Coniferous Forest Humus Research Articles

Manganese availability is negatively associated with carbon storage in northern coniferous forest humus layers

Carbon sequestration below ground depends on organic matter input and decomposition, but regulatory bottlenecks remain unclear. The relative importance of plant production, climate and edaphic factors has to be elucidated to better predict carbon storage in forests. In Swedish forest soil inventory data from across the entire boreal latitudinal range (n = 2378), the concentration of exchangeable manganese was singled out as the strongest predictor (R2 = 0.26) of carbon storage in the extensive organic horizon (mor layer), which accounts for one third of the total below ground carbon. In comparison, established ecosystem models applied on the same data have failed to predict carbon stocks (R2 < 0.05), and in our study manganese availability overshadowed both litter production and climatic factors. We also identified exchangeable potassium as an additional strong predictor, however strongly correlated with manganese. The negative correlation between manganese and carbon highlights the importance of Mn-peroxidases in oxidative decomposition of recalcitrant organic matter. The results support the idea that the fungus-driven decomposition could be a critical factor regulating humus carbon accumulation in boreal forests, as Mn-peroxidases are specifically produced by basidiomycetes.

Behaviour of 137Cs in forest humus detected across the territory of the Czech Republic

The activity concentration of 137Cs in samples of coniferous forest humus collected across the territory of the Czech Republic in 1995 and 2005 was analysed, and it was found significantly correlated with the surface deposition caused by the Chernobyl accident. The effective (12.8 y) and environmental (22.3 y) half-lives of radiocaesium in humus were calculated and compared with those in spruce bark. The impact of important forest stand factors, that is, precipitation, content of organic matter, age of trees and pH, on the behaviour of 137Cs in humus was studied. It was observed that humus samples with a higher proportion of organic matter, higher pH(H2O) and pH(CaCl2) contained higher amounts of 137Cs. Conversely, with the age of trees, the activity concentration of 137Cs in humus is decreasing. Higher precipitation and humus acidity decrease the reduction rate of the 137Cs in humus. These stand factors increase bioavailability of 137Cs in humus. The transfer and retention of available 137Cs in biomass of organisms living in humus for a long time can satisfactorily explain the longer residence time of 137Cs in humus affected by the studied factors.

Cadmium in upland forests after vitality fertilization with wood ash?a summary of soil microbiological studies into the potential risk of cadmium release

The use of wood ash in forestry has been questioned because of the potential risk associated with its cadmium (Cd) content (1–30 mg kg−1). In agriculture, wood ash is only allowed for use as a fertilizer when its Cd content is below 3 mg kg−1. This restriction has not been applied to forest soils and there is a lack of knowledge about the potentially harmful effects of the Cd in wood ash on forest ecosystems. This paper summarizes our recent studies on the microbial communities of boreal coniferous forest humus exposed to Cd-containing wood ash treatment. The main objectives of our studies were to test if the Cd in wood ash has the potential to affect the humus layer microflora of coniferous upland forests and if it has the potential to enter the human food chain. These objectives were tested both in laboratory and field experiments with ash and ash spiked with Cd (in laboratory 400 or 1,000 mg Cd kg−1 as CdO or CdCl2; in field 400 mg Cd kg−1 as CdO). In one study the dissolution of ash was accelerated by irrigating it with simulated acid rain (SAR). Wood ash increased humus layer pH and microbial activities (respiration or thymidine incorporation rates) and changed its microfloral community structure (Biolog, PLFA, 16S or 18S rDNA PCR-DGGE) in both laboratory and field experiments. Spiking ash with Cd induced no further changes in the above-mentioned variables compared to ash alone. The Cd added with wood ash did not become bioavailable as detected with a bacterial biosensor Bacillus subtilis BR151(pTOO24). The form and level of Cd added in the ash had no further effect on the microbiological variables studied. Irrigation of ash with SAR did not increase the amount of bioavailable Cd, although the dissolution rate of the ash was increased. The concentration of Cd in soil water and in the berries of Vaccinium uliginosum and V. vitis-idaea, and the amount of humus bioavailable Cd did not increase with applied ash or ash spiked with Cd although the ash spiked with Cd increased the amount of humus total and extractable Cd in the 4-year field study. Only the ash spiked with Cd and not the unspiked “normal” wood ash resulted in significantly higher Cd concentrations in the mushroom Lactarius rufus and a slight increase in the berries of Empetrum nigrum (first year only). In conclusion, the Cd in wood ash did not become bioavailable and harmful to forest soil microbes, or leach into the humus layer even when treated with simulated acid rain. It is thus safe to use wood ash as a fertilizer in forests. However, since wood ash adds Cd to the environment, it is recommended that the same sites should not be fertilized with wood ash more than once. The effects of wood ash (3 t ha−1) on forest soil humus layer microbes are long-term, lasting at least 20 years, and probably longer if higher application dose and/or hardened ash is used.

