(Pinus (34) grows alkalinity) (17, growth. solution, · RELATION OFWESTERNYELLOWPINE SEEDLINGS TO THE REACTIONOF THECULTURE SOLUTION JOSEPH HOWELL, JR. (WITHSEVENFIGURES) Introduction

RELATION OF WESTERN YELLOW PINE SEEDLINGS TO THEREACTION OF THE CULTURE SOLUTION

JOSEPH HOWELL, JR.

(WITH SEVEN FIGURES)

Introduction

The diversity of habitats under which western yellow pine (Pinus pon-derosa Law.) grows throughout its extensive range indicates the ability ofthis species to adapt itself to many environmental conditions. SAMPSON(34) noted that the species grew best in acid soils and was stunted in alka-line soils, while BAKER (4) found that soil reaction had little effect on thedevelopment of its seedlings. In the forests of the eastern United StatesWHERRY (41) found that conifers had a predilection for the acid soils.BAKER and KORSTIAN (5) made an extensive study of the reaction of soilsin the Great Basin, and found that the western yellow pine grew in soils ofpH 7.0 to 9.0. The writer found that, in the Sierras, western yellow pinegrows on soils of a reaction of pH 5.0 to 8.5. This gives a total knownrange of from pH 5.0 to 9.0, and, from all indications, does not cover theentire range of reaction over which the species can exist.

Accordingly, there were three objectives in this investigation, as fol-lows: (1) To study the range of reaction (acidity and alkalinity) whichthe seedlings of western yellow pine can endure. (2) To observe the effectsof the pH reaction on the growth and development of its seedlings. (3) Todetermine what effect the pH reaction has on the expressed sap of the seed-lings.

ProcedureInvestigators (17, 37) have found that soil and sand cultures are unre-

liable for studies of reaction, in that many other factors influence the re-sults. The greater number of investigators (7, 17, 18, 37) have, therefore,resorted to water cultures, in which they were able to decrease the activityof many interfering factors. In this study water cultures were used inorder to secure as nearly as possible an equality of conditions for plantgrowth. Table I lists the culture media used.

Two milliliters of 0.5 per cent. solution of ferric tartrate were added tothe original culture solution, as well as a like portion each week. Themolar solutions were made up separately, using C.P. salts and ordinary dis-tilled water. The culture solution was made by diluting the requiredamounts of the molar solutions with ordinary distilled water. Care wastaken in mixino the various solutions so as to prevent the precipitation of

657

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658 PLANT PHYSIOLOGY

TABLE ICOMPOSITION OF STOCK AND CULTURE SOLUTIONS

MOLAR CONC. CALIFORNIAGRAMS PER SOLUTION; PH OF

SALTS LITER OF MOLAR SOLU- IONS P.P.M. CULTURESTOCK SOLU- TION PER

TION LITER

gm. ml.Ca(NO,)2 * 4H90. 236.2 3.9 Ca 157 1

K 181KNO3.101.1 3.6 Mg 55 15.2MgSO4 -7H20 246.5 2.2 NO1 709 f

S04 212KH2PO4 136.2 1.1 P04 105

the phosphate ion. The ferric tartrate was added after the other solutionshad been diluted and well mixed in order to prevent the precipitation ofinsoluble iron compounds.

Changes of solution were made every four weeks in order to preventserious changes in the composition of the cultures. The pH values of thecultures were adjusted by the addition of measured quantities of standardsulphuric acid or of potassium hydroxide. The pH values were determinedcalorimetrically (8), with frequent checks with the hydrogen electrode.Examinations and adjustments were made daily because of the rapidchanges in the reaction on the alkaline side of neutrality.

TABLE IIMAXIMUM CHANGES OF REACTION IN 24 HOURS

PH OF SOLUTION MAXIMUM PH OF SOLUTION MANIUCHANGE CHANGE

2.7 0.1 7.0 0.33.0 0.1 8.0 0.34.0 0.2 9.0 0.44.5 0.2 10.0 0.45.0 0.2 11.0 0.56.0 0.2

Selected seeds of western yellow pine collected near Georgetown. Cali-fornia, germinated between sterile blotters, and selected germinated seedswere transferred to the water cultures. Stoneware jars of 14-liters'capacity were used as containers, and two such jars containing 35 seedlingsconstituted a set. The following pH values were used: pH 2.7. 3.0, 4.0,4.5, 5.0, 6.0, 7.0, 8.0, 9.0, 10.0, and 11.0. The plants were allowed to grow



HOWELL: CULTURE REACTION AND PINE SEEDLINGS 659

for a period of 133 days, at the end of which time they were harvested andsubjected to measurement and analysis. The plant material was frozenprior to the physico-chemical and chemical measurements.

