The effects of elevated atmospheric [CO2] on Norway spruce needle parameters

ORIGINAL PAPER

The effects of elevated atmospheric [CO2] on Norway spruceneedle parameters

R. Pokorny • I. Tomaskova • M. V. Marek

Received: 14 June 2010 / Revised: 7 March 2011 / Accepted: 6 April 2011 / Published online: 21 April 2011

� Franciszek Gorski Institute of Plant Physiology, Polish Academy of Sciences, Krakow 2011

Abstract Studies of selected morphological needle

parameters were carried out on young (17–19 year old)

Norway spruce trees cultivated inside glass domes at

ambient (A, 370 lmol (CO2) mol-1) and elevated

(E, 700 lmol (CO2) mol-1) atmospheric CO2 concentrations

[CO2] beginning in 1997. Annual analyses performed from

2002 to 2004 revealed higher values for needle length

(especially for current needles, up to 18%) and projected

needle area (up to 13%) accompanied by lower values for

specific needle area (up to 15% lower, as quantified by

needle mass to projected area ratio) in the E treatment

compared to the A treatment. Statistically significant dif-

ferences for most of the investigated morphological

parameters were found in young needles in the well irra-

diated sun-adapted crown parts, particularly under water-

limiting soil conditions in 2003. This was likely a result of

different water relations in E compared to A trees as

investigated under temperate water stress (Kuper et al. in

Biol Plantarum 50:603–609, 2006). Furthermore, E trees

had much higher absorbing root area, which modified

and enhanced root:shoot as well as root:conductive stem

area proportions. These hydraulic properties and early

seasonal stimulation of photosynthesis forced advanced

needle development in E trees, particularly under limited

soil water conditions. The number of needles per unit

shoot length was found to be unaffected by elevated

[CO2].

Keywords Carbon dioxide � Morphology � Long-term

experiment � Picea abies

Abbreviations

A Ambient CO2 concentration

(370 lmol (CO2) mol-1)

[CO2] CO2 concentration

E Elevated CO2 concentration

(700 lmol (CO2) mol-1)

L Needle length

LA Needle area (projected)

NN Number of needles

NSC Non-structural carbohydrates

SLA Specific needle area

SF Needle shape factor

Introduction

Plants respond to increasing atmospheric CO2 concentra-

tion by acclimation or adaptation at physiological and

morphological levels (Luo et al. 1999; Urban 2003).

Considering the temporal onset, physiological responses

may be categorized as short-term and morphological ones

Communicated by J. Franklin.

R. Pokorny (&) � I. Tomaskova � M. V. Marek

Global Change Research Centre,

Academy of Sciences of the Czech Republic,

Belidla 986/42, 603 00 Brno, Czech Republic

e-mail: [email protected]

R. Pokorny

Department of Silviculture,

Faculty of Forestry and Wood Technology,

Mendel University in Brno, Zemedelska 3,

613 00 Brno, Czech Republic

M. V. Marek

Department of Forest Ecology,

Faculty of Forestry and Wood Technology,

Mendel University in Brno, Zemedelska 3,

613 00 Brno, Czech Republic

123

Acta Physiol Plant (2011) 33:2269–2277

DOI 10.1007/s11738-011-0766-0

as long-term responses. In other words, changes in needle

‘‘function’’ may occur more readily than changes in needle

‘‘morphology’’ (Apple et al. 2000). Leaves are more mor-

phologically diverse and exhibit a greater structural plas-

ticity response in contrasting environmental conditions

than needles. The degree of plant growth responses,

including cell division and cell expansion, is highly vari-

able. It depends mainly on the specie’s genetic predispo-

sition, environment, mineral nutrition status, duration of

CO2 enrichment, and/or synergetic effects of other stresses

(Ainsworth and Long 2005). Morphological changes in

various plant organs due to elevated [CO2] causes changes

in tissue anatomy, quantity, size, shape, and spatial orien-

tation and can result in altered sink strength (Maier et al.

2008). Moreover, plant structural responses to elevated

[CO2] may prove to be more important than physiological

ones in natural competitive conditions (Teugels et al.

1995).

