on the type, and herbivory and damping-off caused by fungal pathogens played important roles in seedling deaths. On one-year-old seedlings, damage of winter.
338•`345
J.
論
文
Temporal
Occurrence
of Dead
Seedlings
SAHASHI*,**, Takanori
SAHASHI,
N.,
Japanese obtain
the
beech
(Fagus
its
and
basic
of the
of July
and
seedlings
Beech
KUBONO* and Tsugio
SHOJI*
was
decreasing
tions
are
seedlings.
of
and
types
three
type,
and
of leaves
From
the
that might
an
and
ex
one-year-old
seemed
FR.)
was
to be of the
GROVE
pathogenic
important
caused
role
in
fungal
seedlings, of
the
current-year for
played
the
four on
important
buds
deaths
or
unfold
of seedlings. Colletotrichum
inoculation
tests
suggesting the
condi of
depending
seedlings, and
specific
light
in
of winter
current-year
disappearances
types
the
end
increased
that
different
in
the
disappearance
pathogens
factors
frequently
no
of occurrences
clearly
damage
current-year
佐 橋 憲 生 ・窪 野 高 徳 ・庄 司 次 男:ブ
four
important
isolated
the
into
seedlings,
damped-off
was to
the
by
and
suggesting
periods
to
One-year-old
seedlings
the
and forests.
of May
season
with
were
of Japanese
detected.
growing
mainly The
end
To
seedlings
experimental
current-year
stands,
seedlings
the was
the
the
ones.
process
two
from
of the
categorized
damping-off
On
mainly
associated
dead
76(4)'94
of
1994•@
of dead
in
in mortality
seedlings
338•`345,
regeneration
quadrats
in
of dead
76:
occurrence
through
in one-year-old
hypocotyls
fungus
play
were
current-year
insects
(PEES.
this
factors
deaths. by
diseased
dematium
illuminance
herbivory
in seedling
ing
light
types
in the
nine
Mortality
important
seedlings
observed
roles
the
Dead
seedlings
the
relative
one
of the
occurred
in number
Soc.
temporal
change
observed.
occurrence For.
phase
in
prominent
gradually
Jpn.
the
seedlings no
of mortality
early
forests,
Soc.
Fungi
Temporal J.
investigated
current-year that
T.:
fungi.
of the
were
after
SHOJI,
BLUME)
decreased
pattern
and
knowledge
causes
Deaths
T.
associated
crenata
possible
with
KUBONO,
beech
For.
of Japanese
and Associated Norio
Jpn.
that
showed
this
fungus
seedlings.
ナ 枯 死 実 生 の 発 生 経 過 とそ れ に 関連 す る菌 類 日林
誌 76: 338∼345, 1994 ブ ナ林 の 更 新 初 期 過 程 につ い て基 礎 的 な知 見 を 得 るた め に,枯 死 実 生 の 発 生 経 過 と そ の原 因 に つ い て 調 査 した 。 当 年 生 実 生 の 枯 死 は5月 下 旬 か ら7月 下 旬 の2カ 月 間 に集 中 し て起 こ り,そ れ 以 降,枯 死 す る実 生 は ほ と ん ど認 め ら れ な か った 。 1年 生 稚 樹 の生 存 個 体 は生 有 期 を 通 して 穏 や か に 減 少 し た 。 当 年 生 実 生 の 死 亡 率 は相 対 照 度 の 低 い 林 床 で高 く,光 条 件 が 実 生 の 消 失 に 関 与 す る重 要 な 要 因 の 一 つ で あ る こ とが 示 唆 さ れ た 。 枯 死 個 体 は 当 年 生 実 生 で は4種 類 の タ イ プ に,1年 生 稚 樹 で は3種 類 の タ イ プ に 類別 で きた 。 当年 生 実 生 の 枯 死 個 体 の 発 生 時 期 は タ イ プ に よ っ て 明 ら か に 異 な っ て お り, 昆 虫 あ る い は小 型 哺 乳 動 物 に よ る 食 害 と菌 類 に よ る立 枯 病 が 重 要 な役 割 を 果 た し て い る こ とが 明 ら か とな っ た 。1年 生 稚 樹 で は,冬 芽 あ るい は そ れ か ら展 開 申 の葉 の 昆 虫 等 に よ る 被 害 が,枯 死 に 至 る重 要 な要 因 で あ る と考 え られ た 。 立 枯 病 に 罹 病 した 当 年 生 実 生 の 胚 軸 か ら はColletotrichum dematium (PERS. ex Fx.)GROVEが 高 率 に分 離 され た。 接種 試 験 の 結 果,本
