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The Daily Course of Water Potential and Leaf Conductance in some New Zealand Plants
Flora (1986) 178: 329-342 VEB Gustav Fischer Verlag J ena
The Daily Course of Water Potential and Leaf Conductance in some New Zealand Plants P. BANNISTER and R. M. KISSEL Department of Botany, University of Otago, Dunedin, New Zealand
Summary The field water potentials of some 23 species, mostly woody plants and ferns native to New Zealand (but including one introduced fern), were measured on various occasions, mostly during the 1982{83 summer. The minimum water potentials recorded in the field were highly correlated with the ability of cut shoots and leaves to avoid low water deficits and low water potentials when artificially desiccated in the laboratory. Species that maintained high water potentials in the field also showed lesser fluctuations in water potential than those that developed low water potentials. Leaf conductances and transpiration rates were measured in five species. Low conductances and transpiration rates were generally associated with those species that maintained high water potentials in the field (e.g. Phymatosorus diversijolius (WILLD.) Pic. SER.), whereas high conductances and transpiration rates were generally associated with species that developed low water potentials (e.g Brachyglottis repanda FoRST.). One species, Metrosideros robusta A. CuNN. showed high conductances and transpiration rates but maintained a higher water potential in the field. Those species that showed the largest reductions of conductance in the early afternoon also showed the best recovery of shoot water potential. For the species examined, the artifical desiccation of cut shoots and leaves in the laboratory provides a guide to minimum water potentials in the field. These appear to be determined by rates of water loss from the shoot rather than the hydraulic conductivity of the soil·plant·atmosphere system.
Introduction Various authors have used the artificial desiccation of cut shoots and leaves as an aid to the interpretation of the water relations of plants in the field. The decline of water content with time has been used to estimate the point of stomatal closure and other transpiration-related parameters (e.g. HYGEN 1953; JARVIS & JARVIS 1963; BANNISTER 1964, 1971; HuTCHINSON 1970). The relationships between water content and water potential have also been given ecological interpretations (e.g. WEATHERLEY & SLATYER 1957; JARVIS & JARVIS 1963; CHEUNG et al. 1975; TYREE & KARAMANOS 1981) as have the relationships between applied pressure and water content derived from pressure chamber (P-V curves). Parameters derived from the analysis of such curves (TYREE & HAMMEL 1972) have been used extensively (e.g. HELLKVIST et al. 1974; CHEUNG et al. 1975; TYREE et al. 1978; HINCKLEY et al. 1981, 1983; JANE & GREEN 1983). Many studies using the aforementioned methods have been applied to only a limited number of species (sometimes only one) and do not usually question the general applicability of the methods to the interpretation of the water relations of a diverse range of species in the field. This study deliberately relates laboratory measures of drought tolerance and avoidance of 23 species to their responses in the field. As little had been published on the water relations of plants native to New 21
Flora, Bd. 178
330
P. BANNISTER and R. M. KISSEL
Zealand until recently (e.g. JANE & GREEN 1983; GREEN & JANE l983a, b), the studies in this paper also supplement the available information.
Material and Methods Species The species exan1ined were the same as those used in a series of laboratory studies of drought resistance and parameters derived from P-V curves (BANNISTER l9R6) and are listed in Table L ·where there is no ambiguity, these species are referred to in thll text by their generic names alone. The plants used for these studies were located mostly in the gardens of the Botany Department, although some were from the municipal Botanic Gardens (about l km distant). The more distant
Table l. Species used in the investigations, their site of collection, abbreviated form, and drought avoidance site
abbr.
drought avoidance
B B B B G
As Bl Dry Phy Pte
0.85 0.4 0.9 1.65 0.7
B B B
Cy Drl Pny
0.25 0.95 0,7
B B B B B
Ag Dey Dbd Dcu Pdh
1.6 1.1 1.3 l.l 1.45
B B G B B G G G B B
Br Le Ls Mr Nf Ns Nm Plg Px Wn
0.65 0.6 0.65 1.5 1.35 0.9
Ferns Asplenium bulbiferum FoRST. f. Blechnum penna-maria (ProR.) KUHN Dryopteris filix-mas (L.) SCHOTT Phymatosorus diversijolius (WILLD.) Pre. SER. Pteridium esculentum (FoRST. f.) KuHN Ericaceousfepacridaceous shrubs Cyathodes jraseri (A. CUNN.) ALLAN Dracophyllum longijolium (J. R. et G. FoRST.) R. BR. Pernettya macrostigma CoL. Coniferous trees and shrubs Agathis australis SALJSB. Dacrycarpus dacrydiodes (A. RrcH.) DE LAUBENFELS Dacrydium bidwillii HooK. f. ex KIRK D. cupressinum LAMB. Podocarpus hallii KIRK Other trees and shrubs Brachyglottis repanda J. R. et G. FoRST. Leptospermum ericoides J. R. et G. FoRST. L. scoparium J. R. et G. FoRST. Metrosideros robusta A. CuNN. Nothofagus jusca (HooK. f.) 0ERST. N. solandri (HooK, f.) OERST. N. menziesii (HooK. f.) 0ERST. Plagianthus betulinus* A. CUNN. Pseudopanax colensoi (HooK. f.) PHILIPSON Weinmunnia racemosa LlNN. f.
* deciduous species Sites of collection: B Gardens of Botany Department; G Municipal Botanic Gardens and environs. Drought avoidance: is the average of the following two measures: (i) time (log 10 hours) to reach 50% relative water content (ii) time (log10 hours) to reach a balancing pressure of 3.45 MPa.
l.O 0.6 1.55 1.25
331
The Daily Course of Water Potential
specimens were sampled less frequently and only at times when minimum water potentials might be expected (e.g. in the early afternoon of hot days). In all cases exposed shoots or leaves of current mature growth were sampled. Sampling took place principally in summer (December 1982-February 1983) although some readings taken during the winters of 1983 and 1984 have been included for comparative purposes. Water potential (Table 2) This was measured in a pressure chamber (ScHOLANDER et al. 1964; RITCHIE & HINCKLEY 1975); details of the particular chamber are given by PoLLOCK (1979). Shoots and leaves were sampled directly into polythene bags and brought with minimum delay to the pressure chamber for the determination of balancing pressures. The shoot or leaf water potential was taken to be the negative of the balancing pressure (i.e. the osmotic pressure of the xylem sap was considered to be negligible). Usually four replicate samples were taken at each measurement. As storage times were minimal and there appeared to be no consistent drift of balancing pressure from the first to the last sample, no elaborate precautions to minimise water loss (e.g. KARLIC & RICHTER 1979) were taken. Drought avoidance The scale of drought avoidance is derived from measurements made in two previous summers (BANNISTER 1986). Both measures are of the time taken (in log10 hours) for the samples to reach
Table 2. Relationships of water potential to time of day (H), date (D), and maximum temperature (T) on day of measurement as determined by multiple regression analyses. Only significant (P < 0.05) partial regression coefficients are shown Constant
partial regression coefficients ln(H)
(ln[H]) 2
D
T
+
+0.0050 -0.0047
-0.0193 -0.0109
%variation accounted for (between means)
Ferns Bl Dry Phy
-1.5982 ( = mean) 17.6697 -14.6593 0.5167 - 0.2986
2.8839
0 60 59
Ericaceousfepacridaceous shrubs Cy Dr! Pny
63.1194 10.1658 31.6452
-51.6669 - 8.6209 -25.2946
+10.2696 + 1.7019 + 5.0334
-0.0235 -0.0063 -0.0113
-0.0562
+0.0019 -0.0033
-0.0191 -0.0339
-0.0042 -0.0057
-0.0350
92 43 49
Coniferous trees and shrubs Ag Dey Dcu Pdh
1.4366 10.9230 11.6649 9.2673
Other trees and shrubs Br 0.8668 Le 17.5295 l\Ir 21.8573 Nf 14.9191 Px 14.6464 Wn 13.1140
0.8409 8.9583 9.1337 7.9456
+ + +
1.7191 l. 7648 1.5149
- 0.5294 -14.6352 -18.0421 -12.2561 -11.9505 -10.9777
+ + + + +
2.7734 3.5813 2.4334 2.3039 2.1389
H is local time (24 h clock) D is days from 1st December 1982 T is maximum daily temperature ( oc) 21*
-0.0035
-0.1464 -0.0231
+0.0029
-0.0043
37 53 67 34
39 65 67 19 49 75
332
P. BANNISTER and R. M. KISSEL
either a relative water content of 50% or a water potential of -3.45 MPa (-500 p.s.i.). In both cases desiccation took place in normal laboratory conditions at a temperature of around 20°C. The two measures are highly correlated (P < 0.001) and are also inversely correlated with the ability of the shoots to withstand low water contents and potentials (i.e. drought tolerance, see BANNISTER 1986). The scale used is the mean of the two measures of drought avoidance. Stomatal conductance and transpiration These were measured on five species only (Phymatosorus, Pseudopanax, Brachyglottis, Metrosideros, Weinmannia), using a Licor LI-1600 steady state diffusion porometer and expressed as mmol m-2 s-1. Measurements of temperature, light intensity and humidity were taken at the same time and used to correlate water loss with environmental factors. Each value is the mean of five samples. Treatment of data It was not possible to measure all species on the same day because of the number of species involved and the fact that only one pressure chamber was available; nor was it desirable to confine one day's measurements to a single species as the main object was to compare species. Consequently the data consists of measurements made at various times, days and species at intervals through the summer. The use of multiple regression analyses of water potential against time of day, maximum daily temperature and data allowed some assessment of the diurnal pattern of water potential, its drift with season and the influence of daily temperature. Samples made during rain were excluded as they were usually significantly different from those made during equivalent dry periods. Only five species, with fewer measurements, were used for leaf conductance and transpiration, and while these were used in multiple regressions of conductance on environmental factors, the principal analysis uses readings that were taken on all five species at approximately the same time of day on three different days (10, 11, 14 February 1983). Multiple regressions and other statistical analyses were made using the general statistical program TEDDYBEAR (WILSON 1975).
