Matyssek, R. (1985). The carbon balance of three deciduous larch species and an evergreen spruce species near Bayreuth (W.-Germany). In H. Turner & W. Tranquillini (Eds.), Berichte, Eidgenössische Anstalt für das forstliche Versuchswesen: Vol. 270. Est

Proc. 3rd IUFR0 Workshop P 1.07-00, 1984. Eidg. Anst. forstl. Versuchswes., Ber. 270 (1985): 123-133.

THE CARBON BALANCE OF THREE DECIDUOUS LARCH SPECIES AND AN EVERGREEN SPRUCE SPECIES

NEAR BAYREUTH (W.-GERMANY) R. Matyssek

Lehrstuhl Pflanzenokologie der Universitat Bayreuth Postfach 3008, 8580 Bayreuth, West Germany

ABSTRACT

Field experiments on carbon and water relations at the leaf and at the whole plant level were carried out near Bayreuth

(W.-Gerrnany) on 33 year old specimens of deciduous Larix decidua, Larix leptolepis, the hybrid of both species and evergreen Picea abies. COz assimilation rates per leaf area were similar in all larches and were 40% higher than those measured in spruce. However, water use efficiency was higher in spruce than in larches. Stern respiration in hybrid larch reached a maximum in July, when stern increment rate declined.

Increased needle density in hybrid crown was achieved by a combination of having the branching pattern of Japanese larch with the needle density of European larch. For all three larches the annual carbon balances showed similar relative costs for stern and root systems. Heterosis in the larch hybrid was mainly based on a more effective needle arrangement and a more spacious crown compared with the par- ent species (complementation principle).

Spruce invested less carbon into non- green crown organs and current-year nee- dles than larches. However, the carbon balance costs for the root system was greater than in the larches. From this study, the evergreen life form exhibited less water and nitrogen uptake than the deciduous species, but also required greater longevity of well-functioning nee- dles.

INTRODUCTION

Among perennial plants, species that are able to form wood appear to have a substantial advantage over those that are strictly herbaceous. Especially trees, by developing woody sterns and arranging as- sirnilatory organs meters aboveground, out- compete smaller plant life forms and gen- erally form the climax in succession

(Ellenberg 1978). It is the transformation of non-green living tissue into non-re- spiring structural biomass, which is still an integral functioning part of the plant, but does not contribute substantially to carbon loss (Schulze 1982). Although prog- ress has been made on understanding the general evolution of the deciduous versus evergreen habit (Axelrod 1966), the de-

tails of the evolution in specific envi- ronments remain to be resolved. For plants of the temperate zones investigations of both carbon balance and allocation have provided insights into ecological signif- icance of deciduous and evergreen foliage types (Schulze 1970, Schulze et al. 1977).

With low assimilation rates, but long nee- dle longevity, evergreen habit enables Picea abies to a higher net productivity than deciduous-leaved Fagus silvatica, de- spite beech possessing rnesophytic leaves requiring only low carbon costs for high carbon returns. However, since gymnosperms and angiosperms have different wood struc- tures and perhaps also different reserve storage capacities, the significance of deciduous versus evergreen habits can be further evaluated (Schulze et al. 1977).

The evergreen spruce Picea abies and de- ciduous larch Larix decidua, two gymno- sperm trees of the same family, were cho- sen for this study to test the conclusions on a more comparable basis.

Hybrid larch (parent species Larix decidua and Larix leptolepis) displays a significant heterosis and has been se- lected by foresters because of its rapid growth, higher productivity and larger size (e.g. Gothe and Schober 1971). How- ever, the functional physiological basis for this heterosis in larch is not known.

From studies of hybrids of herbaceous plants with economical importance i t is known that the analysis of heterosis can be very complex (Sinha and Khanna 1975).

Since the Bayreuth experimental site pro- vided all larch species in question within a close proximity and all with the same age, the approach in this study was to evaluate the heterosis through comparisons of photosynthetic capacity, biomass struc- ture, carbon allocation and annual carbon balance. In this respect, different char- acteristics between larches and the eco- logical significance of deciduous and evergreen foliage for the larch-spruce comparison will be discussed, interpreting hypothetical changes in the observed tree properties.