菌 は ブ ナ 当 年 生 実 生 に 病 原 性 を有 す る こ とが 明 らか に な っ た 。 これ らの 結 果 か
ら,本 菌 が 実生 の 枯 死 ・消 失 に 重 要 な 役 割 を 果 た して い る こ とが 示 唆 さ れ た 。
I. The
Japanese
importance a variety
of wildlife,
In spring,
many
the seedlings
*
Tohoku
**
Author
beech
for timber
Res
crenata
BLUME) forest
but also from the viewpoint and as a genetic
beech seedlings
disappear
to
(Fagus
Introduction
within
. Ctr., For. whom reprint
Prod. should
years
on the forest
Morioka .
020-01森
part
forest
not only because
landscape,
of its
as a biotope
for
of Japan.
floor during
(HASHIZUME and
Res, Inst., be addressed
important
its characteristic
in the northeastern
newly emerge
several
and Forest requests
resource
is a most
of protecting
a short
NOGUCHI, 1977;
period,
but almost
MAEDA, 1988).
林 総 合 研 究 所 東 北 支 所
all of
Although
日林 誌
76(4)'94
339
many studies have been made of this disappearance such as on diseases (KOBAYASHIet al., 1984; KESSLER, 1988; MOSANDL and AAS, 1986; SASAKI, 1977), insect damage (FUKUNAGAet al ., 1982), undergrowth vegetation types (KONISHI et al., 1990), the effect of the dominant undergrowing dwarf bamboo (NAKASHIZUKA,1988), and light conditions (KUDO, 1985), little is known about the mechanisms and the causal agents which are involved in or are responsible for these phenomena . Therefore, it is very important and necessary for the management of the forest to clarify which mechanisms are concerned in this disappear ance. In this paper we report on the mortality of Japanese beech seedlings, detailed observations of dead seedlings, and the temporal occurrence of them induced by some causal factors. We also report possible fungal pathogens isolated from damped-off current-year seedlings. II.
and Methods
1.
Experimental forest and setting up of quadrats
To
observe
quadrats I
Materials
the
in
two
(Tazawako)
consists
four
two
which
is
sequence forests
is
of
stands,
temporal experimental located
forest
quadrats
located
quadrat(Ha,
at
about
stands
about
1•~1m2)
800
(T1•`T4)
termed at
of
a and
m
and
above with
above
set
disappearance
sea
sea
were
of
level
in
in
up. the
seedlings,
in the
numbers set
level
beech
Hakkohda)
different
b (2•~2m2)
700m
was
the
(Tazawako
Oou of
In the
1990
other
made
1).
Mountains
standing
Hakkohda
we
(Table
in
trees.
Akita
In each
experimental
Forest
Mountains
in
a
total
of
Experimental
nine
Forest
Prefecture of the II
Aomori
and
four
forest
(Hakkohda),
Prefecture,
one
up.
