Dry weight growth of Cinnamomum camphora seedlings under different levels of light intensity-香川大学学術情報リポジトリ

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仙回.狗ｃ,ａｇ｡瓦昭αｗαａぬ.7j¶，57(2007)，89-108

Dry

weight

growth

oＩＣｉｍｌａｍｏｍｕｍｃａｍＰｈｏｒａ

ｓｅｅdlings

under

different

levels

of light

intensity

ＫＩＹＯＫＡＺＵＳＵＥＨＩＲＯ

jlaゐ1･z2z∂りげ＆∂jθg3いFizc㎡印げ＆j￡j￡arj∂zl，瓦αg･2wα防zjwrsi印＆ziwαj-cho l-j，乃尨D?zαZ涸76θ-Sj22，j卯皿

ＡＢＳＴＲＡＣＴ

Seedlings of a琲zα謂∂謂zj謂ごαz?zp/zθyz2L. were experimentany grown under din5erent levels of light intensity including lower light intensity below a compensation point. The relationship between mean

plant weight and wide levels of relative illuminance was newly formulated based on the experimenta1 results. Curve for the relationship between relative growth rate （RGR）and relative illuminance calculated from the new equation approximated to the change of experimental values of RGR to relative inuminance.The light compensation point for RGR was higher than that for plant dry weight， and changed to higher light intensity as time passed. The new equation was compared to the previous equations for plant dry weight response to light intensity， and the differences to the previous equations were discussed. lt was shown that the new equation， which includes the property of the previous equations， well expressed survival in early growth stage under the light intensity below a compensation point･ By comparing the light compensation point for RGR calculated from mean plant weights included cotyledon weight and that for RGR from mean plant weights excluded cotyledon weight， it was shown that the seed reserve mass of Cj7謂α謂∂謂M撰a7斑μ2∂m may translocate to seedlings in early growth stage，

Key words : lightcompensation point; light intensity; relative growth rate; seedreserve nlass; shade tolerance

ＩＮＴＲＯＤＵＣＴＩＯＮ

The study on shade tolerance of whole plant is the most important to explain about the mechanism of succession and forest reileneration. There were the classical works

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ＯｎＩ shade 95 ＆Ｉ／ｂｌ shade Ｓ tolerance of whole Blackman ＆Black， tolerance mechanism ａｖｅｎｍｕｔｔｕ

Although

the

＆Westby

Blackm皿's

shade tolerance， may be that general･ They the ｎｏ Plant Ｉ 959）ａｍｏｎｇ

by Blackman et al.（Blackman

＆Wilson，

Recently，there are many

comparative

plant species （Kit咄ｍａ１

_994;

Grubb

1996; Kobe

＆Coates

1997; Walters ＆Reich

method authors have the formulation

derived the

may be the most reasonable

ＩｒどＩ 951a ツ studies of

｢.1996;

999 method for the

，2000） analysis of

referred to the Blackmanls

method. The major reason

by Blackman ＆へvilson（1951a）cannot be aPplied in

important indices for the evaluation of shade tolerance，such as light compensation point for RGR, from the formulations fbr the responses of relative

growth rate (RGR)，net assimilationrate (NAR)and

leaf area ratio(LAR)to

light

intensity.But large erroris unavoidable for RGR,

because RGR

is derived by numerical

differential from the Blackman result， from and The the interva1 way

＆Black

gave up

（

experimental data of Plant weight 1959)actually aPplied the din1うrent the _{generallzatlon}

(Shinozaki＆Hozumi，1960)

equatlon for each

_experimental

relationship between

RGR

and light intensity can be also indirectly derived

relationship between

plant weight and light intensity at each time of growth

(Shinozaki＆Hozumi，

1960).The

most important problem to be solved in this

is the formulation for

HozumiErα1

the relationship between plant weight and light intensity･

(1958)grew

j碩房5czM謂θs油Ez,zθsL.under various levels

intensity，and showed

that the relationship between

mean

plant weight

illuminance

showcd

that

based Ｏｎ showed Suehiro ｖａｒ１０ＵＳ

weight

ｚｅｒｏ satisfied the Sanle the similar that

the reciprocal equation of linear factor. Hozumi

relationship satisfied the

of light

and rdative

（1961）also

reciprocal equation of optimum

factor

experiment ot lmpatiens balsaminaL‥Both

of the equations

Plant weight was reduced to zero when

Ez a/.（1985）cultivated CE/∂jαcrむ1αΓαL

levels and

of light intensity，and showed

relative illuminance satisned the before inuminance reached to zero

relative and that the : equation ｉｌｌｕｍｉｎａｎｃｅ lmpatiens relationshiPs But that reached to zero balsaminalL.under between

