A study on the density of four key faunal groups in arctic soil during the plant growing season
The University Courses on Svalbard (UNIS), Postbox 156, N-9171 Longyearbyen
Abstract
In this study we looked at the density dynamics of four key groups of soil fauna, Collembola, Acari, Nematoda and Enchytraeidae, in soils of two important arctic plant communities during the growing season. To explain the found patterns we related the groups’ densities to different environmental factors (pH, bulk density and moisture). Collembola were the only fauna group that showed significant differences between sites. The change of population densities over time differed significantly between the sites in Nematoda and Enchytraeidae. Even though some significant relationships between soil fauna groups and abiotic factors were found, none of these examined abiotic factors do explain considerable amounts of the variances of the faunal group’s densities. Consequentially, to reach our goal and explain the dynamics of the different key faunal groups in arctic soils, it would be necessary to extend the range of observed environmental factors.
Introduction
Soil organisms have a primary role in the mineralisation of nutrients in soil, and hence plant nutrient acquisition and primary productivity in the arctic ecosystem (Bardgett 2002). Soil fauna as Collembola and Acari have little direct effect on the speed of litter mineralization, but indirectly by cutting the dead material in small pieces so that it becomes easier for the microbes to grow in this substrate. They graze the microbial biomass so that it is renewed faster, and essential nutrients become available for the new microbial biomass production. The quantitative effect of this is thou not known (Olsen 1999). Most mineralisation of nutrients are governed directly by the activities of microbes and their ability to do this is affected strongly by soil animals (Olsen 1999). They can affect microbes either directly by selectively feeding on them, or indirectly by mixing of organic matter, dissemination of microbial propagules, and the alternation of nutrient availability (Bardgett 2002).
Environmental and biological characteristics of arctic soils are not clearly defined, gradients exists from dry to water-logged soils, from pH values of 3,5 to 8,0 in surface soils, from mineral to peat soils, from 100% vegetation cover to less than 5% (Robinson & Wookey 1997). Generally the temperature in the arctic soil is low with a mean temperature in the upper 5 cm in the summer on 7-8 0C, in the winter the temperature can go down to –20 to –30 0C (Olsen 1999). In the winter of Svalbard the permafrost goes all the way up to the soil surface. This may result to that some of the soil fauna dies during the winter and has to be rebuilt during the short arctic summer, this increase will be dependent on temperatures and moisture gradient. Most of the soil fauna is freeze avoiding, and are able to super cool during the winter (Olsen 1999).
As an effect of the harsh climate the diversity of terrestrial invertebrates are relatively low in Arctic areas. On Svalbard geographical isolation has contributed to the low species diversity but still there is a huge activity involving these species in high numbers (Sømme 1999). Dominating groups are Enchytraeidae, Collembola, Acari, Nematoda and larvae of diptera. The bigger size ranging soil fauna elements that are found in more temperate regions are missing, making the role of the small species more important. The composition of the soil fauna varies between different habitats (Sømme 1999). For groups like Enchytraeidae and Nematoda there are little known about the species composition, while for the microarthropods there is more information available. To understand the ecological processes in arctic soil communities there is a need to know more about the spatial and temporal variation in the species abundance (Sømme 1999).
The aims of this study are to determine the density dynamics of four key faunal groups, Collembola, Acari, Nematoda and Enchytraeidae, in soils of two important arctic plant communities during the growing season and to relate them to different environmental factors (pH, bulk density and moisture).
Materials and methods
Faunal groups
In the report on hand, four dominant arctic soil fauna groups, namely Collembola, Acari, Nematoda and Enchytraeidae, will be concentrated on.
Collembola
(springtails) belong to the phylum Mandibulata. The group contains many species
with circumpolar distribution (Bale et al. 1997). They are wingless insects and
possess a forked springing organ under the abdomen (Paul & Clark 1996).
Collembola have an extended life cycle in which they develop slowly to adult
through a succession of nymphal stages. This development shows no evidence of
seasonal synchrony and extends over a period of at least two years (Sømme &
Block 1991; Addison 1977, 1981). Collembola are freeze-avoiding and survive the
winter by increasing their super-cooling capacity. Another adaptation of arctic
Collembola to low temperatures are the life cycles with faster egg development,
higher growth rate and earlier maturation compared to the group’s
representatives in temperate regions (Sømme 1999). Collembola are often related
to moisture-patterned soil, with the highest densities occurring in mesic sites
(Petersen & Luxton 1982). On Svalbard 59 species of Collembola have been
reported (Coulson 2000).
Acari (mites), of the
phylum Chelicerata, (and especially the orobatid mites, which are the dominant
group among arctic Acari) are a cosmopolitan and ancient group, which may have
survived the Pleistocene glaciation in refugia within the Arctic. Their
ecophysical characteristics and life-cycle traits preadapt them for arctic
conditions (Bale et al. 1997). Acari are a freeze-avoiding group. They do not
tolerate freezing of inner fluids, but they strongly increase their
super-cooling capacity during winter (Sømme 1999). Acari are associated with
plant material and litter and therefore their densitiy varies with that of the
patchy arctic vegetation. The bulk of the soil-dwelling Acari is found in the
top 2.5 cm of the soil (Bale et al. 1997). Most Acari have a free-running life
cycle in which the adult is preceded by a larva and three nymphal stages.
Growth and development depend directly on temperature, and life cycles in the
Arctic may extend over several years. There is little apparent synchrony of
life cycles with either season or plant phenology, although population
densities often increase as summer progresses and decline after mid-summer
(Bale et al. 1997). On Svalbard 116 species of Acari have been reported
(Coulson 2000).
