Acid Rain Treatment Research Articles

Interactions of Gremmeniella abietina and Endophytic Fungi in Shoots of Scots Pine Trees Treated with Simulated Acid Rain

1. Detached shoots of Scots pine trees with naturally occurring endophytic fungi were inoculated with mycelium of the pathogenic fungus Gremmeniella abietina. The trees had been subjected to simulated acid rain (pH 3, both H 2 SO 4 and HNO 3 ) or control irrigation (pH 6) during the previous five growing seasons. The shoots were incubated in controlled conditions for 6 weeks, after which they were surface sterilized, cut into pieces and plated on agar medium. The frequency of G. abietina and endophytic isolations was measured. 2. The shoots were often colonized by endophytic fungi, two Hormonema species being clearly dominant. Although the frequency of these fungi tended to be low in trees treated with simulated acid rain, the treatment effect was not statistically significant. The isolation frequency of Hormonema 1 increased significantly with height of the host tree. The frequency of Hormonema 2 isolations differed significantly in two separate sub-areas. The frequency of isolations of G. abietina was not affected by simulated acid rain treatment. 3. Gremmeniella abietina was isolated more often from shoots with Hormonema 2 isolations, which suggests that there are common factors determining the success of the endophyte and G. abietina. On the other hand, the frequency of endophytic isolations was lower than expected in those parts of the shoots invaded by G. abietina, implying that the latter was a stronger competitor

Nuclear polyhedrosis virus of the European pine sawfly, Neodiprion sertifer (Geoffr.) (Hym., Diprionidae) retains infectivity in soil treated with simulated acid rain

AbstractThe effect of simulated acid rain on the infectivity of the nuclear polyhedrosis virus of the European pine sawfly, Neodiprion sertifer (Geoffr.) was studied in southern Finland. Three‐year‐old saplings of Scots pine, Pinus sylvestris (L.), were sprayed once with diluted N. sertifer virus nuclear polyhedrosis (NsNPV) suspension or distilled water; after this they were irrigated during the growing season with ground water (pH 7) or with acidified water of pH 4 or pH 3, adjusted by adding both H2SO3 and HNO3. The ability of virus‐killed N. sertifer larvae to shelter viruses was tested by killing larvae with NsNPV on half of the virus‐treated saplings before the beginning of the irrigation treatments. The persistence of the virus on the foliage and in the soil was tested the following summer by two separate bioassays with European pine sawfly larvae. In the first bioassay, in which larvae were fed once with the foliage of the experimental saplings, no significant difference in mortality among the various treatments was detected. In the second bioassay, in which larvae were fed on pine foliage contaminated with soil from the virus‐treated saplings, virus treatment had a significant effect. In that case, only 4–7% successfully formed cocoons, compared to larval survival of 22% in the absence of the virus. Of the larvae fed with pine twigs contaminated with soil from saplings on which virus‐infected larval cadavers were retained, the mortality rate was 100%. Acid rain treatments did not affect larval survival in either bioassay. Thus, NsNPV infectivity in the field is maintained in the soil but not on the foliage and appears to be unaffected by simulated acid rain.

Pine needle growth and fine structure after prolonged acid rain treatment in the subarctic

