Impact of landspread sewage sludge and earthworm introduction on established earthworms and soil structure

Summary Sewage sludge was applied to twelve 4-m² plots in two forest (mixed hardwood, Norway spruce plantation) site and one old field site. The earthworm Eisenia fetida was introduced to half the control and half the treated plots. Earthworm populations were sampled by formalin extraction and hand-sorting five times in the year following treatment. One year after treatment, soil samples were wet-sieved and water-stable aggregate size-class arrays were determined.The dominant earthworm in the study site, Lumbricus terrestris, increased in density and mean individual biomass in response to sludge treatment in mixed hardwood and old field plots. In the Norway spruce plots, L. terrestris increased in individual biomass but decreased in density following sludge application. The density of the introduced E. fetida rapidly declined in all control plots. One year after introduction, E. fetida was found only in the sludge-treated Norway spruce plot. The introduction of E. fetida with sludge decreased the density and biomass of L. terrestris in the hardwood plots.Sludge treatment increased the percentages of 4-mm diameter water-stable aggregates in old field and hardwood plots. The addition of E. fetida with sludge in the hardwood plots generated no increase in 4-mm water-stable aggregates. In the old field, sludge + E. fetida increased the 4-mm water-stable aggregates. Little change in water-stable aggregates in response to either treatment combination was seen in the Norway spruce site.     

Effects of repeated drought on soil microarthropod communities in the northern Chihuahuan Desert

 Soil microarthropods were sampled in plots centered on creosotebushes (Larrea tridentata) and in plots centered on mesquite (Prosopis glandulosa) coppice dunes. Nine plots in each area were covered by rain-out shelters with greenhouse plastic roofs which excluded natural rainfall and nine plots received natural rainfall. There were differences in the abundance of several mite taxa in soils from the mesquite coppice dune plots. Some taxa (Stigmaeidae, Nanorchestidae, and Entomobryidae) occurred in significantly lower numbers in the soils of the drought plots. Other taxa (Tarsonemidae and Cunaxidae) were more abundant in the drought plots in the mesquite coppice dunes. There were no significant differences in the abundance of any of the dominant taxa of soil microarthropods in the drought and control plots centered on creosotebush. In the creosotebush habitat, there were significantly fewer Prostigmata in the plots exposed to drought. In an area with both creosotebush and mesquite, there were no significant differences in microarthropod population responses to drought and in recovery from drought. The differences in responses of soil microarthropods to drought in creosotebush and mesquite habitats are attributed to the differences in soil stability, litter accumulations, and microclimate associated with the shrubs. Received: 29 December 1997     

Responses of soil microarthropods to changes in soil water availability in tallgrass prairie

 Changes in precipitation and soil water availability predicted to accompany global climate change would impact grasslands, where many ecosystem processes are influenced by water availability. Soil biota, including microarthropods, also are affected by soil water content, although little is known about how climate change might affect their abundance and distribution. The goal of this study was to examine soil microarthropod responses to altered soil water availability in tallgrass prairie ecosystems. Two separate experiments were done. The first utilized control and irrigated plots along a topographic gradient to examine the effects of soil water content on microarthropod densities. Microarthropods, mainly Acari, were significantly less abundant in irrigated plots and were generally less abundant at the wetter lowland sites. The second study utilized reciprocal core transplants across an east-west regional precipitation gradient. Large, intact cores were transplanted between a more mesic tallgrass site (Konza Prairie) and a more arid mixed-grass site (Hays) to determine the effects of different soil water regimes on microarthropod abundance and vertical distribution. Data from non-transplanted cores indicated greater total microarthropod densities at the drier Hays site, relative to the wetter Konza Prairie site. Data from the transplanted cores indicated significant effects of location on Acari densities in cores originating from Hays, with higher densities in cores remaining at Hays, relative to those transplanted to Konza. Acari densities in cores originating from Konza were not affected by location; however, oribatid mite densities generally were greater in cores remaining at Konza Prairie. These results confirm the importance of soil water content in affecting microarthropod densities and distributions in grasslands, and suggest complex, non-linear responses to changes in water availability. Received: 14 April 1998     