Spruce needles usually persist on a tree for 5–15 years.

However, they fully expand within a few weeks after

flushing and remain constant in length until they fall off.

Width, thickness, and mass, on the other hand, tend to

increase as new phloem is produced each year (Flower-

Ellis and Olsson 1993; Barton and Jarvis 1999). Mutual

secondary growth velocity of needle width and thickness,

shrinkage due to water content and/or turgor loss (espe-

cially during intensive needle growth), and specific needle

senescence due to needle carbon balance can all modify

needle shape (Niinemets 1997a). While greater leaf size,

more leaves per plant and higher biomass production under

elevated [CO2] are often noted for many tree species

(Pritchard et al. 1999), the effects of elevated [CO2] on

Norway spruce needle parameters such as needle length,

width and thickness, surface area, and needle mass density

are often not found to be statistically significant (Roberntz

1999; Hall et al. 2009). As Roberntz (1999) pointed out, the

growth of Norway spruce needles is determined mainly by

the amount of available nitrogen. The most important

environmental factor affecting needle morphological

parameters and chemical composition is irradiation (Niinemets

1997a, b).

There are many experimental designs for the investi-

gation of elevated [CO2] on trees: (1) closed systems

(Kellomaki et al. 2000) or open top chambers (Janous et al.

1996), (2) semi-open systems, for example, glass domes

with adjustable lamella windows; Urban et al. 2001), and

(3) free-open air systems (FACE; Lewin et al. 2009). These

last two facilities allow for an investigation of elevated

[CO2] at the ecosystem level during canopy closure, which

permits both sun and shade adapted foliage formation.

Furthermore, microclimatic conditions within the domes

may be adjusted to the natural environment (Urban et al.

2001).

The aim of the present study was to investigate the

morphological changes in Norway spruce needles sub-

jected to long-term, elevated CO2 concentration.

Materials and methods

Stand and site description

The study was conducted at an experimental site Bıly Krız

in the Beskydy Mountains (in the north-eastern part of the

Czech Republic, 908 m a.s.l.). Two glass domes with

adjustable windows (DAW) were used for the experimental

spruce (Picea abies [L.] Karst) stand cultivation. The

dimensions of DAW were 9 9 9 9 7 m. DAWs were used

to maintain the environments at different CO2 concentra-

tions. One DAW was supplied with the ambient (A) CO2

concentration, which increased from 357 to 370 lmol CO2

mol-1 during the period from 1996 to 2004. The second

DAW was permanently supplied with an elevated (E) CO2

concentration (700 lmol CO2 mol-1), and this target value

was maintained for approximately 91% of the growing

season within a range 600–800 lmol CO2 mol-1. During

the remaining time, CO2 concentration was lower due to

tank filling/transport, fumigation system control, or repair.

Due to DAW construction and the air distribution system,

comparable conditions were maintained in the interior of

both domes. The main monitored and controlled parame-

ters of the DAW interiors were: (1) mean atmospheric

[CO2], (2) air temperature, and (3) soil moisture. The air

temperature difference between the domes was negligible

(about 0.2�C on average). The air temperature within the

domes was maintained within the ambient range ±1�C for

approximately 94% of the time. The relative air humidity

inside the domes was significantly (p \ 0.05) lower than

outside (-9.6% on average) except during the driest peri-

ods. Soil moisture did not differ between the domes, and

soil moisture was maintained at values within 5% of that in

open plots by an irrigation system (AMET, CR) that

replenished the soil moisture daily (Fig. 1). The adjustable

windows were automatically closed on the individual walls

of the DAW (to exclude wind incursions into the internal

DAW space) based on wind speed and wind direction in

order to maintain a stable [CO2] inside dome environment.

Under calm conditions, they were kept completely open to

minimize differences in microclimatic parameters between

the domes and the open plot. A detailed description of the

DAW construction and function is given by Urban et al.

(2001).

