t possesses. Th ese effects we re quant ifi ed b y th e m easurem en t o f g rowth rate, moisture eontent , root: sh oot rat io , photosynth et ie rate, transpirat ion rate, s tomata l

co ndu c tan ce and t ran spirat ion rat io (wate r use cf-lie ien ey) in the expe rim ental plants.

MATE !!I A L S ANO :vIET H O O S

G rlJzu / h CO l1diÚOIIS

Tri /iC/1111 aes /iVIIIII L. va r o Barkay an d Zea mays L . varo H aze ra were g ro wn to 31 and 2 1 d respect ive ly JI1 h yd ropon ic culture, after w h ich rh e p lanrs we re h a r"ested.

T h e ma lze p lanrs were ra ised 111 rhe open dur ing Jul y and August unde r eondi t ion s s uitab le fOI' plants possessing th e C4 path way. M idda y irra cli ance was c. 2500 l' E m "s 1 , miclda y temperatures Au ctuated between 2X an d 35 oC and ni g ht temperaru res did not fa ll be low 20 oC, Da ytime rc lat ive humidiry

va ri ed between 20 ancl 35 °o. Th e wheat p lants we re ra ised 111 a fib re-g lass-roofed g reenhouse during

Scptembe r an d October unde r conditions more s u ita h le ror pl an rs possessi ng th e C3 phorosynth eti c pathway. Midday temperarures 111 t he g reenho usc Hu c ru a ted between 25 an d 30 oC w ith nighr rem­penltures berween 7 and 14 oC. Daytime relat ive humidities we re between 25 and 35 (jo bur ni ght- time

humiditi es rose on occas ions to 85 "". M idda y irradia nce on the usuall )' c loud lcss days was measu red at between 700 and 750 l/ E m - t S- l.

¡;;xperilll ell/al de /ail

1 n the maize ex periments, e ig h t p lants were g rown in each of sixtee n 20 l p lasr ic conta ine rs with ho les d rill ed in th e lids to accommodate them . 'rhe plants we re g rown to 21 days on we ll -aerared Long Ash ro n growth med ia modified to co n ta in nitrate-onl y o r am­m o nium -on ly as the 4 mM ni rrogen souree (1I e", irr, 1966); rh e pH of th e solu rion s was m<l in ta in ed at between 7·0 and 7·9 . T ",o eontai n ers of e ight plants eaeh se rved as rhe non -sa line contro l fo r the nitrate­fed pl an ts and a furth e r two for rhe ammo n ium - fed p lan ts. T he othe r conta ine rs we re c1iv ided into 20, 50 and 80 mM NaCI treatments (2 conta ine rs each ) fo r ammonium-fed p lan ts and nitrate-fed plants. Th e p lan ts we re harvesred in pa irs afte r 21 days, div ided in to root and sh oot, and the fresh an d dry we igh t of eaeh p<l lr dete rmin ed . In the wh eat ex pe rim ents no n -sa li ne co n t ro ls ",e re as for th e malze expe r­iments but o nl y one sa lini ty leve l, 60 m M NaC I, was used. T hi s IS th e app rox im ate concentration of sa lini t y in the Negev aqu ife r , ",he re the major so lu te IS NaC I. Previous ex p e rimentation had shown thi s sa linir y leve l to he sati sfac tor y for the produ cti on of

stress symptom s in wheat w itho ut killing th e plants . The remaining conta ine rs "'e re di vid ecl in to 2, 6 and

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12 m :\'1 C a treatme nts (2 co ntaine rs each) fo r salinit y

s tressed nitl'a te -fed a nd ammonium-fed pl ants , Th e p la nts w e re h a rves ted afte r 3 1 d ays and trea ted as in the m a ize e xpe l' im ents , 1 n a ll th e a bo \'e ex pe riments NaCI was add ed to th e nutri e nt solu t io n s unl\' aftcr

th e plants w e re 7 d ay s o ld an d th e n in 20111\1 p e r day i n c re m e nts ,

G a s exclwlIge o llalysis

Net ph o tllsynthe ti c rate (p,,) and tran spiration a l

w ate r lo ss (7~, ) we re d e te rmin ed hy th e use of a P arkin son' s lea f c hmnbe r li nk ed 1'0 an AD C L C A

infrare d g as an a lyse r (A nal yt ica l D eve lopme nt C or­p uration , Hodd esdon , Eng la nd) , Dcte rmination s