EFFECTS OF WATERSHED LIMING ON PICEA RUBENS SEEDLING BIOMASS AND NUTRIENT ELEMENT CONCENTRATION

Effects of watershed liming on the biomass and tissue chemistry of planted Picea rubens Sarg. (red spruce) seedlings were investigated for two growing seasons after two subcatchments in a forested Adirondack, New York (U.S.A.) watershed were limed aerially with 6.89 t ha^-1 of calcitic limestone (CaCO₃). Picea rubens has been the focus of numerous atmospheric deposition research studies, but less well investigated for responses to amelioration. Picea rubens seedlings were planted in limed and reference subcatchments and harvested the first and second growing season after liming to measure total, foliar, and stem (i.e., branch) biomass, and concentrations of Ca, Mg, K, Al, Na, and P in the annual growth increment of foliage and branches. In the second year after liming, both foliage and stem biomass of seedlings from reference plots were at least 50% greater than seedling biomass from limed plots. Seedlings in limed areas had significantly greater foliar concentrations of Mg and P in the first year after liming, but not in the second year. Foliar Ca was not significantly different in limed than reference seedlings. Foliar Al concentrations were greater in reference than limed seedlings, but still below documented toxicity levels. Stem concentrations of Mg, K, and P in seedlings from limed areas decreased significantly between the first and second growing season after liming, while reference seedling stem concentrations either increased or declined only slightly. Correlations among foliar nutrients and foliar biomass from limed plots were negative and suggest an inverse dilution effect. Foliar Al concentrations were negatively correlated with Ca, Mg, K, and P in seedlings from reference plots, but positively correlated in limed plots. The adverse response of P. rubens seedlings to lime may reflect changes in nutrient availability associated with changes in soil pH.     

Nutrients in forest litter treated with naphthalene and simulated throughfall: A field microcosm study

The effects of naphthalene (arthropod exclusion) and simulated throughfall (N, P, K, Ca and Mg) additions on the decomposition and mineralization of dogwood (Cornus florida L.) litter were studied by using a field microcosm approach in a southeastern United States deciduous forest. Treatments without microarthropods decayed more slowly than litter with microarthropods. Simulated throughfall additions alone had no effect on litter decay rates. Fauna, simulated throughfall, and fauna plus simulated throughfall treatments increased the nutrient concentrations of decomposing litter; the treatment with both microarthropods and simulated throughfall generally exhibited the highest nutrient concentrations. Simulated throughfall also significantly increased microarthropod densities in litter. Litter immobilization of elements in throughfall was insignificant in litter with microarthropods; naphthalene-treated litter immobilized up to 8% of the elements contained in simulated throughfall.     

Relationships among fine roots, fungal hyphae and soil microarthropods among different soil microhabitats in a temperate coniferous forest of Chamaecyparis obtusa

The relationships between roots and soil communities are not well understood. We used the ingrowth-core method with L-, FH-, and M-layer substrates to investigate the relationships among soil organic carbon, fine root biomass, hyphal length and the numbers of soil microarthropods. The study was carried out in a temperate forest of the arbuscular mycorrhizal conifer, Chamaecyparis obtusa. The relationships among fine roots, fungi and soil microarthropods were different among soil substrates and faunal taxa. Soil carbon contents, fine root biomass, hyphal length and soil-microarthropod numbers were the highest in the FH-substrate, and the lowest in the M-substrate. For each substrate, the total numbers of soil microarthropods did not positively correlated with soil organic carbon. A positive correlation between fine root biomass and the soil microarthropod numbers was significant only in the M-substrate, but not in the L- and FH-substrates. In M-substrates, strong positive correlations were found between fine root biomass or hyphal length and Mesostigmata or Oribatida numbers, but Collembola numbers were not corelated. Further studies of the regulation mechanism of soil food web structures should note that the soil microarthropods have different responses to C sources according to soil conditions and trophic interactions.     

From forest to fen: Microarthropod abundance and litter decomposition in a southern Appalachian floodplain/fen complex

Our study compared decomposition and litter microarthropod abundance among five plant communities in a mountain floodplain/fen complex located in the southern Appalachian Mountains, USA. We found that the least disturbed plant communities, red maple in particular, have the quickest decomposition, the greatest number of litter microarthropods, the highest soil organic carbon, and the lowest soil pH. Positive correlations were shown between soil organic carbon and total microarthropods; negative correlations were found between soil pH and total microarthropods. No correlations were found between soil moisture and decomposition or total microarthropod numbers. We conclude that soil characteristics related to disturbance, rather than to the presence of a closed canopy, are the main influences on decomposition and litter microarthropods.     

