Distinct co-occurrence patterns of prokaryotic community between the waters and sediments in lakes with different salinity

Exploring environment-specific regulation: Characterizing bacterioplankton community dynamics in a typical lake of Inner Mongolia, China

Lakes serve as heterogeneous ecosystems with rich microbiota. Although previous studies on bacterioplankton have advanced our understanding, there are gaps in our knowledge concerning variations in the taxonomic composition and community assembly processes of bacterioplankton across different environment conditions. This study explored the spatial dynamics, assembly processes, and co-occurrence relationships among bacterioplankton communities in 35 surface water samples collected from Hulun Lake (a grassland-type lake), Wuliangsuhai Lake (an irrigated agricultural recession type lake), and Daihai Lake (an inland lake with mixed farming and grazing) in the Inner Mongolia Plateau, China. The results indicated a significant geographical distance decay pattern, with biomarkers (Proteobacteria and Bacteroidota) exhibiting differences in the contributions of different bacteria branches to the lakes. The relative abundance of Proteobacteria (42.23%) were high in Hulun Lake and Wuliangsuhai Lake. Despite Actinobacteriota was most dominant, Firmicutes accounted for approximately 17.07% in Daihai Lake, suggested the potential detection of anthropogenic impacts on bacteria within the agro-pastoral inland lake. Lake heterogeneity caused bacterioplankton responses to phosphorus, chlorophyll a, and salinity in Hulun Lake, Wuliangsuhai Lake, and Daihai Lake. Although bacterioplankton community assembly processes in irrigated agricultural recession type lake were more affected by dispersal limitation than those in grassland-type lake and inland lake with mixed farming and grazing (approximately 52.7% in Hulun Lake), dispersal limitation and undominated processes were key modes of bacterioplankton community assembly in three lakes. This suggested stochastic processes exerted a greater impact on bacterioplankton community assembly in a typical Inner Mongolia Lake than deterministic processes. Overall, the bacterioplankton communities displayed the potential for collaboration, with lowest connectivity observed in irrigated agricultural recession type lake, which reflected the complex dynamic patterns of aquatic bacteria in typical Inner Mongolia Plateau lakes. These findings enhanced our understanding of the interspecific relationships and assembly processes among microorganisms in lakes with distinct habitats.

Microbial difference and its influencing factors in ice-covered lakes on the three poles

Most lakes in the world are permanently or seasonally covered with ice. However, little is known about the distribution of microbes and their influencing factors in ice-covered lakes worldwide. Here we analyzed the microbial community composition in the waters of 14 ice-covered lakes in the Hoh Xil region of northern Qing-Tibetan Plateau (QTP), and conducted a meta-analysis by integrating published microbial community data of ice-covered lakes in the tripolar regions (the Arctic, Antarctica and QTP). The results showed that there were significant differences in microbial diversity, community composition and distribution patterns in the ice-covered tripolar lakes. Microbial diversity and richness were lower in the ice-covered QTP lakes (including the studied lakes in the Hoh Xil region) than those in the Arctic and Antarctica. In the ice-covered lakes of Hoh Xil, prokaryotes are mainly involved in S-metabolic processes, making them more adaptable to extreme environmental conditions. In contrast, prokaryotes in the ice-covered lakes of the Arctic and Antarctica were predominantly involved in carbon/nitrogen metabolic processes. Deterministic (salinity and nutrients) and stochastic processes (dispersal limitation, homogenizing dispersal and drift) jointly determine the geographical distribution patterns of microorganisms in ice-covered lakes, with stochastic processes dominating. These results expand the understanding of microbial diversity, distribution patterns, and metabolic processes in polar ice-covered lakes.