Results Fig. l gives the mean values and ranges (the difference between maximum and minimum water potentials for individual shoots of the same species), mostly for species that were measured frequently during the summer but also for some that were investigated in winter. Those species that maintain high water potentials (e.g. Phymatosorus) show lesser ranges than those which develop low water potentials (e.g. Cyathodes). Multiple regression analyses revealed that water potentials were generally lower when measured later in the season (except in Dryopteris, Dacrycarpus and Weinmannia where they became higher) and were lower on warmer days, with those species showing low minimum potentials (e.g. Pernettya, Bmchyglottis) showing the greatest sensitivities. Contrasting examples of daily patterns, using raw data, are given in Fig. 2. Most species showed a rapid decline in water potential in the early morning followed by some recovery in the afternoon. Some species ( Brachyglottis, P hymatosorus, Agathis) showed a steady decline during the day, these plants were usually from locations that were somewhat shaded in the morning and more exposed in the afternoon. Blechnum penna-marina showed no marked overall trend with consistently low values throughout, although losses and gains were noted on particular days (Fig. 2). Some species show generally high water potentials (Phymatosorus, Agathis, Pseudopanax), while the water potentials in a number of others (Podocarpus, Dacrydium cupressinum, Dacrycarpus, Dracophyllum, N othofagus fusca, Metrosideros, Weinmannia, Dryopteris) are only a little lower. A futher group ( Brachyglottis, Blechnum,
333
The Daily Course of Water Potential
ecy
ePny oBI 2·0
0...
Br •
OLe
:::!: C/)
(ii
c Q)
0
eLe
a. .... Q)
-:;;
Drle Nf• Mr~
eDcu Mre • eAg Dry eDcy
Qi
~
0 Q)
Px
eBI
3: -o
1·0
0>
c
II:
wn.
-2·0
ePdh
~hy
Pgy
-1·0 Mean field water potential ( MPa)
Fig. 1. Mean and range for field water potentials. (r = 0.747, P < 0.001). Abbreviations for species as m Table 1; summer measurements are indicated by filled circles, winter ones by open circles.
Pernettya, Cyathodes, Leptospermum ericoides) shows much lower water potentials. These differences appear to be related to laboratory measures of drought avoidance and this is confirmed by the strong correlation (P < 0.001) of the minimum field water potential recorded during the summer with the scale of drought avoidance (Fig. 3a). The range of water potentials recorded in the field is also correlated with the same scale (Fig. 3b). Conductance and transpiration Because of the relatively fewer measurements of conductance that were made, the correlations with environment are more tentative (Table 3). The conductance of Phymatosorus increased with light intensity (which is generally low in this fern's habitat). There is evidence for humidity effects in other species, particularly when time of day is taken into account. In Metrosideros conductance declines during the day (as saturation deficits increase), whereas inPseudopanax there is an initial increase in conductance in the morning when saturation deficits are increasing but a decline in the afternoon (particularly when saturation deficits exceed 1.0 kPa). In contrast, Weinmannia leaves showed a consistent increase in conductance as saturation deficits increased (although they never exceeded 1.2 kPa).
334
P.
BANNISTER
and R. M.
KISSEL
0 27
17
X
~~~~ \."'%
----x/-X'
X
I
~.
I
15 ....
X
!>.
~x ~~X--•15
-1
\'•-/
Phymatosorus diversifolius
\
/ X
Metrosideros robusta
0
•\
Blechnum penna- marina
Cyathodes fraseri
c Q)
~
\a/.\x x
X
Ji
10
12
14
•n___•......--......--••...--"
\
X
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of\ 14·~·~ x~·;
·"
·-·
6
X
x \
0~1' 8
-~
00.
X
X
-2
27
16
18
Solar time Fig. 2. Daily values for water potential in summer and winter (where appropriate) for Phymata· sorus diversijolius (high drought avoidance), Metrosideros robusta (intermediate avoidance), Oyathodes jraseri (low avoidance, high tolerance) and Blechum penna-marina (low avoidance, high tolerance but little daily fluctuation in water potential). Crosses indicate winter readings (Metrosideros, early June; Blechnum, mid-July; Phymatosorus late .July 1983). Summer readings are indicated by triangles (November-December 1982), circles (January 1983) or squares (February 1983). Filled symbols link readings made on the same date (indicated by a number); open symbols indicate single readings on separate days.
A more ready comparison of the five species investigated is made by taking averages over 3d in which measurements were made in early morning, mid-morning, around midday and in the early afternoon (solar time, local time is 1 h 40 min ahead in summer). Although there were significant differences (P < 0.001) in both transpiration and conductance between days (with the third day showing lower values than the other two) there is little difference between the reaction of the species on the different days. The interaction of species with days was not significant for transpiration and only just significant (P = 0.03) for conductance (the conductance of Brachyglottis and Phymatosorus was higher and that of Pseudopanax lower on the third day than expected from the previous days. The lowering of transpiration on the third day was associated with only the first and last readings and was little different in the middle (i.e. a significant interaction [P < 0.001] between days and time of day); there was no significant interaction for conductance. Environmental conditions were similar on the 3 d with temperatures ranging between 12 and 19°0 and relative
335
The Daily Course of Water Potential
8:. 6
Phye
t1l
~ -1·0
(a)
Cy
Dcue Dcye
~
PdheA9 • •Px Mre •Dbd
•
Bl
c
0
Ql
0
0.
Le0 e
~
Q;
Ptee As Dry . . •Nm
a;
:s:
~ -2·0 E :::J E c ~
2t1l :s:
eNf
Br
•
Bl
•
• Ls
.'!!
eDrl
0
eNs •ePny Lee
Br
Le
:g
-c
(b)
P~y
(/)
Wn
Dr I
•
D.y
Ql
Nf Dcu
•
Ol
•M'QePx Mr• eAg
eDcy
c
t1l
c:
Pdh
ePig
wn.
•
Phy ()
I
1·0
0·5
0·5
1·5
1·0
1·5
Drought avoidance
Drought avoidance
Fig. 3. (a} Relationship between minimum water potential in the field and drought avoidance < 0.001).
(r = 0.899, P
(b) Relationship between range of water potential in the field and drought avoidance (r = 0. 781, p < 0.001). Species' abbreviations and drought avoidance as in Table 1. Filled circles indicate summer measure· ments, open circles winter ones. In Fig. 3 a the points are means of 2-6, usually 4, replicate samples.
Table 3. Relationships between conductance (C) and date (D), time of day (H), atmospheric saturation deficit (S) maximum daily temperature (T) and light (Q) Phymatosorus
c
= 57.9137
+ 0.4819*Q
(P
< 0.05)
(P
< 0.01)
(P
<
(P
< 0.001)
(P
< 0.001)
M etrosideros C = 228.35- 6.06*H (correlation between S & H, r
=
0.7678, P
< 0.01)
Brachyglottis C
=
3.4189- 0.0841 *S
+ 0.8008*H
0.05)
Weinmannia C
=
94.58- 8.23*T
+ 21.37*8
Pseudopanax C
=
4770.41- 78.23*ln(S)
+ 3872.61 *H- 742.41 *H2
H is the natural logarithm of local time (24 h clock) S is atmospheric saturation deficit in mbar Q is quantum flux in mmol quanta m-2 s-1 T is daily maximum temperature (0 C)
336
P.
BA'l'.'NISTER
and R. M.
KISSEL
r
1·5 150 I
";'
C/l
C/l
N
N
I
I
E
0
E E
E
0
1-0
E
_s
~
c: 0
Q)
u
~ ·c.
c: ~
t5
C/l
:::l
c:
"0
~
.=
100
c:
0 (.)
0·5
5t 9
11
13
15
17
9
Local time
7
9
11 13 Solar time
11
13
15
17
Local time
15
7
9
11 13 Solar time
15
Fig. 4. Mean values for transpiration and conductance for 5 species averaged over 3 d. (a) Transpiration (b) Conductance. Species' abbreviations as in Table 1. Points are mean3 of measurements on five different leaves. Vertical bars indicate the least significant difference (P = 0.05) between means.
humidities between 40 and 70%. On the third day the first reading was somewhat earlier and the last reading later than on the other 2 d. This probably accounts for the differences in transpiration. The different patterns shown by the species is reflected in significant interactions (P < 0.001) between species and time of day for both transpiration and conductance (Fig. 4). All species, except Phymatosorus, show similar patterns of transpiration with an increase in the morning, a peak around the solar noon and a decline in the afternoon (Fig. 4a). Phymatosorus is different in that, it shows a peak in the later morning and little subsequent decline. Peak transpiration rates are in the order Brachyglottis > Metrosideros > Pseudopanax > Weinmannia > Phymatosorus and the average transpiration rates follow the same ranking with significant differences between all species except Brachyglottis and Metrosideros. Peak conductance show a similar order to transpiration rates, except that Metrosideros shows values slightly higher than those in Brachyglottis. In terms of mean conductances, there are no significant differences between either Brachyglott~·s and M etrosideros or W einmannia and Pseudopanax. Peak conductances coincide with peak transpiration rates in all species except Weinmannia and Pseudopanax where they are earlier. M etros~·deros differs from all the other species in that its conductance is already high in the early morning and all the species show slight differences in pattern from one another (Fig. 4b).