The experimental stands enclosed in the DAWs were

planted in the autumn of 1996 using specially prepared

11-year-old saplings. The details of sapling preparation and

evaluation of planting success were described by Marek

2270 Acta Physiol Plant (2011) 33:2269–2277

123

et al. (2000). The soil within each of the DAWs was pre-

viously homogenized to a depth of 40 cm and was lightly

fertilized with Silvamix-forte (17 g m-2) and Ureaform

(21 g m-2) 1 year after the tree planting in order to avoid

yellowing. The artificially established stand, composed of

56 individuals enclosed into the DAW, simulated a mean

stand density of 7,500 trees ha-1. The experimental stand

was established as a set of eight rows. Each row contained

5–9 spruce individuals. In the autumn of 2003, the mean

tree height (±SE) was 3.8 ± 0.6 and 3.7 ± 0.7 m in A and

E, respectively, and the stem diameter at one-tenth of the

tree height was 59 ± 8 and 66 ± 14 mm for the same.

These values did not significantly differ. On the basis

of measured tree height, distance between whorls,

whorl’s branch inclination angle and length, a 2D model of

a representative sample tree in the treatment groups was

drawn using AutoCad for comparison in 2002 and 2004

(Fig. 2).

Sampling procedure

Needle analysis

In the autumn of 2002, thirteen trees from five inner rows

in each treatment dome (A and E) were selected for harvest

analysis. As needles differ in morphological structure,

chemical composition, and physiological activity as a

function of their adaptation to the light environment during

developmental growth (Niinemets 1997a), needle parame-

ters were measured for both sun-adapted and shade-adapted

crown parts. The first four whorls counting downward from

the tree top were distinguished as sun-adapted, as changes

in crown width become less marked moving downward

with the crown depth (Fig. 2). Eight whorls (counted

15

20

25

30

35

40

120 130 140 150 160 170 180 190 200 210Day of year

SM [%

]

EA

2004

15

20

25

30

35

40SM

[%]

2002

15

20

25

30

35

40

SM [%

]

2003

Fig. 1 Soil moisture (SM) in ambient (A) and elevated (E) [CO2]

treatments from the beginning of bud flushing to the end of needle

elongation growth period (on 207 ± 15 days of the year, resulting

from leaf area index seasonal course) during the growing seasons

2002–2004. Dashed line marks lower threshold values of SM for

easily available groundwater in presented stands

Fig. 2 Picture presents mean

crown shape of harvested trees

from A (solid line) and E

(dashed line) treatment in 2002

(a) and 2004 (b). In the

schematic picture of crown (c),

sun adapted (white) and shaded

crown part (grey) are visually

distinguished on the basis of

crown form change

Acta Physiol Plant (2011) 33:2269–2277 2271

123

downward from the tree top) were collected from each

sample tree and used for the characterization of needle

morphological parameters. All whorl branches were cut

and then split into classes according to their order of

branching. In all, eight age classes of shoots and needles

were investigated: c, current; c-1, 1-year old; c-2, 2-year

old, etc. All removed shoots within the needle-shoot age

class were lined up according to their length. The shoots

were then separated into three subclasses based first on

shoot length and secondly on width. Three representative

(i.e. median) shoots from each of these three subclasses

were analysed as sub-samples. Short time (1–2 s) immer-

sion of the shoots into liquid nitrogen was used to remove

the needles from the shoot. All the separated needles from

the shoot were scanned (Astra 1220 P, UMAX; Taiwan).

Continuous application of the image analysis software

ACC (Sofo Brno, Czech Republic) made it possible to

estimate the required set of needle parameters: (1) pro-

jected needle area (LA), (2) needle shape factor (SF), (3)

needle length (L) as derived from needle body circumfer-

ence, and (4) number of objects, i.e. needles. In order to

derive L after needle circumference detection, ACC soft-

ware identified the two spots on the circumference with the

maximum distance. It then fitted an axial axis inside the

object between the spots as a distance equilibrated curve

between the perpendicularly nearest spots on both sides of

the object circumference. SF is a geometrical parameter

describing objects as an image (SF = 4p LA/circumfer-

ence2). Theoretically, SF values range, according to the

image analysis software, from zero for line segments to one

for circle. Although needle width was not directly esti-

mated, SF evaluates the relationship between needle

length and width as needles lay on the scanned plane

(Fig. 3). The number of needles per shoot was normalized

by the shoot length (NN). Needle dry mass (scale 1405 B

MP8-1, Sartorius, Germany) was determined after 48 h of

drying at 80�C to estimate the specific needle area

(SLA-projected needle area to dry needle mass ratio).

