Effects of aluminum on red spruce seedlings in solution culture

Environmental and Experimental BtJlanr, VoL 27, No. 4. pp. 48!t 498, 1987 Primed in Greal Britain.

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0098-8472/87 $3.00 ~ 0.1)0 1987. Per~am.n Journals lad

E F F E C T S O F A L U M I N U M O N R E D S P R U C E S E E D L I N G S IN SOLUTION CULTURE F. C. T H O R N T O N , M. SCHAEDLE and D. J. RAYNAL l:acuhy of Enviromnental and Forest Biology', SUNY College of Environmental Science and Forestry, Syracuse, NY 13210, U.S.A. q,Received 19 December 1986; accepted in revi.~ed,/brm 4 Mar 1987! TnoRxrox F. C., SCHAEDLE ~I. and RAYNAL D..J. Effht,~ ~!1 aluminum on red ~pruee seedlin~.~ m solution culture. ENVIRONMENTALANn EXPERIMENTALBOTANY 27, 489 498, 1987. Red spruce IPicca rubenr Sarg.) seedlings were grown ira solution culture at pH 4.0 with 250, 500, 1000 and 2000/*M A1. To evaluate the cffccts of cuhurc medium concentrations comparisons were made belween A1 efl~'cts in the full strength medium and a 5-tbld diluted medium. Overall, the etti'ct of AI on seedling growth and nutrient composition was more severe in the 1/5 strength medium. In both media A1 reduced root bionmss to a greater degree than shoot biomass. Tap root and shoot elongation were significantly reduced by 250 pM both in the fhll and 1/5 medium. However, total length of lateral roots was greater in the 1/5 strength mcdium compared to the lhll medium. A1 tissue content increased with A1 solution concentration and was substantially larger in fine roots compared to young needles. Needle A1 content was higher in the 1/5 medium. This may explain the greater A1 it\jury observed in l/5 strength mcdium. [t suggests that ionic strength has a significant effect on AI translocation. With the exception of phosphate, A1 reduced tlm, ionic content of plant tissues. The effects were generally more severe in the l/5 strength medium and were observed at the 250 ,uM AI concentration. At higher A1 levels reduction in tissue Mg and Ca may have been sufficiently severe to induce nutrient deficiences. INTRODUCTION

situations the biological factors may override tile purely physical ones. "' T h e characterization of .\I.UMINUM toxicity is an i m p o r t a n t thctor limiting a l u m i n u m eft'ects on plants requires the descripthe productivity of acid soils. :> ULRICH :24 hypotion not only of ionic strength effects but also the thesized that one cause of silver fir (Abies alba quantification of a l u m i n u m c a t i o n - a n i o n interMill./ decline in Europe is elevated soil solution actions. T h e chemical complexity of soil solutions a l u m i n u m in acid soils. Such a possibility has and the strong interaction between ionic coinstimulated several recent studies designed to position, ionic strength and a l u m i n u m phyevaluate the aluminum sensitivity of totoxicity have necessitated solution and sand cultrees. 1~1.I2.[LI5.17,19,22,23 ture methodology to quantity: a l u m i n u m toxicity'. A l u m i n u m phytotoxicity is modified by ionic However, even using these techniques it has not strength, ~' specific ion effects,' j' and possibly the always been possible to define equiw)cally plant n a t u r e of the charge b a l a n c i n g anions. However, response to a l u m i n u m levels. For example, SCHinternal fhctors including the specificity of trans- I E R 117' fbund no effect of a l u m i n u m on height port systems, competition tbr transport sites, increment or biomass a c c u m u l a t i o n in red spruce m u t u a l precipitation, c o m p a r t m e n t a l i z a t i o n and (Picea rubens Sarg.) seedlings grown ira solution m a i n t e n a n c e of electrical neutrality, can modify culture at pH 3.8 and a l u m i n u m concentrations the efli'ct of external physical factors.:l~ I n m a n y as high as 7400 llXI. In contrast, using sand cul489

490

F . C . T H O R N T O N et al.