plant weight

ＷａＳ they did not cultivate Plants

light intensity than a light compensation

point. Their equations

Were

ｎｌｅａｎ _Plant

reduced to under lower

only derived by extrapolating the experimental results obtained under higher light intensity to lower intensity than lt is wen lntenslty seedlings intensity when the aS

a light compensation point

known that the the

light compensation point of leaves occurs at a lower

light intensity during growth is lowered

(Boardman･

Ｉ

of larger-seeded species tended to survive longer under the

below ａｃｏｍＰｅｎｓａｔｌｏｎ exPerlment compensatlon polnt， light 1址ht 977).Further、 level of light

point(S

averimuttu ＆XVestoby， 1996).Therefore，

is conducted the relationship

by induding

the levels of light intensity below a

between mean

Plant weight and lightintensity may

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Dry _{weight growth}

be explained by a ln this study，

oＩＣｉｎｎａｍｏｎｍｍ

different

ｃａｍＤｈｏｒａ _seedlings _under di汀erent

equation from the previous equations

Ｃｉｎｎａｍｏｎ恨肌 different levels onight intensity

The relationshiP

formulated

rate

Were

between mean

1evels oflight mtenslty，

az凹辿θz‘a

seedlingsxvere experimentany

groM

/

nunder

including the levels below the light compensation point. plant weight and wider level of relative illuminance was based on the experimental results. The relationship between relative growth

(RGR)and

lightintensity，and the change of light compensation

also examined m Ｇｎｎａｏｍｕｍ the ＭＡＴＥＲＩＡＬＳＡＮＤＩＶＩＥＴＨＯＤＳｃａｍＤｈｏｍ experiment. Seeds

Universityon November

Xvere １ L.（Lauraceae）， an

collected from the

of Kagawa university at S Ｓｅａ 995.The aiho-cho experlment ，Takamatsu

level).The

seven levels of light

ｃｏｖｅｎｎｇ

of black

the pipe frame (3 m width，

evergreen Planted pomt broad-leaved tree， trees Ｏｎ the waS ｃａｍｐｕｓ with XVaS of tlme used

Kagawa

carried out on the experimental fidd

City(34°20.3'N，134° 1.7'E, 30 m above

intensity(P1゛ P7)were

set for the experiment by

1.5 m dePth and 1.5 m height)with varying number

mesh sheets excePt the full dayli，

32 pots （30 cm diameter; 24 cm depth;

stones in the bottom and medium

with a slow effect kinds the of granular

expenment.

Fresh seeds seed］ＳＯｗｎ ght Plot 10 1iter

(PI).For each level of light intensity，

volume)tilled

soil mixing sumcient

(tradename : MagAmp

K)were

soi1 weights in each reServe reServe ｎｌａｓｓｅｘｐｅｎｍｅｎｔ nlaSS of ｗａＳｆｏａｍｏｕｎｔ

with 1 1iter of pumice of chemical fertilizer prepared. Mixtures with 1 : 1

(Akatama soiland Kanuma

soil)were used for medium

seeds used in the

_experlment

pot，and fresh weight of

(seeds without seed coat

Ｓｏｗｎ _seeds.The nlean estimated

pots. Three seeds were

皿d seedlings were

ａ The ＭＳＯＷｎ relative 0.0499g in each 1ater thinned 狛 were measured of ｔｗｏ soi1

together for every

100 seeds with seed coat

）was measured

together

weight of seed

On Seven Ｏｎｅ December illuminances in each sPots Plant per (8.8， spot

plot(P1-P7)

reServe ｎｌａＳＳＩ ″ ｀ＪＩ︷ｊｌＣｍ

and dry weight

for estimation

Per ln

21 of

of

seed used in this

996，seeds were

interva1 (7 Plants XVere ａｍｏｎｇ Were ＳＯｗｎ m a sPot)Per pot，

therefore grown in

measured four tlmes Ｏｎ _APri1

30, June 27, August 30 and October 30，1996, by the simultaneous reading of digitallux“

meters (Minolta T-I H)，one kept in the open

measurements

ａＳａ

Thc averagcs

each shading

of 32 sPots for the each Plot were

and standard deviation

plot xvere

Ｉ

00％ _(P1)，

control，and other in the

averaged geometrically

of relative i 55.3士3.6％ each for the plot each The plot. 11uminance measured four times in the

(P2)、]7.9

土２

_1％(P3)、9

つＩ

ハ

︷

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(P4)，2.94±0.69％(P5)，2.12±0.40％(P6)and 0.59±0.04％(P7)to full daylight.