ABSTRACTThe growth and morphology of Scots pine needles were studied in a long‐term acid rain experiment in the far north of Finnish Lapland. Pine trees 5 m tall of age 50–70 years were exposed, by spraying the foliage and soil from a height of 2 m, to either clean water (IC) or acidified water over the period 1985–1992, the acidification site being divided into sub‐areas in which the precipitation contained two levels of either sulphuric (Sm, Sh) or nitric (Nm, Nh) acid, or both (SNm, SNh). The treatments with medium and high sulphate‐S over eight consecutive years yielded a total sulphur deposition of 3·4 and 17·1 gm−2, respectively, and those with medium and high nitrate‐N a total nitrogen deposition of 1·1 and 5·9 g m−2. Needles were collected for light and electron microscopy, growth measurements and morphometry. Growth in branch height had decreased by about 40% after 6 years of SNm or SNh treatment, and needle growth by 15% in the SNh trees as compared with the irrigated control trees (IC), although decreases were statistically significant only with respect to the non‐irrigated control trees (DC). Growth of branches and needles was slightly better in the Nh treatment than in the IC group. The areas of the whole needle, the mesophyll and the phloem decreased in response to SNh treatment as compared with IC or DC, and a statistically significant decrease of about 30–40% was seen in the area of the xylem in comparison with DC. Cellular damage was observed following the acid treatments, especially with a high acid load. The damage was manifested in collapse of the cellular compartments, increases in lipid accumulations and swelling or disorganization of the protoplast. Increased vacuolization of the cytoplasm, plasmalemma irregularities and chilling‐type damage to the mitochondria were also observed.

The effects of acid deposition on the biogeochemical cycles of major nutrients in miniature red spruce ecosystems

As part of an experimental study of air pollution effects on tree growth and health, we combined process studies with an ecosystem approach to evaluate the effects of acidic deposition on soil acidification, nutrient cycling and proton fluxes in miniature red spruce ecosystems. Ninety red spruce saplings were transplanted into 1-m diameter pots containing reconstructed soil profiles and exposed to simulated acid rain treatments of pH 3.1, 4.1 and 5.1 for four consecutive growing seasons. All the principal fluxes of the major elements were measured. During the first year of treatments, the disturbance associated with the transplanting of the experimental trees masked any treatment effects by stimulating N mineralization rates and consequent high NO3-, cation, and H+ flux through the soil profile. In subsequent years, leaching of base cations and labile Al was accelerated in the most intensive acid treatment and corresponding declines in soil pH and exchangeable pools of Ca and Mg and increases in exchangeable Al concentrations were observed in the organic horizon. Leaching of Ca2' and Mg2+ also was significantly higher in the pH 4.1 than in the pH 5.1 treatment. Flux of Ca from foliage and soil was increased in response to strong acid loading and root uptake increased to compensate for foliar Ca losses. In contrast, K cycling was dominated by root uptake and internal cycling and was relatively insensitive to strong acid inputs. Cation leaching induced by acidic deposition was responsible for the majority of H* flux in the pH 3.1 treatment in the organic soil horizon whereas root uptake accounted for most of the H* flux in the pH 4.1 and 5.1 treatments. Although no measurable effects on tree nutrition or health were observed, base cation leaching was significantly accelerated by acidic deposition, even at levels below that observed in the eastern U.S., warranting continued concern about acid deposition effects on the soil base status of forested ecosystems.

Influence of simulated acid rain on the flowering dogwood (Cornusflorida) leaf surface

Acidic rainfall has the potential to influence anthracnose incidence and severity in flowering dogwood (Cornusflorida L.) of the eastern United States. One-year-old, nursery-grown flowering dogwood seedlings were exposed to 1 cm of simulated rain 10 times over a 42-day period in 1990. Simulated rains were composed of a mixture of salts typical of ambient rainfall in the eastern United States and pH was adjusted to 5.5, 4.5, 3.5, and 2.5 with sulfuric and nitric acids. Samples were cut from the leaf tip, margin, and midvein of rain-treated trees and prepared for scanning electron microscopy. Cuticular cracking, desiccation, and erosion of trichome surfaces was observed in response to acid rain treatment. Increased degradation of dogwood trichomes was observed with decreasing pH for all samples. Cuticular erosion due to acid rain has the potential to predispose dogwoods in the eastern United States to anthracnose caused by Disculadestructiva sp.nov. (Red.) and an unnamed Discula sp.