Five-year trends in soil arthropod densities in pine forests with various levels of vitality

Summary A comparative field study was conducted to study the correlation between forest vitality and the abundance of soil microarthropods. During 5 years the vitality of six pine forests within the Veluwe area, the Netherlands, was estimated by the number of needle year-classes, while soils were sampled and extracted for various soil microarthropod groups. Within sites the number of needle year-classes in the forest stands fluctuated over the 5 years, while the collembolan family Sminthuridae showed a trend towards a decreasing population density and the density of the cryptostigmatid mite Platynothrus peltifer Koch increased. Among sites there was a significant positive correlation between the number of needle year-classes and the relative abundance of P. peltifer. The results imply that soil microarthropods may indicate changes in physical and chemical factors in relation to soil fertility and vitality of the trees.     

Soil microarthropods as indicators of exposure to environmental stress in Chihuahuan Desert rangelands

 We studied soil microarthropod communities along livestock grazing disturbance gradients, inside and outside grazing exclosures, and on areas subjected to restoration efforts (herbicide and bulldozing) in order to test the suitability of mites as indicators of rangeland soil quality. We found that mite numbers generally increased with decreased grazing disturbance. Soil microarthropods appeared to respond to a complex of factors including soil compaction, depth to an impervious soil layer, below-ground vegetative biomass, and residual effects of herbicide. All of our study plots, except those that had been herbicide treated, were dominated by microbivorous mites of the family Nanorchestidae. The numerical responses of mites, especially nanorchestids, appeared to provide a sensitive indicator of ecosystem health in a Chihuahuan Desert grassland. Received: 29 December 1997     

Limited evidence for short-term succession of microarthropods during early phases of surface litter decomposition

Succession of microarthropods during the decomposition of organic matter is an important concept in soil biology. However, few studies have tested whether the pattern of microarthropod colonisation during decomposition is independent of season. We investigated the pattern of colonisation and dominance of microarthropods on decomposing organic matter placed at two different times. Litterbags containing canola leaf or stem material were placed on the soil surface of a Western Australian agricultural field in July and September 1999. They were collected weekly to fortnightly until November. A final set of bags was collected in May 2000. Mass loss and nutrient contents (C, N, Ca, K, P and S) were measured at each sample time. Microarthropods were sorted to order and the mites to species level. Nematode abundance was determined at each sample time. Mass loss of the leaf and stem material was similar between the two placement times (33% and 15% ash-free dry mass lost over 33 days from leaf and stem material, respectively), although the dynamics of nutrient loss for some elements was different between the two placements. However, over the dry summer, material placed in September continued to lose nutrients whilst there was little additional loss from the material placed in July. A similar pattern of dominance of microarthropod and mite species was found on the leaf and stem material placed in July with the succession of dominant animals more rapid on the stem material. Nematode abundance appeared to increase as populations of microarthropods declined over time. Populations of microarthropods on the material placed in the September samples never achieved similar levels of abundance to that of the July samples, and the dominant fauna groups were dissimilar to those in the July samples for the same degree of decomposition. Our data indicate that the early phase of surface litter decomposition is not a successional process in terms of the microarthropod community irrespective of season and, that abiotic factors are more likely to be determining nutrient loss from organic matter within particular seasons.     

Soil microarthropods are only weakly impacted after 13 years of repeated drought treatment in wet and dry heathland soils

Studies of biological responses in the terrestrial environment to rapid changes in climate have mostly been concerned with aboveground biota, whereas less is known of belowground organisms. The present study focuses on mites and springtails of heathland ecosystems and how the microarthropod community has responded to simulated climate change in a long-term field experiment. Increased temperature and repeated drought was applied for 13 years to field plots located in Wales, The Netherlands and Denmark representing sites of contrasting climatic conditions with respect to precipitation and temperature. This approach provided an opportunity to study biological responses on a local (within sites) and regional scale. Warming treatments increasing night time temperature (0.3–1 °C higher than ambient at 5 cm soil depth) had no detectable effects on the microarthropod communities. Increased intensity and frequency of drought had only weak persistent effects on springtail species composition, but practically no effect on major mite groups (Oribatida, Prostigmata or Mesostigmata) suggesting that ecosystem functions of microarthropods may only be transiently impacted by repeated spring or summer drought.     