Mean daily solar radiation from firstgermination (May 5， 1996)to the 6th harvesting

(November 2，1996)was 16.3 MJ/ ｢at 7nlkamatsu Meteorological Observatory (34°

18.9'N， 134゜ 3.4'E, 9m above sea leve1)，and slightly larger than the mean from 1974 to

1998(16.0 MJ/ ｢)｡

The numbers of germinated seedlings were counted at two or three days interval

from late April to August 23，1996, and the numbers of dead seedlings were also counted after June 27， 1996 (seedlings were already thinned to フper pot)，at two or three days interval｡

Plants were harvested on June 1 5，July 1 3 , August 1 0，September 7，0ctober 5 and November 2 in 1996, and Apri1 12, May 10 and June 7 in 1997. For each harvesting date， 21 plants in the 3 pots randomly selected were harvested. After washing their roots with tap water, their plant height， stem diameters close to root and leafareas were n!easured.

Each plant was separated into root，stem， leaf and remained cotyledons below ground，

and dried for weighing･

ＲＥＳＵＵｒＳ

Germination,mortality and decrease of cotyledon weight

The cumulative germination rates from late April to August 23 in 1996 are shown

for each shading plot in Fig. 1. The germination rates were calculated for sown seeds, but the pots decrease by the harvestings of 4 weeks interval and， therefore，the germination rates were calculated for sown seeds except those in the harvest6d pots. The germination of seedlings in the open plot (PI)was the earliest than those in the other plots，and the germination in more shaded plots were later. The final values of cumulative germination rates in Pl and P2 were higher than those in more shaded plots｡

Seedlings were dead only in the most shaded plot (P7， relative illuminance °

O.59％)in 1 996. The survivorship curve of seedlings in P7 from June 27， 1 996 to

February 22， 1997 is shown in Fig. 2. The numbers of survivors were counted for

seedlings cultivated, but the cultivated seedlings decreased by the harvesting of 4 weeks interval and， therefore， the survival rates were calculated for the cultivated seedlings except the harvested seedlings. After the 6th harvest on November 2，1996， th色number of the cultivated seedlings in P7 was 98 of 14 plots including the dead seedlings， The seedlings in P7 started to die on July 6，1996， and all seedlings in P7 died on February

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97

︵ｚ︶9lej

UO!leU!Ujje19A!lelnUjno

Dry weight growth of C訥以z謂θ謂四n?αz?写油∂M seedlings under different levels onight intensity，

100 ００ Q Q ００００００７６５４３り／・ 10 4/26 Fig.1 心_g W

_9WJ

leA!AjnS

120 100 ００ａＮＱ００４２ 5/16 6/5 _6/25 0bserved date，1996 7/15 8/4 8/24

Cumulative germination rate （％）oＩＣｉｎｎａｍｍｏｍｕｍｃｏｍｐｈｏｒａｌor each level of relative illuminance（PI:100％，P2:55.3％，P3:17.9％，P4:9.21％，P5:2.94％， P6:2.12％，P7:0.59％ 6/27 1 ﾉ2T7 of full daylig㈲ 8/26 9/25 10/25 11/24 12/24 1/23 1996 1!

Fig.2.Survival rate（％）oI Cinnamomum camphora xrxP7（0.59％of fulldaylight）.

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2.12％).The survivorships at harvesting date in P6 were 75.3％(ApriH2)，65,0％(May

10)and 48.8％(June 7)in 1997｡

The seed of a四α謂θ謂z4附is non-endospermic seed， and the seedling is hypogeal，

which cotyledons remain below ground after germination. The cotyledons were

ha,rvested in this experiment but not perfectly. Some cotyledons missed in soil. The mean dry weights of cotyledon were obtained for each level of shading and harvesting time. But the dif1rence of cotyledon weight among the shading level was not significant (P

＞O.05)，because the samples of cotyledon were not sufficient in the 2nd and the later

harvestings. At the l st harvesting， when cotyledon samplesivereconected sufficiently

for examination， cotyledon was larger in more shaded plot (P＜O.025).The mean dry

weights of cotyledon were calculated for each harvesting date regardless of shading

levels.恥mporal change of the mean dry weight of cotyledon was shown in Fig. 3. The

relationship between the mean dry weight of cotyledon (wo:g)and days after the l st

harvesting(z : day)was formulated as follow｡

wo＝0.00633e￣"235゛＋0.00293 (1)

According to equation (1)，wo decreases and approaches to the final weight(O.00293

g)as time passes. About 94％of the initial seed reserve mass (0,0499 g)may be used

︵11︶suopel4oo peu!eujgj Jo lql!eM ＆lp -100 -50 0.1 50 _{100 150 200 250 300 350 400}

Days after first harvesting

Fig.3.Time

trendS of mean dry weight of remained cotyledons below ground. The curve

represents

lhe relationship

calculatedby fitling

equation（1）.