ture m e t h o d o l o g y at similar pH, HUTCI-IINSON~1''~ reported red spruce seedlings d r y weight reductions ranging from 17 to 80{}i, at a l u m i n u m concentrations v a r y i n g ti'om 185 to 5125/~M. R e d spruce has been reported to be in a state of decline t h r o u g h o u t much of its n a t u r a l range in eastern N o r t h A m e r i c a ''~'zt~tbr reasons that are unclear at this time. T o evaluate the possibility that a l u m i n u m toxicity affects red spruce growth, we c o n d u c t e d nutrient culture experiments to quantify the effect of" a l u m i n u m on red spruce seedling root a n d shoot growth, biomass a c c u m u lation a n d m i n e r a l nutrition at different nutrient solution concentrations. MATERIALS

AND

METHODS

Seeds of red spruce o b t a i n e d from the Ministry of N a t u r a l Resources, O n t a r i o , C a n a d a , were used in the experiments. Seeds were surthce sterilized in 30°/i, H.,O~ tot 30 min tbllowed by a 30 min soak in 2001, NaOC1. After rinsing with d i s t i l l e d - d e i o n i z e d water ( D D W ) they were placed in an a e r a t e d solution of Bayleton (triadimefon) c o n t a i n i n g 1.5 mg of" 50°i, w e t t a b l e powder/1 for 24 hr. T r e a t e d seeds were then sown into flats o f T u r f a c e (fritted clay.) and grown tot 5 weeks. Flats were a l t e r n a t e l y w a t e r e d with distilled water and tim culture solution of EDWARDS el al.,':" modified a c c o r d i n g to THORNTON el al. c':~: This solution c o n t a i n e d 0.04 m M KH2PO4, 0.25 m M Ca(NO.3)2, 0.5 m M KNO:~, 0.5 m M MgSO~, 0.5 m M NH4NO3, 10/~M Fe D T P A , 46 # M B, 9 ~ M M n , 0.8 btM Zn, 0.3 /~M Cu a n d 0.05 ILM Mo. After 5 weeks seedlings were gently washed ti~om the flats and placed within holes in a styrofoam m a t and floated in the nutrient solution described above. Seed g e r m i n a t i o n and cultivation of seedlings were c o n d u c t e d in growth c h a m b e r s with a d a y - n i g h t p h o t o p e r i o d of 17 hr d a y at 22°C and 7 hr night at 12':'C and a light intensity of 290 /*E m - sec fi'om a c o m b i n a tion of fluorescent and incandescent bulbs. In E x p e r i m e n t 1 60-day-old seedlings (average height, 13.5 __ 3.3 ram) were grown in solutions with A1 concentrations o f 0, 500, 1000, 2000 and 3000 /~M adjusted to p H 4 and a 0 A1 p H 5 control. A l u m i n u m was a d d e d as a mixture of A1C13 a n d A1e (SO4)~ to avoid excessive a d d i t i o n of either anion. T h e CI and SO~ con-