Nematoda (roundworms),
a phylum of their own, are the most abundant metazoans in the soil on a
worldwide basis, but about their abundance in the arctic soils little is known.
There is an overall uncertainty about this group’s distribution and development
(Paul & Clark 1996). According to Coulson (2000) there have been no
quantitave ecological or physiological studies of the Nematoda in Svalbard.
There are both free-living and parasitic species in this group, but here only
the free-living will be considered. Free-living forms are aquatic and occur in
soils, lakes, streams, sediments, sewage sludge, hot springs and the surface
melt of polar ice caps. The Nematoda are a part of the microfauna, and their
body-size may reach 100 μm (Paul & Clark 1996). 108 species of
free-living and parasitic nematodes have been identified on western Spitsbergen
(Coulson 2000).
Enchytraeidae (potworms) constitute a little known family of aquatic (both marine and freshwater) and terrestrial worms within the phylum Annelida. In length they range from 10 to 50 mm. They are regarded as mesofauna since they occupy pore spaces with a diameter of less than 2 mm (Briones 2001). Enchytraeidae concentrate in the upper soil layers where organic matter is accumulated, although different species show varying vertical distributions (Briones 2001). In a study on Svalbard, Sømme (1999) found that the abundance of this group was always at its lowest in spring, after it had been markedly decreasing in winter, but increased strongly during summer. Enchytaeidae were highly abundant and reproduced rapidly. Moreover, they were dependent on high humidity. It was finally stated, that this group very probably has a great importance in the mineralization cycle in arctic soils. On Svalbard 34 species of Enchytraeidae are known (Coulson 2000).
Site and sampling
Svalbard is a high
arctic archipelago of mountainous islands located between latitudes 74° and
81°N and longitudes 10° and 35°E (Rønning 1996). The temperatures in Svalbard,
especially on the west coast, are much higher than the zonal average because of
the warming influence of the West Spitzbergen Current, a branch of the Gulf
Stream (Rønning 1996). However, the climate is particularly variable and
displays a broad range of climatic stresses to which soil fauna is exposed
(Bale et al. 1997). The study site
was chosen in the climatically most favourable part of Svalbard, in the inner
fjord area of central Spitzbergen (Rønning 1996), where the influence of the
warm marine current is combined with a sheltered topographic position. The area
is therefore not representative for the high Arctic in all respects. The
sampling site was a gentle north-facing tundra slope in the inner part of the
valley Adventdalen (78°10´N, 16°01´E). At the nearby weather station in
Longyearbyen, the mean temperature of the warmest month is 6.5°C and the mean
annual precipitation is 203 mm (Elvebakk 1997).
Samples and
measurements were taken on five different dates (10. June 2001, 24. June 2001,
17. July 2001, 18. August 2001, 2. September 2002[1]). This time span was chosen to approximately
cover the growing season (S.Dutton, pers.
comm.) and the period of high activity of the soil fauna. At earlier or
later times of the year the metabolic, reproductive and locomotory activity of
poikilotherm arctic soil fauna generally will be low due to low ambient
temperatures. Bale et al. (1997) mention a termination of locomotory activity in a range of
cold-adapted arctic microarthropod species at –5°C. Moreover, low activity
would results in a low extraction efficiency (see below).
Ten replicate samples
and measurements of different factors (see below) were taken from two different
zones of the slope respectively: the bottom of the slope, close to the banks of
the valley’s main river Adventelva, a rather wet zone dominated by Alopecurus borealis TRIN. (site name:
ALO), and higher up the slope, a dryer (mesic) zone with Dryas octopetala L. being a main element of the plant community
(site name: DRY). The two mentioned common tundra plants were chosen to delimit
the two sampling zones because they indicate common high Arctic plant
communities contrasting with regard to nutrient cycling (R. Bardgett, pers. comm.).
On each sampling date
the ten replicate samples for each faunal group and each environmental factor
were taken from the same, originally randomly chosen plots (approximately 1 m2)
within each zone. These were marked and localized with the help of GPS. Samples
consisted of some loose soil from under the vegetation layer and of cores of
3.6 cm diameter (area 10,18 cm2). The core depth chosen was 5 cm
from the soil surface. Due to low temperature, low nutrient levels and other
unfavourable conditions in deeper layers, the large majority of arctic soil
organisms are to be found close to the surface (see above), i. e. in the
detritus layer and in the organic horizon immediately below it, both of which
are normally well covered by 5 cm cores (Dutton, pers. comm.; for Acari see Douce & Crossley 1977; for
Enchytraeidae see Briones 2001).
Extraction
For all
four soil fauna groups active extraction methods - based on the animals’ active
movement – were used.
Both microarthropod
groups investigated, Collembola and Acari, were extracted together from the
same core using the Tullgren method: The inverted sample core is exposed to a
temperature gradient. From the top six 60 W light bulbs create a temperature of
approximately 50°C, at the bottom cold tap water runs through a pipe causing
the air to cool down. The microarthropods flee the heat to avoid desiccation
and eventually fall into a funnel at the bottom of the core leading to a test
glass filled with alcohol (70 %) for preservation. The extraction is run for 48
hours and then a high extraction efficiency is assumed to be reached. Both the
extracted Collembola and Acari were counted at x 40 magnification.
Nematoda were
extracted by exposing them to a moisture gradient. A certain amount (about 10
g) of soil sieved with a 2 mm sieve was put on a piece of tissue paper on a
more stable fine mesh. This was then intensely moistened in a water filled
Petri dish or tray, with the main water body under the mesh, and left for 24 h.
Then mesh, paper and soil were removed and a high percentage of the nematoda
from the soil was assumed to have moved through paper and mesh into the water.
They were counted at x 40 magnification.
