2.12. 土地利用履歴の異なるスギ人工林および照葉樹二次林における土壌微生物群集
Structure of soil microbial communities in sugi plantations and semi-natural broad-leaved forests
with different land use history*
Miho Matsushita1, Satoshi Ito2, Sadatoshi Meguro2, Shinsaku Kawachi2
1
2
United Graduate School of Agriculture, Kagoshima University, Japan.
University of Miyazaki, Japan.
*Manuscript submitted for Canadian Journal of Forest Research.
Abstract:
Phospholipid fatty acid (PLFA) profiles were used to evaluate microbial community compositions from different
soil layers of sugi (Cryptomeria japonica) plantations and semi-natural secondary forests in a warm-temperate region
in southeastern Kyushu, Japan. These forests had previously been utilized as meadows or coppices. Cluster analysis
and principal components analysis (PCA) demonstrated the differences in the microbial community structure in the
current vegetations (sugi plantations or semi-natural forests) in the FH layer, but the difference between previous land
use types (meadows or coppices) could be detected in the A layer. In the upper part of the A layer (0-5cm), the influence
of the previous land use history apparently exceeded that of the current vegetation. However, in the deeper part of the
A layer (5-10cm), the influence of the previous history was weaker, and both the influence of the current vegetation and
the previous land use type could be detected. In the FH layer, the significant influences of the current vegetation on the
soil microbial community structure were attributed to the soil chemical characteristics of pH and C/N according to the
result of canonical correspondence analysis (CCA). In the 0-5cm part of the A layer, the organic matter and C and N
contents were related to the influence of the previous type of land use on the microbial community structures.
However, it cannot be assumed that these soil chemical characteristics were the principal factors showing the influence
of the previous land use history, because the difference between the sites was very small. We discuss the importance of
the rhizosphere of the understory for microbial communities in the upper soil layer in a forest.
Keywords: PLFA; Microbial community; Land use history; Sugi plantations; understory.
Introduction
In all ecosystems, soil microorganisms play important
roles in the decomposition of organic matter, nutrient
cycling, and plant nutrient availability. Understanding soil
biology and ecology is increasingly recognized as
important for the restoration and sustainability of
ecosystems. In order to retain or recover the biodiversity
of forest ecosystems, the factors affecting microbial
communities from the viewpoint of forest ecology and
landscape ecology should be clarified. A gradient of
increasing intensity of disturbance represented by a range
of land use histories can capture the variation within soil
chemical characteristics and vegetation across the
landscape, and may provide insights into the complex set
of factors that affect soil microbial biomass and community
structure.
It is well documented that different plant species have
different characteristics of litter quality, root exudates and
nutrient uptake, affecting soil microbial communities and
soil microbial biomasses and their activity (Priha et al.,
2001, Kourtev et al., 2002a, 2002b, Grayston et al., 2004).
Previous land-use histories have been documented, and
it was concluded that previous land use had a significant
effect on species composition and the diversity of forests
(Ito et al., 2004). Thus, it is suggested that the difference
in plant species composition brought about by previous
land use histories could also affect soil microorganisms.
Concerning the relationship between land use history
and the soil microbial community, it was reported that
cultivation or grazing histories had long-term effects on
soil fertility, pH and the microbial community structure in
grassland ecosystems (Steenwerth et al., 2003). In forest
ecosystems, the impact of cultivation or field firing on
soil nourishment circulation has been investigated
(Christine et al. 2001). However, there is little knowledge
about concomitant changes in the soil microbial community
structure due to multiple factors of soil chemical
characteristics and vegetation associated with land use
history in forest ecosystems.
We presumed that a microbial community with the
specific environmental requirements could be selected and
supported in a unique soil environment created in the
area by the alteration of the soil chemical characteristics
according to the land use history of an area. If the soil
environment produced by the previous land use still
remained in the present forest, the evidence of that land
use history should be clearly detectable in the deeper soil
107
layer rather than the surface soil layer, because soil
sequentially accumulates from the top. Therefore, we
hypothesized that 1) the structure of the microbial
community near the soil surface reflects the structure of
the present vegetation, and 2) the structure of the microbial
community in the deeper soil layers reflects the structure
of the past vegetation.