The Daily Course of Water Potential
337
+0·2
.wn
+ 0·1
•Px
al
Cl.. ~
*
0
Br • ePhy
- 0 ·1 L - - - - - - ' - - - - - ' - - - - " - - - - - - 1 0 10 20 30 40
/';. Conductance mmol m-2 s-1
Fig. 5. Relationship between the decrease of conductance from maximum to afternoon minimum (Fig. 4 b) and the corresponding change in water potential for the same period (calculated from Table 2) for 5 species. Species' abbreviations as in Table 1.
Relationships of water potential and conductance The decrease in conductance after the peak value has been attained is related to the degree of recovery of water potential (Fig. 5), estimated from the appropriate regressions in Table 2. Species showing large decreases in conductance (e.g. Metrosideros and Weinmannia) show a good recovery of water potential, whereas those that show the smallest reductions (Brachyglottis, Phymatosorus) show a continued loss of water potential. Metrosideros shows both high conductances and high water potentials which indicates that it is able to maintain open stomata without suffering undue water stress. This species has also been shown to be drought resistant in the field (OGDEN 1976). Winter measurements Some measurements of water potential and conductance were made in winter (Fig. 2, Table 4). They were not greatly different from those made in summer suggesting that the species are metabolically active in winter and are not under any greater water stress than might be found in summer.
Discussion Water potential GREEN & JANE (1983a) have measured water potentials in summer for Weinmannia and Nothofagus menziesii obtaining minimum values of about -1.2 MPa for W einmannia and -1.4 MPa for N. menziesii. The value for W einmannia is similar to that in this paper and that for N. menziesii higher, although the overall
338
P. BANNISTER and R. M. KISSEL
Table 4. Means and ranges for water potential and leaf conductance for species investigated in both summer and winter water potential (MPa) mean
max
min
-0.68 -0.49
-0.26 -0.22
-1.05 -1.01
-0.96 -0.76
-0.25 -0.36
-1.43 -1.73
-1.60 -1.38
-1.00 -0.59
-2.40 -2.75
-1.07 -1.04
-2.59 -2.88
conductance mmol (m-2 s-1) mean
min
max
76 44
58 20
108 66
151 124
96 40
177 144
Phymatosorus 1983 summer *1983 winter Metrosideros 1983 summer 1983 winter Blechnum 1983 summer 1983 winter
Leptospermum ericoides 1983 summer *1984 winter
* species measured at a
-1.87 -1.89
different site in winter
Phymatosorus Town Belt, Dunedin Leptospermum Cromwell George, Central Otago. extreme values for water potential are based on single shoots, those for conductance on means for five replicate leaves.
range of rmmmum water potentials for the five species they examined (-0.9 to -1.4 ~IPa) is less and in accord with the wetness of the habitat. The range of minimal water potentials found in this study is comparable with that in mesic habitats. RICHTER (1976) gives a range of -1.5 to -2.6 MPa (median -1.9 :VIPa) for woody plants from such sites which is very similar to the range in this paper (-1.14 to -2.53 MPa, median -1.67 MPa; -0.85 to -2.53 MPa, median -1.65 MPa if ferns are included). The summer of 1982/83 in Dunedin was not particularly dry. A drought in 1985 produced minima from -1.3 to -6.5 MPa (BANNISTER, unpublished), which overlaps with the range (-3.2 to -7.0 MPa) given by RICHTER (1976) for plants from habitats subject to drought. The minimum water potentials do not relate in any obvious way to field determinations of drought resistance (OGDEN 1976). For example, Metrosideros and Leptospermum spp. are drought resistant, but the former maintains a high water potential while the latter species develop low potentials. Conversely, amongst drought susceptible species, Dacrywrpus and Dacrydium cupressinum maintain high water potentials whereas Brachyglottis develops low potentials. There is, however a close relationship between the behaviour of artifically desiccated cut shoots and responses in the field (Fig. 3a) which suggests that such laboratory studies may provide reasonable predictions of field responses. This further suggests that field water potentials in the investigated mesic habitats are a function of leaf resistance rather than of resistances elsewhere (e.g. in the stems, roots and soil). Similarily GREEN & JANE (1983a) found restricted rooting in wet forest soils but no evidence for the development of extremely low water potentials. However, rapid decreases in stomatal conductance occured when the usual cloud cover was absent (JANE 1983).
The Daily Course of Water Potential
339
Some of the above conclusions may relate to the fact that BANNISTER (1986) found that drought resistance in the species examined was conferred either by an ability to avoid the development of low water potentials or an ability to tolerate low water potentials and rarely by a combination of the two. Other workers (e.g. HINCKLEY et al. 1983) have worked with drought resistant species that combined avoidance with tolerance. Thus, examination of HINCKLEY et al. (1983) shows that drought avoidance (measured as the time taken to reach a critical water content) is inversely correlated to the range of water potentials in the field (as in Fig. 3b), but is positively correlated with minimum water potentials (the opposite to Fig. 3a). However, because of the negative correlation of avoidance and tolerance, Fig. 3b could also be interpreted as a negative correlation of drought tolerance with minimum water potentials which would agree with the data of HINCKLEY et al. (1983). The above conclusions are apparently at variance with recent work that suggests that the control of gaseous exchange is more a function of soil water potential than of leaf water potential (e.g. KuPPERS 1984; GoLLAN et al. 1985; TURNER et al. 1985), although they do support the idea that transpiration rate determines water potential rather than the converse (e.g. SEATON et al. [1977], as interpreted by GOLLAN et al. [1985]). Leaf conductance There were too few measurements made to make definitive relationships between conductance and environmental factors although it is possible that some combination of light intensity and humidity might account for the observed reactions (cf. WHITEHEAD et al. 1981). In most cases (Fig. 4), the conductance is highest before light intensity peaks at the solar noon and decreases in the afternoon when water potentials increase (Figs. 2 and 5). Such decreases in conductance may either be a direct response to decreased humidity in the afternoon or a response to the bulk leaf water potential which was usually at a minimum before noon. The atmospheric saturation deficit was usually < 1.0 kPa and never exceeded 1.6 kPa when conductance measurements were made; humidity resr1onses recorded by other workers (e.g. KUPPERS 1984; GoLLAN et al. 1985; TuRNER et al. 1985) are often apparent only at greater saturation deficits than this. The association of changes in conductance with the degree of afternoon recovery in water potential suggests that even if bulk leaf water potential does not influence leaf conductanC'e the converse is true. Hydraulic conductivity KuPPJ
340
P. BAXKISTER and R. :!\1. KISSEL
of transpiration to changes in water potential, and (in general) high rates of water loss are associated with large changes of water potential while low rates of loss are associated with small changes in water potential, it seems likely that differences in hydraulic conductivity are not great. This is confirmed by estimating hydraulic conductivities from the transpiration of the species in Fig. 4 and water potentials calculated from Table 2. With the limited data available, no significant differences could be detected except between the extremes. The species with the highest hydraulic conductivity ( Brachyglottis) shows high rates of water loss and large changes in water potential whereas the species with the lowest (Phymatosorus) shows both low rates of water loss and small changes in water potential. This study does not appear to support the idea that the lowest water potentials occur in the species with the lowest hydraulic conductivities; if anything it suggests the converse. A more detailed evaluation of hydraulic conductivity is needed and would require the contemporaneous measurement of transpiration and water potential rather than their measurement on different days as in this paper. In conclusion it seems that, at least for the species investigated here, the minimum water potentials in the field can be predicted from the behaviour of cut shoots in the laboratory. Moreover compensatory mechanisms (as found by BANNISTER [1986] in studies of drought resistance and the relationships between water potential and water content) appear to occur. Thus species that develop low water potentials in the field generally show a wide daily range of potentials, high rates of water loss, high drought tolerance and low drought avoidance but (where measured) high leaf conductances (presumably facilitating photosynthesis) and rapid recovery from deficits. Species that maintain high potentials show low rates of water loss (high drought avoidance) but low leaf conductances (restricting photosynthesis) that may be further lowered in the afternoon. Thus species with low drought avoidance generally appear to tolerate low water potentials but maintain open stomata whereas those with high avoidance maintain high water potentials but restrict stomatal aperture.
Acknowledgements The fieldwork was carried out when one of us (RMK) was in receipt of a University of Otago Summer Research Bursary and the purchase of a diffusion porometer was made possible by a grant from the University Grants Committee. Thanks are also due to members of the third· year Botany class of 1983 who made measurements of various species in winter.
References BANNISTER, P. (1964): Stomatal responses of heath plants to water deficits. J. Ecol. 52: 423-432. - (1971): The water relations of heath plants from open and shaded habitats. J. Ecol. 59: 51-64. - (1986): Drought resistance, water potential and water content in some New Zealand plants. Flora 178: 23-40.