Illuminance was recorded for one month as an integrated illumination/h, using a sensor memory (KADEK-UP, Kona system Co., Ltd.) with a sensor for illuminance (IKS-15, Koito), in each of the four forest stands in experimental Forest I as well as in an open area. These were converted to an integrated illumination/day. Then the relative value of an illumination /day was calculated. 2. Marking and examination of the disappearances of the seedlings Current-year colored
beech
numbered
tape
two or three
times
each quadrat
is shown
more
than
once
seedlings
to follow
seedlings,
incidence
of mortality
until
including was
seedlings
newly-developed
in Table
a month
Damaged
with well-expanded
near individual
1. The number late October
from
cotyledons in each
seedlings. of dead when
expressed
as the percentage
marked
Marking
The number seedlings
almost
wilt, were collected
were
quadrat.
of marked
was examined
all of the leaves
to examine of total
by inserting
the cause marked
a wire
with the tape was current-year
seedlings
for two growing
of the seedlings and to isolate seedlings
with
a
undertaken in
seasons
had fallen.
the fungi.
at the time
The
of each
examination.
3.
Isolation of fungi from damped-off seedlings
Damaged
hypocotyls
from
Table
damped-off
1.
Outline
seedlings
of each
were dissected
quadrat
into small pieces
in two experimental
forests
of about
5mm.
They
III
340
were
J . Jpn. For. Soc. 76(4)'94 then
sterilized
sterile
water,
fungi
emerging
with
placed
on
from
80%
ethanol
potato
the
and
sucrose
tissues
a 1:1,000
agar
were
solution
(PSA),
isolated
and
and
of
mercuric
incubated
at
maintained
on
chloride,
15•Ž.
PSA
Three
in
test
washed
three
10 days
after
to tubes
until
times
with
incubation,
identification
was
made.
.
Results
1. Temporal occurrence of dead seedlings Death of the current-year seedlings occurred mainly from the end of May to the end of July. After the middle of August there was no prominent changes in the number of surviving seedlings except for a small decrease which was observed in October (Fig. 1). The mortality rate was the greatest in the T 1 stand where light illuminance was less than in the others (Fig. 2). In this forest stand, great mortality was observed, and more than 90% of the seedlings died before August. In T 2, the stand mortality rate of the seedlings was less than in T 1 stand. Forty-five to 50% of the seedlings died by the middle of July. T 3 and T 4, which had similar patterns of mortalities, had the smallest percentages of mortalities, although illuminances on these sites were similar to that of the T 2 stand (Fig. 2). At the end of the first year, about 50% of the seedlings remained alive. At Hakkohda (Ha), the profile of mortality was similar to that in the T 2 stand. Mortalities
of one-year-old
seedlings
were
less than
those
of the current-year
seedlings
that
decreased
ones.
survived
gradually
and no specific
through during
pattern
The
number
the previous
the
growing
of mortality
of year
season,
was detected.
2. Types of dead seedlings Current-year dead seedlings observed in 1990 were categorized mainly into four types: A seed lings from which hypocotyls were bitten off under cotyledons or from which cotyledons and/or pri mary leaves were chewed by insects or small animals (Fig. 3 A, B); B damping-off of seedlings which was characterized by water-soaked and collapsed lesion in the hypocotyls at soil level (Fig. 3 C); C wilted seedlings showing silvering and curling of leaves with injuries or bites of the tap roots by herbivores, in spite of healthy hypocotyls at soil level (Fig. 3 D, E); D wilted seedlings whose main roots grew only in the litter layers (Fig. 3F). One-year-old were broken
down
with damage or
other
uprooted, Survival as the lings Note:
Black
quadrat T 1•`T and
Ha
a
4 forest forest
of beech seedlings
percentages
and and
rates
white b,
stands stand
symbols
respectively,
of total
marked
show
data
in
in experimental in
experimental
expressed
the
the
same Forest
Forest
seed
obtained forest
stand,
I (Tazawako) II (Hakkohda).
in
seedlings
into
by
were
types:
snowfall;
buds or causes;
bitten
resembling
observed
three
winter
of winter
unknown
which stems
Fig. 1.
dead
categorized
F
leaves
seedlings by insects
seedlings
from
off and underparts
were
Type
A'
in 1991
E seedlings
A in 1990.
