Quantitative PCR of denitrification genes encoding the nitrate, nitrite, and nitrous oxide reductases was used to study denitrifiers across a glacier foreland. Environmental samples collected at different distances from a receding glacier contained amounts of 16S rRNA target molecules ranging from 4.9 ؋ 10 5 to 8.9 ؋ 10 5 copies per nanogram of DNA but smaller amounts of narG, nirK, and nosZ target molecules. Thus, numbers of narG, nirK, nirS, and nosZ copies per nanogram of DNA ranged from 2.1 ؋ 10 3 to 2.6 ؋ 10 4 , 7.4 ؋ 10 2 to 1.4 ؋ 10 3 , 2.5 ؋ 10 2 to 6.4 ؋ 10 3 , and 1.2 ؋ 10 3 to 5.5 ؋ 10 3 , respectively. The densities of 16S rRNA genes per gram of soil increased with progressing soil development. The densities as well as relative abundances of different denitrification genes provide evidence that different denitrifier communities develop under primary succession: higher percentages of narG and nirS versus 16S rRNA genes were observed in the early stage of primary succession, while the percentages of nirK and nosZ genes showed no significant increase or decrease with soil age. Statistical analyses revealed that the amount of organic substances was the most important factor in the abundance of eubacteria as well as of nirK and nosZ communities, and copy numbers of these two genes were the most important drivers changing the denitrifying community along the chronosequence. This study yields an initial insight into the ecology of bacteria carrying genes for the denitrification pathway in a newly developing alpine environment.Primary successional ecosystems, such as glacier forelands and volcanoes, present an ideal opportunity to study the biological colonization of substrates. Since the ice covers of many glaciers have receded over the past century, glacier forelands have released substrates for soil development. Autotrophic colonizers are expected to be important in the initial stages of primary community assembly. Organic substrates for microbial growth, however, might also come from allochthonous dead organic matter and living invertebrates in these environments. Hodkinson et al. (8) therefore recently proposed a previously unrecognized heterotrophic phase which should allow the initial establishment of functional communities. Accordingly, future studies in microbial ecology must account for both autotrophic and heterotrophic colonization along primary successional gradients such as glacier forelands, land lifts, floodplains, landslides, and volcanoes. In the past few years, studies have focused mainly on the composition and activities of the soil microbiota in primary succession of receding glaciers (19,21,24,25). Only a few studies have employed molecular tools to understand the diversity of archaeal and bacterial community structures along the forefields of receding glaciers (2,13,20). Analyses of activity and genetic structures of the nitrate reducer community at the Rotmoosferner glacier have shown that N cycling processes as well as microbial community composition depend on the successional age (...

Human impacts, including global change, may alter the composition of soil faunal communities, but consequences for ecosystem functioning are poorly understood. We constructed model grassland systems in the Ecotron controlled environment facility and manipulated soil community composition through assemblages of different animal body sizes. Plant community composition, microbial and root biomass, decomposition rate, and mycorrhizal colonization were all markedly affected. However, two key ecosystem processes, aboveground net primary productivity and net ecosystem productivity, were surprisingly resistant to these changes. We hypothesize that positive and negative faunal-mediated effects in soil communities cancel each other out, causing no net ecosystem effects.

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The development of soil archaeal community structures in relation to primary succession in bulk and rhizosphere soil was examined across the forefield of the receding Rotmoosferner glacier in Austria. Using cloning and denaturing gradient gel electrophoresis (DGGE) analysis of reverse transcription polymerase chain reaction (RT-PCR) products of extracted 16S rRNA, archaeal community structure was compared over a chronosequence representing approximately 150 years of soil development and to reference sites outside the glacier forefield, representing soil exposed for approximately 9500 years. Archaeal community composition was found to be dominated by members of the non-thermophilic or Group 1 Crenarchaeota, where a dramatic yet highly structured successional sequence was observed. Succession over the 150 years sequence could be identified as occurring in three stages, each of which had a phylogenetically distinct 1.1b crenarchaea community with those organisms present in pioneering and intermediate stages belonging to a lineage distinct from those in developed soils. Climax communities also contained organisms belonging to three other major non-thermophilic crenarchaeal lineages. Comparison of archaeal communities in the rhizosphere indicated that plant species composition was not the major driver of specific crenarchaeal populations. These results indicate the potential role of soil crenarchaea in the development of soil substrates, as well as ecological diversity within and between major Group 1 lineages.

[1] Investigations focusing on the temperature sensitivity of microbial activity and nutrient turnover in soils improve our understanding of potential effects of global warming. This study investigates the temperature sensitivity of C mineralization, N mineralization, and potential enzyme activities involved in the C and N cycle (tyrosine amino-peptidase, leucine amino-peptidase, ß-glucosidase, ß-xylosidase, N-acetyl-ß-glucosaminidase). Four different study sites in the Austrian alpine zone were selected, and soils were sampled in three seasons (summer, autumn, and winter). A simple firstorder exponential equation was used to calculate constant Q 10 values for the C and N mineralization over the investigated temperature range (0-30°C). The Q 10 values of the C mineralization (average 2.0) for all study sites were significantly higher than for the N mineralization (average 1.7). The Q 10 values of both activities were significantly negatively related to a soil organic matter quality index calculated by the ratios of respiration to the organic soil carbon and mineralized N to the total soil nitrogen. The chemical soil properties or microbial biomass did not affect the Q 10 values of C and N mineralization. Moreover, the Q 10 values showed no distinct pattern according to sampling date, indicating that the substrate quality and other factors are more important. Using a flexible model function, the analysis of relative temperature sensitivity (RTS) showed that the temperature sensitivity of activities increased with decreasing temperature. The C and N mineralization and potential amino-peptidase activities (tyrosine and leucine) showed an almost constant temperature dependence over 0-30°C. In contrast, ß-glucosidase, ß-xylosidase, and N-acetyl-ß-glucosaminidase showed a distinctive increase in temperature sensitivity with decreasing temperature. Low temperature at the winter sampling date caused a greater increase in the RTS of all microbial activities than for the autumn and summer sampling dates. Our results indicate (1) a disproportion of the RTS for potential enzyme activities of the C and N cycle and (2) a disproportion of the RTS for easily degradable C compounds (ß-glucose, ß-xylose) compared with the C mineralization of soil organic matter. Thus temperature may play an important role in regulating the decay of different soil organic matter fractions due to differences in the relative temperature sensitivities of enzyme activities.Citation: Koch, O., D. Tscherko, and E. Kandeler (2007), Temperature sensitivity of microbial respiration, nitrogen mineralization, and potential soil enzyme activities in organic alpine soils, Global Biogeochem. Cycles, 21, GB4017,