Effects of simulated acid rain and root‐knot nematode on tomato

Effects were examined of simulated acid rain and of root‐knot nematode, Meloidogyne incognita race 1, on plant growth, yield, photosynthetic pigments and leaf epidermal characters of tomato (Lycopersicon esculentum cv. Pusa Ruby). Sequential inoculation exposures (pre‐, post‐, and concomitant with nematode inoculation) were carried out in a greenhouse. Intermittent treatments of simulated acid rain at pH 3.2 caused white‐to‐tan irregular lesions on both the upper and lower surfaces of tomato leaves. The foliar symptoms were more pronounced on nematode‐infected plants. Simulated acid rain (pH 3.2) and/or nematode infection suppressed plant growth, yield and pigment synthesis, the effects being greatest in post‐inoculation treatments compared with simulated acid rain at pH 6.8. The total weight of fruits per plant was greatly suppressed owing to simulated acid rain or nematode infection. Chlorophyll a was found to be more sensitive to simulated acid rain or nematode infection than other leaf pigments. Root penetration, galling, egg mass production, and fecundity (number of eggs per egg mass) of M. incognita were enhanced at pH 5.6 and suppressed at pH 3.2 compared with pH 6.8. Nematode infection or simulated acid rain at pH 3.2 suppressed stomata and trichome development (number and size). Simulated acid rain treatments at pH 5.6 had a positive effect on number and size of trichomes, but a negative effect on stomata. The apertures of stomata were wider on tomato leaves exposed to simulated acid rain, especially at pH 3.2, than at pH 6.8.

人工酸性雨が数種の農作物の生長・収量および光合成速度に及ぼす影響

Eight species of crop were exposed to simulated acid rain (SO42-: NO3-: Cl-=2:1:2, equivalent ratio) at pH 5.6 (control), 3.0, 2.7 and 2.5 throughout their entire growing periods. Plant were subjected to acid rain treatment three times a week, for one hour with 7-13mm of precipitation at a time. Simulated acid rain at pH 3.0 or below produced foliar visible injury on leaves of all the tested plants in this study. Injury degree of the foliar visible symptoms was varied among plant species. In addition, injury degrees were different among leaf positions: injury was severer in lower lesf position, particularly cotyledons and primary leaves, than upper one. In many cases in this study, foliar visible injury was severer at the early stages of growth than the later stages. Dry weight of rice plants exposed to simulated acid rain at pH below 3.0 was reduced compared with pH 5.6 at early stage of growth. At the middle to late growth stage, however, acid rain treatment did not affect the growth of rice plants. The relationship between pH of simulated acid rain and yield loss in each crop suggested that acid rain at pH 3.0 or less acidity would not cause yield reduction at any crop. In the lower pH range less than 3.0, yield loss acidity in simulated acid rain varied among plant species. The yield of rice was not reduced even at pH 2.5.

Simulated acid rain affects birch leaf endophyte populations

Endophytes were frequently isolated from mountain birch (Betula pubescens var. tortuosa (Ledeb.) Nyman) leaves at a subarctic site where natural air pollution is low. We tested whether simulated acid rain had any influence on the occurrence of endophytes. Dry controls with only ambient rain and irrigated controls treated with spring water of pH 6 were compared with acid treatments at pH 3 and pH 4, prepared by adding both sulphuric and nitric acids. Treatments began in 1985 and leaf samples were taken twice during the summer of 1992. Leaves were surface sterilized, five leaf disks from each leaf placed on malt extract agar, and growing colonies were counted and identified. The most frequently isolated endophyte from birch leaves was a Fusicladium anamorph of Venturia sp. (88% of all the isolates in July and 75% of all the isolates in August), followed by a sterile mycelium and Melanconium sp. The number of endophytes isolated and the species number increased from July to August. Endophytes were most frequently isolated from the basal part of the midrib. The percentage of colonization by endophytes was similar in short and long shoots. More endophytes were isolated from leaves of branches taken at 1 m height than at 2 m height. The stronger acid rain treatment (pH 3) reduced by approximately 25% the number of isolated endophytes in August. Treatments did not have any effect on species composition of endophyte assemblages in birch leaves.

