2
.
4
. Statistical design and data e6aluation CO
2
treatments were carried out in three repli- cate OTC, respectively. For each nutrient supply,
one barley pot was exposed within each OTC. OTC means served as input data for analysis of
variance, using
SPSS
8.0 for Windows SPSS Inc., Chicago. Biomass and nitrogen data represent
CO
2
treatment means 9 standard deviation based on three chamber replicates.
SPAD measurements were taken both on plants in the inner circle left for final harvest and on
border plants. There were no significant differ- ences between these data-sets. SPAD data given
for any particular date represent means of eight to 15 single measurements per OTC and each nutri-
ent supply. Standard deviation bars shown in the graph were calculated using means of three repli-
cate OTC, respectively.
Because of restricted number of border plants available for intermediate flag leaf harvests, no
harvests in replicate OTC could be carried out. Rather, at any harvest date four flag leaves taken
from all three replicate OTC were combined to yield one sample.
3. Results
3
.
1
. CO
2
concentrations and climatic conditions Seasonal CO
2
daily averages measured on top of the canopy from barley crop emergence on JD
127 to final harvest on JD 231 were 366 9 0.9 m
mol mol
− 1
in ambient OTC and 650 9 20 mmol mol
− 1
in elevated OTC Fig. 1. Since no feed- back control was used in the CO
2
-dispensing sys- tem, concentrations in OTC with elevated CO
2
were somewhat influenced by ambient wind speed. With high ambient windspeeds, air in OTC en-
riched with CO
2
was mixed with intruding ambi- ent air which caused CO
2
concentrations to fall. Fig. 1 also presents daily averages for air tem-
perature and global radiation monitored in OTC. Average temperature during crop growth JD 127
to 231 was 19.8°C, cumulative temperature at baseline of 0°C amounted 2079 day-degrees, and
cumulative radiation sum was 1103 MJ m
− 2
. Average vapour pressure deficit VPD in OTC
during daylight hours global radiation \ 50 W m
− 2
from crop emergence to final harvest was 15.04 hPa no VPD data shown in Fig. 1.
3
.
2
. Treatment effects on biomass and yield Barley crops grown under CO
2
enrichment ac- quired 38 more shoot biomass than those grown
under ambient CO
2
concentrations Table 1. Crops fertilized with 14 g N m
− 2
increased shoot biomass by 13 compared with 8 g N m
− 2
. CO
2
enrichment and nitrogen supply interacted posi- tively, i.e. biomass increase due to CO
2
enrich- ment was larger at high N supply than at low N
supply 45 vs. 30 and, vice versa, additional nitrogen had greater impact on shoot biomass at
650 mmul mol
− 1
CO
2
than at ambient CO
2
in- crease 18 vs. 7.
Treatment effects on total grain yield were sim- ilar to shoot biomass responses. Correspondingly,
there were no significant treatment effects on har- vest index. Increases in grain yield due to CO
2
enrichment and additional nutrient supply were solely attributable to increased tillering. Neither
CO
2
enrichment nor additional fertilization had any significant effect on grain yield from main
stems. However, yield from tiller ears was en- larged 2.3-fold under 650 mmol mol
− 1
CO
2
. Addi- tional fertilization increased tiller grain yield by
29. As for shoot biomass and total yield, CO
2
enrichment and nitrogen supply interacted posi- tively on tiller grain yield.
Thousand grain weight TGW of main stem grains was slightly reduced by CO
2
enrichment − 7.5. This caused also a decline in the aver-
age TGW for all grains. There was no such effect on grains from tiller ears. Fertilization did not
affect TGW. Thus, the sink capacity for carbon of one single grain was only slightly affected by the
treatments.
3
.
3
. Treatment effects on nitrogen acquisition In contrast to the effects on shoot biomass and
on yield, CO
2
enrichment did not affect the nitro- gen uptake by the whole shoot or that of the total
grain population. The total amount of nitrogen
A .
Fangmeier et
al .