Study site
The study site was Miyazaki University Forest (502
ha), located in southwestern Japan (131E, 32N). The annual
mean temperature and precipitation is 16.5•• and 2800
mm, respectively. Parts of this forest were previously
utilized as coppices for wood for fuel or as meadows for
hay, but since the 1950s, some of these coppices and
meadows have been replanted with sugi (Cryptomeria
japonica D.Don) and hinoki (Chamaecyparis obtuse Endl.)
plantations. Other remnant coppices and meadows were
abandoned in the 1960s and have since regenerated
naturally, with the secondary forest consisting of both
evergreen and deciduous broad-leaved trees. These seminatural forests have been unmanaged since they were
abandoned. In contrast, the sugi plantations in Miyazaki
University Forest have been managed uniformly according
to a management schedule, including ground preparation
by hand (not using fire or any herbicides), weeding and
shrub-clearing for 10 years after planting without using
any herbicides, with first thinning being done at ca. 25-30
years.
The stands were categorized into four types according
to their previous land use (coppices or meadows) and
their current status (semi-natural secondary forest or sugi
plantation):
1. semi-natural secondary forest developed on abandoned
coppices (abbreviated as Bc);
2. semi-natural secondary forest developed on abandoned
meadows (abbreviated as Bm);
3. sugi plantations established on former coppice sites
(abbreviated as Sc);
4. sugi plantations established on former meadow sites
(abbreviated as Sm).
Three stands per category, or 12 stands altogether, were
selected for data collection in order to collect from stands
with as similar a topography as possible. A single 20m•~20
m plot was positioned in each stand, allowing buffers of
at least 5 m from the stand edge in order to avoid possible
edge effects from different type of patches. Because the
108
former meadow sites had been fragmented into small
patches, one plot for type Bm (Bm1) was limited to
20m•~15 m. The canopy composition of semi-natural
forests that had developed on abandoned meadows (Bm)
and coppices (Bc) was mainly dominated by Quercus
serrata (deciduous) and Castanopsis cuspidata
(evergreen), respectively. The stand age of Bc was 43-71
years, Bm was 37-43 years, Sc was 34-38 years, and Sm
was 35-36 years. The A0 layer was thin, and the surface
soil bare in several places.
Methods
Soil sampling and analysis
Sampling of the 12 sites was conducted in May of 2005.
Fresh litter and twigs were removed from a 15cm2 square
area and ten soil cores per site were taken to the depth of
10cm in the A layer by gently pounding metal rings
(ƒÓ50•~51mm) into the ground. The FH layer and upper
(0-5cm) and lower (5-10cm) part of the A layer were then
divided into separate samples. The samples were sieved
(sieve mesh 2mm) to remove root and stones. All of the
analyses were done with fresh soil and kept at 4•• 1
week from the harvest, except the PLFA analysis, for which
the soils were stored at –20••.
The moisture of the soil was determined by drying the
samples at 105•• for 24 h. The soil organic matter content
was measured as the loss by igniting the dried samples at
700•• for 1 h. Soil pH (H2O) was measured in deionised
water (1:2.5, soil: water). Total organic C and total N were
measured from air-dried samples using an automated CHN
analyzer (Perkin Elmer Series 2 CHNS/O Analyzer 2400).
Dissolved organic carbon (DOC) and dissolved nitrogen
(DN) were measured from the filtered water extract using a
total carbon analyzer (Shimadzu TOC-5000).
PLFA analysis
Phospholipid fatty acid (PLFA) analysis uses the lipids
of the cell membrane within microorganisms as biomarkers
for specific groups of organisms, thus creating a profile
or fingerprint of the microbial community. The total
concentration of PLFA is a measure of the viable microbial
biomass, since phospholipids are readily degraded after
cells die (Zelles, 1997).
The phospholipid extraction and analysis of PLFAs was
conducted as described by Frostegard et al. (1996) with
some modifications (Pennanen et al.,1999). To briefly
summarize this procedure, 2g fresh weight of soil samples
were extracted with a chloroform:methanol:citrate buffer
mixture (1:2:0.8) and the lipids were separated into neutral
lipids, glycolipids and phospholipids in a silicic acid
column. The phospholipids were subjected to mild alkaline
methanolysis and the fatty acid methyl esters were
separated by a gas chromatograph (Shimadzu 18A),
equipped with a frame ionization detector and a DB-1 (J&W
Scientific) capillary column (30 m in length), using He as
the carrier gas. Peak areas were quantified by adding
methyl nonadecanoate fatty acid (19:0) as an internal
standard.
Fatty acids are designated in terms of the total number
of carbon atoms:number of double bonds, followed by
the position of the double bond from the methyl end of
the molecule, indicated by ƒÖ and a number. The prefixes
a, i and br indicate anteiso, iso and unknown branching,
respectively. The prefix cy indicates a cyclopropane fatty
acid and methyl branching (Me) is indicated as the position
of the methyl group from the carboxyl end of the chain.
