1,721,300 research outputs found
The soil fauna community in pure and mixed stands of beech and spruce of different age: trophic structure and structuring forces
No full textScheu S, Albers D, Alphei J, et al. The soil fauna community in pure and mixed stands of beech and spruce of different age: trophic structure and structuring forces. Oikos. 2003;101(2):225-238
Incorporation of plant carbon into the soil animal food web of an arable system
No full textWe used stable isotopes to examine the incorporation of plant carbon into the belowground food web of an agricultural system. Plots were established and planted with maize (Zea mays) in a rye field (Secale cereale) near Gottingen (northern Germany) in May 1999. In October 1999, April 2000, and October 2000, meso- and macrofauna and maize and rye litter were collected in each plot and analyzed for C-13 and N-15 content. N-15 signatures suggested that the soil animal species analyzed span three trophic levels with the trophic position of species varying little in time. The species investigated formed a continuum from primary to secondary decomposers to predators. On average, predator species differed from primary and secondary decomposers by 3.9 delta N-15 suggesting that they fed on a mixed diet of both decomposer groups. The combined analysis of C-13 and N-15 signatures allowed us to identify links between prey and consumer species. In October 1999, shortly after maize residues had been incorporated into the plots, maize-born carbon was present in each of the animal species investigated, including top predators. The incorporation of maize carbon into the belowground food web increased during the following 12 months but the concentration of maize-born carbon never exceeded 50% in any of the species. Furthermore, the ranks of the incorporation of maize-born carbon of the species changed little. The results suggest that the belowground food web relies heavily on carbon originating from plant residues from before the recent two growing seasons. In most species the amount of maize-born carbon increased continuously; however, in some species it decreased during winter, suggesting that these species switched to a diet based more on C3 plants during winter, or predominantly metabolized carbon incorporated during the last growing season. The study documents that the combined analysis of C-13 and N-15 signatures in soil invertebrate species, after replacement of C3 by C4 plants, is a powerful tool to better understand the structure of the belowground food web and the flux of carbon through it
Temporal patterns of resource use in an ecological model of sexual reproduction and geographic parthenogenesis
No full textQuestions: How are the prevalence of sexual reproduction and the phenomenon of geographic parthenogenesis related to resource availability? What is the pattern in space of resource and consumer dynamics? Mathematical methods: A population dynamics model with structured resources in short supply, including a spatial gradient of consumer mortality and resource diversity. Species are modelled using quantitative genetics, combined with random mating for sexuals and clonal reproduction for asexuals. Key assumptions: Resources are limited and re-grow slowly. Only a few consumer genotypes can co-exist locally. The twofold cost of sex is incurred once per season. Conclusions: The advantage of sexual reproduction is due to the ability of the sexual population to generate offspring that can use resources that have not been exploited for some time. Resource use of the sexual population, therefore, changes continuously. This advantage is most significant at the centre of a species' range.Deutsche Forschungsgemeinschaft (DFG) [Dr300/6
Dietary routing of nutrients from prey to offspring in a generalist predator: effects of prey quality
No full text1. Reproduction of female wolf spiders (Pardosa lugubris; Lycosidae) fed with prey of different quality was investigated. Spiders were fed either a single diet of Drosophila melanogaster (Diptera, high quality), Heteromurus nitidus (Collembola, high quality) or Folsomia candida (Collembola, toxic), or a mixed diet of D. melanogaster and H. nitidus, and of D. melanogaster and F. candida. 2. Nutrient flow from prey into females and from females into offspring during egg production was investigated tracing carbon and nitrogen stable isotopes with prey being enriched in C-13 and/or N-15. 3. There was no benefit of mixing different high-quality prey on female biomass and performance, contrasting with earlier results obtained with juvenile spiders. 4. Folsomia candida was toxic for P. lugubris: females, even if fed a mixed diet also containing high-quality prey, did not reproduce and finally died; spiders did not acquire aversion against F. candida. 5. Tracing stable isotopes documented the incorporation of C and N from prey into females and their offspring; dietary nutrients were routed almost exclusively into egg production. 6. Stable isotope analysis strongly supported the assumption that F. candida causes post-ingestive physiological effects in spiders by inhibiting the incorporation of nutrients from other prey
Temporal patterns of resource use in an ecological model of sexual reproduction and geographic parthenogenesis
No full textQuestions: How are the prevalence of sexual reproduction and the phenomenon of geographic parthenogenesis related to resource availability? What is the pattern in space of resource and consumer dynamics? Mathematical methods: A population dynamics model with structured resources in short supply, including a spatial gradient of consumer mortality and resource diversity. Species are modelled using quantitative genetics, combined with random mating for sexuals and clonal reproduction for asexuals. Key assumptions: Resources are limited and re-grow slowly. Only a few consumer genotypes can co-exist locally. The twofold cost of sex is incurred once per season. Conclusions: The advantage of sexual reproduction is due to the ability of the sexual population to generate offspring that can use resources that have not been exploited for some time. Resource use of the sexual population, therefore, changes continuously. This advantage is most significant at the centre of a species' range.Deutsche Forschungsgemeinschaft (DFG) [Dr300/6