MATERIAL AND METHODS

All investigations were conducted on hills near Bayreuth ('Hohe Warte', 450 rn elevation, w.-Gerrnany). The tree species compared were Larix decidua, Larix lepto- lepis, the hybrid of the two preceding

species and Pieea abies. The five indi- vidual trees investigated grew within an area of 70 m2 . The experimental site was situated in a managed artificial multi- species forest, mainly composed of larch, spruce and pine. These trees formed a closed canopy of~ 15-16 m height, with the exception of the larch hybrids, which were emergent with heights of ~20 m. In all larches the lowest needle-bearing branches occurred at "' 9 m height and in spruce in~ 6 m. In 1982, all trees inves- tigated had an age of approximately 33 years. Further informations on the soil and climatic and phenological character- istics at this site have been presented by Benecke et al. (1981) and Matyssek

(1981).

Gas exchange measurements were made with thermoelectrically-controlled cu- vettes which operated on naturally grow- ing attached twigs at 11 m (shadecrown) and 13 m (suncrown) aboveground. The operation of the gas exchange system has been described by Koch et al. (1970), Schulze et al. (1972), Schulze and Kilp- pers (1979). Compared with Matyssek

(1981), this system was extended to in- clude three computerprocessed cuvette sys- te1ns; Two types of experiments were con- ducted in the field: either co 2 assimi- lation and transpiration were measured under natural light, temperature and humidity conditions, or steady-state con- ditions were observed under constant light, temperature and humidity (artifi- cial light source see Benecke et al.

1981). Dewpoint mirrors (Walz, Effel- trich, w.-Germany) were used to measure and control humidity, needle tempera- tures were measured with 0.1 mm copper/

constantan thermocouples, irradiance was measured with several quantum sensors

(LI-COR) and a pyranometer was used as a reference for above-stand solar radia- tion. , Total area of needles was deter- mined using a glass beads technique

(Davies and Benecke 1980).

A special open system was arranged for measurement of stem and branch res- piration on the larch hybrid. Following Havranek (1981), two plexiglass cuvettes impermeable to light were sealed to the bark in stem heights of 1.8 m and 7.5 m;

a third cylindrical chamber enclosed a 30 cm section of a main branch at 13 m aboveground. Respiration and cambial temperature (Pt-100 sensors) were meas- ured continuously, while ambient air was flowed constantly through these chambers.

Changes in stem increment were recorded with mechanical steel ribbon dendrome- ters.

Estimates of the total aboveground biomass distribution and incremental growth were achieved with representative sampling methods. Using a statistical approach, the minimum sampling size need- ed to determine crown parameters required for a harvest of ea. 15 % of all living main branches per tree, and correlations to branch lengths of all living branches per tree were then made to estimate total dry weight of needles, non-green organs, wood increment and lengths of all twigs per crown. Growths increments of stem

wood and calculation of xylem areas were derived from core-probes, sampled as de- scribed by Von Droste zu Hulshoff (1969).

Biomass investigation of the root systems was not possible due to the closeness of trees within the forest (cf. Matyssek 1981).

Estimates of annual carbon balance per tree were based on biomass investi- gations and gas exchange observations.

Since recording of climatic parameters ran over a 12-months period and gas ex- change data on each tree was limited to a shorter period, an empirical model was developed to predict co 2 gains for any given climatic situation. The model com- bined informations from both diurnal tracking and steady-state gas exchange experiments and took into account the distribution of irradiance within the crown and also the differences in sun and shade type needles inside crown (Matyssek 1985, in preparation). Total co 2 loss by stem and branch respiration per tree on an annual basis was calculated on a dry weight basis of wood increment as pro- posed by Linder and Troeng (1980) .Stem and branch respiration properties as well as gas exchange of shade type needles were measured on the hybrid larch and assumed to be the same on the other trees. The behaviour of shade type nee- dles in spruce was adapted from Fuchs

(1974). For carbon balance estimates the dry weight/carbon ratio from Larcher

(1969) was used.

Determination of needle total (Kjeldahl)-nitrogen content were done using a microanalytical method from Strauch (1968). Total xylem sap flow per tree was measured with a mass flow sys- tem described by Cermak et al. (1982).

Representative measurements of xylem wa- ter potential on one year old twigs were measured with a pressure chamber (Scho- lander et al. 1965).

