Effects of Soil Moisture on Ecophysiological Characteristics of Adiantum reniforme var. sinensis, an Endangered Fern Endemic to the Three Gorges Region in China

2008·3.7 MB·English

by  Jian Xiong Liao

on
of Moisture Ecophysiological
Effects Soil
Adiantum
Characteristics of reniforme var. sinensis,
an Endangered Fern Endemic Three Gorges
the
to
Region China
in
—
stract. The effects of soil moisture (80%, 60% and 40% water holding capacity) on dry matter
Auction and allocation, leaf morphological and physiological characteristics were examined in
iantum reniforme var. sinensis, an endangered fern endemic to the Three Gorges region in
ithwest China. Drought stress decreased leaf growth and photosynthetic capacity, and hence
uced total mass, specific leaf area (SLA) and leaf area ratio (LAR). Dry matter allocation into the
fraction, however, increased with decreasing soil moisture. Leaf relative water content (RWC)
t
:reased as soil water depletion, but the differences were insignificant. Such results might be the
u of a physiological balance between the demand for water by the leaves and the water uptake
It
n
by The
soil the roots. decrease in stomatal conductance effectively controlled water loss
(g
s )
sic water use efficiency (WUEi) under drought The increase in proline
stress.
ute to osmotic adjustment, and hence sustained cytomembrane integrality in
under
drought
conditions.
i
m
reniforme var. sinensis, ecophysiological characteristics, fern, soil moisture
Depending on environmental conditions, plants can morphology,
alter their
biomass and
allocation, physiological processes adapt changing
to to
environments
(Via et al., 1995; Sultan, 2001). In order to evade or decrease
the influences of water stress, plants can alter various functional traits such as:
root/shoot ratio (R/S), specific leaf area (SLA) (Turner, 1997; Marcelis et al,
and
1998; Liu Stiitzel, 2004), stomatal regulation, and osmotic adjustment (Liu
and
Stiitzel, 2002a; 2002b). However, there are few studies that address the
ability of ferns to respond to soil water deficiency.
Adiantum
reniforme var. sinensis Y.X. Lin, an evergreen fern of the family
m
Adiantaceae, only 80-480 Wanzhou
is distributed at elevations in District
and Shizhu County Chongqing The
of Municipality 1993; Shi 2005).
(Xie, et
al.,
range
of this species lies within the Three Gorges region of Yangtze River, China.
Due
to overexploitation and the Three Gorges number
Project construction, the
and
distribution of A. reniforme and
var. sinensis are decreasing quickly this
now
species is listed as endangered in the Chinese red data book (Fu, 1992).
The main
habitats of A. reniforme var. sinensis are or steeply sloped
cliffs
rocks with Such
thin soil. conditions result in frequent water (mean
stress soil
Corresponding Ming Wuhan
* author. Xi Academy
Jiang, Botanical Garden, Chinese of Sciences,
LIAO ET ECOPHYSIOLOGICAL
AL.: R
water content ± 2.2% 50%
is 12.8 (w/w), approximately of water holding
A
capacity). Previous studies of reniforme var. sinensis have focused on spore
and Xu
propagation
genetic diversity (Xie, 1993; et al, 1998; Pan et 2005).
al.,
work
has been done on
Little the ecophysiological aspects of the species,
especially as relates to ability to grow in such drought prone
it its habitats.
The
objectives of this study were to investigate the effects of soil moisture on
dry matter production and morphological and
allocation, leaf physiological
We
characteristics. hypothesized that drought stress could change these
ecophysiological characteristics differently, and these changes might compen-
sate for the shortage of water during drought periods. The information
A
obtained will be useful in designing an effective conservation plan
for
Material and Methods
and
Plant material growth conditions.—Unlike members
other of the genus,
A
cm
reniforme var. sinensis a single-leaf fern, 5-20 The leaves are
is tall.
A
cm
kidney-shaped
circular or (2-6 in diameter). Spores of reniforme
var.
Wanzhou
sinensis were collected from 30'N, 108 Chong-
District (30 17'E),
qing, Southwest China, and germinated in October 2004 in the laboratory.
When cm
sporelings reached 2.5 (17 months after germinating), the healthy
and uniform were and cm X
plants selected transplanted into 21 (diameter)
cm
15 (height) pots (six sporelings per pot), filled with a mixture of leaf mold,
peat soil and sand v/v/v). The pots were placed in a growth chamber
(2:1:1,
2
with a 13 h photoperiod, a photon flux density (PFD) of 360 jimol itT \
s
70%
C
humidity and These
relative 24 air temperature. values represented the
A
mean
values of natural habitats of reniforme var. sinensis. Three soil water
treatments were started on March 25, 2006 and each treatment had three
replicates. For the well-watered treatment, plants were watered to 20.6% (80%
of water holding capacity (WHC)). Similarly, for the middle and severe water-
WHC),
stress treatments, water was added to 15.5% (60% of 10.3% (40% of
WHC), respectively. The pots were watered every other day and the soil water
were by commonly-used weight method.