The prefix C (C15:1) indicates that the PLFA has 15 carbon
atoms and one double bond, but the arrangement of the
carbon atoms (e.g., branching position) is not confirmed.
The abbreviations t and c indicate trans and cis
configuration of the double bonds. As for the alphabet to
be assigned to after ù, the bond position is unidentified,
but shows that it is different fatty acid.
The sum of 33 PLFAs was identified. The monoenoic
and cyclopropan unsaturated PLFAs 16:1ƒÖ9, 16:1ƒÖ7,
18:1ƒÖ7, 18:1ƒÖ5, cy17:0, cy19:0 were chosen to represent
Gram-negative bacteria (Zelles 1999). The branched,
saturated PLFAs i14:0, i15:0, a15:0, i16:1, i16:0, i17:0, a17:0,
and some of the monoenoic unsaturated PLFAs 18:1ƒÖ9,
19:1 were chosen to represent Gram-positive bacteria
(Zelles 1999, Bartelt-Ryser et al., 2005). The methylated,
branched, saturated PLFAs 10Me16, 10Me17, 10Me18
were used as an indicator of actinomycetes (Zelles 1999).
The quantity of 18:2ƒÖ6,9 was used as an indicator of the
fungal biomass (fungal PLFA). It was assumed that the
primary source of this eukaryotic PLFA was soil fungi
(Zogg et al., 1997).
Statistical analysis
A two-way analysis of variance (two-way ANOVA) was
carried out on the soil characteristics and the total PLFAs
and that of certain groups to determine statistically
significant differences between the main experimental
factors: current stand status and previous land use. Three
different soil layers were analyzed separately. Comparison
of the means of soil characteristics for different
experimental factors, and correlation analysis between
PLFA and soil characteristics were performed in
FreeJSTAT8.2.
All multivariate analysis was carried out on the PLFA
after log transformation. The microbial community
structures were classified by cluster analysis using a
Euclidian distance matrix based on the PLFA data of all 36
samples (12 sites•~3 layers) and by the ward’s method.
The PLFA data was analyzed by principal components
analysis (PCA). PCA was done separately for the three
different layers of soil samples. The relationship between
the microbial community structure and soil characteristics
was analyzed by canonical correspondence analysis
(CCA). CCA permits direct analysis of the PLFA profiles
in relation to specific environmental variables, like soil
characteristics and site factors. Soil characteristics are
represented by vectors. All multivariate analysis was made
on PC-ORD Version 4 (McCune and Mefford, 1999), a PCbased software program.
Results
Soil chemical characteristics
The soil chemical characteristics of the four stand types
(Bc, Bm, Sc and Sm) and each of the three soil layers (the
FH layer, the 0-5cm and the 5-10cm parts of the A layer),
are shown in Table 1.The results of two-way ANOVA
between the “present vegetation” and “previous landuse type” are also included in the table.
In the FH layer, there were statistically significant
differences only in moisture, pH, the C content and the C/
N ratio. The moisture of Bm was the lowest among the
four sites. The pH and C content of the semi-natural forests
(Bc and Bm) were lower than those of the sugi plantations
(Sc and Sm). The value of the C/N ratio of the semi-natural
forests was higher than those of the sugi plantations.
In two parts (0-5cm and 5-10cm) of the A layer, the soil
chemical characteristics except the dissolved organic
carbon (DOC) and dissolved nitrogen (DN) showed a
similar tendency for the four sites. The organic matter
(OM) of Bm and Sm, which were previously used as
meadows, were higher statistically significantly than Bc
and Sc. The interaction was detected only in the C/N ratio.
Other characteristics significantly differed by current
vegetation type, and the values obtained from the seminatural forests were lower than from the sugi plantations.
As for DOC and DN, there were no significant differences
109
Table.1. Characteristics of the four study sites type.
OM: organic matter, DOC: dissolved organic carbon, DN: dissolved nitrogen.
AVERAGE (•}SD)
A: Present vegetation, B: Previous land-use type.
*, P<0.05; **, P<0.01; ***, P<0.001; n.s: not significant.
Bc: semi-natural secondary forest developed on abandoned coppices; Bm: semi-natural secondary forest
developed on abandoned meadows; Sc: sugi plantations established on former coppice sites; Sm: sugi
plantations established on former meadow sites.
between the four sites in the top 0-5cm part of the A layer.