Effects of larval age and prolonged simulated acid rain on the susceptibility of European pine sawfly to virus infection.

We studied the effect of simulated acid rain treatment of host trees on the susceptibility of the European pine sawfly larvae to virus, and possible differences when larvae of two different ages were infected. Older larvae were less susceptible to virus. Most larvae treated with virus 2 days after they started feeding on experimental foliage (group A) died rapidly within 10 days after the virus treatment, and survival to the end of the larval period was only 8-25%. Larvae treated with virus 1 week later (group B) were less affected by the virus and 36-49% survived. In group A the larval survival in the pH 3 treatment was higher than in other treatments; at the end of the larval period the difference was twofold. In group B there were no clear effects of acid rain on the susceptibility of larvae to virus. The study yielded the following new information: (1) the effect of prolonged acid rain treatment on reducing the efficacy of virus on young larvae was more distinct than in a previous study with shorter exposure to acid rain, and the difference was maintained to the end of larval period; (2) the susceptibility of older larvae to virus was not affected by acid rain treatments; (3) pH inside the needles did not explain the larval mortality caused by virus.

Growth and Xylem Water Potential of White Oak and Loblolly Pine Seedlings as Affected by Simulated Acidic Rain

Effects of simulated acidic rainfall on the growth and water relations of white oak (Quercus albya L.) and loblolly pin (Pinus taeda L.) seedlings grown under two fertility regimes were examined. Seedling of each species grown in a loam soil were exposed to two simulated rains per week of pH 4.8, 4.2 or 3.6 for 26 wk. High and low fertility regimes were imposed by monthly application of one-half and one-quarter concentration, respectively, of Hoagland's solution No. 2. Diameter growth of both species was reduced by exposure to rains of the higher acidities regardless of fertility treatment, and seedlings that received pH 4.2 and 3.6 rains also exhibited greater foliar chlorosis and necrosis than those that received rains of pH 4.8. The high fertility treatment stimulated diameter growth of white oak, but height growth, shoot and root dry weights and total root length were no substantially affected b acid rain or fertility treatments in either species. Following the final rain applications, drought was simulated by withholding irrigation for 2 wk, and seedling xylem pressure potential was then measured using the pressure chamber technique. Xylem pressure potential of white oak seedlings which had received rains of pH 3.6 was significantly lower more » than that of seedlings which had received rains of higher pH, a result that became more pronounced as soil water potential decreased. Rain acidity had little effect on the xylem pressure potential of loblolly pine, however. Soil pH analyses before initiation and after completion of the rain applications indicated that rainfall of pH 3.6 increased soil acidity more than rains of pH 4.2 or 4.8, although changes in soil pH were small overall. 26 refs., 1 fig. 2 tabs. « less

Effects of simulated acid rain on the growth of agricultural crops

Three species of crops, radish, spinach and bush bean, were exposed to simulated acid rain at pH 5.6 (control) to 2.5 throughout their growing periods. Plants were subjected to acid rain treatment three times a week, for one hour with 10mm of precipitation at a time. All the plants exposed to simulated acid rain falls at pH3.0 or below produced visible injury on the leaves. The visible injuries were severe on the cotyledons of radish and spinach and primary leaves of bush bean exposed to rain at pH 2.7 and 2.5, which resulted in the growth reduction of plants at early stages of growth compared to pH 5.6. In none of the cases in this study did treatment at pH 3.0 or higher significantly affect the growth of leaf area or dry weight of whole plants in three species. These results suggest that current ambient levels of rain acidity in Japan, where annual mean pH value is about 4.6, may not affect growth in the three species of crops tested in this study.

