Hnverkan av COz, vatten odr naring p l bildningen av sommarskott hos plantor av Pinus silvestris L.
by
T O R S T E N A L D a N
Department of Reforestation
S K O G S H ~ G S K B E A N
R O Y A L C O L L E G E OF F O R E S T R Y
STOCKHOLM
A B S T R A C T
Results are presented from a study concerning the influence of environ- mental factors on the formation of summer shoots i n young plants of Pinus silvestris L. grown i n plastic green houses. A close relationship is found between the studied factors: GO,, water, nutrients a n d the occurrence of summer shoots. Poor environmental conditions during the first year followed by improved conditions i n t h e following year resulted i n a great number of plants with summer shoots, whereas favourable conditions during the first year resulted i n a low number of plants with summer shoots t h e folloming year.
According to these results the conclusion is drawn that environmental conditions and especially those of the preceding year have a great influence on the formation of summer shoots a n d on the shoot growth as well.
As a hypothesis it i s discussed that carbohydrates i n the plant may in- fluence the formation of summer shoots a n d that this influence is mediated by growth regulators.
31% r e c ~ i v e d 2 December 1970
1. Introduction
Shoot growth in most woody plants is i n general a two-year process with formation of buds during the first year a n d development of shoots during the following year after a period of dormancy. Under certain conditions, however, summer shoot may occur, i.e. the shoot develops during the summer i n the same year in which the bud is formed. So far, this pl~enomenon h a s been very rare among pine trees a n d in practice of small importance. I11 experiments with seedlings of P i l ~ u s silvestris L. i n plaslic greenhouse i t h a s turned out that the frequency of plants with summer shoots has increased to a considerable extent in comparison with conventional growing i n open air. T h e aim of this study has been to investigate the importance of environmental factors for the formation of summer shoots in young Pinrrs siluestris.
Second flushing h a s been described i n the literature by many terms like "second shoot", "mids~zmmer growth", "late season growth",
"summer shoot" a n d "proleplic shoots". However, these terms do not distinguish between shoots formed from the terminal bud and shoots formed from lateral buds a t Lhe base of the terminal bud. As these two types of shoots influence Lhe tree form in different ways, i t is i n this case of importance to distinguish between the two types of shoots.
Thcrefore in this text the tcrrn proleptic shoots refers to shoots which a r e formed from lateral buds a t the base of terminal buds after the first flushing is completed. The Lerm Lamrnas g r o w t h refers to shoots which are formed from terminal buds i n the same way. This terminol- ogy h a s previously been used by other authors, among others Rudolph (1964) a n d Kozlowslti (1964 b ) . T h e term s u m m e r shoot is used when both types of second flushing are referred to.
There are different theories about factors influencing the formation of sunliner shoots in woody planls. Water supply a s well a s nutrients a n d accumulated carbohydrale reserves may be involved i n its forma- tion (Fraser 1958). T h e lendency for summer shoots is greatest i n young plants and decreases with the age of Lhe tree. Iiovalenlio (1960) found a comparatively great number of Larnmas shoots i n one to five- year-old P i n u s siluestris and Pinzzs pallasiana Lamb. but no such shoots were found in the same species t h a t were 10-20 years old.
FValters & Soos (3961) poinled out that thc formation of Laminas growth probably 71-as more influenced by en\ironmental lhan by genetic factors. However, e\en genetic conlrol m a y be involved. Rudolph (1964) found that in Pizlus bunAsianu Lamb. Lanlrnas growth a n d prolepsis and their combinations \ aricd significantly between different provenances which had been studied in nurseries. 'I'herefore he con- sidered Laminas growth and proleps~s to be mainly under genetic control. Ehrenberg (1963) found in Finzzs siluesiris genelic differences belweeii individual progenies a n d provenances and, moreover, a great influence of the environment on the occurrence of prolepsis.
Howe\er, the only viay environmental a n d hereditary factors call affect tree growth is by physiological processes in Lhe plant (Kramer
& Kozlowslii 1960). Experimental e\idence indicates that hereditary
a n d environmental factors can influence tree gromth t h r o ~ ~ g l l growth, regulating substances. Thus, Lhe formation of Lainmas growth has been suggested to be dependent on factors inlluencing the concentra- tion of growlh-promoting subslances in the plan1 ( Studhalter 1955).
