Klemens Ekschmitt

Nematode community structure as indicator of soil functioning in European grassland soils

This investigation analyses whether soil nematode diversity is correlated with soil functional parameters to serve as bioindicator of soil functioning. The analysis focuses on the interrelations of nematofauna, microflora, and soil nitrogen pools. The sites studied represent six major European grassland types: Northern tundra, atlantic heath, wet grassland, seminatural temperate grassland, East European steppe, and mediterranean garigue. Continental and local climate gradients were combined to a wide and continuous range of microclimate conditions. Nematode richness, as indicated by the number of genera, was highest under temperate conditions and declined towards the climatic extremes. Differences in richness affected all nematode feeding types proportionally. Nematode richness was the only parameter among a range of 15 alternatives tested that exhibited consistent correlations with mass and activity parameters of both nematofauna and microflora in the mineral grassland soils (garigue, wet grassland, seminatural grassland, steppe). In the same soils, the nematode Maturity Index was the best indicator of nitrogen status. We conclude that a high nematode richness can generally be seen as a good indicator of an active nematofauna and microflora in mineral grassland soils, and hence as an indicator of the decomposition function. The prospects of exploiting nematode diversity as an indicator of soil functioning are critically discussed.

Soil biodiversity and its implications for ecosystem functioning in a heterogeneous and variable environment

Abstract This paper evaluates theoretical arguments and empirical evidence on the interrelation of soil biodiversity and ecological functioning, in order to identify appropriate methodologies and promising fields of investigation. Predictions from a range of general theories are evaluated against the background of empirical findings and results from models on specific soil ecosystems with reference to the functional effects of species losses (1) within trophic levels, (2) in food-webs, and (3) those that depend on the size of the spatial scale. Difficulties in proving species richness effects empirically arise because (i) a range of mechanisms can compensate species richness effects, (ii) predictions on the effects of species richness are context-dependent, which renders valid generalisations less likely, and (iii) species richness effects are of a probabilistic, rather than a deterministic nature. Generally, the effects of changes in species richness are likely to be stronger in species-poor communities than in species-rich communities. The authors deduce the hypotheses that (a) the species richness within trophic levels is likely to reduce functional gaps in space and time, (b) the species richness across trophic levels of the decomposer food web can enhance synchronisation of subprocesses of nutrient cycling, and (c) differences in species richness are likely to be more pronounced on larger spatial scales. The authors infer that an explicit consideration of spatiotemporal variation is essential in experimentation, as well as in modelling, in order to analyse species richness–function relationships.

Design and evaluation of nematode 18S rDNA primers for PCR and denaturing gradient gel electrophoresis (DGGE) of soil community DNA

Abstract Consensus nematode 18S ribosomal DNA primers were designed by aligning available 18S sequences and identifying a variable region flanked by highly conserved regions. These primers were then used to amplify nematode 18S rDNA from whole soil community DNA extracted from a range of European grassland types. Cloning of the PCR amplicons (778 bp) followed by restriction digest analysis (RFLP) resulted in the recovery of 34 unique nematode sequences from the four grasslands studied. Comparison of these data with the limited number of 18S rDNA nematode sequences currently held in on-line databases revealed that all of the sequences could be assigned to known nematode taxa albeit tentatively in some cases. Two of the sequences recovered from the site in the Netherlands (wet, hay-grassland) were recovered in a clade that included a sequence of the genus Trichodorus whilst other sequences from this site showed similarity with 18S rDNA sequences of the genus Prismatolaimus (five sequences), Xiphinema (one sequence) and Enoplus (one sequence). Of the remaining sequences, two showed some affinity with Mylonchulus (UK, upland peat), four with Steinernema (UK) and one sequence with Mesorhabditis (Hungary, east European Steppe). Three sequences from the Netherlands and one from Hungary were recovered in a clade that included a sequence of the genus Pratylenchoides whilst three further sequences from the Netherlands and two from Hungary were recovered in a clade encompassing the genus Globodera. Of the remaining nine sequences, two (NL6, NL62) formed a distinct lineage within the Adenophorea with 90% bootstrap recovery in a paraphyletic clade that included sequences of Prismatolaimus and Trichodorus. Seven sequences (three from the Netherlands, three from the UK and one from Greece) were left unassigned though the tree topology suggested some relationship (58% bootstrap recovery) with the genus Cephalobus. To assess whether primers used to amplify 18S rDNA might be used to fingerprint genetic diversity in nematode communities in soil, the environmental sequence data were used to design a second set of primers carrying a GC-clamp. These primers amplified a 469 bp fragment internal to the region flanked by the primer set used to derive the nematode trees and were used to amplify 18S rDNA for subsequent analysis using denaturing gradient gel electrophoresis (DGGE). DGGE analysis of six major European grassland types revealed considerable genetic diversity between sites. However, the relationships seen with the DGGE data were inconsistent with previous studies where the same soils had been characterized with respect to functional and morphological diversity. To confirm that this second set of primers was amplifying nematode sequences, selected bands on the DGGE gels were extracted, PCR amplified and sequenced. The final alignment was 337 bases. These analyses revealed the presence of sequence signatures from the genera Paratrichodorus, Plectus, Steinernema, Globodera, Cephalobus and Pratylenchoides.

