Directory UMM :Data Elmu:jurnal:S:Soil Biology And Chemistry:Vol32.Issue3.2000:
Soil Biology & Biochemistry 32 (2000) 351±360
www.elsevier.com/locate/soilbio
Field evidence of the eects of the epigeic earthworm
Dendrobaena octaedra on the microfungal community in pine
forest ¯oor
M.A. McLean a,*, D. Parkinson b
a
Louis Calder Center, Fordham University, 53 Whippoorwill Rd., Armonk, NY 10504, USA
Department of Biological Sciences, University of Calgary, Calgary, Alta., Canada T2N 1N4
b
Accepted 6 September 1999
Abstract
The eects of the invasion of the epigeic earthworm Dendrobaena octaedra on the forest ¯oor microfungal community were
studied in a 90 yr old lodgepole pine forest over 2 yr. Fungi were isolated from the L and FH layers and the Ah and Bm
horizons 1 and 2 yr after the introduction of earthworms to plots. High density and biomass of D. octaedra correlated positively
with fungal dominance and negatively with fungal richness and diversity in the FH layer and the Ah and Bm horizons. High
worm density and biomass dierentiated the fungal communities in the FH layer from those in the L layer and Bm horizons and
increased the similarity between the fungal communities in the FH layer and the Ah horizon. Earthworm activities appeared to
favour the presence of faster growing fungal taxa. # 2000 Elsevier Science Ltd. All rights reserved.
Keywords: Fungal community; Earthworm; Dendrobaena octaedra; Soil fungi; Litter fungi
1. Introduction
It is well known that earthworms, through their
channelling and mixing of organic matter and mineral
soil and comminution of organic matter, have signi®cant eects on soil structure and soil chemical properties and thus on microbial activity and on microbial
populations (Brown, 1995; Edwards and Bohlen, 1996;
Doube and Brown, 1998). Much less is known of the
eects of earthworms on microbial communities (Parkinson and McLean, 1998), although we do know that
earthworm casts are a favourable environment for fungal growth (e.g. Brown, 1995; Edwards and Bohlen,
1996; Doube and Brown, 1998), burial of leaf litter by
anecic earthworms can signi®cantly reduce phytopathogenic fungal propagules (Niklas and Kennel,
* Corresponding author. Tel.: +1-914-273-3078 x18; fax: +1-914273-2167.
E-mail address: [email protected] (M.A. McLean).
1981) and that earthworms can graze selectively on
fungi (e.g. Cooke, 1983; Moody et al., 1995).
A recent invasion of the epigeic earthworm, Dendrobaena octaedra (Savigny) into lodgepole pine forest
¯oors in southwest Alberta, Canada, has provided the
opportunity to investigate the eects of an epigeic
earthworm on microbial activity and the fungal community. Two approaches were used in our investigation: short-term (6 months) laboratory studies
(McLean and Parkinson, 1997a, 1998) and longer-term
(2 yr) ®eld studies (the present experiment; McLean
and Parkinson, 1997b). In this soil the activities of D.
octaedra have signi®cantly altered the organic layers
and upper mineral horizons (McLean and Parkinson,
1997a). These physical changes were accompanied by
decreased microbial biomass and fungal-to-bacterial
ratio in laboratory studies (Scheu and Parkinson,
1994a; McLean and Parkinson, 1997a), and decreased
basal respiration and metabolic quotient in the ®eld
(McLean and Parkinson, 1997b). In laboratory mesocosms, the activities of D. octaedra increased fungal
0038-0717/00/$ - see front matter # 2000 Elsevier Science Ltd. All rights reserved.
PII: S 0 0 3 8 - 0 7 1 7 ( 9 9 ) 0 0 1 6 1 - 3
352
M.A. McLean, D. Parkinson / Soil Biology & Biochemistry 32 (2000) 351±360
species richness, diversity and number of isolates per
particle in the short term (6 months) (McLean and
Parkinson, 1998). This was attributed to increased
spatial heterogeneity, through the addition of casts
and other products of earthworm activities to the
types of organic substrates already present in the soil.