In the autumn of 2003, nine trees per treatment from

border areas of all rows were analysed. Eleven inner trees

per treatment were sampled in 2004. A sampling similar to

the procedure carried out in 2002 (13 sample trees) was

repeated in 2003 and 2004 but up to the sixth whorl and for

six needle age classes. In 2003, the border trees were

analysed, which had been grown under a more enriched

light, at least on one side (they were irradiated at 74% of

the exterior radiation intensity due to window shading;

Urban et al. 2001). In addition, tree competition for light

was suppressed for 1 year due to the schematic harvest of

inner trees in the previous year; PAR transmittance below

the border tree crowns increased about 7% on average after

thinning in 2002. Year 2003 was characterized by drought

periods, which occurred more frequently, occurred earlier

than usual in the spring and lasted longer compared to other

years (Fig. 1).

Root analysis: supporting data

Root systems of 37 trees per treatment were excavated in

2005. An air spade (Air-Spade Technology, Verona, PA,

USA-Model 150/90) was used for root system excavation

(for more information about this technology see Nadezh-

dina and Cermak 2003). In this system, soil is dispersed by

a series of micro-explosions, and solid objects, such as

stones or fine roots (with the exception of mycorrhiza),

remain almost undamaged. Root surface area and root

length were estimated for thickness classes on the last 14

harvested trees (with minimal roots lost by decomposition)

in each treatment. The following five thickness classes

were distinguished according to root diameter: (1)\1 mm,

(2) 1–2 mm, (3) 2–5 mm, (4) 5–20 mm, (5)[20 mm. Root

surface area was estimated from root length and root

diameter in the middle part of the root length by a common

formula for a cylinder. For this purpose, we simplified the

term for absorbing root surface area as the sum of the root

areas of the first two thickness classes.

Statistical processing of the data

Each treatment, A and E, was represented by 9–13 spruce

individuals per analysed year. There is no overlap (no

repeated measures) in the same foliage tissue as different

tree groups were sampled each year. As all replicates of

each treatment resided in only one dome, the study design

may be characterized as a pseudo-replication (Hurlbert

1984). However, Norway spruce does not respond uni-

formly due to a non-clonal origin and potentially high

phenotypic plasticity (Kjallgren and Kullman 2002). It is

presumed that results are not biased by preliminary

character despite the pseudo-replication design. The

statistical software Statistica (StatSoft, Inc., Tulsa, OK,

Fig. 3 In the picture, examples of relationships between shape factor

(SF) and needle size/shape are presented. Objects A and C, and B and

D have the same length. Objects marked with the same small letterhave the same width. The proportions between the object dimensions

are as follows: A(C):B(D) = 1.7:1, a:b = 1.7:1, b:c = 1.7:1. SF of

Ba = 0.8, Aa = 0.6, Ab = Bc = Dc = 0.4, Ac = Cc = 0.25


123

USA) was used for the statistical analysis. One-way and

two-way ANOVA tests were carried out to detect statis-

tically significant differences. In the case of breaching the

assumptions, the non-parametric Mann–Whitney U test

was applied.

Results

Pre-treatment comparison

Morphological parameters of the oldest needles from the

first harvest were taken as a base line for pre-treatment

comparison. The values obtained for all the investigated

needle parameters confirm the starting situation—no sig-

nificant differences between the treatments at the beginning

of the fumigation experiment. For example, average pro-

jected needle area was 11.0 ± 5.4 and 11.5 ± 5.4 mm2

(diff. 4%), and average needle length was 10.1 ± 3.2 and

11.0 ± 3.2 mm (diff. 8%) in A and E treatments,

respectively.

