Effects Of Soil Fauna Research Articles

Soil biodiversity for agricultural sustainability

We critically highlight some evidence for the importance of soil biodiversity to sustaining (agro-)ecosystem functioning and explore directions for future research. We first deal with resistance and resilience against abiotic disturbance and stress. There is evidence that soil biodiversity does confer stability to stress and disturbance, but the mechanism is not yet fully understood. It appears to depend on the kind of stress and disturbance and on the combination of stress and disturbance effects. Alternatively, community structure may play a role. Both possible explanations will guide further research. We then discuss biotic stress. There is evidence that soil microbial diversity confers protection against soil-borne disease, but crop and soil type and management also play a role. Their relative importance as well as the role of biodiversity in multitrophic interactions warrant further study. Henceforth, we focus on the effects of plant and soil biodiversity on nutrient and water use efficiencies as important ecological functions in agroecosystems. The available evidence suggests that mycorrhizal diversity positively contributes to nutrient and, possibly, water use efficiency. Soil fauna effects on nutrient and water use efficiencies are also apparent, but diversity effects may be indirect, through effects on soil structure. We present a conceptual diagram relating plant and soil biodiversity with soil structure and water and nutrient use efficiencies as a framework for future studies. We then consider how cropping systems design and management are interrelated and how management options might be interfaced with farmers’ knowledge in taking management decisions. Finally, we attempt to express some economic benefits of soil biodiversity to society as part of a wider strategy of conserving and using agrobiodiversity.

Bottom–up or top–down control in forest soil microcosms? Effects of soil fauna on fungal biomass and C/N mineralisation

A major question in soil ecology is whether soil food webs are regulated by resources or by predators, i.e. bottom–up (donor) or top–down controlled. We tested the hypothesis that meso- and macrofaunal soil predators can regulate fungivore populations and, thereby cause a top–down cascade effect on fungal biomass and decomposition/mineralisation processes in boreal forest soils. The study was performed as a microcosm experiment with two contrasting soils (humus layers), one poor and one rich in N, and with different combinations of fungivore and predator soil fauna added to “defaunated” soil. In comparison with control microcosms lacking mesofauna (but with nematodes and protozoans), the presence of a diverse Collembola and Oribatida fungivore community significantly reduced the FDA-active fungal biomass or tended to reduce the ergosterol fraction of the fungal biomass in the N-poor humus, but no clear effect could be detected in the N-rich humus. Fungivores as well as fungivores plus predators (a predator community consisting of gamasids, spiders and beetles or a subset thereof) reduced C mineralisation and increased net N mineralisation in both soils. The presence of predators (particularly gamasid mites) reduced collembolan numbers and alleviated the negative effect of fungivores on fungal biomass in the N-poor soil. In the N-rich soil, the presence of predators increased fungal biomass (ergosterol) in relation to the “defaunated” soil. Therefore, a top–down trophic cascade could be detected in the N-poor humus but not in the N-rich humus. Our results suggest that the degree of top–down control in soil fauna communities depends on resource quality and soil fertility.

SOIL FAUNA AND LEAF LITTER DECOMPOSITION IN TROPICAL RAIN FOREST IN XISHUANGBANNA, SW CHINA: EFFECTS OF MESH SIZE OF LITTERBAGS