However, the DOC and DN of the semi-natural forests
were lower than the sugi plantations in the 5-10cm layer.
PLFA profiles
The microbial biomass, as measured by total PLFA,
tended to decrease with an increase in the depth of the
Fig.1. Total PLFA of the samples.
Each value is mean +- standard
error (n=3). Symbols are the same
as shown in table1.
110
soil layer (Fig.1). The total PLFA in the FH layer of the
sugi plantations (Sc and Sm) was significantly lower than
that in the semi-natural forests (Bc and Bm). In the upper
part (0-5cm) of the A layer, the total PLFA was almost the
same level for the four sites, but in the deeper soil layer (510cm), it was again lower in the sugi plantations than in
the semi-natural forest.
Table.2 The PLFA amount of each taxonomic groups of microorganism, the PLFA ratio, and the result of two-way ANOVA
between •gpresent vegetation•h and •gprevious land-use•h
AVERAGE (•}SD)
A: Present vegetation, B: Previous land-use type.
*, P<0.05; **, P<0.01; ***, P<0.001; n.s: not significant.
Symbols are the same as shown in table1.
The PLFA amount for each taxonomic group of
microorganisms, the ratio of PLFA, and the result of twoway ANOVA between the “present vegetation” and
“previous land-use type” are shown in Table 2.
In the FH layer, the PLFA amount of each group except
the gram-positive bacteria was lower in the sugi
plantations than in the semi-natural forest. In addition,
the fungal/bacterial PLFA ratio was lower in the sugi
plantation than in the semi-natural forest, but conversely,
the gram-positive/gram-negative bacterial PLFA ratio was
higher. In the 0-5cm layer, the amount of actinomycetes
and the gram-positive/gram-negative bacterial PLFA ratio
were higher in the sugi plantations than in the semi-natural
forests. No significant tendency was detected in the PLFA
of the other groups. In the 5-10cm layer, the gram-negative
bacterial and fungal PLFA were lower, but the grampositive/gram-negative bacterial PLFA ratio was higher in
the sugi plantation than in the semi-natural forest.
On the dendrogram of the 36 PLFA samples (12 sitesthree soil layers) obtained by cluster analysis (Fig.2), the
36 samples in the first stage were largely classified into
two groups according to the soil layer. The group of the A
layer was further classified into two smaller groups
according to the sampling depth. The group of the FH
layer was clearly divided into two smaller groups according
to the current vegetation (B-: S-). The upper part of the A
layer (0-5cm) group was significantly divided into two
groups by previous land-use type (-c: -m), and the lower
part of the A layer (5-10cm) group was classified into three
groups, Bc, Sc, and the previous meadow type (Bm, Sm).
The PLFA profiles in each of the three soil layers of the
12 stands were analyzed by principal components
analysis (PCA), as shown in Fig. 3. In the FH layer, the
scatter of the PLFA profiles generally corresponding to
the differences of current vegetation was distributed along
PC axis 1, which explained 59.5% of the variation (Fig.3a).
The previous land use types were separated better in the
semi-natural forest sites than in the sugi plantations along
PC axis 2 (23.2% of the variation). In the 0-5cm layer, the
PCA showed characteristic scatter in distinct clusters of
three groups, Bc, Sc and the previous meadow type (Bm
and Sm) (Fig. 3b). On the other hand, in the 5-10cm soil
layer, PCA showed different distributions corresponding
to current vegetation along the first axis, and to previous
land use type along the second axis, respectively (Fig.3c).
111
Fig.2. Cluster dendrogram of 36 (12 sites•~3 soil layers)
samples. The sample name and no. is indicated to the right of
the dendrogram. B: semi-natural forest; S: sugi plantation; -c:
coppice; -m: meadow; FH: FH layer; A: A layer, the 0-5cm
and the 5-10cm layer (-A05:-A510).
Analysis of the loadings of the PLFA on PC1 showed
that the discrimination between current vegetation was
mainly attributed to the higher contents of some PLFAs
characterized by Gram-negative bacteria (19:1ƒÖb,
16:1ƒÖ9, 18:1ƒÖ7) in the FH layer samples (Fig.4a). The
FH layer samples of the previous meadow type sites were
clearly separated along PC2 mainly due to two PLFAs,
15:1 and 18:2b in the Bm and Sm samples.