Needle length

In the 2003 analysis, current needles in sun-exposed whorls

(I–IV) were found to be shorter within a range 11–18% in

Fig. 4 Investigated needle

parameters: L needle length, SFneedle shape factor, LA needle

projected needle area, SLAspecific needle area; from

A ambient [CO2] and E elevated

[CO2] treatment per needle age

class (c current, c-1 1-year-old

needles, c-2 2-year-old needles

etc.). Dots mark the mean value.

Whiskers display the standard

deviation. Stars indicate

statistically significant

differences between the

treatments (p \ 0.05)


123

the A compared to the E treatment. Lower L values (about

5–14%) were also found for all other needle age classes

(Fig. 4). L, as averaged across all whorls and age classes,

was 17 mm in the E treatment compared to 14 mm in the A

treatment. No significant differences in L were found

between the A and E treatments for the various age classes

in 2002 and 2004. In 2002, the 5-year-old needles of both

treatments (i.e. those resulting from the growing season in

1997, Fig. 4) were extremely short (about 4 mm on aver-

age) when compared to the previously developed needles.

This phenomenon was classified as a replanting shock.

Needle width and thickness from needle cross-sections

were investigated in a previous study (Pokorny 2002). Con-

version coefficient (needle crosscut circumference to maxi-

mum diameter ratio) varied widely from 2.27 to 3.14 and was

found to be dependent on needle position within the crown

vertical profile and on needle age (for example, mean c.

coefficient ± SE for current needles equals to 2.51 ± 0.06,

2.39 ± 0.03, and 2.33 ± 0.02 in II, IV, and VI whorl). No

significant differences were found in needle width or thick-

ness. Thus, needle circumference, when the needle lies on a

horizontal plane, correlates with needle length (r = 0.99).

Fig. 5 Investigated needle

parameters: L needle length, SFneedle shape factor, LA needle

projected area, SLA specific

needle area; from A ambient

[CO2] and E elevated [CO2]

treatment per whorls (counted

downward the tree top). Dotsmark the mean value. Whiskersdisplay the standard deviation.

Stars indicate statistically

significant differences between

the treatments (p \ 0.05)


123

Needle shape

In 2002 and 2003, needles from treatment A showed higher

SF values compared to those from E (Figs. 4, 5); in 2003 it

was about 7–14% higher for current needles and about

9–14% higher for other needle age classes on the IV whorl,

with the exception of 2-year-old needles. Generally, SF in

the A treatment was 0.26 ± 0.04 (mean ± SE) and

0.30 ± 0.04; in the E treatment it was 0.24 ± 0.04 and

0.27 ± 0.03 in 2002 and 2003, respectively. In 2004, SF

was 0.27 ± 0.04 for both treatments. In both treatments,

the SF parameter manifested nonspecific changes with

needle age and needle position within the vertical crown

profile. Correlation between L and SF was found to be

insignificant. From the grouped comparison of needle

classes, it followed that the difference between treatments

for SF was about 0.03 as was the difference in needle

length; needle width did not differ between treatments.

Needle area

The needle area values decreased downward with canopy

depth (Fig. 5). In 2002 and 2004, LA showed very similar

trends but with no statistically significant differences

between the treatments. In 2003, differences in the E

treatment decreased more rapidly downward from the tree

top (A slope = -3.5, E slope = -4.0), thus significant

differences were more pronounced in the upper whorls

(Fig. 5). In the upper whorls, current needles in E were

larger (11–13%) within all investigated whorls compared

to A. The projected area of the average needle was

22.5 ± 5.8 mm2 in the E treatment and 19 ± 5.5 mm2 in

A. In the bottom part of the crowns, LA increased in both

treatments in a similar way with needle age and with

position in the horizontal plane (i.e. moving from the tree

crown edge inward to the crown interior with progressing

age of the needles, Fig. 4). In the upper part of the

crown near the transient zone between sun- and shade-

adapted needles (at the IV whorl) statistically significant

differences in LA ranged from 9 to 20% (Figs. 4, 5)

between the E and the A treatment within the corre-

sponding needle age classes.