contents controlled
May
Measurements.— weeks Photosynthetic PFD-
Six later (10 2006),
response curves were measured with a portable gas exchange measuring
C0
system USA). and temperature
(LI-6400, Li-Cor, Lincoln, air in the leaf
2
moP
PFD
chamber were maintained 360 umol 1 and 24
C, respectively.
at
-1
m~ 2 m" 2 A
800 umol 1 and decreased stepwise umol
started s" to
at s
.
new
was
time interval of 90 given for the leaf to equilibrate to the conditions
s
in each measurement. Saturation PFD, compensation PFD, and PFD-saturated
were Leaf water use
photosynthetic rate (P estimated. intrinsic efficiency
max
)
was P and conductance
(WUEi) calculated using stomatal saturation
max at
(g
s )
PFD. Chlorophyll (Chi) was extracted using ethanol and acetone v/v). The
(1:2,
concentrations Chi a and Chi b in extracts were determined from
of
absorbances 663 and 645 nm, respectively, with a UV-2100 spectrophotom-
at
eter (Unico, Shanghai, China). Leaf relative water content (RWC) was
AMERICAN FERN VOLUME NUMBER
JOURNAL:
98
1
<
indicate significant differences (P 0.05).
Dry matter accumnlation
(g) LA 2
(cm
(%WHC)
Root Stem Leaf a
Total plant
)
i 5:5
ESS
S±Kf
3
izr^
0.273
W
measured -W
as [(W )/(W X100] according Bans and Weatherley
r to
d
d
s )
Membrane
(1962). stability index (MSI) was calculated (1-CVC X100
as
2 )
according to the method of Sairam et (1997/1998). Five leaf discs cm
al. (0.7
diameter) were immersed in twice-distilled water 24 C 30 min. The
at for
was DDS-11A
electrical conductivity (CJ recorded by conductormeter
a
min
(Shanghai, China). After 15 boiling water bath, the conductivity was
when
measured
the temperature reduced about 24 C
to (C Proline content in
2 ).
3%
was
leaves extracted aqueous
in solution of sulphosalicylic acid and
determined by method Zhang
the of et (1990). After measurements were
al. all
made,
were
six intact individuals harvested from
the three replicate pots. Total
was
leaf area (LA) determined using
a portable leaf area meter (Li-Cor-3000,
NE, USA)
Lincoln, before samples were C
all dried in an oven 80
at for at least
72 h. Leaf area per unit leaf mass (specific leaf area, SLA), leaf area per unit of
mass
total (leaf area ratio, LAR), root mass per unit of mass mass
total (root
RMR)
and
mass/shoot mass
ratio, root (R/S were determined according
ratio) to
Hunt
(1978).
Statistical analysis.— Statistical analysis was conducted using SPSS
13.0 for
windows
(SPSS Inc., Chicago, USA). All means were expressed with
their
ANOVA
standard and compared
error (± SE) using one-way by
followed
least
<
significant difference (LSD) post-hoc
analysis
(P
0.05).
Results
Dry
matter production and The
allocation.— and stem
differences in root
mass between
the water treatments were and mass
insignificant, but
leaf total
WHC
were WHC
40%
significantly lower under 80%
than under
that (Table
1).
LA
was
significantly smaller under lower water The
treatments. ratios of leaf
area to leaf mass (SLA) and to total mass (LAR) were also smaller under lower
RMR
water
treatments and
(Fig. 1). R/S, however, increased with the decrease
Photosynthetic and
characteristics water use For
efficiency.— three
soil
water
treatments, net photosynthetic
rate (P increased rapidly and reached
n
)
their constant PFD
at similar saturation Table P however,
(Fig.
2, 2). max
,
decreased
as soil moisture decreased and was
there a significant difference
WHC
between 40% and 80%
treatments
(Table compensation
Contrarily,
2).
LIAO ET ECOPHYSIOLOGICAL RESPONSES TO SOIL WATER
AL.:
275
•Q
in
220
65
"I' III
~
0.4
ill
ill
60% 40% 80% 60% 40%
80%
WHC)
Water (%
treatments
Effe isture on leaf and root characteristics of A. reniforme var. sinensi
Fig. 1.
LAR, RMR, mass R/S, root/shoot Data are the
specific leaf rea; le if area ratio; root ratio; ratio.
± SEofsixreplicates. Di fferent letters in each graph indicate significant differences (P<0.0
3
—
•—
60%
—
\
*—
40%
200 300 400 500 600 700 800
100
m"V)
PFD
umol
(
moisture on photon flux density (PFD) response curve of net photosynt
Fig. 2. Effects of soil
CO
rate of A. nuufnrnw var. sinensis. P„ were measured at concentration of 360 umol n
(I'J z
2
and temperature of 24 C, with PFD values ranging from to 800 umol in s~\ Data are the n
±
SE
of three replicates.
30 AMERICAN FERN JOURNAL: VOLUME NUMBER
98
(2008)
1
Table Effects of moisture on photosynthetic
2. soil characteristics of A. reniforme
var. sinensis.