In the 0-5cm part of the A layer, the discrimination of
previous land use types along PC1 was mainly attributed
to the presence of PLFA 18:1ƒÖ7 in previous coppices
type sites (Bc and Sc), and 18:2ƒÖb in Bc and the lack of
15:1 in Sc (Fig.4b). In the 5-10cm layer, 18:1ƒÖ7 and
112
Fig.3. The scores of the sites in PC analysis of the phospolipid
fatty acids (PLFAs) of the samples. a: FH layer, b: A layer 05cm, c: A layer 5-10cm. Circles represent the semi-natural
secondary forest and squares the sugi plantations. Open symbols
represent sites developed on the abandoned meadow and closed
symbols sites developed on the abandoned coppice.
16:1ƒÖ7t were not detected in many sugi plantation sites,
and 18:2ƒÖb was detected only in Bc. PLFA a17:0 was
detected only in previous meadow type sites (Bm and
Sm), and got a high score on PC 2 (Fig.4c).
Relationship between PLFA profiles and soil chemical
characteristics
Fig.4. Scores of the of the phospolipid fatty acids (PLFAs) of
the samples. a: FH layer, b: A layer 0-5cm, c: A layer 5-10cm.
Using canonical correspondence analysis (CCA), we
attempted to identify the factors which could explain the
pattern of the PLFA profiles (Fig. 5; Table 3). In the FH
layer, the scatter generally corresponding to the
differences of current vegetation was distributed along
the first axis, which explained 56.7% of the variation
(Fig.5a). The soil characteristics that largely account for
the variation in the microbial community structure of the
current vegetation were distributed along Axis 1. The C/N
ratio, moisture and pH gave a significant positive
correlation for Axis 1, and the N content gave a negative
Fig.5. CCA ordination biplot of the 12 sites of four stand types.
Circles represent semi-natural secondary forest, squares sugi
plantations. Open symbols represent sites developed on the
abandoned meadow and closed symbols sites developed on the
abandoned coppice. Soil characteristics included to the CC
analysis are presented as vectors and are moisture, pH, carbon
content (C), total nitrogen content (N), dissolved nitrogen (DN),
dissolver organic carbon (DOC) and carbon to nitrogen ratio (C/
N). a: FH layer, b: A layer 0-5cm, c: A layer 5-10cm.
correlation for Axis 2 (Table 3). In the 0-5cm layer, the CCA
showed the scatter in distinct clusters of three groups,
Bc, Sc, and the previous meadow type sites (Bm and Sm)
(Fig.5b). The organic matter and C and N contents gave a
significant negative correlation for Axis 1 and the C/N
113
Table.3. Correlation coefficients of the soil characteristics to the first and second axis of CCA
ratio gave a negative correlation for Axis 2. The clusters
of the 5-10cm layer had a similar pattern as that in the 05cm layer; however, the vectors lengths and the angles of
their positions with respect to the two axes were different.
The CCA biplot of the previous meadow type sites
separated Bm from Sm (Fig.5c). Moisture and organic
matter gave a significant negative correlation for Axis 1,
and all soil chemical characteristics except the C/N ratio
related to Axis 2.
Discussion
Some reports on the chemical characteristics in forest
soils have shown that the pH and C/N ratios were higher
in sugi plantations than in broadleaf tree forests (Toda et
al., 1996, Ichikawa et al., 2002, 2003a, 2003b), as was also
the case in our study. They supposed that the higher
levels of pH and C/N ratio would be attributed to the
characteristics of sugi litter, in particular to its high Ca
content and quality (Katou et al., 1989, Sawada et al., 1991).
Our results also indicated a lower fungal/bacterial PLFA
ratio and a higher gram-positive/gram-negative bacteria
PLFA ratio in the FH layer samples of the sugi plantation
(Table 2). The higher pH would thus be suitable for the
growth of bacteria, and the lower pH would be suitable
for the growth of fungi (Killham, 1994, Frostegard et al.,
1996, Grayston et al., 2005). Our results are also supported
by Bååth et al. (2003), who found that gram-positive
bacteria gave a positive correlation with soil pH.
In the A layer, the influences of land use history on
microbial community structure were related to organic
matter and C and N content as soil nutrient. Steenwerth et
al. (2003) suggested that the high productivity, the annual
complete die-off of a plant community, and the dense
accumulation of roots in the upper 10cm of soil could
cause meadows to build a large pool of active soil organic
matter. Our sites, which were previously used as meadows,
114
may also have accumulated organic matter in the soil for
that reason. However, it cannot be assumed that these
soil chemical characteristics were the principal factors
showing the influence of the previous land use history,
because the difference between the sites was very small.
In our study sites Bc, Bm, Sc and Sm, the understory
plant species diversity of and the influence of land use
history on the sites has already been clarified by Ito et al.