Differences of bacterioplankton communities between the source and upstream regions of the Yangtze River: microbial structure, co-occurrence pattern, and environmental influencing factors

The source area of the Yangtze River is located in the hinterland of the Qinghai-Tibet Plateau, which is known as the "Earth's third pole." It is the water conservation area and the natural barrier of the ecosystem of the Yangtze River basin. It is also the most sensitive area of the natural ecosystem, and the ecological environment is very fragile. Microorganisms play key roles in the biogeochemical processes of water. In this paper, the bacterioplankton communities in the source and upstream regions of the Yangtze River were studied based on 16S rRNA high-throughput sequencing, and their environmental influencing factors were further analyzed. Results showed that the upstream region had higher richness and diversity than the source region. The predominant bacterial phyla in the source and upstream regions were Proteobacteria, Firmicutes, and Actinobacteriota. The bacterial phyla associated with municipal pollution and opportunistic pathogen, such as Firmicutes and Actinobacteriota, were more abundant in the upstream. By contrast, distinct planktonic bacterial genera associated with mining pollution, such as Acidiphilium and Acidithiobacillus, were more abundant in the source region. The co-occurrence network showed that the interaction of bacterioplankton community is more frequent in the upstream. The bacterioplankton community compositions, richness, and functional profiles were affected by the spatial heterogeneity. Moreover, variation partitioning analysis further confirmed that the amount of variation in the source region independently explained by variables of altitude was the largest, followed by water nutrient. This paper revealed the spatial distribution of planktonic bacterial communities in the source and upstream regions of the Yangtze River and its correlation with environmental factors, providing information support for ensuring the health and safety of aquatic ecosystems in the Yangtze River Basin.

Chemical composition of soil carbon is governed by microbial diversity during understory fern removal in subtropical pine forests

Understory vegetation has an important impact on soil organic carbon (SOC) accumulation. However, little is known about how understory vegetation alters soil microbial community composition and how microbial diversity contributes to SOC chemical composition and persistence during subtropical forest restoration. In this study, removal treatments of an understory fern (Dicranopteris dichotoma) were carried out within pine (Pinus massoniana) plantations restored in different years in subtropical China. Soil microbial community composition and microbial diversity were measured using phospholipid fatty acids (PLFAs) biomarkers and high-throughput sequencing, respectively. The chemical composition of SOC was also measured via solid-state 13C nuclear magnetic resonance (13C NMR). Our results showed that fern removal decreased alkyl C by 4.2 % but increased O-alkyl C by 15.6 % on average, leading to a decline of alkyl C/O-alkyl C ratio, suggesting altered chemical composition of SOC and lowered SOC recalcitrance without fern. Fern removal significantly lowered the fungi-to-bacteria ratio, and it also reduced fungal and bacterial diversity. Partial correlation analysis revealed that soil nitrogen availability was a key factor influencing microbial diversity. Bacterial diversity showed a close relationship with the Alkyl C/O-alkyl C ratio following fern removal. Furthermore, the microbial community structure and bacterial diversity were responsible for 18 % and 55 % of the explained variance in the chemical composition of SOC, respectively. Taken together, these analyses jointly suggest that bacterial diversity exerts a greater role than microbial community structure in supporting SOC persistence during understory fern removal. Our study emphasizes the significance of understory ferns in supporting microbial abundance and diversity as a means of altering SOC persistence during subtropical forest restoration.

Bacterial and Microeukaryotic Community Compositions and Their Assembly Processes in Lakes on the Eastern Qinghai-Tibet Plateau

Bacterial and microeukaryotic community compositions and their assembly processes have remained challenging and remained unclear in lake ecosystems on the Qinghai-Tibet Plateau (QTP). We revealed the diversity and community compositions, driving factors, ecological assembly processes, and co-occurrence networks of bacterial and microeukaryotic communities in water bodies of the eight lake ecosystems across the Eastern QTP. The results demonstrated that the predominant bacteria in most samples were Proteobacteria, with an average relative abundance of 41.78%, whereas the most abundant of microeukaryotes differed among the sample sites. The redundancy analysis revealed that latitude and pH were the most important driving factors in shaping the bacterial and microeukaryotic community compositions. Homogeneous selection (56.40%) was the dominant process in assembling the bacterial communities, whereas dispersal limitation (67.24%) was the major process in governing the microeukaryotic communities. Furthermore, dissolved organic carbon and salinity were the major factors mediating the balance of deterministic and stochastic assembly processes in the bacterial and microeukaryotic communities. Both the bacterial and microeukaryotic community co-occurrence networks exhibited topological features of modularity and non-random topological features. The results offer insights into the mechanisms underpinning bacterial and microeukaryotic diversities and communities in the lake ecosystems on the QTP.

