Groom: Water relations of Myrtaceae shrubs during drought 
Results 
Climate and groundwater levels 
Perth and the surrounding environs (including the 
Lexia chain of wetlands) experienced an exceptionally 
dry spring to autumn period (Sept 2000-April 2001) with 
only 98 mm of rainfall, compared to the long-term 
average of 258 mm (Fig 2A). In comparison, the previous 
spring to autumn period was exceptionally wet, with 139 
mm of rain recorded in January 2000 (average is 9 mm). 
Between October 2000 and July 2001 mean daily 
maximum temperatures peaked during February (30.2 
°C) with the lowest maximum temperatures recorded in 
July (18.8 °C; Fig 2A). Highest (17.4 °C) and lowest (6.0 
°C) mean daily minimum temperatures were also 
recorded in February and July respectively. 
At all three topographical positions, groundwater 
levels were at their lowest by March 2001 and remained 
so when remeasured in July 2001 (Fig 2B), representing a 
decrease in groundwater levels ranging from 0.77 m 
(embankment) to 1.08 m (dampland) compared to 
October 2000 levels. At permanent monitoring bores 
situated within close proximity to the study sites (Fig 
1A), groundwater levels did not increase until September 
2001 (Fig 2C). In 2000 (a year of near-average rainfall) 
groundwater levels in these bores began to rise in June, 
as a result of April-May rainfall. By October 2001, 
groundwater levels at all sites had recovered to October 
2000 levels. 
Seasonal water relations 
There was no significant difference in morning 
stomatal conductance or transpiration data between 
species in either spring or winter (Fig 3A, B). Both 
dampland species (A. fascicularis and P. ellipticum) had 
significantly higher (P < 0.001) transpiration and stomatal 
conductance values (transpiration: 1.5-5.3 mmol m' 2 s' 1 ; 
conductance: 0.09-0.23 mol nr 2 s 1 ) than the other species 
in summer. £. pauciflora at both the embankment and 
midslope sites had the lowest values of transpiration and 
stomatal conductance (transpiration: ~0.1 mmol nv 2 s' 1 ; 
conductance: < 0.01 mol nr 2 s’ 1 ). A. fascicularis transpired 
at the same rate (~ 2 mmol nv 2 s 1 ) and had the same 
seasonal stomatal conductance (~ 0.1 mol m' 2 s* 1 ) 
throughout the study (Fig 3A, B). For H. angustifolium 
and E. pauciflora occurring on the embankment and 
midslope (E. pauciflora only) sites, there was a significant 
decrease in transpiration and stomatal conductance 
between spring and summer. In H. angustifolium there 
was no significant difference between summer and 
winter transpiration and stomatal conductance data. 
Winter stomatal conductance values were similar to those 
recorded pre-drought in spring for both the embankment 
and midslope E. pauciflora, in contrast to transpiration 
values (Fig 3B). 
Comparison of WP pd data between species for a given 
season showed that there was no significant differences 
between the two dampland species or between the 
embankment and midslope stands of E. pauciflora . Spring 
data varied from -0.09 (P. ellipticum) to -0.26 (H. 
angustifolium) MPa (Fig 3C); winter data varied from - 
0.15 (H. angustifolium ) to -0.57 MPa (E. pauciflora; 
midslope). E. pauciflora had significantly lower (P=0.0001) 
summer WP pd (of around -3.3 MPa) in relation to the 
other species, with H. angustifolium the next lowest WP pd 
(-1.1 MPa). The two dampland species had summer WP pd 
> -1 MPa (Fig 3C). Summer WP pd was always 
significantly more negative than spring and winter data 
(Fig 3C). There was no significant difference between 
Dampland Embankment Midslope 
-► 
increase in groundwater depth 
Figure 3. Seasonal water relations patterns. A: morning stomatal 
conductance, B: morning transpiration and C: predawn xylem 
water potential, for four myrtaceous shrub species occurring at 
three positions differing in groundwater depth. Morning data 
combines mid-moming and midday data (n = 6); predawn data 
were obtained from 3 individuals per species; values are mean ± 
se. Probability values are presented from a one-way ANOVA 
comparing seasonal differences within a species. Similar letters 
indicate no significant difference between means (Tukey's HSD 
test, P<0.05). 
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