Ｊこ l l 】

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Dry weight growth of C泌汝7脚び脚1折7cほ碍辿び心seedlings under different levels of light intensity，

for the construction of seedlings and respiration loss. Supposing that the mean dry

weight of cotyledon decrease as shown by equation (1)even before the l st harvesting，

the cotyledon weight of 8 1 days (March 26， 1996)before the l st harvesting equals to the initial seed reserve mass. Therefore， seeds may staft the action for germination after late March.

Time

trend of mean

plant weight

Time trend of mean plant weight are shown in Fig.4 for each shading level (P1-P7). Mean plant weight was obtained by multiplying the survival rate at harvesting time to

mean

plant weight of survivors.M/eights of cotyledons and dead leaves were excluded

from mean plant weight. 0nly for P6 and P7，mean

plant weights of survivors are also

shown by broken lines (P6' and P71).The mean plant weights in PI-P6 trend to increase

︵切︶ 100 1 0 １ IL111!eM lueld uee14j 0.1 0.01 ０ 50 100 ₂₅₀ ₃₅₀

Days afterlrst harvesting

Fig.4.Time trends of mean plant weight for each level of relalive illuminance （PI:100％，

P2:55.3％，P3:17.9％，P4:9.21％，P5:2.94％，P6:2.12％，P7:O.59％of fulldaylight）.

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with time，but those after the fifthharvesting increase slowly compared with those before the 4th harvesting The mean Plant weights in Pﾌincrease a littlefrom the l st harvesting

harvesting show the tendency to become larger than that of the l st harvesting， but do not exceed the initial seed reserve mass.

The relationships between

relativeilluminance

and mean

plant weight

The

relationships between

mean

plant weight

(w)and

re141tivemuminance

(/1)

are shown in Fig. 5a fQr from the lst harvesting (Jun.15,1996)to

the 6th harvesting

(Nov.2,1996)，and

shown in Fig. 5b for from the 7th harvesting (Apr.12,1997)to

the

gth harvesting (Jun.5,1997).The

following equation is fittedto the w ￣y relation for

cach harvesting 1 0 １ 0.1 ︵1︶s ‘lql!9M lulld ul91N 0 . 0 1 0 . 0 0 1 0 . 0 0 1 OJun.15 ●Jul.13 △Aug.10 ▲Sep.7 □Oct.5 ■Nov.2 （ａ） 0,01 0.1

Relative illuminance, f(daylight=1)

1 0 0 1 0 １︵11︶4clql!9s lueld ＣｇＱ５一 0 . 1 0 . 0 1 OApr.12 ●May 10 ムJun.7 （ ♭ ）１ 0 . 0 1 0.1 Relative illuminan｡｡,f(daylight=1) １

Fig. 5. Relationships between mean plant weight (,4/)and relativeilluminance (りull daylight

＝1)for each harvesting time in 1996(a)and 1997(b).The curves represent the

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Dry weight growth of Cizz‘2謂θ謂zj謂cα謂μ1θΓaseedlings under different levels of light intensity，ＷＩ - Ｃ --

熹

戸

十召

②

whereA，凧C

and /7are the coemcients sPecificto the exPerimental condition other

than y:The

values of coefficientsin equation (2)were

determined by the Marqua

-

rdt

method(vid.

Tone， 1982)，a nonlinear least squares√asΣ ￨(w･bi−w･･l)/w,j 2is

minimizedjn

which w｡h，isthe observed values of w and w｡｡lis the calculated values

of w by equation (2)for each harvesting. The unit of w and y used gram and relative

illuminance to full daylight ( ゜1)for calculation， respectively･ The Curves in Fig.5

indicate the relations shown by equation (2).The curves well nt for the observed values

ofw(P＜O.0 1 in all harvestings).The obtained values of coefncients in equation (2)

and the coemcients of determination (R2)for each harvesting are given inlable l.The

coefncients of determination were calculated by Kan (1990).Time trends ofA,召，C and

力areshown in Fig. 6. The values ofAdecrease rapidly until the 4th harvesting, but the later values decrease gradually excePt a littleincrease in the 7th harvesting. The values of召 show the similar trend toA.The values of C gradually decrease until the 6th harvesting with keeping small positive values， but later decrease to negative values. The values of lz were nearly equal to l in the l st and 2nd harvestings and gradually increase from the 3rd harvesting to the 6th harvesting, but again nearly equal to l after the 7th harvesting when all plants dead at P7.

Table l

The obtained values of coefficientsin Equation （2）and the coefficients of

determinant（R2）for

each harvesting.

