Journal of the Royal Society of Western Australia, 87(3), September 2004 
Table 5 
Shoot and root dry weights of Banksia prionotes and B. littoralis seedlings after 54 days of total submergence in comparison to well- 
watered seedlings. Values are mean ± SD for 4 plants. % change indicates an increase (+) or decrease (-) in relation to pre-flood data. P 
values based on a f-test comparing well-watered and submerged data. 
54 days of submergence 
% change 
Well-watered Submerged P Submerged 
B. prionotes 
Dry weight (g) 
Total 
1.14 ±0.51 
0.33 ± 0.08 
0.0070 
-38 
Shoot 
0.57 ± 0.26 
0.18 ± 0.08 
0.0166 
-47 
Root 
0.57 ± 0.25 
0.16 ± 0.02 
0.0038 
-27 
Root:shoot ratio 
1.01 ±0.12 
1.1 ± 0.63 
0.7774 
+93 
RGR - total (mg g* 1 day 1 ) 
14.5 
-8.7 
RGR - shoot (mg g* 1 day' 1 ) 
9.7 
-12.5 
B. littoralis 
Dry weight (g) 
Total 
1.80 ± 0.36 
1.02 ± 0.23 
0.0236 
+54 
Shoot 
0.49 ±0.11 
0.37 ± 0.07 
0.1801 
+35 
Root 
1.31 ± 0.28 
0.65 ± 0.25 
0.0227 
+55 
Rootishoot ratio 
2.75 ± 0.55 
1.83 ±0.90 
0.1483 
+2 
RGR - total (mg g -1 day 1 ) 
18.9 
8.2 
RGR - shoot (mg g* 1 day 1 ) 
13.5 
8.4 
photochemistry after 17 days of flooding compared with 
that of pre-flooded seedlings (Fig 2), and a significant 
difference when compared with well-watered seedlings 
(Table 4). As flooding continued, there was a significant 
decrease in both fluorescence parameters, resulting in a - 
72 to -87% change after 54 days. A decrease in was 
associated with decreased stomatal conductance, as the 
two variables were positively linearly correlated (r = 0.88, 
P < 0.01). 
Submergence 
All submerged B. littoralis seedlings survived after 54 
days, although many of the existing leaves were a lighter 
green compared to controls, measurements taken on 
the 17 ,h day were not significantly different (P = 0.3500) 
between well-watered (0.44 ± 0.03) and submerged 
seedlings (0.32 ± 0.20). Submerged plants had 
significantly lower total and root dry weight than well- 
watered plants, but not shoot dry weight (Table 5), with 
a 54% increase in total dry weight in relation to pre-flood 
seedlings. There was no significant difference in 
root:shoot ratios between the control and submerged 
plants. 
All B. prionotes seedlings died after 54 days of 
submergence. measurements taken on the 17 th day 
showed a significant difference (P = 0.0050) between 
well-watered (0.41 ± 0.03) and submerged seedlings (0.21 
± 0.05). Submerged plants had significantly lower dry 
weight than well-watered plants (Table 5), with a 38% 
reduction in total dry weight in relation to pre-flood 
seedlings, represented by negative RGR values. There 
was no significant difference in rootishoot ratios between 
controls and submerged plants. 
Discussion 
Mortality, physiology and growth data support the 
hypothesis that B. littoralis seedlings are more flood 
tolerant than B. prionotes seedlings. Banksia prionotes was 
unable to survive long periods (> 70 days) of flooding, 
and displayed many of the physiological and 
morphological responses typical of flood-intolerant 
species. These include stomatal closure, which has been 
associated with a decrease in root hydraulic conductivity 
(Davies & Flore 1986; Else et al. 2001), a decline in 
photosynthetic capacity, reduced growth and increased 
mortality. Banksia littoralis also displayed a reduction in 
stomatal conductance and photosynthetic performance 
(O^,,) in response to flooding, but not to the same extent 
as B. prionotes and, like most flood tolerant species, was 
able to resume photosynthesis after the flooding 
treatment ceased. 
There is evidence to suggest that a decrease in 
stomatal opening and its limitation on C0 2 intake, 
followed by a decrease in total leaf area, are the main 
factors contributing to reduced carbon uptake and 
reduced whole plant biomass in flooded seedlings (Smith 
& Moss 1998; Mielke et al. 2003). This is partially 
supported by this study, except that photosynthetic 
processes were directly affected by damage sustained to 
photochemical reaction centres (as indicated by a 
reduction in F v /F m and O psn ratios). Despite this 
reduction in photosynthetic performance, B. littoralis was 
able to maintain levels of that were > 50% of that in 
well-watered plants, resulting in an increase in biomass 
that was 97% greater than pre-flood plants after 72 days 
of flooding. For flooded B. prionotes seedlings a reduction 
in relative growth rate can be directly linked to a 
reduction in photosynthetic activity, despite the lack of 
significant differences in biomass allocation. 
The higher rate of B. prionotes mortality may be closely 
linked to the roots inability to survive and function under 
oxygen-deficient conditions. This caused severe 
physiological dysfunction, resulting in a progressive 
decline in photosynthetic performance. For B. littoralis 
seedlings to survive more than 100 days of flooding 
implies adaptations that promote oxygen and nutrient 
uptake. This may include the formation of aerenchyma 
120 
