Soil respiration of two dominant tundra communities under controlled temperatures in Changbai Mountain, Northeast China

Numerous seasonal snowpacks exist on alpine tundra of Changbai Mountain, Northeast China. The structure and species composition are distinct between snowpack and nonsnowpack communities, implying the difference in ecological processes in the subsurface. In order to clarify the relationship between soil respiration with thermal condition in snowpacks, as well as its seasonal variation, the respiration in response to temperature was measured based on simulated experiments. In addition to soil temperature, primary productivity was also investigated by harvesting the current-year aboveground growth. Field sampling was conducted in two community types: Rhododendron aureum community occurred in snowpack and Vaccinium uliginosum var. alpinum community (as reference) in snow-free area. An Li-8100 soil respiration system (Li-COR Co.) was used for measuring CO₂ release. Soil organic matter, total nitrogen and available nitrogen were analyzed. Hydrolizable nitrogen in Vaccinium community was 370–585 mg kg^?1, total nitrogen was 0.298%–0.468%, and organic matter was 13.5%–17.3%. In Rhododendron community, hydrolizable nitrogen was 445–583 mg kg^?1, total nitrogen was 0.465%–0.696%, and organic matter was 15%–22%. Organic matter within 10 cm depth was 4.07 kg m^?2 in Vaccinium community, and 5.31 kg m^?2 in the other. Temperature-dependent equations indicated that Q₁₀ values in both communities were around 2, with the ranges of 1.81–2.67 in Vaccinium community and 1.67–2.21 in Rhododendron community. The temperature-dependent equation was formed as y = ae^bx, where y is respiration rate (μmol kg^?1 h^?1), a and b are coefficients, and x is temperature in Celsius degree. Coefficient a was 52–148 in Vaccinium community and 34–167 in Rhododendron community, with significant variation among samples taken in different years. The daily respiration (g C kg^?1 d^?1) equation was y = 0.021733e^0.084063x for Vaccinium community, and y = 0.023482e^0.06x for Rhododendron community, both varied significantly with season. As to yearly respiration rate, it was 8.57–17.96 g C kg^?1 a^?1 in Vaccinium community, with a peak in May and relatively even in other time. The yearly respiration calculated by an integrated equation fitted with samples taken in all seasons was 10.24 g C kg^?1 a^?1. By covering Vaccinium community with a quilt in the field during the winter, soil temperature was slightly raised. During the frozen season, the temperature was raised by approximately 1.5 °C. Hence the annual respiration was 544.41 g C m^?2, 12 g C m^?2 higher than that of the reference. Respiration for Rhododendron community was in the range of 4.57–21.15 g C kg^?1 a^?1, with its maximum in May. By the integrated equation, it was 10.35 g C kg?1a^?1or 537 g C m^?2 a^?1. The yearly respiration was 441–544 g C m^?2 a^?1 in Vaccinium community and 449–486 g C m^?2 a^?1 in Rhododendron community. Taking the form of respiration on the basis of per kg of organic carbon, it was 118 g C (kg C)^{? 1} a^?1 in Vaccinium community and 101 g C (kg C)^{? 1} a^?1 in Rhododendron community. In particular, winter respiration in Vaccinium community was 2.10 g C kg?1, or 20.50% of yearly total, and merely 1.59% in the coldest month. While in Rhododendron community, it was 3.40 g C kg?1, or 32.84% of yearly total, significantly higher than that in Vaccinium community. The respiration in Rhododendron community at elevation 2260 m was 468.21 g C m^?2 a^?1, and the biomass growth was 400 g C m^?2 a^?1. In contrast, due to the thinner snow cover, in elevation 2036 m the biomass growth was 225.0 g C m^?2 a^?1 versus the respiration rate of 486.60 g C m^?2 a^?1. Leaf area index varied significantly in Rhododendron communities, ranging from 1.48 to 3.14, also owing to the difference in snow depth. As a contrary, in Vacciniumu community, the biomass growth was 120.75 g C m^?2 a^?1 and the leaf area index was 1.58. In conclusion, snowpacks provide a suitable condition for microbiomes in the winter, and contribute a large proportion of respiration. This also implies the vigorous activity in nitrogen release during the frozen season, which results in the rapid thriving of plants after snowmelt.     

