全 文 ：Variation of Water_Use Efficiency of Leymus chinensis and Cleistogenes squarrosa
in Different Plant Communities in Xilin River Basin , Nei Mongol
CHEN Shi_Ping , BAI Yong_Fei , HAN Xing_Guo＊
(Laboratory of Quantitative Vegetation Ecology , Institute of Botany , The Chinese Academy of Sciences , Beijing 100093 , China)
Abstract:　Water is usually considered to be a key limiting factor for the growth and reproduction of steppe
plants in the Xilin River Basin , Nei Mongol.Foliarδ13C values , an indicator of long_term intercellular carbon
dioxide concentration and thus of water_use efficiency (WUE)in plants , were measured on Leymus chinensis(Trin.)Tzvel.and Cleistogenes squarrosa(Trin.)Keng.in six communities of different habitats in the Xilin
River Basin.The foliar δ13C values of both species tended to increase with decreasing soil water content
(SWC)and a significant negative correlation was found between foliar δ13C values and SWC in different soil
layers , indicating that the two species could change WUE according to water availability.We also found rela-
tively constant leaf water contents(LWC)of the two species in different habitats.Our results implied that the
two steppe species might have adapted to different soil water regimes either through adjusting stomatal conduc-
tance to get a proper WUE , or through enhancing the osmosis_regulating ability to keep a relatively stable
LWC.Our findings could partially explain why the two plant species have awide distribution range and become
dominant in the Xilin River Basin.
Key words:　Xilin River Basin;Leymus chinensis;Cleistogenes squarrosa;water_use efficiency;δ13C value
　　Water_use efficiency (WUE), i.e.the amount of
carbon biomass produced per unit water transpired by the
plant , is one such trait that can contribute to productivity
when water resources are scarce (Wright et al , 1988).
WUE is traditionally determined either as the ratio of pho-
tosynthesis(A)to transpiration(E)over short time or as
the ratio of dry matter accumulation to water consumption
over a longer time interval , for instance , a growing sea-
son.The former gives instantaneous estimates of WUE(A/E)and the latter gives a long_term WUE.The long_
term method cannot be easily determined because it could
need a tremendous amount of labor input in addition to
practical difficulties involved in the simultaneous measure-
ment of transpiration and root biomass in the field(Wright
et al , 1988).The instantaneous method , although easily
conducted , may not necessarily correlate with long_term
plant performance (Martin and Thorstenson , 1998).
Clearly , new , reliable methods for measuring WUE of
plants need to be employed.
More recently , δ13C has been developed as a tool to
measure WUE , because a strong positive correlation is
found betweenδ13C and WUE (Farquhar et al , 1989).
δ13C is partly determined by Ci/Ca , the ratio of CO2
concentrations in the leaf intercellular spaces to that in the
atmosphere (Farquhar et al , 1982 , 1989;Farquhar and
Richards , 1984).This ratio differs among plants because
of the variation in stomatal opening (affecting the supply
rate of CO2), and the variation in the chloroplast demand
for CO2.So the carbon isotope ratio of plant tissue pro-
vides an integrated measurement of internal plant physio-
logical and external environmental properties influencing
photosynthetic gas exchange over the time when the car-
bon was fixed(Smedley et al , 1991).
The application of stable isotope technique to ecolog-
ical studies was limited in China (Sun et al , 1993;Lin
et al , 1994 , 1995;Yan et al , 1998;Liang et al ,
2000;Su et al , 2000;Qu et al , 2001).Most of the
ecological research using stable isotopes in China was
mainly found in geological field , and the limited literature
so far reported in terrestrial ecosystems was focused on
forest ecosystems , while studies on grassland ecosystems
were rare.
Xilingol grassland belongs to arid and semi_arid
grassland zone.Water is the most important factor limiting
ecosystem productivity.In general , it appears that species
native to arid or semi_arid environments show no change
or an increase in WUEwith decreasing water supply(Toft
et al , 1989).Cohen(1970)predicted that the water_use
pattern should become more conservative during drought.
In this study , δ13C values of two common C3 and C4
grasses , i.e.Leymus chinensis and Cleistogenes squar-
rosa , were determined in six different communities in the
Xilin River Basin.The main objectives of our research
work are:1)to study the variations of the water_use pat-
tern in different habitats and to test Cohen s hypothesis;
2)to find the strategies of two plant species to adapt to
different habitats , especially different soil moisture
regimes , through comparing the variations of their WUE
in different communities.