Response of Ammophila breviligulata to acid rain and low soil pH

The effects of simulated acid rain and low soil pH on the growth of Ammophila breviligulata (Cape Strain), American beach grass, were studied in greenhouse experiments. Plants treated with acid rain were shorter, but shoot density, live shoot biomass, and rhizome biomass were not adversely affected by the acid rain treatments. Root biomass was greatest in the acid rain treatments. A manipulated soil pH of 4.0, typical of that found in field sites of dying beach grass, resulted in significantly reduced plant height, shoot density, shoot biomass, and rhizome biomass. Root biomass was greater in the low pH treatment and was six times greater than rhizome biomass in that treatment while the root to rhizome ratio was approximately 1∶1 in the control — likely a reflection of the plant's response to decreased nutrient availability in the low pH soil. Acid rain treatment of dune sand resulted in the leaching of Al, a potentially phytotoxic element.

Effects of acid rain treatments on the birch rust, Melampsoridium betulinum and birch, Betula pendula

AbstractEffects of acidic rain on birch rust and on the growth of Betula pendula seedlings were studied by irrigating with acidic water at pH 3, 4 and 5.6. The seedlings were inoculated with uredospores of Melampsoridium betulinum and the development of rust and the severity of rust infection was examined. The increasing acidity of the irrigation water did not affect on the development of the rust, but the nitrogen in the acidified water resulted in an extension of seedling growth, and hence the leaves became senescent at a later date in autumn and the rust grew for a longer time.

Structural responses of needles of conifer seedlings to acid rain treatment

summaryThe mesophyll ultrastructure of needles of Norway spruce [Picea abies (L.) Karst.] and Scots pine (Pinus sylvestris L.) seedlings was examined in the course of experimental acid rain treatment lasting three years. The pH 3‐treated needle mesophyll cells exhibited thicker granal packing in their chloroplasts than the dry control needles after one season's irrigation. Starch occurrence had decreased due to pH treatment when the whole hardening and rest period was considered. Chloroplast shapes were seen to vary from ellipsoid to irregular, especially in the pH 4 and pH 3‐treated needles, due to divisions during hardening. The mean area of mesophyll chloroplasts in the hardened state after three seasons, irrigation was largest (10.3 μm2) in the pH 3‐treated needles, which also contained the smallest number of dark‐stained plastoglobuli. Starch occurrence in the hardened mesophyll cells in October reflected disturbances in the hardening processes in the pH 3‐treated needles.

ダイズの無機成分吸収におよぼす人工酸性雨の影響

Adverse effects of acid rain on the growth of plants include acidification of soils and the subsequent leaching of basic cations and release of certain elements in potentially toxic concentrations from soil. The present study describes changes in the elemental conditions of cultivated soil and soybean plants exposed to simulated acid rain.The cultivated soil pH (soil: H2O=1:2.5) at the upper layer (0-5cm) was significantly decreased with increasing acidity of simulated acid rain. At pH 2.0, the contents of soluble basic cations, Mn and Zn in water (soil: H2O=1:5) were significantly increased in the upper soil layer (0-5cm) compared with pH 5.6. As a result of these changes on soil conditions, the uptake rate of basic cations, Cu, Mn and Zn by the soybean plants were increased by exposing the simulated acid rain at pH 2.0. These results suggested that the concentration of Mn and Cu in plant are available to estimate the acidification of soil with acid rain.On the other hand, despite the contents of soluble Al in 1N CH3COONH4 was increased and of soluble P in water was decreased with decreasing pH of soil in the upper soil layer, P uptake rate by soybean plants was increased at pH 2.0. Any effects of toxic element were not observed at all pH treatments.These results suggested that soil chamistry may change significantly in upper layer by simulated acid rain treatment at pH 3.0 or below, but the effects of such changes were not important on the growth and yield of soybean plants under the normal manuring practice.