The incidence of Type A, which ranged from 10.2% on T4 b to 44.6% on T 3 a, was relatively great in all five forest stands observed (Table 2). The incidence of Type B was particularly large in he T 1 stand where illuminance was small. Type Coccurred from 2.1% to 23.2% depending on the quadrat, but no relationships with stands or quad
IV
日林 誌
76(4)'94
341
Fig. 2.
Light
conditions
in experimental
Forest
I
(Tazawako) Note: Light illuminance was recorded for one month as an integrated illumination/h in one of the two quadrats in each of the four forest stands as well as in an open area, and the relative value of illumination/ day was calculated. rats were observed.
The
occurrence
of the Type D was very rare.
Among the three types observed in one-year-old seedlings, Type F, which ranged from 4.3% on T 1 b and T 3 a to 22.4% on T 4 b was observed on all quadrats (Table 3). The occurrences of the remaining two types, E and A', were relatively few except Type A' on T 4 b. 3. Temporal occurrence of each category of dead seedlings The periods of occurrences for the four types observed in the current-year dead seedlings were clearly different from each other (Table 4, Fig. 4). Type A occurred during late May to early July followed by the occurrences of Types B and C which were dominant during early June to mid-July and during early July to late August, respectively. Type D was typical during late July to mid-August, although the number of seedlings of this type was very small. Although Type F damage occurred in winter or during the unfolding of leaves from winter buds (Fig. 4, arrowheads), death of seedlings continued for three months depending on individual plants. Type A' was observed mainly on T4 b for short periods in July. 4. Fungi isolated from damped-off seedlings Colletotrichum dematium (PERS. ex FR.) GROVE was isolated at a great frequency from damped-off seedlings collected from both experimental forests (Table 5). At Tazawako, Phoma sp, was isolated from 30% of the seedlings tested, although the incidence of this fungus was small at Hakkhoda. Fusarium spp., Phomopsis spp., and Alternaria spp., known to cause diseases on various kinds of plants, were also isolated, but the isolation percentages of these fungi were small. There was little difference in fungal species isolated from the two experimental forests. In preliminary within
inoculation
20 days after
tests
both wound
of beech seedlings and no-wound
with C. dematium,
inoculation .
more than 90% of the seedlings
died
procedures.
Discussion
Our present studies showed that the deaths of current-year seedlings occurred for two months after emergence which is in accord with other studies made by KONISHIet al. (1990), HASHIZUMEand NOGUCHI
342
Fig. 3.
J. Jpn. For. Soc. 76(4)'94
Photographs
showing
typical
types
of current-year
dead seedlings
Notes: A and B: Type A seedlings from which hypocotyls were bitten off under cotyledons or from which cotyledons and/or primary leaves were bitten off. A, Remaining hypocotyls; B, Bitten off upper-parts; C, Type B seedlings characterized by water-soaked symptoms in the hypocotyls at the soil level; D, Type C seedlings showing wilting (right side) in spite of healthy hypocotyls (arrowheads), compared with Type B seedlings (left side); E, Damaged tap root observed in Type C seedlings; F, Type D seedlings with abnormal tap roots. Bars represent 2cm in A, B, C, D, and F and 1 mm in E.
日林 誌
Table
76(4)'94
2.
343
Incidence of four types of current-year dead seedlings in each forest stand
Table
4.
Temporal (A•`D) of est
of
observation
of
current-year
dead
Japanese I
beech
in
four
experimental
types
seedlings For
(Tazawako)
*
The incidence of each category was expressed as the percentage of the total number of marked seedlings.
Table
3.
Incidence dead
of three
seedlings
types
in each
of one-year-old forest
stand
* The incidence of each category was expressed as the percentage of the total number of marked seedlings.