centrations of all treatments were equalized by a p p r o p r i a t e additions of NaC1 and Na.,SO~. A "salt c o n t r o l " with NaC1 and N a . , 5 0 , additions sufficient to provide C1 and SO4 concentration equal to that of the 3000 l l M AI t r e a t m e n t was also included in the experiment. Since seedling growth in the salt controls in E x p e r i m e n t 1 was reduced, a second experiment was c o n d u c t e d in which we did not balance anionic concentrations of the treatments. T h e experimental design of E x p e r i m e n t 2 was a 2 x .5 x 16 [~tctorial consisting of two m e d i a treatinents (M), five A1 concentrations (AI), and 16 replicate seedlings per t r e a t m e n t c o m b i n a t i o n (tbur pots with tbur seedlings/pot). T h e two m e d i a treatments were full strength m e d i u m as described in E x p e r i m e n t 1 and 1/5 m e d i u m in which all nutrients were supplied at 1/5 the ratc of the full m e d i u m . Concentrations of A1 in each m e d i u m were 0, 250, 500, 1000 and 200{) # M . Periodic s a m p l i n g of" m e d i a for Ca, Mg, K, P and A1 verified that t h r o u g h o u t the experiment concentrations of" these elements in both media groups r e m a i n e d within _+.5°,,o of desired levels. A l u m i n u m speciation was also monitored d u r i n g the e x p e r i m e n t as described by, BARNES. :e:' No detectable difference in total or m o n o m e r i c AI was observed, confirming that the A1 present was p r i m a r i l y monomeric. T h e acidity of solutions was adjusted every 2 days with either 1N HCI or 1N N a O H . N u t r i e n t solutions were completely renewed weekly. Each t r e a t m e n t included four replicate 7.2 1 pots containing lbur seedlings each. Pots were a r r a n g e d at r a n d o m within the chamber. T h e e x p e r i m e n t was t e r m i n a t e d after 35 days. At harvest, seedling shoots were washed with D D W , dried at 65°C a n d weighed. Roots were washed in successive 1 min washes of D D W , 0. l m M CaCI a n d D D W , then dried and weighed. Eight seedlings were chosen at r a n d o m fi'om each t r e a t m e n t tbr d e t e r m i n a t i o n o1 elemental composition. New terminal shoot growth tbrmed during the e x p e r i m e n t was used tbr needle nutrient analysis and second o r d e r roots or higher were removed from root systems tbr root tissue analysis. Details of elemental analysis of seedlings arc described by THORNTON el a[. ''-'~'-':~' Estimates ot lateral root length and root density of seedlings were m a d e using tbur seedlings per A1 × m e d i u m

EFFECTS OF A L U M I N U M ON RED SPRUCE SEEDLINGS combination. To determine effects on root length the three longest lateral roots from individual seedlings were measured. R o o t density was determined by counting secondary rootlets in the central 5-cm segment of the lateral roots. O t h e r experimental conditions were the same as described tbr Experiment 1 except that 90-dayold seedlings (average height 24.6 ___6.0 mm) were tlsed al the initiation of the experiinent. Significance of treatment effects was evaluated by analysis of variance. Unless otherwise stated statistical significance ret~'rs to the 0.05 probability level. Where appropriate, Fisher's protected l.east Significant l)ifference (LSD) was used to compare means. RESULTS

&'edli,g 2r,,a',th In Experiment 1 the salt control treatment (4.5 m M NaCI and 2.25 m M Na~SO4) significantly reduced the growth of red spruce (Table 1). Except tbr differenccs in taproot elongation and root dry weight there was no significant difference between the salt control and the 500 ItM A1 treatment which contained 3.75 m M NaCI and 1.85 m M Na.,SO,. Thus, without a salt response curve it is not possible to determine whether the observed growth reduction in the 500 ItM A1 treatment results from a sodium salt effect or an A1 toxicity effect. At higher A1 concentrations (2000 3000 ktM), the effect of balancing ions is expected to be smaller since proportionally smaller amounts of Na were added, and A1 might have been the cause of growth reductions at higher A1 concentrations. Except fin" the presence of sodium in the tissues, the composition of seedlings grown in this experiment was very similar to plants in Experiment 2 grown in the absence of NaCl and Na2SO4. In the second thctorial experiment, only the main elt'ects of A1 and medium on plant size and weight are presented since analysis of variance showed the A1 x medium interaction was not significant. Root biomass exhibited greater sensitivity to AI in solution than shoot biomass in both media (Table 21). Statistically significant reductions in root biomass were observed at the 500 llM AI level in the full medium and at 250 ltkl A1 in the 1/5 medium. T h e pattern of total