PFD, photon
flux density; P PFD-saturated photosynthetic and WUE,,
max rate; stomatal
g
, s
conductance and intrinsii watei ua effi( iency at saturation PFD, respectively. Data are the means
column
indicat, significant differences (P<0.05).
i 3
P PFD PFD
Saturation WUEi
max
g
s
m
(%WHC) m
(Limol 2 s" 1 (umol m" 2 s" 1 (mol 2 (umol mol
s
*) *)
)
)
E2
80%
Sis
§2"
BIB
60%
40%
± a
30.67 3.10
P-Value
PFD WHC
was 40%
under
the highest
condition. At saturation PFD, water
WUEj
stress significantly reduced but was
not changed.
significantly
g
s
,
Chlorophyll membrane
content, relative water content, index and
stability
content—
proline Content of Chi a and Chi a+b decreased with
the decrease of
soil moisture and there were significant differences between 40% and 80%
WHC
treatments
(Table 3). Soil water status, however, did not affect Chi b
content and Chi
alb.
RWC
Leaf and MSI among
did not
differ the water treatments, but proline
content
increased with
significantly water
soil depletion (Table
4).
Phenotypic
plasticity plays an important
role in the ability of plants to adapt
changing environments by
to
buffering the on
effect of natural selection acting
genotypes
Ge
(Scheiner, 1993;
et al, 2004). In the present study, water
soil
status strongly affected the growth and
physiological
characteristics of A.
LA
reniforme
and
var. sinensis. photosynthetic capacity declined with
decreasing which
moisture,
soil resulted in a decrease of leaf mass and thus
mass
under
total drought However,
stress. the decreases and mass
in leaf total
were SLA LAR
less than in LA, so and reduced under
drought
stress too. In
contrast, dry matter (RMR
allocation into the root fraction and R/S) was
significantly higher under
drought than under
stress well-watered
treatment.
These
might be
the result of a physiological balance between demand
the
for
Table
Effects of moisture on
3. soil chlorophyll (Chi) content of A. reniforme Data
var. sinensis.
means
are the ± SE m
of three
replicates. Different each column
letters indicate significant
d ffe (P<0.05).
(%WHC)
g'DW)
Chi a (mg Chi o (mg g~ 7 DW) g^DW)
Chi Chi a+b (mg
i
¥
± a
0.07 ! 4.89 0.46
60%
ab
±
0.19* 4.32 0.22
llb
a
°' D.12 ± b
3.94 0.12
E,
oL*
P-Value o
LIAO ET ECOPHYSK STATUS
AL.: lTER
)
RWC
(%WHC)
MSI
Treatments
(%)
(
RWC,
water by the leaves and the water uptake from by the The the
soil roots.
common
index for estimating water status in leaves (Hsiao, 1973), did not
decrease significantly under drought further indicated maintaining
stress,
A
may
water balance be one strategy for remforme var. sinensis to acclimate to
changing water conditions.
In this study, and P decreased significantly under drought stress,
max
g
s
WUEi
whereas did not change and the values increased. This
statistically
A
under drought
indicated stomatal regulation of reniforme sinensis
var.
With
decreased photosynthesis but effectively controlled water the
stress loss.
increase of water Chi a decreased but Chi b did not change
soil stress,
Therefore, the decreased Chi a content might be another reason
significantly.
under
photosynthesis decrease drought.
for
many
Water the accumulation of proline in species (Delauney
deficit triggers
and Verma, 1993; Yin et 2005; Bertamini et 2006). Significantly higher
al., al.,
proline contents in lower soil moisture were also found in A. reniforme var.
may
sinensis. The accumulation of proline contribute to maintaining proper
between and osmolarity under water
balance extra-cellular intracellular stress.
cytomembrane and
Therefore MSI, an indicator of integrality in structure
compared normal water
remained almost unaffected treatment,
function, to
could osmotic adjustment such as proline.
partly attribute to
and
morphological physiological
In conclusion, dry matter allocation, leaf
A
and
were acquire
responses of reniforme var. sinensis beneficial to utilize soil
However,
water and hence survive under critically drought conditions. the
and
such mass, photosynthetic capacity chlorophyll
fitness-related as total
traits,
80% WHC,
content, were highest under which revealed that A. reniforme var.
higher moisture photosynthetic carbon gain. This
sinensis favors soil for its is
A
which showed
reniforme
consistent with previous investigation, that var.
grew moist but well-drained slope habitats than others (Xie,
sinensis better in
The however, few and dispersed and
1993; Shi et 2005). favored habitats, are
al.,
are disturbed by human activities and the ongoing construction of the Three
A
mainly on
Gorges Project. Currently, reniforme var. sinensis is distributed cliffs
or steeply sloped bare rocks with thin soil, which water stress appears frequently
and few human disturbances (Pan et al., 2005; Shi et al., 2005). Thus, for the
management
effective conservation of the endangered species, a of the remaining
should be taken provide
conservation to sufficient
natural habitats or ex-situ
which biomass accumulation.
water essential for efficient
availability is
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