Soil respiration of two dominant tundra communities under controlled temperatures in Changbai Mountain, Northeast China

Numerous seasonal snowpacks exist on alpine tundra of Changbai Mountain, Northeast China. The structure and species composition are distinct between snowpack and nonsnowpack communities, implying the difference in ecological processes in the subsurface. In order to clarify the relationship between soil respiration with thermal condition in snowpacks, as well as its seasonal variation, the respiration in response to temperature was measured based on simulated experiments. In addition to soil temperature, primary productivity was also investigated by harvesting the current-year aboveground growth. Field sampling was conducted in two community types: Rhododendron aureum community occurred in snowpack and Vaccinium uliginosum var. alpinum community (as reference) in snow-free area. An Li-8100 soil respiration system (Li-COR Co.) was used for measuring CO₂ release. Soil organic matter, total nitrogen and available nitrogen were analyzed. Hydrolizable nitrogen in Vaccinium community was 370–585 mg kg^?1, total nitrogen was 0.298%–0.468%, and organic matter was 13.5%–17.3%. In Rhododendron community, hydrolizable nitrogen was 445–583 mg kg^?1, total nitrogen was 0.465%–0.696%, and organic matter was 15%–22%. Organic matter within 10 cm depth was 4.07 kg m^?2 in Vaccinium community, and 5.31 kg m^?2 in the other. Temperature-dependent equations indicated that Q₁₀ values in both communities were around 2, with the ranges of 1.81–2.67 in Vaccinium community and 1.67–2.21 in Rhododendron community. The temperature-dependent equation was formed as y = ae^bx, where y is respiration rate (μmol kg^?1 h^?1), a and b are coefficients, and x is temperature in Celsius degree. Coefficient a was 52–148 in Vaccinium community and 34–167 in Rhododendron community, with significant variation among samples taken in different years. The daily respiration (g C kg^?1 d^?1) equation was y = 0.021733e^0.084063x for Vaccinium community, and y = 0.023482e^0.06x for Rhododendron community, both varied significantly with season. As to yearly respiration rate, it was 8.57–17.96 g C kg^?1 a^?1 in Vaccinium community, with a peak in May and relatively even in other time. The yearly respiration calculated by an integrated equation fitted with samples taken in all seasons was 10.24 g C kg^?1 a^?1. By covering Vaccinium community with a quilt in the field during the winter, soil temperature was slightly raised. During the frozen season, the temperature was raised by approximately 1.5 °C. Hence the annual respiration was 544.41 g C m^?2, 12 g C m^?2 higher than that of the reference. Respiration for Rhododendron community was in the range of 4.57–21.15 g C kg^?1 a^?1, with its maximum in May. By the integrated equation, it was 10.35 g C kg?1a^?1or 537 g C m^?2 a^?1. The yearly respiration was 441–544 g C m^?2 a^?1 in Vaccinium community and 449–486 g C m^?2 a^?1 in Rhododendron community. Taking the form of respiration on the basis of per kg of organic carbon, it was 118 g C (kg C)^{? 1} a^?1 in Vaccinium community and 101 g C (kg C)^{? 1} a^?1 in Rhododendron community. In particular, winter respiration in Vaccinium community was 2.10 g C kg?1, or 20.50% of yearly total, and merely 1.59% in the coldest month. While in Rhododendron community, it was 3.40 g C kg?1, or 32.84% of yearly total, significantly higher than that in Vaccinium community. The respiration in Rhododendron community at elevation 2260 m was 468.21 g C m^?2 a^?1, and the biomass growth was 400 g C m^?2 a^?1. In contrast, due to the thinner snow cover, in elevation 2036 m the biomass growth was 225.0 g C m^?2 a^?1 versus the respiration rate of 486.60 g C m^?2 a^?1. Leaf area index varied significantly in Rhododendron communities, ranging from 1.48 to 3.14, also owing to the difference in snow depth. As a contrary, in Vacciniumu community, the biomass growth was 120.75 g C m^?2 a^?1 and the leaf area index was 1.58. In conclusion, snowpacks provide a suitable condition for microbiomes in the winter, and contribute a large proportion of respiration. This also implies the vigorous activity in nitrogen release during the frozen season, which results in the rapid thriving of plants after snowmelt.     