Background and Aims The influence of soil fauna on litter decomposition is rarely explored in tropical rain forest. This study examined the effect of soil fauna on the decomposition of mixed substrate by litter bag technical at two tropical seasonal rain forest plots in Xishuangbanna,SW China in year of 2000. The following questions were considered in the present study: 1) What roles do soil fauna play in regulating litter mass loss and decomposition rate? 2) How do soil fauna influence litter nutrient release? Methods In order to examine the role of soil macro-mesofauna in mass loss and nutrient release of litter,litter bags with both fine mesh size (0.15 mm) that excludes the soil macro-mesofauna population from litter and coarse mesh size (2 mm) that allows soil fauna access to litter were used in this experiment. Mass loss and C,N,P,S,K,Ca,and Mg concentrations of leaf litter were determined from the litter in two different mesh size litterbags at monthly intervals. The soil fauna were extracted by hand and by heating the samples. Key Results Higher relative density and taxonomic diversity of total soil fauna were found in the bags with 2 mm mesh size (22.3-21.77 individuals and 2.67-2.83 orders per g of dry litter) compared to the bags with 0.15 mm mesh size (2.88-2.77 individuals and 0.27-0.28 orders per g of dry litter). Collembola and Acari were the most abundant group,and Hymenoptera(ant),Coleoptera,Hemiptera,Diptera,Diplopoda,Isopoda,Araneae,Pseudoscorpiones were common groups of soil fauna in litter bags with 2 mm mesh size. There were very few individuals of Collembola and Acari in the 0.15 mm litter bags. Our results suggested that soil macro-mesofauna contributed more to the decomposition of leaf litter in 2 mm litter bags than that in 0.15 mm litter bags. The higher mass loss rate (around 71%),decomposition rate (k=1.88-2.44),and nutrient release in litter bags with 2 mm mesh size than in litter bags with 0.15 mm mesh size (34%-35%,k= 0.48- 0.58) indicated a significant influence of soil macro-mesofauna on mass loss and nutrient release in tropical seasonal rain forest. The release rates of N,S and Ca that could be attributable to the soil macro-mesofauna were higher than other elements whereas K release rate that could be attributable to the soil macro-mesofauna was the lowest. Soil macro-mesofauna caused greater decreases in C/N and C/P ratios in litter bags with 2 mm mesh size than litter bags with 0.15 mm mesh size. There were negative relationships of the percentage of litter mass remaining with order richness and individuals abundance of soil fauna. However,a positive relationship between Shannon-Wiener index of soil fauna and the decomposition rate was found. Conclusions This study suggests that the presence of soil fauna accelerated plant litter decomposition in the tropical seasonal rain forest. The litter mass loss attributable to the soil macro-mesofauna was about 46%. The effects of soil macro-mesofauna on the nutrient release rates were different among elements. The diversity of soil fauna may have important ecosystem consequences,particularly in tropical rain forest.

Effects of soil fauna on litter decomposition

Forest litter is the physical makeup part of forest ecosystem. The rate of decomposition of forest litter is low in temperate and cool temperate zones. There is important significance to search and utilize the function of soil animals, in order to probe the material circulation and energy flow in forest ecosystem. We selected three kinds of mesh bag with different mesh size, in which, large pore mesh bag is large enough to permit the activities of all kinds of soil animals, medium mesh bag is designed to exclude the function of soil macrofauna, while small mesh bag is small enough to exclude the effects of any kind of soil animals as far as possible. The decomposition time is three years. The studying results show that: the decomposing speed of the bags with big meshes, under functions of all kinds of soil animals, faster than the bags with medium meshes, under functions of medium and small soil animals, as well as the bags with small meshes that excluding all possibility of functions of soil animals; in the process of decomposition of litter, relationship of the litter lost weight with number of soil animals is not obvious clearly; the degree of functions of soil animals to soft litter higher than hard litter; according to the analysis of diversity index, no regular changes will happen to the diversity of soil animals as the time of decomposing samples lengthen.

Soil ecological interactions: comparisons between tropical and subalpine forests.

Soil fauna can influence soil processes through interactions with the microbial community. Due to the complexity of the functional roles of fauna and their effects on microbes, little consensus has been reached on the extent to which soil fauna can regulate microbial activities. We quantified soil microbial biomass and maximum growth rates in control and fauna-excluded treatments in dry and wet tropical forests and north- and south-facing subalpine forests to test whether soil fauna effects on microbes are different in tropical and subalpine forests. Exclusion of fauna was established by physically removing the soil macrofauna and applying naphthalene. The effect of naphthalene application on the biomass of microbes that mineralize salicylate was quantified using the substrate induced growth response method. We found that: (1) the exclusion of soil fauna resulted in a higher total microbial biomass and lower maximum growth rate in the subalpine forests, (2) soil fauna exclusion did not affect the microbial biomass and growth rate in the tropical forests, and (3) the microbial biomass of salicylate mineralizers was significantly enhanced in the fauna-exclusion treatment in the tropical wet and the south-facing subalpine forests. We conclude that non-target effects of naphthalene on the microbial community alone cannot explain the large differences in total microbial biomass found between control and fauna-excluded treatments in the subalpine forests. Soil fauna have relatively larger effects on the microbial activities in the subalpine forests than in tropical dry and wet forests.