RESULTS

1. Diurnal and Annual Courses of Needle Gas Exchange

In Fig. 1 daily courses of climate and gas exchange parameters are presented for the three larch species under compa- rable ambient conditions. Courses of C02 assimilation rate and stomatal conduct- ance for water vapour appear mainly de- pendent on changes of irradiance and am- bient air humidity. No marked differences in C02 assimilation rates or stomatal behaviour were detectable. Only during the early and late daytime hours did the mesophyllinternal C02 concentrations dif- fer due to the locally different light conditions. Maximal assimilation rates

(Amax) under constant conditions for annual courses are shown in Fig. 2. The steady-state experiments under non-lim- iting climate conditions were light>900µ E/m2 /s, needle temp. 12-18°c, .cl w ~ 8mbar / bar, see Matyssek (1981). On a leaf area basis, the suncrown needles of spruce

Lorix Bayreuth 1000

7 E 500

;:

1000 1,

~ ⁵⁰⁰

2, E

40

E

_~~

20 0

~

20

.,, :;

..s

10

;:

<l 0

t

0 E 0 2-

<{

·~

~ ] ⁵⁰

..s ,;~

0

e _a.

~-200

0 0

above

12 t lhl

16 20 24

Figure 1. Diurnal courses of irradiance (I), needle temperature (Tl), diffenence in water vapour concentration (~w), CO2 assimilation rate (A), stomatal con- ductance for water (gH20), CO2 concen- tration in mesophyll intercellulars (ci) for Larix decidua 31.7.82

Larix leptolepis 31.7.32 - - - - - Larch hybrid 3.o.82

(All values as means of readings per minute)

Boyreuth Larix dee x !ep

o suncrown

• shodecrown

"'lorix deciduo } _suncrown oLaro: !eptotep1s

/

~

Picea abies~stmcrown l year old needles

M A M A 0 N

50 lanx

!eptotep1s

^{. ...} /

Bayreuth

0 t<--+---+---+---+---+---t-i

50

i

⁰

<{ Larix

/.

0 ¹⁰⁰ decidua

,;,,

le

_]

.. _.

^,

..s

50 ^~ ';

:J:

^*

.

0 Prcea ab1es

50 ^/:·

/

2

0

2 4 6

A=~(µmotm-.?s-i l

Figure 3. Long-term responses of maximal Co2 assimilation rate (Amax), and stomatal conductance at Amax (gH2O) to non-limiting climatic conditions during annual courses

* from BENECKE et al. 1981, o 1981

• 1982

+ Larch hybrid, shadecrown 1981

Figure 2. Combined annual courses of maximal CO2 assimilation rate (Amax), at non-limiting climatic conditions for

Larch hybrid 1980 - 1982

Larix decidua,L. leutolenis 1981 1982

Picea abies 1931 - 1982

displayed assimilation rates ea. 40% low- er than those measured in larches. Fig. 2 also shows the longer assimilation period for spruce as compared with that of the deciduous trees. Among larch species, Amax values were roughly similar, al- though the hybrid tended to exhibit slightly higher photosynthetic capacity

{also shown by Benecke et al. 1981) . Schulze and Hall (1982) have shown that the slope of Amax related with stornatal conductance at Amax during longterrn changes describes water use efficiency.

When values of Amax through the year were plotted against stornatal conductance at Amax, there was an indication of bet- ter water use efficiency for Larix lepto- lepis and Picea abies than for Larix decidua {Fig. 3). The hybrid appeared intermediate between the two parent spe- cies. During the vegetation period, the Kjeldahl nitrogen contents were ea. 10%

higher in larch hybrid than in parent species {hybrid"' 30rngN/gDW; parents ~26 rngN/gDW; spruce"' lSrngN/gDW) • This corre- lated well with the slight differences in Amax, although unavoidable influences of heterogenous twig material even within same crown zone on C02 gas exchange can- not be excluded completely as well as in- fluences of changing plant water status.

2. Stern and Branch Respiration Fig. 4 presents the annual courses of stern and branch respiration, stern in- crement and ambient air temperature.

First there was a small change in stern respiracion activity after several warm days in March. This coincides with the beginning of needle development and was followed by another more significant in- crease in stern respiration (Fig. 4A), which started synchronously with the on- set of radial stem growth in mid-May

(Fig. 4B,C). When maximum growth inten- sity had delined in July, the activity of stern respiration reached a maximum, most likely due to the activity of newly- formed xylem cells that may have been still alive (see Havranek 1981). Differ- ences in stern respiration between both stern heights (despite of comparable an- nual wood formation) may reflect differ- ent time spans for lignifying of newly- formed xylem cells or different amounts of parenchyrnatic cells. However this was not investigated. The time course of branch respiration appeared to be rela- tively constant through summer. In prin- ciple similar annual courses of bark area related stern respiration as in larch hy- brid (Fig. 4A) are reported for Pinus sylvestris (Linder and Troeng 1980) and for Pinus cembra and Larix decidua at alpine timberline {Havranek 1981, pers.

comm.) .