Ecology of testate amoebae communities from aquatic habitats in the Zackenberg area (Northeast Greenland)

A total of 67 taxa, belonging to 15 genera, were recorded from aquatic samples collected in Zackenberg (Northeast Greenland). Most taxa belong to the genera Difflugia, Centropyxis, Nebela and Euglypha. Trinema lineare showed the highest relative abundance. Seven taxa were recorded for the first time in the Arctic. A TWINSPAN classification reveals two groups, reflecting a local geographical distinction. In the ponds of the old Zackenberg delta area (group 1), two assemblages were found: the Paraquadrula globulosa-Cyphoderia perlucidus assemblage and the Difflugiella crenulata-Cryptodifflugia compressa assemblage. The lakes, the pools and ponds east of the Zackenberg river (group 2) also harbour two assemblages: the Trinema enchelys-Euglypha sp.1 assemblage and the Centropyxis aerophila-Difflugia globulosa assemblage. Although the lakes are chemically unique, having extremely low values for turbidity, colour, SiO²⁻ ₂, Cl⁻ and hardness, this is not reflected in the characteristic testacean communities. Accepted: 24 April 1999     

Distinct microbial communities associated with buried soils in the Siberian tundra

Cryoturbation, the burial of topsoil material into deeper soil horizons by repeated freeze–thaw events, is an important storage mechanism for soil organic matter (SOM) in permafrost-affected soils. Besides abiotic conditions, microbial community structure and the accessibility of SOM to the decomposer community are hypothesized to control SOM decomposition and thus have a crucial role in SOM accumulation in buried soils. We surveyed the microbial community structure in cryoturbated soils from nine soil profiles in the northeastern Siberian tundra using high-throughput sequencing and quantification of bacterial, archaeal and fungal marker genes. We found that bacterial abundances in buried topsoils were as high as in unburied topsoils. In contrast, fungal abundances decreased with depth and were significantly lower in buried than in unburied topsoils resulting in remarkably low fungal to bacterial ratios in buried topsoils. Fungal community profiling revealed an associated decrease in presumably ectomycorrhizal (ECM) fungi. The abiotic conditions (low to subzero temperatures, anoxia) and the reduced abundance of fungi likely provide a niche for bacterial, facultative anaerobic decomposers of SOM such as members of the Actinobacteria, which were found in significantly higher relative abundances in buried than in unburied topsoils. Our study expands the knowledge on the microbial community structure in soils of Northern latitude permafrost regions, and attributes the delayed decomposition of SOM in buried soils to specific microbial taxa, and particularly to a decrease in abundance and activity of ECM fungi, and to the extent to which bacterial decomposers are able to act as their functional substitutes.     

Coexistence of bisexual and unisexual populations of Nysius groenlandicus in the Zackenberg Valley,Northeast Greenland

The seed‐feeding true bug Nysius groenlandicus (Zetterstedt) (Heteroptera: Lygaeidae) has temperature and humidity preferences similar to many desert‐inhabiting insects. Nevertheless, it is widely distributed in Greenland and occurs even in high arctic areas. This seeming paradox implies that the species has developed physiological, ecological, and behavioral mechanisms that enable it to cope with the extreme arctic environment. One of these adaptations is its ability to reproduce both sexually and asexually. Sexual reproduction is most common in coastal populations, whereas asexual reproduction (parthenogenesis) occurs mainly in inland populations. Preliminary data from the Zackenberg Valley in Northeast Greenland indicated that both reproductive strategies occurred within the same area. We therefore decided to focus on this area to find evidence of (1) coexistence of unisexual and bisexual populations, (2) factors that correlate with the distribution of the two reproductive types, and (3) morphological differences between females from sexual and asexual populations. We sampled N. groenlandicus at 51 sites within the Zackenberg area. Males and females were found in almost equal numbers in only four of the samples, and only in samples taken close to the coast line, whereas samples from the inner part of the valley consisted almost entirely of females. Thus, the distribution of uni‐ and bisexual populations at the local scale agreed with the pattern previously found for Greenland as a whole. Using data obtained from two climate stations operated in the area, we showed that average summer temperatures tend to be more favorable for N. groenlandicus in the inner part of the valley than at the coast. The inland populations inhabited small isolated patches, whereas the sexual populations were found in the more homogeneous areas along the coast. Data support the hypothesis that coexistence of the two reproductive types is maintained by a combination of environmental variability, which gives sexual reproduction an advantage, and metapopulation dynamics characterized by frequent extinctions and re‐colonizations, which favors asexual reproduction. Head width of females from unisexual populations was on average 7% larger than that of females from bisexual populations. The mechanism behind this morphological difference needs further investigation.     

