composition in a calcareous soil (pHH o 5.8) were stud- ied. Litterbags (45 µm and 1 mm mes:fi size) containing freshly fallen beech leaf litter were exposed to ...
Bio! Fertil Soils (1991) 11:151-156
Biology and Fertility
ofSoils
© Springer-Verlag 1991
Effects of acid rain on leaf-litter decomposition in a beech forest on calcareous soil V. Wolters II. Zoologisches Institut der Universität Göttingen, Abteilung Ökologie, Berliner Str. 28, W-3400 Göttingen, Federal Republic of Germany Received October 2, 1990
Summary. The effects of simulated acid rain an litter decomposition in a calcareous soil (pHH o 5.8) were studied. Litterbags (45 µm and 1 mm mes:fi size) containing freshly fallen beech leaf litter were exposed to different concentrations of acid in a beech forest an limestone (Göttinger Wald, Germany) for 1 year. Lass of C, the ash content, and COrC production were measured at the end of the experiment. Further tests measured the ability of the litter-colonizing microflora to metabolize 14C-labelled beech leaf litter and hyphae. The simulated acid rain strongly reduced COrC and 14COrC production in the litter. This depression in production was very strong when the input of protons was 1.5 times greater than the normal acid deposition, but comparatively low when the input was 32 times greater. Acid deposition may thus cause a very strong accumulation of primary and secondary C compounds in the litter layer of base-rich soils, even with a moderate increase in proton input. The presence of mesofauna significantly reduced the ability of the acid rain to inhibit C mineralization. The ash content in the 1-mm litterbags indicated that this was largely due to transport of base-rich mineral soil into the litter. Key words: Acid rain - Mesofauna - Decomposition -
Beech forest - Calcareous soil - Litterbag belled beech leaf litter
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C-la-
lt is generally assumed that the impact of acid rain is
much stronger in acid than in nutrient-rich soils (Kelly and Strickland 1987). Nevertheless, it has been argued that the functional relationships between organisms that live in nutrient-rich soils, and are thus not adapted to an acid environment, may be extremely sensitive to acidification (Ulrich 1987; Schaefer 1991). This would significantly accelerate the effect of acid rain an essential processes in seemingly well buffered soils. Confirmation of this hypothesis has been provided by an investigation of acid rain effects in a natural and a limed moder soil (Walters 1991). The effects of acid rain an the early stages of litter
decomposition was as strong in the limed so:ll as in the natural soil, because the litter-colonizing organisms in the limed soil, in contrast to those in the natural soil, were not able to recover rapidly once the acid rain ceased. Simulated rain containing various proton concentrations was applied to a calcareous soil in the Göttinger Wald area (Germany) to study its effect an biotic interactions in a nutrient-rich soil. This is a well established method for studying the effects of acid rain an soil organisms and soil processes (Bäath et al. 1980; Francis 1986). The study reported here was focussed on the mineralization of various C components in beech leaf litter which had been exposed to simulated rain of various acidities for 1 year in the field. Since the mesofauna plays a key role in regulating microbial activity during litter decomposition, the effects of acid rain an the interactions between mesofauna and microflora were also studied, using litterbags (Witkamp and Crossley 1966). This technique has some well known shortcomings (e.g. modification of microclimate, mass export by animals). However, the use of litterbags has provided interesting information about decomposition processes (Seastedt 1984). Th~~ results reported in the present paper confirm that this approach may be particularly useful for analyzing the effects of environmental stress on biotic interactions during decomposition processes (Lahm 1980).
Materials and methods
Study site The experiment was carried out in the Göttinger Wald area (southern Lower Saxony, Germany). The study site is located about 8 km east of Göttingen on a plateau 400- 420 m above sea level. The area is covered by 100- to 130-year-old beech trees (Fagus sylvatica L.). The annual mean temperature is 7.9 °C, with a mean annual rainfalll of 720 mm. The bedrock is Triassic limestone, overlain by a mull humus soil. According to the German classification system, the soil at the site where the field experiment was carried out is classified as Terra fusca [Chromic Cambisol (FAO), 1)'pic Eutrochrept (USDA)]. The pHH 0 of the soil was 5.8, exchangeable Ca was 160mEq kg- 1 soil, th1~ c!a} content was 45% dry weight, and the organic C content was 5.1 % dry weight.
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Experimental conditions
the simulated rain and parameters of C mineralization, and between COz-Ctotal• 14COz-Cieaf• and 14COz-Crungi were analysed by correlation methods.
An experiment to determine the effects of increased acid loading of precipitation on soil biotic processes was set up in May 1984. From this time until May 1988, seven randomly selected 1-m2 plots were watered with simulated acid rain containing various proton concentrations. To study the effects of the acid treatment on biotic activity in the litter layer, 20 litterbags containing freshly fallen beech leaves were exposed in the L layer of each plot for 1 year. The litterbags were made from polystyrene containers (8 x 8 x 5 cm) with a 25-cm 2 opening in each side and a 45-cm 2 opening at the top and the bottom. The openings were covered with gauze in two different mesh sizes, one of 45 µm (to exclude macrofauna and most of the mesofauna) and the other of 1 mm (to exclude macrofauna only). Each litterbag contained 1 g dry weight of freshly fallen beech leaf litter, which had been collected at the study site immediately after leaf fall. The litter was washed with distilled water, carefully dried at 40 °C, and rewetted before being used to fill the litterbags. After placement in the experimental plots in November 1986, all litterbags were covered with beech leaves to hinder acid deposition by interception. In November 1987, the litterbags were collected again and transferred to the laboratory for analysis.
Results
At the end of the exposure period the pH in the experimental plots (L/Ah) was 5.8/5.6 for Hi (control), 5.7/5.0 for Hl.5, 5.7/4.8 for H2, 6.1/5.1 for H4, 5.415.4 for H8, 5.115.4 for H16, and 4.7/4.9 for H32. Between 16 and 22% of the initial C was lost from the litterbags during the 1-year exposure period. No significant treatment effect on this parameter was found by two-way analysis of variance. The rates of COrCtotal> 14COrCieaf• and 14 COrCrungi production in the control treatment at the end of the exposure period are shown in Fig. 1. With 546.8 µg C g- 1 day- 1 the rate of COrCtotal production was significantly lower than 14COrCieaf production (774.5 µgCg- 1 Cday- 1; P