Salinity change induces distinct climate feedbacks of nitrogen removal in saline lakes

Current estimations of nitrogen biogeochemical cycling and N2O emissions in global lakes as well as predictions of their future changes are overrepresented by freshwater datasets, while less consideration is given to widespread saline lakes with different salinity (representing salinization or desalinization). Here, we show that N2O production by denitrification is the main process of reactive nitrogen (Nr, the general abbreviations of NH4+-N, NO2--N and NO3--N) removal in hypersaline lake sediments (e.g. Lake Chaka). The integration of our field measurements and literature data shows that in response to natural salinity decrease, potential Nr removal increases while N2O production decreases. Furthermore, denitrification-induced N2 production exhibits higher salinity sensitivity than denitrification-induced N2O production, suggesting that the contribution of N2O to Nr removal decreases with decreasing salinity. This field-investigation-based salinity response model of Nr removal indicates that under global climate change, saline lakes in the process of salinization or desalination may have distinct Nr removal and climate feedback effects: salinized lakes tend to generate a positive climate feedback, while desalinated lakes show a negative feedback. Therefore, salinity change should be considered as an important factor in assessing future trend of N2O emissions from lakes under climate change.

Spatial pattern and co-occurrence network of microbial community in response to extreme environment of salt lakes on the Qinghai-Tibet Plateau

Microbial communities are important components of alpine lakes, especially in extreme environments such as salt lakes. However, few studies have examined the co-occurrence network of microbial communities and various environmental factors in the water of salt lakes on the Qinghai-Tibet Plateau. From May to June 2019, nine samples from seven salt lakes with water salinity ranges from 13 to 267‰ on the Qinghai-Tibet Plateau were collected. There were great differences between low-salinity samples and high-salinity samples in the inorganic salt ion concentration, pH, and biodiversity. In addition, the microbial community sturcture in low-salinity samples and high-salinity samples differed, suggesting that each sample has its own specific species. The co-occurrence network suggests that salinity was the most important forcing factor. We believe that salinity and inorganic salt ions can result in differences in microbial community in different salt lakes. This sequencing survey of multiple salt lakes with various salinities on the Qinghai-Tibet Plateau enhances our understanding of the response of microbial communities to environmental heterogeneity.

Salinity Is a Key Determinant for the Microeukaryotic Community in Lake Ecosystems of the Inner Mongolia Plateau, China

The arid and semiarid areas experienced remarkable lake shrinkage during recent decades due to intensive human activities and climate change, which would result in unprecedented changes of microeukaryotic communities. However, little is known about how climate change affects the structure and ecological mechanisms of microeukaryotic communities in this area. Here, we used an 18S rRNA gene-based high-throughput sequencing approach to explore the structure, interspecies interaction, and assembly processes of the microeukaryotic community in lake ecosystems of the Inner Mongolia Plateau. As a direct result of climate change, salinity has become the key determinant of the lacustrine microeukaryotic community in this region. The microeukaryotic community in this ecosystem can be divided into three groups: salt (Lake Daihai), brackish (Lake Dalinuoer) and freshwater lakes. Co-occurrence network analysis revealed that salinity shapes the interspecies interactions of the microeukaryotic community. This causes interspecies interactions to change from antagonistic to cooperative with an increase in salinity. Phylogenetic-based β-nearest taxon distance analyses revealed that stochastic processes mainly dominated the microeukaryotic community assembly in lake ecosystems of the Inner Mongolia Plateau, and salinity stress drove the assembly processes of the microeukaryotic community from stochastic to deterministic. Overall, these findings expand the current understanding of interspecies interactions and assembly processes of microeukaryotic communities during climate change in lake ecosystems of the Inner Mongolia Plateau.