Terrestrial soil diatom assemblages from different vegetation types in Zackenberg (Northeast Greenland)

A total of 81 taxa were observed from 30 soil samples taken from 5 different vegetation types in Northeast Greenland. Most of the dominant diatoms are well-known cosmopolitan aerophilic taxa; only Caloneis aerophila and Pinnularia lagerstedtii are less widespread species. The valve lengths of P. borealis and Hantzschia amphioxys are correlated with the moisture content of the soils. Average cell number/g dry weight of soil amounts to 1,120,000 ± 740,000. In a TWINSPAN classification, the soils of the different vegetation types are separated, with the exception of the Vaccinium soils, which are grouped partly with the Cassiope samples and partly with the Salix soils. In a CCA ordination diagram, the Navicula atomus–Fragilaria elliptica assemblage shows a positive correlation with organic content and pH and a negative one with permafrost depth. The Pinnularia divergentissima var. martinii–P. obscura assemblage is positively correlated with moisture. The Pinnularia lagerstedtii–Caloneis aerophila assemblage is positively correlated with permafrost depth and negatively with pH and moisture. Accepted: 27 November 1999     

Structure of microbial communities of peat soils in two bogs in Siberian tundra and forest zones

The structure and functional activity of microbial complexes of a forest oligo-mesotrophic subshrub- grass-moss bog (OMB, Central Evenkiya) and a subshrub-sedge bog in the polygonal tundra (PB, Lena River Delta Samoylovsky Island) was studied. Soil of the forest bog (OMB) differed from that of the polygonal tundra bog (PB) in higher productivity (C_org, N_total, P, and K reserves), higher biomass of aerobic chemoorganotrophs (2.0 to 2.6 times), and twice the level of available organic matter. The contribution of microorganisms to the carbon pool was different, with the share of C_mic in C_org 1.4 to 2.5 times higher in PB compared to OMB. Qualitative composition of the methane cycle microorganisms in PB and OMB soils differed significantly. Methanogenic archaea (Euryarchaeota) in the shrub-sedge PB of tundra were more numerous and diverse than in the oligo-mesotrophic bog (OMB) and belonged to six families (Methanomassiliicoccaceae, Methanoregulaceae, Methanobacteriaceae, Methanomicrobiaceaee, Methanosarcinaceae, and Methanotrichaceae), while members of only four families (Methanosarcinacea, Methanobacteriaceae, Methanotrichaceae, and Methanomassiliicoccaceae) were revealed in OMB. In both bogs, methane-oxidizing bacteria belonged to Alphaproteobacteria (II) and Gammaproteobacteria (I). Methanotroph diversity was higher in OMB than in PB. Microbial communities of PB soils had higher potential activity of methanogenesis and methanotrophy compared to those of OMB. Methanogenic and methanotrophic activities in PB were 20 and 2.3 times higher, respectively, than in OMB.     

Occurrence and diversity of fungal entomopathogens in soils of low and high Arctic Greenland

Knowledge of the occurrence, distribution and diversity of pathogens of insects and arachnids (entomopathogens) in the Arctic is very limited. Climate change is expected to affect Arctic terrestrial arthropod communities and therefore also host–pathogen interactions, given that entomopathogens are present. We conducted a survey of fungal entomopathogens in soil samples collected at four localities in Greenland; two at low Arctic sites (Ritenbenk and Disko Island) and two at sites in the high Arctic (Zackenberg and Danmarkshavn). Fungi were isolated from soil samples using larvae of the insect species Galleria mellonella (Lepidoptera) and Tenebrio molitor (Coleoptera) as baits providing evidence that the fungal isolates were indeed entomopathogenic. Five fungal species (Ascomycota; Hypocreales) were found: Isaria fumosorosea Wize, Isaria farinosa (Holmsk.) Fr., Beauveria bassiana (Bals.) Vuill., Beauveria pseudobassiana Rehner and Humber and Tolypocladium inflatum W. Gams (syn.?=?T. niveum). I. farinosa was found at all four localities, while I. fumosorosea was detected in single samples at each of three localities including both high Arctic sites. Only the locality on Disko Island revealed B. bassiana, whereas B. pseudobassiana was isolated at the three other sites. T. inflatum was only found on Disko Island and only isolated with T. molitor as a bait insect. The results document that fungal entomopathogens are widely distributed in the soil environment in Greenland. Entomopathogens should therefore be included in future studies of arthropod ecology in the Arctic.     

