1,720,979 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
Soil nematodes associated with the mammal pathogenic fungal genus Malassezia (Basidiomycota : Ustilaginomycetes) in Central European forests
No full textScreening forest soil nematodes for associated fungi by PCR, and sequencing the internal transcribed spacer detected the human, and other mammals, pathogenic fungus Malassezia in association with soil nematodes for the first time in Europe. Malassezia restricta and M. globosa were associated with the nematode genus Malenchus sp., whereas another nematode, Tylolaimophorus typicus hosted only M. restricta
Millipedes and earthworms increase the decomposition rate of N-15-labelled winter rape litter in an arable field
No full textEffects of millipedes and earthworms on the decomposition of N-15-labelled litter of winter oilseed rape were investigated in a microcosm field experiment over a period of 264 days on an oat field near Gottingen managed by integrated farming. A total of 32 microcosms were filled with defaunated soil. N-15-labelled rape litter was placed either on top of the soil or buried into the soil simulating mulching and ploughing, respectively. To the microcosms nine adult individuals of Blaniulus guttulatus (Diplopoda) and two of Aporrectodea caliginosa (Lumbricidae) were added separately or in combination. In general, the presence of the animals accelerated the decomposition rate of the litter material. The effects were most pronounced in the presence of Aporrectodea caliginosa. The total amount of nitrate, ammonium and the amount of N-15 leached from the microcosms was increased in the presence of earthworms or of both earthworms and millipedes, Both species proved to be important members of the detritus food web of the agricultural system studied
Resource dynamics in an early-successional plant community are influenced by insect exclusion
No full textThe exclusion of insects from terrestrial ecosystems may change productivity, diversity and composition of plant communities and thereby nutrient dynamics. In an early- successional plant community we reduced densities of above- and below-ground insects in a factorial design using insecticides. Beside measuring vegetation dynamics we investigated the effects of insect exclusion on above- and below-ground plant biomass, below-ground C and N storage by plants, litter quality, decomposition rate, soil water content, soil C:N ratio, nutrient availability and soil microbial activity and biomass. The application of soil insecticide had only minor effects on above- and below-ground biomass of the plant community but increased carbon content in root biomass and total carbon and nitrogen storage in roots. In one of the three investigated plant species (Cirsium arvense), application of soil insecticide decreased nitrogen concentration of leaves (- 12%). Since C arvense responded positively to soil insecticide application. this effect may be due to drought stress caused by root herbivory. Decomposition rate was slightly increased by the application of above-ground insecticide, possibly due to an impact on epigeic predators. The application of soil insecticide caused a slightly increased availability of soil water and an increased availability of mineralised nitrogen (+30%) in the second season. We explain these effects by phenological differences between the plant communities, which developed on the experimental plots. Microbial biomass and activity were not influenced by insecticide application, but were correlated to above-ground plant biomass of the previous year. Overall, we conclude that the particular traits of the involved plant species, e.g. their phenology, are the key to understand the resource dynamics in the soil. (C) 2004 Elsevier Ltd. All rights reserved
Microflora, Protozoa and Nematoda in Lumbricus terrestris burrow walls: a laboratory experiment
No full textAnecic earthworms Lumbricus terrestris L. were kept in laboratory microcosms containing soil and litter from a lime (Tilia cordata) and beech (Fagus sylvatica) forest. Nutrient (mineral nitrogen and phosphorus) contents, microbial activity and densities of protozoa and nematodes were determined in burrow walls and control soils after 165 days. Well-developed burrow linings consisting of earthworm faeces were formed in the "Tilia" treatment, but not in the "Fagus" treatment, presumably because beech litter was not an adequate food resource for L. terrestris. Consequently, increases in microbial biomass, basal respiration and microbial volume in burrow walls compared to surrounding soil were significant in the "Tilia" treatment only. However, in both treatments burrow walls were strongly enriched in mineral nitrogen and phosphorus. The density and biomass of protozoa were significantly greater in burrow walls compared to the control soil. The numbers of naked amoebae increased by similar factors of 4 and 3.5 in burrow walls of the "Tilia" and "Fagus" treatment, respectively. Flagellate density increased more than tenfold in burrow walls of the "Tilia" treatment but only twofold in the "Fagus" treatment. In addition, a comparatively large ciliate population was present in burrow walls in the "Tilia" treatment. The total