The organic layers in mesocosms containing high numbers of earthworms were completely homogenized (i.e.
the organic layers were composed solely of casts). We
hypothesize that the longer term (2 yr) eects of these
worms will be reduced spatial heterogeneity and therefore decreased fungal species richness and diversity.
Knowing that D. octaedra attains maximum growth in
the FH layer and Ah horizon (McLean et al., 1996),
and that the physical eects of its mixing activities are
strongest in these horizons, we hypothesize that its
eects on the fungal community will be most intense
in these horizons.
We have investigated the eects of D. octaedra on
the fungal community in the ®eld over 2 yr, in the context of the previous hypotheses.
2. Materials and methods
2.1. Site description
This experiment was conducted in a 90 yr old lodgepole pine (Pinus contorta Loud. var. latifolia Engelm.)
forest ¯oor in the Kananaskis Valley in the Rocky
Mountains of southwestern Alberta, Canada. For a
more detailed description see McLean and Parkinson
(1997b).
2.2. Experimental design
Five pairs of plots 1 by 2 m were set up in August
1993 in a part of the pine forest which surveys had
shown to be free of earthworms. Within each pair of
plots, two treatments (worms added, no worms added)
were randomly assigned. To each of the worm-treated
plots 250 immature and 70 mature specimens mÿ2 of
Dendrobaena octaedra were added, with a total biomass of 3.3 g d.w. mÿ2.
Plots were sampled in September 1994 and September 1995 for assessment of worm abundance and biomass and the occurrence of fungal taxa. The F and H
layers were not separated in this experiment since in
all cases worm activities had mixed them together. An
Ah horizon had developed in one of the plots at 1 yr
and in both plots at 2 yr in the high worm treatment
and had not formed in the low worm treatment plots
at either time.
2.3. Earthworm abundance and biomass
Earthworms were heat extracted (Kempson et al.,
1963) from 10.5 cm dia cores taken from each plot at
each sampling time, and classi®ed as small immatures
(
www.elsevier.com/locate/soilbio
Field evidence of the eects of the epigeic earthworm
Dendrobaena octaedra on the microfungal community in pine
forest ¯oor
M.A. McLean a,*, D. Parkinson b
a
Louis Calder Center, Fordham University, 53 Whippoorwill Rd., Armonk, NY 10504, USA
Department of Biological Sciences, University of Calgary, Calgary, Alta., Canada T2N 1N4
b
Accepted 6 September 1999
Abstract
The eects of the invasion of the epigeic earthworm Dendrobaena octaedra on the forest ¯oor microfungal community were
studied in a 90 yr old lodgepole pine forest over 2 yr. Fungi were isolated from the L and FH layers and the Ah and Bm
horizons 1 and 2 yr after the introduction of earthworms to plots. High density and biomass of D. octaedra correlated positively
with fungal dominance and negatively with fungal richness and diversity in the FH layer and the Ah and Bm horizons. High
worm density and biomass dierentiated the fungal communities in the FH layer from those in the L layer and Bm horizons and
increased the similarity between the fungal communities in the FH layer and the Ah horizon. Earthworm activities appeared to
favour the presence of faster growing fungal taxa. # 2000 Elsevier Science Ltd. All rights reserved.
Keywords: Fungal community; Earthworm; Dendrobaena octaedra; Soil fungi; Litter fungi
1. Introduction
It is well known that earthworms, through their
channelling and mixing of organic matter and mineral
soil and comminution of organic matter, have signi®cant eects on soil structure and soil chemical properties and thus on microbial activity and on microbial
populations (Brown, 1995; Edwards and Bohlen, 1996;
Doube and Brown, 1998). Much less is known of the
eects of earthworms on microbial communities (Parkinson and McLean, 1998), although we do know that
earthworm casts are a favourable environment for fungal growth (e.g. Brown, 1995; Edwards and Bohlen,
1996; Doube and Brown, 1998), burial of leaf litter by
anecic earthworms can signi®cantly reduce phytopathogenic fungal propagules (Niklas and Kennel,
* Corresponding author. Tel.: +1-914-273-3078 x18; fax: +1-914273-2167.