To extract
Enchytraeidae, an inverted core was exposed to a moisture and temperature
gradient in a wet extractor as described by Briones (2001) for 5 hours.
Enchytraeidae fled the heat and sought the aquatic environment. The further
procedure was corresponding to that applied to the microarthropods. The
extraction efficiency is assumed to be very high (Briones 2001).
Collembola, Acari and
Enchytaeidae densities were computed per m2, Nematoda density per
100 g sieved fresh soil.
Abiotic factors
To measure soil pH
similar amounts of soil sieved with a 2 mm sieve and deionised water were well
mixed. After sedimentation the pH of the water (= soil pH) was measured with a
pH meter (model HANNA HI 9025).
Core dry weight was
determined after drying for 24 h at 105 °C. Bulk density was then computed as
(dry weight/volume).
The soil moisture percentage is defined as (wet weight – dry weight)*100/ (dry weight). To obtain dry soil, a known mass of fresh soil sieved with a 2 mm sieve was dried at 105°C for 48 h and cooled down in a desiccator.
Data analyses
We assume similarly
high extraction efficiencies for all samples at both sites, and therefore
counted numbers were treated as total density numbers and not projected. Basic
data handling was done in MS Excel 2000, all further statistical treatments
(two-way ANOVA, transformations, linear regressions) were done in SYSTAT 9. The
frequency distributions of all four soil fauna group densities and of soil
moisture were positively skewed. The underlying data were therefore loge-transformed
to alter the distribution to normal type. From the Nematoda data two outlier
values were excluded preceding further data treatment. Two-way ANOVAs were
carried out to explore the differences between soil fauna group densities at
different sites and different dates. By regression analyses we explored
correlations of abiotic factors with organism group densities.
Results
For Collembola there was a significant difference between densities at different dates as well as at different sites (Table 1). Acari densities were neither significantly different with respect to date nor to site (Table 1). Nematoda showed highly significant difference between densities on different dates, as well as for the interaction between date and site (Table 1). Enchytraeidae showed the same pattern as Nematoda. Detailed information about the ANOVA parameters and results are shown in Table 1.
Figures 1 to 4 show the dynamics of Collembola, Acari, Nematoda and Enchytraeidae over the growing season at both sites.
Figure 1.
Changes in densities of Collembola
over the sampling season at the two different sites; error bars indicate
standard deviation (whole bars DRY, dotted bars ALO).
Figure 2.
Changes in densities of Acari
over the sampling season at the two different sites; error bars indicate
standard deviation (whole bars DRY, dotted bars ALO).
Figure 3. Changes in densities of Nematoda over the sampling season at the two different sites; error bars indicate standard deviation (whole bars DRY, dotted bars ALO).
Figure 4.
Changes in densities of Enchytraeidae
over the sampling season at the two different sites; error bars indicate
standard deviation (whole bars DRY, dotted bars ALO).
Table 1. Two-way ANOVA results, organism groups’ densities against date and site. Fdf date, df site, df error. Significant P-values (<0.05) bold.
|
|
|
Collembola |
|
Acari |
|
Nematoda |
|
Enchytraeidae |
||||
|
|
|
F1, 4, 83 |
P |
|
F4, 1, 79 |
P |
|
F4, 1, 88 |
P |
|
F4, 1, 79 |
P |
|
Source |
|
|
|
|
|
|
|
|
|
|
|
|
|
date |
|
4.180 |
0.004 |
|
1.300 |
0.277 |
|
26.964 |
0.000 |
|
17.306 |
0.000 |
|
site |
|
9.847 |
0.002 |
|
0.284 |
0.595 |
|
0.069 |
0.793 |
|
0.040 |
0.842 |
|
date*site |
|
1.096 |
0.364 |
|
1.415 |
0.237 |
|
4.496 |
0.002 |
|
3.703 |
0.008 |
Linear regression showed a nearly significant positive relationship between Collembola densities and pH values (Figure 5, Table 2). In contrast, a significant negative relationship was found between Nematoda densities and pH (Figure 6, Table 2). There was a significant negative relationship between bulk density values and the densities of Acari and Nematoda, while Enchytraeidae were positively related to bulk density (Figure 7, Table 2). There was no significant relationship between moisture and any of the four organism group densities (Figure 8, Table 2). More information is given in Table 2.
Figure 5. Scatter graph with regression line showing the relationship between Collembola and pH, density data are log-transformed (unit: log [no ind./m2]).
Figure 6. Scatter graph with regression line showing the relationship between Nematoda and pH, density data are log-transformed (unit: log [no ind./100 g fresh soil]).
Figure 7. Scatter graphs with regression line showing the relationship between Nematoda, Acari and Enchytraeidae and bulk density (kg/m3), density data are log-transformed (unit: log [no ind./m2]).
Table 2.
Linear regression,
log-transformed organism group densities against abiotic factors. Significant
and close to significant P-values (<0.055) bold.
|
Factors |
|
Collembola |
|
Acari |
|
Nematoda |
|
Enchytraeidea |
||||||||
|
|
|
F1, 91 |
P |
R2 |
|
F1, 87 |
P |
R2 |
|
F1, 96 |
P |
R2 |
|
F1, 88 |
P |
R2 |
|
pH |
|
3.786 |
0.055 |
0.040 |
|
3.351 |
0.071 |
0.037 |
|
5.071 |
0.027 |
0.050 |
|
0.004 |
0.951 |
0.000 |
|
bulk density |
|
2.394 |
0.125 |
0.026 |
|
3.859 |
0.053 |
0.042 |
|
6.856 |
0.010 |
0.067 |
|
7.519 |
0.007 |
0.079 |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
F1,93 |
P |
R2 |
|
F1,89 |
P |
R2 |
|
F1,98 |
P |
R2 |
|
F1,88 |
P |
R2 |
|
moisture |
|
0.921 |
0.340 |
0.010 |
|
0.566 |
0.454 |
0.006 |
|
0.925 |
0.339 |
0.009 |
|
3.172 |
0.078 |
0.035 |
Discussion
Population dynamics
Collembola
As mentioned before, Collembola have free-running life cycles usually requiring at least two years per generation, and their population development is asynchronous and hardly dependent on season. On this background our finding of significant differences between densities of this group at different sampling dates is surprising. Still, the fluctuations of Collembola densities were rather moderate (and the standard deviations high) over the sampling season. The differences might be due to a seasonal trend in population recruitment (Douce and Crossley 1977).