Y. N. S., TYREE, M. T., & DAINTY, J. (1975): Water relations parameters on single leaves obtained in a pressure bomb and some ecological interpretations. Can. ,J. Bot. 53: 1342-1346.
CH~;uNG,
GREEN, T. G. A., & JANE, G. T. (1983a): Diurnal patterns of water potential in the evergreen cloud forests of the Kaimai Ranges, North Island, New Zealand. N. Z. J. Bot. 21: 379-389. - - (1983b): Changes in osmotic potential during bud break and leaf development of Nothojagus menziesii, Weinmannia racemosa, Quintinia acutijolia, and Ixerba brexioides. N. Z. J. Bot. 21: 391-395.
The Daily Course of Water Potential
341
GoLLAN, T., TuRNER, N.C., & ScHULZE, E.·D. (1985): The responses of stomata and leaf gas exchange to vapour pressure deficits and soil water content. III. In the sclerophyllous woody species Nerium oleander. Oecologia, Berlin (West) 65: 356-362. HELLKVIST, .T., RICHARDS, G. P., & JARVIS, P. G. (1974): Vertical gradients of water potential and tissue water relations in sitka spruce trees with the pressure chamber. J·. app. Ecol. 11: 637-677. HINCKLEY, T. M., DUHME, F., HINCKLEY, A. R., & RICHTER, H. (1981): Water relations of drought· hardy shrubs: osmotic potential and stomatal reactivity. Plant, Cell and Environ. 3: 131-140. - - - - (1983): Drought relations of shrub species: assessment of the mechanisms of drought resistance. Oecologia Berlin (West) 59: 344-350. HuTCHINSON, T. C. (1970): Lime chlorosis as a factor in seedling establishment on calcareous soils. II. The development of leaf water deficits in plants showing lime-chlorosis. New Phytol. 69: 143-157. HYGEN, G. (1953): On the transpiration decline of excised plant samples. Norske Vid. Akad. Skr. 1 math.·nat. Kl. l: 1-84. JANE, G. T. (1983): Mortality of Native Forest Vegetation in the Kaimai Ranges. Unpublished D. Phil. thesis, University of Waikato. GREEN, T. G. A. (1983): Utilisation of pressure-volume techniques and non-linear least squares analysis to investigate site induced stresses in evergreen trees. Oecologia, Berlin (West) 57: 380-390. JARVIS, P. G., & .JARVIS, M. S. (1963): The water relations of tree seedlings. IV. Some aspects of tissue water relations and drought resistance. Physiol. Plant. 16: 501-516. KARLIC, H., & RICHTER, H. (1979): Storage of detached leaves and twigs without changes in water potential. New Phytol. 83: 379-384. KuPPERS, l\1. (1984): Carbon relations and competition between woody species in a central European hedgerow. II. Stomatal responses, water use and hydraulic conductivity in the rootjleaf pathway. Oecologia, Berlin (West) 64: 344-354. 0GDEK, J. (1976): Notes on the influence of drought on the bush remnants of the Manawatu Lowlands. Proc. N. Z. Ecol. Soc. 23: 92-98. PoLLOCK, K. M. (1979): Aspects of the Water Relations of Some Alpine Species of Chionochloa. L'npublished Ph.D. thesis, University of Otago, N. Z. RICHTER, H. (1976): The water status in the plant: experimental evidence. In: LANGE, 0. L., KAPPEN, L., & SCHULZE, E.-D. (eds.): Water and Plant Life. Heidelberg. 42-58. DUHME, F., GLATZEL, G., HINCKLEY, T. M., & KARLIC, H. (1981): Some limitations and applications of the pressure-volume curve technique in ecophysiological research. In: GRACE, J., FoRD, E. D., & JARVIS, P. G. (eds.): Plants and their Atmospheric Environment. Oxford. 263-272. RITCHIE, G. A., & HINCKLEY, T. M. (1975): The pressure chamber as an instrument for ecological research. Adv. Ecol. Res. 9: 165-254. ScHOLANDER, P. F., HAMMEL, H. T., HEMMINGSTEN, E. A., & BRANDSTREET, E. D. (1964): Hydrostatic pressure and osmotic potentials in leaves of mangroves and some other plants. l'roc. Nat. Acad. Sci., U.S.A. 51: 119-125. SEATO:-<, K. A., LANDSBERG, J .•T., & SEDGELY, R. H. (1977): Transpiration and leaf water potentials of wheat in relation to changing soil water potential. Aust. J. agric. Res. 28: 355-367. TURNER, N.C., ScHULZE, E.-D., & GoLLAN, T. (1985): The responses of stomata and leaf gas exchange to vapour pressure deficits and soil water content. II. In the mesophytic herbaceous species Helianthus annuus. Oecologia, Berlin (West) 65: 348-355. TYREE, M. T., & HAMMEL, H. T. (1972): The measurement of turgor pressure and the water relations of plants by the pressure-bomb technique. J. exp. Bot. 23: 267-282. KARAMANOS, A. ,J. (1981): Water stress as an ecological factor. In: GRACE, J., FORD, E. D., & JARVIS, P. G. (eels.): Plants and their Atmospheric Environment. Oxford. 237-262. CHEUNG, Y. N. S., McGREGOR, M. E., & TALBOT, A. J. B. (1978): The characteristic seasonal and ontogenetic changes in the tissue water relations of Acer, Populus, Tsuga and Picea. Can. J. Bot. 56: 635-647.
342
P. BANXiSTER and R. ::\1. KrssEr, The Daily Course of Water Potential
WEATHERLEY, P. E., & SLATYER, R. 0. (1957): Relationship between relative turgidity and diffusion pressure deficit in leaves. Nature (London) 179: 1085-1086. WHITEHEAD, D., 0KALI, D. U. U., & FASEHt;K, F. E. (1981): Stomatal response to environmental variables in two tropical forest species during the dry season in Nigeria. J. appl. Ecol. 18: 571-587. WrLsox, J. B. (1975): Teddybear- A statistical system. N. Z. Statistician 10: 36-42. Received January 10, 1986 Authors' address: Prof. PETER BANNISTER and Mrs. RUTH M. KISSEL, Department of Botany, LTniversity of Otago, P.O. Box 56, Dunedin, New Zealand.
Flora (1986) 178: 342 VEB Gustav Fischer Verlag J ena
Buchbesprechung SLOBODDA, S.: Pflanzengemeinschaften und ihre Umwelt. 1. Auflage. - Leipzig-JenaBerlin: Urania-Verlag 1985.-254 S., zahlr. Abb. (Zeichnungen und Farbfotos) Ganzleinen, 24,00 M. Der Autor hat sich zur Aufgabe gestellt, ftir die breite interessierte Offentlichkeit ,eine Einftihrung in die Vielfalt unserer heimischen Pflanzengemeinschaften und die ihnen innewohnenden Gesetzmiil3igkeiten zu geben". Man kann ihm bescheinigen, daf3 er die Aufgabe gut gelOst hat. In anschaulicher Weise und lebendiger Sprache schildert er die wichtigen Formationen unserer Pflanzendecke. Die einzelnen Kapitel tragen Uberschriften, die den Leser neugierig machen. Ausgehend von einer vegetationsgeschichtlichen Einfiihrung unter besonderer Berticksichtigung der vegetationsveriindernden Rolle des Menschen werden die Laubwiilder, Nadelholzforste, Xerothermrasen, Moore, Wiesen, Gewiisser und Ackerunkrautfluren abgehandelt. Dabei schildert der Autor nicht nur die Vegetation in ihrem Artenreichtum, ihrer jahreszeitlichen Entwicklung und Struktur sondern auch den Standortbezug, 6kologische Besonderheiten und wirtschaftliche Bedeutung der Pflanzenbestiinde. An passender Stelle werden auch wichtige Methoden und Begriffe dargestellt, die ftir das Verstiindnis der Vegetation von Bedeutung sind (z. B. Aufnahmemethodik, Lebensformen, vVurzelprofile, Bodentypen, Gewiissertypen). Zahlreiche Zeichnungen und Farbfotos veranschaulichen die Aussagen und bereichern das Buch. Leider liil3t die Farbwiedergabe der Fotos hiiufig zu wtinschen tibrig. Zusammenfassende Kapitel tiber die Beziehungen der Glieder cines Okosystems zueinander und tiber Naturschutzbelange beschlieJ.len das Buch, das mit viel Engagement ftir die heimische Pflanzenwelt und ihre Erhaltung geschrieben ist. Ein Register der deutschen und wissenschaftlichen Pflanzennamen, der Pflanzengesellschaften und Fachbegriffe triigt zur Erschliel3ung des Buches bei. Sicher ist manches zu beanstanden, auch nachzutragen. Unbedingt hiitte die Ruderalvegetation, die Pflanzenwelt, die der Leser vor der Hausttir findet, berticksichtigt werden sollen. Auch die Vegetation der Ktiste fehlt. Manche geographischen Beztige hatten deutlicher formuliert werden sollen. Man merkt auch, dal3 bei der Vegetationsdarstellung die stidlichen Gebiete der DDR etwas zurtickhaltend behandelt wurden. Alles in allem haben wir ein Buch vor uns, das Wissenschaftlichkeit mit Allgemeinverstiindlichkeit verbindet, das die Vegetation und die Aufgaben der Vegetationskunde der breiten Offentlichkeit nahebringt und bei seinem annehmbaren Preis viele Freunde finden wird. W. HILBIG, Halle (Saale)
The Daily Course of Water Potential and Leaf Conductance in some New Zealand Plants P. BANNISTER and R. M. KISSEL Department of Botany, University of Otago, Dunedin, New Zealand
Summary The field water potentials of some 23 species, mostly woody plants and ferns native to New Zealand (but including one introduced fern), were measured on various occasions, mostly during the 1982{83 summer. The minimum water potentials recorded in the field were highly correlated with the ability of cut shoots and leaves to avoid low water deficits and low water potentials when artificially desiccated in the laboratory. Species that maintained high water potentials in the field also showed lesser fluctuations in water potential than those that developed low water potentials. Leaf conductances and transpiration rates were measured in five species. Low conductances and transpiration rates were generally associated with those species that maintained high water potentials in the field (e.g. Phymatosorus diversijolius (WILLD.) Pic. SER.), whereas high conductances and transpiration rates were generally associated with species that developed low water potentials (e.g Brachyglottis repanda FoRST.). One species, Metrosideros robusta A. CuNN. showed high conductances and transpiration rates but maintained a higher water potential in the field. Those species that showed the largest reductions of conductance in the early afternoon also showed the best recovery of shoot water potential. For the species examined, the artifical desiccation of cut shoots and leaves in the laboratory provides a guide to minimum water potentials in the field. These appear to be determined by rates of water loss from the shoot rather than the hydraulic conductivity of the soil·plant·atmosphere system.