Soil respiration of Alaskan tundra at elevated atmospheric carbon dioxide concentrations

Summary CO₂ efflux from tussock tundra in Alaska that had been exposed to elevated CO₂ for 2.5 growing seasons was measured to assess the effect of long- and short-term CO₂ enrichment on soil respiration. Long-term treatments were: 348, 514, and 683 μll⁻¹ CO₂ and 680 μll⁻¹ CO₂+4°C above ambient. Measurements were made at 5 CO₂ concentrations between 87 and 680 μll⁻¹ CO₂. Neither long- or short-term CO₂ enrichment significantly affected soil CO₂ efflux. Tundra developed at elevated temperature and 680 μll⁻¹ CO₂ had slightly higher, but not statistically different, mean respiration rates compared to untreated tundra and to tundra under CO₂ control alone.     

北极苔原土壤中可培养细菌的分离及其抗菌活性测定

【目的】北极地区具有高纬度、低温、高辐射等独特的环境条件。北冰洋及周围大面积的陆地区域鲜有人类踪迹,其中微生物数量不可低估。本研究旨在了解北极土壤中的可培养微生物的多样性及其抗菌活性。【方法】对来源于北极黄河站附近的7份不同植物根下苔原土壤进行直接涂布和富集培养后涂布。【结果】共获得细菌菌株721株,对其中608株进行细菌16S rRNA基因序列测定,归属于86个属,229个种,主要分布于变形菌门(Proteobacteria,54.3%)、放线菌门(Actinobacteria,21.2%)、拟杆菌门(Bacteroidetes,12.8%)、厚壁菌门(Firmicutes,10.0%)和奇异球菌门(Deinococcus-Thermus,1.6%)。其中从16S rRNA基因序列同源性推测有22株细菌菌株为潜在新种/属。从分离菌株中筛选出16株可抑制金黄色葡萄球菌(Staphylococcusaureus)或鲍氏不动杆菌(Acinetobacterbaumannii)生长的拮抗菌。【结论】获得了北极土壤地区特有的微生物菌株资源,为进一步筛选拮抗菌的活性物质提供了菌株基础。     

Acidobacteria in microbial communities of the bog and tundra lichens

Bacterial communities of the lichens from a Sphagnum bog (Karelia) and tundra (Vorkuta oblast) were investigated. Members of the phylum Acidobacteria were numerous in the thallus of living and decaying lichens (3.8 × 10⁸ cells/g), constituting 6 to 32% of the total bacterial number. Pure cultures of acidobacteria were isolated from the samples of living and decaying lichen thallus. Ten of them were identified and classified as members of subgroup 1 of the Acidobacteria. The hydrolytic activity of two strains isolated from the living and decomposing zones of the thallus was investigated. They were capable of growth on xylan, starch, pectin, laminarin, and lichen extract. Acidobacteria were shown to be a stable and numerous component of microbial communities of the bog and tundra lichens.     

Seasonal variation in enzyme activities and temperature sensitivities in Arctic tundra soils

Arctic soils contain large amounts of organic matter due to very slow rates of detritus decomposition. The first step in decomposition results from the activity of extracellular enzymes produced by soil microbes. We hypothesized that potential enzyme activities are low relative to the large stocks of organic matter in Arctic tundra soils, and that enzyme activity is low at in situ temperatures. We measured the potential activity of six hydrolytic enzymes at 4 and 20 °C on four sampling dates in tussock, intertussock, shrub organic, and shrub mineral soils at Toolik Lake, Alaska. Potential activities of N‐acetyl glucosaminidase, β‐glucosidase, and peptidase tended to be greatest at the end of winter, suggesting that microbes produced enzymes while soils were frozen. In general, enzyme activities did not increase during the Arctic summer, suggesting that enzyme production is N‐limited during the period when temperatures would otherwise drive higher enzyme activity in situ. We also detected seasonal variations in the temperature sensitivity (Q₁₀) of soil enzymes. In general, soil enzyme pools were more sensitive to temperature at the end of the winter than during the summer. We modeled potential in situβ‐glucosidase activities for tussock and shrub organic soils based on measured enzyme activities, temperature sensitivities, and daily soil temperature data. Modeled in situ enzyme activity in tussock soils increased briefly during the spring, then declined through the summer. In shrub soils, modeled enzyme activities increased through the spring thaw into early August, and then declined through the late summer and into winter. Overall, temperature is the strongest factor driving low in situ enzyme activities in the Arctic. However, enzyme activity was low during the summer, possibly due to N‐limitation of enzyme production, which would constrain enzyme activity during the brief period when temperatures would otherwise drive higher rates of decomposition.     