491

dry weight response to AI was similar to shoot response. This was expected since shoot weight was four to nine times higher than root weight. T a p r o o t elongation was significantly afl>cted only by AI concentration (Fig. IB). For both the full and 1/5 strength media taproot length decreased with increasing AI in solution. AI 250 ktM A1 taproot elongation was reduced by 16 and 11" b in the full and 1/5 media, respectivcl.~. Length of the longest lateral roots was also reduced but to a lesser extent lhan taproot elongation (Fig. IA). However, the overall mean length of laterals was significantly greater ill the I/5 medium than those at lull strength (263 and 229 ram, respectively). T h e overall mean root density was 14.4 laterals per 5-cm segment ot'rool. Shoot elongation of red spruce seedlings was very sensitive to AI in solution (Fig. ICI. Aluminum at 250 # M reduced height increment 15"~, in the tull and 29% in the 1/5 media. Thus height growth was reduced at A1 concentrations where seedling biomass was not affected. Height growth increment of spruce seedlings in the lull strength media was significantly greater than the l/5 media at every A1 concentration except tbr the 2000 ItM level where they were equal (Fig. 1C). Because height growth increment was recorded only as a measure of the terminal shoot growth, the biomass component of the lower branches was not accounted tiw. Thus reduction in height growth did not always correspond with biomass reduction.

31ineral nulrilion Tissue aluminum omlent. As expected, AI concentration of needles increased with increasing A1 in solution (Fig. 2A). There was no significant effect of either medium or aluminum × medium on needle A1. Except tbr the 2000 ktM treatments where seedlings suffered acute AI phytotoxicity, needle AI concentration was higher in the l/5 medium than in seedlings grown in the full medium. Regression analysis showed a significantly larger initial slope tbr the 1/5 medium compared to the tull medium.' l,, Alumiimm concentration in root tissue (Fig. 3A) generally increased linearly with increasing AI in solution. Root tissue A1 concentration was approximately 1000-laid higher than A1 needle concentration. Aluminum concentration of" roots grown in the

F . C . T H O R N T O N el al.

492

Table 1. F~ff'ectof aluminum and salt on the growth of red spruce. Meam o/25 plant,~

AI concentration

Height increment

Tap root increment

(/~nl)

/mm)

(ram)

Shoot

Root

Total

34 27 24 21 9 9 6

98 93 65 47 33 9 18

327 251 241 218 173 190 51

84 58 38 38 22 19 1(5

417 309 281 257 196 210 78

0 0 sahcontrol* 500 1000 2000 3000 LSD,, ....

Dry weight (mg/scedling)

* NaC14.5 mM and Na2SO 4 2.25 mM added to balance anions in the 3000

/tM A1 treatment.

Table '2. Eft'eel oJ'alumiman and media concenlration on lhe weight (fred spruce seedlings A1 concentration (~zM)

Full strength medium

(rag seedling)

1/5 strength medium

Shoot dry wcight 0 250 500 1000 2000

573.2 549.1 579.8 543.0 234.0 LSD, os(A1,63.9;M, 101.1;AI*M, ns)

0 250 500 1000 2000

135.2 143.7 94.6 54.4 27.1 LSD,.,,~(AI, 17.4:M, ns; AI*M , ns)

0 25O 500 1000 2000

713.6 692.8 674.4 602.4 261.4 LSDII,~(AI, 74.6;M, 118.5; AI*M, ns)

517.3 493.4 394.7 343.1 243.3 Root dry weight 126.3 104.9 83.2 36.2 23.8 Total dry weight

full m e d i u m were higher at 250, 500 and 1000 # M A1 c o m p a r e d to the same A1 levels at 1/5 strength. In the heavily d a m a g e d roots of seedlings grown at 2000/~M A1, root tissues c o n ta in e d the same a m o u n t of A1 regardless of m e d i u m strength.

