Directory UMM :Data Elmu:jurnal:S:Soil Biology And Chemistry:Vol32.Issue11-12.oct2000:
Soil Biology & Biochemistry 32 (2000) 1671±1681
www.elsevier.com/locate/soilbio
Introduction of the epigeic earthworm Dendrobaena octaedra
changes the oribatid community and microarthropod abundances
in a pine forest
M.A. McLean*, D. Parkinson
Department of Biological Sciences, University of Calgary, Calgary, AB, Canada T2N 1N4
Accepted 5 April 2000
Abstract
The eects of the activities of the epigeic earthworm Dendrobaena octaedra on the oribatid community and microarthropod
abundances were studied in a 90-year old pine forest over 2 years. Oribatids were extracted from the L and FH layers and the
Ah and Bm horizons at 1 and 2 years and data were analyzed using principal component analysis (PCA). High worm biomass
correlated positively with oribatid species richness and diversity in the L layer. In the FH layer, worm biomass accounted for
83% of the variation in the oribatid community data and correlated negatively with oribatid species richness. High worm
biomass correlated with decreases in the abundances of 18 oribatid species, and the total abundances of adult and juvenile
oribatids, astigmatids, mesostigmatids, Actinedida and Arthropleona in the FH layer. These eects were attributed to the
changes in the physical structure of the organic layers of the soil. In the Ah and Bm horizons the C±N ratio accounted for 72±
97% of the variation in the oribatid species and microarthropod group data. The abundances of O. nova, other Oppioidea,
several Brachychthoniidae, C. cuspidatus and adult (in the Ah horizon only) and juvenile oribatids, and Arthropleona were
positively correlated with the C±N ratio. This re¯ected the mixing of less decomposed organic matter into the lower horizons by
D. octaedra. 7 2000 Elsevier Science Ltd. All rights reserved.
Keywords: Dendrobaena octaedra; Earthworm invasion; Oribatid community; Microarthropods
1. Introduction
There is con¯icting evidence of the eects of earthworms on soil microarthropods (arthropods between
200 mm and 2 mm, including mites and Collembola).
Increased microarthropod abundance and diversity
(Marinissen and Bok, 1988; Loranger et al., 1998),
decreased abundance (Dash et al., 1980; Yeates, 1981)
and mixed eects (Yeates, 1981; Hamilton and Sillman, 1989; McLean and Parkinson, 1998; Maraun et
al., 1999) have all been reported. Mechanisms which
* Corresponding author. Louis Calder Center, Fordham University, 53 Whippoorwill Road, Armonk, NY 10504, USA. Tel.: +1914-273-3078 X 18; fax: +1-914-273-2167.
E-mail address: mclean@murray.fordham.edu (M.A. McLean).
have been invoked to explain these eects have
included: (1) alteration in the physical structure of the
soil (Marinissen and Bok, 1988; Hamilton and Sillman,
1989; Loranger et al., 1998; McLean and Parkinson,
1998; Maraun et al., 1999); (2) alteration of the chemical or physical characteristics of organic matter (OM)
and its eects on the soil microbes (Yeates, 1981;
Hamilton and Sillman, 1989; Loranger et al., 1998;
Maraun et al., 1999); (3) competition for food (Brown,
1995); and (4) predation (Dash et al., 1980). Some of
the discrepancies between these studies are undoubtedly due to the diering eects of earthworms of
dierent ecological strategy on soil physical structure
and OM dynamics. Feeding of anecic earthworms (larger litter feeding species with permanent vertical burrows) increases the organic matter content and
porosity of mull soils, and therefore might be expected
0038-0717/00/$ - see front matter 7 2000 Elsevier Science Ltd. All rights reserved.
PII: S 0 0 3 8 - 0 7 1 7 ( 0 0 ) 0 0 0 8 3 - 3
1672
M.A. McLean, D. Parkinson / Soil Biology & Biochemistry 32 (2000) 1671±1681
to improve the physical and chemical characteristics of
the soil for microarthropods. However, feeding by epigeic earthworms (smaller litter feeding species con®ned
to the organic and upper mineral layers) mixes mineral
material into the organic layers, and might be expected
to reduce physical and chemical soil qualities for
microarthropods in the organic layers of the soil.
