Long-term and realistic global change manipulations had low impact on diversity of soil biota in temperate heathland

In a dry heathland ecosystem we manipulated temperature (warming), precipitation (drought) and atmospheric concentration of CO(2) in a full-factorial experiment in order to investigate changes in below-ground biodiversity as a result of future climate change. We investigated the responses in community diversity of nematodes, enchytraeids, collembolans and oribatid mites at two and eight years of manipulations. We used a structural equation modelling (SEM) approach analyzing the three manipulations, soil moisture and temperature, and seven soil biological and chemical variables. The analysis revealed a persistent and positive effect of elevated CO(2) on litter C:N ratio. After two years of treatment, the fungi to bacteria ratio was increased by warming, and the diversities within oribatid mites, collembolans and nematode groups were all affected by elevated CO(2) mediated through increased litter C:N ratio. After eight years of treatment, however, the CO(2)-increased litter C:N ratio did not influence the diversity in any of the four fauna groups. The number of significant correlations between treatments, food source quality, and soil biota diversities was reduced from six to three after two and eight years, respectively. These results suggest a remarkable resilience within the soil biota against global climate change treatments in the long term

Litter quality indirectly influences community composition, reproductive mode and trophic structure of oribatid mite communities: a microcosm experiment

Abstract Our knowledge of the assembly processes of species-rich oribatid mite communities is fairly limited. Also, very little information is available on the effects of habitat factors on these processes. In this paper, the role of litter quality in pattern formation was investigated in a microcosm experiment using the ‘‘home-field advantage’’ approach. Native (home) and foreign (away) types of microarthropod assemblages were extracted from three types of litter samples (Turkey oak, Scots pine and black locust tree), and transferred alive into ‘home’ and ‘away’ samples, which have been defaunated and reinoculated with microorganisms to form microcosms. Microarthropods were extracted from the microcosms after incubation for 3–12 months. In addition to species identification and abundance records, some chemical properties of thelitter were measured. We hypothesized that oribatid mite communities deteriorate, the proportion of parthenogenetic individuals decreases and the proportion of omnivorous individuals increases in ‘away’ microcosms in contrast to ‘home’ systems. Pine and oak litter were favourable for all the three types of oribatid communities since their community traits in these types of litter were found to be similar to ‘home’ litter. Black locust litter was favourable only for its native oribatid community in the long run. The proportion of parthenogenetic individuals partly supported our hypothesis, mainly in black locust litter. The relative abundance of omnivorous individuals did not differ significantly between treatments. Litter quality is likely to influence oribatid mite assemblages only indirectly

Landscape geological age explains large scale spatial trends in oribatid mite diversity

To understand the overwhelming species richness in soil the focus of attention has traditionally been on local soil conditions, such as physical and chemical characteristics. Regional factors like landscape history have been largely ignored. The aim of our study was to assess the importance of geological site age and local site conditions on oribatid mite species richness in undisturbed forest soils. We wanted to evaluate the processes underlying spatial changes in oribatid species richness at the regional level. We selected 41 sites across the Netherlands with different forest types, located on soils with varying levels of humidity and nutrient richness. The selected sites formed a clear spatiotemporal gradient in geological site age, ranging from Holocene sites along the west coast and rivers towards Pleistocene sites in the east of the country. Five samples were collected at each site. Oribatid mites were counted and identified to the species level. In total 145 oribatid mite species were recorded. We observed that oribatid mite species richness across sites was positively affected by site age. Soil nutrient status, water availability, soil type, or forest vegetation type had rather a local modulating effect on soil mite diversity. The increase in species diversity with geological site age was mainly due to an increase in sexually-reproducing species, with an apparent high competitive ability, but lower reproduction rate. Our results suggest that spatial patterns of soil animal community diversity and composition can be significantly determined by geologic age at the regional level. © 2012 Springer Science+Business Media Dordrecht

Concordance between plant species, oribatid mites and soil in a Mediterranean stone pine forest

Biological interactions between above-ground and below-ground organisms are not clearly defined among communities with regard to compositional patterns. The study investigates the concordance of species assemblages between vascular plants and oribatid mites and soil chemical properties with special attention to the role of vegetation structure, i.e. tree, shrub and herbaceous cover, for biological components. Data were collected in a Mediterranean coastal Nature Reserve using sampling design based on random selection of plots with cover of stone pine (Pinus pinea L.) exceeding 15%. Agreement of distribution patterns was verified by Spearman's rank correlation coefficient applied to pairs of matrices of plot scores by principal component analysis (plants, mites and soil) and the Mantel test. The feasible role of vegetation cover on plant and mite assemblages was tested by redundancy analysis (RDA). Significant correlations were found for biological assemblages, indicating congruent plant-mite compositional patterns. On the other hand, the hypothesis of concordance between biological communities and soil was rejected. Moreover, RDA showed that vegetation cover was a driver of both plant and oribatid mite assemblages. In particular, herbaceous cover proved to be a good proxy for the two biological communities investigated, with different taxa linked to forest clearings and to areas with denser tree cover. Our results indicate that soil features were not of primary importance for below-ground and above-ground community assemblages in the study area. In the light of our findings and ongoing threats in coastal areas, we recommend that management measures be directed at maintenance of diversified vegetation structure, which may ensure above-ground and below-ground biodiversity with diverse biological community assemblages