Community food web, decomposition and nitrogen mineralisation in a stratified Scots pine forest soil

A soil community food web model was used to improve the understanding of what factors govern the mineralisation of nutrients and carbon and the decay of dead organic matter. The model derives the rates of C and N mineralisation by organisms by splitting their uptake rate of food resources into a rate at which faeces or prey remains are added to detritus, a rate at which elements are incorporated into biomass, and a rate at which elements are released by organisms as inorganic compounds. The functioning of soil organisms in the mineralisation of C and N was modelled in the soil horizon of a Scots pine forest. The organic horizon was divided into three distinct layers, representing successive stages of decay, i.e. litter, fragmented litter, and humus. Each of the layers had a different, quantitative, biota composition. For each layer the annual C and N mineralisation rates were simulated and compared to observed C and N mineralisation rates from organic matter in stratified litterbags. Simulated C and N mineralisation was relatively close to measured losses of C and N, but the fit was not perfect. Discrepancies between the observed and predicted mineralisation rates are discussed in terms of variation in model parameter values of those organisms that showed the highest contribution to mineralisation rates. The measured, and by the model predicted, significant decrease in mineralisation rates down the profile was not explained by the biomass of the primary decomposers and only partly by the total food web biomass. Modelling results indicated that indirect effects of soil fauna, due to trophic interactions with their resources, are an important explanatory factor. In addition, the analyses suggest that community food web structure is an important factor in the regulation of nutrient mineralisation. The model provided the means to evaluate the contribution of functionally defined groups of organisms, structured in a detrital food web, to losses of C and N from successive decay stages.

Soil organic matter distribution as influenced by enchytraeid and earthworm activity

Loam and sandy soils, and the earthworm casts produced with 14C-labelled plant material in both soils, were incubated in airtight glass vessels with and without enchytraeids to evaluate the effects of soil fauna on the distribution and fragmentation of organic matter. After 1, 3, and 6 weeks, the amount of C mineralised was determined in soils and earthworm casts, and the soil was fractionated into particulate organic matter (POM), the most active pool of soil organic matter, after complete physical dispersion in water. The percentage weight of fine fractions (0–50 µm) was 67.4% in the loam soil. Sand (coarse, i.e. 150–2,000 µm and fine 50–150 µm) represented 87.2% of total weight in sandy soil, while the percentages of C (PC) were 23.2% in coarse POM (2,000–150 µm) and 11.9% in fine POM (150–50 µm). These percentages were higher than those in loam soil, i.e. 3.4% (coarse POM) and 5.4% (fine POM). The PC in coarse POM (9.50%) and fine POM (16.4%) remained higher in casts from sandy soil than in casts from loam soil (4.7% in coarse and 14.3% in fine POM). The highest percentages of 14C-labelled leaves were found in fine fractions, 55.9% in casts from loam soil and 48.8% in casts from sandy soil. The C mineralisation of the added plant material was higher in casts from the sandy soil (20.3%) than from the loam soil (13.5%). Enchytraeids enhanced C mineralisation in the bulk sandy soil, but did not affect the mineralisation of added plant material in either soil. The main enchytraeid effect was enhancement of the humification process in the bulk sandy soil, the casts from this soil, and the bulk loam soil.