Specific needle area

Specific needle area values did not differ significantly

between the treatments; however, they did show similar

variability with needle age and needle position within the

vertical crown profile (Figs. 4, 5). In 2003, significant

differences between the treatments were found in III and

IV whorls. In these whorls, the SLA values for all needle

age classes were 11–15% lower in the E treatment com-

pared to the A; significant differences, however, were

found only between treatments in the three youngest age

classes (Fig. 4). A comparison of the SLA values summed

across the entire vertical crown profile shows that newly

formed needles in the E treatment were more dense (3–5%

on average, data extracted from Figs. 4, 5).

Number of needles

The number of needles per shoot length unit did not sig-

nificantly differ between the treatments in any of the study

years. The average number of needles per one centimetre

of shoot length for both treatments was 16 ± 2 (maximum

differences neared 3%). For both treatments, the mean NN

values were lowest for the first whorl, afterwards mean NN

values rapidly increased to a maximum for the II and III

whorls and then they slowly decreased again. NN linearly

decreased with the shoot age from current to old ones.

For all morphological parameters, current needles

dominantly affected the mean value for the tree as a whole

(Fig. 4) due to their high proportion within the juvenile tree

crown (35% for current and 27% for 1-year old). On the

other hand, mean values per whorl were less influenced by

current needle parameters as the proportion of current

needles decreased within the crown moving downward

from the tree top (about -17% per whorl).

Root to leaf relationship

E trees exhibited about 27% higher total surface area of

fine-absorbing roots (Table 1) and even about 62%

(p [ 0.05) higher dry mass than A trees. Also, total surface

area of needles per tree was found to be about 15% higher

in E than in A. The absorbing root surface area to total

Table 1 In the upper part of table, physiological parameters cha-

racterising water relations in ambient (A) and elevated (E) treatments

are presented

Parameter A E

GTsaa (mmol cm-2 s-1 MPa-1) 0.37 0.35 n.s.

GTsac (mmol cm-2 s-1 MPa-1) 0.27 0.33 *

wXa (-MPa) 1.14 1.46 n.s.

wXb (-MPa) 0.91 1.33 *

LAtc (m2 tree-1) 32.5 ± 12.5 37.4 ± 11.2 n.s.

RAa (m2 tree-1) 42.2 ± 22.0 51.0 ± 18.4 n.s.

GTsa soil-to-leaf hydraulic conductance expressed by sapwood

transverse area, wX daily shoot water potential (both estimated

in August 2003, see Kupper et al. 2006). In the bottom of table,

evaporative surface areas of tree (LAt total needle surface area) and

root absorbing (RAa total fine roots surface area) [notes for statistical

significance: * p \ 0.05, n.s. p [ 0.05 (not significant)]a Upper crown partb Shaded crown partc Whole crown


123

surface needle area ratio was 1.3:1 in A and 1.4:1 in E.

Highly significant correlation between the total needle

surface area and the absorbing root surface area of tree was

found in the A treatment (r = 0.81, p = 0.01), while these

two variables correlated less in the E treatment (r = 0.62,

p [ 0.05).

Discussion

The investigated needle parameters did not differ signifi-

cantly between the treatments in 2002 and 2004. However,

significant differences were found in 2003, and there could

be several explanations for these results found in 2003.

Firstly, the weather conditions during the growing sea-

son of 2003 were quite distinguished from the other years;

drought periods occurred more frequently, earlier in the

spring and lasted longer compared to the other years of

the study (Fig. 1). These differences could explain the

decreases in L, LA and increases in SF and SLA values. As

in our previous study, trees grown under elevated [CO2]

were found to be better adapted to water stress and more

economical in their soil water use, especially under water-

limited conditions (Kupper et al. 2006); thus, needle

parameters were more strongly affected by drought in the

A compared to the E treatment. Most of the differences can

be found in young needles, as they likely have higher water

content and are more sensitive to drought than older nee-

dles, especially during the intensive elongation growth

phase (Hellkvist et al. 1974 for Sitka spruce). Yet, relative

water content of needles (calculated as the difference

between fresh and dry needle weight to its dry weight ratio)

did not differ significantly between the treatments.

