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ORNU-P-519
STIEP
OCT 301964
Bosnijden
EFFECTS OF A PESTICIDE ON BIOTA AND BREAKDOWN OF FOREST LITTER*
D. A. Crossley, Jr. and Martin Witkamp
Radiation Ecology Section, Health Physics Division
Oak Ridge National Laboratory, Oak Ridge, Tennessee

LEGAL NOTICE
The report
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* Research sponsored by the U. S. Atomic Energy Commission under
contract with the Union Carbide Corporation.
Biological breakdown of organic litter and subsequent release of
minerals from this litter has been studied extensively by foresters,
agronomists, 200 logists, and microbiologists. Work on the evaluation of
the separate roles of fauna and microflora on breakdown and minerali.
zation, however, 18 limited. In the present study effects of soil fauna
and microflora on the breakdown of oak leaves in the field were separated
by using naphthalene. Naphthalene greatly reduced numbers of leaf-
fragmenting arthropods but did not affect the microflora. These changes
in biota and subsequent effects on weight loss and loss of a mineral
(cesium, as estimated with +34Cs) were measured throughout the first
year of breakdown of the oak litter.
In the experimental procedure twelve 1 x 1 m plots of oak leaf
litter (Quercus alba L.) received levels of 100, 35, 10, or 0 8 of
naphthalene flakes (3 replicates x 4 treatments). Naphthalene had to
be reapplied at about 4 week intervals during winter and at weekly
intervals during summer when evaporation was rapid. On each l m plot
five litter bags (1 x 1 dm nylon net with 1 mm openings) each containing
2.5 8 of air dry oak leaves were put out on the forest floor in autumn.
These leaves contained +34cs which had been introduced by trunk inocu-
lation (Auerbach et al, 1964) when leaves were green. Cesium occurs
mainly in ionic form (Brown, 1964) and its behavior closely resembles
that of potassium.
Weekly measurements on litter bags provided data ca loss of
weight, loss of 134C8, and numbers of arthropods. Intact litter bags
were brought into the laboratory for y scintillation counting and Berlese
funnel extraction of arthropods; the litter bags were then returned to
field sites. Biweekly measurements were made of soil + litter respiration
and of microbial densities. Respiration of litter + soil was measured
as co, avolution during two l-hr periods under round plastic boxes ( 15 cm
diameter, 6 cm high). Dilution plate counts of bacteria on nutrient agar
and fungi on peptone-dextrose agar with 3 ppm of bengal rose and strepto-
mycin were made using leaf litter from bags and soil collected under
bage. Direct counts of fungi and bacteria were made on leaf discs (5 mm
diameter) bleached with peroxide and colored with methylene blue in
lactic acid. At the end of the first year of decay, all litter from the
m? plots was collected, dried, and weighed.
Arthropod populations in the 200 g naphthalene plots were from
2 to 15 times lower and averaged 22% as numerous as populations in the
control plots. Many of the animals found in the naphthalene plots were
capable of flight, or were predators or larger leaf consumers which
presumably were only traversing these plots. Fluctuations in the soil
fauna population were not of a clear seasonal character, as is usual
for soil microflora, but rather successional and similar to those
described previously by Crossley and Hoglund (1962).
Seasonal changes in the colony plaie were similar to those
described previous
namely, increases of about 1 order of
magnitude during the season. Both fungal and bacterial counts were
not significantly different for plots with and without naphthalene.
In contrast there was a significant difference between direct
counts of bacteria on the stained leaf discs (Fig. 1). On leaves with
naphthalene bacterial counts increased 3 fold from January to March and
t?,* decreased again. On leaves without naphthalene bacterial counts
increased gradually with the result that both types of leaves showed
equal bacterial densities on their surfaces in August and September..
Direct measurements of fungi on the discs also increased during the
year, though less rapidly than did the bacteria. Differences between
fungal counts from leaves with and without microfauna were only signifi.
cant at the 10% level of probability.
A probable reason for the early rise of bacteria on leaves with
naphthalene as compared to leaves without naphthalene is the utilization
of easily decomposable tissue of killed arthropods in the naphthalene
plots. This utilization would be mainly by bacteria and would culminate
in early spring after a temperature induced lag during the winter time.
For fungi this phenomenon would be less pronounced.
