SummaryA microcosm-based approach was used to study impacts of plant and chemical factors on the bacterial community structure of an upland acidic grassland soil. Seven perennial plant species typical of both natural, unimproved ( Nardus stricta , Agrostis capillaris , Festuca ovina and F. rubra ) and fertilised, improved ( Holcus lanatus, Lolium perenne and Trifolium repens ) grasslands were either left unamended or treated with lime, nitrogen, or lime plus nitrogen in a 75-day glasshouse experiment. Lime and nitrogen amendment were shown to have a greater effect on microbial activity, biomass and bacterial ribotype number than plant species. Liming increased soil pH, microbial activity and biomass, while decreasing ribotype number. Nitrogen addition decreased soil pH, microbial activity and ribotype number. Addition of lime plus nitrogen had intermediate effects, which appeared to be driven more by lime than nitrogen. Terminal restriction fragment length polymorphism (TRFLP) analysis revealed that lime and nitrogen addition altered soil bacterial community structure, while plant species had little effect. These results were further confirmed by multivariate redundancy analysis, and suggest that soil lime and nitrogen status are more important controllers of bacterial community structure than plant rhizosphere effects.

Understanding the links between plant diversity and soil communities is critical to disentangling the mechanisms by which plant communities modulate ecosystem function. Experimental plant communities varying in species richness, evenness, and density were established using a response surface design and soil community properties including bacterial and archaeal abundance, richness, and evenness were measured. The potential to perform a representative soil ecosystem function, oxidation of ammonium to nitrite, was measured via archaeal and bacterial amoA genes. Structural equation modeling was used to explore the direct and indirect effects of the plant community on soil diversity and potential function. Plant communities influenced archaea and bacteria via different pathways. Species richness and evenness had significant direct effects on soil microbial community structure, but the mechanisms driving these effects did not include either root biomass or the pools of carbon and nitrogen available to the soil microbial community. Species richness had direct positive effects on archaeal amoA prevalence, but only indirect impacts on bacterial communities through modulation of plant evenness. Increased plant evenness increased bacterial abundance which in turn increased bacterial amoA abundance. These results suggest that plant community evenness may have a strong impact on some aspects of soil ecosystem function. We show that a more even plant community increased bacterial abundance, which then increased the potential for bacterial nitrification. A more even plant community also increased total dissolved nitrogen in the soil, which decreased the potential for archaeal nitrification. The role of plant evenness in structuring the soil community suggests mechanisms including complementarity in root exudate profiles or root foraging patterns.

This study exploited the contrasting major element chemistry of a pegmatitic granite to investigate mineralogical influences on bacterial community structure. Intact crystals of variably weathered muscovite, plagioclase, K-feldspar, and quartz were extracted, together with whole-rock granite. Environmental scanning electron microscopy revealed a diversity of bacterial structures, with rods and cocci clearly visible on surfaces of all mineral types. Bacterial automated ribosomal intergenic spacer analysis was used to generate a ribotype profile for each mineral. A randomization test revealed that community fingerprints differed between different mineral types, whereas canonical correspondence analysis (CCA) showed that mineral chemistry affected individual bacterial ribotypes. CCA also revealed that Al, Si, and Ca had a significant impact on bacterial community structure within the system, which contrasts with the finding within fungal communities that although Al and Si also had a significant impact, K rather than Ca was important. The bacterial populations associated with different minerals were different. Members of each of these populations were found almost exclusively on a single mineral type, as was previously reported for fungal populations. These results show that bacterial community structure was driven by the chemical composition of minerals, indicating selective pressure by individual chemical elements on bacterial populations in situ.

Floristically diverse Nardo-Galion upland grasslands are common in Ireland and the UK and are valuable in agricultural, environmental and ecological terms. Under improvement (inputs of lime, fertiliser and re-seeding), they convert to mesotrophic grassland containing very few plant species. The effects of upland grassland improvement and seasonality on soil microbial communities were investigated at an upland site. Samples were taken at five times in one year in order to observe seasonal trends, and bacterial community structure was monitored using automated ribosomal intergenic spacer analysis (ARISA), a DNA-fingerprinting approach. Differences in soil chemistry and bacterial community structure between unimproved and improved grassland soils were noted. Season was also found to cause mild fluctuations in bacterial community structure, with soil samples from colder months (October and December) more correlated with change in ribotype profiles than samples from warmer months. However, for the majority of seasons clear differences in bacterial community structures from unimproved and improved soils could be seen, indicating seasonal influences did not obscure effects associated with improvement.

A microcosm-based approach was used to study impacts of plant and chemical factors on the fungal community structure of an upland acidic grassland soil. Seven plant species typical of both unimproved and fertilised grasslands were either left unamended or treated with lime, nitrogen, or lime plus nitrogen. Fungal community structure was assessed by a molecular approach, fungal ARISA, while fungal biomass was estimated by measuring soil ergosterol content. Addition of nitrogen (with or without lime) had the largest effect, decreasing soil pH, fungal biomass, and fungal ribotype number, but there was little corresponding change in fungal community structure. Although different plant species were associated with some changes in fungal biomass, this did not result in significant differences in fungal community structure between plant species. Addition of lime alone caused no changes in fungal biomass, ribotype number or community structure. Overall, fungal community structure appeared to be more significantly affected through interactions between plant species and chemical treatments, as opposed to being directly affected by changes in individual improvement factors. These results were in contrast to those found for the bacterial communities of the same soils (Kennedy et al., 2004), which changed substantially in response to chemical (lime and nitrogen) additions.3