Given the paucity of data on the eects of earthworms on soil microarthropods and the diculties of
arriving at any conclusions based on soils in which
earthworms have previously been active, we were fortunate to be able to study the recent invasion of the
epigeic earthworm Dendrobaena octaedra into lodgepole pine forest in SW Alberta, Canada. We used two
approaches: short-term (6 months) laboratory studies
(McLean and Parkinson, 1997a, 1998), and longer
term (2 years) ®eld studies (McLean and Parkinson,
1997b, 2000, the present study). Under conditions of
optimum moisture and temperature in mesocosms
(intact soil cores 30 cm diameter 25 cm high), the activities of D. octaedra increased oribatid diversity and
abundances (McLean and Parkinson, 1998). This was
attributed to an increase in spatial heterogeneity
through the addition of casts to the organic materials
already present. However, since organic layers in the
mesocosms with the highest worm numbers were completely homogenized at the end of 6 months, we hypothesized that the longer term (2 years) eects of D.
octaedra would be decreased oribatid diversity and
microarthropod abundance.
2. Materials and methods
2.1. Site description
The site of this experiment was a 90-year old lodgepole pine (Pinus contorta var. latifolia Engelm.) forest
in the Kananaskis Valley of SW Alberta, Canada. For
a more detailed description see McLean and Parkinson
(1997b).
2.2. Experimental design
Five pairs of plots 1 m 2 m were set up in August
1993 in a part of the lodgepole pine forest which surveys had shown to be free from earthworms. Within
each pair of plots, two treatments (control without
earthworms and treatment with worms) were randomly
assigned. The epigeic earthworm Dendrobaena octaedra
(Savigny) was added to the worm plots at numbers
equivalent to its 1993 ®eld density of 250 immatures
and 70 matures mÿ2, with a total biomass of 3.3 g d
wt mÿ2. The earthworms used were heat extracted
(Kempson et al., 1963) from pine forest ¯oor in a part
of the forest where earthworms had already been
established for a few years.
In September 1994 and September 1995 the plots
were sampled for microarthropod abundances and for
assessment of worm abundance and biomass.
2.3. Earthworm abundance and biomass
At each sampling time one core 10.5 cm diameter
was taken from each plot and the earthworms present
were heat extracted (Kempson et al., 1963) and
counted as small (
www.elsevier.com/locate/soilbio
Introduction of the epigeic earthworm Dendrobaena octaedra
changes the oribatid community and microarthropod abundances
in a pine forest
M.A. McLean*, D. Parkinson
Department of Biological Sciences, University of Calgary, Calgary, AB, Canada T2N 1N4
Accepted 5 April 2000
Abstract
The eects of the activities of the epigeic earthworm Dendrobaena octaedra on the oribatid community and microarthropod
abundances were studied in a 90-year old pine forest over 2 years. Oribatids were extracted from the L and FH layers and the
Ah and Bm horizons at 1 and 2 years and data were analyzed using principal component analysis (PCA). High worm biomass
correlated positively with oribatid species richness and diversity in the L layer. In the FH layer, worm biomass accounted for
83% of the variation in the oribatid community data and correlated negatively with oribatid species richness. High worm
biomass correlated with decreases in the abundances of 18 oribatid species, and the total abundances of adult and juvenile
oribatids, astigmatids, mesostigmatids, Actinedida and Arthropleona in the FH layer. These eects were attributed to the
changes in the physical structure of the organic layers of the soil. In the Ah and Bm horizons the C±N ratio accounted for 72±
97% of the variation in the oribatid species and microarthropod group data. The abundances of O. nova, other Oppioidea,
several Brachychthoniidae, C. cuspidatus and adult (in the Ah horizon only) and juvenile oribatids, and Arthropleona were
positively correlated with the C±N ratio. This re¯ected the mixing of less decomposed organic matter into the lower horizons by
D. octaedra. 7 2000 Elsevier Science Ltd. All rights reserved.
Keywords: Dendrobaena octaedra; Earthworm invasion; Oribatid community; Microarthropods
1. Introduction
There is con¯icting evidence of the eects of earthworms on soil microarthropods (arthropods between
200 mm and 2 mm, including mites and Collembola).