Carryover Effects of Acid Rain and Ozone on the Physiology of Multiple Flushes of Loblolly Pine Seedlings

Abstract The effects of acid rain and ozone exposure on loblolly pine (Pinus taeda L.) seedlings in the Piedmont of North Carolina were assessed over two exposure seasons (1987-1988). Direct effects and carryover effects of long-term exposure on the photosynthetic potential and photopigment concentrations of different needle age-classes were studied. Three half-sib families were grown in open-top field chambers and exposed to two acid rain treatments (pH 5.3 or 3.3) and five ozone exposures delivered in proportion to ambient concentrations (0.5x to 3.0x ambient) in a complete factorial design. Ozone significantly affected photosynthesis but there were no statistically significant effects of add rain nor any ozone x acid rain interactions. In 1987, photosynthesis of the 1987 first-flush progressively diverged among the ozone treatments except between charcoal-filtered (CF ≈ 0.5x ambient) and nonfiltered air (NF). At the end of the first season, photosynthesis was reduced 24% at 1.5x compared to CF and more than 80% at 2.25x and 3.0x. Chlorophyll and carotenoid concentrations were similarly reduced at elevated ozone exposures. In 1988, photosynthesis of the 1987 first-flush in the elevated ozone treatments remained lower. Early in the second season, the 1988 first-flush had a 25% to 50% lower photosynthetic potential at 2.25x and 3.0x compared to CF. This carryover effect on the photosynthetic potential before significant cumulative exposure was progressively smaller in the later 1988 flushes. In the late season flushes in the highest ozone treatments, photosynthesis was significantly higher than in the lower ozone treatments. For. Sci. 37(4):1078-1098.

Interaction of Simulated Acid Rain with Ozone on Freeze Resistance, Growth, and Mineral Nutrition in Citrus and Avocado

The combined effects of O3 and acid rain on freeze resistance, growth, and mineral nutrition were studied using broadleaf-evergreen citrus and avocado trees. Using a factorial design, `Ruby red' grapefruit (Citrus paradisi L.) trees on either Volkamer lemon (Citrus volkameriana Ten. & Pasq.) or sour orange (Citrus aurantium L.) rootstock and `Pancho' avocado trees (Persea americana Mill.) on `Waldin' rootstock were exposed to O3 and acid rain for 8 months in open-top chambers under field conditions. The O3 treatments were one-third ambient (0.3X), ambient (1X), twice ambient (2X), or thrice ambient (3X). Ambient O3 concentrations averaged 39.1 nl·liter-3 over a 12-hour day. The acid rain treatments had a pH of 3.3, 4.3, or 5.3 and were applied to simulate long-term rainfall averages. In general, the effects of acid rain on growth and freeze resistance were small. Rain of high acidity (pH = 3.3) offset the negative effects of O3 on growth (total leaf mass) in avocado and grapefruit/Volkamer lemon trees. In contrast, rain of high acidity magnified the detrimental effects of O3 on electrolyte leakage of leaf disks at subzero temperatures, especially for citrus. Freeze resistance, determined by stem and whole-plant survival following freezing temperatures, was lower in the most rapidly growing trees. Consequently, for trees exposed to a combination of O3 and acidic rain, leaf electrolyte leakage did not correlate significantly with stem survival of freezing temperatures. We conclude that the danger of acid rain to citrus and avocado in Florida is rather slight and would only present a potential problem in the presence of extremely high O3.

Carbohydrate changes in shortleaf pine (Pinusechinata) needles exposed to acid rain and ozone

Four genotypes of shortleaf pine (Pinusechinata Mill.) were grown in open-top chambers in the Piedmont Region of South Carolina. The seedlings were exposed to several combinations of ozone (near zero, ambient, 1.7 × ambient, or 2.5 × ambient) and acid rain (pH 3.3, 4.3, or 5.3). Glucose, sucrose, total reducing sugars, and starch contents of the pine needles were determined initially and at 5- to 12-week intervals during the following 38 weeks of exposure. Needles exposed to acid rain and ozone treatments followed the seasonal trends normally encountered in carbohydrate content, but there were some statistically significant differences in the quantities of individual carbohydrate components after prolonged exposure. In general, those needles exposed to higher levels of ozone (1.7 or 2.5 × ambient) had lower levels of starch and sucrose, with higher levels of both glucose and total reducing sugars. The starch levels in needles exposed to elevated ozone showed decreased values throughout the dormant period at all pH levels. Similarly, the sucrose levels were significantly lower in the high ozone and high acid rain treatment after 38 weeks of exposure. These results indicate that air pollutants may be affecting the carbon allocation balance within the needles.