644.3 598.3 477.9 379.3 277.2

Needle nutrienl composition. Analysis of" variance of the needle nutrient content c o n f r m e d the existence of highly significant A1 effects. Needle concentration of Ca, M g and P were significantly atfected by m ed i a strength. The aluminum × m e d i u m interaction was only significant

EFFECTS OF A L U M I N U M ON RED SPRUCE SEEDLINGS

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il~le°

120 lO~

~

150 50

493


[

MnI

-B

4o 2O ,~o ~o

~o~

~

o

2~0d0 ,~

AI(uM}

C

60 5~

• ,,.° I

.,.d I

10 o 2~o~

I~oo

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(uM)

l"u;. l. ttcight and root growth of red spruce sccdlings as a function of AI solution concentration. Q) Q) O Full medium; • • • 1/5 medium. A. Lateral voo! lcngth. B. Tap root elongation. C. Height ire'tease.

l~r calcium and magnesium. A l u m i n u m × m e d i u m interaction term lbr AI, K and P app r o a c h e d significance ( F - 2.00, P - 0.104: 2.18, P - 0 . 0 7 9 ; and 2.12, P - 0 . 0 8 7 , respectively). Calcium and M g concentrations (Figs 2B, 2C) of needles were highly sensitive to increasing AI in solution. In the full m e d i u m significant reduction of needle Ca was first observed at 500 l l M A1 ( 11 ~'(,) and M g at 250 I~M A1 (27°~,) when c o m p a r e d to the 0 AI controls. In the 1/5 strength m e d i u m the effect of A1 on reducing Ca and M g concentration was more d r a m a t i c . Even at 250 tlX.l AI, Ca and M g tissue concentrations were reduced by 40 and 82"0, respectively. M e a n Ca concentration, a v e r a g e d over the AI treatments,

was 0.80 mg/g in the full m e d i u m and 0.67 lng/g in the 1/5 strength medium. For Mg, tile mean concentration fi)r the AI treatments was reduced fi'om 0.64 mg in the tull m e d i u m to 0.34 mg in the l/5 m e d i u m . These differenees were slatislically significant. Both AI and m e d i a concentration had a sio-nificant effect on needle P (Fig. 2E~. AI cmacentrations of" 500 HM or more signifieantly reduced needle P. In the dilute m e d i u m , tissue P concentrations were lower than in full m e d i u m in the 0 500 # M range but did not difl>r from that of the full m e d i u m at 1000 and 2000 ItM AI. M e a n needle concentratiml tot P was 2.20 mg/g in the full m e d i u m and 1.78 mg/g at 1/5-strength. T h e K concentration of needles (Fig. 21)) was

494

F.C. THORNTON

B

A

O.2O AI llld

0.18

~

[

Mnl

1.6

0.16

1.4

0.14

1.2

0

,

1

et al.

2

t

0.10 0.08

~>________.

/.

O.8

0.6 o 0.4

0.08 0.04

0.2 i

0.02 0

i

250 500 250 500

1000 /u (u~0

2000

i

I(X)O AI ( ~ )

2

O ~

D

t AIIscl •

0i/

I c

1,14

Mlsd

~

AI x M nil

[

O.

~1(31

Af x Mis d

~8

i

0

l

250 500

I

i

1000 AJ (uM)

(uld)

2000

E

a. 1 L

0

A

250500

L

1000

{~

2

At (uM)

F]o. 2. Effect of At solution concentration on the compositionof red spruce foliage. C) Q) @ Full medium; • • • 1/5 medium. A. Aluminum. B. Calcium. C. Magnesium. D. Potassium. E. Phosphate.

EFFFCTS OF A L U M I N U M ON RED SPRUCE SEEDLIN(;S

B

A, 18 16 14 12

Ailsd [

495

Mild I

1J~ 1.6 1.4

1.2( "al 1.o

0.8

8 6 4 2

0.6 0.4 O.2 25O 5O0

1000 AI (ul~

0 250 500

2000

1000 AJ (old)

2OOO

D

C 1.0

AIIsd ~

O,.E

Mns

0.e

0.4

"~ 10

0.2 '

2

1000

0 2

2000

5o0

1000 ~J (.M)

20oo

12

lo~ ' ~ "

I

-,,. I E

e, I

2

o 2~o~

1~o

2~o

AJ (ulVO

FIe.. 3. Effect of Al solution concentration on the composition of red spruce fine roots. O O (2) Full medium; • • • 1/5 medium. A. Aluminum. B. Calcium. C. Magnesium. D. Potassium. E. Phosphate.