\",e re m a d e on fiv e sep a rate plants b e long in g to each t r eatm e nt and th e results fo r each trea tm ent

ave raged , F o r mai ze pl a nts, gas exchange d e te r ­rnin a ti o n s \Ve re made an ho ur be fo re midda y al' an i rradi an ce 0 1' 250ü ¡t1-;: m ~ S- I, a tempe rature 0 1' 35 oC

a nd an ambi e nt relati\'e humidity 0 1' 30 !l ", For

\", h ea t pl ants , t h ese d e te rmin ati o ns we re m ad e at an irradi an ce 0 1' 700 I I E m-~ s 1, a tempe rature 0 1' 28 oC

a nd a n ambi e nt re lat ive humidi ty 01' 35 "" , Stol11i1ta l conduc ta n ce (e,) to wa te r vap o ur was calculated

f rom th ese fi g ures us ing Parkin so n 's fo rmulae (AD C LCA in s tru c ti on manual, 1986), and trans piration r a ti o (TR) was ca lcu la ted b y di\'iding T, by p", G as exchange d e terl11in ati o n s we re mad e on cl ear days 1

0 1' 2 days b efore th e date 01' h a lTes t ,

RE SU LT S

T h e resp ecti ve g ro \Vth res p o nse 01' nitra te- and a ml11 oniul11-fed mai ze p lants to salinit y stress can be

o b se r ve d in th e datn rccO l'ded in Tab le 1, Fro m th ese data it is obv iou s th a t nitrate -fed p la nts a re fa r m o re

salt-to le rant than th e ir ammonium-fed counte rpa rts und e r th e ex perimenta l conditions, vVh e reas nitra te ­

fe d plants sho w ed no redu ction in dry mass and only

a s li ght reducti o ll in fres h l11 ass up 1' 0 th e 50111\1 sal inity leve l, th e effect 0 1' salini t ~ , o n th e fresh a nd dry m ass 01' ammonium-fed pl an ts e \'e n a t a cOll centration 01' 20 1ll ~ 1 was \'e ry m a rk ed nnd

becam e in c reas ing ly so with in c reas ing sa lini ty, \V hil e a ll th e nitra te -fed p la nts w e re still g ro \\' ing

\'i goro u s ly at th e ílO m\'1 sa lini ty le ve l, m any o f t he alllmoniull1-fcd p la nts \I'e re sho \l'ing s ig ns o f se\'e re wilt and sOlll e lI'e re actu a ll y d y in g , Th e contras t 01' th e salinity res po nse of th e pl:lI1ts fed rh e t\l 'O

nitrog en sources is am p lified b~' th e fa e t th a t unde r non- salin e condition s th e allllll o niul11 - fed pl an ts

w et'e pe rcep t ibly large r t h an th e nitrate- red plants , a fenture alread y n o te d b y lVI urph~' (1 984- ),

An inspec tion 0 1' th e shoot: roo t ra tio s reeo rd ed in Table 1 sh o \Vs that in plants red b o th nitrogen sou rces th e sa 1 i n i t y e A'ee t on g rOll'th was m o re

noti cea ble in th e s hoo ts rhan 111 th e roots , A

relllarkablc feature of th e non -sa linity-stressed

plants in (hi s ex pe rim cnt \I'as rha t ('he rres h \I 'e ig hr shoo t: roo t nlti os in the <lmlll o niulll fcd pl a nts \Ve r lO s lll a ll e r than those 0 1' t h e nitra te-fed pl a n ts, Thus th e

re tarding effec t 01' allll1lolliulll nutriti o n on roo t g rOl\'th o b se l'l'ed in C3 plan ts su ch as b a rl ey an d

\I 'h eat (Le wi s & C h adwi c k , 1984-; L e \l'is, F ulto n & Von Ze le wski, 1987) \I 'as no t appa re n t in thi s C"¡' plant, Th e re \I'as al so a s li g ht d ec rease in th e Ill o is ture conte nt 0 1' both <Ill1lll o niul11 and nirnHe red p lants \\'ith inc reas in g salinity ,