3. Crown Biomass and Distribution of Light

Table 1 shows that all larch species displayed similar ratios for green to nongreen crown organs. This contrasted with the branching pattern of the main axes, where European larch had highest branch density, Japanese larch the low- est and the hybrids were more similar to the Japanese parent. However, hybrids

{ .s

c s

'

J

2

I

I

²⁰

E

~

0 0

20

"' 0

·S

!

F3oyreuth

stem height ~ 1 8 m A

•7Sm o13mbrnnch

ri\ __

I !\ \ ·-·---.

.-·

/ ^'-

I /·-· \ ,\

. / \ _\

. / I .-·, ,-•- , ,,.t\,~),,1;-- . - -- - ..::::...

I . . . . ,

__

-.,/~...._, ... ---~..,,-

-

..._ ./"'-..,

___ "

^'

:;e:::;;;'::::::- ' ,/ -- --- ^~

-·

8 mo, grnwlh ,ote

l(f\

~::;,:',~::y . lt. \J'::::~. . '

1/ \\/'x\/"\.

• C

/\ ^{/\./\ ,/\}

( vj ^{·,,J "\ -}

. . ,,

/\i'j

f\

!,/·

\J

M A A

Figure 4A. Annual course of stern and branch respiration rate {R), at different stern heights at 10°c (mean values perweek) Figure 4B. Stern increments at two differ- ent stern heights (symbols as in A)

Figure 4C. Air temperature in crown 12 rn aboveground.

displayed highest needle density, carrying ea. 30% more needle dry weight per meter stern height of living crown than either of the parents. This needle distribution for the hybrid was achieved by combining the high branch and twig length density of Japanese larch with the high needle densi- ty on branches from the European larch, the latter fact being confirmed also by differences in shortshoot numbers per twig length. Assuming the same conductive prop- erties for the xylem in all larches, the data in Fig. 5 suggest the higher needle density per crown stern lengths in the hy- brids requires a higher conductive xylem area. In fact the slopes are 30% flatter for hybrids compared with the parent spe- cies (drawn lines). This means that the xylem conductive area per unit stern length was higher in the hybrids.

Spruce differed in needle dry weight from larches by a factor of 2.5, when sun needles of all species were compared on a total surface area basis. This explains main differences between spruce and larches in table 1. Although branching pattern appeared similar to larches, spruce invested less structural costs into non- green crown organs.

TABLE 1: Characteristics of Crown Biomass (DW drv weiqht)

Larix dee. X lep. Larix Larix Picea leptolepis clecidua abies

I II

total branch and :t;yzi:l):

DW

_(g/) 4.22

total DH needles · 3.41 3.36 3.32 1. ·10

g number of branches ( 1 / )

stem. length of living crown m 13.6 15.8 12. 1 22.9 17. 5 total DW needles (kg/ )

stem length of living crown m 0.89 1. 16 0.68 0.73 1 .50

total leng:th of twig:s and branches (m/ )

stem length of living crown 406 408 367 275 358

m

total DW needles (g/)

total length of twigs and branches 2 .18 2.85 1. 85 2.66 4.20 m

number of short shoots 1

twig length ( 1cm) 0.7-1.2

----

^{0.6-0.7 0.8-1.5}

----

total DW wood

total length of twigs and branches (g/ ) m

20

]:

:c 0,

·.;

.c

~ 10

;:;;

Larix Boyreuth

0 0~----~s~o----1~00 _ _ _ _ _ 1s~o----1200 Conductive xylem area (cm2}

Figure 5. Conductive stem xylem area of living crown as related to stern height

drawn lines: actual values

dashed line: simulation values from Figure 10

Larch hybrid (2 individuals) Larix decidua

Larix leptolepis

Figure 6. Crown shapes of trees con- sidered based on branch measurements (cf.

MATYSSEK 1981) and needle distribution:

d light exposed needles in suncrown p near stem (proximal) needles in sun-

crown and distal needles in shade- crown (assumed as shade type needles) s : proximal needles in shadecrown

percentages show proportions of needle types as total dry weight biomass of all crown needles

9. 19 9.72 6. 72 8.84 4.61

Lorix dee x lep Boyreuth, July 1982

100 , - - - - , - - - - , - - - - , - - - - , - - - - , - - - - , - - - - , - - ~

C 0

-g_ 0 l.O

200

o near stem suncrown {--clear - - -overcast

• lower shodecrown --cteor and overcast

600 1000 1400

Photon flux density outside crown (µmolrrr1s·1)

Figure 7. Larch hybrid: Percentages to which ambient photon flux density is lowered for positions in near stem sun- crown and lower shadecrown

20

Laro:: Lanx Lorn: Piceo

deci duo teptotep1s dee x lep abies

18 d 6l. .,. I.I. ·1. 72 ¼ ,o ¼

p 30 .,. l.9 •1. 26 .,. SO¼

s 6¼ ^7¾ 2¼ 10 •1.