Received:2002-04-01　Accepted:2002-06-06
Supported by the State Key Basic Research and Development Plan of China(G2000018607)and Know ledge Innovation Program of The Chinese Academy of Sci-
ences(KSCX1_08).
＊Author for correspondence.E_mail:.
植　物　学　报　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　
Acta Botanica Sinica　2002 , 44(12):1484-1490
1　Materials and Methods
1.1　Study site
Xilin River Basin(43°26′N-44°29′N , 115°32′E-117°12′E)is located in the typical steppe zone of Nei
Mongol Plateau , close to the Da Hinggan Ling Mountains
on the eastern edge.Topographically , this area , being
about 10 000 km
2
in size , declines gradually from east to
west , varying from 1 500 to 950 m in elevation.Chestnut
and dark chestnut soils are the zonal soil types.The study
area has semi_arid continental temperate steppe climate
with dry spring and moist summer.Based on the records
of 22 meteorological stations around the Xilin River
Basin , the annual precipitation decreases gradually from
400 mm in the southeast to 250mm in the northwest.An-
nual mean temperature increases from southeast to north-
west , ranging from 0.5 to 2.1 ℃.
1.2　Plots selection
Our study was conducted in the Nei Mongol Grass-
land Ecosystem Research Station (IMGERS), The Chi-
nese Academy of Sciences , which is located in the middle
reaches of the Xilin River.Six plant communities were
selected.They were dominated by Achnatherum splen-
dens , Filifolium sibiricum , Leymus chinensis , Stipa
grandis , Caragana microphylla and Artemisia frigida ,
respectively .These six communities could represent a soil
water gradient depending on relative elevation and soil
types.They were salt meadow , meadow steppe , typical
steppe and degraded typical steppe communities , respec-
tively (Table 1).
1.3　Plant materials
Leymus chinensis , one of the most important species
in Nei Mongol Steppe with wide ecological amplitude , is a
perennial rhizome C3 grass and intermediate xerophytic
steppe species.Cleistogenes squarrosa , a perennial bunch
C4 grass and typical xerophytic steppe species , is a domi-
nant species in the lower layer of L .chinensis and Stipa
spp.grassland communities.
1.4　Sampling and analyses
From 23 to 25August 2001 , a sampling transect was
randomly positioned in each plant community and five
spots in the line were selected for sampling.Distance be-
tween two spots was about 30 m.Fully expanded leaves
from at least 10 individuals of each plant species were
collected in every spot , dried at 70 ℃, ground to 80
mesh and analyzed.The leaf water content was deter-
mined at the same time through weighing the fresh and
oven_dried leaves.Since C.squarrosa was a rare species
in the Filifolium sibiricum community , plot 2 was exclud-
ed in its sampling.Soil water content of three layers(0-
20 cm , 20-40 cm , 40-60 cm)was determined at ev-
ery spot through weighting the wet and oven_dried soils.
Carbon isotope composition was measured by Finni-
gan MAT252 mass spectrometer in the Stable Isotope Lab-
oratory , Institute of Geology and Geophysics , The Chinese
Academy of Sciences.
δ13Cl (‰)=(
13
C/12C)l-(13 C/ 12C)s
(13C/ 12C)s ×1 000
where δ13C l is leaf δ13C value , (13C/12C)l and
(13C/12C)s are the carbon abundance ratios of the leaf
and the standard PDB , respectively.
1.5　Meteorological data
Meteorological data , including air temperature , pre-
cipitation and relative humidity , were collected from the
Nei Mongol Grassland Ecosystem Research Station (Fig.
1).
1.6　Statistical analyses
Statistical analyses (variance and correlation)were
conducted , and means were compared using the statistical
procedures of the Microsoft Excel 2000(ANOVA for sig-
nificant mean differences in soil water content (SWC),
leaf water content (LWC)andδ13C of two grasses among
different communities and correlation analyses).
2　Results
2.1　Variation of SWC in different communities
The SWC gradually decreased from plot 1 to plot 6(Fig.2).As a whole , A.splendens and F .sibiricum
communities had the highest SWC and the best soil water
status;L .chinensis community took the second place;
S .grandis , C.microphylla and A.frigida communi-
ties had the lowest SWC and were driest.