496

I:. C. T H O R N T O N el al.

significantly affected by A1 solution concentrations. In the 1/5 medium K tissue concentration increased by 24'?i, over the controls and then declined at 2000 ItM A1 to the control level. In the tull medium K levels declined linearly to 1000 p M A1 and then increased at the 2000 t,M A1 solution concentration. At 2000 /~M A1 seedlings in full and 1/5 medium had the same needle K concentration, confirming that at this toxic" A1 solution concentration, tissue composition was independent of medium strength. Reel nulrienl composilion. Analyses of variance of the elemental analysis of roots ti'om Experiment 2 confirm the significant effect o f A l and media. All elements were affected by A1 and media, except for K where Inedium eft'cot was not signiticant. The aluminum x medium interaction was significant only lbr root A1, P and Mg. Reductions in Ca, Mg and K (Figs 3B, C, D) were measurable at the 250 /tM A1, regardless of medium strength. These reductions were especially dramatic tbr Ca and Mg in the l/5strength medium (48"..0 tbr Ca and 60(!.{, for root Mg). At the 2000 ItM treatment, reductions of'K, Ca and M g concentration of roots varied between 60 and 910.i, compared to the 0 A1 controls. Root P levels reflected the low P concentration ot" the medium used: 50/~M tbr thc thll medium and 10 pM lbr the 1/5 medium. Root P was significantly greater in all treatments of the tull medium compared to 1/5 strength except tbr the 2000 /tM A1 treatment (Fig. 3F). In the fldl medium root P reached a m a x i m u m of 250 ItM A1 and then declined linearly with increasing solution AI concentration. Ill tile 1/5 medium all AI treatments had greater root P concentration than controls. However, tissue P concentrations increased only at 250 and 500/~M A1. DISCUSSION

T h e phytotoxicity of an element is not only determined by its activity but is modified by the total ionic concentration of the media, the ratios of'difl~rent ions and the speeitic ionic effects. Since these tactors are not independent of one another, assessment of plant response to AI is always contbunded to varying degrees by these interrelationships. One way to balance media ionic concentration is to use "neutral salts." Sodium

salts have been used successfully in many systems. However, our attempt to balance anion concentrations by adding NaCI and Na.,(S()4) (Experiment 1) thiled because red spruce was found to be sensitive to low concentrations of Na salts. Addition of 9.0 m M Na reduced shoot growth of red spruce (Table 1) signilicamly. It was therefore not possible to compensate A1related anion additions with Na salts. Growth of red spruce in our experimental system was vigorous. In the control media treatments total dry weight more than doubled in 35 days and seedling height tripled. Red spruce grew well in the 1/5 strength medium which is reflccwd in the near identical size and weight of the controls. This permitted direct comparisons between seedlings grown in the full and 1/5 media. With the exception of the 2000 tzM treatment where no growth occurred and the roots turned brown, shoots and roots, including root tips, appeared normal at all A1 levels. Overall the A1 effect on seedlings was more severe in the 1/5-strength medium; in both media root biomass was more afl'eeted than shoot weight. At 9000 ttM A1, differences between the media were not significant; acute A1 toxicity was observed. The effect of media strength suggests that A1 phytotoxicity might be related to ..'\1:~ activity since in the more dilute lower ionic strength medium its activity coefficients were larger. Good correlations between AI activities and plant growth have bcen reported fbr eotibe seedlings) 14 Coffee seedlings grown in media where ionic strength was reduced by 75",, developed toxicity symptoms and showed reduced growth at low A1 concentrations when compared to controls. PAVAN and gINGHAM 1;, suggested that the probable cause of AI phytotoxicity at low ionic concentration was increased activity of A1 in these solutions. However, protective effects of anions and cations as well as reduced competition during uptake in the more dilute m e d i u m cannot be excluded as

possible causes. Aluminum concentration of needles and {inc roots increased with increasing A1 in solution as reported tbr other tree speeles. Ctt'l''l ...... Needle A1 concentrations were very similar to those reported by SCZHIER17' but only about 1/3 to I/2 that reported by HUTCHINSON.:Ira The higher AI

