Fig. 1. Contribution of senescent leaves to total leaf biomass in five plant species exposed to four levels of ozone
for a growing season. Species are from left to right A. ptarmica black bars, C. nigra striped bars, E. cannabinum grey bars,
M. caerulea dotted bars and P. lanceolata white bars. For significance levels see Table 2.
nl l
− 1
O
3
in the second week of August. During the whole season, AOT40 in the NF treatment
remained below the 3 month critical level of 3 ml l
− 1
h, which was proposed by the UN-ECE Ka¨renla¨mpi and Ska¨rby, 1996. The summer of
1997 thus represents a summer with low ozone exposure.
In the NF + + treatments ozone concentra- tions occasionally reached 120 nl l
− 1
in early June and 150 nl l
− 1
in August. There were no signifi- cant differences between the treatment replicates.
The AOT40 and exposure duration at the final harvest differed between species Table 1 and the
AOT40 varied between 17.7 ml l
− 1
h for Lychnis flos-cuculi and 29.6 ml l
− 1
h for D. decumbens in the NF + + treatments.
3
.
2
. Visible injury and senescence Foliar injury was first observed in Eupatorium
cannabinum in the NF + + chambers 4 weeks after the onset of the fumigation. The ozone-re-
lated spots appeared on the upper surface of the first order leaves. Leaves that were produced later
in the season did not show foliar injury. In the middle of the season, small whitish spots were
observed in the centre of leaves of L. flos-cuculi. These rather un-specific symptoms occurred only
in some plants from the NF + + treatment and were accompanied by a structural change of the
mesophyll, which appeared to be water-soaked.
Until the intermediate harvest no signs of ozone-enhanced senescence were observed at the
weekly visual assessments. At the final harvest senescence appeared to be significantly affected by
ozone in five species Table 2, Fig. 1. Ozone-en- hanced senescence was paralleled by a significant
reduction of green leaf area in A. ptarmica, E. cannabinum and Plantago lanceolata Fig. 2.
3
.
3
. Growth responses ANOVAs were calculated separately for the
two harvests for each of the ten species Table 2. Results of significant ozone treatment effects are
presented for the response parameters shoot biomass, leaf area and number, and root and
flower biomass.
Fig. 2. Green leaf area in three plant species exposed to four levels of ozone for a whole season. Species are from left to
right A. ptarmica black bars, E. cannabinum grey bars and P. lanceolata white bars. For significance levels see Table 2.
3. Results
3
.
1
. Ozone concentrations In the beginning of June, mean hourly concen-
trations of ambient ozone exceeded 70 nl l
− 1
for only a few days, but reached a maximum of 100
J .
Franzaring et
al .
En 6
ironmental and
Experimental
Botany
44 2000
39 –
48
43
Table 2 Effects of ozone treatment on various growth parameters of wet grassland species determined at two harvests a and plant traits of the ten wet grassland species determined in ozone-free air b
a
Species b
a Final harvest for harvest dates see Table 1
a
Traits in O
3
free air Intermediate harvest after 28 days
a
Root Shoot
Root: RGR
SLA Senescence
b
Leaf Shoot
Flower Leaf
Leaf Stem
SLA Flower
RGR g g
− 1
day
− 1
number
d
cm
− 2
g
− 1
weight area
c
weight
d
weight weight
shoot weight
number area
Leaf Leaf
Percent weight
number weight
A. ptarmica 0.003
0.037 0.048
n.d. n.s.
B 0.001
n.s. 0.002
n.s. n.s.
n.s. 0.197
236 0.046
0.002 0.005
0.023 n.s.
0.001 n.d.
0.001 B
0.001 n.s.
n.d. n.p.
n.s. n.p.
C. nigra n.p.
0.123 150
n.s. n.s.
0.044 n.s.
n.s. n.s.
n.s. n.s.
n.s. 0.046
C. disseclum n.s.
n.s. n.s.
n.s. n.s.
0.091 159
n.s. n.s.