Harvesting date １２３４５６７︵Ｓ９ J u n , 1 5 , 1 9 9 6 J u l . 1 3 , 1 9 9 6 A u g . 1 0 , 1 9 9 6 S e p . 7 , 1 9 9 6 0 c t . 5 , 1 9 9 6 N o v . 2 , 1 9 9 6 ■ ㎜㎜㎜㎜㎜㎜ J J ㎜皿 - l ㎜㎜㎜㎜㎜㎜㎜皿㎜㎜㎜ A p r . 1 2 , 1 9 9 7 M a y l 0 , 1 9 9 7 J u n . 7 , 1 9 9 7 Å 7.33 1.26 0.193 0.0383 0.0334 0.0157 0.0244 0.0221 0.0178 召２１０ 60 01 423 １０８２ｊｊ００ 0.115 ---0.0603 0.0423 0.0401 Ｃ 0.0290 0.0264 0.0207 0.0182 0.00584 0.00133 −0.667 −0.839 −1.09 万１０１１ 05 990 30 57 ″｀Ｊ ″｀。。‘ Ｉ１ 71 １０１００ 990 982 R2 0.9673 0.9895 0.9967 0.9907 0.9979 0,9953 0.9924 0.9962 0.9840

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ＡＣ 1 0 １ 0.1 0.01 0.2 0 -0. ２４６ -0.8 -1 -1.2 ０ 100 200 300 Days after 11rst harvesting

1 0 0 2 0 0 3 0 0 1 0 ｜ 0.1 0.01 400 4 0 0 1.8 CD 9 １１ 11 り／一１１ 0 ， 0 ，８６４２０００ _{100 200 300}

Days after first harvesting

1 0 0 2 0 0 3 0 0

400

4 0 0

Days afterfirstharvesting Daysafter11rstharvesting

Fig. 6. Time trends oM， ∂，C and 削￨n equation (2).Broken line is C＝OforC and /l＝l for /7 respectively.

Responses of RGR

to relativemuminance

Relative growth rate (RGR)from

time zjto time z2can be derived as fonows

(Blackman＆Wilson

1951b).

ＲＧＲ -ＩＷ占訴 --

/四w2￣/qw1

t1￣号？ (3)

where wl and w2 are mean plant weight at zl and z2，respectively, and log is natural

logarithm. The values of RGR are calculated directly by substituting the obtained

data of w in each harvesting time to equation (3)，and the values of RGR calculated

by this method are hereafter called 'lthe observed values'l of RGR. The relationships

between mean plant weight (w)and relative muminance (y)are formulated as shown

in equation (2).The relationships between relative illuminance and RGR are derived

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︵ｊの。ａ

ｔＪ／１１)ＳＤＵ

(s51asgJ/11)UgU

Dry weight growth of C泌心琲7θ用附召cぶ男辿θ印seedlings under difkrent levels of light intensity，

Logarithm of relative illuminance

(daylight=100)

(sslagaq︲1/1)SDU

(sfas

t.11/11)SOU

(daylight=100)

(sMgs9.s/2)HDa

(daylight=100)

Fig.7a.Relationships between relativegrowth rate (RGR)and common logarithm of relative

illuminance(full daylight ＝100)foreach harvesling period in 1996. Solid circles

represent the values calculated directly bv equation (3).The curves represent the

relationships calculated from equations (2)and(3).R 2 : coefficienlof determination。 *:P＜0,01，＊*:P＜0.05. (ssl99'v‘1'.l/l)U91:1 １ Lr︶ 0 1r︶ｏ７ -1 (ssl99al'.1/1)llOI!:1 １ＬＱ０１ｎ００一 − 1

Logarithm of relative illuminance (daylight=100)

Fig.7b.Relationships between relative growth rate (RGR)and common logarithm of relative

illuminance(full daylight ＝100)for each harvesting period in 1997. Solid circles

represenl lhe values calculated directly by equation(3).The curves represent the

relationships calculaled from equations (2)and(3).R2 : coefficientof determination，

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harvesting to equation (3).The relationships are hereafter called ¨the calculated curves¨

of RGR.

The relationships between

relativeilluminance

け)and

RGR

obtained from the

present experiment

are shown

in Fig. 7a and Fig. 7b. Curves indicate the calculated

curves of RGR.

The values of RGR

were calculated per 4 weeks. The unit of mean plant

weight is gram. The common logarithm of relative illuminance (daylight °100)are

used for horizontal axes in Fig. 7 afterBlackman＆NVilson(1951b).The calculated

curves of RGR well fitfor the observed values of RGR until the 6th harvesting (Nov.2。

1996)(P＜0.01 or P＜0.05)，but do not fit for those afler the 7th harvesting (Apn12，

1997）（P＞0.05）.

limporal

change

oflight compensation

point

Light intensity, where net photosynthesis takes zero in light-photosynthesis curve of a leaf, is used as the light compensation point. Three types of light compensation point are considered from the results of this experiment. First is a relative inuminance at which

ＲＧＲニO in RGR −y relation. This light compensation (∫よ)is considered as the value

for a whole plant different from the value for single leaf (Blackman＆WIlson 1951b).