Increased microarthropod abundance and diversity
(Marinissen and Bok, 1988; Loranger et al., 1998),
decreased abundance (Dash et al., 1980; Yeates, 1981)
and mixed eects (Yeates, 1981; Hamilton and Sillman, 1989; McLean and Parkinson, 1998; Maraun et
al., 1999) have all been reported. Mechanisms which
* Corresponding author. Louis Calder Center, Fordham University, 53 Whippoorwill Road, Armonk, NY 10504, USA. Tel.: +1914-273-3078 X 18; fax: +1-914-273-2167.
E-mail address: mclean@murray.fordham.edu (M.A. McLean).
have been invoked to explain these eects have
included: (1) alteration in the physical structure of the
soil (Marinissen and Bok, 1988; Hamilton and Sillman,
1989; Loranger et al., 1998; McLean and Parkinson,
1998; Maraun et al., 1999); (2) alteration of the chemical or physical characteristics of organic matter (OM)
and its eects on the soil microbes (Yeates, 1981;
Hamilton and Sillman, 1989; Loranger et al., 1998;
Maraun et al., 1999); (3) competition for food (Brown,
1995); and (4) predation (Dash et al., 1980). Some of
the discrepancies between these studies are undoubtedly due to the diering eects of earthworms of
dierent ecological strategy on soil physical structure
and OM dynamics. Feeding of anecic earthworms (larger litter feeding species with permanent vertical burrows) increases the organic matter content and
porosity of mull soils, and therefore might be expected
0038-0717/00/$ - see front matter 7 2000 Elsevier Science Ltd. All rights reserved.
PII: S 0 0 3 8 - 0 7 1 7 ( 0 0 ) 0 0 0 8 3 - 3
1672
M.A. McLean, D. Parkinson / Soil Biology & Biochemistry 32 (2000) 1671±1681
to improve the physical and chemical characteristics of
the soil for microarthropods. However, feeding by epigeic earthworms (smaller litter feeding species con®ned
to the organic and upper mineral layers) mixes mineral
material into the organic layers, and might be expected
to reduce physical and chemical soil qualities for
microarthropods in the organic layers of the soil.
Given the paucity of data on the eects of earthworms on soil microarthropods and the diculties of
arriving at any conclusions based on soils in which
earthworms have previously been active, we were fortunate to be able to study the recent invasion of the
epigeic earthworm Dendrobaena octaedra into lodgepole pine forest in SW Alberta, Canada. We used two
approaches: short-term (6 months) laboratory studies
(McLean and Parkinson, 1997a, 1998), and longer
term (2 years) ®eld studies (McLean and Parkinson,
1997b, 2000, the present study). Under conditions of
optimum moisture and temperature in mesocosms
(intact soil cores 30 cm diameter 25 cm high), the activities of D. octaedra increased oribatid diversity and
abundances (McLean and Parkinson, 1998). This was
attributed to an increase in spatial heterogeneity
through the addition of casts to the organic materials
already present. However, since organic layers in the
mesocosms with the highest worm numbers were completely homogenized at the end of 6 months, we hypothesized that the longer term (2 years) eects of D.
octaedra would be decreased oribatid diversity and
microarthropod abundance.
2. Materials and methods
2.1. Site description
The site of this experiment was a 90-year old lodgepole pine (Pinus contorta var. latifolia Engelm.) forest
in the Kananaskis Valley of SW Alberta, Canada. For
a more detailed description see McLean and Parkinson
(1997b).
2.2. Experimental design
Five pairs of plots 1 m 2 m were set up in August
1993 in a part of the lodgepole pine forest which surveys had shown to be free from earthworms. Within
each pair of plots, two treatments (control without
earthworms and treatment with worms) were randomly
assigned. The epigeic earthworm Dendrobaena octaedra
(Savigny) was added to the worm plots at numbers
equivalent to its 1993 ®eld density of 250 immatures
and 70 matures mÿ2, with a total biomass of 3.3 g d
wt mÿ2. The earthworms used were heat extracted
(Kempson et al., 1963) from pine forest ¯oor in a part
of the forest where earthworms had already been
established for a few years.
In September 1994 and September 1995 the plots
were sampled for microarthropod abundances and for
assessment of worm abundance and biomass.
2.3. Earthworm abundance and biomass
At each sampling time one core 10.5 cm diameter
was taken from each plot and the earthworms present
were heat extracted (Kempson et al., 1963) and
counted as small (