(1977) in F. crenata and by OHKUBOet al. (1989) in F. japonica, and that gradual deaths occurred in one-year-old seedlings. The greatest mortality rate was observed in T 1 stand with less illuminance than the others, sug gesting that light conditions might be one of the important factors in seedling survival as pointed out by previous workers (HASHIZUME and NOGUCHI, 1977; HASHIZUME and YAMAMOTO, 1975; KUDO, 1985; MAEDA, 1988). In the T 2 stand, however, although illuminance was similar to that
of T 3 and T 4, the mortality
light conditions,
therefore,
rate was more
may be involved
(in one of the two quadrats,
in seedling
T 2 a).
Factors
other than
deaths.
Many studies related to seedling deaths or disappearances have been undertaken (KONISHIet al., 1990; MAEDA,1988; NAKASHIZUKA, 1988). However, little is known about the mechanisms which are involved in or are responsible for the disappearances. There have been some reports describing possible causes of the seedling deaths such as herbivories, fungal attacks, droughts, physical injuries, light deficiency (HASHIZUME
344
J. Jpn. For. Soc. 76(4)'94
Fig. 4.
Diagrammatic
representation
of the
temporal
occurrence
of
each category of dead seedlings Notes: Arrowheads show the time of insect and/or unknown damages. Type A, B, C, D, E, F and A': refer to the text.
and YAMAMOTO,1975; KONISHI et al., 1990; MAEDA,1988; NAKASHIZUKA, 1988) but they have been insufficient because of few observations during a growing season and no detailed descrip tions of dead seedlings. In addition, there has been little knowledge as to when the death in duced by each causal agent occurred. The results of the present studies revealed that there were four major types of the death of current-year seedlings and three types of one year-old ones. It was also shown that the period of occurrence for each type of current-year seed lings was clearly different from each other and that, among them, herbivory (Type A) and damping-off by fungal pathogens (Type B) a) Sixty eight and 23 seedlings collected at Tazawako and played important roles in the mortality in the first Hakkohda, respectively, were used for fungal isolations. growing season. Type A occurred mainly during b) Number of seedlings from which each fungus was iso lated. late May to early July followed by Type B. Similar phenomena were reported by MAEDA (1988) who studied the temporal sequence of dead seedlings. Type B increased with decreases of illumi nance. MOSANDLand AAS (1986) showed that opening the canopy reduced the amount of fungal damage. This Type B, therefore, may be affected by light conditions. C. dematium was frequently isolated from the diseased hypocotyls of the damped-off Type B seedlings in both experimental forests. Fungi belonging to the genus Colletotrichum cause anthracnose in various kind of plants worldwide and SASAKI(1977) showed that C. dematium was weakly pathogenic to Japanese beech seedlings. In addition, preliminary inoculation tests using mycerial mats of C. dematium showed that this fungus was pathogenic to current-year beech seedlings. The results of the present study, therefore, suggested that this fungus might play an important role in the occurrence of Type B seedlings depending on environ mental conditions. Type C was due to damaged tap roots (Fig. 3 E), and it was distinguished from Type B (Fig. 3 D). This observation is important, because previously there were no reports relating to this type. For one-year-old seedlings, three major types of dead seedlings were observed, but they were clearly different from those observed in current-year seedlings except for Type A' which resembled Type A. In these seedlings, no Type B induced by fungal attacks was observed throughout the growing season, and Type F played an important role in seedling deaths. The growth and development of the seedlings, which affect Table
5.
Fungi
isolated
B) beech
from
seedlings
damped-off
(Type
日林 誌
76(4)'94
345
the responses to biotic and/or abiotic stress, may explain the differences . Further
studies
detailed ances
should
pathogenicity
be undertaken
or virulence
to clarify
the conditions
of C. dematium
related
and to evaluate
to disease
development
as well as
the role of fungus in seedling
disappear
in the field. Acknowledgements
We thank
Mr. N. KAMATA and Mr. Y. IGARASII, Tohoku
Research
Institute,
for their
Tsukuba,
for fungal
help throughout
identification
Research
this work.
and for critical
Center,
Forestry
reading
Literature K.,
mortality
KURATA, of first
Soc.:
59•`60.