Relating microarthropod community structure and diversity to soil fertility manipulations in temperate grassland

We aimed to identify patterns of diversity in a below-ground community of microarthropods (mites and Collembola) after 15 months of a nutrient (calcium and nitrogen) manipulation experiment, located at the Natural Environment Research Council (NERC) Soil Biodiversity Site in Scotland, UK. We found that microarthropod densities increased with elevated soil fertility, but we detected no concurrent change in the diversity of soil microarthropods (mites and Collembola combined). That microarthropod density increased concurrently with improvements in soil fertility and plant productivity suggests that soil microarthropod communities are predominately regulated by bottom-up forces, driven by increased energy transfer via plant inputs to soil, providing increased food resources for fauna. However, that we found no concurrent change in the diversity of soil microarthropods provides little support for the idea that the diversity of soil fauna is positively related to their population density, primary productivity or improvements in soil conditions resulting from nutrient manipulations. However, we did find that microarthropod communities of more fertile sites contained a greater proportion of predators suggesting that more energy was transferred to higher trophic levels under elevated soil fertility. Our findings suggest that unlike plant communities, soil faunal diversity may not be strongly regulated by competition in productive situations, since competitive exclusion might not occur due to increased predation. Whilst we conclude that soil microarthropod diversity at our study site has not been affected by the nutrient additions to date, in the longer term we predict that changes in community composition and diversity could arise, most likely through top-down regulation of the soil food web.     

Combined effects of abiotic factors on Collembola communities reveal precipitation may act as a disturbance

Global increases in temperature and atmospheric CO₂, coupled with increasingly sporadic and intense precipitation regimes, may affect the biodiversity of boreal forest communities, potentially leading to shifts in functional process rates such as decomposition. However, the effects of these factors on microarthropod community composition have not been thoroughly studied in combination in controlled settings. We conducted a full factorial experiment exposing moss/soil mesocosms to three temperatures (11.5, 15.5, and 19.5 °C), two CO₂ levels (430 ppm and 750 ppm), and three moisture levels (drought, intermediate, and saturated conditions) for 18 weeks. Following treatment, we quantified effects on species diversity of a representative group of mesofaunal microarthropods, the Collembola. We also quantified the effects of these factors on the distribution of collembolan body sizes as an indicator of functional changes in the community. We found that moisture regime was a dominant factor, with increased precipitation leading to decreased collembolan abundance and richness. The mechanisms of these detrimental effects are unclear but may be due to the saturation of air-filled soil pore space or competition with moisture-tolerant species. Severe precipitation regimes caused a general loss of abundance in species of all sizes, which may have long term effects on boreal forest soil food webs.     

Responses of springtail and mite populations to prolonged periods of soil freeze-thaw cycles in a sub-arctic ecosystem

The effect of temperature changes on soil communities is an important aspect when estimating the effects of a predicted climate change. The aim of this investigation was to increase knowledge on how freeze-thaw cycles alter the soil microarthropod community in the sub-arctic. The abundance of springtails and mites was investigated after three seasons of prolonged periods of freeze-thaw cycles in the field, and the presence or absence of migration barriers, at two different field sites. Dome shaped transparent plastic greenhouses were successfully used as a novel method to increase freeze-thaw cycle frequencies in the soil. At a fellfield site, freeze-thaw treatment did not lead to significant differences in the five main soil faunal groups, but increased abundance were seen in a number of separate taxa. There was no freeze-thaw treatment effect on soil microbial biomass or soil nutrients, although treatments interacted as inorganic N increased in the separate freeze-thaw and migration barrier treatments. By contrast, at a glade site responses were strong due to more pronounced increases in the number of freeze-thaw cycles. The highest numbers of Collembola after 2 years of treatment were found in the freeze-thaw plots, in combination with migration barriers. The freeze-thaw treatment here also resulted in more Oribatida, microbial biomass C and dissolved organic C. A common hypothesis is that an increased number of freeze-thaw cycles would result in elevated winter mortality in microarthropods due to increased risk of inoculative freezing. However, we observed no increased mortality due to freeze-thaw events. Rather, there was a stimulation of soil microarthropods and microbial biomass, perhaps due to a prolonged period of microbial and faunal activity when the soil is repeatedly frozen and thawed compared to a constantly frozen soil.     

