J OURNAL OF C RUSTACEAN B IOLOGY, 33(3), 440-443, 2013
SOIL LIMING MITIGATES THE NEGATIVE EFFECT OF SIMULATED ACID RAIN ON
THE ISOPOD, PORCELLIO SCABER
Jeffrey D. Tompson, Jeffrey S. Fish, and Timothy S. McCay ∗
Department of Biology, Colgate University, Hamilton, NY 13346, USA
ABSTRACT
Terrestrial isopods are sensitive to variability in the pH-buffering capacity of soils, partly because of their high requirement for calcium.
Acid deposition resulting from air pollution can reduce the quality of the environment for isopods and other forest-floor animals through
the reduction of available calcium and increased acidity. We examined the potential for calcium carbonate (lime) application in soil to
mitigate negative effects of simulated acid deposition on the isopod, Porcellio scaber Latreille (1804), in laboratory microcosms. Growth
rate of animals was lower when subjected to strongly acidic simulated precipitation compared to weakly acidic simulated precipitation.
Animals in limed microcosms had higher growth rates and lower risk of mortality than those in conditions without lime. Whole-body
calcium concentration was higher for isopods in limed than unlimed microcosms receiving strongly acidic simulated precipitation. These
results underscore the importance of buffering substrates for isopods and suggest that application of lime may be a productive mitigative
technique in areas affected by acid rain.
K EY W ORDS: acid rain, Isopoda, liming, Porcellio scaber, soil acidification
DOI: 10.1163/1937240X-00002136
I NTRODUCTION
Terrestrial isopods have high calcium requirements because
of both the development and frequent molting of their
mineralized cuticle (Ouyang and Wright, 2005), and also the
need for a gut pH suitable for microbial cellulolytic activity
and proper digestion of plant polysaccharides (Zimmer,
2002). The woodlouse, Porcellio scaber Latreille (1804),
does not maintain optimum gut conditions for microbial
cellulolytic activity when litter (food) pH is depressed below
3.5 (Zimmer and Topp, 1997), and for these reasons isopods
generally are most common in areas with well-buffered soils
(Souty-Grosset et al., 2005).
Emissions from the burning of fossil fuels increase the
concentrations of sulfuric and nitric acids in atmospheric
moisture and result in decreased pH of atmospheric deposition in the northeastern United States and other regions
(Driscoll et al., 2001). Chronic acidic deposition results in
leaching of calcium and other base cations from litter and
soil (Likens et al., 1996). Thus, acid deposition can reduce
the quality of the environment for isopods and other calciphilic animals including certain snails, millipedes, and vertebrates (Rusek and Marshall, 2000; Lovett et al., 2009).
Changes in the abundance of these soil animals can, in turn,
affect rates of litter decomposition (Rusek and Marshall,
2000).
The addition of buffers, such as calcium carbonate lime,
can ameliorate many of the negative effects of acidification
(Driscoll et al., 1996). Liming consistently results in an
increase in the abundance of land snails (Johannessen and
Sohøy, 2001), but the effects of liming on other groups
∗ Corresponding
varies (Shore and Mackenzie, 1993; Buckton and Ormerod,
1997; Fisk et al., 2006). Despite the high general calcium
requirements of isopods and their association with wellbuffered soils, we lack evidence for a positive effect of
liming on isopods (Ormerod and Rundle, 1998). Hence,
we examined the effect of simulated acid rain and the
addition of calcium carbonate lime on Porcellio scaber and
measured growth rates, mortality, and organismal calcium
concentration of animals grown in laboratory microcosms.
M ATERIALS AND M ETHODS
Woodlice of arbitrary age and sex were obtained from Carolina Biological
Supply (Burlington, North Carolina, USA). Porcellio scaber is a European
species introduced into natural environments throughout the world (Jass and
Klausmeier, 2000); it is a relatively acid-tolerant species (Sutton, 1980).
Microcosms were based on Zimmer et al. (2005) and were made of
round PVC pipe (H = 5 cm; D = 10 cm) divided into equal quarters using
acrylic partitions and covered with a clear Petri dish to prevent escape and
desiccation. Each quarter of each microcosm contained 100 g (dry mass)
of soil and 2 g of leaf litter. Litter was replaced every ten days. Soil and
litter were collected from a forest within the Adirondack State Park, New
York State (43°42 N, 74°58 W). Soils, which were acidic spodosols, were
collected within 10 cm of the surface, air dried, and sieved (5 mm). Litter
consisted of a mix of fallen leaves of yellow birch (Betula alleghaniensis),
American beech (Fagus grandifolia), and red maple (Acer rubrum). The
litter and soil were likely colonized by ambient microbes.