Element concentrations in boreal, coniferous forest humus layers in relation to moss chemistry and soil factors

Concentrations of 15 elements (Al, Ca, Cd, Cr, Cu, Fe, K, Mg, Mn, Na, Ni, P, Pb, S and Zn) in the current annual growth increments of the ectohydric feather moss, Hylocomium splendens, were compared with those in the humus layer (Of+Oh) of coniferous forests at 353 sites throughout Finland. Moss concentrations in the moss increments were considered measures of atmospheric deposition of these elements. Concentrations in both moss and humus layer samples were negatively correlated with latitude, except Mn (moss) and Cr and Ni (humus layer), indicating a direct effect of deposition. Spearman correlations between concentrations in moss and humus layer samples were significant (P<0.05) for all elements; that for Pb concentrations was the highest (rs=0.60) while those for the other elements were ≤0.48. Using thickness and organic matter content of the humus layer, clay content of the mineral soil (5–20 cm layer) and the concentration in the moss explained between 8% (Cd) and 44% (Cr, Mg) of the variation in the concentrations in the humus layer samples. It was concluded that, for most elements, concentration in the humus layer are a poor indicator of current atmospheric deposition levels, at least in relatively unpolluted regions such as Finland.

Decomposition rate of organic substrates in relation to the species diversity of soil saprophytic fungi.

Despite the great interest concerning the relationship between species diversity and ecosystem functioning, there is virtually no knowledge as to how the diversity of decomposer microbes influences the decomposition rate of soil organic matter. We established a microcosm study in which the number of soil fungi was investigated in relation to the system's ability to (i) degrade raw coniferous forest humus, and (ii) use resources that were either added to the systems or released into the soils after a disturbance (drought). With the exception of the most diverse treatment, in each of the six replicates of each of the six diversity treatments (1, 3, 6, 12, 24 or 43 taxa), fungal taxa were randomly chosen from a pool of 43 commonly isolated fungal species of raw humus. Two months after initiation of the study CO2 production increased as fungal diversity increased, but in the species-poor end of the diversity gradient only. Addition of various energy resources to the microcosms generally increased the level of soil respiration but did not affect the shape of the diversity-CO2-production curve. Rewetting the soil after severe drought resulted in a rapid flush of CO2, particularly in the most diverse communities. The biomass of the fungi in the non-disturbed soils, and soil NH4-N concentration and soil pH in both disturbed and non-disturbed systems were slightly but significantly higher in the diverse than in the simple systems. Fungal species richness had no influence on the organic matter content of the humus at the end of the experiment. The results suggest that the functional efficiency of fungal communities can increase with the number of fungal taxa. This diversity effect was, however, significant at the species-poor end of the diversity gradient only, which implies considerable functional equivalency (redundancy) among the decomposer fungi.

Cadmium-containing wood ash in a pine forest: effects on humus microflora and cadmium concentrations in mushrooms, berries, and needles

The cadmium (Cd) concentration of wood ash (1–30 mg·kg–1) is higher than allowed for agriculture fertilizers (3 mg·kg–1). Therefore, the objectives of this field study were to test if the Cd of wood ash has the potential to affect the coniferous forest humus microflora and if Cd enters the human food chain. These objectives were tested with ash (A) and Cd-spiked ash (ACd, 400 mg Cd·kg–1) at a fertilization rate of 3 t·ha–1. Microbial community structure, respiration, needle litter decomposition, growth rates and Cd tolerance of bacteria, and the bioavailability of Cd were measured. Also, Cd concentrations of humus, soil percolation water, mushrooms, fruits and leaves of berries, and needles were determined. The amount of Cd in the percolation water or bioavailable Cd, measured with a bacterial biosensor, and Cd tolerance of bacteria did not increase, although the ACd treatment increased the amount of humus total and extractable Cd. Only the ACd and not the A treatment caused Cd concentration increment in Lactarius rufus and berries of Empetrum nigrum. In spite of the high Cd concentration of the spiked ash, it did not have harmful effects on humus microorganisms during this 4-year study. Thus, wood ash is safe to use as a fertilizer in forests.