Phosphorus availability and microbial respiration across different tundra vegetation types

Phosphorus (P) is an important nutrient in tundra ecosystems that co-limits or in some cases limits primary production. The availability of P is largely driven by soil characteristics, e.g., pH, organic carbon, and abundance of P-sorbing elements such as aluminium (Al) or iron (Fe). We tested how vegetation and soil properties relate to P availability across different tundra vegetation types. The different soil P fractions in the organic horizon were measured and plant foliar nitrogen (N) to P ratio and a plant bioassay was used as indicators of plant nutrient status. Microbial bioassays were used to study microbial respiration kinetics and in response to carbon, N, and P amendments. The distribution of P fractions differed significantly across vegetation types; labile fractions of P were less abundant in meadow sites compared to heath sites. Calcium-phosphates seemed to be an important P-fraction in meadows, but were only found in lower concentrations in the heath. There were only small differences in NaOH–extractable P between the vegetation types and this correlated with the distribution of oxalate-extractable Al. Plant N:P ratios and the plant bioassay indicated decreasing P availability from dry heath to mesic heath to mesic meadow. The microbial bioassay suggests that the heterotrophic microbial community is C-limited with N as a secondary limiting nutrient although there were indications that microbial P availability was lower in the meadow sites. Overall, we suggest that the observed variations in soil P across vegetation types are affecting both plant and microbial function although the differences seem to be relatively small.     

Bacterial and fungal community structure in Arctic tundra tussock and shrub soils

Fungal and bacterial community structure in tussock, intertussock and shrub organic and mineral soils at Toolik Lake, Alaska were evaluated. Community structure was examined by constructing clone libraries of partial 16S and 18S rRNA genes. The soil communities were sampled at the end of the growing season in August 2004 and just after the soils thawed in June 2005. The communities differed greatly between vegetation types, although tussock and intertussock soil communities were very similar at the phyla level. The communities were relatively stable between sample dates at the phyla and subphyla levels, but differed significantly at finer phylogenetic scales. Tussock and intertussock bacterial communities were dominated by Acidobacteria, while shrub soils were dominated by Proteobacteria. These results appear consistent with previous work demonstrating that shrub soils contain an active, bioavailable C fraction, while tussock soils are dominated by more recalcitrant substrates. Tussock fungi communities had higher proportions of Ascomycota than shrub soils, while Zygomycota were more abundant in shrub soils. Recent documentation of increasing shrub abundance in the Arctic suggests that soil microbial communities and their functioning are likely to be altered by climate change.     

长白山苔原带土壤动物群落结构及多样性

长白山苔原生态系统对环境变化非常敏感,一旦破坏很难恢复。土壤动物是陆地生态系统的重要组成部分,联系着地上和地下生态系统。为探讨长白山苔原带土壤动物群落的组成、结构和多样性特征,于2009年5月、7月和9月对上部和下部苔原带土壤动物进行了研究。研究表明:长白山整个苔原带土壤动物优势类群为甲螨亚目、节跳虫科和球角跳虫科。下部苔原亚带土壤动物个体数和类群数多,群落结构较为复杂。土壤动物的个体数随生境和时间变化有很大波动,类群数变化则较小。在7月份个体数最少,而类群数随着时间的变化有减少的趋势。土壤动物的垂直分布随时间和生境的不同而异。上部苔原亚带9月的甲螨亚目(P﹤0.01)、革螨亚目(P﹤0.05)及下部苔原亚带5月的甲螨亚目、革螨亚目、辐螨亚目(P=0.03,P=0.011,P=0.027)0—5 cm土层显著高于凋落物层;下部苔原亚带5月的球角跳虫科(P=0.001)及各月的节跳虫科和山跳虫科在各层之间存在显著差异(P=0.001,P=0.036,P=0.005,P=0.001,P=0.04,P=0.009)。两个亚带土壤动物多样性随时间的变化都有递减的趋势。土壤动物的多样性指数、丰富度指数和均匀度指数均是下部苔原亚带高于上部苔原亚带,而优势度指数则相反。相似性指数表明两个亚带土壤动物群落组成上存在一定的差异,各类群的相对数量差异在9月最大。下部苔原亚带的生境条件较适宜土壤动物生存,生物多样性较高。     

