全 文 ：Received 5 Dec. 2003 Accepted 15 Jul. 2004
Supported by the National Natural Science Foundat ion of China (30300245), the Knowledge Innovation Program of The Chinese Academy
of Sciences (KSCX1-08) and the State Key Basic Research and Development Plan of China (G2000018603).
* Author for correspondence. E-mail: .
http://www.chineseplantscience.com
Acta Botanica Sinica
植 物 学 报 2004, 46 (10): 1155-1162
Compositional Dynamics of Plant Functional Groups and Their Effects on
Stability of Community ANPP During 17 yr of Mowing Succession on
Leymus chinensis Steppe of Inner Mongolia, China
BAO Ya-Jing1, 3*, LI Zheng-Hai2, 3, ZHONG Yan-Kai3
(1. Laboratory of Quantitative Vegetation Ecology , Institute of Botany , The Chinese Academy of Sciences , Beijing 100093, China;
2. Innovation Base of Regional Ecological Environment Protection, Chinese Research Academy of
Environmental Science , Beijing 100012, China;
3. College of Life Sciences , Inner Mongolia University , Huhhot 010021, China)
Abstract: Using field experimental data of 17 yr of mowing succession of Leymus chinensis (Trin.) Tzvel.
steppe of Inner Mongolia (Nei Mongol), we analyzed the dynamics of community composition based on plant
functional groups (PFGs), explored the relationship between changes of the PFGs proportion in community
and the community annual net primary production (ANPP), and examined the influences of structural
parameters on functional parameters. Our results showed that during 17 yr of mowing succession, changes
in both community structure and function took place. The roles of different PFGs varied appar-ently with
mowing succession: the dominance of rhizome grasses was replaced successively by annuals and biennials,
tall bunch grasses, and short bunch grasses. Following 17 yr of mowing, the community became co-
dominated by rhizome grasses, tall bunch grass, and short bunch grass. ANPP correlated significantly with
annual precipitation in control plot, but not in successive mowing plot. Annual precipita-tion explained
more than 62% of the annual variability in ANPP of control plot, whereas annual variation of ANPP in
mowing plot was mainly driven by successive mowing disturbance. The community ANPP showed resilience
to mowing disturbance and kept relatively stable initially through internal regulation of PFGs, and declined
to a lower level with structural changes of the community after about 5 yr, and then again maintained at a
stable level through structural regulation. Therefore, in mowing succession the commu-nity structure
represented by PFGs changed gradually while the community function represented by ANPP declined
abruptly. The community relied on constantly regulating the structure to maintain the function stability.
The community function would degrade after its structure changed to certain degree.
Key words: Leymus chinensis steppe; mowing succession; functional groups dynamics; annual net
primary production (ANPP); community; stability
The typical steppe dominated by Leymus chinensis is
the zonal vegetation that occurs extensively in temperate
steppe region of China and in the eastern Eurasian temper-
ate steppe, with a total area of about 420 000 km2. It has
been disturbed heavily by grazing and mowing in China,
which resulted in characteristic vegetation pattern.
L. chinensis steppe of Inner Mongolia (Nei Mongol) is
a relatively well-studied and understood ecosystem. Past
researches included the analysis of net primary productiv-
ity (NPP), community structure, photosynthesis of leaves
and communities, dynamics of soil water and nutrient
contents, biomass of soil microorganism and their enzy-
matic activity, etc. (Jiang, 1990; Xiao et al., 1996; Chen and
Wang, 1998).
“Plant functional group” (or plant functional type)
refers to a group of plant species that have similar responses
to a suite of environmental conditions (Shugart, 1996). The
species can be grouped on the basis that they use the same
resource or by their response to specified perturbation
(Hobbs, 1996), or grouped based on growth form (Hobbie
et al., 1993), regeneration phase (Leishman and Westoby,
1992), life histories, phenology and physiology.