Ne t photos ~ ' nth e ri c rate sho \l'ed no s i ,~nifl cant res po n se to sa linity s tress except rol' the se \'e re ll' wilted <1 lllmonium red l1lai ze plants exposed 1'0

80 n1\'1 Na Cl (Tabl e 2), In thi s case it is d o ubtful \\'h e th e r reduced ph o tosy nth es is was du e 1'0 rhe io ni c effec t 0 1' rh e sa linit\, 0 1' rhe nutri e nt so lution , as \I 'ate r

s tress had a p parentll' a lread\' eau sed pl a nt cnlhpse and él co nside ra bl e d ec rease in s to l1lata l eondu c tance ,

Stol1latal condu c tance showed n s li g hr d ec lin e \I' it h inc reas in g sa linity, in s pite 0 1' \I'hi ch t ran spirati o n

rate s ho\l'ed som e inc rease (Tablc 2) , Th e excepti o ns

Table 2. R espollse of ne/ ph% sy llllte/ic raf e, /rallspira/io ll raf e, s/ ollla/al co lldl/I'/a//ce allrl /rallsp i ra/io// r atio

(-lOa/el' uliliz a/ioll eifi ci e//cy) oJ /l/aize plall/s lo difIerl' 1l1 sllli// i ly u il/ cl' //Iralio // s, ,1I(, (/SIIl" ' III l' ll l s (/ r t' "lr mc lI ± s t a nda rd rle7.' i a /ioll froJ/l /lt e /l/ea 11 ,

NaCI conc, (mM)

o 50 SO

o 50 80

Net photosynth eti c rate (pm o ] m " s- ')

25,95 ± 1,90 27-5 1±3 '2 1 24'64 ± I'SI

28' 11 ±3 '75 2S '39 ± O'83 15,62 ± 10'45

Transpirari on rate (mmol m 's ' )

Stomatal Condu ctan ce (to 1-1 ,,0 molecul es ) (mm o-I m " s ' )

N itrare-fed plants

8'0.J. ± 0 52 376±32 9'1 7± O'19 33 7 ±39 9,44 ± O'.J.3 302 ± 39

Allll1lonium-fed pl ants

9'.J.2± 049 I002± 046 7'24± 2,58

420 ±83 373± 45 190 ± f 19

rrra n s rir~lti on

rati o

(mol I-I ,O/ mol Ca,)

309 333 383

335 353 .J.64

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to thi s were th e 80 111 M sa linity-s tressed a l11l11 o niul11-

red p la n ts whi ch sho wed seve re re ta rdat io n 0 1' sto l11 ata l condu c tan ce and tra n spirat io n ra teo TR sho\Ved an in c rease w ith sa li n ity concen t ratio n ( i. e. a d ecrease in wate r- use e Hi c ie ncy) in hoth a l11l11 o niul11-a nd ni t rate- red pl ants, es pec ia ll y in th e SO 111 :\1 sa lini ty-s tressed al11l11 o niul11 - reJ p lants.

In th e ex pe ril11 enta ti o n \Vith wh ea t p lan ts o nl y (m e salinity leve l was used (60 111 M l\: aC I) . Th e calciul11 leve l wa s vHri ed he tween 2 111:\1 (approximate ly th e no rl11 al leve l found in L o n g As hton nu t ri ent so lu­t ions) a nd 12 111:\1 in o rd e r to obse rve ",hether th e b ene fic ia l cflec t 0 1' Ca un th e g ruwth u r salini tv st ressed ni t rate g ru wn b a rl ey planrs (1lu fla ke r & Ra in s, 1(86) eould a lso be fo un d in sa lini ty-st ressed

ni t rate and a111 111 0 niu111 -grown wh ea t. Th ese results a re rep o r ted in T abl es 2 and 4. I t ",as no t p oss ibl e to

in ves ti gate thi s ea lciu111 d fee t in salini ty-s tres;;ed 111 a ize plants b eca u se u f th e earl y e nd 0 1' t h e gro",ing sea son .