Introduction Various authors have used the artificial desiccation of cut shoots and leaves as an aid to the interpretation of the water relations of plants in the field. The decline of water content with time has been used to estimate the point of stomatal closure and other transpiration-related parameters (e.g. HYGEN 1953; JARVIS & JARVIS 1963; BANNISTER 1964, 1971; HuTCHINSON 1970). The relationships between water content and water potential have also been given ecological interpretations (e.g. WEATHERLEY & SLATYER 1957; JARVIS & JARVIS 1963; CHEUNG et al. 1975; TYREE & KARAMANOS 1981) as have the relationships between applied pressure and water content derived from pressure chamber (P-V curves). Parameters derived from the analysis of such curves (TYREE & HAMMEL 1972) have been used extensively (e.g. HELLKVIST et al. 1974; CHEUNG et al. 1975; TYREE et al. 1978; HINCKLEY et al. 1981, 1983; JANE & GREEN 1983). Many studies using the aforementioned methods have been applied to only a limited number of species (sometimes only one) and do not usually question the general applicability of the methods to the interpretation of the water relations of a diverse range of species in the field. This study deliberately relates laboratory measures of drought tolerance and avoidance of 23 species to their responses in the field. As little had been published on the water relations of plants native to New 21
Flora, Bd. 178
330
P. BANNISTER and R. M. KISSEL
Zealand until recently (e.g. JANE & GREEN 1983; GREEN & JANE l983a, b), the studies in this paper also supplement the available information.
Material and Methods Species The species exan1ined were the same as those used in a series of laboratory studies of drought resistance and parameters derived from P-V curves (BANNISTER l9R6) and are listed in Table L ·where there is no ambiguity, these species are referred to in thll text by their generic names alone. The plants used for these studies were located mostly in the gardens of the Botany Department, although some were from the municipal Botanic Gardens (about l km distant). The more distant
Table l. Species used in the investigations, their site of collection, abbreviated form, and drought avoidance site
abbr.
drought avoidance
B B B B G
As Bl Dry Phy Pte
0.85 0.4 0.9 1.65 0.7
B B B
Cy Drl Pny
0.25 0.95 0,7
B B B B B
Ag Dey Dbd Dcu Pdh
1.6 1.1 1.3 l.l 1.45
B B G B B G G G B B
Br Le Ls Mr Nf Ns Nm Plg Px Wn
0.65 0.6 0.65 1.5 1.35 0.9
Ferns Asplenium bulbiferum FoRST. f. Blechnum penna-maria (ProR.) KUHN Dryopteris filix-mas (L.) SCHOTT Phymatosorus diversijolius (WILLD.) Pre. SER. Pteridium esculentum (FoRST. f.) KuHN Ericaceousfepacridaceous shrubs Cyathodes jraseri (A. CUNN.) ALLAN Dracophyllum longijolium (J. R. et G. FoRST.) R. BR. Pernettya macrostigma CoL. Coniferous trees and shrubs Agathis australis SALJSB. Dacrycarpus dacrydiodes (A. RrcH.) DE LAUBENFELS Dacrydium bidwillii HooK. f. ex KIRK D. cupressinum LAMB. Podocarpus hallii KIRK Other trees and shrubs Brachyglottis repanda J. R. et G. FoRST. Leptospermum ericoides J. R. et G. FoRST. L. scoparium J. R. et G. FoRST. Metrosideros robusta A. CuNN. Nothofagus jusca (HooK. f.) 0ERST. N. solandri (HooK, f.) OERST. N. menziesii (HooK. f.) 0ERST. Plagianthus betulinus* A. CUNN. Pseudopanax colensoi (HooK. f.) PHILIPSON Weinmunnia racemosa LlNN. f.
* deciduous species Sites of collection: B Gardens of Botany Department; G Municipal Botanic Gardens and environs. Drought avoidance: is the average of the following two measures: (i) time (log 10 hours) to reach 50% relative water content (ii) time (log10 hours) to reach a balancing pressure of 3.45 MPa.
l.O 0.6 1.55 1.25
331
The Daily Course of Water Potential
specimens were sampled less frequently and only at times when minimum water potentials might be expected (e.g. in the early afternoon of hot days). In all cases exposed shoots or leaves of current mature growth were sampled. Sampling took place principally in summer (December 1982-February 1983) although some readings taken during the winters of 1983 and 1984 have been included for comparative purposes. Water potential (Table 2) This was measured in a pressure chamber (ScHOLANDER et al. 1964; RITCHIE & HINCKLEY 1975); details of the particular chamber are given by PoLLOCK (1979). Shoots and leaves were sampled directly into polythene bags and brought with minimum delay to the pressure chamber for the determination of balancing pressures. The shoot or leaf water potential was taken to be the negative of the balancing pressure (i.e. the osmotic pressure of the xylem sap was considered to be negligible). Usually four replicate samples were taken at each measurement. As storage times were minimal and there appeared to be no consistent drift of balancing pressure from the first to the last sample, no elaborate precautions to minimise water loss (e.g. KARLIC & RICHTER 1979) were taken. Drought avoidance The scale of drought avoidance is derived from measurements made in two previous summers (BANNISTER 1986). Both measures are of the time taken (in log10 hours) for the samples to reach
Table 2. Relationships of water potential to time of day (H), date (D), and maximum temperature (T) on day of measurement as determined by multiple regression analyses. Only significant (P < 0.05) partial regression coefficients are shown Constant
partial regression coefficients ln(H)
(ln[H]) 2
D
T
+
+0.0050 -0.0047
-0.0193 -0.0109
%variation accounted for (between means)
Ferns Bl Dry Phy
-1.5982 ( = mean) 17.6697 -14.6593 0.5167 - 0.2986
2.8839
0 60 59
Ericaceousfepacridaceous shrubs Cy Dr! Pny
63.1194 10.1658 31.6452
-51.6669 - 8.6209 -25.2946
+10.2696 + 1.7019 + 5.0334
-0.0235 -0.0063 -0.0113
-0.0562
+0.0019 -0.0033
-0.0191 -0.0339
-0.0042 -0.0057
-0.0350
92 43 49
Coniferous trees and shrubs Ag Dey Dcu Pdh
1.4366 10.9230 11.6649 9.2673
Other trees and shrubs Br 0.8668 Le 17.5295 l\Ir 21.8573 Nf 14.9191 Px 14.6464 Wn 13.1140
0.8409 8.9583 9.1337 7.9456
+ + +
1.7191 l. 7648 1.5149
- 0.5294 -14.6352 -18.0421 -12.2561 -11.9505 -10.9777
+ + + + +
2.7734 3.5813 2.4334 2.3039 2.1389
H is local time (24 h clock) D is days from 1st December 1982 T is maximum daily temperature ( oc) 21*
-0.0035
-0.1464 -0.0231
+0.0029
-0.0043
37 53 67 34
39 65 67 19 49 75
332
P. BANNISTER and R. M. KISSEL
either a relative water content of 50% or a water potential of -3.45 MPa (-500 p.s.i.). In both cases desiccation took place in normal laboratory conditions at a temperature of around 20°C. The two measures are highly correlated (P < 0.001) and are also inversely correlated with the ability of the shoots to withstand low water contents and potentials (i.e. drought tolerance, see BANNISTER 1986). The scale used is the mean of the two measures of drought avoidance. Stomatal conductance and transpiration These were measured on five species only (Phymatosorus, Pseudopanax, Brachyglottis, Metrosideros, Weinmannia), using a Licor LI-1600 steady state diffusion porometer and expressed as mmol m-2 s-1. Measurements of temperature, light intensity and humidity were taken at the same time and used to correlate water loss with environmental factors. Each value is the mean of five samples. Treatment of data It was not possible to measure all species on the same day because of the number of species involved and the fact that only one pressure chamber was available; nor was it desirable to confine one day's measurements to a single species as the main object was to compare species. Consequently the data consists of measurements made at various times, days and species at intervals through the summer. The use of multiple regression analyses of water potential against time of day, maximum daily temperature and data allowed some assessment of the diurnal pattern of water potential, its drift with season and the influence of daily temperature. Samples made during rain were excluded as they were usually significantly different from those made during equivalent dry periods. Only five species, with fewer measurements, were used for leaf conductance and transpiration, and while these were used in multiple regressions of conductance on environmental factors, the principal analysis uses readings that were taken on all five species at approximately the same time of day on three different days (10, 11, 14 February 1983). Multiple regressions and other statistical analyses were made using the general statistical program TEDDYBEAR (WILSON 1975).