16 ^I

I

I

d / p ^I

t

^ll. ' ^{I I}

i

^{d IP I I I}

E ^I d Ip

12 ^I ' - - - ^I

vi

- , -

_I I

I p I s ^I

p I s I

10

~ 3 2 1 0 3 2 1 0 3 2 1 0

Radial crown extent ion (ml

Fig. 6 depicts the amounts and dis- tribution of shade type needles for shade crown or near-stem (proximal) positions.

As a consequence of the needle distribu- tion in larch hybrid the light received at any given light intensity outside the crown was nearly constant at 14% in the lower shadecrown, but decreased from 50%

to 17% in the near-stem crown with in- creasing photon flux (Fig. 7). These cor- relations were not affected significantly by clear or overcast skies, and lower photon fluxes with a higher relative pro- portion of diffusive irradiance were not so much reduced.

4. Annual Carbon Balance per Tree Table 2 compares the annual CO2 gains per tree on a needle dry weight ba- sis. For the light conditions depicted in Fig. 7, the near-stem needles inside the crown of hybrid larch produced three fourths as much as the sun type needles and the shadecrown needles one third of the amount of

co

2 assimilated by light exposed suncrown needles. As in Fagus silvatiaa the shade needles of larch dis- played a lower light compensation point and appeared to use light more efficient- ly than sun needles (based on a curve fitting model) (cf. Schulze 1970, Retter 1965 in Larcher 1976). For a given time period during the summer all larches as- similated the approximately same amount of CO2. Scatter in the

co

2 totals be- tween larches lie within the accuracy of the applied

co

2 assimilation model

(Matyssek 1985, in preparation). Spruce with evergreen one-year sun needles dis- played a distinctly lower

co

2 gain than larches for the time period considered.

Since in 1982 March was already rather mild and warm, for spruce this month is already regarded as the beginning of the main assimilation period. Thus, CO2

gains from November 1981 to February 1982 accounted for 10% of the gains in the re- maining months. Assuming for spruce a main assimilation period comparable to larch,

co

₂ gains for winter-months would result in 23%.

The allocation of carbon gains is shown in Fig. 8. 'Net carbon gain/

crown' was derived from daily net

co

₂

balance of measured twigs, including respiration of non-green parts. For larch respiration was calculated for bare twigs. Costs of cone respiration were assumed to be the same as presen- ted by Linder and Troeng (1981). The biomass costs of male flowers were as- signed to the preceding year (Annual costs for reproductive organs can change from year to year significantly (Matyssek 1985, in preparation)). In Fig. 8A the differences in absolute carbon amounts between larches were due only to differ- ent tree dimensions, but generally the allocation percentages were similar.

Spruce with a smaller carbon investment into new needles than larches achieved a comparable aboveground biomass increment.

The structural and respiratory costs per organ were united in Fig. 8B. Here i t be- comes more evident that in hybrid larch the stem consumed a higher amount of car- bon than the root system, while in the parent species the total costs for stem and root were nearly equal. For the sec- ond individual hybrid larch investigated, this tendency was confirmed. While in larches the total costs for roots ranged between 25-35% of annual carbon input, spruce allocated ea. 50% to the root. E- ven taking into account twig respiration during winter months, which had already been included in the annual net carbon gain, allocation for roots in spruce would still be greater than in larches.

TABLE 2: Comparisons of Annual CO2 Gains per Needle Dry Weight in 1982 Larix dee. X lep. Annual CO2 Gain ^{(g /} _g ⁾ (%)

suncrown needles _D.U

10G.0 (distal)

near stem suncrown needles

1 0. 1

(proximal) 77. 7

shadecrown needle 4.2 32.3

suncrown needles (distal) CO2 Gain 1 5 . 5.- 3 1 . 8 . 8 2 (g/ ) g Deviations (as ^%) from corn- mon mean of 11 . 6 g/a

Larix dee. X lep. 1 0. 4 - 1 0

Larix decidua 11 . 4

-

2

Larix leptolepis 13. 1 + 13

Picea abies 2. 1

--

(one year old needles)