EI;'FECTS OF A L U M I N U M ON RED SPRUCE SEf.~,DI,IN(;S levels reported by HUTCHINSON" IIl~were p r o b a b l y the result of including all shoot needles in analysis since older leaves are known to contain higher a m o u n t s of A1 than y o u n g e r tissues. '``.,> H i g h e r A1 needle c o n c e n t r a t i o n in the 1/5 m e d i u m is of interest since root AI concentrations in seedlings grown in the full m e d i u m were significantly greater than at full strength (Fig. 3A). This implies translocation of a larger fraction of A1 in the seedlings grown at low ionic strength. PAVAN a n d BINOHAM:I4 a t t r i b u t e d a similar observation to higher A1:~' activity in dilute media. However, in lheir experiments AI activities and nutrient concentrations were c h a n g e d simultaneously, leaving open the possible direct ion effects. In our system the plants in the 1/5 strength m e d i u m had a larger total length of lateral root a r e a and this contounds interpretation. 'H' F u r t h e r m o r e , changes in A1/ion ratios a n d alteration of memb r a n e p e r m e a b i l i t y m a y also be as responsible for higher translocation rates. Since we do not know how a n d where A1 enters the translocation pathway, mechanistic explanations of this p h e n o m enon r e m a i n speculative. As has been d e m o n s t r a t e d tbr m a n y species, :> A1 m a y severely reduce tissue cation concentralions. However, reductions in elemental content are not always reflected in reduced plant biomass. Needle M g concentration was the most d r a m a t i c a l l y reduced element just as it was in root tissue. 17, T h e 0.2 m g / g found in needles could be sufficiently low ~'~' to affect g r o w t h directly. Needle calcium concentrations were also signiticantly reduced by A1. In the 1/5 strength m e d i u m reduction was from 1.5 m g / g in the controls to 0.2 m g / g in the high AI treatments. This low c o n c e n t r a t i o n is still within a range for norm a l growth of red spruce. :l"~ Even though there was greater Ca in the root tissue of seedlings in the 1/5 strength m e d i u m , lower Ca needle concentration in shoots suggests that A1 m a y have a h e r e d Ca transport. A reduction in Ca t r a n s p o r t by AI and other polyvalent cations has been demonstrated with several species. ':~: HUTCHINSON ~1(' suggested that m o d e r a t e Ca deficiencies occurred in spruce needles c o n t a i n i n g from 0.5 to 0.8 mg C a / g needle d r y weight. I f this is the case, spruce seedlings in our 1000 a n d 2000/*M treatments in both m e d i a m a y have suffered Ca deficiencies ~Fig. IB).

