Latitudinal distribution of microbial communities in anaerobic biological stabilization ponds: effect of the mean annual temperature

Biogeographic, Driving Factors, Assembly, and Co-occurrence Patterns of Archaeal Community in Biocrusts

Archaea exhibit strong community heterogeneity with microhabitat gradients and are a non-negligible part of biocrust's microorganisms. The study on archaeal biogeography in biocrusts could provide new insights for its application in environmental restoration. However, only a few studies on assembly processes and co-occurrence patterns of the archaeal community in patchy biocrusts have been reported, especially considering the number of species pools (SPs). Here, we comprehensively collected biocrusts across 3,500 km of northern China. Different successional biocrusts from various regions contain information of local climate and microenvironments, which can shape multiple unique archaeal SPs. The archaeal community differences in the same successional stage exceeded the variations between successional stages, which was due to the fact that the heterogeneous taxa tended to exchange between unknown patches driven by drift. We also comparatively studied the driving forces of community heterogeneity across three to ten SPs, and assembly and co-occurrence patterns were systematically analyzed. The results revealed that the impact of spatial factors on biogeographic patterns was greater than that of environmental and successional factors and that impact decreased with the number of SPs considered. Meanwhile, community heterogeneity at the phylogenetic facet was more sensitive to these driving factors than the taxonomic facet. Subgroups 1 (SG1) and 2 (SG2) of the archaeal communities in biocrusts were dominated by Nitrososphaeraceae and Haloarchaea, respectively. The former distribution pattern was associated with non-salinity-related variables and primarily assembled by drift, whereas the latter was associated with salinity-related variables and primarily assembled by homogeneous selection. Finally, network analysis indicated that the SG1 network had a higher proportion of competition and key taxa than the SG2 network, but the network of SG2 was more complex. Our study suggested that the development of the archaeal community was not consistent with biocrusts succession. The dominant taxa may determine the patterns of community biogeography, assembly, and co-occurrence.

Soil Properties Interacting With Microbial Metagenome in Decreasing CH4 Emission From Seasonally Flooded Marshland Following Different Stages of Afforestation

Wetlands are the largest natural source of terrestrial CH4 emissions. Afforestation can enhance soil CH4 oxidation and decrease methanogenesis, yet the driving mechanisms leading to these effects remain unclear. We analyzed the structures of communities of methanogenic and methanotrophic microbes, quantification of mcrA and pmoA genes, the soil microbial metagenome, soil properties and CH4 fluxes in afforested and non-afforested areas in the marshland of the Yangtze River. Compared to the non-afforested land use types, net CH4 emission decreased from bare land, natural vegetation and 5-year forest plantation and transitioned to net CH4 sinks in the 10- and 20-year forest plantations. Both abundances of mcrA and pmoA genes decreased significantly with increasing plantation age. By combining random forest analysis and structural equation modeling, our results provide evidence for an important role of the abundance of functional genes related to methane production in explaining the net CH4 flux in this ecosystem. The structures of methanogenic and methanotrophic microbial communities were of lower importance as explanatory factors than functional genes in terms of in situ CH4 flux. We also found a substantial interaction between functional genes and soil properties in the control of CH4 flux, particularly soil particle size. Our study provides empirical evidence that microbial community function has more explanatory power than taxonomic microbial community structure with respect to in situ CH4 fluxes. This suggests that focusing on gene abundances obtained, e.g., through metagenomics or quantitative/digital PCR could be more effective than community profiling in predicting CH4 fluxes, and such data should be considered for ecosystem modeling.