In resent years, ecologists have placed increasing em-
phasis on the use of functional classification of organisms
when describing the structure and function of ecosystems
(Friedel and Bastin, 1988; Heal and Grime, 1991; Keddy,
1992; Nobel and Gitay, 1995; Bai et al., 2001). Many studies
have indicated that plant functional groups (PFGs) can be
used to capture the main features of the response of differ-
ent vegetation types to a variety of disturbances and
Acta Botanica Sinica 植物学报 Vol.46 No.10 20041156
climatic events. Categorizing plants into groups is an obvi-
ous way to deal with the complexity of multi-species com-
munities (Prentice et al., 1992).
This paper reports the results from an experiment set up
in 1982 to examine the effects of successive mowing on L.
chinensis steppe. Earlier results from this experiment were
reported by Zhong (1991; 1999), in which they concen-
trated on variations in the dominant grassland species.
In this study, we classified 53 species of a L. chinensis
steppe community located on Xilin Gol of Inner Mongolia
into 8 plant functional groups (PFGs) based on their life
forms, growth forms, and morphology. We focused on
dynamics of PFGs in L. chinensis steppe over 17 yr of
successive mowing with the aim of exploring relationship
between variability of PFGs composition and annual net
primary production (ANPP), to determine the influences
of structural parameters on functional parameters, and to
examine in detail the effects of successive mowing on com-
munity ANPP and its interactive effects with precipitation
fluctuation.
1 Meterials and Methods
1.1 Study site and climate
Our study was conducted on a Leymus chinensis (Trin.)
Tzvel. site in proximity to the Grassland Ecosystem Re-
search Station (IMGERS) in the Xilin Gol League, Inner
Mongolia (43°33 N, 116°40 E, ca. 1 225 m a.s.l.). The site is
representative of the temperate steppe region of China,
which is dominated by L. chinensis. It is on a gentle slope
(a slope of 2-4 degrees) on secondary basalt beside Xilin
River. The soil is a Dark Chestnut with a humus layer of
20-30 cm thick and a calcic layer below 50-60 cm.
The climate of the area is temperate, semiarid steppe
with cold and dry winters and warm and relatively humid
summers. Annual precipitation averaged 351 mm over 18 yr
from 1982 to 1998, with a standard deviation of 69.3 mm and
a range from 283.2 to 507.0 mm. Average annual tempera-
ture was 0.53 °C with a standard deviation of 0.72 °C over
the same period. Maximal precipitation and temperature
occur between May and September, and minimal occur in
December, January and February. The annual potential
evaporation ranges 1 600 to 1 800 mm, which is 4-5 times of
precipitation. The combination of high temperature with
high humidity in summer provides suitable condition
for the growth of steppe plants. The frost-free period is
91 d and the growing season for steppe plants is about
150 d.
1.2 Vegetation
L. chinensis, an eurytopic xerophyte rhizome grass,
accounts for approximately 50% of the biomass in this plant
community. Secondary species are densely tufted xero-
phytes such as Stipa grandis, Achnatherum sibiricum,
Koeleria cristata, and Agropyron michnoi. Grasses con-
stitute about 70% of the biomass while forbs make up the
balance. There are about 75 forb species with taproots or
bulbs, which account for 87% of all plant species in the
community. The site had been subjected to grazing by sheep
and cattle until 1978 when grazing was excluded with a
fenced exclosure (Jiang, 1988). The community is now rep-
resentative of a late seral stage.
The height of flowering tillers is about 50-60 cm and
the leaf layer is about 30 cm. Vegetative ground cover is
about 30%-40% and can reach 70% in years with high
precipitation. Average aboveground biomass was 199 g/m2
with a standard deviation of 52 g/m2 over 17 yr from 1982 to
1998.