Wood ash fertilization alters the forest humus Archaea community

The combined and separate effects of Cd and wood ash on Archaea from coniferous forest humus were studied in a microcosm experiment. Nonmetric multidimensional scaling of the denaturing gradient gel analysis of polymerase chain reaction amplified 0.9 kb 16S ribosomal DNA fragments revealed changes in archaeal communities due to the ash treatments. Cd with or without ash did not further influence the result. Representatives of the ash and control communities were cloned, grouped by restriction fragment length polymorphism analysis and finally sequenced. All sequences belonged to non-thermophilic Crenarchaea.

Does simulated acid rain increase the leaching of cadmium from wood ash to toxic levels to coniferous forest humus microbes?

Abstract Wood ash contains Cd in concentrations not permitted for fertilization use in agriculture (>3 mg kg(-1)). It has been shown that spiking ash with Cd to concentrations of 1000 mg kg(-1) induced no further changes in humus microbial activity and community structure as ash alone. To accelerate the weathering process and thus to liberate the spiked Cd from the ash, three treatments - wood ash (A), Cd spiked wood ash (ACd, 1000 mg Cd kg(-1) ash), both applied at a fertilization rate of 5000 kg ha(-1), together with a control (C) - were performed in microcosms and incubated in field condition under two types of irrigation - water and simulated acid rain. During the incubation period of one growing season the simulated acid rain plots received a sulfur load of 3.64 g S m(-2), which was 15 times more than the S deposition on the water irrigated plots. The treatments resulted in a mean Cd increase of the humus from 0.23 mg kg(-1) of the C treatment to 0.52 and 39.5 mg kg(-1) of the A and ACd treatments, respectively. The irrigation had no further effect on the result. The microbial activity, measured as soil basal respiration, and the microbial community structure, measured as humus phospholipid fatty acid and 16S and 18S polymerase chain reaction/denaturing gradient gel electrophoresis patterns, changed only due to the ash (A and ACd treatments) fertilization irrespective of the irrigation. The bacterial biosensor, emitting light in the presence of bioavailable Cd, did not react to any of the treatments. This result shows that Cd in ash was not leached into the humus due to increased deposition of acidified rain.

Does simulated acid rain increase the leaching of cadmium from wood ash to toxic levels to coniferous forest humus microbes?

Wood ash contains Cd in concentrations not permitted for fertilization use in agriculture (>3 mg kg −1). It has been shown that spiking ash with Cd to concentrations of 1000 mg kg −1 induced no further changes in humus microbial activity and community structure as ash alone. To accelerate the weathering process and thus to liberate the spiked Cd from the ash, three treatments – wood ash (A), Cd spiked wood ash (ACd, 1000 mg Cd kg −1 ash), both applied at a fertilization rate of 5000 kg ha −1, together with a control (C) – were performed in microcosms and incubated in field condition under two types of irrigation – water and simulated acid rain. During the incubation period of one growing season the simulated acid rain plots received a sulfur load of 3.64 g S m −2, which was 15 times more than the S deposition on the water irrigated plots. The treatments resulted in a mean Cd increase of the humus from 0.23 mg kg −1 of the C treatment to 0.52 and 39.5 mg kg −1 of the A and ACd treatments, respectively. The irrigation had no further effect on the result. The microbial activity, measured as soil basal respiration, and the microbial community structure, measured as humus phospholipid fatty acid and 16S and 18S polymerase chain reaction/denaturing gradient gel electrophoresis patterns, changed only due to the ash (A and ACd treatments) fertilization irrespective of the irrigation. The bacterial biosensor, emitting light in the presence of bioavailable Cd, did not react to any of the treatments. This result shows that Cd in ash was not leached into the humus due to increased deposition of acidified rain.