This light compensation point is obtained by numerical calculation｡

ln this report， weights of cotyledon remained below ground were excluded from

mean plant weight. lf cotyledon weights are included， mean plant weight increase a

little.Cotyledon weight decreases with time, but do not become to zero. The final weight

is considered a container of seed reserve mass. The mean final weight of cotyledon is

estimated as O.0499 g･ The relationships between mean plant weight added cotyledon

weight excluded this nnal weight and relative illuminance satisfy the similar relationship

to equation (2)for each harvesting. The light compensation point (y≒2)for new RGR

obtained by new w −∫relations is calculated by the same procedure｡

Third is a relative illuminance when w ° O in w- / relation. This type of light

compensation points is shown when C ＜O in equation (2).The light compensation

point(石3)for w is derived from equation (2)as follow ・

-（ −ＡＣ召Ｃ十１治Ｉうう４ぐ

These three types of light compensation point do not always compensate the future

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Dry weight growth of a皿ar?1θ訓四2cαy?7ρ11∂z7zseedlings under different levels of light intensity

一一一一２ 1.5 １ 0.5

︵訳︶lu!od

uo!lesugduJool＠!1

J−゛

100 300

Days

after first harvesting

Fig.8.Temporal changes of light compensation points estimated by diffe-rent procedures. Solid circles， open circlesand open triangles represent y°cl，fc2 and fc3， respectively,See text in detai l｡

Table 2 The estimated values onght compensation point（％）.Three types of

lightcompensation point （た1，た2 and た3）were estimated by different

procedure.See text in detail｡

Harvesting period or date

Jun.15 −Jul. 13，1996 Jul. 1 3 −Aug. 10,1996 Aug. 10 −Sep. 7j996 Sep.7 −Oct. 5，1996 0ct.5 −Nov. 2,1996 Apr. 12 ’May 10, 1997 May 10 −Jun. 7, 1997 Apr. 12，1997 May 10j997 Jun.7，1997 八1 ０１０ 35 １１ 69 Ｉフー１２２ 74 29 06 几2 １ 24 ︵５１１ 0 ，85 ごＪフー１２２ 76 26 07 八3 １１１ 77 85 89

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caned¨light compensation point¨in this paper｡

Temporal changes of the estimated values of light compensation points obtained from this experiment are shown Fig.8 and Table 2. The light compensation points for w were not obtained before the 6th harvesting. There is a large difference between 私l and石2in a period of the l st and 2nd harvesting， but differences are smaller in the later harvesting･ ln spite of irregular change， all values of light compensation points show the tendency

approaching to about 2％of relative illuminancewith time. Among the values after the

7th harvesting， the two light compensation points for RGR are higher than that for mean plant weight.

DISCUSSION

Hozumi el al.（1958）grew Hibiscus MoscheutosL.under various levels of light

intensity，and showed that the relationship between mean plant weight （w）and lelative

illuminance（y）satisned the following equation.

１Ｗ -Å ｙ十召，

whereAand召are the coemcients specinc to the experimental conditions other than

y: The growth factor satisfying equation (5)is called a ¨linear factor¨by Shinozaki ＆

Kira(1958).Based on the similar experiment of加pdasゐ｢g ｢uL.,Hozumi(1961)

showed again that the same relationship satisfied the following equation.

ＩＷ -Å ｙ

Åソ十7j

ｊ／Ｏぐ

whereA,Å'and召are the coemcients specific to the experimental conditions other

than y. Equation (6)gives a maximum value of mean plant weight at an optimum

levels of y. The growth factor satisfying equation (6)is called an ¨optimum factorl' by Shinozaki＆Kira(1958).

Equations(5)and(6)indicate that w approaches to straight line with gradient l

at lower f on both logarithmic co-ordinates， and w approaches to zero at y →O. Suehiro

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Dry weight growth of aziz2α謂θ謂M謂cαMp/zθΓとzseedlings under different levels of light intensity，

1evels o臼ight intensity, and found out that mean plant weight approaches to curve with

steePer gradient than l at lower rdative illuminance on log-log co‘ordinates. They

therefore apPlied the following equation to the relationshiP between mean Plant weight

(w)and

relativeinuminance

(∫)

ＩＷ

- Å

ヂー八

ｏｒＡ’

十ぶけ一八）＋肌

゜O in equation 7 as follow.

ＩＷ

- Å

ｙ一八

十召 (7) (8)

The

value of yo in equations (7)and(8)indicate

the relativeinuminance

where

plant weight is reduced to zero，and may

be regarded as a kind of light compensation

point. Putting ∫＝j − yo in equation (7)or(8)，equation(7)or(8)coincides

with

equation(6)or(5)，respectively｡

The

results after the 7th harvesting in this experiment

are regarded as み≒l and

satisfyequation (8).When

/1° 1，equation (2)is shown as follow.