E-mail address: [email protected] (M.A. McLean).
1981) and that earthworms can graze selectively on
fungi (e.g. Cooke, 1983; Moody et al., 1995).
A recent invasion of the epigeic earthworm, Dendrobaena octaedra (Savigny) into lodgepole pine forest
¯oors in southwest Alberta, Canada, has provided the
opportunity to investigate the eects of an epigeic
earthworm on microbial activity and the fungal community. Two approaches were used in our investigation: short-term (6 months) laboratory studies
(McLean and Parkinson, 1997a, 1998) and longer-term
(2 yr) ®eld studies (the present experiment; McLean
and Parkinson, 1997b). In this soil the activities of D.
octaedra have signi®cantly altered the organic layers
and upper mineral horizons (McLean and Parkinson,
1997a). These physical changes were accompanied by
decreased microbial biomass and fungal-to-bacterial
ratio in laboratory studies (Scheu and Parkinson,
1994a; McLean and Parkinson, 1997a), and decreased
basal respiration and metabolic quotient in the ®eld
(McLean and Parkinson, 1997b). In laboratory mesocosms, the activities of D. octaedra increased fungal
0038-0717/00/$ - see front matter # 2000 Elsevier Science Ltd. All rights reserved.
PII: S 0 0 3 8 - 0 7 1 7 ( 9 9 ) 0 0 1 6 1 - 3
352
M.A. McLean, D. Parkinson / Soil Biology & Biochemistry 32 (2000) 351±360
species richness, diversity and number of isolates per
particle in the short term (6 months) (McLean and
Parkinson, 1998). This was attributed to increased
spatial heterogeneity, through the addition of casts
and other products of earthworm activities to the
types of organic substrates already present in the soil.
The organic layers in mesocosms containing high numbers of earthworms were completely homogenized (i.e.
the organic layers were composed solely of casts). We
hypothesize that the longer term (2 yr) eects of these
worms will be reduced spatial heterogeneity and therefore decreased fungal species richness and diversity.
Knowing that D. octaedra attains maximum growth in
the FH layer and Ah horizon (McLean et al., 1996),
and that the physical eects of its mixing activities are
strongest in these horizons, we hypothesize that its
eects on the fungal community will be most intense
in these horizons.
We have investigated the eects of D. octaedra on
the fungal community in the ®eld over 2 yr, in the context of the previous hypotheses.
2. Materials and methods
2.1. Site description
This experiment was conducted in a 90 yr old lodgepole pine (Pinus contorta Loud. var. latifolia Engelm.)
forest ¯oor in the Kananaskis Valley in the Rocky
Mountains of southwestern Alberta, Canada. For a
more detailed description see McLean and Parkinson
(1997b).
2.2. Experimental design
Five pairs of plots 1 by 2 m were set up in August
1993 in a part of the pine forest which surveys had
shown to be free of earthworms. Within each pair of
plots, two treatments (worms added, no worms added)
were randomly assigned. To each of the worm-treated
plots 250 immature and 70 mature specimens mÿ2 of
Dendrobaena octaedra were added, with a total biomass of 3.3 g d.w. mÿ2.
Plots were sampled in September 1994 and September 1995 for assessment of worm abundance and biomass and the occurrence of fungal taxa. The F and H
layers were not separated in this experiment since in
all cases worm activities had mixed them together. An
Ah horizon had developed in one of the plots at 1 yr
and in both plots at 2 yr in the high worm treatment
and had not formed in the low worm treatment plots
at either time.
2.3. Earthworm abundance and biomass
Earthworms were heat extracted (Kempson et al.,
1963) from 10.5 cm dia cores taken from each plot at
each sampling time, and classi®ed as small immatures
(