Disproportional enhancement of fine root surface area to

needle surface area per tree led to a more favourable ratio

between absorbing and evaporative areas in E compared to

A treatment. For Norway spruce, potential area for gas

exchange may be even more disproportional to increased

needle surface area; however, stomatal density (stomata per

mm2, or frequency- based on number of stomata per mil-

limetre of needle length) does not change with increasing

atmospheric [CO2] (Dixon and Wisniewski 1995; Barton

and Jarvis 1999), as stomatal conductance is reduced

(Ainsworth and Rogers 2007).

Secondly, while the upper parts of all crowns were

irradiated by equal radiation intensities (Urban et al. 2001),

the border trees analysed in 2003 were grown under well

irradiated conditions on one side. Spunda et al. (2005)

documented significantly higher values of daily courses of

net CO2 assimilation for E-trees cultivated within DAWs

at irradiances above 250 lmol m-2 s-1. Furthermore,

in comparison with A, the E treatment displayed a dimi-

nution of mid-day photosynthesis depression that was

predominantly caused by stomatal closure leading to a

subsequent decrease of intercellular [CO2] (Spunda et al.

2005). The occurrence of higher L and LA and lower SLA

may be a result of high net CO2 assimilation and assimilate

consumption dominated by the growth of young develo-

ping needles in the E treatment. Although continuous

assimilate accumulation in currently formed needles could

lead to an acclimation depression of assimilation under

elevated [CO2], this depression occurred immediately after

the end of the needle/shoot expansion growth, principally

during the second part of the growing season (Urban and

Marek 1999).

Korner (2003) found that the size of carbon reserves and

carbon storage was an indicator of a plant’s ‘‘fueling’’

status with respect to the balance of C-source vs. C-sink

activity. It was found that elevated CO2 concentration had

a positive effect on carbohydrate accumulation, namely an

increase in the sucrose, glucose and starch content of

spruce needles (Urban and Marek 1999; Cabalkova et al.

2007; Teslova et al. 2010). Non-structural carbohydrates

(NSC) content may increase by 70% and starch content by

26% (Teslova et al. 2010). Cabalkova et al. (2007) speci-

fied that E needles grown under lower as well as higher

light intensity had higher levels of NSC content compared

to A needles, and that older needles showed increased

accumulation of NSC during the time before bud break in

order to support the growth of developing needles later on.

She found that CO2 concentration increased not only the

quantity but also the size of the starch granules (Cabalkova

et al. 2008). Thus, photosynthesis stimulated in springtime

due to a modified radiation regime of the border trees and

the NSC content as a potential ‘‘fuel’’ supporting current

needle growth may have more positively affected needle

size in E, as compared to A.

The number of needles per unit shoot length may

increase with increasing irradiance and tree size (Niinemets

and Kull 1995). For example, nitrogen deficiency caused

significant reductions in needle size and number of needles

per shoot in Sitka spruce (Chandler and Dale 1995). As the

DAW’s internal conditions, including nutrient availability

were comparable between the treatments (Urban et al.

2001), we presume that elevated [CO2] had no effect on the

number of needles per shoot length. Barton (1997) also

found the number of needles per shoot length for Sitka

spruce remained completely unaffected by elevated CO2

cultivation conditions.

Although elevated [CO2] tends to enhance needle

length, projected area and needle mass density, our results

showed that elevated [CO2] did not significantly affect

these needle morphological parameters of young Norway

spruce trees. Needle morphological parameters, including

length, projected area and specific area, differed signifi-

cantly only in sun-adapted crown parts of trees grown


123

under sufficient irradiation, especially under conditions of

limited soil–water availability, which occurred during an

intensive needle growth period. It seems that suppressed

needle growth under limited soil–water availability as

reflected by needle morphological parameters was more

pronounced in A than in E.

Acknowledgments The authors are grateful for the financial sup-

port by grants no. SP/2d1/70/08 and SP/2d1/93/07 of the Ministry of

Environment of the Czech Republic and no. IAA600870701 GA AV,

and Governmental Research Intention no. AV0Z60870520. English

language correction by Mrs. Gabrielle Johnson and Mrs. Lissa Veil-

leux is gratefully acknowledged.

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The effects of elevated atmospheric [CO2] on Norway spruce needle parameters

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