Changes in nematode communities following cultivation of soils after fallow periods of different length

Abstract The composition of the nematofauna was studied in four soils that differed in the length of fallow restoration period since previous cultivation. The longest fallow period was 21 years. Plots were sampled for 2 years after starting cultivation of the fallow soils. The treatments were ranked following a restoration–exploitation gradient depending on fallow duration and the number of years of millet cultivation after fallow clearing; components of the nematofauna were analysed for correlation with this ranking. The nematode community structures at the first date of sampling during cultivation clearly reflected the length of the fallow period. Nematode community structures in the fallow soils rapidly approached those in the continuously cultivated soil; they were hardly distinguishable during the second year of cultivation. One-third of the recorded nematode taxa exhibited pronounced responses to the cultivation. Mononchidae, Anatonchidae, Tylencholaimoidea, Acrobeles , Pseudacrobeles , Tylenchidae and Helicotylenchus preferred sites of more mature successional status, while Dorylaimoidea, Tylenchorhynchus and Rhabdolaimidae dominated the cultivated sites. The maturity index (MI) did not distinguish the management regimes. The plant parasite index (PPI) tended to decrease with higher restoration status linked to greater abundance of the Tylenchidae in these situations. The decrease of fungal to bacterial feeders reflected a decreasing importance of the fungal decomposition pathway after resuming cultivation.

Effects of the nematofauna on microbial energy and matter transformation rates in European grassland soils

The effect of the nematofauna on the microbiology and soil nitrogen status was studied in 6 major European grassland types (Northern tundra (Abisko, Sweden), Atlantic heath (Otterburn, UK), wet grassland (Wageningen, Netherlands), semi-natural temperate grassland (Linden, Germany), East European steppe (Pusztaszer, Hungary) and Mediterranean garigue (Mt. Vermion, Greece). To extend the range of temperature and humidity experienced locally during the investigation period, soil microclimates were manipulated, and at each site 14 plots were established representing selected combinations of 6 temperature and 6 moisture levels. The investigated soils divided into two groups: mineral grassland soils that were precipitation fed (garigue, wet grassland, seminatural grassland, steppe), and wet organic soils that were groundwater fed (heath, tundra). Effects of the nematofauna on the microflora were found in the mineral soils, where correlations among nematode metabolic activity as calculated from a metabolic model, and microbial activity parameters as indicated by Biolog and ergosterol measurements, were significantly positive. Correlations with bacterial activity were stronger and more consistent. Microbial parameters, in turn, were significantly correlated with the size of the soil nitrogen pools NH4, NO3, and Norganic. Furthermore, model results suggested that there were remarkable direct effects of nematodes on soil nitrogen status. Calculated monthly nematode excretion contributed temporarily up to 27% of soluble soil nitrogen, depending on the site and the microclimate. No significant correlation among nematodes and microbial parameters, or nitrogen pools, were found in the wet organic soils. The data show that the nematofauna can under favourable conditions affect soil nitrogen status in mineral grassland soils both directly by excretion of N, and indirectly by regulating microbial activity. This suggests that the differences in nitrogen availability observed in such natural grasslands partly reflect differences in the activity of their indigenous nematofauna.

On the quality of soil biodiversity indicators: abiotic and biotic parameters as predictors of soil faunal richness at different spatial scales

Abstract Direct measurement of soil biodiversity is expensive, and therefore a substitution of measurement by indication is desirable. We analysed three large datasets for the potential to predict the diversity of soil faunal groups from other parameters. The datasets represent different spatial scales, namely grassland nematodes on an European scale, forest collembola on a regional scale, and grassland ants on a local scale. We tested two groups of parameters as possible surrogates for species richness: (1) environmental parameters, such as climate, soil and vegetation characteristics, and (2) community parameters, such as higher taxon richness, indicator taxa, and maximum dominance. Climate and soil parameters were significantly correlated with biodiversity in all datasets. However, in spite of the large variety of measurement types analysed, prediction quality of environmental variables was weak and the explained proportion of variance ranged generally below 50%. Richness was subject to considerable stochastic variation among subsamples (CV=20–60%) thereby evading a narrow correlation with environmental parameters. Higher taxon richness, based on taxa of intermediate hierarchical order, proved the best predictor of richness in collembola and nematodes explaining 55 and 89% of total variance, respectively. A combination of two ant species was the best predictor of ant richness explaining 59% of total variance. The authors conclude that a rough guess of soil faunal diversity can be cost-effectively derived from environmental data while an estimate of moderate quality can be obtained with reduced taxonomic effort. The precise richness of a soil community, however, is subject to autogeneous community dynamics, to biotic interactions with other populations, and to conditions in the past, and can therefore only be retrieved by immediate investigation of the community itself. Criteria for the quality of indicator parameters are discussed.

