Effects of long-term soil warming and fertilisation on microarthropod abundances in three sub-arctic ecosystems

Soil microarthropod responses to long-term soil warming and increased fertilisation by addition of NKP or litter were assessed in three subarctic ecosystems. The experiment was carried out at three different field sites, where temperature and fertilisation manipulations had been running for 3–5 years (glade), 11 years (fellfield), and 12 years (heath) at the time of sampling. In the glade soil, warming led to decreases in Collembola and Gamasida, and increases in Oribatida, although effects were inconsistent between years. Actinedida densities were increased by fertilization, while Acaridida had higher densities in the treatment with both fertilisation and warming. In the fellfield, we found increased densities of Oribatida, Gamasida and Actinedida in the fertilised treatments, and some increases in Oribatida and decreases in Collembola and Gamasida in warming treatments. In the heath, there were increased densities of Collembola, Oribatida and Actinedida in the fertilised treatments, but we found no strong effects of warming. We suggest that the responses found in this study comply with the assumption that soil microarthropods are bottom-up controlled, and the observed changes are probably linked to changes in food availability more than direct climatic influences.     

Soil microarthropod response to the application of entomopathogenic nematode-killed insects in maize and flower strip habitats

Insects killed by entomopathogenic nematodes (EPN) represent a resource with which soil arthropods can interact. These interactions can be positive for EPN (e.g., arthropods serve as parasitic or phoretic hosts) or negative (e.g., EPN serve as prey). Plant diversity and soil disturbance may influence these interactions. We investigated the effects of maize and flower strip habitats on microarthropod abundance and community composition in soil surrounding greater wax moth larvae, Galleria mellonella, infected with the EPN Steinernema carpocapsae (Sc). In the first year of the experiment (2005), we compared microarthropod communities responding to burial of Sc-killed insects with a control (no soil disturbance). In 2006, we added two control treatments: burial of freezer-killed insects and sham burial. Soil samples (including G. mellonella) were collected 2 and 20 days (2005) or 2 and 12 days (2006) after application. In 2005, arthropod abundance and community composition were similar between maize and flower strip habitats. In 2006, we detected more arthropods in the maize than the flower strips. In both years, community composition differed between treatments providing resources (Sc-killed and freezer-killed insects) and those without (sham burial and no disturbance), with the greatest difference on the final sampling date. Soil surrounding Sc-killed and freezer-killed insects contained more dipterans, acarid mites, staphylinid beetles, onychiurid and entomobryid collembolans, and immature and male mesostigmatid mites than soil at sham burial and no disturbance sites. Most of these taxa are capable of nematophagy; however, EPN relative abundance was not associated with arthropod community composition.     

Life-history tactics of soil microarthropods

A sound basis for defining life-history tactics was obtained by reviewing life-history traits. This involved an explanation of the ecological implications of thelytoky (automictic or apomictic), arrhenotoky, amphitoky, sexual reproduction, semelparity, iteroparity, seasonal iteroparity, and the relationship between semelparity and juvenile development. Several forms of synchronization of life cycles with environmental conditions were classified, ranging from the ability to overcome harsh seasonal conditions to obligate diapause dormancy. Ecologically, this involves adaptations to environmental conditions ranging from irregularly occurring and unpredictable events to regularly occurring and predictable conditions. Dispersal traits were grouped as directional migration (phoresy) and undirectional migration (anemochory). Distinctions were made between facultative and obligate phoresy and between carrier-specific and carrier-unspecific phoresy. A multi-dimensional system of tactics was outlined, based on well-defined underived traits. This system was compared with one- and two-dimensional schemes described by MacArthur and Wilson (1967), Grime (1977), and Southwood (1977) and with the multi-dimensional system described by Stearns (1976). For each tactic, relationships with the main biotopes in which it occurs were defined. Examples of species showing certain tactics were selected from the taxonomic orders of microarthropods. The generality of the traits for various groups of organisms and of the classification of life-history tactics developed was explored.     