In contrast, the significant differences between densities of this group at the two different sampling sites, with the Dryas site having the higher densities, is indeed striking, since it is the only such difference that could be found for any group. The highest densities of Collembola have been found in mesic sites (see above), which confirms our finding. However, the significance might just be due to the chosen sampling season: Hypothesizing a seasonal recruitment trend (see above), figure 1 gives some reason to assume an earlier recruitment peak of Collembola at the Dryas site (at or before the first sampling date) than at the Alopecurus site (around mid-July). The time of high Collembola density would then be well covered by the sampling time at the latter site, but not at the former.
Based on the obtained
data it is difficult to connect the density of Collembola to any environmental
factor, it was not found to be significantly related with any of the three
factors tested. Still, the nearly significant relationship with pH has to be
mentioned, because a significant difference between pH-values at the two sites
was found and pH might therefore be a basis for the mentioned differences in
Collembola density between sites. Nevertheless, pH is a factor of modest
relevance in this context, as it only accounts for 4% of the Collembola density
variations. Mukherjee and Banerjee (1993) even found pH-values of a similar
range not to be significantly correlated with Collembola density at all.
Based on the
literature, moisture was expected to have a stronger influence on this groups’
density than actually found. In studies on Svalbard, Hodkinson et al. (1996) found that survival of
Collembola at supranormal temperatures (potential summer microclimate
conditions) was longer under wet than in dry conditions. Block et al. (1994) state the same for hyponormal summer temperatures. The reason for
the fact that no significant relation was found is but possibly of
methodological nature. For the regression we assumed a logarithmical
relationship between soil moisture percentage and Collembola density. However,
since mesic habitats have been found to contain maximum densities (see above)
and since our samples therefore presumably included soils both below and above
optimum moisture conditions, a logarithmical relation is not especially likely.
Acari
No significant differences
between Acari densities were found, neither at different sampling dates nor at
different sites. The change of densities over time neither differed
significantly between the two plant communities. The only conspicuous major
change of density at both sites was that towards the last sampling date in the Dryas site, which can possibly be blamed
to the fact that we took the last samples in 2002, one season later. This high
stability of Acari densities meets the expectations: Most orobatid Acari have free-running
life cycles which may extend over several years, and there is little apparent
synchrony with season (see above). However, Bohnsack (1971) and Douce &
Crossley (1977) report that population densities often increase as summer
progresses and decline after mid-summer. This cannot be supported by our data,
probably due to the overriding effects of the basic stability and low
resolution of our data.
None of the three
abiotic factors were significantly related to Acari densities. The relation
between Acari and bulk density is close to significant, but as the latter does
only account for a good four percent of the variance, it is of little help for
explaining the found dynamics of Acari densities.
Similar to that of
Collembola, summer survival of Acari on Svalbard at supra- and hyponormal
temperatures is also longer under wet than in dry conditions (Hodkinson et al. 1996; Block et al. 1994). As the methodological considerations
mentioned when discussing the relation of Collembola density and moisture are
likely to apply to Acari as well, it is, however, not especially surprising
that no significance in the relation of Acari and moisture could be found. Such
a relation would though be expected to be less pronounced than in Collembola
anyway, because low soil moisture content in summer affects Collembola with a
more negative impact than Acari (Hodkinson et al. 1994; Coulson et al. 1996)
and generally the occurrence the former is often more closely related with soil
moisture patterns than that of the latter (Petersen & Luxton 1982).
Nematoda
Density of Nematoda differed significantly between dates. The change of Nematoda density over time differs significantly between the sites.
Both the pH and the bulk density showed a significant relation to the density of Nematoda. The density of Nematoda is negatively correlated to both pH and bulk density. However these abiotic factors only explain 5% and 6,7% respectively of the density variance. It is difficult to discuss why pH and bulk density have so little influence on the dynamics of Nematoda, because only few studies have surveyed the factors that determine this group’s dynamics and ecology in Arctic environments (Coulson 2002). This group is aquatic, it was therefore surprising that moisture did not have any significant relation to the density of Nematoda (see methodological discussion above).
For the Dryas site the density graph shows a W-shaped curve, with two minima. What this fluctuation reflects is difficult to explain from the graph. It might be fluctuations between favorable and less favorable conditions, e.g. pH and bulk density, or it may be due to factors we do not discuss in this paper.
Enchytraeidae
Density of Enchytraeidae differed significantly between dates. The change of Enchytraeidae density over time differs significantly between the sites. The only abiotic factor showing a significantly relationship with the density of Enchytraeidae was bulk density, and this correlation was positive. Nevertheless, this only explains 7,9% of the Enchytraeidae density variations.
The density of Enchytraeidae at both sites follows the same trend, whit relatively large density difference between the season peak in relation to the first and last sampling. This fits in with the study of Sømme (1999): The population is depending on a marked increase in density in the start of the growing season, compensating for high winter mortality.