Results Fig. l gives the mean values and ranges (the difference between maximum and minimum water potentials for individual shoots of the same species), mostly for species that were measured frequently during the summer but also for some that were investigated in winter. Those species that maintain high water potentials (e.g. Phymatosorus) show lesser ranges than those which develop low water potentials (e.g. Cyathodes). Multiple regression analyses revealed that water potentials were generally lower when measured later in the season (except in Dryopteris, Dacrycarpus and Weinmannia where they became higher) and were lower on warmer days, with those species showing low minimum potentials (e.g. Pernettya, Bmchyglottis) showing the greatest sensitivities. Contrasting examples of daily patterns, using raw data, are given in Fig. 2. Most species showed a rapid decline in water potential in the early morning followed by some recovery in the afternoon. Some species ( Brachyglottis, P hymatosorus, Agathis) showed a steady decline during the day, these plants were usually from locations that were somewhat shaded in the morning and more exposed in the afternoon. Blechnum penna-marina showed no marked overall trend with consistently low values throughout, although losses and gains were noted on particular days (Fig. 2). Some species show generally high water potentials (Phymatosorus, Agathis, Pseudopanax), while the water potentials in a number of others (Podocarpus, Dacrydium cupressinum, Dacrycarpus, Dracophyllum, N othofagus fusca, Metrosideros, Weinmannia, Dryopteris) are only a little lower. A futher group ( Brachyglottis, Blechnum,
333
The Daily Course of Water Potential
ecy
ePny oBI 2·0
0...
Br •
OLe
:::!: C/)
(ii
c Q)
0
eLe
a. .... Q)
-:;;
Drle Nf• Mr~
eDcu Mre • eAg Dry eDcy
Qi
~
0 Q)
Px
eBI
3: -o
1·0
0>
c
II:
wn.
-2·0
ePdh
~hy
Pgy
-1·0 Mean field water potential ( MPa)
Fig. 1. Mean and range for field water potentials. (r = 0.747, P < 0.001). Abbreviations for species as m Table 1; summer measurements are indicated by filled circles, winter ones by open circles.
Pernettya, Cyathodes, Leptospermum ericoides) shows much lower water potentials. These differences appear to be related to laboratory measures of drought avoidance and this is confirmed by the strong correlation (P < 0.001) of the minimum field water potential recorded during the summer with the scale of drought avoidance (Fig. 3a). The range of water potentials recorded in the field is also correlated with the same scale (Fig. 3b). Conductance and transpiration Because of the relatively fewer measurements of conductance that were made, the correlations with environment are more tentative (Table 3). The conductance of Phymatosorus increased with light intensity (which is generally low in this fern's habitat). There is evidence for humidity effects in other species, particularly when time of day is taken into account. In Metrosideros conductance declines during the day (as saturation deficits increase), whereas inPseudopanax there is an initial increase in conductance in the morning when saturation deficits are increasing but a decline in the afternoon (particularly when saturation deficits exceed 1.0 kPa). In contrast, Weinmannia leaves showed a consistent increase in conductance as saturation deficits increased (although they never exceeded 1.2 kPa).
334
P.
BANNISTER
and R. M.
KISSEL
0 27
17
X
~~~~ \."'%
----x/-X'
X
I
~.
I
15 ....
X
!>.
~x ~~X--•15
-1
\'•-/
Phymatosorus diversifolius
\
/ X
Metrosideros robusta
0
•\
Blechnum penna- marina
Cyathodes fraseri
c Q)
~
\a/.\x x
X
Ji
10
12
14
•n___•......--......--••...--"
\
X
16
6
aV
8
a~
X
~.:......---·--------.. 10
12
14
-1
)\
~
of\ 14·~·~ x~·;
·"
·-·
6
X
x \
0~1' 8
-~
00.
X
X
-2
27
16
18
Solar time Fig. 2. Daily values for water potential in summer and winter (where appropriate) for Phymata· sorus diversijolius (high drought avoidance), Metrosideros robusta (intermediate avoidance), Oyathodes jraseri (low avoidance, high tolerance) and Blechum penna-marina (low avoidance, high tolerance but little daily fluctuation in water potential). Crosses indicate winter readings (Metrosideros, early June; Blechnum, mid-July; Phymatosorus late .July 1983). Summer readings are indicated by triangles (November-December 1982), circles (January 1983) or squares (February 1983). Filled symbols link readings made on the same date (indicated by a number); open symbols indicate single readings on separate days.
A more ready comparison of the five species investigated is made by taking averages over 3d in which measurements were made in early morning, mid-morning, around midday and in the early afternoon (solar time, local time is 1 h 40 min ahead in summer). Although there were significant differences (P < 0.001) in both transpiration and conductance between days (with the third day showing lower values than the other two) there is little difference between the reaction of the species on the different days. The interaction of species with days was not significant for transpiration and only just significant (P = 0.03) for conductance (the conductance of Brachyglottis and Phymatosorus was higher and that of Pseudopanax lower on the third day than expected from the previous days. The lowering of transpiration on the third day was associated with only the first and last readings and was little different in the middle (i.e. a significant interaction [P < 0.001] between days and time of day); there was no significant interaction for conductance. Environmental conditions were similar on the 3 d with temperatures ranging between 12 and 19°0 and relative
335
The Daily Course of Water Potential
8:. 6
Phye
t1l
~ -1·0
(a)
Cy
Dcue Dcye
~
PdheA9 • •Px Mre •Dbd
•
Bl
c
0
Ql
0
0.
Le0 e
~
Q;
Ptee As Dry . . •Nm
a;
:s:
~ -2·0 E :::J E c ~
2t1l :s:
eNf
Br
•
Bl
•
• Ls
.'!!
eDrl
0
eNs •ePny Lee
Br
Le
:g
-c
(b)
P~y
(/)
Wn
Dr I
•
D.y
Ql
Nf Dcu
•
Ol
•M'QePx Mr• eAg
eDcy
c
t1l
c:
Pdh
ePig
wn.
•
Phy ()
I
1·0
0·5
0·5
1·5
1·0
1·5
Drought avoidance
Drought avoidance
Fig. 3. (a} Relationship between minimum water potential in the field and drought avoidance < 0.001).
(r = 0.899, P
(b) Relationship between range of water potential in the field and drought avoidance (r = 0. 781, p < 0.001). Species' abbreviations and drought avoidance as in Table 1. Filled circles indicate summer measure· ments, open circles winter ones. In Fig. 3 a the points are means of 2-6, usually 4, replicate samples.
Table 3. Relationships between conductance (C) and date (D), time of day (H), atmospheric saturation deficit (S) maximum daily temperature (T) and light (Q) Phymatosorus
c
= 57.9137
+ 0.4819*Q
(P
< 0.05)
(P
< 0.01)
(P
<
(P
< 0.001)
(P
< 0.001)
M etrosideros C = 228.35- 6.06*H (correlation between S & H, r
=
0.7678, P
< 0.01)
Brachyglottis C
=
3.4189- 0.0841 *S
+ 0.8008*H
0.05)
Weinmannia C
=
94.58- 8.23*T
+ 21.37*8
Pseudopanax C
=
4770.41- 78.23*ln(S)
+ 3872.61 *H- 742.41 *H2
H is the natural logarithm of local time (24 h clock) S is atmospheric saturation deficit in mbar Q is quantum flux in mmol quanta m-2 s-1 T is daily maximum temperature (0 C)
336
P.
BA'l'.'NISTER
and R. M.
KISSEL
r
1·5 150 I
";'
C/l
C/l
N
N
I
I
E
0
E E
E
0
1-0
E
_s
~
c: 0
Q)
u
~ ·c.
c: ~
t5
C/l
:::l
c:
"0
~
.=
100
c:
0 (.)
0·5
5t 9
11
13
15
17
9
Local time
7
9
11 13 Solar time
11
13
15
17
Local time
15
7
9
11 13 Solar time
15
Fig. 4. Mean values for transpiration and conductance for 5 species averaged over 3 d. (a) Transpiration (b) Conductance. Species' abbreviations as in Table 1. Points are mean3 of measurements on five different leaves. Vertical bars indicate the least significant difference (P = 0.05) between means.
humidities between 40 and 70%. On the third day the first reading was somewhat earlier and the last reading later than on the other 2 d. This probably accounts for the differences in transpiration. The different patterns shown by the species is reflected in significant interactions (P < 0.001) between species and time of day for both transpiration and conductance (Fig. 4). All species, except Phymatosorus, show similar patterns of transpiration with an increase in the morning, a peak around the solar noon and a decline in the afternoon (Fig. 4a). Phymatosorus is different in that, it shows a peak in the later morning and little subsequent decline. Peak transpiration rates are in the order Brachyglottis > Metrosideros > Pseudopanax > Weinmannia > Phymatosorus and the average transpiration rates follow the same ranking with significant differences between all species except Brachyglottis and Metrosideros. Peak conductance show a similar order to transpiration rates, except that Metrosideros shows values slightly higher than those in Brachyglottis. In terms of mean conductances, there are no significant differences between either Brachyglott~·s and M etrosideros or W einmannia and Pseudopanax. Peak conductances coincide with peak transpiration rates in all species except Weinmannia and Pseudopanax where they are earlier. M etros~·deros differs from all the other species in that its conductance is already high in the early morning and all the species show slight differences in pattern from one another (Fig. 4b).