Reducing the dimensionality of soil microinvertebrate community datasets using Indicator Species Analysis: Implications for ecosystem monitoring and soil management

Soil microinvertebrates are closely associated with soil decomposition and nutrient cycles and may be particularly responsive indicators for soil management practices. However, identification of appropriate bioindicator species for many systems has been severely limited by a lack of information on species taxonomy, distribution, and functional role. We evaluated Indicator Species Analysis (ISA) as an objective method for assessing the indicator potential of different taxa without regard to their ecological role or expected management response. Restricting ordination and site classification to significant indicator morphotaxa reduced the dimensionality of the community data matrix by 69% while only slightly decreasing the efficiency of unsupervised classification (from 87.2 to 84.4%); the percentage of total variability explained by first two PCA axes increased following ISA. When these same indicator morphotaxa were used to classify an independent set of samples, the percentage of total variability explained by the first two PCA axes increased from 55.3 to 65.2%; cluster analysis of the test dataset correctly classified 47 out of 50 plots by cover type (94% accuracy). However, restriction of analysis to indicator morphotaxa alone reduced detection of differences between sampling dates relative to the complete dataset. Although care needs to be taken to ensure that the dataset used for indicator selection is fully representative of underlying temporal and spatial variability, ISA appears to overcome many of the limitations associated with parametric and multivariate approaches for identifying indicator morphotaxa and has the potential to greatly reduce the taxonomic expertise and labor costs associated with sorting and identification of soil microarthropods.     

Dynamics and stratification of functional groups of micro- and mesoarthropods in the organic layer of a Scots pine forest

This paper addresses the abundance, biomass and microstratification of functional groups of micro- and mesoarthropods inhabiting the organic layers of a Scots pine forest (Pinus sylvestris L.). An experiment using stratified litterbags, containing organic material of four degradation stages, i.e., freshly fallen litter, litter, fragmented litter and humus, was performed over a period of 2.5 years. Statistical data analysis revealed that each organic layer had a different, characteristic species composition that changed with time following successive degradation stages. Species of Acari, Araneae and Collembola were assigned to different functional groups based on taxonomy, microstratification, food type or feeding mode. The abundance and biomass carbon of functional groups were dependent on the organic layer and most functional groups showed a particular preference for one of the upper organic layers. Temporal and spatial differences in density and biomass carbon of functional groups could partly be related to fluctuations in the soil climate, although effects of trophic interactions could not be ruled out. A general decline in abundance and biomass, especially in populations of fungal feeders, during the last year of the study could not be explained by a reduction in litterbag volume, changed litter chemistry or soil climate, but was attributed to an indirect effect of a remarkable increase in soil coverage by wavy hair grass, Deschampsia flexuosa (L.). The analysis demonstrated that species diversity, microhabitat specification, soil fauna succession, and degradation stages of organic material are interrelated. The results obtained indicate that both the chemistry of organic matter and decomposition rates have an important effect on trophic relationships and community structure. Received: 26 June 1997     

Management intensity affects traits of soil microarthropod community in montane spruce forest

This study examined the influence of forest management intensity (3 unmanaged, 3 mild managed, 5 intensively managed stands) on soil microarthropods in montane spruce forest. We particularly focused on Oribatida and Collembola which play important roles in organic matter decomposition and nutrient cycling. Our results showed a significant shift from fungivory and carnivory to detritivory in the Oribatida community accompanying management intensification. Similarly, parthenogenetic oribatid mite species contributed more to the community in intensively managed forests and the presence of Collembola species with developed furca increased with management intensification. Although there was no remarkable influence of management intensity on total densities or diversity indices, important and significant shifts in species composition and functional groups showed that soil functions and processes were affected by forest management. Trait assessment indicates a shift in roles Oribatida play in decomposition; fragmentation and comminuting of undecomposed litter seems to gain importance in the intensively managed forest, whereas fungivorous species affect primary decomposers through feeding on fungi in the unmanaged forest.     

Soil mesofauna dynamics,wheat residue decomposition and nitrogen mineralization in buried litterbags

The effect of soil microarthropods and enchytraeids on the decomposition of wheat straw in buried litterbags was studied by selective admission and exclusion. Litterbags with 20 m mesh size admitted nematodes, but excluded microarthropods, although temporarily. After 27 weeks of incubation part of these litterbags were colonized, probably through egg-deposition of mainly fungivorous Collembola and mites. When litterbags with a complete microarthropod community (1.5 mm mesh size) were compared to litterbags with strongly reduced microarthropod numbers (20 m mesh size), no differences between decomposition rates were found. However, in colonized 20-m mesh bags, we found reduced decomposition rates compared to the coarse mesh litterbags, probably due to overgrazing of the fungal population by large numbers of fungivorous microarthropods. These large numbers might be caused by the absence of predators. Extraction of microarthropods as well as enchytraeids and nematodes from the coarse mesh litterbags showed a distinct succession during decomposition. The decomposition process was dominated in the first phase by bacterivorous nematodes, nematophagous and bacterivorous mites, and in the later phase by fungivorous nematodes, fungivorous and omnivorous mites and Collembola, and predatory mites. This succession is indicative of a sequence from bacterial to fungal dominated decomposition of the buried organic matter. The results indicate that the decomposition rate is predator controlled.     