Already in 1828 Reed suggcstcd a connection bet\\-een the occurrence of growth-promoting substances and Lainmas gram-th i n lemon. Since then many other investigalors h a l e accepted Llie same basic idea, e.g.
L)anilo\ ( 1946) a n d Champagnat ( 1934).
This study has been carried out during the years 1967 to 1969 a t the Agrena experiment nursery siluated in the central part of Sweden where the Department of Reforestation a t the Royal College of Forestry in 1965 started a research and d e ~ e l o p n i e n t project with the working name: "Operalion mechanical planting". One of the aims of Lhe project mas to create and investigate a n a l t e r n a t i ~ e to the con- ventional method of growing forest tree seedlings in open air. This was carried out in plastic greenhouses here seedlings of forest trees n e r e grown in different levels oi nutrients, waler a n d carbone dioxide in order to bring about optimum environmenlal conditions. Preliminarj results from these esperinients have been presented by the initiator a n d project leader Professor Gustaf S i r h , Royal College of Forestry
(Sirkn 1967, 1968, 1969).
2. Material and methods
The experiments may be divided in t n o group" those with the a i m of studying the influence of environmental conditions during the preceding year and those with Lhe aim of studying the influence of current condilions on the formation of summer shoots in Scots pine /Pinus siluestris). For the experiments Lmo different types of green- houses haxe been used, the Finnish Cslko-house i n 1967 a n d 1968 a n d
Lhe Swedish Deje-house i n 1969.
In all experiments peat was used as g ~ * o w t h substrate a n d nutrients werc supplied i n solution (Wallco L-65/13; for the composition see Ingestad 1967). Ca a n d N g were supplied a s dolomite which was mixed i n the peat before soning in a n amount of 1 kglms peat. In experiments with GO,, nutrients a n d water were supplied through irrigation systems i n the greenhouses while i n other experimenls this was done manually.
d soil moisturc o l 80 % of the saturation value of peat was used .which h a s turned oul to be Lhe optimum ~ a l u c for growth of pine seed- lings in peat ( E l o ~ v s o n 1971).
The seed was of a Varmland provenance and of the same origin i n all experiments (no. 14670).
In the following t e s t the term 110-plants stands for plants which are grown one season, 210-plants stands for plants n h i c h a r e gro\vn two seasons a n d are not transplanted and the term 111-plants stands for plants n h i c h are gromn tv-o seasonr and are transplanted after the first season.
Measurements of height were made every other week according to statistical methods used in the nursery experiments. The height of the plants mas mcasured from the ground lo the terminal bud, i.e. occur- ring Lammas shoots are included i n these measurements of two-year- old plants. This may to some extcnl influence the results from the height measureinenls in Lhese experiments. T h e disEribution of Lam- inas growth i n the different experimental plols shows t h a t they are most frequent in plots showing poor height growth a n d I ice Yersa (Fig.
1, Table 2 a ) which to a certain degree bring about a n equalization of differences in height gron-th. T h e mean ~ a l u e s from the height of the different plots were calculaled and compared. A s o n l ~ one ecologicaI factor w:ls ~ a r i e d between the different plols this procedure seems t o
bc a salisfactorg way of obtaining a measure of the optimum degree which \\.as used. The total number of suinruer shoots i n the different plots were recorded about every forlniglit.
2.1. Experiments with COa
After preliminary experiments in 1963 and 1966 a n experiment with different levels of CO, was started in 19G7. This experiment was arranged in 10 blocks which each consisted of 600 111-plants and sown plots nicasuring 3 mZ. Two of lhe greenhouses employed were divided into four sections of equal s i ~ e by ~ ~ a l l s of plastic. Each section con- stituted a n experiment block. In the different sections CO, was supplied a t a level of 1,200, 2,400, 3,000, 3,600 ppm respectively. W i t h a n a p p r o ~ i n i a t i v e l e ~ e l in normal air of 300 ppm these values correspond to a n increased C0,-level of 4, S, 10 and 12 times rcspectively. In the following year (1968) the walls between the different sections were removed. I n one house the C0,-lcrcl was held a t 3,000 ppm and in the other no CO, w a s supplied. All plastic foil in the greenhouses was PVC which has a \cry slight permeability to CO,. T h e experiment also in- cluded reference areas in the open air a n d in greenhouse without CO,-
~ " p p l y .