abundance of protozoa was significantly correlated with the contents of inorganic N and P in the samples (r=0.68 and 0.63 respectively, P<0.03) suggesting that protozoan grazing participated in the mobilisation of nutrients from microbial biomass. The total nematode density was increased in burrow walls by a factor of 3 in the "Tilia" treatment (mostly due to bacterivorous nematodes), but was not affected in the "Fagus" treatment. In both treatments density of fungivorous nematodes increased, while that of plant parasites decreased in burrow walls compared to the control soil. It is concluded that the grazing pressure of protozoa and nematodes may control the dynamics of the microbial succession in earthworm burrow walls, strongly affecting nutrient cycling processes in these microhabitats
Effects of plant diversity on Collembola in an experimental grassland ecosystem
No full textThe response of species numbers and density of Collembola to manipulation of plant species richness (1, 2, 4, 8, 32 species) and number of plant functional groups (grasses, legumes and non-legume herbs) was studied in an experimental grassland at the Swiss BIODEPTH site (Lupsingen, Switzerland) in October 1997. Plant species richness or number of plant functional groups did not affect total diversity of Collembola, however, the number of Collembola species increased in the presence of legumes and the grass Trisetum flavescens. The abundance of Protaphorura armata increased but that of Hypogastruridae/Neanuridae significantly decreased with increasing number of plant functional groups. Other groups including the herbivorous Symphypleona did not respond to plant species richness and plant functional groups. Possibly, Hypogastruridae/Neanuridae species are weak competitors declining in density if the density of other Collembola groups increase. In general, the effect of the number of plant functional groups on the densities of collembolan taxa was stronger than that of plant species richness. Changes in Collembola density and diversity in part was likely caused by increased soil microbial and fine root biomass in treatments with higher plant functional group diversity. The presence of legumes resulted in an increase in the densities of total Collembola, Symphypleona/Neelipleona and Isotomidae indicating that they benefited from the high litter quality and the increased microbial biomass in the rhizosphere of legumes. The results suggest that microbivorous soil invertebrates are controlled by food quality rather than quantity. Furthermore, they indicate that presence of certain plant species and functional groups may be more important for collembolan community structure than the diversity of plant species and functional groups per se
Plant diversity effects on soil heterotrophic activity in experimental grassland ecosystems
No full textThe loss of plant species from terrestrial ecosystems may cause changes in soil decomposer communities and in decomposition of organic material with potential further consequences for other ecosystem processes. This was tested in experimental communities of 1, 2, 4, 8, 32 plant species and of 1, 2 or 3 functional groups (grasses, legumes and non-leguminous forbs). As plant species richness was reduced from the highest species richness to monocultures, mean aboveground plant biomass decreased by 150%, but microbial biomass (measured by substrate induced respiration) decreased by only 15% (P = 0.05). Irrespective of plant species richness, the absence of legumes (across diversity levels) caused microbial biomass to decrease by 15% (P = 0.02). No effect of plant species richness or composition was detected on the microbial metabolic quotient (qCO(2)) and no plant species richness effect was found on feeding activity of the mesofauna (assessed with a bait-lamina-test). Decomposition of cellulose and birchwood sticks was also not affected by plant species richness, but when legumes were absent, cellulose samples were decomposed more slowly (16% in 1996, 27% in 1997, P = 0.006). A significant decrease in earthworm population density of 63% and in total earthworm biomass by 84% was the single most prominent response to the reduction of plant species richness, largely due to a 50% reduction in biomass of the dominant 'anecic' earthworms. Voles (Arvicola terrestris L.) also had a clear preference for high-diversity plots. Soil moisture during the growing season was unaffected by plant species richness or the number of functional groups present. In contrast, soil temperature was 2 K higher in monocultures compared with the most diverse mixtures on a bright day at peak season. We conclude that the lower abundance and activity of decomposers with reduced plant species richness was related to altered substrate quantity, a signal which is not reflected in rates of decomposition of standard test material. The presence of nitrogen fixers seemed to be the most important component of the plant diversity manipulation for soil heterotrophs. The reduction in plant biomass due to the simulated loss of plant species had more pronounced effects on voles and earthworms than on microbes, suggesting that higher trophic levels are more strongly affected than lower trophic levels
- …