2.2 　Variation of LWC of L.chinensis and C.
squarrosa in different communities
As to LWC of L .chinensis , no significant difference
was found between communities(Fig.3).For C.squar-
rosa , LWC of plots 1 and 6 was significantly higher than
that of plots 3 , 4 and 5.These results indicated that both
L .chinensis and C.squarrosa could postpone dehydra-
tion when soil moisture is depleted and keep a relatively
stable water status in vivo under different SWC condi-
tions.
Table 1　Characteristics of the study sites in Xilin River Basin , Nei Mongol
Plot No. Community type Situation Altitude (m) Soil type　　 Land use type
1 Achnatherum splendens community 43°44.925′N , 116°40.629′E 1 190 Meadow soil Grazing pasture
2 Filifolium sibiricum community 43°29.418′N , 116°49.643′E 1 380 Dark chestnut soil Mowing field
3 Leymus chinensis community 43°32.895′N , 116°40.708′E 1 250 Dark chestnut soil Fenced plot
4 Stipa grandis community 43°32.322′N , 116°33.117′E 1 180 Chestnut soil Fenced plot
5 Caragana microphylla community 43°35.748′N , 116°44.419′E 1 210 Chestnut soil Fenced plot
6 Artemisia frigida community 43°37.967′N , 116°39.397′E 1 180 Chestnut soil Heavi ly grazed
CHEN Shi_Ping et al:Variation of Water_Use Efficiency of Leymus chinensis and Cleistogenes squarrosa in Different Plant Communities 1485　
Fig.1.　Weather conditions of Nei Mongol Grassland Ecosystem Research Station in 2001.
A.Precipitation.B.Relative humidity.C.Temperature.D.Vapor pressure.
Fig.2.　Variation of soil water content (SWC)of three soil layers
in six plots.
Plot 1 to plot 6 represent Achnatherum splendens community , Fi li-
folium sibiricum community , Leymus chinensis community , Stipa
grandis community , Caragana microphylla community and Artemisia
frigida community , respectively.The same letter denotes non_
significant difference , while different letters denote a significant dif-
ference(α=0.05).
Fig.3.　Variation of leaf water content(LWC)of Leymus chinensis
and Cleistogenes squarrosa in different plots.
A.Leymus chinensis.B.Cleistogenes squarrosa (no plot 2).
2.3　Variation ofδ13Cl of L.chinensis and Cleisto-
genes squarrosa in different communities
The foliarδ13C (δ13C l)of L.chinensis was more
negative than that of C.squarrosa , which was mainly
caused by their different photosynthetic pathways.C3 and
C4 plants have distinct isotopic composition because of the
difference in their primary carboxylating enzyme(Rubisco
1486　 植物学报　Acta Botanica Sinica　Vol.44　No.12　2002
and PEP carboxylase for C3 and C4 plants , respectively).
C3 plants have δ13C values of approximately -28‰,
whereas C4 plants are approximately -14‰(O Leary ,
1988;Farquhar et al , 1989).
For L.chinensis , the δ13Cl value in plot 1 is most
negative , plots 4 , 5 , 6 the most positive , and plots 2 , 3
in the middle (Fig.4).Similar trends were also found in
theδ13C l of C.squarrosa except in plot 5 , which was
more negative than that in plot 4 and plot 6.The more
negativeδ13C l in plot 5 might be due to the relatively low
intensity of irradiance.Although the SWC of plots 4 , 5
and 6 is similar , the mean height of plants and biomass
per unit area of plot 5 were much higher than those of
plots 4 and 6(the average height of plant in plots 5 , 4
and 6 were 22.69 , 16.28 and 8.97 cm;biomass were
240.22 , 81.46 and 113.44 g/m2 , respectively).As a
lower layer component of these plant communities , C.
squarrosa in plot 5 was more shaded than in plots 4 and
6.Since the decrease of irradiance level will result in a
decrease of δ13C value and the reduction of WUE , the
δ13C l of C.squarrosa of plot 5 should be relatively more
negative than that of plots 4 and 6.
Fig.4.　Variation ofδ13Cl value of Leymus chinensis and Cleisto-
genes squarrosa in different plots.
A.Leymus chinensis.B.Cleistogenes squarrosa (no plot 2).