In previous experiments, seedling variation had been found to be great,the probable error varying from -- 15 to ± 45 per cent. of the means, de-

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PH OF SOLUTIONCurves showing effects of reaction on seedlings of western yellow pine.

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PLANT PHYSIOLOGY

PH OF SOLUTION.

FIG. 3. Curves showing effects of reaction on the pH values of the plant sap.

pending on the measure. The measures for height growth had the smallestprobable error; those for the green weights and dry weights showed thelargest probable error.

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FIG. 4. March of height growth for seedlings; each curve indicates a definite pHreaction.

I



HOWELL: CULTURE REACTION AND PINE SEEDLINGS 661

ResultsIn this experiment it was found that seedlings of western yellow pine

would exist over an extensive range of reaction (figs. 1, 2, 3, 4). Thegrowth limit on the acid side was at pH 2.7, but the growth limit was unde-

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C DFtIG. 5. Western yellow pine seedlings grown in culture ranging in pH from 2.7

to 7.0: A, pH 2.7; B, pH 4.0; C, pH 5.0; D, pH 7.0.



662 PLANT PHYSIOLOGY

termined for the alkaline range. However, a few plants existed in culturesof pH 11.0 for the term of the experiment, and this may be taken as thelimit of growth for the alkaline range. This gives a total range of reac-tion of from pH 2.7 to pH 11.0.

The general appearance of the plants growing in the acid solutions wasstriking when contrasted with those grown in the alkaline cultures (figs.5, 6). The seedlings in the acid solutions were vigorous and well developedwhile those in the alkaline cultures were stunted and chlorotic.

Physical measurements of the seedlings were taken at the terminationof the growth period and are presented in table III.

s5

..U... 80~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~....

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fIG. 6. Western yellow pine seedlings grown in culture solutions of 9.0 and 10.0:A,. pH 9.0; B, pH 10.0.

Height growth measurements were taken at intervals of seven days andpresent an interesting set of growth curves (fig. 4). Three distinct bandsare formed; namely, the acid band, the alkaline band, and the single curvefor the acid growth limit. These curves give ample evidence as to theefficacy of the acid cultures. The growth rate of the plants was littlediminished at the termination of the experiment, whereas in the alkalinecultures the rate of growth was greatly retarded. The plants growing inthe very acid culture (pH 2.7) had a negligible growth rate.

The length of the tap root was affected by the reaction of the culture.Those in the acid media appeared healthy and vigorous, whereas those inthe alkaline solutions were brown and thickened, with a tendency to disin-



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HOWELL: CULTURE REACTION AND PINE SEEDLINGS

tegrate. The roots of the plants growing in the cultures of pH 2.7 werethickened and brittle. The number of lateral roots followed the same trendas the length of tap roots, and therefore it is reasonable to assume that theywere dependent on this factor.

The dry weights of plants have been considered as criteria for metabo-lism, but in this case it was not possible to obtain the dry weights. Thegreen weights followed the trend of the height of tops, exhibiting the usualpoints of weakness. It was evident that the reaction of the culture mediuminfluenced growth and development of the seedlings.

Immediately after harvesting, the plant material was frozen and, for 48hours, held at a temperature of -200 C. The frozen tissue was quicklythawed in hot water and the sap expressed in a small hand-press. The ex-pressed sap, refrozen, was preserved for future studies.

The pH value of the mixed sap was determined by the hydrogen elec-trode (8), at the same time that the titration curves were made (fig. 7).

P H

l- -- \

--V MLS NAOH -O

_- SC1FS-10NA 1Ain *4a

FIG. 7. Titration curves for the plant sap from the tops and roots of plants grownin the cultures at pH 4.0 and 9.0.

The pH values for the sap from the tops tended to vary from the acid tothe alkaline side; however, the values decreased at pH 4.0, 4.5, and 5.0.The values for the sap from the roots followed the same trend as did thosefor the tops. In all cases the sap was found to be distinctly acid.