1.2 Methods
1.2.1 Setting of the mowing experiment plots and sam-
pling method On L. chinensis steppe site, permanent
plots for study of mowing succession were established in
1982 in order to explore the appropriate mowing date and
frequency. The plots included nine mowing treatments and
an un-mown control, and each replicated six times. The
area of each plot was 2 m×2 m. A permanent quadrat of 1
m2 was placed in the center of each plot. All living and
recent dead herbaceous biomass was clipped at 6 cm above
the ground level within the quadrat and separated by
species; other 3 m2 in each plot was also clipped at the
same time. To minimize edge effects, adjacent plots were
separated by ca. 2 m2. Six randomly selected quadrats were
sampled in the adjacent natural grassland as un-mown con-
trol for the corresponding period (Zhong et al., 1991).
Number of plants, heights, and biomass of each species
presenting within each quadrate were measured, and all
samples were collected and dried to constant weight at 55
°C and weighted.
In this study, ANPP was estimated in August each year
from 1982 to 1998. We chose one of the treatments (mowing
once annually on 16 August) and un-mown control for the
corresponding period, aboveground biomass of all species
was clipped in each quadrates on 16 August of each year in
both treatment that corresponded approximately to the time
of peak biomass.
Harvesting current live plus recent dead biomass at the
time of peak standing crop has been used to estimate ANPP
for steppe vegetation types (Barnes, 1983; Knapp, 1984;
Lauenroth, 1992). This method provides a close estimate to
ANPP when production is dominated by species with
BAO Ya-Jing et al.:Compositional Dynamics of Plant Functional Groups and Their Effects on Stability of Community ANPP
During 17 yr of Mowing Succession on Leymus chinensis Steppe of Inner Mongolia, China 1157
similar phonologies. In this study, our estimates of ANPP
were lower than actual ANPP because that clipping was
not made at ground level and that belowground biomass
was not included. Nevertheless, those estimates should be
adequate for purpose of comparing ANPP between mow-
ing succession and natural vegetation of the region.
The percentage of total ANPP in each year contributed
by different functional groups was calculated based on the
ANPP data described above.
1.2.2 Methods of analysis and calculation Data used in
the paper were calculated by using the following method:
Q = Σ Bi
Q, ANPP of the community; n, the species number in the
community; Bi, biomass of the ith population.
F =Σ Bi
F, ANPP contributed by a specific functional group; m, the
species number in the functional group.
Xi = ×100%
Xi, the percent age of ith f unctio nal gr oup in the
community.
CV (%) = ×100
M, the mean of ANPP; S, the standard deviation of ANPP
from 1982 to 1998.
The data analyses and charts were made using Microsoft
Excel 2000, Sigma Plot 2000 and SPSS 8.0.
2 Results
2.1 Functional classification of steppe plants
Raunkiaer (1934) described a scheme in which the func-
tional capabilities of plants were defined in terms of the
disposition and seasonality of meristems (buds). This
scheme attempted to define the functional characteristics
of plants as “life form” on the basis of easily observed
structural properties. Life forms are the exterior exhibition
format of life to adapt environment. The species with same
life form have not only resembling posture but also adapt-
ing characters.
According to the life form system defined by Raunkiaer
(1934), the steppe plants can be categorized into five groups:
microphanerophyte, chamaephyte, geocryptophyte,
hemicryptophyte, and therophyte.
In this paper, we expanded the Raunkiaer classification,
and categorized the steppe plants into eight functional
groups including shrubs, subshrubs, rhizome grasses, short
bunch grasses, tall bunch grasses, hemicryphyte forbs,
geophyte forbs, annuals and biennials, in accordance with
their life form, growth form and morphogeny (Table 1).