Microbial populations from soil evaluated by the dilution plate
method did not show significant differences between plots with and
without naphthalene presumably because no naphthalene penetrated into
the soil. Earthworms appeared in both plots in equal numbers. ·
Respiration rates for litter + soil were identical for plots with
and without naphthalene presumably because of the large influence of
co, from soil.
After 50 weeks in the field, control litter (no naphthalene) had
lost 60% of the initial weight; litter treated with 100 & additions of
naphthalene had lost 45% of the initial weight (Hg. 2). Cesium-134 Loss
rates showed a similar difference. Percentages of Ce lost by bagged
leaf litter in plots receiving 100 g naphthalene and in control plots
were 84% and 92.5%, respectively. Plots receiving 36 or 10 g naphthalene
were intermediatIn weight and 134C: loss rates. These trends in weight
and radiocesium 1088es observed for individual bags were confirmed by
measurements on bags left undisturbed for the entire year and on weights
of total forest floor remaining in the 12 plots.
The difference in retention of radiocesium in control and experi-
mental plots is greater than would be expected from change in weight
alone. Utter treated with naphthalene not only retained more weight
but retained more cesium per unit weight as well. A probable explanation
18 that the activities of the soil fauna tend to fragment the litter and
thus' expobe a greater surface to the leaching action of rainwater. It
appears, then, that the activities of the soil fauna are effective in
promoting the release of stored minerals from leaf litter, above and
beyond their feeding activities.
Data obtained in this experiment are only relative, since arthro-
pods were not completely eliminated from the naphthalene treated plots.
The experiment shows, however, that the effect of the soil fauna on
weight loss and mineral loss from leaf litter 18 of major importance.
Kurcheva (1960), working in Russia, performed a similar experiment and
achieved even more dramatic results. Oak litter treated with naphthalene
lost only 9% of its original weight, whereas litter without naphthalene
lost 55% during a 140 day experiment. These data were obtained using
Quercus robur L. which retaine its leaves until spring. Probably, thon,
the readily soluble materials had already leached out when the experimant
was started in the spring. Litter without soil fauna thus lost little
weight.
The experiment described in this paper quantifies the importance
of soil microflora and soil fauna to the breakdown of forest litter and
mineralization of +*Cs. New techniques in such studies--radioisotopes,
litter bags, use of insecticides, and other experimental approaches--can
provide a fresh insight into the ecological problems confronting biologists
and agronomists alike. Such experimentation 18 best approached from a
functional viewpoint; that is, an over-all consideration of the ecosystem
as a dynamic unit, and the soil fauna and soil microflora as parts of
that unit.
REFERENCES
Auerbach, s. I., J. S. Olson, and H. D. Waller. 1964. Landscape investi-
gations using caesium-137. Nature 201( 4921): 761-764.
Brown, G. N. 1964. Cesium in Liriodendron and other woody species:
Organic bonding sites. Science 143:368-369.
Crossley, D. A., Jr., and M. P. Hoglund. 1962. A litter-bag method for
the study of microarthropods inhabiting leaf litter. Ecology
43(3):571-573.
Crossley, D. A., Jr., and M. Witkamp. 1964. Forest so11 mites and
mineral cycling. Acarologia (in press).
Kurcheva, G. F. 1960. (Role of invertebrates in the decomposition of oak
litter). Soviet S011 Science (AIBS translation of Pochvovedeniye)
4:360-365 (Russ. pp. 16-23).
g. 1. Microbial concentrations on the surface of oak leaves with and
without arthropods during the first year of decay.
UNCLASSIFIED
ORNL - DWG 63-3931

WEIGHT RETENTION
-Cs134 RETENTION
PERCENT RETENTION
oo 090
A. NAPHTHALENE
AO CONTROL
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TIME (weeks )
F18. 2. Retention of weight and of 134C8 by bagged leaf litter.
"Naphthalene" . 100 g naphthalene por m. "Control" - no
naphthalene. (After Crossley and Witkamp, 1964).
ORNL-DWG-No. 63-1931
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This report was prepared as an account of Government sponsored work. Neither the United
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As used in the above, "person acting on behalf of the Commission" includes any em-
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disseminates, or provides access ko, wny information pursuant to his employment or contract
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