Picea abies (distal) CO2 Gain Nov-Feb/Mar-Oct 10.2 % (one year old needles) CO2 Gain Nov-Mar/Apr-Oct* 22.9 %

*Apr-Oct comparable to vegetation peri- od of larch

A

et carbon gain/crow biomass increment

stem branches •twigs needles cones

respiration stem main axes twigs (winter) cones d'flowers

1273-8482)

root (increment+

respiration)

B

increment•

respiration for non~green crown organs stem root system

C~content in cur rent year needles

Lor ix

dee x lep

Lar1x dee x lep

32.0 kg 100¼ 1609kg 100¼

Lorix dec1duo

LOflX P1cea

leptolep1s ab1es

0 50

•1. of net carbon gain/crown

DISCUSSION

To evaluate the significance of a deciduous or evergreen foliage in a tree, one must consider the special constraints of the habitat in question and as a re- sponse to this, the carbon, water and nutrient relations typical for each of these foliage types (Schulze 1982). In montane forests in the central Alps Picea abies is dominant, whereas in sub- alpine stands Larix decidua can be domi- nant (Tschermak 1935, in Ellenberg 1978).

Following investigations by Richards (1981) on Larix lyallii, a North-Ameri- can timberline tree, the advantages of deciduousness in such a habitat ,,,as found to be more adaptive to atmospheric frost drought and mechanical damage du- ring cold season. During summer, high light demanding mesophytic leaves have high water use too. This was considered a 'disadvantage' to deciduousness by Richards and could explain the distribu- tion limits of Larix lyallii to regions with sufficient water supply. Indeed, steady-state experiments with Bayreuth larches resulted in two-fold higher transpiration rates on a leaf area basis than for spruce and a seven times higher water loss per needle dry weight of to- tal crown (Matyssek 1985, in prepara- tion). Of course, the Bayreuth site did not represent the natural habitats of both species, but investigations can be seen as a 'laboratory experiment in the

Bayreuth.1982

Lori x leptoleprs

Picea abies

1644kg 100¼ 19.78 kg 100¼

1nc ! ude d in net go in

Fiqure 8 A. Annual carbon balance for the trees considered. Carbon input and costs given as absolute and relative values.

Figure 8 B. Summed carbon costs for plant organs, derived from percentages of Figure '3 A

field' with plant material of same age and under same environmental conditions, which allows direct comparisons. (A Bayreuth- timberline comparison is presented by Benecke et al. 1981). Differences in

co

₂

assimilation for sun needles at the leaf level found in this study, were essential- ly the same as described for deciduous and evergreen foliage by Schulze (1982). In this respect larches appear to have great- er assimilation rates than Fagus silvatica which had assimilation rates of 3.3 µmol

co

_2;m2 /s (Schulze 1970). Although Bayreuth and Solling (where the Schulze (1970) pro- ject was conducted) represent somewhat different habitats, the assimilation rates of spruce at both sites were similar

(Fuchs at al. 1977) and allow to regard Picea abies as a link for the Larix-Fagus comparison. Thus, in the respect, the conifer larch operates like an angiosperm tree due to deciduousness. Considering C02 assimilation rates on a needle dry weight basis with respect to carbon costs invest- ed for carbon returns (Schulze 1982), dif- ferences between tree types become even more distinct (Matyssek 1981, Matyssek 1985, in preparation).

Comprehensive comparisons between tree types require annual carbon balance determination per plant. However, as pointed out by Benecke and Nordmeyer (1982), since these determinations are usually based on estimates, the carbon costs of organs not directly measured (e.g. root

system) will be more affected by small inaccuracies in calculated carbon input.

Determinations of light distribution in tree crowns appear to be most important (cf. Turton 1981). Also stem respiration is important, but has been infrequently measured in the field (e.g. Havranek 1981, Linder and Troeng 1980, Benecke and

Nordmeyer 1982). Despite a generally similar annual course of respiration rate in Pinus sylvestris as compared to larch- es in this study, Pinus sylvestris re- spired less carbon than carbon allocated in stem wood increment (Linder and Troeng 1980), which contrasts with results of this study or those from Benecke and Nord-

meyer (1982) for Nothofagus solandri and Pinus contorta. However, different lengths of vegetation period may be responsible for such differences due to continued respiration of other stem tissues (e.g.

cambium), when annual stem wood increment is already completed (Linder pers. comm.).