2.2 Dynamics of PFGs roles in mowing succession
The grassland composition changed markedly and the
proportion of ANPP contributed by different PFGs also
varied under successive mowing disturbance in the L.
chinensis community (Fig.1). As the constructive group of
primary community, rhizome grass was initially predomi-
nant in the community (about account for 64% of total
ANPP), but subsequently declined during the period from
1982 to1988 (accounted for only 11.7% in 1989) under suc-
cessive mowing, whereas annual and biennials (increased
from 2% in 1982 to 34% in 1987) and hemicrycryphyte forbs
(from 6% in 1982 to 28% in 1989) increased. Tall bunch
grasses, short bunch grasses and shrubs were least af-
fected in the corresponding period. Tall bunch grasses
maintained the proportion of 15%-20% of total ANPP, short
bunch grasses 3%-6%, and shrubs 5%-8%. Vegetation
composition also shifted from one dominated by rhizome
grass to that co-dominated by several groups including tall
bunch grasses, hemycryphyte forbs, and rhizome grasses,
especially annuals and biennials that made up the most
proportion of total ANPP in 1987 and 1988. But this ap-
peared to be a transient state. After about 10 yr of succes-
sive mowing, annuals and biennials gave way to short bunch
grasses. The quantity of short bunchgrasses kept approxi-
mately constant from 1982 to 1990, but their proportion in
the community increased rapidly from 1990 to 1992 and
became the dominant group (accounted for 34% of total
ANPP in 1992); thereafter, this group fluctuated at 23.4% of
community ANPP (with a standard deviation of 9.4%). Along
with the succession, it was observed that the ANPP of
rhizome grasses in the community decreased during 1983-
1988 and its proportion increased gradually in 1993-1998
(accounted for 32% in 1998). Ultimately, they became co-
dominant groups with tall bunchgrass and short bunch-
grass in the community. Annuals and biennials made up
very small proportions in community by the end of 17 yr of
mowing succession (only accounted for 4%).
Shrubs generally did not make up a significant propor-
tion of ANPP in L. chinensis steppe (this group contrib-
uted for 7.4% of the total ANPP in 1982). Successive mow-
ing reduced shrubs. The group of shrubs disappeared from
the community after 14 yr of mowing. Sub-shrubs were least
affected. This group kept relative constant during the mow-
ing succession (accounted for 3.1% with a standard devia-
tion of 1.7% of total ANPP during 17 yr of mowing
succession).
Hemicryptophyte forbs maintained relative constant in
the first several years (accounted for 5.4% with a standard
i =1
n
i =1
m
Fi
Q
S
M
Acta Botanica Sinica 植物学报 Vol.46 No.10 20041158
deviation of 1.8% of total ANPP from1982 to 1985), but
increased after 1986 and kept higher proportion (accounted
for 16.3% with a standard deviation of 4.7% of total ANPP
from 1986 to 1998).
We carried out the principal component analysis (PCA)
on the correlation matrix with a data set composed of ANPP
proportions of eight PFGs for 17 yr. PCA yielded two prin-
cipal components (PC) with eigenvalues >1, which explained
67.69% of total variations. The first PC (PC1, 43.76%) had
hi gh pos it ive lo adings o f shor t bunc hgrass es ,
hemicryptophyte forbs and Geophyte forbs, but negative
loading of, in descending order of importance, shrubs,
Table 1 The classification of plant functional groups in Leymus chinensis community of Inner Mongolia steppe
Life fo rm
Functional groups Characters Species Community role
Relat ive
(based on Raukiar) ANPP (%)
Microphanerophyte Shrubs Perennat ing buds Caragana microphyl la Companion 7 .44
is 20-30 cm h igh
Chamaephyte Subshrubs Perennat ing buds Artemisia frigida, Koch ia prostra ta Companion 1 .40
is 0-10 cm high
Geocryptophyte Rhizome grass es W ith horizon tal Leymus chinensis, Agropyron Cons tructive 64. 13
Include rh izome rh izome michnoi, Carex korshinskyi
Calex
Geophyte forbs W ith horizon tal Iri s tenuifol ia, Poten tilla acaul i, Companion 0 .65
rh izome or bu lb P. b ifurca , Galium verum,