During 1967 Lhe CO, was supplied from CO,-tubes which were con- nected by plastic lubes with the different sections. In each section perforated lubes were connected a n d placed on the ground. T h e CO,- supply was controlled by a timer (Micro-Matic type 6-111) which through a magnetic valve controlled the f l o v from the gas tubes. In addition, there was a light relay (Micro-Matic type F ) which a t a given light intensity increased Lhc C0,-supply in order to compensate the greater C0,-consumption by the plants a t higher light intensities. The timer was adjusted so t h a l the gas flow slarted approxiniately one hour after sunrise a n d was closed about half a n hour before ventilation began. I n the afternoon the C0,-supply was started nlanually when ventilation of the greenhouses had ceased and continued until one hour before sunset. In w e r y section Lhe C0,-supply could be adjusted by a graduated valx e. Control of the C 0 , - l c ~ el was made every day, a t which time all values a s well a s adjustments mere noted. A Riken-Keiki CO,- analyzer was used for these measurements. During 1968 a n d 1969 the C0,-source was propane burners which were placed i n the middle of the houses. The C0,-supply mas conlrolled by a timer and a light relay a s described a b o ~ e. The resnlls from the experinients with CO, will be reported in a sepnrale paper ( S i r h & A l d h 1971).
2.2. Experiments with water
Thc occurrence of summer shoots i n different levels of water was investigated i n experiments carried out by Elowson (1971). T h e plants were sown under the standard conditions of the nursery. During their second yegetation period the plants were grown i n five different levels of moisture namely 50, 60, 70, 80, a n d 90 per eent of the saturation value of peat. Each experimental plot consisted of a plastic container measuring 40 x 60 x 10 cm i n which 50 plants were placed. T h e moisture was checked by weighings and the amount of water which was supplied to the containers mas determined i n this way. Three dif- ferenl series with three repetitions of each moisture h e 1 were in- cluded in the experiments which were performed i n a greenhouse without C0,-supply. In all about 2,250 111-plants were studied in this experiment,
2.3. Experiments with nutrients
T h e influence of nutrients on the formation of summer shoots was studied in a two-years experiment. During the first year the plants were son-n a n d supplied wit11 nutrients a t four different levels namely 0.3, 1.0, 1.5 and 3.0 g N per 1112 a n d week. During the following year the nutrient supply was 3.0 g N per n12 a n d week in all plots. Before the second year the plants were thinned so that there were 50 plants in each container. These were of the same type a s described above. T h e experiments were carried out i n a C0,-atmosphere of 3,000 ppm. I n all 1,800 plants were included in this experiment.
3. Results
The studied enr,ironmental factors: CO,, water a n d nutrients all h a d influence on the formation of summer shoots. F r o m the experiments it is clear that there is a connection between enrironmental conditions during the preceding year a n d the occurrence of summer shoots during the following year. Plants which were grown under favourable environ- mental conditions during the first year had a smaller number of sum- mer shoots during the following year than plants which TTere grown under less favourable conditions during their first year.
Figure 1 shows that llie height gron-th during the first a n d second year was best a t a C0,-level of 3,000 ppm. Figure 2 shows the occur- rence of summer shoots i n the same experiment during the second year. From Figure 3 the same tendency is obvious in spite of less opti- m u m conditions during the second year.
I n experiments with nutrients the supply was varied only during the first year. During the following year the nulrient supply was equal to all plots. Figure 4 rereals t h a t the best nutrient conditions during the first year resulted i n a decreased number of plants with Eaninias growth and prolepsis during the next year, while suboptimum nutrient supply during thc first year caused a n increased number of plants with Lammas growth and prolepsis during the following year.
These two experiments indicate that fa\ ourahle environmental condi- tions during the first yctrr result in small occurrence of summer shoots in the follom-ing year, while the following two experiments show that improped en~ironimental conditioiis during the second year result i n a n increased number of planls with summer shoots.
Elovison (1970) has prol-ed that the o p t i m u n ~ substrate moisture for growth of pine seedlings in peat is ahoul 80 per cent of the satura- tion value. Figure 5 illustrates the fact that the greatest number of plants with Larnnias growth and prolepsis occurred in plots with the most fa7 ourable moisture condilions.