Th e fr esh and dry mass data reeo rded in Tabl e 3

sho w that und e r non-sa li n e eo nd irio n s, nitra te ­g rown wheat p la n ts \\T re large r than am111 0 niUIll­g ruw n plants, a rea ture co n t rast ing ",ith th e results rep o rted above fo r m a ize pla n ts . Like ma ize, h O\\'­

eve r , th e am l11 o n i1l111-g row n wh eat plan!s s howecl a g rea te r se ns it iv ity to sa lt s tress th a n di d the nitra te g rown p lants (42 7..'S. 33 "lO fresh mass g ro wth re ta rdati o n ) . ,},h e s hoot: rou t ra ti os in bo th <I m­moniul11- anJ nitra te-fed p la n ts dropped p e reeptibh' in response to sa li nity, indi ca ting that shoot g rO\\'th was l11 0 re sc ve rcl y af-ree ted by salinit y rhan root g row th .

In a l11111 onium - fed plants rhe Ic\T I 0 1' ealcillm in th e feedin g 111 edi a produ ced no s ig nifl ca nt efleet o n th e g rowth rate 0 1' t he sa lini ty-s tressed p lants (T abl e 3). 1 n ni t rate- fed pl a n ts , however , pl ants p rov ided \V ith hi gh e r eo ncentrat io ns 0 1' ealc ium in th e ir feedin g 111 ed ia s ho wed d ec reased sens it iv ity to s<1l­ini ty, th e fresh mass o f sal ine -st resse cl p lan ts g ro",in g in 12 111M C a b e ing 11 "" greate r than th use gro",in g in 2 111M C a . Th ese d a ta se r ve l"O suppon th e e vid c nee of HuA'a ke r & Raill s ( 19R6) th at ealc ium se n 'es as a pro teetant 1'01' th e ni t ra te tra nspo rter in th e prese nce o f sa lini ty , lead in g to g rea te r produ c t iv it y in salinit v­stressed pl a n ts.

Th e gas exchange d a ta sho wn in T a b le + do not indica te an y pe rcept ib le e A'ect of sa linit v n I' ca lci ll lll co neentrat io n u n th e ra te o f ne t ph<Hosy nth es is in ammo nillm - 0 1' ni t ra te-fed wh eat plan!s. Th e re does no t appear ro be an y s tat is ti call y signili eant effee t 0 1' calciulll u r sa li n ity leve l on s tolllara l eondu e tanee, tran spiratio n rate 0 1' TR in wh eal' p lants unde r th e ex pe rim enta l eonJitions.

IlI ~CllSS I ()N

Th e 111 0s t s ig nifi ca n t flndin gs 0 1' th e ex pe ril11 en tat io ll re po rted above are tha t in bo th h ydro po ni ea lh'

Table 4. Respollse of lIe / ph%sYII/ltetic ro/e, Irallspira/ioll ro/e, s/o/ll a/al cOlldllc/allce alld /rallspira/ioll ra/io (wa ter u/iliza /ioll efficiellcy) of w hea/ p/allls /0 differell/ cOllcen/ra/ioIlS alld eOlllbilla/iollS of C a alld NaC/

Ca conc. (mM)

NaCJ con c . (mM)

Net photosynth ct ic rate

Transpiration rate

Stomata l conducta nce (to ¡--l.,O molecul es ) (mmo-I m 2 S- I)

' 1 'ranspi ration ratio

(/,mo l m 's ') (mmo l m - ' S ') (m o l H,O j mol CO,)

N itrate-fed plallts

2 2 6

] 2

()

60 60 60

8'5 1 ± O'50 R32 ± 1 73 9·29 ± ()'9 2 8·75± 1· IO

5'8 1 ±ü'46 5·-1-6± 1·11 6'97±O-1-9 7,25 ± O'61

280 ± 29·3 2 17 ± 6,H 285 ± 16, 1 298 ± 35 ·6

683 656 75 0 832

Ammonium-fed plants

2 2 6

12

o 60 60 60

875 ± 1 26 7·9 1 ± 1· 2-1-8'2X ± O'72 7'59 ± 0'53

H9 ± ()'81 6,3 2 ± 1· 53 6·38±O·56 6·0-1- ± O·6-1-

330 ± -1-8·R 226±73 1 268 ± 277 237±39'2

856 799 770 796

l\ 'leasurements "'ere made at a n irrad ian ce of 70() /' E m 's " a tempe raturc of 26- 28 oC and an amb ient re l ati\'t~ humidity of 35 "".