Soil Fauna Transport Versus Radionuclide Migration

From a questionnaire on radioecological topics circulated in the framework of the IUR/EURADOS/EULEP Concerted Action supported by the EC it was concluded that the effect of soil fauna on the redistribution of radionuclides in soils has never been given sufficient attention. The limited data in existence suggest than faunal effects on displacement of radionuclides may be dominant over physicochemical migration. On the basis of a given dataset, an earthworm model is presented which shows that the activity decrease in the top soil layer due to bioturbation may compete with fast physicochemical migration at rates of 1 to 10 cm.y-1. The model represents a suggestion of how to treat faunal actions and what kind of data are necessary to operate such models.

Book review

For many decades in the late 20th century, the processes involved in the formation of soil organic matter (SOM) (also known as humification) constituted one of the most important areas of scientific inquiry in soil science. However, these processes have not been included in modern models of SOM dynamics, despite their relevance to quantifying carbon stabilisation (i.e., sequestration) in soil. Furthermore, modern models have focussed on mineralisation processes (e.g., mainly microbial heterotrophic respiration) and have not included the important effects of soil fauna that are known as key agents of SOM formation. To address these issues, we developed a modelling approach predicated on the existence of definable stoichiometric relations among the processes leading to SOM formation that are mediated by soil biota (e.g., correlations among biotic respiration, production of faunal excrement, and necromass as sources of SOM formation). Soil respiration, a core rate variable in all SOM models, was associated with the production of faunal by-products in soil food webs as precursors of stable SOM, specifically micro- and meso-faunal excrement, necromass, and earthworm casts. We developed a food-web based module, using a synthesis of decades of published data, to describe micro- and meso-faunal excrement and necromass production. We developed a separate module for anecic earthworms, with explicit representation of processes related to fresh casts. The contributions of these two modules were compiled and integrated with the ROMUL model of SOM dynamics, without changing the structure of the original model. These modules enabled calculation of the proportional contribution of faunal by-products to humification (i.e., recalcitrant SOM formation) and carbon sequestration. Testing of the new version of the model, known as Romul_Hum, showed consistent accumulation of faunal by-products in the “final” SOM fractions: the well-decomposed SOM of the organic soil horizons and the stable SOM of the mineral soil.

CO2 efflux from a Mediterranean semi-arid forest soil. II. Effects of soil fauna and surface stoniness

Many forest soils in the Mediterranean basin areshallow and contain high amounts of gravel in theorganic layers. Recent studies on soil organic matteraccumulation have shown high amounts of organic matteroccurring mainly in soils with high levels ofstoniness at the soil surface. The gravel layer mayaffect the microclimatic conditions of the soilsurface and probably the distribution and activity ofsoil fauna.

Decomposition of Crop Residues in Banana-Based Cropping Systems of Uganda

ABSTRACT In banana-based cropping systems of Uganda, complex strategies of organic resource management have developed. The traditional method of cultivation includes surface mulching the banana mats with the pseudostems, leaves and peels following harvests. Bananas are frequently intercropped and a wide range of other plant residues are retained as surface mulches. The most common of these intercrops are beans (Phaseolus vulgaris) and maize (Zea mays). The decomposition and nutrient release of banana pseudostems, leaves and peels, maize stover and bean trash was studied. Black plastic litter bags were placed in the field and recovered after 0, 2, 4, 8, 16 and 32 weeks. The effect of soil fauna was estimated by altering the screen openings of the litter bags (2 vs 5 mm). For fresh banana pseudostems, litter bags were place on the surface or buried to study the effect of soil incorporation. Litter materials were analysed for C, N, P, K and lignin. The results were fit to first order exponential decline and the decomposition coefficient (k) used to calculate the time to 50% mass and nutrient loss (t50). The organic resources decomposed in the order bean trash > banana peel > maize stover = banana pseudostems > banana leaves. Exclusion of soil macrofauna (2–5 mm) delayed decomposition of banana pseudostems, when applied as mulch. When field availability and tissue concentrations are taken into account, banana leaves and bean trash have the greatest potential to recycle N (25 and 29 kg ha−1 yr−1, respectively) and banana leaves and pseudostem recycle the greatest amounts of K (43 and 26 kg ha−1 yr−1). The combined contribution of banana leaves, pseudostems, maize stover and bean trash to recycling nutrients in this farming system was 69 kg N and 147 kg K ha−1.