On site bioremediation of hydrocarbon-contaminated Arctic tundra soils in inoculated biopiles

There is a need to develop technology to allow the remediation of soil in polar regions that have been contaminated by hydrocarbon fuel spills. Bioremediation is potentially useful for this purpose, but has not been well demonstrated in polar regions. We investigated biopiles for on-site bioremediation of soil contaminated with Arctic diesel fuel in two independent small-scale field experiments at different sites on the Arctic tundra. The results were highly consistent with one another. In biopiles at both sites, extensive hydrocarbon removal occurred after one summer. After 1 year in treatments with optimal conditions, total petroleum hydrocarbons were reduced from 196 to below 10 mg per kg of soil at one site, and from 2,109 to 195 mg per kg of soil at the other site. Addition of ammonium chloride and sodium phosphate greatly stimulated hydrocarbon removal and indicates that biodegradation was the primary mechanism by which this was achieved. Inoculation with cold-adapted, mixed microbial cultures further stimulated hydrocarbon removal during the summer immediately following inoculation. At one site, soil temperature was monitored during the summer season, and a clear plastic cover increased biopile soil temperature, measured as degree-day accumulation, by 30-49%. Our results show that on-site bioremediation of fuel-contaminated soil at Arctic tundra sites is feasible.     

Activity and species composition of aerobic methanotrophic communities in tundra soils

The low-temperature, methane-oxidizing activities and species composition of methanotrophic communities in various tundra bog soils were investigated by radioisotopic and immunofluorescent methods. Methanotrophic bacteria carried out the methane oxidation process through all horizons of seasonally thawed layers down to permafrost. The highest activity of the process has been observed in the water surface layer of overmoistured soils and in water-logged moss covers. Up to 40% of¹⁴CH₄ added was converted into¹⁴CO₂, bacterial biomass, and organic exometabolites. By immunofluoresecent analysis it was demonstrated that the representatives of I+X (Methylomonas, Methylobacter, andMethylococcus) and II (Methylosinus, Methylocystis) methanotrophic groups occurred simultaneously in all samples at 61.6% and 38.4%, respectively. The number of methane-oxidizing bacteria in the ecosystems studied was 0.1–22.9×10⁶ cells per gram of soil. Methanotrophic organisms ranged from 1% to 23% of the total bacterial number.     

The effect of nutrient deposition on bacterial communities in Arctic tundra soil

The microbial communities of high‐latitude ecosystems are expected to experience rapid changes over the next century due to climate warming and increased deposition of reactive nitrogen, changes that will likely affect microbial community structure and function. In moist acidic tundra (MAT) soils on the North Slope of the Brooks Range, Alaska, substantial losses of C and N were previously observed after long‐term nutrient additions. To analyse the role of microbial communities in these losses, we utilized 16S rRNA gene tag pyrosequencing coupled with community‐level physiological profiling to describe changes in MAT bacterial communities after short‐ and long‐term nutrient fertilization in four sets of paired control and fertilized MAT soil samples. Bacterial diversity was lower in long‐term fertilized plots. The Acidobacteria were one of the most abundant phyla in all soils and distinct differences were noted in the distributions of Acidobacteria subgroups between mineral and organic soil layers that were also affected by fertilization. In addition, Alpha‐ and Gammaproteobacteria were more abundant in long‐term fertilized samples compared with control soils. The dramatic increase in sequences within the Gammaproteobacteria identified as Dyella spp. (order Xanthomonadales) in the long‐term fertilized samples was confirmed by quantitative PCR (qPCR) in several samples. Long‐term fertilization was also correlated with shifts in the utilization of specific substrates by microbes present in the soils. The combined data indicate that long‐term fertilization resulted in a significant change in microbial community structure and function linked to changes in carbon and nitrogen availability and shifts in above‐ground plant communities.