g rown m a ize a nd \\'heat, ammonium-fed plants s h o\V

a co n s ide rably g reate r se n s iti\ ' ity to sa linit~ , than do

nitrate-fcd p lants , an eHect that is lik e ly to b e

e nhan ced und e r fle ld conditions , The ca u se 01' t hi s

e ffect is not imm ediate ly appa re nt but could possib ly

be ascribed to o n e 01' the fol lowing factors,

(a) 1n \Vheat and maize, nitrate ass imil atio n takes

p lace primaril y in the shoot and amlllonium ass imi­

lat ion in the roor. As the roots are in imlll ed iate

contact \Vith the sa lin e containing nutri ent medium

it is possib le that nitrogen assimi lat ion 111 am­rnonium-fed p lants is dis located by ionic eA'ects

w hi ch \Vould not intcrfere with leaf-based nitrogcn ass imilation,

(b) In nitra te-fed p la nts a mal ate- nitrate shuttl e is

operative b e t\-veen s hoot a nd root (Ben-Zioni, Vaadia

& Lips, 1970), The abse n ce of this shuttle in

ammonium -fed plants co uld bring about ion trans­

locato r y prob lems which are exace rbated bv the uptake of NaC! .

(e) The ass imilation 01' th e bu lk 01' nutri e nt

n itroge n III the roots of ammoniulll-fed plants

necessitates the diversion of large quantities 01' carbon to thc root to pro\' ide th e carbon ske leton s 01' the products 01' nitrogen assimilation . It is possible

that this carbon metabolism is inhibited b v the

presen ce of high conccntrations 0 1' sodium and c h loridc ions in the mot,

Th e results 01' this expe rim c nta tion a lso indicare

that in maize and wh eat, inhibition of photosynthl:s is

is not one of the manifestations of sa linity toxicity except as a secondary e/lect in already h eav'i ly

damaged p lants . S uppress ion of nitrate uptake or

assim ilation which ca n be partIy reli e \'ed by the

presence of hi g h co n centration s of calc iulll does appear to be a contributory factor to sa linit y toxicity

in wheat, Our co n c lus ion s a re that oSll1otic factors r esultin g in cu rtaillll ent of ce ll g rowth and eventua l

leaf wilt \\,e t'e the prime cause of sa linity toxi c it\" in

th e ex p e rim enta l plants, but further research on th e

water statu s of sa li nity st t'essed \\'heat and Illaize

plants und e r' th e abo\'e conditions is necessary to confirm this v ie \\',

A C " NO \V L "De E\\ ENT S

O. A,. 1\1. Lc\\·is is gratefu l to 1"i1e Ben-Curion U ni \·ersit\· of the ~ege\' and to the Founuati"n for Hesea rc h

De\'c lopment (eS I R) for thci r 11n'1I1 c i01I ass islancc' in thi s project.

HEFLiHEN C ES

flEN-/' IONI, A., \· .-\ .-\I) IA, Y. So: LII", S. 11. (1(!lO), Corrl'iatinns b et\\'ccn nitT ~II:L' redu cl" io n, protcin s\'nthe sis alld 111:II¡¡t t.:.' ;.J CC UIlHI ­

lation. P/¡ysi% g ill PIIII//rlrilll/ 23, 1'03') 10+7.

J)O\\" NTON , \V. J. S. ( 1977). Photosvnlhesis in salt- stressed grape­"¡Iles . . -lustra¡¡(ln ]011,.110/ (~r Planl PI¡ysin/ogy 4, I S3 I ()~.

1 f¡ ':I. .-\l .. 11. \1. So: \I EN(; I-:I., K. ( 19 74). " ilrogen JI1l'1aholi s l11 of yOll llg b:lrley p lants as aA'ectcd b~ ' !\.f:IC I s;l linjt ~ · :lnd porassiunl. ellll//III/r! Soil SI, +S7 +(, 2 .