Influence of two exotic earthworm species with different foraging strategies on abundance and composition of boreal microarthropods

In North America, many species of European earthworms have been introduced to northern forests. Facilitative or competitive interactions between these earthworm species may result in non-additive effects on native plant and animal species. We investigated the combined versus individual effects of the litter-dwelling earthworm Dendrobaena octaedra Savigny, 1826 and the deep-burrowing species Lumbricus terrestris L., 1758 on microarthropod assemblages from boreal forest soil by conducting a mesocosm experiment. Soil cores from earthworm-free areas of northern Alberta, Canada, were inoculated with D. octaedra alone, L. terrestris alone, both worm species together, or no earthworms. After 4.5 months, microarthropods were extracted from the soil, counted, and identified to higher taxa. Oribatid mites were further identified to family and genus. Abundance of microarthropods was significantly lower in the treatment containing both species than in the no earthworm treatment and the L. terrestris treatment. Oribatida and Prostigmata/Astigmata differed significantly among treatments and were lowest in the treatment containing both earthworm species, followed by the D. octaedra treatment, although post-hoc pairwise comparisons were not significant. Within the Oribatida, composition differed between the control and L. terrestris treatments as compared to the D. octaedra and both-species treatments, with Suctobelbella and Tectocepheus in particular having higher abundances in the control treatment. Effects of the two earthworm species on microarthropods were neither synergistic nor antagonistic. Our results indicate that earthworms can have strong effects on microarthropod assemblages in boreal forest soils. Future research should examine whether these changes have cascading effects on nutrient cycling, microbial communities, or plant growth.     

Changes in spatial distribution of fungal propagules associated with invertebrate activity in soil

Soil fungal species density and aggregation had changed 6 months after spring burning and raking in a Wisconsin prairie. Fungal species density had increased by 29% in burned relative to raked or undisturbed plots; species density was highest at the soil surface in burned and raked plots, and lowest at the surface in undisturbed plots. Fungal propagules of the same species were less aggregated in burned and raked plots than in undisturbed. These changes imply greater mixing of fungal propagules in soil of burned and raked plots than in undisturbed plots. The physical effects of burning and raking and the properties of fungal spores do not account for the changes. It is argued that soil invertebrates are responsible for the mixing because: (1) at any depth in soil, density of mites and collembola increased concurrently with fungal species density; and (2) path analysis shows that fungal species density is equally associated with microarthropod density and root biomass after burning, but after raking, fungal species density was more strongly associated with root biomass than microarthropods.     

Responses of soil microarthropods to inorganic and organic fertilizers in a poplar plantation in a coastal area of eastern China

Soil microarthropod community is an essential functional unit of soil food webs. Fertilizers can induce an alteration of quantity and quality of food for soil fauna and trigger profound changes in soil faunal communities. We initiated this study to examine the influence of organic and inorganic fertilizers on soil microarthropods in poplar plantations (Populus deltoides) in a coastal region of northern Jiangsu, eastern China. We established a control and four fertilizer application treatments: low and high levels of organic fertilizers, low and high levels of inorganic fertilizers. Organic fertilizer amendments increased both soil organic carbon (C) and total nitrogen (N), whereas inorganic fertilizer had a positive significant effect on soil total N. The application of both inorganic and organic fertilizers resulted in significantly reduced soil pH. We found that both inorganic and organic fertilizers increased the abundance of all soil microarthropods, bacterivorous Acari, and hemiedaphic and epedaphic Collembola, but had no influence on the total taxonomic richness, Shannon diversity index and DG diversity index of the microarthropod community. The abundance of soil microarthropods was positively correlated with soil C and N, and negatively with pH. Our results indicate that changes in the quality and quantity of soil organic matter and other immediate chemical properties after fertilizer application can increase the abundance of soil microarthropods, but have a limited influence on their diversity in the coastal alkaline soils of eastern China.     