(2004). In both current vegetation types (sugi plantations
and semi-natural forests), the previous meadow type sites
had a lot of perennial forbs, and the previous coppices
type sites are abundant in evergreen shrubs and trees. It
has been reported that microbial communities in fieldcollected soils beneath the two exotics and the native
Vaccinium spp. were clearly different in both their
structure and function, nitrogen dynamics and litter
decomposition (Ehrenfield et al., 2001, Kourtev et al., 2002a,
2002b). In a pot experiment, plant species affected the soil
microbial community structure and activity by the
differences in the quality of litter and the nitrogen uptake
of roots (Kourtev et al., 2003). In our results, the previous
land use type had a significant influence on the soil
microbial community in the A layer, which was deeper than
the FH layer. Therefore, the influence of previous land
use type could be determined from the roots of the
understory, not directly by the leaf litters supplied from
the understory. It is well known that plant species have a
selective influence on microbial communities in
rhizospheres (Grayston et al., 1998, Smalla et al., 2001,
Priha et al., 1999).
The discrimination of microbial community structures
by the previous land use was attributed to some single
fatty acids, not to the overall PLFA composition (Table 2,
Fig.4). This may suggest the existence of a special
microbial community structure, which could live together
with the specific plant species, as Priha et al. (1999) also
showed that the quality, not the quantity of organic matter
supplied from plant species influenced the soil microbial
community. Therefore, the plant species composition of
the understory would be a significant factor affecting the
difference in the microbial community structure between
the previous land use types in the A layer, aside from the
soil chemical characteristics. Another reason might be that
the canopy composition and tree age were different
between Bc and Bm. The Bc site contained two relatively
old stands of 67 years, as compared with the other stands
of 30–39 years. The microbial community structure was
definitely divided in the semi-natural secondary forest as
compared with the sugi plantation (Fig.3a). If the canopy
composition was different, the quality of the leaf litter and
moisture would be different, also. These influences of
canopy composition should be detected in the deeper
layer as the evidence of land use history. However, the
difference in the microbial community structure by previous
land use was detected in sugi plantations, though Sm and
Sc had stands that were similar ages (SM=31-32 years;
SC=30-34 years). Thus, these results supported the fact
that previous land use would be the critical factor affecting
the microbial community structure, persisting for at least
several decades after the establishment of plantations.
Many researchers have reported that the influence of
vegetation was significantly detected in the organic soil
more than the mineral soil (Priha et al., 1999, 2001). One
reason for this is that in the organic soil, there was more
diversity to start with, which makes it possible for different
groups to be enriched in different conditions, whereas
the original microbial community in the mineral soil was
probably less diverse. In this study, the total PLFA of the
0-5cm layer samples was 1.2-2.1 times as large as those of
the 5-10cm layer samples. Thus, the influence of
environment was definitely detected in the 0-5cm layer
rather than in the 5-10cm layer. In addition, herbaceous
plants tend to have dense roots that spread out but do
not reach deep down, and even the roots of woody plants
are shallow but dense when the tree is young (Karizumi,
1979). These factors also support the fact that the influence
of the land use history of an area clearly appears in the
upper part of the A layer.
As described above, in our study sites the influence of
current vegetation appeared in the FH layer and the
influence of the previous land use history definitely
appeared in the upper part of the A layer (0-5cm). Both
influences were detected together in the deeper layer (510cm). The influence on current vegetation by leaves
supplied from a dominant species could gradually
penetrate into the forest soil from the surface to a deeper
layer. However, a distinctive microbial community
structure could be formed in the 0-5cm soil layer by the
microorganisms group strongly influenced by the root of
the understory concentrated in the upper part of the forest
soil.
The influence of the previous land use history on the
microbial community structure could have been
maintained by the roots of the understory in the stands,
even if the plant vegetation had drastically changed. In
order to restore and maintain forest ecosystems, including
the soil microbial community structure, it is therefore
necessary to manage the native understory, to use a felling
method that maintains the existing understory as much as
possible, and to artificially introduce key species of the
understory that were lost in the past to forest sites.
Acknowledgements
We would like to express our sincere gratitude to Professor
Rauni Sterommer of Helsinki University in Finland for
showing us how to investigate the soil microbial
ecosystem, and for reviewing this paper and giving us
valuable comments. We are also deeply thankful to Dr.
Taina Pennanen of the Finnish Forest Research Institute
for showing us, in her laboratory, the detailed procedure
for doing the PLFA method.
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