94
Javier Retana, Josep Maria Espelta, Marc Gracia and Miquel Riba
A
0.09
30
28
........ 0.08
-
26
.
b
.........
~
';'
>.
24
en
N
0.07
N
E
E
u
22
u
en
.....,
....., 0.06
20 0::
0::
~
«
18
Z
0.05
16
d
0.04
14
8%
16%
36%
60%
80%
LIGHT LEVELS (% PAR)
B
0.09
30
28
........ 0.08
-
26
.
........
~
';'
>.
en
N
0.07
b
24 N
E
a
a
E
u
22
u
en
.....,
....., 0.06
a
20 0::
a
0::
~
«
18
Z
0.05
16
0.04
14
400
550
700
850
WATER LEVELS (I m- Z yr-' )
Fig. 7.3. Changes in leaf area ratio (LAR, white dots) and net assimilation rate (NAR, black dots)
of potted holm oak seedlings throughout A light and B water gradients. Bars are 1 SE. Letters indicate significantly different values (P 1996). Concerning light, holm oak seedlings exhibited the typical inverse relationship between NAR and LAR: NAR increased with light, while LAR decreased (Fig. 7.3). The fact that no differences in seedling RGR with light
were found above 36% of incident light might be a consequence of the lack of
variation in NAR and LAR beyond this light level. This inability of holm oak
seedlings to increase their growth rates in high light levels because of the
lack of improvement in their assimilation rates has also been previously re-