Use of biochar/persulfate for accelerating the stabilization process and improving nitrogen stability of animal waste digestate

In China, the growing amount of digestate from anaerobic digestion produced by animal husbandry is an emerging challenge. A common treatment used to eliminate this digestate is long-term stabilization ponds. However, this process can lead to a shortage of digestate storage space and loss of nitrogen nutrients within the digestate. To alleviate those shortcomings, this study developed an efficient stabilization pond using biochar and persulfate (BC/PS treatment). Using this treatment, the germination index (GI) of the digestate increased from 56% to 85% and the stabilization efficiency increased nearly 2.7 times. In addition, the dehydrogenase activity (DHA) in the BC/PS treatment remained between 0.47 and 0.91 μg/(g·h) across the 40 days, which indicated that BC/PS had a positive effect on microbial inactivation. In the traditional stabilization process (CK treatment), dissolved organic nitrogen (DON) decreased from 47.77 mg/L to 0.81 mg/L and ammonium nitrogen almost disappeared. The BC/PS treatment led to the promotion of nitrogen nutrient composition. Particulate total nitrogen (21.49% of total nitrogen) decomposed into dissolved total nitrogen and the DON increased from 47.77 to 58.89 mg/L. The BC/PS treatment showed a faster stabilization time, good microbial inactivation, lower toxicity, and stable nitrogen nutrient composition of the digestate compared to traditional methods.

Biogeographic distribution of bacterial, archaeal and methanogenic communities and their associations with methanogenic capacity in Chinese wetlands

Natural wetlands and anthropogenic paddy fields are the dominant biogenic sources of atmospheric methane emission which have been speculated as the most probable sources for the increase of post-2006 atmospheric methane. Regional differences in CH₄ emission is possibly due to microbial biogeographic distribution. Here we collected soils from 19 wetlands from different regions in China. The methane production capacity (MPC) was measured for each soil samples and varied from 1.11 to 841.94mg/kg dry soil. High throughput sequencing was employed to investigate the diversity and composition of bacterial, archaeal and methanogenic communities. Similar biogeographic patterns for bacterial, archaeal and methanogenic communities along the latitudinal gradient were observed, and the biogeographic assemblies of different microbial groups were driven by concurrent factors, including edaphic variables (total organic carbon, total phosphorus and pH) and climatic variables (annual frost days, mean annual temperature, direct solar radiation and mean annual precipitation). MPC was significantly correlated with TOC concentration, and in addition, various functional taxa were positively correlated with MPC (P<0.05), for example, Sphingomonas, Syntrophomonas, Methanospirillum and Methanoregula, indicating their potential contributions in the methanogenic process, and many of them were fermentative bacteria and methanogens. Network analysis showed that some syntrophs, sulfate-reducers and methanogens were tightly co-occurred in one module, suggesting their involvements in cross-linked functional processes. Our study implicated both temperature and substrate availability altered the biogeographic patterns of microbial community as well as methane production potential in Chinese wetlands.

Latitudinal distribution of microbial communities in anaerobic biological stabilization ponds: effect of the mean annual temperature

Considering wide utilization and high methane fluxes from anaerobic biological stabilization ponds (ABSPs), understanding the methanogenesis in ABSPs is of fundamental importance. Here we investigated the variation and impact factors of methanogenesis in seven ABSPs that spanned from the north to the south of China. Results showed that methanogen abundance (7.7 × 10⁹ -8.7 × 10¹⁰  copies g^-1 dry sediment) and methanogenic activities (2.2-21.2 μmol CH₄  g^-1  dry sediment h^-1 ) were considerable for all sediments. Statistical analysis demonstrated that compared with other factors (ammonium, pH, COD and TOC), mean annual temperature (MAT) showed the lowest P value and thus was the most important influencing factor for the methanogenic process. Besides, with the increasing MAT, methanogenic activity was enhanced mainly due to the shift of the dominant methanogenic pathway from acetoclastic (49.8-70.7%) in low MAT areas to hydrogenotrophic (42.0-54.6%) in high MAT areas. This shift of methanogenic pathway was also paralleled with changes in composition of bacterial communities. These results suggested that future global warming may reshape the composition of methanogen communities and lead to an increasing methane emission from ABSPs. Therefore, further research is urgently needed to globally estimate methane emissions from ABSPs and re-examine the role of ABSPs in wastewater treatment.