En 6
ironmental and
Experimental
Botany
44 2000
151 –
164
156
Table 1 Yield and biomass of barley crops exposed to CO
2
enrichment at two levels of nitrogen supply Elevated CO
2
650 9 19 Ambient CO
2
366 9 0.9 Nitrogen supply
Results of analysis of variance
a
based on open-top field Parameter
chamber means m
mol mol
− 1
m mol mol
− 1
g m
− 2
N CO
2
N Adjusted R
2
CO
2
interaction PB0.001
P 1400 9 27
967 9 73 P = 0.021
14 Shoot biomass acquisition g
0.947 PB0.001 m
− 2
= 0.001
8 909 9 23
1190 9 48 P
14 P = 0.013
PB0.001 0.934 PB0.001
Grain yield total g m
− 2
762 9 10 515 9 48
= 0.002
492 9 7.5 631 9 32
8 P
Grain yield tillers g m
− 2
P = 0.032 PB0.001
170 9 49 14
420 9 17 0.938 PB0.001
= 0.004
8 148 9 4.3
310 9 27 51.4 9 0.4
0.604 P = 0.003
n.s. n.s.
Thousand grain weight all 14
54.2 9 1.2 grains g
P = 0.015 8
53.7 9 0.5 49.6 9 2.6
n.s. n.s.
n.s. n.s.
Thousand grain weight tiller 48.2 9 1.3
46.5 9 0.8 14
grains g 8
44.6 9 2.7 46.5 9 2.2
a
n.s., not significant P\0.05.
Fig. 2. Chlorophyll breakdown assessed as SPAD values during flag leaf senescence in spring barley crops exposed to
ambient or elevated CO
2
at two levels of nitrogen supply. Data represent means 9 standard deviation from three repli-
cate OTC. Regression lines were calculated using logistic func- tions.
with 8 g N m
− 2
contained 11.2 g N m
− 2
in their shoots. Thus, not only nitrogen from fertilization
but also from pools in the soil and from mineral- ization served as sources for the crops. Crops
provided with 14 g N m
− 2
contained less nitrogen in the shoots 13.3 g m
− 2
than was supplied as mineral fertilizer. Most of the nitrogen found in
the shoots at final harvest was allocated to the grains which contained 77 of total shoot N on
average. This nitrogen allocation pattern was not influenced by the treatments Table 2.
Nitrogen concentrations expressed as of dry weight both in straw and in grain samples were
not significantly affected by nutrient supply. This suggests that no nitrogen deficiency occurred in
crops provided with only 8 g N m
− 2
. CO
2
enrich- ment, on the other hand, reduced the nitrogen
concentration of the straw by 34 and that of grains by 24. Since nitrogen concentrations in
grains from main stems and from tillers, and treatment effects on it, were nearly identical, only
average grain nitrogen concentrations are pre- sented in Table 2. As a consequence of decreased
nitrogen concentrations in the tissues, the nitro- gen use efficiency of barley crops was improved
by 35 due to CO
2
enrichment.
3
.
4
. Treatment effects on flag leaf senescence
3
.
4
.
1
. Chlorophyll breakdown Chlorophyll content was assessed non-destruc-
tively during flag-leaf senescence using a Minolta SPAD meter. SPAD values obtained from JD 191
to 209 are shown in Fig. 2. Assessments started right before chlorophyll breakdown began. Before
breakdown, chlorophyll content in crops grown under elevated CO
2
were significantly lower than under ambient CO
2
ANOVA results not shown. However, no significant effects of nutrient supply
on chlorophyll degradation were observed. Pro- gress of chlorophyll breakdown was significantly
enhanced by CO
2
enrichment. In crops grown at 650 mmol mol
− 1
CO
2
, chlorophyll degradation to 50 of the maximum values was already achieved
on JD 199, whereas it took until JD 203 to get the same degree of degradation at ambient CO
2
. found in barley shoots was 13.2 g m
− 2
at ambient CO
2
and 13.4 g m
− 2
at elevated CO
2
when the plants had high nutrient supply Table 2. At low
fertilization, the shoots contained 11.2 g m
− 2
nitrogen ambient CO
2
or 11.3 g m
− 2
nitrogen elevated CO
2
. The amount of nitrogen in the grains of the crops at maturity was 9.83 ambient
CO
2
and 10.7 g m
− 2
elevated CO
2
at high N supply, and 8.60 and 8.75 g m
− 2
at low N supply, respectively, without any significant impact of
CO
2
enrichment. However, nitrogen acquisition in grains on main stems decreased by 26 under
CO
2
enrichment corresponding to the decrease in nitrogen concentration in grains see below. Ni-
trogen acquisition by tiller grains increased by 75 when the plants were grown at 650 mmol
mol
− 1
CO
2
which results both from the 2.3-fold increase in tiller grain yield, and the 26 decrease
in grain nitrogen concentration, at elevated CO
2
. Nitrogen supply influenced crop nitrogen acqui-
sition both for straw and grains. Crops fertilized
A .