0.027 0.001
n.s. n.s.
n.d. n.s.
n.s. n.s.
n.d. n.p.
n.s. n.p.
D. decumbens n.p.
0.070 147
n.s. n.s.
n.s. n.s.
n.s. n.s.
B 0.001
B 0.001
0.002 0.006
B 0.001
0.020 E. cannabinum
n.s. n.s.
0.047 0.176
364 n.s.
n.s. n.s.
n.s. n.s.
n.s. n.s.
n.s. n.s.
n.s. n.s.
n.s. n.d.
n.s. L. flos-cuculi
n.s. 0.104
192 n.d.
n.s. n.s.
n.s. n.s.
n.s. n.s.
n.s. n.s.
n.s. n.s.
n.s. n.s.
n.s. 0.158
L. salicaria 244
n.s. n.s.
n.s. 0.040
n.s. 0.001
n.s. 0.030
0.032 0.013
n.s. n.s.
n.s. 0.044
n.s. 0.004
n.s. 0.087
202 M. caerulea
0.005 0.003
0.027 n.s.
n.s. 0.002
B 0.001
B 0.001
n.s. 0.008
n.s. n.s.
0.007 0.110
P. lanceolata 167
n.s. n.s.
n.s. n.s.
n.s. n.s.
n.s. 0.003
0.007 n.s.
n.s. n.s.
n.p. n.p.
n.p. 0.090
n.s. 185
S. pratensis n.s.
n.s. n.s.
n.s.
a
Values represent the P-values from ANOVAs indicating significant treatment effects. N.d., not determined; n.s., not significant; n.p., not present.
b
Refers to senescent and dead leaves and their proportion of leaf total.
c
Green leaf area at final harvest.
d
Refers to flowers or inflorescences.
J .
Franzaring et
al .
En 6
ironmental and
Experimental
Botany
44 2000
39 –
48
44
Fig. 3. The effect of ozone on shoot weights of four species at two harvests. The intermediate harvest H1 was performed on half of the plants after 28 days and the final harvest H2 when seeds had ripened. Boxes represent treatment means, error bars represent + S.E. and stars indicate significant ozone treatment effects,
P B 0.05, P B 0.01, P B 0.001.
3
.
4
. Shoot biomass Four species showed significant shoot biomass
responses to ozone. Growth reductions were ob- served in A. ptarmica at the intermediate harvest
and in C. dissectum and E. cannabinum at the final harvest Fig. 3. A significant growth stimulation
occurred in M. caerulea at the intermediate har- vest. Moreover, P. lanceolata showed a trend
towards growth reductions at both harvests and C. nigra a trend towards growth stimulations at
the final harvest, but in both species these were not statistically significant.
3
.
5
. Leaf area and number Total leaf area could only be determined at the
intermediate harvest before any senescence was observed. Leaf area was significantly affected by
ozone in three species. In A. ptarmica it was reduced and in C. nigra and M. caerulea it was
significantly increased by ozone P-levels in Table 2. Leaf number was determined at the intermedi-
ate harvest and was reduced by ozone in A. ptarmica and increased in M. caerulea P-levels in
Table 2.
3
.
6
. Roots and flowers Belowground biomass was determined only at
the intermediate harvest. Root weights were sig- nificantly affected by ozone in A. ptarmica, C.
dissectum, L. salicaria and M. caerulea. However, RSR was affected in only three species. In A.
ptarmica a strong reduction occurred in the NF + treatment, while a significant decrease in RSR due
to elevated ozone was observed in C. dissectum. An increase of RSR in the elevated ozone treat-
ments was obtained in M. caerulea Figs. 3 and 4.
Visual assessments of the plants did not reveal any effects of ozone on the timing, duration and
extent of flowering. At the final harvest seven species had produced flowers. Flower numbers
were not affected by ozone, but significant ozone treatment effects on flower weight were observed
in E. cannabinum and P. lanceolata. In the former species mean flower biomass was highest in the
NF + treatments, while in the latter plants from the NF treatments produced highest flower
biomass.
4. Discussion