In one experiment plants were sown under the slandard conditions of the nursery, i.e. without C0,-supply and with standard supply of water and nutrients. Before their second growing season the plants were placed in different C0,-levels. During the first shoot growth in
i t , cm
First Second
3 0 0 1,200 2,400 3,000 3,600 C0,-level f i r s t year, p p m 3 0 0 3,000 3,000 3 0 0 0 3,000 (1 second year,ppm Open a i r G r e e n h o u s e
Figure 1. Height growth of Scots pine during two years in different levels of CO,.
C02-level f i 4 ye,ar, ppm 3,000 300 3,000 3,000 3,000 3,000 " second year, ppm Figure 2. Occurrence of summer shoots in 2-year-old (I/,) plants of Scots pine. The plants
are grown in the different C0,-levels as indicated. No summer shoots were noted in plots in t h e open air.
1,200 2,400 3,000 3,600 C0,-level f i r s t y e a r 3 0 0 3 0 0 3 0 0 3 0 0 11 second year
Figure 3. Occurrence of Larnmas growlh and prolepsis in 2-year-old (11,) plants of Scots pine. The plants are grown during Lhe first gear in different GO,-atmospheres and during the second year in t h e s a n e C0,-atmosphere.
spring there were only sinall divergences belween plants i n different CO,-le~els i n this experiment. I-Iowever, examination of the occurrence of summer shools i n the later par1 of the summer showed that there were great differences between the varied treatments. Figure 6 shows that the number of planls with summer shoots was greatest in CO,- levels which previously were proved to be the most favourable for growth.
Shoot growth seems lo be more dependent on the conditions of the preceding year than of current conditions (Figure 7 ) However, the
A d d e d f e r t i l i ~ e r , g ~ / peat m ~
a n d w e e k f i r s t y e a r
Figure 4. Influence of different nutrient supply during t h e first year on current height growth and on t h e occurrence of summer shoots cluring t h e following year.
Plants n o t transplanted.
Substrate moisture, % of saturation value
Figure 5. Influence of varied substrate moisture during lhe second year on the formation of summer shoots in 2-year-old. (I/,) plants of Scots pine. During the first year the plants were gronn under standard conditions of the nursery.
3 0 0 1,200 2,400 3,000 3,600 C0,-level second year, ppm Figure G. Occurrence of summer shoots among 2-year-old ( I / , ) plants of Scots pine which
during their first year were grown in greenhouse without C0,-supply and during t h e second year in different levels of CO,.
Height, cm
i I
First Second year year
300 3,000 COz-level f i r s t year, ppm 3,0 0 0 3 0 0 1 ' second year, p p m
Figure 7. Comparison I~etween the height growth of 2-year-old (I/,) plants which are grown in 3,000 ppm C0,-atmosphere during the first and second gear respectively and t h e other year without C0,-supply.
Table I . Height growth during the seeond year in per ceut of the height growth of the firs1 year.
C0,-level first gear, ppm 300 300 3,000 3,000
C0,-level second year, ppm 300 3,000 300 3,000
Relative growth, % 186 200 156 180
elongation will not be cnlirely independent of current environmental conditions. F r o m Table 1 i t is clear that a n increase of CO, during the second year causes a n increased relatiye elongation growth. Lowering of the GO,, on the other hand, causes n somewhat decreased relative growth in comparison with unchanged conditions.
In all experinienls the most frequent type of late season growth was proleptic shoots, i.e. shoots forrned from the lateral buds a t the base of Lhe terminal bud (Figure 6 a ) . I n connection with the formation of proleptic shoots there is a slrong inhibition of the apical dominance which thus results i n a fork-shaped plant. H o w e ~ e r , in plants which have been studied for two years after Lhe formation of sunimer shoots the terminal bud flushed in a normal way in the following spring. I n some cases the lernlinal shoot h a s been somewhat shorter t h a n these
formed from buds on the proleptic shoot of lhe previous year. Occa- sionally a new leading shoot h a s been formed i n this way.