Microbial response to multiple-level addition of grass organic matter in lake sediments with different salinity

Water surface expansion of saline lakes usually causes the inundation of surrounding grassland, leading to the increase of terrestrial grass organic matter (OM) input to the lakes and the decrease of lake salinity. However, the influence of terrestrial grass OM input increase and salinity decrease on organic carbon mineralization and microbial community composition remains unknown in saline lakes. Here, microbial mineralization of terrestrial grass (Achnatherum splendens) OM at different quantity levels in lake sediments with different salinity was investigated by performing microcosm experiments. The results showed that the CO2 production rates increased with the increase of grass OM supply in the studied sediments with different salinity, which may be driven by certain microbial groups (e.g., Bacteroidota, Firmicutes and Ascomycota). The increase of grass OM supply reduced the richness of prokaryotic community, which will decrease the size and complexity of the studied microbial networks, but increase the interaction between prokaryotic and fungal taxa. Taken together, our results suggest that the increase of terrestrial grass OM input caused by lake expansion would enhance the mineralization of organic carbon and affect the community composition and interactions of related microorganisms in lake sediments with different salinity.

Functional Metabolic Diversity of Bacterioplankton in Maritime Antarctic Lakes

A summer survey was conducted on the bacterioplankton communities of seven lakes from Byers Peninsula (Maritime Antarctica), differing in trophic and morphological characteristics. Predictions of the metabolic capabilities of these communities were performed with FAPROTAX using 16S rRNA sequencing data. The versatility for metabolizing carbon sources was also assessed in three of the lakes using Biolog Ecoplates. Relevant differences among lakes and within lake depths were observed. A total of 23 metabolic activities associated to the main biogeochemical cycles were foreseen, namely, carbon (11), nitrogen (4), sulfur (5), iron (2), and hydrogen (1). The aerobic metabolisms dominated, although anaerobic respiration was also relevant near the lakes’ bottom as well as in shallow eutrophic lakes with higher nutrient and organic matter contents. Capacity for using carbon sources further than those derived from the fresh autochthonous primary production was detected. Clustering of the lakes based on metabolic capabilities of their microbial communities was determined by their trophic status, with functional diversity increasing with trophic status. Data were also examined using a co-occurrence network approach, indicating that the lakes and their catchments have to be perceived as connected and interacting macrosystems, where either stochastic or deterministic mechanisms for the assembling of communities may occur depending on the lake’s isolation. The hydrological processes within catchments and the potential metabolic plasticity of these biological communities must be considered for future climate scenarios in the region, which may extend the growing season and increase biomass circulation.

Diversity and abundance of diazotrophic communities of seagrass Halophila ovalis based on genomic and transcript level in Daya Bay, South China Sea

Seagrass ecosystems are among the most productive marine ecosystems, and diazotrophic communities play a crucial role in sustaining the productivity and stability of such ecosystems by introducing fixed nitrogen. However, information concerning both total and active diazotrophic groups existing in different compartments of seagrass is lacking. This study comprehensively investigated the diversity, structure, and abundance of diazotrophic communities in different parts of the seagrass Halophila ovalis at the DNA and RNA level from clone libraries and real-time quantitative PCR. Our results indicated that nearly one-third of existing nitrogen-fixing bacteria were active, and their abundance might be controlled by nitrogen to phosphorus ratio (N:P). Deltaproteobacteria and Gammaproteobacteria were dominant groups among the total and active diazotrophic communities in all samples. These two groups accounted for 82.21% and 70.96% at the DNA and RNA levels, respectively. The genus Pseudomonas and sulfate-reducing bacteria (genera: Desulfosarcina, Desulfobulbus, Desulfocapsa, and Desulfopila) constituted the significant fraction of nitrogen-fixing bacteria in the seagrass ecosystem, playing an additional role in denitrification and sulfate reduction, respectively. Moreover, the abundance of the nitrogenase gene, nifH, was highest in seawater and lowest in rhizosphere sediments from all samples. This study highlighted the role of diazotropic communities in the subtropical seagrass ecosystem.