The titration curves for the sap, both of the tops and the roots, formdefinite and strong buffer curves. The sap from the roots had distinctlyless buffer action than the sap from the tops. These results showed thatthe sap of the roots was more dilute or contained less material that wascapable of acting as a buffer.

665



66PLANT PHYSIOLOGY

The freezing-point depressions were taken with a Haidenhain ther-mometer, standardized with freshly boiled distilled water. The resultingdata showed that the sap was affected directly or indirectly by the reactionof the cultures.

The saponification number, acid number, and iodine number, all ofwhich were found by using standard methods, varied and usually showeddifferences in the general trend at pH 4.5 and 7.0. The constituents of thesap possibly were altered as to quantity and quality. This alteration in theplant sap presumably affected the endurance of the plants toward theeffects of reaction. The physiology of this point will be discussed in an-other section.

Other measurements were made, the results of which are given intable III.

A change in the pH values of the cultures was noted, with the resultthat the plants were found to influence the specific reaction. Plants areknown to absorb ions (1, 2, 7, 19, 21, 22, 23, 24, 29, 31, 36, 37) from solu-tion and thereby change its reaction. Also, the plant may excrete ions (19,25) and in that way alter the pH value. Upon examination of the solu-tions for a decrease in the ions, it was found that absorption was negligibleand could not cause any great change in reaction (table IV). The excre-tion of carbon dioxide was next studied in some detail, but the results wereagain negligible. No further examinations were made, but it was assumedthat some organic substances were excreted by the seedlings, causingchanges in the reaction. The magnitude of the change of reaction dependsupon the buffer action of the solution. The potassium acid phosphate wasthe buffer agent in the solution, but this was precipitated in the alkalinesolutions as insoluble calcium phosphate.

TABLE IVABSORPTION OF IONS BY THE SEEDLINGS

MILLI-EQUIVALENTS*ION

FIRST SET SECOND SET THIRD SET MEAN

Ca 0.180 0.095 0.075 0.117P04 0.270 0.111 0.084 0.155NO3 0.166 0.055 0.056 0.092

* One hundred plants for 10 hours.

There was little doubt that the plants were instrumental in changing thereaction of the cultures in some manner, such as through the absorption orexcretion of ions or molecules.

666




Certain investigators (5, 26) have stated that western yellow pine failsto grow when large quantities of lime are present in the soil. To deter-mine the accuracy of this statement, one set of plants was grown in a cul-ture containing no calcium; another in a culture containing an average of1000 p.p.m. of calcium; and a third in a culture containing an adequateamount of calcium, with the alkalinity produced by the addition of sodiumhydroxide. The solutions were kept at pH 9.0. The results were notgreatly different in all cases, but the plants growing in the solutions con-taining an excess of calcium were superior to the other two. The sodium-treated plants were inferior to the others. The plants, according to thisevidence, withstood large quantities of calcium; they also could exist in asolution deficient in calcium.

The leaves of the seedlings in the alkaline solutions were yellowish incolor, and it was assumed that the plants could not assimilate and translo-cate sufficient iron (37). The metabolism of the plants seems to be dis-turbed in the alkaline media, thus producing a poor color in the leaves.Also, iron has been found to become insoluble after having been in solutionfor a reasonable time.

DiscussionSeveral investigators (2, 28, 30, 33, 35, 41) have casually studied the

effects of soil reaction on forest trees, although little work has been carriedon in detail. The opinion of European investigators is that the reactionof the soil is a potent factor in forest planting, natural regeneration, andforest production. The conifers were observed to prefer an acid reactionfor their best growth, and soils under coniferous forests were found to beon the acid side of neutrality. Conifers did not do well on the alkalinesoils, but certain tolerant species withstood an alkaline condition and com-peted with more resistant plants.

The concentration of the soil solution (1, 2, 18, 20, 21, 22, 24, 39) is animportant factor in plant growth. Also there must be considered the con-centration of each ion, since HOAGLAND (19, 21) and others have foundthat there is a minimum quantity which limits maximum growth. Smallvariations in the concentration do not appreciably affect the growth of theplants. The concentration of the soil solution also influences the concen-tration of the sap (23) ; it affects certain ions (36), and in turn alters thebuffer system (24, 29).