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No full textWe investigated if the commonly used aggregation of organisms into trophic guilds, such as detritivores and predators, in fact represent distinct trophic levels. Soil arthropods of a forest-meadow transect were ascribed a priori to trophic guilds (herbivores, detritivores, predators and necrovores), which are often used as an equivalent to trophic levels. We analysed natural variations in N-15/N-14 ratios of the animals in order to investigate the trophic similarity of organisms within (a priori defined) trophic guilds. Using trophic guilds as an equivalent to trophic level, the assumed stepwise enrichment of N-15 by 3.4% per trophic level did not apply to detritivores; they were only enriched in N-15 by on average 1.5% compared to litter materials. Predators on average were enriched in N-15 by 3.5% compared to detritivores. Within detritvores and predators delta N-15 signatures varied markedly, indicating that these trophic guilds are dominated by generalist feeders which form a gradient of organisms feeding on different resources. The results indicate that commonly used trophic guilds, in particular detritivores and predators, do not represent trophic levels but consist of subguilds, i.e. subsets of organisms differing in resource utilization. In particular, in soil and litter food webs where trophic level omnivory is common, the use of distinct trophic levels may be inappropriate. Guilds of species delineated by natural variations of stable isotope ratios are assumed to more adequately represent the structure of litter and soil food webs allowing a more detailed understanding of their functioning.Deutsche Forschungsgemeinschaf
Do endogeic earthworms change plant competition? A microcosm study
No full textPlants compete for limited resources. Although nutrient availability for plants is affected by resource distribution and soil organisms, surprisingly few studies investigate their combined effects on plant growth and competition. Effects of endogeic earthworms (Aporrectodea jassyensis), root-knot nematodes (Meloidogyne incognita) and the spatial distribution of N-15 labelled grass litter on the competition between a grass (Lolium perenne), a forb (Plantago lanceolata) and a legume (Trifolium repens) were investigated in the greenhouse. Earthworms promoted N uptake and growth of L. perenne. Contrastingly, shoot biomass and N uptake of T. repens decreased in the presence of earthworms. P. lanceolata was not affected by the earthworms. We suggest that earthworms enhanced the competitive ability of L. perenne against T. repens. Nematodes increased the proportion of litter N in each of the plant species. Litter distribution (homogeneous vs. patch) did not affect the biomass of any plant species. However, P. lanceolata took up more N-15, when the litter was homogeneously mixed into the soil. The results suggest that endogeic earthworms may affect plant competition by promoting individual plant species. More studies including decomposers are necessary to understand their role in determining plant community structure
Earthworms and litter distribution affect plant-defensive chemistry
No full textStudies on plant-defensive chemistry have mainly focused on plants in direct interaction with aboveground and occasionally belowground herbivores and pathogens. Here we investigate whether decomposers and the spatial distribution of organic residues in soil affect plant-defensive chemistry. Litter concentrated in a patch ( vs. homogeneously mixed into the soil) led to an increase in the aucubin content in shoots of Plantago lanceolata. Earthworms increased total phytosterol content of shoots, but only when the litter was mixed homogeneously into the soil. The phytosterol content increased and aphid reproduction decreased with increasing N concentration of the shoots. This study documents for the first time that earthworms and the spatial distribution of litter may change plant-defensive chemistry against herbivores
The influence of fertilizer addition, cutting frequency and herbicide application on soil organisms in grassland
No full textIn Europe, grasslands are among the most important agricultural systems which are subject to continuous management intensification, potentially threatening ecosystem services. We analysed the impact of management of permanent grassland, i.e. fertilizer addition (-NPK and +NPK), cutting frequency (one and three cuts per year) and herbicide application targeting either dicotyledons or monocotyledons, on microorganisms and soil animals. Microbial biomass decreased in treatments cut once with fertilizer addition. However, in treatments cut thrice, microbial biomass did not decline with fertilizer addition, suggesting that cutting frequency alleviates the detrimental effect of fertilizer input. Fungal but not bacterial phospholipid fatty acid biomarkers varied with sward composition, indicating fungi more sensitively respond to changes in grassland management and sward composition than bacteria. The abundance of dipterans and beetles increased with fertilizer addition but decreased with sward-cutting frequency. Epigeic earthworms benefited from a reduced proportion of monocotyledons. The results indicate that microbial parameters more sensitively respond to intensification of management practices in grassland than to soil animals, in particular, early after changes of management practices.Ministry of Science and Culture of Lower Saxony; Niedersachsisches Vora
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