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Tardigrades are omnipresent microfauna with scarce record on their ecology in soils. Here, we investigated soil inhabiting tardigrade communities in five contrasting polar habitats, evaluating their abundance, diversity, species richness, and species composition. Moreover, we measured selected soil physico‐chemical properties to find the drivers of tardigrade distribution among these habitats. In spite of reported tardigrade viability in extreme conditions, glacier forelands represented a habitat almost devoid of tardigrades. Even dry and wet tundra with soil developing for over more than 10 000 years held low abundances compared to usual numbers of tardigrades in temperate habitats. Polar habitats also differ in species composition, with Diaforobiotus islandicus being typical species for dry and Hypsibius exemplaris for wet tundra. Overall, tardigrade abundance was affected by the content of nutrients as well as physical properties of soil, i.e. content of total nitrogen (TN), total organic carbon (TOC), stoniness, soil texture and the water holding capacity (WHC). While diversity and species composition were significantly related to soil physical properties such as the bulk density (BD), soil texture, stoniness, and WHC. Physical structure of environment was, therefore, an important predictor of tardigrade distribution in polar habitats. Since many studies failed to identify significant determinants of tardigrade distribution, we encourage scientists to include physical properties of tardigrade habitats as explanatory variables in their studies. [ABSTRACT FROM AUTHOR]

Temperate coniferous forest soils are considered important sinks of soil organic carbon (C). Fresh C inputs may, however, affect soil microbial activity, leading to increased organic matter decomposition and carbon dioxide production. Litter consists of labile and recalcitrant fractions which are thought to be utilized by distinct microbial communities and at different rates during the growing season. In this study, we incubated the whole litter (LC + RC), the labile (LC) and the recalcitrant (RC) fractions with the coniferous soil at two temperatures representing spring/autumn (10 °C) and summer (20 °C) for one month. Soil respiration and microbial community composition were regularly determined using phospholipid fatty acids as biomarkers. The LC fraction greatly increased soil respiration at the beginning of the incubation period but this effect was rather short-term. The effect of the RC fraction persisted longer and, together with the LC + RC fraction, respiration increased during the whole incubation period. Decomposition of the RC fraction was more strongly affected by higher temperatures than decomposition of the more labile fractions (LC and LC + RC). However, when we consider the relative increase in soil respiration compared to the dH2O treatment, respiration increased more at a lower temperature, suggesting that available C is more important for microbial metabolism at lower temperatures. Although C was added only once in our study, no changes in microbial community composition were detected, possibly because the microbial community is adapted to relatively low amounts of additional C such as the amounts naturally found in litter. [ABSTRACT FROM AUTHOR]

Both plant species and CO2 concentration can potentially affect rhizodeposition and consequently soil microbial activity and community composition. However, the effect differs based on plant developmental stage. We focused on the effect of three plant species (forbs, grasses, and N2‐fixers) at an early stage of development on root C deposition and fate, soil organic matter (SOM) mineralization and soil microbial community composition at ambient (aCO2) and elevated (eCO2) CO2 levels. Plants were grown from seed, under continuous 13C‐labelling atmospheres (400 and 800 µmol mol−1 CO2), in grassland soil for three weeks. At the end of the growth period, soil respiration, dissolved organic C (DOC) and phospholipid fatty acid (PLFA) profiles were quantified and isotopically partitioned into root‐ and soil‐derived components. Root‐derived DOC (0.53 ± 0.34 and 0.26 ± 0.29 µg mL soil solution−1) and soil‐derived CO2 (6.14 ± 0.55 and 5.04 ± 0.44 µg CO2‐C h−1) were on average two times and 22% higher at eCO2 than at aCO2, respectively. Plant species differed in exudate production at aCO2 (0.11 ± 0.11, 0.10 ± 0.18, and 0.58 ± 0.58 µg mL soil solution−1 for Plantago, Festuca, and Lotus, respectively) but not at eCO2 (0.20 ± 0.28, 0.66 ± 0.32, and 0.75 ± 0.15 µg mL soil solution−1 for Plantago, Festuca, and Lotus, respectively). However, no differences among plant species or CO2 levels were apparent when DOC was expressed per gram of roots. Relative abundance of PLFAs did not differ between the two CO2 levels. A higher abundance of actinobacteria and G‐positive bacteria occurred in unplanted (8.07 ± 0.48 and 24.36 ± 1.18 mol%) and Festuca‐affected (7.63 ± 0.31 and 23.62 ± 0.69 mol%) soil than in Plantago‐ (7.04 ± 0.36 and 23.41 ± 1.13 mol%) and Lotus‐affected (7.24 ± 0.17 and 23.13 ± 0.52 mol%) soil. In conclusion, the differences in root exudate production and soil respiration are mainly caused by differences in root biomass at an early stage of development. However, plant species evidently produce root exudates of varying quality affecting associated microbial community composition. [ABSTRACT FROM AUTHOR]