Short and long-term effects of wood ash on the boreal forest humus microbial community

The short-term effects of loose and hardened wood ash on the coniferous forest humus layer microbes were studied 1–3 years after fertilization. The experiment was performed using two fertilization levels (3 and 9 t ash ha −1) and repeated in two coniferous forest stands of different site fertility. It was hypothesized that the effects of hardened wood ash on soil microbes are of less magnitude when compared to loose ash due to the slower dissolution rates. The long-term effects of loose ash (3 t ash ha −1) were studied in four forest stands of different site fertility 18 years after ash application. In order to study ash effects, the microbial activity (basal respiration- and thymidine incorporation rates) and microbial community structure (PLFA pattern) were determined. The results showed that irrespective of the forest site fertility, ash fertilization induced the same responses in the humus layer. It raised the microbial activity and changed the community structure. The changes were related to the dose and form of ash applied. Applying the same fertilization rate induced comparatively more changes to the loose wood ash sites than hardened wood ash sites, due to the detected slower dissolution of hardened ash into the humus. The effects of wood ash were long-term. Changes in the humus microbial activity and PLFA pattern were still detectable after 18 years.

Influence of soil fauna and habitat patchiness on plant (Betula pendula) growth and carbon dynamics in a microcosm experiment.

We tested (1) how the presence of a diverse soil faunal community affects ecosystem carbon balance and (2) whether habitat patchiness modifies the influence of soil fauna on plant growth and carbon dynamics. We constructed cylindrical microcosms that contained coniferous forest humus and different litter materials either mixed or in separate patches, and in the presence or absence of diverse soil mesofauna. A birch seedling was planted in the centre of each microcosm. The experiment continued for two growing periods during which net carbon assimilation was measured continuously. At the end of the experiment, the microcosms were destructively sampled for plant biomass, soil fauna, and soil physical and chemical properties. All systems, independently of treatment, were net CO2 producers in the beginning. In the presence of a diverse fauna, the plant growth was drastically increased, and the mixed-litter systems respired more than the patchy ones. During the second season, the patch effect disappeared, while the birch seedlings and mosses continued to grow better in the microcosms with diverse fauna. In the long term, patchiness did not modify the effect of fauna on plant growth or carbon balance. By the end of the experiment, the carbon balance approached zero in the refaunated microcosms, while it remained negative in the "simple" systems. The weak impact of patchiness in comparison to the faunal effect may be due to a homogenising role of plant roots and progressive decay of the substrates.

Microbial communities in boreal coniferous forest humus exposed to heavy metals and changes in soil pH—a summary of the use of phospholipid fatty acids, Biolog® and 3H-thymidine incorporation methods in field studies

This paper summarises our recent field studies on the microbial communities of boreal coniferous forest humus exposed to environmental stress, heavy metals and changes in humus pH. The microbial community was measured using the phospholipid fatty acid (PLFA) and Biolog® analyses, and the actual factor in the environment exerting the selective pressure on the bacterial community was estimated with the help of tolerance determinations using the 3H-thymidine incorporation technique. The field experiments showed that the structure of the microbial community inhabiting the boreal coniferous forest humus was influenced by changes in humus pH and heavy metal concentrations at levels where no, or only small, effects on the microbial biomass or carbon mineralization rate were seen. The alterations in the humus PLFA patterns were related to the abundance of the major groups of microorganisms, bacteria and fungi. Changes in the relative proportions of Gram-negative and Gram-positive bacteria, including actinomycetes, were also shown. With the help of the 3H-thymidine incorporation technique, it was demonstrated that forest humus bacterial communities exposed to heavy metals or alterations in humus pH were able to adapt to the environmental disturbance in question. When combining the results from the PLFA and 3H-thymidine analyses, it was revealed that the increased tolerance of the humus bacterial community to heavy metals or to altered pH resulted at least partly from a change in microbial species composition. Coniferous forest humus seemed to contain a bacterial group, consisting mainly of Gram-positive bacteria, which were adapted more easily to the acidifying environment and a group of bacteria, mainly Gram-negative ones, which were more easily adapted to the humus with a higher pH. The Biolog® technique, which determines the community level physiological profile (CLPP) of the bacterial community was less sensitive and less suitable than the PLFA analysis to detect the characteristics of the forest humus microbial community. The 3H-thymidine incorporation technique was the most sensitive of the techniques used in this study to detect the influence of environmental disturbances on the microbial community. In addition, a gradient of coniferous forest stands having naturally different humus pH because of the different site properties was studied to compare these natural microbial communities with the communities subjected to anthropogenic change in humus pH. In order to reveal the similarity of the humus samples with respect to their community structure, the PLFA patterns from all the field studies were subjected to multivariate cluster analysis. The structure of the forest humus microbial community was shown to be strongly influenced by the indigenous fertility of the coniferous forest site type, which was in turn related to humus nutritional status, pH, moisture, tree species and ground vegetation. Thus, a prerequisite for successful determination of the impacts of environmental stress on forest humus microbial community is the homogeneity of the forest site types between the experimental plots.