ＩＷ−Ｃ一一 Å デ十召

Equation(9)is

transformed as follow.

ＩＷ一

- Å

(斑ﾌ＋1)2

ｙ十ＡＣ召Ｃ十１＋召召Ｃ十１ (9) Ｉぐ O）

By replacing A/(jC＋1)2 withA，j/(jC＋1)with j and −AC/(jC＋1) j･・ j° /。｡,｀S ，･ /｡,｀4 ・・1 。･ /nx ，/'iノハ･¶ｧ1 /'1/八

with石in

equation (10)，equation(9)coincides

to equation (8)atCく0.When

C く0，

yo(＝石3

in equation (4))is obtained from equation (2)as shown in equation (4).

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Equation(2)shows that w →C aty→O， and w →1/召十Cat∫→oo. The values

of C and l!B 十C indicate the lower and upper limits of w， respectively･ At / →O，w

is positive when C ＞O， but w is negative when C ＜O. Real values of w cannot take

negative values， and therefore seedling will die. XVhen seedling germinates， seedling body is constructed by seed teserve mass and seedling weight may be kept positive even at∫'O. Then the value of C keep positive. Under the light intensity lower than a light compensation point, seedling weight decreases with time by respiration loss and seedling

will die soon. After all seedling died at y ° O，the value of C take negative. The time required for seedling death of the species with large seed reserve mass may be longer than that with small seedreserve n!ass evenif they have the same light compensation point.

The w −∫curves drawn by equation (2)for different values ofA(＝0.01，0.02,0.04)

under constant 召(゜O.1)，C(二〇.03)and /z(゜1.5)are shown in Fig， 9a. The w

￣

∫curves move in paranel with∫axis for the change ofA.The w -y curves for different

values ofみ(＝1，1.5，2)under constantA(＝0.02)，召(＝0.1)and C(＝0.03)are

also shown in Fig. 9b. The value of /zindicates the slope of the w −y curve in the middle range of∫on both logarithmic axes. The slope of the w ￣y curves become steeper in the middle range ofy for increasing of lz as shown in Fig. 9b.

The relationships between relative illuminance and mean plant weight are compared in Fig. 10 for the case applying all the data at the sixth harvesting to equation (2)(fine

curve,thenjz＝1.71 and C ＝0.00130)and thecaseapplying the data in PI ￣P5 atthe

same harvesting to equation (2)with ｈ＝ 1 (tick curve; then．ｈ＝ l and C ' − 0.496).

The w −yrelation seem to be well approximated by equation (2)with C ＜O and ｈ＝

l on both normal axes，but there are large differences between the data in lower∫and

the w −y curve shown by equation (2)with c ＜o and 11 ' l on both logaJjthmic axes.

Rgure

10 also indicates that the w ￣∫relationshown by equation (2)with

/z＞1

and

C＞O

is approximately shown by equation (2)with

C ＜O

andみ'l

in sumciently

higher range ofythan the light compensation point.

There is a point of inflexionunder the condition of /z＞1 in equation (2)，and the

curvedrawn by equation (2)is

convex downward

at y ＜

ａｎｄｃｏｎｖｅｘｄｏｗｎｗａｒｄａｔダ＞ Å 召 Å 召ｊｌみぐ（ /Z ＋ｊｌｊｌ万ぐ（ /z ＋ｊｌ蹟１蹟Ｉ

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Ｗ

1 0

１

0 . 1

0 . 0 1

Dry weight growth of ar謂a謂∂謂M/?l cαz?写7/zθΓaseedlings under diff1rent levels of light intensity･

0 . 0 0 1 0 . 0 1 １Ｗ 1 0 １ 0 . 1 0 . 0 1 0 . 0 0 1 ｆ 0 . 0 1 ｆ 0 . 1 １

Fig.9.The change of the ･4/− f curves on both logarithmic axes drawn by equation (2)for

(a)different values ofﾒ1(＝0.01，0.02，0.04)under constant S(＝0.1)，C(＝0.03)

and /1(＝1.5)，and(b)different values oｌｈ(＝1，1.5，2)under constanM (＝0.02)，S

(＝0.1)and C(＝0.03). ９８７ C ljUDg N ︵l︶44 ‘1＠!9“q”9ld ”9911ヽ’一１０ - １

Relative illuminance, f(daylight=￨)

1 0 １ 0.1 ︵11︶4’ ‘lqj!s W8ld C Cg Q 芝 0.01 0 . 0 0 1 0 . 0 0 1 0 . 0 1 0 . 1 １

Relative illuminance, f(full daylight=1) Fig.10.The comparison between the case applied all dala in the sixth harvesting to equation