Comparison of alternative farming systems. II. Earthworm population density and species diversity

Effects of soil fauna on soil quality are largely unknown. Our objective was to learn whether long-term soil management has significantly affected earthworm species and populations at two Iowa locations. Soil cores were collected in fall 1989, spring 1990, and fall 1990 from a long-term tillage study in Polk County, Iowa, involving monoculture of corn (Zea mays L.) with either no-tillage, fall disking, fall chisel plowing, or fall moldboard plowing. Species found wereLumbricus terrestris(L),Octolasion tyrtaeum(Savigny),Aporrectodea trapezoides(Duges),A. turgida(Eisen), andA. tuberculata(Eisen), withO. tyrtaeumdominant across all treatments. As the amount of tillage increased, the number of earthworms generally decreased. InBoone County, Iowa, we compared the populations of mature and immature earthworms and cocoons on two adjacent fields, one managed conventionally, the other managed with an alternative farming system for more than 20 years. The predominant species was A. tuberculata. Regardless of management practice, the most worms were found in Canisteo soil on the toeslope landscape position.

Soil Fauna Increase Betula Pendula Growth: Laboratory Experiments With Coniferous Forest Floor

The effects of soil fauna on the growth and nutrient contents of birch seedlings were studied in laboratory microcosms simulating the complexity of a coniferous forest floor. In one set of microcosms partially sterilized soil was reinoculated with soil microorganisms only; another set was reinoculated with microorganisms and a diverse soil fauna. A birch seedling (Betula pendula) was planted in each microcosm, all of which were incubated in a climate chamber with various temperature and illumination regimes. During two growing periods birch—leaf, stem, and root biomasses were 70%, 53%, and 38% greater, respectively, in the presence of fauna. The N and P contents of leaves were °3— and 1.5—times higher, respectively, in the refaunted microcosmms than in the controls with microorganisms only. The amount of K, Ca. and Mg in leaf tissue were almost the same in both treatments. Despite the greater leaf biomass, and therefore more effective transpiration, the water content of the soil remained significantly higher in the refaunted microcosms. The results clearly indicate that soil fauna, via enhanced nutrient mobilization and favorable changes in the structural soil properties, expert a positive influence on plant growth.

Soil fauna and soil structure

Significant effects of soil fauna on soil structure are achieved mainly by a few groups among the larger soil invertebrates that are widely distributed and generally present in large numbers. Of these groups the most important are earthworms, termites and ants. The review deals mainly with earthworms, which are distributed throughout all but the coldest and the driest regions of the world. The effects of termites and ants on soil structure are also discussed. These groups of soil animals are also widely distributed, but are most common and most effective in influencing soil structure in tropical and warm temperate regions. A brief section deals with the influence of microarthropods, which are commonly found in large numbers, but because of their small size are unable to make large burrows in the mineral soil horizons, and are largely confined to pre-existing voids in litter and surface soil horizons. Their faecal pellets are granular and largely organic, with little included mineral soil material, and they sometimes make up the major proportion of forest litter layers. Quantitative assessment of the influence of earthworms on soil structure is available, but information on other groups is largely qualitative. The burrows of earthworms contribute to macroporosity and so influence water infiltration and aeration. Anecic species, that live in semi-permanent burrows opening to the soil surface and feed at the surface, provide more or less vertical channels for water infiltration and gas exchange. Endogeic species, that burrow continuously in search of food within the soil, provide more horizontally oriented, frequently extensive and intersecting networks of macropores that promote water movement and gas diffusion. Burrows that penetrate soil surface crusts are particularly important for water entry to the soil. Water movement through pores of the dimensions of earthworm burrows is important only when rainfall or irrigation supplies water at rates that exceed the capacity of the soil surface for capillary uptake. The combination of increase in surface area available for capillary uptake through the burrow walls and of hydraulic pressure resulting from the column of water in a water-filled burrow increases infiltration. Occupied burrows of anecic species may be sealed with soil or plant litter by the resident earthworm when water is ponded on the soil surface, or blocked by the earthworm's body, so as to be ineffective for water infiltration. When burrows are air-filled they provide surfaces that penetrate below ground and facilitate gas exchange.

