• Energy Research

It is widely accepted that bacterial community composition and diversity in remote alpine lakes are structured by environmental conditions such as nutrient status and temperature. However, the mechanisms that underlie and structure bacterial community composition and diversity in alpine lakes remain unclear. We used 16S rRNA gene-based Illumina MiSeq sequencing to investigate the complex ecological interactions between bacterial communities and nutrient status in Kalakuli Lake, an alpine glacial-fed lake in Muztagh Ata of the westernmost Tibetan Plateau. Our results indicated that the bacterial community was dominated by the Actinobacteria and Proteobacteria. The results of threshold estimates showed that there were apparent shifts in dominance from the Proteobacteria to Actinobacteria groups associated with increasing carbon to nitrogen (C:N) ratio, and the change points were 6.794 and 2.448, respectively. Using multiple statistical methods, we found that the abiotic factors of dissolved organic carbon and total nitrogen had substantial impacts on bacterial diversity, while bacterial community compositions were significantly correlated with both the biotic element of bacterial abundance and the abiotic ones, temperature and pH. These findings demonstrated that the C:N ratio played a significant role in shifting dominant bacterial assemblages in the Kalakuli watershed and provided evidence of nutrients affecting bacterial community composition and diversity. We argue that this study could further shed light on how climate change-induced glacial retreat may impact bacterial communities in glacial-fed lakes under future global warming scenarios.

The spatial distribution of microbial communities has recently been reliably documented in the form of a distance-similarity decay relationship. In contrast, temporal scaling, the pattern defined by the microbial similarity-time relationships (STRs), has received far less attention. As a result, it is unclear whether the spatial and temporal variations of microbial communities share a similar power law. In this study, we applied the 454 pyrosequencing technique to investigate temporal scaling in patterns of bacterioplankton community dynamics during the process of shrimp culture. Our results showed that the similarities decreased significantly (P = 0.002) with time during the period over which the bacterioplankton community was monitored, with a scaling exponent of w = 0.400. However, the diversities did not change dramatically. The community dynamics followed a gradual process of succession relative to the parent communities, with greater similarities between samples from consecutive sampling points. In particular, the variations of the bacterial communities from different ponds shared similar successional trajectories, suggesting that bacterial temporal dynamics are predictable to a certain extent. Changes in bacterial community structure were significantly correlated with the combination of Chl a, TN, PO4 (3-), and the C/N ratio. In this study, we identified predictable patterns in the temporal dynamics of bacterioplankton community structure, demonstrating that the STR of the bacterial community mirrors the spatial distance-similarity decay model.

Climate change-induced glacial melting is a global phenomenon. The effects of climate change-induced melting on the microbial ecology in different glacial-fed aquatic systems have been well illuminated, but the resolution of seasonal dynamics was still limited. Here, we studied bacterial community composition and diversity in a glacial-fed Tibetan lake, Lake Ranwu, to elucidate how glacial-fed aquatic ecosystems respond to the seasonal glacial melting. Obvious seasonal variations of bacterial dominant groups were found in Lake Ranwu and inlet rivers. In April, the majority of OTUs belonged to the Bacteroidetes, Actinobacteria and Proteobacteria. The Proteobacteria increased to the most abundant phylum in July and November, while the Bacteroidetes and Actinobacteria decreased about 50% over seasons. Most key discriminant taxa of each season's community strongly associated with specific environmental variables, suggesting their adaptation to seasonal environments. Bacterial alpha diversity varied among seasons and exhibited strongly negative correlations with conductivity. Conductivity was the major driving force in determining the seasonal variation of bacterial community composition. Fluctuated conductivity was one of the consequences of seasonal melting of glaciers. This study offered evidence for the unique seasonal dynamics pattern of bacterial communities responding to glacial melting. Moreover, this study may provide a reference for assessing the long-term effects of glacial retreat on glacial-fed aquatic ecosystems.

Atmospheric CO2 concentration is increasing, largely due to anthropogenic activities. Previous studies of individual free-air CO2 enrichment (FACE) experimental sites have shown significant impacts of elevated CO2 (eCO2) on soil microbial communities; however, no common microbial response patterns have yet emerged, challenging our ability to predict ecosystem functioning and sustainability in the future eCO2 environment. Here we analyzed 66 soil microbial communities from five FACE sites, and showed common microbial response patterns to eCO2, especially for key functional genes involved in carbon and nitrogen fixation (e.g., pcc/acc for carbon fixation, nifH for nitrogen fixation), carbon decomposition (e.g., amyA and pulA for labile carbon decomposition, mnp and lcc for recalcitrant carbon decomposition), and greenhouse gas emissions (e.g., mcrA for methane production, norB for nitrous oxide production) across five FACE sites. Also, the relative abundance of those key genes was generally increased and directionally associated with increased biomass, soil carbon decomposition, and soil moisture. In addition, a further literature survey of more disparate FACE experimental sites indicated increased biomass, soil carbon decay, nitrogen fixation, methane and nitrous oxide emissions, plant and soil carbon and nitrogen under eCO2. A conceptual framework was developed to link commonly responsive functional genes with ecosystem processes, such as pcc/acc vs. soil carbon storage, amyA/pulA/mnp/lcc vs. soil carbon decomposition, and nifH vs. nitrogen availability, suggesting that such common responses of microbial functional genes may have the potential to predict ecosystem functioning and sustainability in the future eCO2 environment.

Soil fungi fill pivotal ecological roles in biogeochemical processes, particularly dominating decomposition of lignin. Little is known, however, about the responses of different fungal groups to climate warming with respect to bacteria. In this study, using barcode pyrosequencing, we showed that short-term (15 months) of field exposure of an alpine meadow to warming (elevated 1 and 2 °C) did not markedly alter the overall soil fungal community structures and α-diversity on Tibetan Plateau, but the average β-diversity dramatically decreased in response to warming. However, soil respiration rates were stimulated in the growing season, which significantly (P < 0.001) correlated with soil temperature. Particularly, warming triggered dramatic shifts in the community structure of dominate Ascomycota and rare taxa (relative abundance < 0.1 %). In addition, the abundances of specific Basidiomycota-affiliated members significantly increased, while Ascomycota showed a range of responses to warming. Collectively, we conclude that the fungal communities are resistant to short-term warming, though variations are observed in certain species and rare taxa. This report indicates that changes in a relatively small subset of the soil fungal community are sufficient to produce substantial changes in function, such as CO(2) efflux rates.