Allium anisopodium, A. senescens,
A. condensa tum, A. bidentatum,
A.tenu issimum, A. ramosum
Hemicryp tophyte Tall bunch grasses Perennat ing buds St ipa grandis, Achnatherum sibiricum Dominan t 15. 10
is t iller
Short bunch grasses Perennat ing buds Cleistogenes squarrosa, Companion 3 .38
is t iller Koeloria crista ta, Poa attenua ta
Hemicryp tophyte Mos t species in Artemisia pubescens, Serra tu la Companion , playing 6 .08
forbs this group belong cen tauroides, Heteropappus altaicus, an importan t role
to companion o f Leontopodium leontopodio ides, in community
the community Senecio k irilou ii, Gueldenstaed tia structu re and
and have more verna, Astragalus ga lact iters, phys iognomy
flamboyant flowers Oxytropis myriophylla, Thermopsis
lanceola ta, Potenti lla tanaceti folia,
P. verticillaris, Pulsatil la tenuiloba,
Bupleurum scorzonerifol ium,
Saposhnikovia divarica ta,
Pedicularis stria ta, Cymbarria
dahurica, Adenophora
stenanthina, A. cripata, Si lene
jenisseensis, Melandrium apricum,
Phlomis mongol ica, Adenophora
stenophylla
Therophyte Annuals and The quant ity of Artemisia scoparia, Salsola col lina, Opportun is tic 1 .92
biennials th is g roup fluctu- Dontostemon micranthus,
ates with the rain- Orostachys malacophyllus,
fall at d ifferen t Schizonepeta multi fida, Saussurea
periods in p rimary japon ica, Chenopodium arista tum,
community C. g laucum, C. album
ANPP, annual net primary production .
rhizome grasses and annuals and biennials. Loadings on
the second PC (PC2, 23.83%) were dominated by annuals
and biennials at the positive side but rhizome grasses at
the negative side, indicating a shift in PFGs composition
along the axis. Those results indicated that the changes of
relative ANPP of different functional groups could be de-
tected in response to environmental changes caused either
by climatic extremes or by mowing disturbance.
Along the first ordination axis, the shrubs and rhizome
gr ass e s de cr e as e d and s ho r t bunc h gr ass e s ,
hemicryptophyte forbs and geophyte forbs increased in
the community. Along the second ordination axis, annuals
BAO Ya-Jing et al.:Compositional Dynamics of Plant Functional Groups and Their Effects on Stability of Community ANPP
During 17 yr of Mowing Succession on Leymus chinensis Steppe of Inner Mongolia, China 1159
and biennials and tall bunch grasses increased but rhizome
grasses decreased.
The results of PCA showed the changing tendency of
community composition and the direction of 17-yr mowing
succession. Figure 2 shows that the composition of com-
munity changed along one direction from 1982 to 1989, but
from 1989, the succession direction reversed.
2.3 Influence of successive mowing on the dynamics of
community ANPP
Figure 3 shows the annual changes of ANPP in L.
chinensis community in successive mown plot and un-
mown control plot (here the ANPP was equivalent to 80%
of actual aboveground ANPP due to harvesting at 6 cm
above the soil surface). The annual variation showed, in
typical steppe of Inner Mongolia, the ANPP of L.chinensis
community on both plots fluctuated greatly, with the high-
est value of 220.6 g/m2 in 1982 and the lowest value of
100.5 g/m2 in 1983 in control plot, but the lowest ANPP only
38 g/m2 in1997 in mowed plot. The coefficients of variation
in ANPP were 19% in control and 42% on mowed plot. The
ANPP was mainly controlled by precipitation because of
sufficient solar irradiance in this region. In order to esti-
mate the contribution of precipitation to current year ANPP,
we calculated the total precipitation from the mid-August
of the previous year to the mid-August of the current year.
Correlation analysis showed that ANPP correlated signifi-
cantly to annual precipitation (R2 = 0.621, P = 0.01) in con-
trol plot, but not in successive mowing plot (R2 = 0.209, P =
0.437). Annual precipitation explained more than 62% of
the annual variability in ANPP of the control plot, whereas
annual variation of ANPP in mowing plot was mainly driven
by successive mowing disturbance.
