Agriculture Reference
In-Depth Information
(FACE) in Switzerland recorded a large and immediate increase in N
2
O
emissions following the application of ammonium nitrate in solution.
This response was 27% greater at an atmospheric CO
2
concentration of
600
mol mol
−1
. However, in the
FACE experiment in low fertilized grassland, Kammann
et al
. (1999)
reported that increased N
2
O fluxes between enriched and ambient
atmospheric CO
2
sites happened mainly during the summer-autumn
vegetation period, and not during the 2 months following fertilizer
application. These findings were suggested to be connected with a higher
microbial population and to the turnover of this microbial biomass during
freeze-thaw periods (Kammann
et al
., 1999).
Plants grown under elevated CO
2
concentrations appeared to produce
more biomass. Statistically significant differences in total dry weight (Table
4.12.1) were found between different levels of CO
2
(
P
< 0.001) and differ-
ent levels of N (
P
< 0.01). Allocation to shoot (Table 4.12.1) was increased
statistically both by the N (
P
< 0.01) and the enriched CO
2
(
P
< 0.001),
the trend among treatments being as follows: N
0
(ACO
2
)<N
1
(ACO
2
)
<N
0
(ECO
2
)<N
1
(ECO
2
). However, the largest increment (
P
< 0.05) in
allocation of dry matter to plant roots promoted by elevated CO
2
(Table
4.12.1) was observed when N was limiting (272% increment compared
with 72% occurring at the high N fertilization rate). As a result, the influ-
ence of doubling the CO
2
concentration in our experiment was to increase
the root : shoot (R : S) ratio (
P
< 0.05) only at the low rate of N input.
The quantity of rhizosphere soil obtained from spring barley plants
(Table 4.12.1) varied significantly (
P
< 0.001) with CO
2
concentration.
The pattern observed followed that obtained for total plant dry matter.
However, the ratio of rhizosphere soil to root dry weight (data not shown)
did not vary significantly with different levels of CO
2
or N, suggesting that
the proportion of C exuded per unit root mass was similar under different
CO
2
µ
mol mol
−1
compared with that at 350
µ
concentrations.
Therefore,
the
effect
of
CO
2
concentration
on
Table 4.12.1.
Effect of atmospheric CO
2
concentration and N supply on dry weight distribution
and N plant uptake of spring barley plants grown for 25 days.
Total plant
dry weight
1
Shoot dry
weight
1
Root dry
weight
1
R : S
3
ratio
Rhizosphere soil
dry weight
2
N plant
uptake
1
N
0
(ACO
2
)
279
a
239
a
41.5
a
0.18
a
3.56
a
13
a
N
1
(ACO
2
)
437
b
380
b
56.6
a
0.15
a
6.45
b
24
b
N
0
(ECO
2
)
660
c
506
c
154.2
c
0.31
b
15.44
c
25
b
698
c
600
d
97.5
b
0.16
a
13.53
c
44
c
N
1
(ECO
2
)
1
dw and N plant uptake in mg per pot;
2
dw in g per pot;
3
root-to-shoot dw ratio.
Mean values in the same column followed by the same letter do not differ statistically (Student's
t-test, P< 0.05).
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