2.4　Relationship between SWC and δ13Cl
Significantly negative correlation was found between
SWC andδ13C l of L .chinensis and C.squarrosa(Fig.
5).For C.squarrosa , a more significantly negative cor-
relation exists between SWC and δ13C l excluding plot 5 ,
because of the more negativeδ13C l in plot 5.Sinceδ13C l
is generally considered as an indicator of WUE of plants ,
the WUE of L .chinensis and C.squarrosa was also neg-
atively correlated with soil water content (SWC), that is ,
the WUE increased with the decrease of SWC.
Fig.5.　Correlation between soil water content (SWC) and δ13C l
value of Leymus chinensis and Cleistogenes squarrosa.
A.Leymus chinensis.B.Cleistogenes squarrosa.C.Cleistogenes
squarrosa (excluding plot 5).
3　Discussion
δ13C value is a sensitive indicator of WUE in natural
ecosystems(Toft et al , 1989).More negative foliarδ13C
indicates higher Ci/Ca ratios , resulting from either lower
chloroplast demand for CO2 or greater stomatal conduc-
tance affecting the supply rate of CO2 and transpiration ,
and hence plant water-use efficiency (Ehleringer and
Cooper , 1988;Farquhar et al , 1989).Stable carbon
isotope discrimination therefore provides a useful measure
of integrated carbon/water balance in plants over longer
periods , and is generally well correlated with plant water-
use efficiency (Farquhar et al , 1988).Up to now , it is
generally accepted that water_use efficiency is correlated
withδ13C values in C3 and C4 plants(Peterson and Fry ,
1987;Ehleringer and Cooper , 1988;Johnson et al ,
1990;Madhavan et al , 1991;Henderson et al , 1992 ,
1998;Ehleringer , 1993;Ebdon et al , 1998;Arslan et
al , 1999;Su et al , 2000).Stable carbon isotope frac-
tionation(δ13C)in desert plants is partially determined
by environmental conditions , such as water availability
and vapor pressure deficit of air(VPD)(Farquhar et al ,
CHEN Shi_Ping et al:Variation of Water_Use Efficiency of Leymus chinensis and Cleistogenes squarrosa in Different Plant Communities 1487　
1988;Hubick and Gibson , 1993).
Ehleringer and Cooper (1988)found that along a
soil moisture gradient from the relatively wetter wash to
the relatively drier slope , leaf carbon isotope ratios in-
creased in all species , indicating that water_use efficiency
increased as soil water availability decreased.Stewart et
al (1995)observed an increase in δ13C with decreasing
rainfall.Similar results were also documented (Comstock
and Ehleringer , 1984 , 1992;Sobrado and Turner ,
1986).In a more recent research along grassland zone of
the Northeast China Transect (NECT), Su et al (2000)
found that δ13Cl value and WUE of L .chinensis de-
creased with increasing annual average precipitation and
air temperature.The results in this paper are consistent
with the findings of the researchers above.
In this study , for L .chinensis and C.squarrosa , a
strong negative correlation existed between δ13C l value
and SWC of three soil layers in six different habitats , that
is , WUE of the two plant species increased with the de-
crease of soil water availability.As water was withheld ,
an increase in A/ E , and concomitant decrease in Ci ,
was demonstrated in some plant species (Toft et al ,
1989;Ehleringer , 1995;Lin et al , 1996).Since the
increase in WUE was brought about by either a decrease
in g (stomatal conductance)without a change in A , or
by a greater relative decrease in g compared to A(Toft et
al , 1989), the variation of WUE in our experiment might
be caused by stomatal action.Decreasing water availabili-
ty can result in the decrease of transpiration by increasing
stomatal closure and hence enhancing water_use efficiency
of plants.