Half of the 40 microcosms were selected for lime application. Reagent
grade calcium carbonate (99% CaCO3 , Sigma-Aldrich, Co.) was introduced to the homogenized soil at a concentration of 800 g m−2 (Johannessen and Solhøy, 2001). Two watering solutions were prepared using
distilled water and concentrated sulfuric acid (Zimmer and Topp, 1997):
weakly acidic (pH 5.0), and strongly acidic (pH 3.0). Solutions were maintained within 0.1 pH unit of our putative treatment levels. Our experimental design was a 2 × 2 factorial with the main effects: 1) soil liming, and
2) acidity of watering solution. Ten microcosms were randomly allocated
author; e-mail: [email protected]
© The Crustacean Society, 2013. Published by Brill NV, Leiden
DOI:10.1163/1937240X-00002136
TOMPSON ET AL.: LIMING EFFECTS ON PORCELLIO SCABER
to each treatment group for a total of 40 microcosms. Each microcosm included four animals, one in each quarter, for a total of 160 experimental
animals. Animals could not move among microcosm quarters.
Isopods were allocated to quarters without regard to sex or age. Mean
mass of animals did not differ among treatments at the beginning of the
experiment (P > 0.05). The four animals within each microcosm were
considered subsamples in analyses of mass-change and body calcium; thus,
microcosms were the sample units for these analyses (n = 10). When
animals died, the remaining animals within the microcosm were used to
calculate mass-change and body-calcium for the microcosm.
The initial live mass of each animal was recorded to the nearest mg, and
the microcosms were moistened with 15 ml of the appropriate watering
solution with a spray bottle. Masses of animals were measured every 5
days for 25 days. Immediately following each weighing period, 10 ml of
watering solution was sprayed over each microcosm using a spray bottle.
The experiment was conducted in a climate-controlled room (Model NQ2L Lighted and Refrigerated Biological Incubator, Environmental Growth
Chambers, Chagrin Falls, Ohio) at 18°C, 70% relative humidity, and a
light:dark cycle of 16:8 hours.
Five days after the end of the 25-day test period, surviving isopods were
removed from the microcosms and euthanized by freezing. We determined
whole-body calcium composition of these organisms using inductively coupled plasma atomic emission spectroscopy (PerkinElmer Optima 3000SC)
following wet digestion (Parkinson and Allen, 1975), and measured soil
pH in three randomly selected microcosms to represent each experimental subgroup. Additionally, we measured soil pH in three microcosms that
were subjected to deionized water throughout the experiment for purposes
of comparison but were not used to support animals during the study.
Repeated-measures analysis of variance was used to test for the effects
of liming and watering-solution pH on change in animal mass over time.
Tests were modified for all within-subjects effects (time and time-bytreatment interactions) using the Greenhouse-Geisser adjustment to correct
for temporal autocorrelation (Milliken and Johnson, 1992). We analyzed
the effects of liming and watering-solution pH on whole-body calcium
concentrations using 2-way analysis of variance. These analyses were
completed using IBM SPSS Statistics, release 19.0.0. Differences in the
frequency of mortality were analyzed with log-likelihood ratio (G) tests
(Sokal and Rohlf, 1995) using R (Ihaka and Gentleman, 1996).
R ESULTS
Although soil pH at the end of the study was affected by
both acidity of the watering solution (F2,12 = 113.2, P <
0.001) and lime (F1,12 = 37 435.6, P < 0.001), acidity of
the watering solution had a relatively smaller effect on soil
pH (range of about 0.3 units) than liming (range of about 3
units; Table 1). The principal effect of the watering solution,
therefore, was probably to acidify the surfaces of the leaf
litter, which intercepted the majority of the solution, and
the principal effect of liming was to change the calcium
availability and pH of the soil itself.
The pH of the watering solution affected growth rates of
isopods (F1,36 = 10.40, P = 0.003), with smaller average
growth rates in microcosms receiving strongly acidic water (0.096% increase in mass per 5-day interval) compared
441
Fig. 1. Mean change in mass (%) of isopods (Porcellio scaber) from
weight at onset of experiment in limed and unlimed microcosms receiving
weakly acidic and strongly acidic simulated precipitation. Error bars
represent one unit of standard error above and below the average percent
change.
to weakly acidic water (1.046%; Fig. 1). Liming also had a
significant effect on isopod growth rates (F1,36 = 7.47, P =
0.010), with higher growth rates at limed (0.974%) compared to unlimed (0.168%) plots. There was no interaction
between liming and water acidity in affecting growth rate
(F1,36 = 0.80, P = 0.378). However, there was a three-way
interaction involving time, liming, and watering-solution pH
(F3,107 = 5.90, P = 0.001). Over time, the difference between
unlimed microcosms receiving strongly acidic water and
limed microcosms receiving strongly acidic water increased;
whereas, the difference due to liming was more consistent
for microcosms receiving weakly acidic water (Fig. 1).
