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 agricultural traffic and crop management on collembola and microbial biomass in arable soil

Collembola and microbial biomass C were investigated in a field experiment with controlled agricultural traffic and crop rotation over a period of 27 months. The wheel-induced compactive efforts were applied according to management practices within the crop rotation of sugar beet, winter wheat, and winter barley. Increasing wheel traffic produced increasing soil compaction, mainly due to a reduction in surface soil porosity. Increasing soil compaction was accompanied by a decrease in microbial biomass C and the density of collembola. The influence of soil compaction on microbial biomass C was smaller than that of the standing crop. However, for collembola, especially euedaphic species, a reduction in pore space appeared to be of more importance than the effects of a standing crop. Within the crop rotation, microbial biomass C and the density of collembola increased in the order sugar beet, winter wheat, and winter barley.     

Effect of season, location and fire on Collembola communities in buttongrass moorlands, Tasmania

Collembola of buttongrass moorlands in Tasmania were surveyed monthly over a 12 month period, using sweep nets and pitfall traps, at two locations, one at 760 m and the other at 325 m altitude. At each location, there were two pairs of sites with each pair straddling a fire boundary. The younger regrowth sites had been burnt less than 12 years previously and the older regrowth sites burnt more than 24 years previously. Nearly 30,000 individuals were collected belonging to 42 taxa. Most Collembola were identified to morphospecies with virtually all mature specimens identified to genus level and immature specimens recognised to family level. Three named species were recorded. Genera with Gondwanan (41%) and cosmopolitan (33%) distributions dominated the Collembola of buttongrass moorlands. The Collembola communities differed significantly between locations and this, in part, reflected differences in vegetation. Brachystomellidae, Odontellidae, Paronellidae, Katiannidae n. gen. and Sminthurididae were more common at the high altitude sites where the vegetation contained more grasses and sedges and occurred on relatively fertile soils. Parakatianna spp., cf. Tomocerura spp., cf. Drepanura sp., Sminthurinus spp. and Rastriopes sp. were more common at the low altitude sites where the vegetation contained more shrubs and occurred on relatively infertile soils. The Collembola community differed significantly between seasons with one group of taxa being more common in autumn and/or winter (Acanthomurus spp., cf. Tomocerura spp., Paronellidae, Lasofinius spp., Polykatianna cf. aurea, Parakatianna spp., Sminthurinus spp. and Katianna spp.) and another group of taxa more common in summer or summer and autumn (Odontellidae, cf. Drepanura sp., Rastriopes sp., Corynephoria sp. and Dicyrtomidae). We found some evidence of a difference between Collembola communities in the two ages of regrowth we compared but only for the low altitude sites. Polykatianna cf. aurea, Parakatianna spp., Sminthurinus spp., cf. Tomocerura spp. and Rastriopes sp. were caught in lower numbers on young regrowth sites compared with old regrowth sites. We also present data from another low altitude site where we used a space-for-time design to further investigate the impact of fire on Collembola. We found a significant positive relationship between age of buttongrass regrowth and the number of Rastriopes sp. caught and this was correlated with the ground cover of plant species within the family Myrtaceae.     

Hierarchical classification of environmental factors and agricultural practices affecting soil fauna under cropping systems using Bt maize

The population dynamics of soil organisms under agricultural field conditions are influenced by many factors, such as pedology and climate, but also farming practices such as crop type, tillage and the use of pesticides. To assess the real effects of farming practices on soil organisms it is necessary to rank the influence of all of these parameters. Bt maize (Zea mays L.), as a crop recently introduced into farming practices, is a genetically modified maize with the Cry1Ab gene which produces a protein toxic to specific lepidopteran insect pests. To assess the effects of Bt maize on non-target soil organisms, we conducted research at a field site in Foulum (Denmark) with a loamy sand soil containing 6.4% organic matter. The study focused on populations of springtails (Collembola) and earthworms (Oligochaeta) from samples taken at the beginning and at the end of the maize crop-growing season during 2 consecutive years. Farming practices, soil parameters, the biological structure of soil communities, and the type and age of the crop at the time of sampling, were used as attributes to predict the total abundance of springtails and biomass of earthworms in general and the abundance or biomass for specific functional groups (epigeic, endogeic and anecic groups for earthworms, and eu-, eu to hemi-, hemi-, hemi to epi- and epiedaphic groups for Collembola). Predictive models were built with data mining tools, such as regression trees that predict the value of a dependent variable from a set of independent variables. Regression trees were constructed with the data mining system M5′. The models were evaluated by qualitative and quantitative measures of performance and two models were selected for further interpretation: anecic worms and hemi-epiedaphic Collembola. The anecic worms (r²=0.83) showed preferences for less clay and more silt soil with medium pH but were not influenced directly by farming practices. The biomass of earthworms was greater in early autumn than in spring or late autumn. Biomass of hemi-epiedaphic Collembola (r²=0.59) increased at the end of the maize growing season, while higher organic matter content and pH tended to increase their biomass in spring. Greater abundance of Collembola was also noted in early autumn if the crop was non-Bt maize. The models assessed by this research did not find any effects of the Bt maize cropping system on functional groups of soil fauna.     