When I,ammas growth occurs iL is generally i n combination with proleptic shoots (Figure S b ) . Lainmas growth alone occurred only in esceplional case v h i c h makes il possible lo neglect the few occurring plants of this type in the test. The occurrence of proleptic shoots a n d the combination Lanunas growth-proleptic shoots a t different times during the summer is represented i n Table 2 a. The ratio between these two types of late season growth is shown i n Table 2 b. Comparing the figures of 25 J u n e a n d 16 September i n Table 2 b i t is clear t h a t Laiimias growth in combination with prolepsis becomes a n increasing part of late season growth during the later part of the summer.
In some respects sunlrner shoots have different morphological characteristics in comparison with normal ones. Thus, conlmonly there are three needles in each whorl on suimner shoots, while the nor- mal n ~ u n b e r is two (Figure S a, S h ) . Another type of shoot is shown i n Figure S c. This type bears single primary needles of the same type as i n one-year-old plants. Even the buds in this type of shoots are the lypical "juvenile" ones, i.e. one single bud without any laterals.
Table 2 a. Occurrence of sumnler shoots at different times during sulnmer. Figures given in per cent of total number of plants in each plot. Figures in brackets refer to plants with both Lammas growth and prolepsis.
CO, level, ppm D a t e of s u r v e y
Table 2 1). Occurrence of plants nilh both Lammas growth and prolepsis at different times of the summer. Figures given in per cent of the total number of plants with summer shoots.
CO,-level, ppm Date of s u r v e y
Figure 8. Different types of summer shoots in Scots pine.
(a) Proleplic slloots x i t h three needles in each n7horl (I) vliile t h e normal shoots hear two needles in each whorl (2). Terminal b u d has not flushed (3).
(b) Larnmas growth and prolepsis, both will1 three ncedles in each whorl (1).
Xorrnal shoot x i t h two needles in each whorl (2).
(c) Proleptic shoot with "juvenile" shape, i.e. single primary needles (1) and without laleral buds (2). Sorrnal shoot with two needles in each ~ ~ 1 1 o r l (3).
4. Discussion
The results from the different experiments confirm the well-linown facL that there is a slrong conneclion bet~veen the environmental condi- tions during Lhe first year a n d the shoot growlh during the following year (Iiozlowslii 1964 b ) . This is valid not only for the shoot growth in spring b u l also for the forination of summer shoots. Thus, the freque~lcy of summer shoots could he rclalcd Lo the enviroilinental conditions of the preceding year. The results from this sludy indicate that a fa+onrable constellation of c n ~ i r o n m e n t a l facL0r.s during the preceding year is followed by a slrong shoot growth in spring and a small number of plants with summer shoots in the following year. On the contrary, poor enviroimlental conditioi~s during the first year are rollowed by a n increased number of plants with summer shoots.
Shoot growl11 has prrriously been proved to he dependent essentially on carbohydrate reserves i n the plant a n d no1 on a current photosyn- thesis (ICozlosdii 1955, l95S, 1962, 1963, 1964 a, b ) . Newirth (1959) proved for Pinus silvestris that the normal shoot growth mas dependent on nutrient resents i n older needles. If these were removed t h e shoot
~ r o w t h was inhibited. I<ozlowsIii & Clause11 (1966) found a rapid decrease in d r y weight in one-year-old needles of Pinzzs resinosa during shoot growth mainly because of trsnslocation of carbohydrates from the needles to lhe expanding shoot. Rutter (1957) found shoot growth of young Pinzzs silvestris to be completed in the middle of June. On 26 May, when approximately half the shoo1 growth was completed, the whole plants had decreased in d r y weight.
T h e results u n e q u i ~ o c a l l y show t h a t enviroilmental factors have in- fluence on the formation of summer shoots. F a ~ o u r a b l e current condi- tions seem to be a prerequisite for its formalion. Evidently there is also a coilnection betm-een the shoot growth i n spring a n d the forina- tion of sunliner s h o o k a s well as between the conditions during the previous season a n d the shoot growth i n the following spring.
Thus, if the plant owing to suboptimum environinental conditions has no possibilities of storing enough carbohydrate reserves i n the roots, stem a n d needles, this will influence the development of the shoot the following year. The foregoing m a y be summarized in the following schedule.
First year A Gromih.
B Nutrient reserw.; arc built up and stored.
Second year -1 Sutrient reseryes are used for shoot growth.
B Some of the growth is performed by products from a current photosynthesis.
C Nutrient reserves are built up and stored.