Sømme (1999) also stated that Enchytraeidae is dependent on high humidity, it is therefore surprising that the moisture prosentage did not show any significant effect on the Enchytraeidae density (see methodological discussion above).
General considerations
Even though some
significant relationships were found between soil fauna groups and abiotic
factors, none of these examined abiotic factors do explain considerable amounts
of the variances of the faunal groups’ densities. Consequentially, to reach our
goal and explain the dynamics of the different key faunal groups in arctic
soils, it would be necessary to extend the range of environmental factors that
are observed and related, with regard to both abiotic and biotic factors.
Especially to relate soil temperature would
presumably be promising, since all the discussed faunal groups are poikilotherm
and accordingly their metabolism, growth, development and activity depend
directly on this factor (Bale et al. 1997). In terms of temperature, however,
not only long-term averages (e. g. monthly means) should be considered, but
also the extreme values. As
Bale et al. (1997) point out, extreme climatic events,
even if infrequent, are probably more significant for survival of arctic soil
organisms. Moreover, to gain a deeper understanding of soil fauna dynamics,
other factors like organic matter content of the soil, which is related to food
availability (Hodkinson & Wookey 1999), would additionally have to be
analysed.
Many of the obtained
data for population densities (and also some of those on environmental factors)
show particularly high standard deviations. This is probably due to the
heterogeneous habitat structure and patchy distribution of arctic soil fauna
that especially exploits favourable microhabitats (Bale et al. 1997). This
hypothesis is supported by the Collembola, which are remarkably mobile
(Hertzberg et al. 1994) and therefore capable of moving to favourable patches,
showing the highest standard deviations of densities. Patchiness of the arctic
soil therefore might be one reason for not finding more significant differences
between the different population densities and dynamics. On this background
more than ten replicate samples might be necessary especially when working on
arctic soil fauna dynamics.
Another reason for
high variability of the data may be that classification of the two plant
communities was only based on one indicator species each. A more thorough
vegetation analysis of the two sites chosen might have revealed a less
homogeneous plant community pattern than assumed.
Two major shortcomings
that have been mentioned before should be highlighted. Firstly, the assumption
of a logarithmical relationship between environmental factors, especially soil
moisture percentage, and soil fauna density might not be appropriate in the
factor range sampled. Other ways of transformation of the environmental data
prior to regression should therefore be considered.
Secondly, the
compatibility of sampling data from two different summer seasons is generally
questionable. The density data across all fauna groups did neither differ much
between the start and the end of our sampling season nor did they generally
increase over this time span. Assuming the sampling period to cover the most
active (reproduction) period (see above) and the winter to be a season of
increased mortality (Bale et al. 1997) or at least of decreased recruitment (see Bohnsack (1971) for Acari, Douce & Crossley
(1977) for Acari and Collembola) for arctic soil fauna groups, this comes as a
surprise. However, non-compatibility of the last date’s data, which were
obtained in a different season, could serve as explanation for this.
Drawing conclusions or
even speculating about differences between nutrient cycling dynamics at the two
different plant communities we examined, dominated by Alopecurus borealis and Dryas
octopetala respectively, is very difficult. We found significant differences
between sites only for Collembola densities, density changes over time differed
between the two communities in Nematoda and Enchytraeidae. These findings give
some ideas of what might be responsible for potential differences in nutrient
cycling intensity or timing between both communities. But when looking into
this question more thoroughly, one must be aware of the fact that not only
density, but also the degree of activity of soil fauna will have an important
effect on nutrient cycling. Hodkinson & Wookey (1999) underline this by
pointing out that variable summer temperature does appear to pose only few
problems for survival of tundra soil organisms, whereas their contribution to
ecosystem processes is largely temperature dependent. For example, the arctic
Collembolan Onychiurus arcticus TULLBERG displays exceptionally high Q10
values (Block et al. 1994). This again points to the probably great importance
of temperature as a factor governing arctic soil fauna dynamics.
Acknowledgements
We are much indebted to Stephen Dutton, Lancaster, for providing us with the main part of the used raw data and for advice especially on materials and methods and to Ingibjörg S. Jonsdottir, Longyearbyen, for guidance especially concerning statistical analyses.
[1] Note that in contrast to the other
samples/measurements, those for the last date were not taken in 2001 but in
2002. Nevertheless, the data will be treated as if obtained during the same
season.
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Appendix I Raw data: soil fauna sample
counts and measurements of abiotic factors at both sites.