The effect of mesoclimate on Collembola diversity in the Zádiel Valley, Slovak Karst (Slovakia)

In 2002–2004 an investigation of Collembola communities in the Zádiel Valley (Slovak Karst, Slovakia) was carried out. The karst valley is characterised by climatic and vegetation inversion. To assess the effect of mesoclimate inversion upon soil Collembola five sites were selected in hypsometric sequence from the karst plateau down the valley: (1) subxerophilous pasture – ass. Glechomo–Festucetum, (2) lime wood – ass. Mercuriali–Tilietum, (3) beech wood – ass. Dentario bulbiferae-Fagetum, (4) maple–hornbeam wood – ass. Aceri–Carpinetum, and (5) secondary oak wood. In total 152 soil Collembola species were collected, the numbers for particular sites ranging between 70 and 108. Evidently higher species richness was observed in soil of the beech wood compared to other selected forest plots. Thirteen species revealed affinity to inversed (wet and cold) stands of beech (3) and maple–hornbeam wood (4), four of them represented montane species, whereas five species clearly preferred thermophilous sites (1, 2, 5). The presence of 11 montane species at the bottom of the gorge (4) documented the inverse character of the site: Ceratophysella sigillata, C. silvatica, Friesea albida, Deutonura albella, D. stachi, Superodontella lamellifera, Tetrodontophora bielanensis, Heteraphorura variotuberculata, Kalaphorura carpenteri, Orthonychiurus rectopapillatus and Plutomurus carpaticus. Abundance of Folsomia quadrioculata significantly correlated with the soil microclimate – moisture (p < 0.01, r = 0.92). Distribution data on Collembola were performed by cluster (PC-ORD) and CCA ordination techniques. Collembolan communities of two neighbouring forest stands with identical soil type (rendzina) – lime (2) and beech wood (3) – were the most similar in species composition. Meso-/microclimatic gradients within a karst landscape play an important role in determining diversity and community structure of the soil Collembola.     

Bottom-up down from the top: Honeydew as a carbon source for soil organisms

Honeydew produced by aphids is a well-studied food source for mutualistic ants. Although considerable amounts drop onto the soil surface there are hardly any studies dealing with the potential effects of this additional C source for soil organisms, particularly those living at the soil surface. We studied this question by simulating honeydew and investigating plots under Populus canescens formerly infested with aphids on two ruderal sites differing in soil organic matter content and vegetation cover. The simulated honeydew input increased microbial biomass with some delay in week 10. Both natural and simulated honeydew raised the activity densities of an epigeic Collembola taxon, the Bourletiellidae, but not of the dominant Hemisotoma thermophila. The honeydew effect varied over time and with the site, and was more pronounced at the nutrient-poor site for Collembola, but not for microbial biomass. Ant consumption reduced the amount of honeydew reaching the soil surface by 50%. The activity density of H. thermophila was negatively related to ants and spiders, hinting at a top-down control. Honeydew clearly acts as a bottom-up force for soil organisms, which is however only part of the complex network connecting the food webs of primary producers and decomposers.     

Responses to light in a soil-dwelling springtail

It has been widely assumed that Collembola respond to light, but until now there has been very little experimental proof of this. Field observations allowed to distinguish soil-dwelling species that would escape from light from surface-dwelling species that would be attracted to light. However, the supposed effect of light could be due to other factors such as temperature or dryness. We demonstrated that individuals of the collembolan species Heteromurus nitidus (Entomobryidae), when placed in a light gradient (temperature and moisture being homogeneous), clustered in the darker area. This effect occurred rapidly and changes in the distribution of animals persisted after illumination ceased. This shows light to act as a strong repellent for this soil-dwelling collembolan species.     

Chemical communication in Ceratophysella sigillata (Collembola: Hypogastruridae): intraspecific reaction to alarm substances

When disturbed or damaged, the winter-active collembolan Ceratophysella sigillata releases a strong aromatic odour, which can be perceived even by humans. The efficiency of the substances released as an intraspecific alarm substance was investigated. C. sigillata showed distinct reactions to chemicals released by conspecifics; crushed conspecifics, cuticle washings (with pentane) and whole body extracts (with methyl acetate) were tested. Our results demonstrate that a very sensitive intraspecific avoidance reaction is present to the substances released by crushed C. sigillata as well as to washings and extracts: extracts from as little as half a springtail induced a significant avoidance reaction in conspecifics. Alarm substances were present in all instars of C. sigillata including eggs, and all instars of C. sigillata tested showed similar reactions to the extracts or crushed conspecifics.