Effects of soil fauna on leaching of nitrogen and phosphorus from experimental systems simulating coniferous forest floor

Long-term experiments (97–98 weeks) were carried out in macrocosm systems simulating the complexity of coniferous forest soil. The macrocosms were partially sterilized by freezing, thawing and drying, then re-inoculated with microbes alone or microbes + soil fauna. Removable microcosms containing birch litter, spruce litter, or humus were inserted into the substrate humus in the macrocosms. Two experiments used organic matter only, and in the third there was mineral soil below the humus. The macrocosms were incubated in climate chambers that simulated both summer and winter conditions. At 4- to 6-week intervals the substrates were irrigated for analyses of pH, total N, NH 4 + −N, NO 3 − −N, and PO 4 3− −P in the leachates. At the end of each growing season a destructive sampling was performed, including analyses of KCl-extractable N and P. Leaching of NH 4 + and PO 4 3− from both the litter and the total systems was significantly enhanced by the soil fauna. There were also differences in mineralization of N and P between the refaunated systems, apparently due to divergent development of the faunal communities. In general, fauna affected KCl-extractable nutrients from the litter positively, although this effect was less evident than in the leaching water. In the humus and mineral soil the fauna significantly increased the release of N and P, especially in the later stages of the experiments. Soil pH was higher in the presence of fauna, but there was no difference in the pH of the leachates. Not only invertebrate-microbial interactions, but also mutual relationships among fauna were important in the nutrient dynamics.

The Effect of Soil Fauna on Litter Mass Loss and Nutrient Loss Dynamics in Arctic Tundra at Barrow, Alaska

Litterbags and arthropod defaunation techniques were used to evaluate the effects of soil—litter fauna on loss of dry matter and nutrient elements from native litter in arctic tundra. A control and a naphthalene—treated plot were established in each of three microhabitats. Faunal populations, litter dry mass and % N, and the concentration of Ca, Na, Mg, Mn, P, Zn, and K in the litter were measured from each litterbag. Litterbags were collected at 10—d intervals during the 1974 nonfrozen season and twice in 1975. Litter mass and nutrient loss differed among habitats and exhibited differing responses to defaunation, as did dry mass loss. Generally greater dry mass loss and less nutrient loss occurred from the litter in the control than in the corresponding defaunated plot. Nutrient loss was greater in plots that are subjected to natural periodic flooding than in plots never flooded. Loge regression lines of percent mass loss vs. days are reported for each plot on a calendar year and a nonfrozen season basis. Results of this study are compared with results from decomposition studies in other arctic and temperate systems.

Some pedological features affecting the permeability of hillside soils in Caydale, Yorkshire

AbstractWeekly interflow and permeability data were obtained for 15 sites in two field plots in North Yorkshire. Both plots are similar in terms of lithology, slope, micro‐relief, climate and soil type, one being dominated by rough pasture grasses and the second by bracken. One factor which explained 75 per cent of the variation in interflow was the difference between topsoil and subsoil permeabilities, the former always being the greater. This permeability difference is discussed in terms of soil texture, porosity and plant‐rooting systems. Textural contrasts are considered insufficient to cause the large‐scale variations in permeability observed throughout the year. Being a fixed variable, texture cannot influence a characteristic which varies from one week to the next. Contrasts in total porosity between topsoil and subsoil also effected no discernible influence on measured permeability differences, although measures of association increased as smaller pores were excluded from the analysis. Utilizing only those pores drained at 20 cm of water tension, highly significant correlations were established. In the plot dominated by bracken, greater ‘lateral permeabilities’ are produced by well‐developed systems of Pteridium rhizomes. As the advancing front of such rhizomes extends forwards at quoted rates of up to 45 cm/yr, the rear portions decay, leaving horizontal ‘tubes’ in the soil. Recognized omissions from this analysis are the effects of soil fauna and desiccation fissures.