(2)(fine curve)and the case applied data of PI-P4 in the same harvesting to

equation(2)with /7＝1(tick curve)on(a)both normal axes and (b)both logarithmic

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The survivings below the light compensation in early growth stage are expressed by

downward convex curve in lowerj

The most available method to infer the shade tolerance of seedlings may be

measurement of a light compensation point， namely， the light intensity at which there is a balance between photosynthesis and respiration in a whole plant. For this purpose，

some investigators （Blackman＆XV11son 1961b，Mahmoud＆Grime 1974）have

cultivated plants under various levels of light intensity，and obtained the light intensity at which RGR ° O in RGR-light intensity relation. But the experimental values of RGR

directly calculated from experimental results have large variations as shown in the

present results especially after the 7th harvesting （Apr,12， 1997）（Fig. 7b）.lt may be !.__.____!1_1_え_JC_._.__.1_J.Il jl r ，i l .1 1｀ 1｀』 7｀●/Ny･● i ･● 哺.゜，･j impossible to formulate directly from the relationships b6tween RGR and light intensity･

lt is avoidable that the experimental value of RGR has a large error, because RGR is

calculated by numerical differential as shown in equation (3)(Shinozaki＆Hozumi

1960).Thereforejt may be better procedure that the relationship between plant weight and light intensity is formulated， the relationships between RGR and light intensity are derived from plant weight −light intensity relations，and a light compensation point of RGR on the relationship between RGR and light intensity is estimated. ln spite of large

variations of experimental values of RGR/'the calculated curves¨of RGR well show

the tendency of the experimental values of RGR to light intensity. Equation (2)we11 fit for the relationships between the observed values of mean plant weight and relative

inuminance(P＜o.01 in all harvestings)，therefore，1'the calculated curves¨ofRGR and

light compensation points may be reliable. But their confidence limits are not obtained

because the relationships between RGR and relative illuminance are not shown by

slmple llnear regresslon.

There was a large difference between two types of light compensation point

obtained for RGR only in the period between the l st and 2nd harvestings. ln the most

shaded plot (P7 : O.59％of full daylight)，the value of RGR calculated by mean plant

weight of seedling only took a positive value only in this period and the seedlings in P7 started to die on July 6，1996, just before the 2nd harvesting. Seedreserve nlasshas been

thought to play important role to shade tolerance (Leishman＆XVestby 1994).Those

results suggest a甜zα謂θ謂M謂a2扉ρ/zθz7zseedling directly depend on seed reserve mass

only in early short period after germination. lf seed reserve rapidly translate to seedling， shade tolerance of seedling itself may be play important role after rapid translocation of seed reserve. lf seed reserve slowly translate to seedling， seedling maybe survive longer even if seedling itself is intolerant. Two types of light compensation point obtained

for RGR were more than 2％of fun daylight in the period between the 7th and gth

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Dry weight growth of Cj琲2α謂θz71zlz7zcαﾀ7zμzθπ2seedlings under different levels of light intensity･

daylight)were also dead in the second year after germination｡

The value of八3 means that all seedlings die under lower light than this value at

its harvesting time. The seedlings in the most shade plot (P7 : 0.59％of full daylight) started to die on July 6，1 996， and all seedlings finany died on February 1 8，1 997. This

result shows that some seedlings oI Cinnamomum camphora survive until about 8

months after germination under lower light condition below the light compensation point ofRGR.

ＡＣＫＮＯＶＶＬＥＤＧＮＩＥＮＴＳ

The author is indebted

to the students of Biological

Laboratory， Faculty of

Education，Kagawa

university, for theirhelp during the experiment. Useful suggestions

and criticisms on a draft of this paper by lx/1r.

Ivlasahiro Nagano

are also sincerely

acknowledged.

ＲＥＦＥＲＥＮＣＥＳ

BLACKMAN G.E.＆IVILsoN G.L.(1951a)Physiological and ecological studies in the

analysis of plant environment. VI. The constancy for different species of a logarithmic

relationship between net assimilation rate and light intensity and its ecologica1

significance.Anz2 ｢sげ召θ包月y況S. 15 : 63-94.

BLACKMAN G.E.＆M/ILsoN G.L.(1951b)Physiological and ecological studies in

the analysis of plant environment. VII. An analysis of the different effects of light

intensity on the net assimilation rate，leaf-area ratio，and relative growth rate of

different species.Åﾀひ1α/sげ召∂zαzzy｣/V.S.15:373-408.

BLACKMAN G.E.＆BLACK J.N.(1959)Physiological and ecological studies in the

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N.K.(1977)ComParative

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