.t97

Needle concentration of P was little att'ected by solution AI levels below 500 /IM bul was significantly reduced in the 1000 and 2000 FLM treatments. 4 ~GHIERl ; observed a significant reduction in needle P at 50 mg A1/I , 1851 # M All, a finding very similar to ours. Using tilt" P deficiency criterion of l.4 mg P/g tbr red spruce developed by SWAN'~" seedlings in the 2000/~M t r e a t m e n t m a y have suffered P deficiencies since mean P concentration was 1.04 mg/g. T h e p a t t e r n of root P concentration in our experiments difl'ered m a r k e d l y ti'om other findings with spruce by HUTCHINSONLI,~ and SCHIER.' It, Both researchers reported little effect of Al on the: P concentration ofrools. In our thll strength medium, which was very similar to that o f HUTCHINSON ~o and SCHIER, 17, r o o l P increased significantly with increasing A1 up to 500 [IM and then declined to 1/2 the concentration of the control at 2000/2M A1. A similar trend has been reported tbr honeylocusl (Glendilsia lriacanlho., 1,. ! and sugar m a p l e (:leer saccharum Marsh.) grown in solution cuhure, e'_,.'_,:~Signiticantly lower P root concentrations were measured in the 1.,'5 strength m e d i u m than the full m e d i u m at every AI concentration except tor the 2000 # M Ireatment. Lower root P concentrations in the 1/5 m e d i u m were p r o b a b l y the result of less AI- P precipitation on root surfaces a because of lower solution phosphate concentration. O u r experiments were not designed to test tl~e role of (la as a specific protective agent nor the i m p o r t a n c e of (la/Al ratios in AI ph)-totoxicitx. However, our root elongation d a t a do not support the concept of Ca/Al ratios as ,l d e t e r m i n i n g tactor in A1 response 'l-'' since a 5 10-tbld change in the ratio had no etDct on root growth. W h e t h e r (la alone acts as a protective agent cannot be determined fiom these experiments since changes in Ca concentration were associated with changes ill ionic strength. However, HVTCHINSON ~'' tbund that v a r y i n g m e d i a composilion of Ca within a range of4~16 mg (100-400 # M Ca) did not all'co! the growth of red spruce. Increasing tt~e (:a concentration in solution also did not diminish the injurious efl'ecl of A1 on the growth ot'cotlbe.' i~ O u r findings su~gesl that under h,w tmtrient conditions, red spruce m a y be more sensitive m AI than earlier reported, eel':; T h e differences between studies m a y be related both to the

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THORNTON

different e x p e r i m e n t a l p r o c e d u r e s a n d the genetic v a r i a t i o n in seedling t o l e r a n c e to A1 w h i c h is 19, k n o w n to exist in s o m e specms. " S i g n i f i c a n t g r o w t h r e d u c t i o n s in red spruce w e r e o b s e r v e d at 2 5 0 / * M A1 a n d o u r d a t a suggest a d v e r s e effects m a y be measurabh~ at e v e n l o w e r A1 concentrations. •

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11.

12.

13. Acknowledgemenls Wc thank C. Zippercr tot con> petcnt technical assistance. This is a contribution ti'om tlre A L B I O S proiect, supported by contract RP2365 from the Electric Power Research Institute.

14.

15. REFERENCES 1. ALVA A. K., EDWARDS D. Q., ASnER C. J. and BLAMEY F. P. C. (1986) Effects of phosphorus/aluminum molar ratios and calcium conccntration on plant response to ahuninuna toxM~y. Soil Sci. Soc. Am. J. 50, 133- 137. 2. BARNESR. A. (1975) The determination of specific forms of ahnninum in natural waters. (;Tlem. Geol. 15, 177 191. 3. CLARKSON D. T. and SANDERSONJ. '.1971) Inhibition of tim uptake and long-distance transport of calcium bv aluminmn and other polyvalent cations. ,]. evp. Bot. 22, 837 85l. 4. CVMMINOSJ. R., ECKERT R. T. and EVANS I~. S. (1986) Effect of aluminum on :~eP uptake and translocation by red spruce seedlings. Can. J. For. Res. 16, 864 867. 5. EDWARDSJ. H., NORTON B. D. and KIRKPATRI6'K H. C. (1976) Ahuninum toxicity symptoms in peach seedlings. J. Am. Soc. Horl. Sci. 101, 139 142. 6. EPSTEIN E. (1972) Mineral nutrition ~jplants: principles and per,~pectivea. J o l m Wiley, New York. 7. EWENS M. and LEmH R. A. (19115) Thc efl'ect of nutrient solution composition on the length of root hairs of wheat ( Trilicum aeslivum L.) ,]. exp. Bol. 36, 713 724• 8. FoY C. D., CHANEY R. L. and WniTr: M. C. (1978) The physiology of metal toxicity in plants. Ann. Roy. Plant Pt{>iol. 29, 511- 566. 9. HORNBECK J. ,~r. a n d SMITH R. B. {1985) Documentation of red spruce decline. Uan. J. For. Res. 15, 1199 1201. 10. HUTCHINSON T. C . Bozm L. and .'k,IUNoz-VI';GA M. (1986) Response of five species ofconil~r seed-

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