Fangmeier et
al .
En 6
ironmental and
Experimental
Botany
44 2000
151 –
164
158
Table 2 Nitrogen acquisition of barley crops exposed to CO
2
enrichment at two levels of nitrogen supply Parameter
Nitrogen supply Elevated CO
2
Results of analysis of variance
a
based on open-top field Ambient CO
2
650 9 19 mmol 366 9 0.9 mmol
g m
− 2
chamber means mol
− 1
mol
− 1
CO
2
N CO
2
N Adjusted R
2
interaction n.s.
PB0.001 n.s.
13.4 9 0.2 14
13.2 9 0.4 0.826 P = 0.001
Shoot nitrogen acquisition g m
− 2
8 11.2 9 0.8
11.3 9 0.3 0.440 9 0.017
0.787 P = 0.001 PB0.001 n.s.
n.s. Straw nitrogen content dry
14 0.737 9 0.100
weight 0.627 9 0.070
8 0.467 9 0.029
PB0.001 n.s.
n.s. 0.865 PB0.001
14 Main stem grain nitrogen
4.89 9 0.32 6.62 9 0.49
acquisition g m
− 2
8 6.12 9 0.30
4.53 9 0.22 1.40 9 0.04
0.904 PB0.001 PB0.001
n.s. n.s.
Grain nitrogen content dry 14
1.92 9 0.10 weight
8 1.75 9 0.11
1.39 9 0.02 PB0.001
n.s. n.s.
0.932 PB0.001 Nitrogen use efficiency g DM g
104.0 9 3.6 73.4 9 3.6
14 N
− 1
8 81.3 9 5.6
104.5 9 1.4
a
n.s., not significant P\0.05.
3
.
4
.
2
. Time course of soluble protein content Time-course of total soluble proteins in barley
flag leaves Fig. 3 was very similar to that of chlorophyll. Concentrations were in general lower
when the plants were grown under CO
2
enrich- ment. Under ambient CO
2
, a reduction of protein contents to 50 of maximum was achieved on JD
197.5, whereas at 650 mmol mol
− 1
CO
2
protein content was reduced to 50 already on JD 196.
Thus, protein breakdown appeared to be acceler- ated by CO
2
enrichment, but was somewhat less affected than chlorophyll disassembling.
3
.
4
.
3
. Degradation of RubisCO LSU, SSU, and cytochrom b
559
LSU breakdown was clearly accelerated under CO
2
enrichment Figs. 4 and 5. No LSU could be detected any longer on JD 195, and afterwards, in
plants grown under 650 mmol mol
− 1
CO
2
, whereas flag leaves from plants grown under am-
bient CO
2
still had nearly maximum LSU con- tents at that time. Decline of the SSU level
differed signficantly from that of LSU. At ele- vated CO
2
concentrations, degradation of SSU started only after JD 192. On JD 198, there was
still some SSU 6 of maximum contents de- tectable. At ambient CO
2
, no clear degradation of SSU towards the end of the sampling period
could be observed. Cyt b559 was longer detectable than LSU, but its level started to decline some-
what earlier than the level of SSU. Opposite to LSU and SSU, levels of Cyt b559 appeared to
decline somewhat more rapidly at ambient CO
2
than at elevated CO
2
.
4. Discussion