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.     

福建牛姆林自然保护区天然林植物区系组成分析

对福建省牛姆林6个天然林样地的植物区系组成统计分析结果表明，牛姆林天然林的植物种类组成丰富，在2900m^2范围有248种高等植物分属82科153属，其中蕨类植物11科14属16种，裸子植物3科3属3种，被子植物71科136属229种，种子植物属的系数为61．69；区系地理成分较为复杂，属的地理成分以热带分布型为主，63．36％的热带地理成分及32．82％的温带地理成分显示出牛姆林地处南亚热带北缘的地理特点。     

Dispersal of microarthropods in forest soil

This experiment was a part of a research on the soil community in anthropogenous birch stands in Finland. In that study it was found that communities of Collembola are similar in birch stands of different origin (cultivated field or spruce forest), while the communities of Oribatida are essentially different. When compared to original spruce forest, the communities of both groups are different.Cultivation eliminates the populations of most microarthropod species, that have to disperse after reforestation from the surrounding areas. The aim of the experiment was to study the ambulatory dispersal of soil microarthropods. It was carried out in plastic boxes filled with an intact block of defaunated surface soil taken from a birch stand that was established ca. 30 years earlier on a cultivated field. A strip of intact spruce forest soil was placed at one end of the boxes to harbour the source populations. At the opposite end we placed a row of pitfall traps. Soil samples were taken every two weeks at increasing distances from the source soil using a metal corer, and animals were extracted in a high gradient apparatus. The pitfalls were also emptied every two weeks. The experiment lasted for ten weeks.Pitfall and soil sample data gave an estimation of the maximum dispersal rate for each species or genus. The distance that the populations could potentially disperse in 30 years (age of the stand) indicated that some, but not all of the species could have actively migrated to the central parts of the birch stand (30 m).     

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.     

Endemic Collembola, privileged bioindicators of forest management

Our study compared the soil collembolan community at three semi-natural sites (a beech forest, a beech–fir forest and a fir stand) and three managed sites (Norway spruce, beech–fir and fir). Collembola were extracted from a total of 60 samples with a Berlese–Tullgren funnel, counted and identified to species level. A total of 7187 specimens, representing 51 species and 37 genera, were collected. There were significant differences between managed and natural forests (t-test, P=0.000). The communities and their population densities were significantly lower in the managed site: 51 species with 708,498 ind m⁻² in the semi-natural forests to 36 species and 306,042 ind m⁻² in the managed stands. The endemic component suffered a particularly severe decrease in species richness and abundance (57% and 71% lower in the managed forests, respectively). These species with narrow distribution and small local populations are doubly vulnerable to alterations of environmental conditions. They are very sensitive to loss of their natural habitat owing to human intervention and thus represent useful indicators of tolerance to environmental stress. We highlight the need to take endemic species into consideration in studies on the conservation of biodiversity because they are most at risk of extinction. Semi-natural forests are refuges for endemic species and should be protected.     

Litter microarthropod responses to canopy herbivory,season and decomposition in litterbags in a regenerating conifer ecosystem in Western Oregon

Summary The microarthropod community response to season, change in foliage litter quality during decomposition, and manipulated canopy herbivory by insects was measured in litterbags under 10-year-old Douglas-fir, Pseudotsuga menziesii (Mirb.) Franco, in western Oregon. Collembola accounted for 35% of the total fauna, oribatid mites for 29%, and fungivorous actinedids for 22%.The community structure was affected by responses to canopy defoliation, season, and changes in litter quality. Of 33 taxa, three were significantly more abundant under trees subject to lepidopteran defoliation (20% foliage removal), compared to other treatments, indicating responses to defoliator-induced changes in litter environment. Most taxa (23) showed seasonal fluctuations in abundance related to the seasonal pattern of temperature and precipitation and to the pattern of N and Ca mobilization from litterbags. Five taxa showed significant longterm trends in abundance, indicating responses to changes in litter quality, perhaps a loss of P and K.These data indicate that microarthropod communities respond qualitatively to environmental changes, including canopy defoliation. The qualitative changes can affeet decomposition processes.     