Decomposition,nutrient loss and microarthropod densities in herbicide-treated grass litter in a Georgia piedmont agroecosystem

A litterbag experiment was made to investigate the influence of the herbicides atrazine, paraquat and glyphosate on several aspects of the decomposition of grass litter in a fallow field. Litter-bags containing dried Johnson grass (Sorghum halepense) leaves were dipped in herbicide solutions at recommended and 10 × recommended field application rates, placed in the field, and randomly collected every 3 weeks from July to November 1982. At the highest treatment levels of paraquat and glyphosate, the leaves showed slower weight loss, faster losses of P, Ca and Mg, and higher densities of microfloral-grazing microarthropods than untreated controls. Using a conceptual model of the decomposition subsystem, it is hypothesized that herbicide treatment altered the system by (1) promoting microbial utilization of the herbicide or additive as a carbon source; (2) increasing the importance of microarthropod grazing relative to comminution; (3) eliminating or reducing the importance of the predatory microarthropods; and (4) increasing the rate of nutrient loss from the litter via microbial and microarthropod activity. The system thus became simplified with fewer recycling loops, accelerated soluble nutrient loss, and slower decay of carbon from the leaf tissue.     

Physico-chemical indicators and microarthropod communities as influenced by no-till, conventional tillage and nitrogen fertilisation after four years of continuous maize

A multidisciplinary study was carried out over four years in Northern Italy on a silt loam under continuous maize. The experimental design was a split-plot with four replicates; the main factor was the soil management system, conventional tillage (CT) or no-tillage (NT), while the secondary factor was N fertilisation. At the end of the trial, soil samples were taken from all plots at four depths (from 0 to 20 cm). In these samples the following were determined: pH, soil organic carbon (SOC), total N, available P, exchangeable K, cation exchange capacity (CEC), electrical conductivity (EC) and water aggregate stability (WAS). Soil compaction was measured during the last three years, after maize harvesting. To study the microarthropod community, soil samples (0–10 cm depth) were taken six times over the four years. Our results show that NT significantly increased SOC (+15.8%), total N (+9.6%), C/N (+5.3%), exchangeable K (+37.1%) and WAS (+64.8%). The stratification ratio for exchangeable K reached 2.15 for NT plots. N fertilisation, on the other hand, had no significant effect on most of the physico-chemical indicators, except for pH, CEC and EC. Soil compaction was significantly higher for NT compared with CT up to a depth of 25–30 cm. During the last year, interesting reductions in soil penetration resistance for NT were measured, up to 300–430 kPa in the 2.5–12.5 cm layer. As for the microarthropods, Acari were more sensitive to tillage compared with Collembola, and the Wardle V index proved to be a good indicator of the response to tillage. N fertilisation with 300 kg N ha⁻¹ had a negative effect on the total microarthropod abundance. The Shannon diversity index gave fluctuating and significantly different results: over the years results were split alternately between the two tillage systems. The QBS-ar index, calculated for all the four years of the study, ranged between 48 and 72, values typical of intensively cultivated soils. The results obtained suggested that it was not influenced by the tillage system. Therefore, this index seems to be unsuitable for detecting the influence of tillage management and N fertilisation on the microarthropod community.     

Petroleum fractions in soil: Effects on populations of nematoda,enchytraeidae and microarthropoda

We investigated the effects of light fuel oil and hydraulic oil on the invertebrate populations of deciduous forest soil. On 9 May 1973, 6.251 oil m^?2 was spread on test plots. At the last sampling in October 1974 22% of the fuel oil and 47% of the hydraulic oil remained in the soil. Both types of oil almost totally destroyed the populations of microarthropods, and practically no recovery was observed by the end of the study. Fuel oil destroyed most Enchytraeidae but about half the enchytraeid population survived the hydraulic oil. Immediately after treatment with fuel oil the population of nematodes decreased, but after July 1973 their numbers were twice those found in control plots. Hydraulic oil had no immediate effect, but gradually the numbers of nematodes increased to many times that of the control plots. During the second year, the numbers of nematodes decreased.