From Fig.3, we can see that the ANPP under different
Fig.1. Dynamics of plant functional groups (PFGs) over mow-
ing succession in Leymus chinensis steppe.
Table 2 Component matrix of principal component analysis (PCA)
Component
1 2
Short bunch grasses 0 .787 - 0 . 4 55
Tall bunch grasses 0 .435 0 .621
Hemicryptophyte fo rbs 0 .739 0 .353
Shrubs - 0 . 8 60 0 .233
Subshrubs 0 .481 0 .250
Annuals and bienn ials - 0 . 3 43 0 .751
Rhyzome grass es - 0 . 7 15 - 0 . 6 11
Geophyte forbs 0 .739 - 0 . 3 68
Us ing principal component analys is as ext ract ion method and two
componen ts extracted .
Fig.2. Principal component analysis (PCA) ordination plot of
17 yr mowing succession in a Leymus chinensis steppe commu-
nity from 1982 to 1998 based on a correlation matrix associated
with annual net primary production (ANPP) proportion of func-
tional groups. The number indicates sampling year. REGR, Re-
gression method.
Fig.3. Comparison of annual net primary production (ANPP)
of community between mown and control plot.
Acta Botanica Sinica 植物学报 Vol.46 No.10 20041160
treatments remained similar from 1982 to 1985, but displayed
marked differences between the control and mown plots
after 1986, and that the ANPP in mown plots decreased
more rapidly than in the control. The two curve lines had
similar fluctuation tendency for the most years and there
was a highly significant correlation between mown and
control plots (R2 = 0.711, P = 0.001).
3 Discussion
3.1 Factors influencing the dynamics of PFGs during
mowing succession
The composition of PFGs in the L. chinensis community
varied constantly during mowing succession. In primary
community, rhizome grasses are the constructive group or
dominant group, tall bunch grasses are the next dominant
group, and short bunch grasses and forbs are companion
groups. With successive mowing, annuals and biennials,
tall bunch grasses and short bunch grasses became domi-
nant groups; whereas rhizome grasses, short bunch grasses
and tall bunch grasses became co-dominant groups at the
end of 17-yr mowing succession.
Because the classification of PFGs in our research was
based on growth form, life form and morphology, on the
one hand, high growth form, such as shrubs, rhizome
grasses, and high bunch grasses suffered more damage
from mowing than short growth forms such as short bunch
grasses; on the other hand, different life forms had differ-
ent regeneration strategies. The groups reproducing by
seed such as annuals and biennials and some of forbs dif-
fered in response to mowing from that by colonization such
as rhizome or bunch grasses. Mowing in mid-August would
influence setting and distribution of seeds. Because of lack
of seed source, the soil seed bank would decrease after
several years. Continuous long term mowing has great in-
fluence on the amount of viable seeds in soils. For example,
after being mowed continuously for 45 yr, the amount of
seeds was only 22.57% of that in undisturbed area in grass-
land (Bao et al., 2000). This may be main cause of declining
annuals and biennials in the late phase of 17 yr of mowing
succession. Different PFGs responded differently to mow-
ing because of differences in morphology. For example, for
rhizome grasses represented by L. chinensis, the leaves
mainly located at 10 cm above ground, thus mowing would
remove most of the aboveground parts, and similarly for
tall grasses. But for tall bunch grasses, most of leaves lo-
cated at the base of plant, thus less influenced than tall
rhizome grasses by the mowing clipping 6 cm above the
soil surface. Due to differences in survival strategies, when
most of aboveground parts of community were removed,
some groups made up of opportunistic species such as
annuals and biennials would take up vacated niche and
resource when environmental conditions are favorable,
especially when precipitation was abundant. To sum up,
the dynamics of PFGs composition during mowing succes-
sion is the interactive results of tolerance to mowing of
individuals and competition between populations.