Therefore, the annual carbon balance can only give trends for carbon costs of different plant organs. Larches in this study consume similar amounts of carbon for growth and increment of roots as for stem, whereas in spruce the root system becomes prominent in the carbon balance.

In the spruce-beech comparisons Schulze (1981) did not measure stem respiration, but added estimated costs for stem res- piration to the root system. Despite this, the deciduous tree would still need less costs for roots than the ever-

A

water loss 1108 83)(kg}

needle dry weight (g) nitrogen content {g) annual C-goin {kg}

water loss (108 83)(kg}

needle dry weight ( g) nitrogen content ( g) annual C-ga1n {kg)

DETERMINATIONS

only with new needles cons 1dered

1) some needle dry weight, but with needles from Larix decidua

green one. High carbon costs for roots have been reported for the evergreen Pinus sylvestris (Linder and Troeng 1980). Also in another comparison Benecke and Nordmeyer (1982) found that Pinus contorta needed slightly more amounts of carbon for roots than did Nothofagus solandri. Since the latter tree renews most wintergreen leaves every year, i t appears more to be similar to the de- ciduous Fagus silvatica. Also, on a to- tal plant level the larches investigated appear like deciduous angiosperms, keep- ing in mind however, that local water and nutrient supply may affect r·oot growth drastically (Linder and Troeng 1980, Axelsson pers. comm.).

Results derived from field experi- ments primarily describe a given state of plant behaviour, and i t can be diffi- cult to interpret the ecological signif- icance of such results. Therefore, as proposed by Schulze (1982) and Schulze et al. (1983a), theoretical simulations for changed environmental conditions and plant properties can be helpful to inter- pret the quality of plant behaviour. Al- though perhaps an oversimplification Fig.

9 shows hypothetical changes in spruce and larch properties and illustrates the significance of foliage type in this study. As shown in Fig. 9A, any assump- tion which makes a spruce gradually de- ciduous results either in huge carbon gains coupled with greater needs for wa- ter and nitrogen, or results in ever- green-foliage similar water and nitrogen

ASSUMPTIONS

2Jlorch needles with torch needle density in spruce crown

3)dry weight of new spruce needles as larch needles

4) a deciduous spruce would need 6 3 kg larch needles to maintain equal annual carbon 901n

B Larix dec1dua

needle dry weight as spruce needles water toss 110883Kkg}

needle dry weight ( g)

nitrogen content { g} 133 annual C~goin {kg)

Figure 9. Changes of tree properties under simulated conditons:

A: Spruce being changed to a deciduous tree B: Larch being changed to an evergreen tree

uptake, but with a much lower annuel car- bon gain. Creating a deciduous spruce, but keeping the evergreen annual carbon gain constant, would result in a tree like Larix deeidua, while Larix would be unable to exist like an evergreen plant

(Fig. 9B). I t is obvious that same annual carbon gain can be achieved by two dif- ferent principles: (1) being deciduous implies high water and nitrogen uptake during the assimilation period, (2) being evergreen reduces water and nitrogen de- mands, but requires longevity of well- functioning needles. Therefore, being evergreen in temperate zones appears not only to be a response to low light and low temperature, but furthermore, an adaptation to limited water and nutrient supply (cf. Schulze 1982). This may also explain the higher investments of carbon into roots in evergreens. Only severe drought periods with risks of leaf losses, either in the cold or warm seasons, would promote evolution of deciduousness. This agrees 1) with the conclusions of 'Ri- chards (1981) for timberline situations and 2) the conclusions of Axelrod (1966) on the origin of deciduousness in tempo- rarily-arid low latitudes. Further re- search in carbon balances on partly ever- green Larix lyallii or larch-similar, but evergreen Cedrus seems promising. In the Alps the main factors for zonation be- tween spruce and larch appear to be sim- ilar as found by Richards (1981) for the American timberline, i.e. leaf damages and water relations during winter (cf.

Tranquillini 1979).

A second question of interest in this study is an explanation for the heterosis effect of larch hybrid. Heter- osis is defined manifested as a hybrid vigor and is the phenotypic expression

DETERMINATIONS

of a genetic phenomenon (Shull 1914, in Sinha and Khanna 1975). For larch hybrids, high vigor does not seem to be achieved by features intermediate between parent larches. As Gothe and Schober (1971) point out, the crown shape of the hybrid is wider than the broad shape of the Jap- anese larch and the narrow one of Euro- pean larch. This observation agrees with results in Table 1, but Gothe and Schober

(1971) do not analyse the reasons for this heterosis. The complexity of such an analysis was reviewed by Sinha and Khanna