111 the normal case the sleps A and B during the second year seem to be close to each olher a n d not distinguishable a s two different steps hut as a continuons growth. If during the first year the plant owing to poor enrironmental conditions can neither produce nor consec~uently store adequale amounts of nulrienta, Lhe step A during the following year (second year) i esults i n a poor shoot gron th.
I<ozlor~slii & Iieller (1966) dixide species of woody plants in the temperate zone into two different groups with respect to shoot growth characteristics a n d dependency on carbohydrate reserves for shoot elongalion. In the first group-which includes the Pinrrs species-the shoots are predetermined in Lhe minter bud. According to this theory shoot formation in\ol\es bud differenliation during the first year a n d extension of the preformed parls milhin the bud into a shoot during the second year. I n the second group the shoots are not fully preformed in the n inter bud and holh early and late lea\ es are produced. Ranked under this group are, for inslance, several P o p z ~ l u s species.
According lo the foregoing the nuinher of leaf primordia and cells i n the future shool is fixed already i n Ihc bud (Sacher 1954, I<ozlowslii 1938, 1963). This means that i r n p r o ~ e d e n ~ i r o n m e n l a l conditions during the shoot growlh cannol influence the size of the shoot by a n increased cell number but by affecting the cell enlargement. Of course this is possible only u p to a certain limit. A high photosynthetic activity after the buds are formed may cause a n enrichment of carbohydrates i n the plant l o such a n exlent that the capacity for the plant to store it is wholly utilized. This in t u r n may affect the formation of a new shoot. Probably there is some mechanism involved which is influenced by the carbohydrate state of the plant and which can affect bud break a n d shool g r o v l h . If such a pathway exists, this is not the normal way for control of bud l~realc a n d shoot growth hut neither are summer
f $5;
< L M Y O U R A B L E en v i r o n m e n t d conditionst I
\L large carbohydrate reserves
FA VO U R A B L E envl'rsnmenta/ condifions
early formation
a c t i v i t y
1
late f o r m a t i o n
of buds of b u d s
c a r b o h y d r a t e s a r e c a r b o h y d r a t e s a r e stored i n needles, used f o r c u r r e n t stem and r,oots shoot g r o w t h
\1
Is e c o n d f l u s h
J/
m o r e t i s s u e s f o r (= s u m m e r s h o o t ) s t o r i n g c a r b o h y d r a t e s
a r e a v a i l a b l e
Fig. 9. Proposed possibilities for influence of e m ironmental factors on the formation of summer shoots in seedlings of Scots pine.
shoots a noriilal occurrence. In fact, there are ITYO abnormal phenomena in\ ol-\ed in Lhc formalion of summer shoot^ n h i c h 11oLh arc affecled b~
growth regulators, Firstly, the bud break and formation of shoots with- out pa\sing a complete dormancy period and, secondly, the inhibited apical dominance.
Day length and light conditions a r c i n addition Lo temperature factors which h a \ c heen proTed to influence Lhc onset and termination of dormancy. Thc effects of these faclors arc probably mediated by growth regulators such a s gibberelins, cytoliinins, auxins a n d in- hibitors. h possihlc explanation of thc formation o f summer shoots seems to lac that the levels or functions of one or inore of Lhese growth
regulators a r e affected by carbohydrates which a r e stored in the plan1 and that this mechanism exists beside the normal pathway.
This hypothesis might be connected to the above-mentioned observa- lion of Kovalenlto, that summer shoots arc inost frequent in young plants a n d that the tendency for their formation decreases with the age.
In other words, small plants with limited space for storage of nutrient reserves are furnished with a mechanism which enables them to use a surplus of carbohydrates for a second flush, mhile bigger plants or trees have better possibilities for storage of such a surplus i n needles, stem a n d roots. The schedule in Figurc 9 illustrates the behaviour of plants in different enxironmcntal conditions according to this theory.