II E\\TIT , E. J. ( 1966). SI/I/d (//,,1 WII/a ('''////1'1' !lI l' /llOds //s l'd i// /il l' S /lIdy nI Planl .VI/tri/ion. 'T'l'c hnical C Olnn1L1TÚ catio!1 :\lo. 22 (rc\'ised), C 0I111l10!l\\'ca lrh l1ureau 01' Ilorticulrllral i1nd PI;ln­tation Crops, Eas t :VlalJing, COl11l11ol1\\"ealth :\ g ri c u ltur:11 Bureaux. fo'arnhal11 n.o~ ' al. Englalld,

1-ILTFA"I·:n, R. C. So: R .-\l NS , D. "V. ( 1986). N lISIO ':f/ici"lI ty liS i'z{llltnted by S assimi/a/ioll in har/e.\' (',\"!>()sed /n salilli/I', 111 : SIII! l/lid Plall/ Inlerar/ion 'W /IIt Snlilli/\', Kearnc\' FOllnd ,;rioll Fin.'­Y ear Repon 19RO 1485 ( EcI. hy .i LL"lL'\' ), ;)1'.3.1 3R. Di\' is iol1 nI' .-\gri cll lturc anJ :\atlll':d Rcsoun:cs, L1Ili\'crsit\, 01' Cal iforlli: I, J3erk e Jev. .

I, E\\"IS, (J .. -\. \1. So: C IIAII\\ 'W", :-i . ( 19R.1) . ...\11 ,e,,, il1\"estigatiol1

into Ilitr()gen ~l ss inlila tinn in h yd rollollica ll y-gro\\'1l h:lrle~' ( H ord('1I111 7'1I!gare l ., C\' , C liIlJlL'r) in rl' sponse lo nitrat l'. ,lInnH)J1iutll <llld tllixl'd nitra re and anllllOlúuln llutrit"ioll, ¡V(ln'

¡Jilyll/logisl 95, üJS 6+r,.

LE"''', O. A. :'1 1.. FL·I.TO N, 13. So: \ ' t1 N ZELE\\"Si;l, .-\ . A. A. ( 19H 7). Dif-rcrcnrial disrributioll 0 1' c:Jrbo ll in respo nse lo niIT, ¡te. al11lTIOniul11 and nitratc + anlnloniulll nutritioll in \\'h ea t , In : ¡I/o.-gol/ir N i/rogell ¡1lNoholisl/I (EcI. by \\'. R. L' lIri e h. P . J. Aparicio, 1'. J. S\Tett So: F . C astillo). pp . 2+0 2+-' . :-iprin¡.:er­\"erlag, I.lcrlil1.

;VlnIPIIY, A. T . (19X+I . .4 "N sI/Id.\' uf lile cJ.feds uf I/ilrall' ,

(llJ'UlInnilllll ond I/ilra l(' plus al1UIlO''¡U11I /11111';';011 ;1/ Zca :V1ays L. !\!I.Se. 'Th cs is, l Tni\'crs it y of C<lpC 'To\\'n .

Rt\ WSO N , H . IVI. (19X6 l. Gas e"change and g ro\\'th in \\'h ea t "mi burley grnwn in salt . Auslra!i(lll JOIII'lIflI (~r Planl Pltysi%/-{y 13, +75 +89.

TEHMAAT , A. & \l1l ' NNs, R . ( 1 'J¡)G). Ust'S (JI' co ncc ntr"ted nlacrol1utTicnt su lu tion {"o scpar:ltc OSI11oti c fr0l11 ~<ll' I- spcc il -i c

erIee ts on plant grO\\'th . .4l1slra!i1/1I ]II/I/'II(I! uf P!I/III Pilysiu!o¡.;y 13, SO'J 522.

TEnH\', !\l. & \Vt\I.IJH O:-; , L. J. ( I'JH6). Salinity respon ses 01' crop plants in te rms (JI' kar expans ion and pho\'(IS)'nth cs is. 1 n: Soi! (llId Planl In/ f'fllr/;oll wi,1t Sa/ini,.\', Kc arney Foundatioll Fi \'c­Yca r Repun 191>0 1<)1>5 (ElI. b y J. Lctcy), pp . 11 - 17, ])i"isinn nI' Ag ri culture ancl l'\atura l Resources , U ni"crs it )' nI' Ca liforni a, I3nkclcy.