Effect of simulated acid rain on the epicuticular wax of Scots pine needles under northerly conditions

The long-term effects of simulated acid rain treatment (pH 4 and pH 3) on the physicochemical characteristics of the needle surfaces in a natural stand of Scots pine was investigated in the extreme north of Finland during the period 1985–1988. By the end of this period, the pH 3 treated pines had received a sulphur load of 7.48 g m−2 and a nitrogen load of 2.62 g m−2, and the pH 4 treated pines a sulphur load of 1.23 g m−2 and a nitrogen load of 0.43 g m−2 in addition to ambient deposition. No visible symptoms of acid rain injury were observed in the needles, but their growth was significantly reduced. Delayed development of the epistomatal waxes and four types of deformed stomatal complex, namely narrow, half-formed, occluded, and double-sized, were found by scanning electron microscopy. The total number of deformed stomatal complexes in the pH 4 treated pine needles was over 50% greater than in dry control specimens and over 70% greater than in water controls. The rapid erosion of young, undeveloped waxes increased needle wettability (11%) significantly, but the quantity of chloroform-soluble waxes had decreased only slightly. The effects of acid rain on the epicuticular waxes were accentuated during unfavourable growing seasons with reduced effective temperature sums. Key words: acid rain, Scots pine, epicuticular wax, wettability.

Biological processes in two beech forest soils treated with simulated acid rain—a laboratory experiment with Isotoma tigrina (insecta, collembola)

The effect of simulated acid rain on soil biotic processes was studied in a beech forest on moder soil using experimental chambers containing intact soil cores sampled in the Soiling research area (Germany). Substrate from a limed area was included in order to analyse the influence of a modified state of base saturation on the reaction of soil organisms to acid rain. Water adjusted to pH 4.15 with H 2SO 4 was applied to the control treatments to simulate the proton deposition by precipitationand water adjusted to pH 2.95 was applied to the acid rain treatments to simulate the proton input by stemflow water. In the acid treatment of the natural soil, CO 2-C production, C mineralization of the litter colonizing microflora, microbial biomass in the F layer and leaching of nitrate-N were reduced. In contrast, the metabolic quotient of the F microflora as well as leaching of mineral-N (ammonium-N + nitratc-N) were increased by acid rain. According to its effect on CO 2-C production in the L layer as well as on (he mineralization of 14C-labelled beech litter, the negative effect of acid rain on the early stage of litter decomposition was especially strong. After termination of the acid rain regime, the litter colonizing microflora responded rapidly and their 14CO 2 production approached that of the controls within 3 weeks. The collcmbolan species Isotoma Harma reduced C mineralization of the litter colonizing microflora, diminished the biomass and the metabolic quotient of the microflora in the F layer and accelerated the leaching of mincral-N in the pH 4.15 treatment of the natural soil. For many properties measured these effects were significantly different in the lime and in the pH 2.95 treatments. In the acid rain treatment of the natural soil, I.tigrina diminished the acid-induced leaching of mineral-N and accelerated the recovery of the litter colonizing microflora after acid rain had been terminated. The mesofauna may thus form an important part of the biological buffering system in the organic layer of acid soils. In the limed soil, the effect of acid rain on many of the properties measured was less pronounced than in the natural soil. It was thus concluded that liming of acid forest soils increases the buffering capacity of biotic processes against acid stress. However, the buffering effect on the early stage of litter decomposition was diminished by the fact that in the limed soil, in contrast to the natural soil. the litter-colonizing microflora was not able to respond rapidly after termination of the acid rain regime. In contrast to its effect in the natural soil, I. tigrina did not accelerate recovery.