Mortality was significantly higher in unlimed (24 out
of 40) compared to limed (12 out of 40) microcosms
(G1 = 4.08, P = 0.043). Watering solution acidity had no
significant effect on the survival of isopods (G1 = 1.79, P =
0.181), though there was a trend toward higher mortality in
Table 1. Mean (± SE) acidity (pH) of soils used in a laboratory study of
isopod (Porcellio scaber) growth and survival (n = 3 randomly selected
microcosms). Microcosms were watered with strongly acidic (pH 3.0) or
weakly acidic (pH 5.0) water over the course of the 25-day experiment;
calcium carbonate lime was mixed with soils of half of the microcosms
at 800 g m−2 . Data from microcosms watered with distilled water were
provided for comparison.
Watering solution
Strongly acidic (pH 3.0)
Weakly acidic (pH 5.0)
Distilled water
Limed
Unlimed
7.91 ± 0.02
7.86 ± 0.04
8.06 ± 0.02
4.61 ± 0.04
4.92 ± 0.04
5.04 ± 0.04
Fig. 2. Mean whole-body elemental calcium concentration (PPM) of
isopods (Porcellio scaber) surviving in a study of the effects of simulated
acid rain and liming on isopod growth and survival. Only samples with
a dry-mass 50 mg were used (Ntotal = 23). Error bars represent one
standard error.
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JOURNAL OF CRUSTACEAN BIOLOGY, VOL. 33, NO. 3, 2013
microcosms receiving strongly acidic water (22 out of 40)
than in those receiving weakly acidic water (14 out of 40).
There was no association between watering-solution acidity
and liming with respect to isopod mortality (G1 = 0.06, P =
0.089).
We measured elemental calcium for isopods in 23 microcosms that supported a dry weight of at least 50 mg of
surviving organisms at the end of the study. Though main
effects for liming (F1,23 = 0.46, P = 0.506) and watering acidity (F1,23 = 2.55, P = 0.127) were not significant,
there was an interaction between liming and watering acidity
(F1,23 = 12.25, P = 0.002; Fig. 2). In microcosms receiving
strongly acidic water, calcium concentration of isopods living in limed microcosms was higher than for isopods living
in unlimed microcosms. In microcosms receiving weakly
acidic water, the difference between calcium concentration
of animals in limed and unlimed microcosms was less clear.
D ISCUSSION
Isopods in our microcosms sprayed with strongly acidic
water (pH 3.0) were likely consuming litter that was close
to or below the threshold (pH 3.5) reported by Zimmer
and Topp (1997), below which animals are unable to
maintain a gut pH suitable for cellulolytic microorganisms
and digestive processes. These animals grew more slowly
than animals in microcosms sprayed with weakly acidic
water. Animals raised in microcosms with limed soils grew
and survived at higher rates than those on poorly buffered
soils. Because the soil did not likely influence the chemistry
of litter, animals must have directly benefitted from the
soil itself. Although certain isopods have been reported to
consume soil, the nutritional importance of soil consumption
is poorly understood (Zimmer, 2002).
In a laboratory experiment, P. scaber preferred substrates
with pH 5.7 among alternatives ranging from pH 2 to pH
9 (Sastrodihardjo and van Straalen, 1993), and in the field
isopods are often most common on soils with relatively high
pH (Sutton, 1980). The mechanisms underlying substrate
preferences in isopods are poorly understood, and it is possible that preferences may relate to nutritional demands. Limited data regarding the geographical distribution and habitat
associations of terrestrial isopods indicate that, although P.
scaber is sometimes found on acidic soils, most species tend
to be found on calciferous soils (Sutton, 1980; Oremorod
and Rundle, 1998). Our results suggest that this might be
particularly true in areas receiving strongly acidic precipitation. We found that soil liming had a greater impact on
growth rates of isopods that were subjected to strongly acidic
simulated precipitation than weakly acidic simulated precipitation.
Although regulations pursuant to the United States Clean
Air Act and its amendments have resulted in decreased
deposition of sulfate and increased precipitation pH in
the United States (Driscoll et al., 2003), the exchangeable
calcium and pH of soils in the northeastern United States
have continued to decrease (Warby et al., 2009). The
continued acidification of soils in Europe has also been
described (Wesselink et al., 1995). Indeed, Likens et al.
(1996) warned that a reduction in the buffering capacity
of soil may greatly prolong terrestrial recovery from acidic
deposition. Our results underscore the importance of the
geological substrate to the quality of habitat for isopods.
More field studies are needed to understand the relative
importance of mineral substrates and litter quality to isopods
and other calcium-dependent soil animals in areas affected
by acidic deposition.
ACKNOWLEDGEMENTS
We thank C. Adams, D. Goldstein and M. Zimmerman for help with elemental analyses. Funding was provided by a National Science Foundation
Cross-disciplinary Research at Undergraduate Institutions (C-RUI) grant,
number DBI-0442222.
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R ECEIVED: 19 July 2012.
ACCEPTED: 6 December 2012.
AVAILABLE ONLINE: 24 January 2013.