HASHIZUME, growth
(in
H.
and
of
natural
M.
and
year
YAMAMOTO,
seedlings
Y.
of Fagus
(1982)
crenata
Products
are also due to Dr . S. KANEKO, FFPRI, of this manuscript.
This research was supported in part by a grant-in-aid (Bio Cosmos program) Agriculture, Forestry and Fisheries, Japan (BCP-94-III-B-01).
FUKUNAGA,
and Forest
Thanks
from the Ministry of
cited
Studies
on
damaged
by
natural
regeneration
insects.
Trans.
of
Fagus
34 th Mtg.
crenata
Kantoh
(I)
Branch,
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Jpn.
On For.
Japanese)
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K.
(1977)
seedlings
in
Studies
beech
on
the
forest.
process
Bull.
of formation
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of beech
For.
10:
forest
31•`49.
(III).
(in
Regeneration
Japanese
with
and English
summary) HASHIZUME,
H.
emergence KESSLER,
W.
and
YAMAMOTO,
and
disappearance
(1988)
Sozialistishe KOBAYASHI, with KONISHI,
T.,
A.,
KUDO,
Wurzelfaule
SASAKI,
K.
H.
an
K.
(1985)
SUZUKI,
of beech
For.
Jungpflanzen
95th
and
Soc.:
process
Trans.
86 th von
of
Mtg.
the
Japanese
Jpn.
Eiche
and
For.
beech
Soc.:
Rotbuche
durch
K.
(1984)
Mtg.
Jpn.
W.
(1990)
Trans. (Fagus
353•`354.
Disappearance For. Survival
42 th
439•`440. of beech
Mtg.
crenata) (in
of Japanese
Soc.:
R. and
chen
NAKASHIZUKA, bamboo OHKUBO
AAS,
Kalkalpen.
T.,
japonica
T. (Sasa NIWA, forest
G.
(1986)
(1988)
A., in
Regeneration
KAJI, the
and
Holzwirt.
kurilensis). M.
41:
and
Res.
3:
HAMAYA,
Chichibu
fall
and
Cylindrocarpon
destructans.
beech
crenata
Branch,
growing
seedlings
and
fungi
associated
Jpn.
under
BLUME) For.
seedlings
Soc.:
different
on
97•`100.
degrees
the
(in
different
Japanese)
of illumination.
Trans.
Bedeutung
von
BLUME). Special
Keimlingspilzen
im
Bull. Coll. Agric.
Bergmischwald
der
ostbayeris
471•`475.
of beech
Ecol.
Seed
Japanese)
Japanese)
Vorkommen
Forst-und
(I).
(in
Japanese)
(Fagus
Tohoku
seedlings
(in
MAEDA, T. (1988) Studies on natural regeneration of beech (Fagus crenata Utsunomiya Univ. 46: 79. (in Japanese with English summary) MOSANDL,
forests
226•`227.
110•`111.
vegetation.
Viability Jpn.
Regeneration
TANAKA,
Trans.
TAKAHASHI,
Mtg.
38: and
damping-off.
of undergrowth
96 th
(1975)
of seedlings.
Forstwirtschaft
the
types
S.
(Fagus
crenata)
after
the
simultaneous
death
of undergrowing
dwarf
21•`35. T.
Mountains,
(1989)
Nut
central
fall,
Japan.
production, Jpn.
and
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39:
seedling
survival
17•`26.
(in
in
a natural
Japanese
with
Fagus English
summary) SASAKI,
K.
(1977)
Materials
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the
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flora
of Japan
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Mycol.
Soc.
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18:
343•`345.
(Received November
15, 1993)
