Iron (Fe) minerals possess a huge specific surface area and high adsorption affinity, usually considered as rust tanks of organic carbon (OC), playing an important role in global carbon storage. Microorganisms can change the chemical form of Fe by producing Fe-chelating agents such as side chains and form a stable complex with Fe(III), which makes it easier for microorganisms to use. However, in seasonal frozen soil thawing, the succession of soil Fe-cycling microbial communities and their coupling relationship with Fe oxides and Fe-bound organic carbon (Fe-OC) remains unclear. We characterized changes in the Fe phase, Fe-OC, Fe-oxidizing bacteria (FeOB), and Fe-reducing bacteria (FeRB) in the subsoil and analyzed the microbial mechanism underlying Fe-OC changes in alpine grassland by constructing a composite structural equation model (SEM). We found that the Fe(III) content consistently exceeded that of Fe(II). Among the three types of Fe oxides, organically complex Fe (Fe-p) decreased from 2.54 to 2.30 gkg(-1), whereas the opposite trend was observed for poorly crystalline Fe (Fe-o). The Fe-OC content also decreased (from 10.31 to 9.47 gkg(-1); p < 0.05). Fe-cycling microorganisms were markedly affected by the thawing of frozen soil (except FeRB). Fe-p and Feo directly affected changes in Fe-OC. Soil moisture (SM) and FeOB were significant indirect factors affecting Fe-OC changes. Freeze-thaw changes in the subsoil of alpine grassland in Central Asia significantly affected FeOB and Fe oxides, thus affecting the Fe-OC content. To the best of our knowledge, this was the first study to examine the influence of Fe-cycling microorganisms on the Fe phase and Fe-OC in the soil of alpine grassland in Central Asia. Overall, our findings provide scientific clues for exploring the biogeochemical cycle process in future climate change.

This study presents features of airborne culturable bacteria and fungi from three different sites (Lanzhou; LZ; 1520 m ASL, Lhasa; LS; 3640 m ASL and Qomolangma; ZF; 4276 m ASL) representing urban (LZ and LS) and remote sites (ZF) over the Tibetan Plateau (TP). Total suspended particle (TSP) samples were collected with an air sampler (Laoying 2030, China) on a quartz filter. Community structures of bacteria and fungi were studied and compared among three different locations. The average levels of bacterial load in the outdoor air ranged from approximately 8.03 x 10(1)to 3.25 x 10(2)CFU m(-3)(Colony forming unit per m(3)). However, the average levels of fungal loads ranged from approximately 3.88 x 10(0)to 1.55 x 10(1)CFU m(-3). Bacterial load was one magnitude higher at urban sites LZ (2.06 x 10(2)-3.25 x 10(2)CFU m(-3)) and LS (1.96 x 10(2)-3.23 x 10(2)CFU m(-3)) compared to remote sites ZF (8.03 x 10(1)-9.54 x 10(1)CFU m(-3)). Similarly, the maximum fungal load was observed in LZ (1.02 x 10(1)-1.55 x 10(1)CFU m(-3)) followed by LS (1.03 x 10(1)-1.49 x 10(1)CFU m(-3)) and ZF (3.88 x 10(0)-6.26 x 10(0)CFU m(-3)). However, the maximum microbial concentration was observed on the same day of the month, corresponding to a high dust storm in Lanzhou during the sampling period. The reported isolates were identified by phylogenetic analysis of 16S rRNA genes for bacteria and ITS sequences for fungi amplified from directly extracted DNA. Bacterial isolates were mostly associated withProteobacteria,Eurotiomycetes and Bacillus, whereas fungal isolates were mostlyAspergillusandAlternaria. Overall, this is a pioneer study that provides information about the airborne microbial concentration and composition of three sites over the TP region depending on environmental parameters. This study provided preliminary insight to carry out more advanced and targeted analyses of bioaerosol in the sites presented in the study.

Recently, very active studies have been undertaken on the response and stability of permafrost carbon pool and key biogeochemical processes in permafrost regions to climate warming. By observing the significant differences in microbial community structure in regions of seasonal frost and permafrost, it is evident that microbes play key roles in the conversion of permafrost carbon. This paper reviews research progress at the cutting edges on the conversion and decomposition of permafrost carbon to climate warming and subsequent changes in microbial activities over the past decade. Findings indicated that: (1) Freezethaw cycles of soils in the active layer in permafrost regions showed an increasing annual trend and the existing survival patterns of permafrost microbes may be altered by the increasing freeze-thaw frequency; and (2) Soil microbes are an essential part of the cold-regions ecosystem and they play vital roles in soil carbon and nitrogen cycling, the mineralization and decomposition of soil organic matter. Thus, climate warming and subsequent permafrost degradation affect the conversion and decomposition of permafrost carbon, resulting in changes in CO2 and CH4 emissions, soil environmental factors, and soil microbial community structures. The laws for governing permafrost carbon conversion and the self-regulation mechanisms of soil microbes are important for natural ecosystems and environments in cold regions, and affect the strengths of greenhouse gas sources and sinks in permafrost regions.

This paper reviews the literature on cold-adapted micro-organisms which might exist in ice and permafrost. Properly identified, microbial markers in the cryolithozone could be used in palaeoenvironmental reconstructions, in distinguishing between epigenetic and syngenetic depositional sequences, and in the recognition of secondary thaw unconformities. Cryobiological problems include (1) whether the bacteria are dead, dormant or in the active state, and (2) what factors determine the preservation of cell structures. A possible consequence of permafrost thawing, based upon predicted global warming scenarios, is that there may be an increase in microbial activity and an increase in active layer thickness.