The hydrogen-ion concentration, having been studied in reference toagricultural plants (2, 40), has been found to influence the rate of growth.A greater number of plants prefer a slightly acid medium for their bestgrowth. The seedlings of western yellow pine prefer an even greater de-gree of acidity than do most cultivated plants. The absorption of nitrates

667



PLANT PHYSIOLOGY

(20) has been found to be greater in the acid solutions, and would, there-fore, increase the rate of growth of the seedlings.

Consequently, the behavior of western yellow pine seedlings in prefer-ing acid soils is not different from that of other plants, the only differencebeing that they prefer a more acid medium. As found by WHERRY (41),most conifers prefer an acid soil rather than a neutral or alkaline one.

The pH value of the various plant tissues is characteristic (3, 12, 13,32); the cell sap is usually acid and the protoplasm alkaline. The mixedsap for the western yellow pine seedlings was decidedly acid. However,no examination was made of the various tissues. The mixed saps were wellbuffered, as shown by the titration curves, although slight differences areto be noted. The buffer system of a plant may be affected by the externalmedia, according to THERON (37) and others (14, 29), and this system isaffected by the acid and alkaline reserves in the plant. Some investigatorshave concluded that certain specific substances are responsible for the buf-fer system. In the expressed sap of the plants used in this experiment,large quantities of catechol tannins were found, as well as other resinousmaterials.

The seedlings growing in the alkaline cultures were chlorotic and insome cases the yellow color was pronounced. Chlorosis has been attributedto many sources (11), but it was evident in this experiment that a lack ofiron in the leaves was responsible. The plants either did not assimilatethe element properly or failed to translocate it after assimilation. Thekind of iron compound (9, 11, 38) and the type of iron have great influenceon the ability of the iron to remain in solution. Even with the best of careit was not possible to relieve the situation. This appearance of the seed-lings can be used as an indicator of adverse alkaline soils.

As has previously been stated, the plants were capable of changing thepH value of the culture medium, although the change was usually slight,except in the alkaline cultures. By what process the seedlings changed thereaction of the solutions remains unknown. Their ability to bring aboutthis change does not mean that the plants would effect any great chance inso well buffered a medium as the soil.

The constituents of the sap of the plants determine to some extent theirability to withstand environmental factors. Plants with a sap that ishighly buffered will usually withstand a wide range of conditions. Thereare in evidence points which investigators (2, 16) have designated as iso-electric. In this case these points are at pH 4.5 and 7.0, and they werenoticeably inferior to those in the cultures of lower and higher pH values.Plants subject to these conditions would therefore be inferior and lesslikely to withstand competition.

668




The hydrogen ion (7, 10, 27) has been considered more toxic than thehydroxyl ion, but it has been shown in this experiment that the reverse istrue. Since such is the case in this study, the best forests should be in theregions of slightly acid soils, and the seedlings produced in alkaline mate-rials would be inferior in form and color.

HESSELMAN (15) concludes that soil acidity is closely related to theform of available nitrogen. In this case then the plants should assimilatenitrogen in larger quantities in the acid solutions; and since the quantityof nitrogen used by western yellow pine seedlings is small, there should belittle danger of competition.

Summary1. Western yellow pine seedlings prefer an acid medium for their best

growth.2. Under field conditions other factors may have more influence on

growth than the soil reaction.3. The osmotic pressure of the sap indicates that soil reaction affects

the seedlings as well as do certain other factors.4. The buffer system of the seedlings is dependent on the organic ma-

terials found in the sap as well as on the inorganic substances.5. The ability of the seedlings to change reaction is not to be construed

as an effective measure in reducing soil alkalinity. Debris from the forestcover may be more effective because of the relatively high resin content.

6. Calcium is not deleterious to the seedlings. The fact that the plantdoes not assimilate the ion in alkaline soils may be of more importance.

7. The seedlings withstand a diversity of conditions, especially in re-gard to soil acidity and alkalinity.

UNIVERSITY OF CALIFORNIA,BERKELEY, CALIFORNIA.

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to the hydrogen ion concentration. Jour. Gen. Physiol. 5: 81-88.1922.

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669



PLANT PHYSIOLOGY

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23. , and . The composition of the cell sap of

670




the plant in relation to the absorption of ions. Jour. Gen. Physiol.5: 629-646. 1923.

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