Impact of agricultural subsidies on biodiversity at the landscape level

Agricultural management is a major factor driving the change of faunal richness in anthropogenic landscapes. Thus, there is an urgent need to develop tools that allow decision-makers to understand better intended and unintended effects of agricultural policy measures on biodiversity. Here we demonstrate the potential of such a tool by combining a socio-economic model with the biodiversity model GEPARD to forecast the response of bird and carabid species richness to two scenarios of agricultural subsidies: (1) subsidies based on production levels and prices and (2) direct income support that is independent of production levels. We focussed on farmland of the Lahn-Dill area, Germany, as an example of European regions with low intensity farming. GEPARD predicts faunal richness and is based on multi-scaled resource-selection functions. Under both scenarios the area of predicted losses in species richness of birds and carabids was larger than the area of predicted gains in species richness. However, the area with predicted losses of avian richness was smaller under the direct income support scenario than under the production-based subsidy scenario, whereas the area with predicted losses of carabid species richness was smaller under the production-based subsidy scenario than under the direct income support. Yet locally, richness gains of up to four species were predicted for carabids under both scenarios. We conclude that the sometimes contrasting and heterogeneous responses of birds and carabids at different localities suggest the need for spatially targeted subsidy schemes. With the help of the GIS-based approach presented in this study, prediction maps on potential changes in local and regional species richness can be easily generated.

Changes in nematode communities after manuring in millet fields in Senegal

Changes in the soil nematofauna community structure were followed in nine millet fields on seven farms in two villages in Senegal during one cropping cycle. Cultivation practices were done by field owners. One plot in each field was divided into two subplots; in one of these, manure (20 t ha-1) was added at sowing. Before the manure input, at mid-cycle and at millet harvest, the structure of the nematode fauna was studied. Soil physico-chemical characteristics, microbial carbon and plant production were measured at sowing and at millet harvest. In the sub-plots where manure was added, millet yield increased by 155%, the mineral nitrogen content of the soil increased by about 45%, while nitrogen flux increased by 150% and microbial biomass by 65%. The significant enrichment of soil by manure led to a 75% increase in total nematode population density at mid-cycle and to a 30% increase at harvest time. The density of opportunistic bacterial-feeding and fungal-feeding nematodes was significantly larger with than without manure. This result is similar to those of comparable studies in temperate areas; however the relative abundance of enrichment opportunists was extremely low with regard to that found under similar conditions in temperate ecosystems. Furthermore, the abundance of the c-p 2 bacterialfeeding nematodes, belonging mainly to the family Cephalobidae, was strongly correlated with soil microbial biomass. The other c-p feeding guilds showed no correlation with nitrogen flux, or soil microbial biomass.

Increased energy maize production reduces farmland bird diversity

Producing energy crops as an alternative to fossil fuels in order to reduce CO2 emissions will lead to large‐scale changes in agricultural landscapes. Here, we quantify the potential impact of an increase in maize fields on the diversity of farmland birds by means of high resolution (25 × 25 m) land‐use scenarios. We generated scenarios in which the area of maize production in Germany increases from presently 2.6 to 2.9, 3.6 and 4.3 million ha, corresponding to the energy crop production targets of the German Renewable Energy Act for the years 2020, 2035 and 2050. To test the mitigating potential of conservation measures, each scenario was generated in a standard version and a landscape protection version, with the latter excluding valuable farmland areas from being converted into maize fields. Nine species of farmland birds belonging to the governmental indicator scheme for sustainable land‐use in Germany were modelled for the six nation‐wide scenarios. The models predicted that only the Northern Lapwing and the Little Owl might profit from extended maize production. Despite this, the total number of breeding pairs of the indicator species was predicted to decline by about 0.4 million breeding pairs in the most intensive scenario. Protection of valuable farmland did not mitigate these negative effects in the models. Our findings suggest that increased production of energy crops conflicts with conservation of biological diversity.

Efficient Placement of Nest Boxes for the Little Owl (Athene noctua)

Abstract The use of artificial nest boxes to bolster populations of endangered cavity-nesting birds has increased significantly, but spatial variation of nest-box occupancy rates and breeding success within a nest-box population has been little studied. In a case study with 798 Little Owl (Athene noctua) nest boxes established in central Germany, we analyzed the dependence of occupancy rate and breeding success on the characteristics of the surrounding habitat. The analysis focused on two aspects of general concern for nest-box management: (1) whether nest boxes were occupied for breeding or were left unoccupied, and (2) whether Little Owls had different reproductive rates, depending on the location of nest boxes. A high resolution (1 × 1 m) land-use map was used to analyze species-habitat relationships, and Generalized Linear Mixed Models were used to predict suitable nest-box locations. During the period from 2004 to 2006, 544 (68%) of the nest boxes were never occupied, 144 (18%) housed birds with low breeding success and only 108 (14%) housed pairs that produced more than 2.35 nestlings annually, a reproductive rate thought necessary for population stability. Nest boxes were more likely to be occupied if they were located near orchards, at lower altitude, and in areas of higher densities of fields and less forest. Higher breeding success was associated with fallow fields and field margins, and with greater distance to roads and forests. Our results suggested that the efficiency of this nest-box program could be substantially increased if unoccupied nest boxes were relocated to sites where occupancy is more likely, and if unproductive nest boxes were relocated to locations that would enhance breeding success.