The Daily Course of Water Potential
337
+0·2
.wn
+ 0·1
•Px
al
Cl.. ~
*
0
Br • ePhy
- 0 ·1 L - - - - - - ' - - - - - ' - - - - " - - - - - - 1 0 10 20 30 40
/';. Conductance mmol m-2 s-1
Fig. 5. Relationship between the decrease of conductance from maximum to afternoon minimum (Fig. 4 b) and the corresponding change in water potential for the same period (calculated from Table 2) for 5 species. Species' abbreviations as in Table 1.
Relationships of water potential and conductance The decrease in conductance after the peak value has been attained is related to the degree of recovery of water potential (Fig. 5), estimated from the appropriate regressions in Table 2. Species showing large decreases in conductance (e.g. Metrosideros and Weinmannia) show a good recovery of water potential, whereas those that show the smallest reductions (Brachyglottis, Phymatosorus) show a continued loss of water potential. Metrosideros shows both high conductances and high water potentials which indicates that it is able to maintain open stomata without suffering undue water stress. This species has also been shown to be drought resistant in the field (OGDEN 1976). Winter measurements Some measurements of water potential and conductance were made in winter (Fig. 2, Table 4). They were not greatly different from those made in summer suggesting that the species are metabolically active in winter and are not under any greater water stress than might be found in summer.
Discussion Water potential GREEN & JANE (1983a) have measured water potentials in summer for Weinmannia and Nothofagus menziesii obtaining minimum values of about -1.2 MPa for W einmannia and -1.4 MPa for N. menziesii. The value for W einmannia is similar to that in this paper and that for N. menziesii higher, although the overall
338
P. BANNISTER and R. M. KISSEL
Table 4. Means and ranges for water potential and leaf conductance for species investigated in both summer and winter water potential (MPa) mean
max
min
-0.68 -0.49
-0.26 -0.22
-1.05 -1.01
-0.96 -0.76
-0.25 -0.36
-1.43 -1.73
-1.60 -1.38
-1.00 -0.59
-2.40 -2.75
-1.07 -1.04
-2.59 -2.88
conductance mmol (m-2 s-1) mean
min
max
76 44
58 20
108 66
151 124
96 40
177 144
Phymatosorus 1983 summer *1983 winter Metrosideros 1983 summer 1983 winter Blechnum 1983 summer 1983 winter
Leptospermum ericoides 1983 summer *1984 winter
* species measured at a
-1.87 -1.89
different site in winter
Phymatosorus Town Belt, Dunedin Leptospermum Cromwell George, Central Otago. extreme values for water potential are based on single shoots, those for conductance on means for five replicate leaves.
range of rmmmum water potentials for the five species they examined (-0.9 to -1.4 ~IPa) is less and in accord with the wetness of the habitat. The range of minimal water potentials found in this study is comparable with that in mesic habitats. RICHTER (1976) gives a range of -1.5 to -2.6 MPa (median -1.9 :VIPa) for woody plants from such sites which is very similar to the range in this paper (-1.14 to -2.53 MPa, median -1.67 MPa; -0.85 to -2.53 MPa, median -1.65 MPa if ferns are included). The summer of 1982/83 in Dunedin was not particularly dry. A drought in 1985 produced minima from -1.3 to -6.5 MPa (BANNISTER, unpublished), which overlaps with the range (-3.2 to -7.0 MPa) given by RICHTER (1976) for plants from habitats subject to drought. The minimum water potentials do not relate in any obvious way to field determinations of drought resistance (OGDEN 1976). For example, Metrosideros and Leptospermum spp. are drought resistant, but the former maintains a high water potential while the latter species develop low potentials. Conversely, amongst drought susceptible species, Dacrywrpus and Dacrydium cupressinum maintain high water potentials whereas Brachyglottis develops low potentials. There is, however a close relationship between the behaviour of artifically desiccated cut shoots and responses in the field (Fig. 3a) which suggests that such laboratory studies may provide reasonable predictions of field responses. This further suggests that field water potentials in the investigated mesic habitats are a function of leaf resistance rather than of resistances elsewhere (e.g. in the stems, roots and soil). Similarily GREEN & JANE (1983a) found restricted rooting in wet forest soils but no evidence for the development of extremely low water potentials. However, rapid decreases in stomatal conductance occured when the usual cloud cover was absent (JANE 1983).
The Daily Course of Water Potential
339
Some of the above conclusions may relate to the fact that BANNISTER (1986) found that drought resistance in the species examined was conferred either by an ability to avoid the development of low water potentials or an ability to tolerate low water potentials and rarely by a combination of the two. Other workers (e.g. HINCKLEY et al. 1983) have worked with drought resistant species that combined avoidance with tolerance. Thus, examination of HINCKLEY et al. (1983) shows that drought avoidance (measured as the time taken to reach a critical water content) is inversely correlated to the range of water potentials in the field (as in Fig. 3b), but is positively correlated with minimum water potentials (the opposite to Fig. 3a). However, because of the negative correlation of avoidance and tolerance, Fig. 3b could also be interpreted as a negative correlation of drought tolerance with minimum water potentials which would agree with the data of HINCKLEY et al. (1983). The above conclusions are apparently at variance with recent work that suggests that the control of gaseous exchange is more a function of soil water potential than of leaf water potential (e.g. KuPPERS 1984; GoLLAN et al. 1985; TURNER et al. 1985), although they do support the idea that transpiration rate determines water potential rather than the converse (e.g. SEATON et al. [1977], as interpreted by GOLLAN et al. [1985]). Leaf conductance There were too few measurements made to make definitive relationships between conductance and environmental factors although it is possible that some combination of light intensity and humidity might account for the observed reactions (cf. WHITEHEAD et al. 1981). In most cases (Fig. 4), the conductance is highest before light intensity peaks at the solar noon and decreases in the afternoon when water potentials increase (Figs. 2 and 5). Such decreases in conductance may either be a direct response to decreased humidity in the afternoon or a response to the bulk leaf water potential which was usually at a minimum before noon. The atmospheric saturation deficit was usually < 1.0 kPa and never exceeded 1.6 kPa when conductance measurements were made; humidity resr1onses recorded by other workers (e.g. KUPPERS 1984; GoLLAN et al. 1985; TuRNER et al. 1985) are often apparent only at greater saturation deficits than this. The association of changes in conductance with the degree of afternoon recovery in water potential suggests that even if bulk leaf water potential does not influence leaf conductanC'e the converse is true. Hydraulic conductivity KuPPJ
340
P. BAXKISTER and R. :!\1. KISSEL
of transpiration to changes in water potential, and (in general) high rates of water loss are associated with large changes of water potential while low rates of loss are associated with small changes in water potential, it seems likely that differences in hydraulic conductivity are not great. This is confirmed by estimating hydraulic conductivities from the transpiration of the species in Fig. 4 and water potentials calculated from Table 2. With the limited data available, no significant differences could be detected except between the extremes. The species with the highest hydraulic conductivity ( Brachyglottis) shows high rates of water loss and large changes in water potential whereas the species with the lowest (Phymatosorus) shows both low rates of water loss and small changes in water potential. This study does not appear to support the idea that the lowest water potentials occur in the species with the lowest hydraulic conductivities; if anything it suggests the converse. A more detailed evaluation of hydraulic conductivity is needed and would require the contemporaneous measurement of transpiration and water potential rather than their measurement on different days as in this paper. In conclusion it seems that, at least for the species investigated here, the minimum water potentials in the field can be predicted from the behaviour of cut shoots in the laboratory. Moreover compensatory mechanisms (as found by BANNISTER [1986] in studies of drought resistance and the relationships between water potential and water content) appear to occur. Thus species that develop low water potentials in the field generally show a wide daily range of potentials, high rates of water loss, high drought tolerance and low drought avoidance but (where measured) high leaf conductances (presumably facilitating photosynthesis) and rapid recovery from deficits. Species that maintain high potentials show low rates of water loss (high drought avoidance) but low leaf conductances (restricting photosynthesis) that may be further lowered in the afternoon. Thus species with low drought avoidance generally appear to tolerate low water potentials but maintain open stomata whereas those with high avoidance maintain high water potentials but restrict stomatal aperture.
Acknowledgements The fieldwork was carried out when one of us (RMK) was in receipt of a University of Otago Summer Research Bursary and the purchase of a diffusion porometer was made possible by a grant from the University Grants Committee. Thanks are also due to members of the third· year Botany class of 1983 who made measurements of various species in winter.
References BANNISTER, P. (1964): Stomatal responses of heath plants to water deficits. J. Ecol. 52: 423-432. - (1971): The water relations of heath plants from open and shaded habitats. J. Ecol. 59: 51-64. - (1986): Drought resistance, water potential and water content in some New Zealand plants. Flora 178: 23-40.