(1975), where two possibilities appear to be most probable: (1) 'Complementation', where the hybrid would unite all those features of parents leading to better vigor and (2) higher net primary produc- tion, based on a more effective combina- tion of net

co

₂ assimilation rate and total leaf area. Even assuming that the

co

2 assimilation rate of the hybrid was not significantly higher than those of the parents, the combination of branching pattern in Larix leptolepis and needle density in Larix deeidua would represent the complementation principle and result in a higher leaf area. This implies a higher net primary production per hybrid tree, but not per needle biomass as al- ready shown in Schulze et al. (1983b). In turn, all factors influencing net pri- mary production or sinks for assimilates already inside crown, like cones, will also influence stem growth as described by many examples (e.g. Eis et al. 1965).

Hence, more needles per crown would first require an adequately thick stem to sup- ply water and nutrients, but all the pro- duction surplus would be available for other purposes, e.g. flower and cone pro- duction in huge numbers or for an in- crease in stem length. The latter fact would create an advantage in a light-

ASSUMPTIONS DETERMINATIONS

some needle density as calculated

Lar1x leptotep1s Lar1x dec1dua and hybrids volume increase Lar1x dee x lep in crown stem

needle dry we1ght{g)

'""+ ^{SoOO+ D □} "'"'"

annual C-goin (kg) 16 44 22 80

--+ -

H actual volume

m crown stem

-

same branching-pattern as Larix dec1duo LOflX leptolepis and hybrids

needle dry we,ght{g) 5130

t--- ^{'"'.♦ □ D}

Hybr,d II

annual C~goin (kg l 16 09 21 so

--➔ - f➔

1--l 1--1

40dm 3 40dm³

Figure 10. Changes of tree properties under simulated conditio~s:

European and Japanese larches are changed into hybri~ larches, and the volume of crown stem is adjusted to high needle density

competitive habitat (cf. Klippers 1983).

Again, some simple hypothetical simula- tions illustrate the significance of the hybrid properties. From calculations shown in Fig. 10, both parent larches are transformed to small hybrids. In- crease in needle biomass for ea. one third would result in a ea. 25% increase in annual carbon gain. But the higher leaf biomass would also require a higher conductive area in stem xylem. The dash- ed line in Fig. 5 simulates the adapted conductive xylem area, now being exactly parallel to that of the hybrids. The same xylem area in hybrids would supply approximately equal amounts of nee- dles as in the simulated small hybrids.

The assumption that thicker stems in hybrid just respond to the demand of a greater needle density in crown appears fulfilled, adjusting stem volumina of parent trees by the proportion of the larger xylem area needed (Fig. 1O,dotted area). For stem lengths with same needle amount in the crown top, the stem volu- mina of all four trees considered would now be very similar.

This calculation is valid, only if the conductive properties in xylem of all larches considered are similar, which has been confirmed by microana- tomical studies (Schweingruber 1978, Grosser 1977), and own observations with electron microscope. Larch in this re- spect is also very similar to spruce.

Similar stomatal behaviour and minimal daily water potential in all larches con- sidered would exclude a higher water need in the hybrid needles per se. This contrasts with the conclusions of Schul- ze et al. (1983b), where the interpreta- tion was based on preliminary data on leaf characteristics. Furthermore, be- fore definite characterization of xylem conductivity, problem should be defined exactly, since wide tracheids could re- sult in high flow resistances (risk of cavitation) as well as narrow ones with high friction on inner walls (cf. Zim- mermann and Milburn 1982).

Recalculating carbon balances in Fig. 10 for changed parent species would not clearly result in a similar pattern of annual carbon cost for stem and root, as shown for the real hybrid in Fig. 8.

However, larch hybrid features cannot be regarded as absolutely constant, because a wide amplitude in hybrid vigor is known, and even among the most produc- tive ones usually found in planted for- ests some differences are possible

(Reemtsma pers. comm.). In summary, heterosis in larch hybrids is mainly based on a more effective arrangement of needles in a spacious crown structure than in either Larix leptolepis or Larix deeidua.

ACKNOWLEDGEMENTS

I want to thank Prof.Dr. Schulze for providing this project and many help- ful discussions as well as Dr.

u.

Benecke, Dr. W. Havranek, Dr. R. Hasler and Prof.

Dr. Boyer for constructive suggestions.

I gratefully acknowledge support by

Dr. Cermak for providing a system for sap flow measurement in stem xylem. Special thanks I want to express to Prof.Dr.

Ehleringer for editing my 'German-like' English.

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