Influence of microarthropod abundance and climatic factors on weight loss and mineral nutrient contents of Eucalyptus leaf litter during decomposition

Summary Densities of the different taxa of microarthropods per gram of litter in litter bags varied widely from the rainy to the dry season. Collembola and Acarina constituted more than 86% of the total microarthropods, and occurred in significantly greater numbers in the coarse-mesh bags than the fine-mesh bags. There were no fauna in the litter of suspended bags. The average weight loss was greater in the coarse-mesh bags (50.4%) than in the fine-mesh bags (44.5%), and the suspended bags (7.4%). Similarly, the concentrations of N and Ca were greater in the litter of coarse-mesh bags compared to that of the fine-mesh bags. In contrast, the concentrations of P and K were comparatively lower in coarse-mesh bags. The mass loss of litter showed a negative linear correlation with the total Collembola and with litter temperature. The N concentrations in the litter in both the mesh bags showed negative correlations with the abundance of total Collembola, and with that of Lepidocyrtus sp. and Sminthuridae, and rainfall. The N concentration in the litter in the coarse-mesh bags was positively correlated with the total number of arthropods but, surprisingly, was negatively correlated with the total number of Acarina. The concentration of Ca showed negative correlations with rainfall and litter moisture only. The P concentration showed positive correlations with total Collembola, with Lepidocyrtus sp. and Sminthuridae in both the mesh bags, with rainfall in the fine-mesh bags, and with total microarthropods in the coarse-mesh bags.     

The effects of the insecticide chlorpyrifos on spider and Collembola communities

The effects of chlorpyrifos on aquatic systems are well documented. However, the consequences of the pesticide on soil food webs are poorly understood. In this field study, we hypothesised that the addition of a soil insecticide to an area of upland grassland would impact spider and Collembola communities by decreasing numbers of spiders, consequently, causing an increase in detritivore numbers and diversity.Chlorpyrifos was added to plots on an upland grassland in a randomised block design. Populations of Collembola and spiders were sampled by means of pitfall traps (activity density) and identified to species.Twelve species of Collembola were identified from the insecticide-treated and control plots. Species diversity, richness and evenness were all reduced in the chlorpyrifos plots, although the total number of Collembola increased ten-fold despite the abundance of some spider species being reduced. The dominant collembolan in the insecticide-treated plots was Ceratophysella denticulata, accounting for over 95% of the population.Forty-three species of spider were identified. There were a reduced number of spiders in insecticide-treated plots due mainly to a lower number of the linyphiid, Tiso vagans. However, there was no significant difference in spider diversity between the control and insecticide treatments.We discuss possible explanations for the increase in abundance of one collembolan species in response to chlorpyrifos and the consequences of this. The study emphasises the importance of understanding the effects of soil management practices on soil biodiversity, which is under increasing pressure from land development and food production. It also highlights the need for identification of soil invertebrates to an ‘appropriate’ taxonomic level for biodiversity estimates.     

Impact of cultivation management in an agroecosystem on hot spot effects of earthworm middens

In comparison to the surrounding soil, hot spot effects of middens of the epianecic earthworm Lumbricus terrestris were determined under different field conditions on a loamy sand. The impact of 3 different management systems was studied: 1. unmulched; 2. straw mulching; 3. intermediate crop: Sinapis alba. Furthermore, we considered 2 different crops (bean, lupine) and their growth stages. We monitored different enzyme activities and abiotic parameters of soil at 6 sampling dates between April and August 1998 parallel to abundances of microfauna (soil protozoa) and mesofauna (Enchytraeidae, Collembola, mites). The analysis of earthworm middens revealed enhanced enzyme activities and increased mesofaunal abundances. Differences between midden and reference samples were significant during the whole vegetation period and became maximal during ripening of crops. We found a distinct but not significant increase in individual numbers of soil flagellates in midden areas during leafing and heading of crops. Values of the studied parameters tended to be higher in bean plots but generally the crop impact on midden properties was not significant. Our results showed a significant positive synergistic effect between earthworm middens and intermediate crop. Straw mulching supported the hot spot effects of middens.