Effects of temperature and moisture fluctuations on an experimental soil microarthropod community

Summary We established an experiment in microcosms with coniferous forest humus and birch leaf litter for testing the effects of constant vs. diurnally fluctuating temperature and uniform vs. varying moisture, on the population densities and species richness of Collembola and Mestostigmata. These parameters and the vertical distribution of populations were analysed by layers (top, centre, bottom) at two samplings (weeks 10 and 27). The hypotheses were that populations of at least some species benefit from fluctuating microclimate, and that varying conditions permit more species to coexist than uniform conditions. At fluctuating temperature regime, four species and total Collembola were more abundant, and species richness of Collembola was higher. One mite species and total Mesostigmata were more numerous at constant temperature. One collembolan species was more abundant at varying moisture, and one mite species at constant moisture. We conclude that the data support our hypotheses, though the observed differences between treatments were not very marked. Some species appeared to share their environment vertically.

Effect of Cd-containing wood ash on the microflora of coniferous forest humus.

The use of wood ash in forestry has been questioned because the cadmium (Cd) concentration of ash, which varies between 1 and 20 mg kg(-1) ash, exceeds the level allowed for fertilizers (3 mg kg(-1)) used in agriculture. To investigate the combined and separated effects of Cd and ash on the forest humus microflora, pumice or wood ash, spiked with a water-soluble (CdCl(2)) or -insoluble (CdO) form of Cd at three levels (0, 400 and 1000 mg kg(-1)), were applied at a fertilization level of 5000 kg ha(-1) in a laboratory microcosm study. The trial consisted of 60 microcosms (five replications per treatment), which were incubated in darkness at +20 degrees C and a constant relative air humidity of 60%. After two months the humus in the microcosms was sampled. Analyses of CO(2) evolution to measure the overall microbial activity and of phospholipid fatty acid (PLFA) pattern to measure microbial community structure were performed. The substrate-use patterns of Biolog EcoPlates were analyzed as a measure of bacterial functionality. Finally the bacterial (3)H-thymidine incorporation in the presence of different concentrations of Cd and the number of colony forming units (cfu) of bacteria on nutrient agar in the presence of 0, 5 and 20 mg Cd l(-1) agar were applied to measure Cd tolerance. The use of pumice (pH of humus under the pumice 4.0) did not induce any changes in the above variables compared to two untreated microcosms (humus pH 3.9). Pumice was therefore used to distribute the Cd evenly over the humus surface in order to estimate the possible effect of Cd without ash (pH of humus under the ash 7.0). The application of ash increased the microbial activity, changed the PLFA and substrate-use patterns and increased cfu compared to the humus under pumice. The form and level of Cd in the ash had no further effect on this result. In the humus under pumice the level, but not the form of Cd decreased the microbial activity and changed the PLFA pattern compared to the unspiked pumice. None of the treatments induced bacterial tolerance to Cd. Ash thus protected the humus microflora from the harmful effects of Cd.

Effect of Cd-containing wood ash on the microflora of coniferous forest humus

The use of wood ash in forestry has been questioned because the cadmium (Cd) concentration of ash, which varies between 1 and 20 mg kg −1 ash, exceeds the level allowed for fertilizers (3 mg kg −1) used in agriculture. To investigate the combined and separated effects of Cd and ash on the forest humus microflora, pumice or wood ash, spiked with a water-soluble (CdCl 2) or -insoluble (CdO) form of Cd at three levels (0, 400 and 1000 mg kg −1), were applied at a fertilization level of 5000 kg ha −1 in a laboratory microcosm study. The trial consisted of 60 microcosms (five replications per treatment), which were incubated in darkness at +20°C and a constant relative air humidity of 60%. After two months the humus in the microcosms was sampled. Analyses of CO 2 evolution to measure the overall microbial activity and of phospholipid fatty acid (PLFA) pattern to measure microbial community structure were performed. The substrate-use patterns of Biolog EcoPlates were analyzed as a measure of bacterial functionality. Finally the bacterial 3H-thymidine incorporation in the presence of different concentrations of Cd and the number of colony forming units (cfu) of bacteria on nutrient agar in the presence of 0, 5 and 20 mg Cd l −1 agar were applied to measure Cd tolerance. The use of pumice (pH of humus under the pumice 4.0) did not induce any changes in the above variables compared to two untreated microcosms (humus pH 3.9). Pumice was therefore used to distribute the Cd evenly over the humus surface in order to estimate the possible effect of Cd without ash (pH of humus under the ash 7.0). The application of ash increased the microbial activity, changed the PLFA and substrate-use patterns and increased cfu compared to the humus under pumice. The form and level of Cd in the ash had no further effect on this result. In the humus under pumice the level, but not the form of Cd decreased the microbial activity and changed the PLFA pattern compared to the unspiked pumice. None of the treatments induced bacterial tolerance to Cd. Ash thus protected the humus microflora from the harmful effects of Cd.