|
DATE |
Site |
Rep. |
Bulk density |
Moisture |
pH |
Soil Nematodes |
Mites |
Collembola |
Encytraeids |
|
|
|
|
g/m3 |
(%) |
|
no/100g fresh soil |
no/m2 |
no/m2 |
no/m2 |
|
10-Jun-01 |
DRY |
1.00 |
191166.05 |
35.34 |
6.39 |
1260.00 |
51086.77 |
31438.01 |
982.44 |
|
10-Jun-01 |
DRY |
2.00 |
92545.65 |
77.52 |
6.45 |
760.00 |
3929.75 |
18666.32 |
1964.88 |
|
10-Jun-01 |
DRY |
3.00 |
189248.57 |
59.67 |
6.51 |
420.00 |
9824.38 |
3929.75 |
2947.31 |
|
10-Jun-01 |
DRY |
4.00 |
152382.39 |
74.55 |
6.50 |
560.00 |
2947.31 |
14736.57 |
2947.31 |
|
10-Jun-01 |
DRY |
5.00 |
669968.08 |
52.16 |
6.12 |
740.00 |
7859.50 |
25543.39 |
1964.88 |
|
10-Jun-01 |
DRY |
6.00 |
366252.86 |
75.51 |
6.13 |
620.00 |
1964.88 |
23578.51 |
1964.88 |
|
10-Jun-01 |
DRY |
7.00 |
265258.24 |
63.54 |
5.89 |
800.00 |
8841.94 |
21613.63 |
2947.31 |
|
10-Jun-01 |
DRY |
8.00 |
325140.17 |
55.41 |
5.60 |
680.00 |
7859.50 |
22596.07 |
4912.19 |
|
10-Jun-01 |
DRY |
9.00 |
126781.27 |
79.44 |
6.06 |
1040.00 |
1964.88 |
16701.44 |
1964.88 |
|
10-Jun-01 |
DRY |
10.00 |
514797.47 |
65.94 |
5.64 |
780.00 |
4912.19 |
23578.51 |
6877.07 |
|
24-Jun-01 |
DRY |
1.00 |
881514.75 |
16.43 |
6.27 |
300.00 |
10806.82 |
6877.07 |
1964.88 |
|
24-Jun-01 |
DRY |
2.00 |
761753.25 |
37.79 |
6.26 |
250.00 |
9824.38 |
10806.82 |
4912.19 |
|
24-Jun-01 |
DRY |
3.00 |
1275085.34 |
21.20 |
6.31 |
120.00 |
14736.57 |
11789.26 |
4912.19 |
|
24-Jun-01 |
DRY |
4.00 |
921526.77 |
26.72 |
6.53 |
180.00 |
5894.63 |
15719.01 |
2947.31 |
|
24-Jun-01 |
DRY |
5.00 |
1068572.59 |
25.89 |
5.90 |
320.00 |
1964.88 |
31438.01 |
19648.76 |
|
24-Jun-01 |
DRY |
6.00 |
524041.32 |
48.96 |
6.70 |
100.00 |
3929.75 |
5894.63 |
10806.82 |
|
24-Jun-01 |
DRY |
7.00 |
950896.49 |
22.01 |
5.75 |
90.00 |
1964.88 |
9824.38 |
3929.75 |
|
24-Jun-01 |
DRY |
8.00 |
949689.99 |
24.39 |
6.28 |
350.00 |
3929.75 |
11789.26 |
5894.63 |
|
24-Jun-01 |
DRY |
9.00 |
594500.90 |
46.36 |
5.94 |
80.00 |
7859.50 |
13754.13 |
4912.19 |
|
24-Jun-01 |
DRY |
10.00 |
578901.54 |
53.26 |
6.05 |
140.00 |
13754.13 |
26525.82 |
1964.88 |
|
17-Jul-01 |
DRY |
1.00 |
795328.15 |
37.12 |
6.21 |
600.00 |
2947.31 |
15719.01 |
8841.94 |
|
17-Jul-01 |
DRY |
2.00 |
928010.86 |
31.10 |
6.12 |
200.00 |
4912.19 |
13754.13 |
6877.07 |
|
17-Jul-01 |
DRY |
3.00 |
738750.60 |
46.77 |
6.33 |
320.00 |
9824.38 |
13754.13 |
19648.76 |
|
17-Jul-01 |
DRY |
4.00 |
455765.77 |
52.27 |
5.98 |
520.00 |
2947.31 |
4912.19 |
13754.13 |
|
17-Jul-01 |
DRY |
5.00 |
930108.06 |
33.49 |
5.75 |
840.00 |
5894.63 |
9824.38 |
14736.57 |
|
17-Jul-01 |
DRY |
6.00 |
1033268.40 |
29.68 |
6.12 |
800.00 |
4912.19 |
24560.95 |
15719.01 |
|
17-Jul-01 |
DRY |
7.00 |
1348746.92 |
23.15 |
6.03 |
920.00 |
4912.19 |
16701.44 |
6877.07 |
|
17-Jul-01 |
DRY |
8.00 |
1505586.11 |
16.64 |
6.26 |
740.00 |
1964.88 |
6877.07 |
12771.69 |
|
17-Jul-01 |
DRY |
9.00 |
559776.04 |
47.59 |
5.82 |
600.00 |
2947.31 |
11789.26 |
13754.13 |
|
17-Jul-01 |
DRY |
10.00 |
749272.65 |
40.62 |
6.08 |
1480.00 |
5894.63 |
7859.50 |
12771.69 |
|
18-Aug-01 |
DRY |
1.00 |
555666.89 |
48.97 |
6.45 |
220.00 |
6877.07 |
14736.57 |
9824.38 |
|
18-Aug-01 |
DRY |
2.00 |
641929.12 |
33.30 |
6.32 |
130.00 |
2947.31 |
7859.50 |
14736.57 |
|
18-Aug-01 |
DRY |
3.00 |
474657.86 |
42.72 |
6.21 |
170.00 |
4912.19 |
11789.26 |