The expression of polysialylated neurons in the dentate gyrus of the hippocampal formation of young (postnatal day 40), mature (postnatal day 80) and aged (postnatal day 540) male Wistar rats has been investigated by immunohistochemical techniques employing a monoclonal antibody specific for neural cell adhesion molecule-linked alpha 2,8 polysialic acid. A strong immunoreactivity was found on the cell bodies, dendrites and axons of granule-like neuronal cells at the border between the hilar region and the granule cell layer of the young rat. In the mature animal the number of immunoreactive neurons declined dramatically and were virtually absent in the aged group. Using an alternative fixation procedure, glial fibrillary acidic protein-positive and polysialylated astroglia processes were found in close proximity to the dendrites of the polysialylated granule-like cells. The number of astroglial processes traversing the granule cell layer showed a similar age-dependent decline to that observed with the polysialylated neurons. Glial fibrillary acidic protein-positive and polysialylated stellate astroglia were present throughout the hippocampal formation, but did not show the marked age-dependent decline observed with the astroglial processes in the granule cell layer. The neuronal dendrites and astroglial processes exhibited a strict numerical ratio in the young and mature animal and, in double immunofluorescence studies with anti-polysialic acid and anti-glial fibrillary acidic protein, the astroglial processes exhibited apparent points of cell and/or dendritic contact. These findings suggest that loss of polysialylated astroglial processes precedes the decline in polysialylated dentate neurons.

Abstract7 Changes in soil microbial community structure due to 8 improvement are often attributed to concurrent shifts in 9 floristic community composition. The bacterial and 10 fungal communities of unimproved and semi-improved 11 (as determined by floristic classification) grassland soils 12 were studied at five upland sites on similar geological 13 substrata using both broad-scale (microbial activity and 14 fungal biomass) and molecular [terminal restriction 15 fragment length polymorphism (TRFLP), automated 16 ribosomal intergenic spacer analysis (ARISA)] ap-17 proaches. It was hypothesized that microbial community 18 structure would be similar in soils from the same 19 grassland type, and that grassland vegetation classifica-20 tions could thus be used as predictors of microbial 21 community structure. Microbial community measure-22 ments varied widely according to both site and grassland 23 type, and trends in the effect of grassland improvement 24 differed between sites. These results were consistent with 25 those from similar studies, and indicated that floristic 26 community composition was not a stable predictor of 27 microbial community structure across sites. This may 28 indicate a lack of correlation between grassland plant 29 composition and soil microbial community structure, or 30 that differences in soil chemistry between sites had larger 31 impacts on soil microbial populations than plant-related 32 effects. 35 Introduction 36 Grassland plant communities can often be described in 37 terms of the characteristic species that make up their 38 composition. However, the extent of coupling between 39 grassland plant composition and soil microbial structure 72In recent years, the National Vegetation Classifica-73 tion (NVC) system [49] Total soil ergosterol was quan-167 tified as described previously [9]. Briefly, 5 g soil was 168 vortexed and sonicated with methanol and potassium 169 hydroxide solution at 0-C. Subsequently, after incuba-170 tion at 85-C for 30 min, followed by cooling at 4-C for 171 20 min, high-performance liquid chromatography 172 (HPLC)-grade pentane was used to extract ergosterol 173 from the soil mixture. Three pentane extracts were 174 combined and dried under N 2 gas before being redis-175 solved in methanol and filtered through 0.2-mm Teflon 176 filters, then analyzed on a Waters Sugar Analyzer I HPLC 177 system (Elstree, Hertfordshire, UK). Incorporation of an 178 internal ergosterol standard allowed the extraction effi-179 ciency of ergosterol from soil in these experiments to be 180 estimated at 87 T 4.7%. 181Total Soil DNA Extraction and Purification.Total 182 soil DNA was extracted as previously described [8]. 183 Briefly, soil (0.5 g) was added to tubes containing glass and 184 zirconia beads, to which hexadecyltrimethylammonium 185 bromide (CTAB) extraction buffer was added. After 186 incubation at 70-C for 10 min, phenol/chloroform/ 187 isoamylalcohol (25:24:1) was added and tubes were 188 then shaken in a Hybaid Ribolyser (Ashford, UK) at 189 5.5 m/s for 30 s. F...

Seasonal and management influences on the fungal community structure of two upland grassland soils were investigated. An upland site containing both unimproved floristically diverse (U4a) and improved mesotrophic (MG7b) grassland types was selected. Samples from both grassland types were taken at five times in one year. Soil fungal community structure was assessed using fungal automated ribosomal intergenic spacer analysis (ARISA), a DNA-profiling approach. A grassland management regime was found to strongly affect fungal community structure, with fungal ARISA profiles from unimproved and improved grassland soils differing significantly. The number of fungal ribotypes found was higher in unimproved than improved grassland soils, providing evidence that improvement may reduce the suitability of upland soil as a habitat for specific groups of fungi. Seasonal influences on fungal community structure were also noted, with samples taken in autumn (October) more correlated with change in ribotype profiles than samples from other seasons. However, seasonal variation did not obscure the measurement of differences in the fungal community structure that were due to agricultural improvement, with canonical correspondence analysis indicating grassland type had a stronger influence on fungal profiles than did season.Key words: upland grasslands, fungal automated ribosomal intergenic spacer analysis, seasonality, improvement, canonical correspondence analysis.