Responses of co-occurring populations of Dendrobaena octaedra (Lumbricidae) and Cognettia sphagnetorum (Enchytraeidae) to soil pH, moisture and resource addition

Summary Dendrobaena octaedra (Lumbricidae) and Cognettia sphagnetorum (Enchytraeidae) are the two most dominating soil invertebrates in terms of biomass in boreal coniferous forest soils. A microcosm experiment was set up in order to study the influence of pH, moisture and resource addition on D. octaedra and C. sphagnetorum when both species are simultaneously present. Two kinds of coniferous forest humus were used as substrate, pine stand humus (pH 4.2), and spruce stand humus (pH 4.6); in the third treatment the pine stand humus was adjusted with slaked lime (CaOH 2 ) to the same initial pH as the spruce stand humus. Each substrate was adjusted to water contents of 25%, 42.5% and 60% of WHC (referred to as ‘dry’, ‘moist’ and ‘wet’). In the second part of the experiment, spruce needle litter and birch leaf litter were separately added into the pine stand humus (‘moist’, unlimed) and compared with a control without litter. The microcosms were plastic jars with 75 g (d.m.) of humus, into which 4 specimens of D. octaedra and 70 specimens of C. sphagnetorum were added. D. octaedra showed the highest biomass and C. sphagnetorum the lowest biomass in the spruce stand humus with higher pH. Moisture did not affect earthworms, while C. sphagnetorum thrived best at the highest moisture. Addition of both kinds of litter increased the numbers and biomass of D. octaedra , while on C. sphagnetorum resource addition had little effect. The results help to explain the abundance of these two species in coniferous forests differing in soil acidity, moisture and fertility.

Plant effects on the soil community: A microcosm experiment

An experiment was carried out in microcosms for testing the hypothesis that a higher level of primary production should maintain a decomposer community with higher biomass and activity. Microcosms with coniferous forest humus and a diverse microbial and faunal community were divided into three sets: (1) control without plants, (2) with birch seedlings in full illumination, and (3) with birch seedlings, shaded to reduce the net primary production. During 16 weeks of incubation at +16 °C, no treatment effects were found in numbers or biomass of taxonomic or functional groups of soil organisms, nor in the system respiration in darkness. The community structure of the shaded systems differed from that of the other two treatments (CCA analysis). High organic content of the soil and long time-lag in the system response were considered the main reasons for the small difference between the treatments.

Habitat patchiness affects decomposition and faunal diversity: a microcosm experiment on forest floor

Environmental heterogeneity has been intensively studied, but little is known about relationships between habitat patchiness and soil processes. The aim of this study was to investigate (1) the impact of patchiness of the litter layer on the decomposer community and litter decomposition rate, and (2) whether the impact of soil fauna on the rates of processes differs in relation to patchiness. An experiment was carried out in microcosms with coniferous forest humus and four kinds of litter with different C:N ratios or stages of decomposition, either separately (i.e. in patches) or mixed with each other. Microarthropod species diversity was better maintained in the patchy systems. In the absence of soil fauna, community respiration was higher in the patchy microcosms, but in the presence of fauna the opposite pattern was observed. The contribution of soil fauna to the rate of decomposition was clearly greater in the mixed litter systems. Based on the results, a hypothesis is presented that in the patchy litter layer the soil fungi can create connections between different materials located some centimeters apart, thus enhancing decomposition, while in the mixed litter the scale of millimeters is more appropriate for the soil fauna, known to accelerate the process rates.