16701.44 |
|
DATE |
Site |
Rep. |
Bulk density |
Moisture |
pH |
Soil Nematodes |
Mites |
Collembola |
Encytraeids |
|
|
|
|
g/m3 |
(%) |
|
no/100g fresh soil |
no/m2 |
no/m2 |
no/m2 |
|
18-Aug-01 |
DRY |
4.00 |
269743.28 |
60.13 |
6.02 |
120.00 |
1964.88 |
6877.07 |
17683.88 |
|
18-Aug-01 |
DRY |
5.00 |
701161.67 |
25.54 |
5.63 |
90.00 |
3929.75 |
10806.82 |
10806.82 |
|
18-Aug-01 |
DRY |
6.00 |
379179.23 |
47.39 |
6.04 |
310.00 |
2947.31 |
12771.69 |
3929.75 |
|
18-Aug-01 |
DRY |
7.00 |
754127.89 |
31.36 |
5.98 |
210.00 |
5894.63 |
5894.63 |
10806.82 |
|
18-Aug-01 |
DRY |
8.00 |
928813.18 |
22.35 |
6.17 |
190.00 |
0.00 |
9824.38 |
21613.63 |
|
18-Aug-01 |
DRY |
9.00 |
783739.85 |
29.99 |
6.01 |
80.00 |
982.44 |
11789.26 |
13754.13 |
|
18-Aug-01 |
DRY |
10.00 |
469270.88 |
50.31 |
5.96 |
110.00 |
1964.88 |
16701.44 |
13754.13 |
|
2-Sep-02 |
DRY |
1.00 |
19650.23 |
172.30 |
6.35 |
696.00 |
55992.14 |
18664.05 |
0.00 |
|
2-Sep-02 |
DRY |
2.00 |
39300.45 |
89.17 |
6.18 |
1090.00 |
3929.27 |
0.00 |
12770.14 |
|
2-Sep-02 |
DRY |
3.00 |
58950.68 |
42.43 |
6.04 |
927.00 |
5893.91 |
982.32 |
0.00 |
|
2-Sep-02 |
DRY |
4.00 |
78600.90 |
59.90 |
6.01 |
905.00 |
10805.50 |
9823.18 |
4911.59 |
|
2-Sep-02 |
DRY |
5.00 |
98251.13 |
48.15 |
5.85 |
5839.00 |
48133.60 |
3929.27 |
7858.55 |
|
2-Sep-02 |
DRY |
6.00 |
117901.36 |
127.12 |
6.40 |
193.00 |
6876.23 |
3929.27 |
0.00 |
|
2-Sep-02 |
DRY |
7.00 |
137551.58 |
102.28 |
6.38 |
275.00 |
0.00 |
3929.27 |
0.00 |
|
2-Sep-02 |
DRY |
8.00 |
157201.81 |
106.05 |
5.59 |
19.00 |
2946.95 |
3929.27 |
0.00 |
|
2-Sep-02 |
DRY |
9.00 |
176852.03 |
42.39 |
6.20 |
1906.00 |
9823.18 |
9823.18 |
0.00 |
|
2-Sep-02 |
DRY |
10.00 |
196502.26 |
26.61 |
6.33 |
2358.00 |
7858.55 |
11787.82 |
0.00 |
|
10-Jun-01 |
ALO |
1.00 |
213953.15 |
62.99 |
5.89 |
2000.00 |
9824.38 |
2947.31 |
9824.38 |
|
10-Jun-01 |
ALO |
2.00 |
1033524.69 |
56.27 |
5.43 |
1340.00 |
11789.26 |
12771.69 |
1964.88 |
|
10-Jun-01 |
ALO |
3.00 |
932770.23 |
62.44 |
5.61 |
1600.00 |
982.44 |
982.44 |
6877.07 |
|
10-Jun-01 |
ALO |
4.00 |
738614.69 |
62.02 |
5.72 |
530.00 |
1964.88 |
4912.19 |
13754.13 |
|
10-Jun-01 |
ALO |
5.00 |
345572.54 |
64.74 |
5.35 |
2000.00 |
3929.75 |
0.00 |
5894.63 |
|
10-Jun-01 |
ALO |
6.00 |
146492.41 |
70.18 |
6.02 |
500.00 |
14736.57 |
21613.63 |
10806.82 |
|
10-Jun-01 |
ALO |
7.00 |
477464.83 |
69.52 |
5.67 |
530.00 |
1964.88 |
21613.63 |
8841.94 |
|
10-Jun-01 |
ALO |
8.00 |
936181.47 |
57.04 |
5.24 |
800.00 |
2947.31 |
6877.07 |
5894.63 |
|
10-Jun-01 |
ALO |
9.00 |
383712.18 |
67.10 |
6.27 |
1340.00 |
3929.75 |
0.00 |
2947.31 |
|
10-Jun-01 |
ALO |
10.00 |
408558.67 |
60.18 |
5.88 |
2800.00 |
10806.82 |
9824.38 |
4912.19 |
|
24-Jun-01 |
ALO |
1.00 |
715164.42 |
40.34 |
6.08 |
320.00 |
4912.19 |
5894.63 |
2947.31 |
|
24-Jun-01 |
ALO |
2.00 |
397111.75 |
62.01 |
5.98 |
690.00 |
8841.94 |
16701.44 |
6877.07 |
|
24-Jun-01 |
ALO |
3.00 |
721857.96 |
40.93 |
5.88 |
240.00 |
0.00 |
982.44 |
982.44 |
|
24-Jun-01 |
ALO |
4.00 |
886284.42 |
41.12 |
6.17 |
170.00 |
12771.69 |
26525.82 |
3929.75 |
|
24-Jun-01 |
ALO |
5.00 |
266202.89 |
73.95 |
6.05 |
360.00 |
5894.63 |
18666.32 |
8841.94 |
|
24-Jun-01 |
ALO |
6.00 |
896317.83 |
39.30 |
5.90 |
420.00 |
8841.94 |
22596.07 |
10806.82 |
|
24-Jun-01 |
ALO |
7.00 |
379578.29 |