3.2 The driving factors of function degradation of L.
chinensis steppe
As one of functional parameters of community, the
ANPP decreased after 1985-1986 in successively mown
community compared to un-mown control, i.e. the function
of steppe ecosystem degraded. In semi-arid steppe, water
is the major driving factor of the dynamics of ANPP. In our
research, the ANPP of un-mown control community was
significantly correlated to annual precipitation, while there
was no correlation in mowed community. These results in-
dicated that the successive mowing caused the changes of
community composition and the decline of ANPP, and that
the steppe ecosystem shifted away from optimum condi-
tions and degraded. Under this situation, the ability of the
grassland to support livestock would decrease, which led
to decreasing productivity of animal-products.
Many researchers consider the degradation of steppe
ecosystem being a combined action between natural agents
and anthropogenic agents, i.e. climate change and long
term unsustainable grazing, grass cutting, and land
reclamation. Our results confirmed that unsustainable utili-
zation is the main driving factor of steppe degradation. The
ANPP fluctuated with precipitation in un-mown commu-
nity and decreased after several years in successive mowed
community. It is apparent that anthropogenic agents are
the main driving factors of steppe degradation. In fact, al-
though Xilin Gol steppe has been utilized for over 1 000 yr,
the steppe ecosystem began to show signs of degradation
at least 50 yr ago. In particular for the past 10 yr, the degra-
dation has become more evident due to over-grazing and
successive mowing.
3.3 The relationship between the structure and function
If we look upon the PFGs composition as structure pa-
rameter and the ANPP as function parameter, we could ex-
plore the relationship between structure and function of
steppe ecosystem by comparing dynamics of PFGs com-
position and ANPP over mowing succession.
Detailed trends could be revealed when the data in Fig.
1 are compared with the data in Fig.3. We found that the
changes of community structure, i.e. the shift of dominance
between functional groups, had been progressing gradually,
but community function degraded in an abrupt manner.
BAO Ya-Jing et al.:Compositional Dynamics of Plant Functional Groups and Their Effects on Stability of Community ANPP
During 17 yr of Mowing Succession on Leymus chinensis Steppe of Inner Mongolia, China 1161
The ANPP was not influenced by mowing disturbance in
the first several years (i.e. from 1982 to 1985). From 1986-
1987, the community ANPP declined to a lower level and
fluctuated with precipitation. Although mowing did not have
a significant effect on total ANPP during 1982-1985, the
community composition and the proportion of ANPP of
different functional groups varied, which suggested that
the community structure changed frequently. The ANPP of
whole community showed certain time lag effects to mow-
ing disturbance and maintained certain level by regulating
the proportion of PFGs in this phase.
When community structure changed to certain degree,
the community function would decline sharply. The phase
of 1986 to 1987 can be regarded as a critical phase for the
degradation of community function. Before this phase, the
community maintained a higher functional level depending
on interior regulation, and showed a time lag effect of ANPP
to mowing disturbance. After this phase, ANPP declined to
a lower level and fluctuated constantly with changes in
climate. At the same time the structure of community
changed sequentially with mowing disturbance. The switch-
ing of dominance among the functional groups continued,
tall bunch grasses and short bunch grasses became the
dominant groups successively. All of those suggested that
the community maintained its functional level on a new
meta-stable states relying on regulation of PFGs
composition.
It is obvious that when the changes of community struc-
ture reach certain degree, its function would degrade under
disturbances, and the maintenance of community function
would depend on the continuous structure regulation.
Our results suggested that community composition was
more sensitive to mowing disturbance than total ANPP,
Schindler (1990) found that species were more sensitive to
stress than ecosystem functions such as primary
production, respiration and nutrient cycling, apparently
owing to redundancy in those groups that carry out key
ecosystem functions. We postulate that the time lag re-
sponses of total ANPP to mowing disturbance was con-
tributed by redundancy in those PFGs in first phase of
mowing succession.
Acknowledgements: The authors are very grateful to Dr.
HAN Xing-Guo and Dr. SUN Jian-Xin from Institute of
Botany, The Chinese Academy of Sciences, for their criti-
cal review and revising of the manuscript.
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