Y. N. S., TYREE, M. T., & DAINTY, J. (1975): Water relations parameters on single leaves obtained in a pressure bomb and some ecological interpretations. Can. ,J. Bot. 53: 1342-1346.
CH~;uNG,
GREEN, T. G. A., & JANE, G. T. (1983a): Diurnal patterns of water potential in the evergreen cloud forests of the Kaimai Ranges, North Island, New Zealand. N. Z. J. Bot. 21: 379-389. - - (1983b): Changes in osmotic potential during bud break and leaf development of Nothojagus menziesii, Weinmannia racemosa, Quintinia acutijolia, and Ixerba brexioides. N. Z. J. Bot. 21: 391-395.
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GoLLAN, T., TuRNER, N.C., & ScHULZE, E.·D. (1985): The responses of stomata and leaf gas exchange to vapour pressure deficits and soil water content. III. In the sclerophyllous woody species Nerium oleander. Oecologia, Berlin (West) 65: 356-362. HELLKVIST, .T., RICHARDS, G. P., & JARVIS, P. G. (1974): Vertical gradients of water potential and tissue water relations in sitka spruce trees with the pressure chamber. J·. app. Ecol. 11: 637-677. HINCKLEY, T. M., DUHME, F., HINCKLEY, A. R., & RICHTER, H. (1981): Water relations of drought· hardy shrubs: osmotic potential and stomatal reactivity. Plant, Cell and Environ. 3: 131-140. - - - - (1983): Drought relations of shrub species: assessment of the mechanisms of drought resistance. Oecologia Berlin (West) 59: 344-350. HuTCHINSON, T. C. (1970): Lime chlorosis as a factor in seedling establishment on calcareous soils. II. The development of leaf water deficits in plants showing lime-chlorosis. New Phytol. 69: 143-157. HYGEN, G. (1953): On the transpiration decline of excised plant samples. Norske Vid. Akad. Skr. 1 math.·nat. Kl. l: 1-84. JANE, G. T. (1983): Mortality of Native Forest Vegetation in the Kaimai Ranges. Unpublished D. Phil. thesis, University of Waikato. GREEN, T. G. A. (1983): Utilisation of pressure-volume techniques and non-linear least squares analysis to investigate site induced stresses in evergreen trees. Oecologia, Berlin (West) 57: 380-390. JARVIS, P. G., & .JARVIS, M. S. (1963): The water relations of tree seedlings. IV. Some aspects of tissue water relations and drought resistance. Physiol. Plant. 16: 501-516. KARLIC, H., & RICHTER, H. (1979): Storage of detached leaves and twigs without changes in water potential. New Phytol. 83: 379-384. KuPPERS, l\1. (1984): Carbon relations and competition between woody species in a central European hedgerow. II. Stomatal responses, water use and hydraulic conductivity in the rootjleaf pathway. Oecologia, Berlin (West) 64: 344-354. 0GDEK, J. (1976): Notes on the influence of drought on the bush remnants of the Manawatu Lowlands. Proc. N. Z. Ecol. Soc. 23: 92-98. PoLLOCK, K. M. (1979): Aspects of the Water Relations of Some Alpine Species of Chionochloa. L'npublished Ph.D. thesis, University of Otago, N. Z. RICHTER, H. (1976): The water status in the plant: experimental evidence. In: LANGE, 0. L., KAPPEN, L., & SCHULZE, E.-D. (eds.): Water and Plant Life. Heidelberg. 42-58. DUHME, F., GLATZEL, G., HINCKLEY, T. M., & KARLIC, H. (1981): Some limitations and applications of the pressure-volume curve technique in ecophysiological research. In: GRACE, J., FoRD, E. D., & JARVIS, P. G. (eds.): Plants and their Atmospheric Environment. Oxford. 263-272. RITCHIE, G. A., & HINCKLEY, T. M. (1975): The pressure chamber as an instrument for ecological research. Adv. Ecol. Res. 9: 165-254. ScHOLANDER, P. F., HAMMEL, H. T., HEMMINGSTEN, E. A., & BRANDSTREET, E. D. (1964): Hydrostatic pressure and osmotic potentials in leaves of mangroves and some other plants. l'roc. Nat. Acad. Sci., U.S.A. 51: 119-125. SEATO:-<, K. A., LANDSBERG, J .•T., & SEDGELY, R. H. (1977): Transpiration and leaf water potentials of wheat in relation to changing soil water potential. Aust. J. agric. Res. 28: 355-367. TURNER, N.C., ScHULZE, E.-D., & GoLLAN, T. (1985): The responses of stomata and leaf gas exchange to vapour pressure deficits and soil water content. II. In the mesophytic herbaceous species Helianthus annuus. Oecologia, Berlin (West) 65: 348-355. TYREE, M. T., & HAMMEL, H. T. (1972): The measurement of turgor pressure and the water relations of plants by the pressure-bomb technique. J. exp. Bot. 23: 267-282. KARAMANOS, A. ,J. (1981): Water stress as an ecological factor. In: GRACE, J., FORD, E. D., & JARVIS, P. G. (eels.): Plants and their Atmospheric Environment. Oxford. 237-262. CHEUNG, Y. N. S., McGREGOR, M. E., & TALBOT, A. J. B. (1978): The characteristic seasonal and ontogenetic changes in the tissue water relations of Acer, Populus, Tsuga and Picea. Can. J. Bot. 56: 635-647.
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WEATHERLEY, P. E., & SLATYER, R. 0. (1957): Relationship between relative turgidity and diffusion pressure deficit in leaves. Nature (London) 179: 1085-1086. WHITEHEAD, D., 0KALI, D. U. U., & FASEHt;K, F. E. (1981): Stomatal response to environmental variables in two tropical forest species during the dry season in Nigeria. J. appl. Ecol. 18: 571-587. WrLsox, J. B. (1975): Teddybear- A statistical system. N. Z. Statistician 10: 36-42. Received January 10, 1986 Authors' address: Prof. PETER BANNISTER and Mrs. RUTH M. KISSEL, Department of Botany, LTniversity of Otago, P.O. Box 56, Dunedin, New Zealand.
Flora (1986) 178: 342 VEB Gustav Fischer Verlag J ena
Buchbesprechung SLOBODDA, S.: Pflanzengemeinschaften und ihre Umwelt. 1. Auflage. - Leipzig-JenaBerlin: Urania-Verlag 1985.-254 S., zahlr. Abb. (Zeichnungen und Farbfotos) Ganzleinen, 24,00 M. Der Autor hat sich zur Aufgabe gestellt, ftir die breite interessierte Offentlichkeit ,eine Einftihrung in die Vielfalt unserer heimischen Pflanzengemeinschaften und die ihnen innewohnenden Gesetzmiil3igkeiten zu geben". Man kann ihm bescheinigen, daf3 er die Aufgabe gut gelOst hat. In anschaulicher Weise und lebendiger Sprache schildert er die wichtigen Formationen unserer Pflanzendecke. Die einzelnen Kapitel tragen Uberschriften, die den Leser neugierig machen. Ausgehend von einer vegetationsgeschichtlichen Einfiihrung unter besonderer Berticksichtigung der vegetationsveriindernden Rolle des Menschen werden die Laubwiilder, Nadelholzforste, Xerothermrasen, Moore, Wiesen, Gewiisser und Ackerunkrautfluren abgehandelt. Dabei schildert der Autor nicht nur die Vegetation in ihrem Artenreichtum, ihrer jahreszeitlichen Entwicklung und Struktur sondern auch den Standortbezug, 6kologische Besonderheiten und wirtschaftliche Bedeutung der Pflanzenbestiinde. An passender Stelle werden auch wichtige Methoden und Begriffe dargestellt, die ftir das Verstiindnis der Vegetation von Bedeutung sind (z. B. Aufnahmemethodik, Lebensformen, vVurzelprofile, Bodentypen, Gewiissertypen). Zahlreiche Zeichnungen und Farbfotos veranschaulichen die Aussagen und bereichern das Buch. Leider liil3t die Farbwiedergabe der Fotos hiiufig zu wtinschen tibrig. Zusammenfassende Kapitel tiber die Beziehungen der Glieder cines Okosystems zueinander und tiber Naturschutzbelange beschlieJ.len das Buch, das mit viel Engagement ftir die heimische Pflanzenwelt und ihre Erhaltung geschrieben ist. Ein Register der deutschen und wissenschaftlichen Pflanzennamen, der Pflanzengesellschaften und Fachbegriffe triigt zur Erschliel3ung des Buches bei. Sicher ist manches zu beanstanden, auch nachzutragen. Unbedingt hiitte die Ruderalvegetation, die Pflanzenwelt, die der Leser vor der Hausttir findet, berticksichtigt werden sollen. Auch die Vegetation der Ktiste fehlt. Manche geographischen Beztige hatten deutlicher formuliert werden sollen. Man merkt auch, dal3 bei der Vegetationsdarstellung die stidlichen Gebiete der DDR etwas zurtickhaltend behandelt wurden. Alles in allem haben wir ein Buch vor uns, das Wissenschaftlichkeit mit Allgemeinverstiindlichkeit verbindet, das die Vegetation und die Aufgaben der Vegetationskunde der breiten Offentlichkeit nahebringt und bei seinem annehmbaren Preis viele Freunde finden wird. W. HILBIG, Halle (Saale)