58.69 |
6.12 |
480.00 |
3929.75 |
7859.50 |
2947.31 |
|
DATE |
Site |
Rep. |
Bulk density |
Moisture |
pH |
Soil Nematodes |
Mites |
Collembola |
Encytraeids |
|
|
|
|
g/m3 |
(%) |
|
no/100g fresh soil |
no/m2 |
no/m2 |
no/m2 |
|
24-Jun-01 |
ALO |
8.00 |
455897.98 |
57.31 |
5.43 |
280.00 |
0.00 |
1964.88 |
982.44 |
|
24-Jun-01 |
ALO |
9.00 |
932798.95 |
31.03 |
6.37 |
330.00 |
3929.75 |
4912.19 |
3929.75 |
|
24-Jun-01 |
ALO |
10.00 |
1138645.55 |
32.27 |
6.12 |
260.00 |
1964.88 |
982.44 |
4912.19 |
|
17-Jul-01 |
ALO |
1.00 |
618534.89 |
47.70 |
5.86 |
210.00 |
982.44 |
9824.38 |
22596.07 |
|
17-Jul-01 |
ALO |
2.00 |
440363.35 |
55.80 |
5.91 |
380.00 |
11789.26 |
12771.69 |
5894.63 |
|
17-Jul-01 |
ALO |
3.00 |
873567.76 |
36.64 |
6.06 |
480.00 |
3929.75 |
4912.19 |
18666.32 |
|
17-Jul-01 |
ALO |
4.00 |
1133599.39 |
29.37 |
6.11 |
220.00 |
4912.19 |
6877.07 |
23578.51 |
|
17-Jul-01 |
ALO |
5.00 |
409963.16 |
59.57 |
5.93 |
170.00 |
6877.07 |
0.00 |
25543.39 |
|
17-Jul-01 |
ALO |
6.00 |
696875.96 |
45.83 |
5.77 |
340.00 |
4912.19 |
27508.26 |
12771.69 |
|
17-Jul-01 |
ALO |
7.00 |
356553.08 |
56.68 |
6.19 |
290.00 |
3929.75 |
24560.95 |
7859.50 |
|
17-Jul-01 |
ALO |
8.00 |
978446.77 |
31.34 |
6.02 |
180.00 |
10806.82 |
26525.82 |
14736.57 |
|
17-Jul-01 |
ALO |
9.00 |
766719.64 |
42.74 |
5.96 |
470.00 |
2947.31 |
4912.19 |
31438.01 |
|
17-Jul-01 |
ALO |
10.00 |
852674.25 |
42.20 |
5.89 |
520.00 |
2947.31 |
11789.26 |
10806.82 |
|
18-Aug-01 |
ALO |
1.00 |
597282.16 |
38.27 |
5.85 |
120.00 |
6877.07 |
11789.26 |
18666.32 |
|
18-Aug-01 |
ALO |
2.00 |
716270.02 |
45.59 |
6.10 |
210.00 |
7859.50 |
3929.75 |
11789.26 |
|
18-Aug-01 |
ALO |
3.00 |
433676.17 |
42.46 |
6.21 |
240.00 |
2947.31 |
2947.31 |
7859.50 |
|
18-Aug-01 |
ALO |
4.00 |
668250.42 |
44.57 |
6.06 |
150.00 |
5894.63 |
6877.07 |
14736.57 |
|
18-Aug-01 |
ALO |
5.00 |
541814.51 |
48.71 |
5.81 |
420.00 |
4912.19 |
6877.07 |
13754.13 |
|
18-Aug-01 |
ALO |
6.00 |
536160.27 |
51.71 |
6.22 |
80.00 |
8841.94 |
15719.01 |
27508.26 |
|
18-Aug-01 |
ALO |
7.00 |
364103.52 |
54.49 |
6.05 |
140.00 |
5894.63 |
11789.26 |
16701.44 |
|
18-Aug-01 |
ALO |
8.00 |
670677.62 |
26.54 |
5.96 |
290.00 |
2947.31 |
7859.50 |
7859.50 |
|
18-Aug-01 |
ALO |
9.00 |
443104.69 |
47.37 |
6.02 |
170.00 |
4912.19 |
3929.75 |
8841.94 |
|
18-Aug-01 |
ALO |
10.00 |
825625.71 |
37.02 |
5.99 |
140.00 |
5894.63 |
21613.63 |
4912.19 |
|
2-Sep-02 |
ALO |
1.00 |
19650.23 |
60.45 |
5.86 |
967.00 |
0.00 |
982.32 |
982.32 |
|
2-Sep-02 |
ALO |
2.00 |
39300.45 |
88.81 |
5.93 |
1519.00 |
7858.55 |
4911.59 |
0.00 |
|
2-Sep-02 |
ALO |
3.00 |
58950.68 |
48.29 |
6.07 |
1082.00 |
0.00 |
982.32 |
982.32 |
|
2-Sep-02 |
ALO |
4.00 |
78600.90 |
31.29 |
6.01 |
1549.00 |
0.00 |
0.00 |
4911.59 |
|
2-Sep-02 |
ALO |
5.00 |
98251.13 |
127.01 |
5.88 |
104.00 |
4911.59 |
982.32 |
0.00 |
|
2-Sep-02 |
ALO |
6.00 |
117901.36 |
131.15 |
6.03 |
226.00 |
982.32 |
20628.68 |
4911.59 |
|
2-Sep-02 |
ALO |
7.00 |
137551.58 |
103.98 |
5.87 |
376.00 |
17681.73 |
7858.55 |
1964.64 |
|
2-Sep-02 |
ALO |
8.00 |
157201.81 |
43.72 |
5.08 |
1321.00 |
4911.59 |
982.32 |
0.00 |
|
2-Sep-02 |
ALO |
9.00 |
176852.03 |
85.94 |
6.25 |
99.00 |
0.00 |
13752.46 |
15717.09 |
|
2-Sep-02 |
ALO |
10.00 |
196502.26 |
82.57 |
5.79 |
624.00 |
0.00 |
982.32 |
2946.95 |