As far a s apical dominance is concerned there are several theories about its control ( B r o x n , hlcA21pine & Kormanili 1967). Most of these theories involw influence by growlh regulators ~ v h i l e other show in- fluence by nutrienl metabolites in the plant. However, the inhibited apical doiniilance v h i c h occurs i n connection with the formation of proleptic shoots musk be regarded as a special case where the terminal bud is temporarily blocked. All theories concerning apical dominance deal nit11 the problem of how axillary buds are depressed in one way or another. As this i \ not the case in regard to l)roleptic shoots, olller explanalions of Lhis phcnoinei~on might be possible. Differences in the concentration of growth regulators belween terrninnl and laleral buds are one possibility \vhich has formed the ljasis for a present investiga- tion ( A l d h 1971, Aldkn & Eliasson 1970).
1 C I I \ O W L E D G E M E i L T S
I r ~ r a h to expre5s 1 1 1 ~ 5lncere a n d grateful thanks to in> chief, Professor Gustaf Sirbn, head of Ilepartment of Reforestation, Roq a1 College of Forestry, Stocliholm f o r con3lant support, advice a n d criticism during this study. I am also very i n ~ t c l i indebted to Dr Lennart Eliasqon, Department of Botany, C n i ~ e r s i t y of Stocltholin for man\ valuable diccussions a n d criticism. My rincere thanlib a r e al5o due to AIr K i l ~ Forshccl for excellent drawings and to i\Irc Eir o r Hcdqa15t for t > p i n g the iiinnu5cript.
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sammaiifat tning
Inverkan av C02, vatten och naring pb bildningen av sommarskott hos plantor av Pinus silvestris L.
Den normala sliottskjutningen a r 110s flertalet vetlviixter en t v i i r i g process nied knoppbildning under det forsta Bret och skottskjutning under pifoljande 5r. Under vissa betingelser kan einellertid s. k, sornrnarskott bildas vilket innebiir att skottskjutningen sker sainina Br soin ltnoppen bildats. Forekoms- ten av solnrnarskott hos tallplantor h a r hittills varit av ringa omfattiling och i praktiken saknat betydelse. I och med inforandet av nya drivningsmetoder i plantskolor h a r dock problemet fc~tt storre aktualitet. I forsoli ined drivning av tallplantor i plastvasthus h a r antalet soinnlarsliott oliat inycket starkt i jiinlforelse med dess forekomst vid konventionell odling 115 friland.
Den foreliggande undersokningen h a r utforts u n d e r Bren 1967 till 1969 r i d Sliogshogskolans forsoksplantskola i dgrcna, L a x i d a r institlitionen for skogsf6ryngring vid Skogshiigskolan u n d e r Br 1965 pBborjade ett forsknings- och utvecklingsprojekt med arbetsnainnet: n0peration niaskinplanteringn.
Ett av syftena med detta projekt var att jiirnfora olika niiljofaktorers bety- delse for tillvasten av skogstradsplantor vid drivning i plastviixth~zs.
Resultaten visar att de undersolita faktorerna CO,, vatten och niiring 13%- verkade bildningen av sornnlarskott hos tvMriga tallplantor samt att en gynnsam niilj6 under (let it- sommarskotten bildas torde vara en fiirutsZi1- ning for deras uppkomst. E n inoptimal iniljij under sRdc1:"iret ined en fSr- biittrad miljo under foljande Br medforde en hog frekvens, nledan en gynn- sam rniljij under s 5 d d i r e t resulterade i en l i g frekvens av plantor nied som- inarsltott.
Sltottbildningen 110s vissa vecivaster -- diiribland Pinusarter - Br enligt Kozlowski & Keller (196G) forutbestiiind redan vid knopphildningen (Sa- cher, 1954; I<ozlowski, 1958, 1963). Enligt clenna teori 5r antalet bladanlag och celler i det blivande skottet fixerat redan i knoppen. Detta rnedfor att en gynnsam iuiljii under skottslijutningsBret inte kan pi\-erlia skottets storlek genoin ett okat antal c,eller utan endast cellernas storlek. E n hog fotosyn- tetislr aktivitet i plantan lian diirvid medfora en anriktning av kolhydrater son1 inte anviinds for skottskjutningen utan lagras up11 som reservnlring.
Som en hypotes och mojlig forklaring till uppltomsten av sornmarskott disku- teras mojligheten av att en s5clan ansamling av kolhydrater i plantan lian p i v e r k a utbildningen av sommarskott. E n s5dan piverlian bor riinligtvis ske via tillviixtregulatorer.
Electronic version
O Studia Forestalia Suecica 2002 Edited by J.G.K.Flower-Ellis