Passioura (1982) hypothesized two contrasting
strategies that plants may have evolved in arid and semi_
arid lands:conservative and prodigal , which represent
plant populations with higher or lower WUE , respective-
ly.Cohen (1970)proposed a model , which predicted
that the water_use pattern should become more conserva-
tive during drought.Our data from community_wide study
supported Cohen s hypothesis.A more positiveδ13C val-
ue indicates a more conservative water_use pattern.When
water availability decreased , Leymus chinensis and Cleis-
togenes squarrosa employed more conservative water_use
patterns.The two plant species in typical steppe and de-
graded typical steppe communities (plots 4 , 5 and 6)
have a conservative water_use strategy , especially in ex-
tended drought because it can regulate stomata in different
water availability habitats;whereas the populations in salt
meadow and meadow steppe communities(plots 1 and 2)
have a prodigal water_use strategy , which maintains high-
er stomatal conductance and thus probably enables higher
yields.Other studies have also shown similar patterns of
δ13C in response to drought (Ehleringer , 1993;Wand et
al , 1999;Li , 2000).In the deserts of western North
America , higher(less negative)δ13C values are typically
found in species exposed to prolonged droughts in arid
deserts (Ehleringer , 1993), or to long_lived species(Schuster et al , 1992), which run a higher risk of expe-
riencing serious drought during their lifetime.Short_lived
species and those occupying wetter microhabitats , such as
washes , tend to have a lower (more negative)δ13C and
lower water_use efficiency under conditions of high re-
source availability.Theirδ13C values therefore indicate a
reasonable overall level of water-use efficiency and a sur-
vival strategy during water stress.
LWC of L .chinensis and C.squarrosa kept rela-
tively constant in six different habitats , which suggested
that the two plant species could keep a relatively stable
water status in vivo under different SWC conditions.Os-
motic adjustment is generally considered to be the main
mechanism for turgor maintenance under water_deficient
conditions , which enables plants to maintain metabolic
activity , growth and productivity during drought.Studies
on the physio_ecological mechanisms of four plant species
under drought stress in Xilin River Basin showed that L.
chinensis had strong ability to adjust osmosis and water
retention , and C.squarrosa had high activity of protec-
tive enzyme system①.
In conclusion , as two abundant plant species in the
typical steppe communities of Xilin River Basin , both L.
chinensis and C.squarrosa grow well under different soil
water status.Two mechanisms might be employed by the
two species:either through adjusting stomatic conduc-
tance to get a proper WUE or through enhancing osmosis_
regulating ability to keep a relatively stable LWC.Water_
use efficiency features may significantly influence the out-
come of competitive interactions (Cohen , 1970), and
may finally determine species composition in the commu-
nity.From a physiological perspective , traits that influ-
ence water loss and the ability to compete for limited soil
water should determine which plants will be able to colo-
nize the given locations along these gradients(Schuster et
al , 1992), which might partially explain why these two
plant species had wide distribution range and became
dominant in the Xilin River Basin.
As an indicator of WUE , δ13C of leaves provides
useful information for studies on the strategies of grasses
in response to different water regimes.Further research on
other grasses in the six different communities is recom-
mended to understand the water use strategies of other
grasses as well as the entire communities.
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内蒙古锡林河流域不同植物群落中羊草和糙隐子草
水分利用效率的变异
陈世苹　白永飞　韩兴国＊
(中国科学院植物研究所植被数量生态学开放研究实验室 , 北京 100093)
摘要:　用稳定性同位素技术 , 研究了锡林河流域不同群落和生境下羊草(Leymus chinensis(Trin.)Tzvel.)和糙隐子
草(Cleistogenes squarrosa(Trin.)Keng.)叶片δ13C值及其水分利用效率的变化。结果表明 ,在不同生境下 , 羊草和糙
隐子草叶片δ13C 值随土壤水分含量的降低而增大 , 并与不同土层土壤水分含量均表现出极显著的线性负相关关
系;而二者的叶片水分含量与土壤水分含量无显著的相关关系。这一结果说明 , 羊草和糙隐子草的水分利用效率
均随土壤水分含量的降低而提高 ,而叶片水分含量保持相对稳定。这两种植物可能通过调节气孔导度 、提高水分
利用效率和增强渗透调节能力等生理生态机制适应水分状况不同的生境 , 从而使它们能够在锡林河流域不同植物
群落中广泛分布并成为建群种或优势种。
关键词:　锡林河流域;羊草;糙隐子草;水分利用效率;δ13C 值
中图分类号:Q948.1　　　文献标识码:A　　　文章编号:0577-7496(2002)12-1484-07
收稿日期:2002-04-01　接收日期:2002-06-06
基金项目:国家重点基础研究发展规划项目(G2000018607);中国科学院知识创新工程重大项目(KSCX1-08)。
＊通讯作者。E_mai l:。
(责任编辑:王　葳)
1490　 植物学报　Acta Botanica Sinica　Vol.44　No.12　2002