Substrate and/or substrate-driven changes in the abundance of methanogenic archaea cause seasonal variation of methane production potential in species-specific freshwater wetlands

Planktonic Bacterial and Archaeal Communities in an Artificially Irrigated Estuarine Wetland: Diversity, Distribution, and Responses to Environmental Parameters

Bacterial and archaeal communities play important roles in wetland ecosystems. Although the microbial communities in the soils and sediments of wetlands have been studied extensively, the comprehensive distributions of planktonic bacterial and archaeal communities and their responses to environmental variables in wetlands remain poorly understood. The present study investigated the spatiotemporal characteristics of the bacterial and archaeal communities in the water of an artificially irrigated estuarine wetland of the Liaohe River, China, explored whether the wetland effluent changed the bacterial and archaeal communities in the Liaohe River, and evaluated the driving environmental factors. Within the study, 16S rRNA quantitative PCR methods and MiSeq high-throughput sequencing were used. The bacterial and archaeal 16S rRNA gene abundances showed significant temporal variation. Meanwhile, the bacterial and archaeal structures showed temporal but not spatial variation in the wetland and did not change in the Liaohe River after wetland drainage. Moreover, the bacterial communities tended to have higher diversity in the wetland water in summer and in the scarce zone, while a relatively higher diversity of archaeal communities was found in autumn and in the intensive zone. DO, pH and PO₄-P were proven to be the essential environmental parameters shaping the planktonic bacterial and archaeal community structures in the Liaohe River estuarine wetland (LEW). The LEW had a high potential for methanogenesis, which could be reflected by the composition of the microbial communities.

Rhizospheric effects on the microbial community of e-waste-contaminated soils using phospholipid fatty acid and isoprenoid glycerol dialkyl glycerol tetraether analyses

We performed the study of rhizospheric effects on soil microbial community structure, including bacteria, fungi, actinomycete, and archaea, at an electronic waste (e-waste) recycling site by analyzing the phospholipid fatty acid (PLFA) and isoprenoid glycerol dialkyl glycerol tetraether (GDGT) contents. By comparing PLFA and isoprenoid GDGT profiles of rhizospheric and surrounding bulk soils of 11 crop species, we observed distinct microbial community structures. The total PLFA concentration was significantly higher in rhizospheric soils than in non-rhizospheric soils, whereas no obvious difference was found in the total isoprenoid GDGT concentrations. The microbial community structure was also different, with higher ratios of fungal-to-bacterial PLFAs (F/B) and lower relative abundance of Gram-positive bacteria in rhizospheric soils. The extent of rhizospheric effects varied among plant species, and Colocasia esculenta L. had the greatest positive effects on the total microbial biomass. Dissolved organic carbon and pH were the main environmental factors affecting the microbial community represented by PLFAs, while the archaeal community was influenced by copper and zinc in all soils. These results offer a comprehensive view of rhizospheric effects on microbes in heavy metal and persistent organic pollutant co-contaminated soil, and provide fundamental knowledge regarding microbial ecology in e-waste-contaminated soils.

Potential effects of ultraviolet radiation reduction on tundra nitrous oxide and methane fluxes in maritime Antarctica

Stratospheric ozone has begun to recover in Antarctica since the implementation of the Montreal Protocol. However, the effects of ultraviolet (UV) radiation on tundra greenhouse gas fluxes are rarely reported for Polar Regions. In the present study, tundra N2O and CH4 fluxes were measured under the simulated reduction of UV radiation in maritime Antarctica over the last three-year summers. Significantly enhanced N2O and CH4 emissions occurred at tundra sites under the simulated reduction of UV radiation. Compared with the ambient normal UV level, a 20% reduction in UV radiation increased tundra emissions by an average of 8 μg N2O m-2 h-1 and 93 μg CH4 m-2 h-1, whereas a 50% reduction in UV radiation increased their emissions by an average of 17 μg N2O m-2 h-1 and 128 μg CH4 m-2 h-1. No statistically significant correlation (P > 0.05) was found between N2O and CH4 fluxes and soil temperature, soil moisture, total carbon, total nitrogen, NO3--N and NH4+-N contents. Our results confirmed that UV radiation intensity is an important factor affecting tundra N2O and CH4 fluxes in maritime Antarctica. Exclusion of the effects of reduced UV radiation might underestimate their budgets in Polar Regions with the recovery of stratospheric ozone.

Methane production potential and emission at different water levels in the restored reed wetland of Hangzhou Bay

Changes in the hydrological conditions of coastal wetlands may potentially affect the role of wetlands in the methane (CH₄) cycle. In this study, the CH₄ production potential and emissions from restored coastal reed wetlands at different water levels were examined in eastern China at a field scale in two phenological seasons. Results showed that the total CH₄ flux from reeds at various water levels were positive, indicating that they were “sources” of CH₄. During the peak growing season, CH₄ flux from reeds was greater than that during the spring thaw. CH₄ flux from reeds in inundated conditions was greater than that in non-inundated conditions. The CH₄ production potential during the peak growing season was far greater than that during the spring thaw. However, the effect of water level on wetland CH₄ production potential differed among seasons. The correlations among CH₄ production potential, soil properties and CH₄ flux change at different water level. These results demonstrate that water level was related to CH₄ production and CH₄ flux. The growing season also plays a role in CH₄ fluxes. Controlling the hydrological environment in restored wetlands has important implications for the maintenance of their function as carbon sinks.

Thermoplasmatales and Methanogens: Potential Association with the Crenarchaeol Production in Chinese Soils

Crenarchaeol is a unique isoprenoid glycerol dibiphytanyl glycerol tetraether (iGDGT) lipid, which is only identified in cultures of ammonia-oxidizing Thaumarchaeota. However, the taxonomic origins of crenarchaeol have been debated recently. The archaeal populations, other than Thaumarchaeota, may have associations with the production of crenarchaeol in ecosystems characterized by non-thaumarchaeotal microorganisms. To this end, we investigated 47 surface soils from upland and wetland soils and rice fields and another three surface sediments from river banks. The goal was to examine the archaeal community compositions in comparison with patterns of iGDGTs in four fractional forms (intact polar-, core-, monoglycosidic- and diglycosidic-lipid fractions) along gradients of environments. The DistLM analysis identified that Group I.1b Thaumarchaeota were mainly responsible for changes in crenarchaeol in the overall soil samples; however, Thermoplasmatales may also contribute to it. This is further supported by the comparison of crenarchaeol between samples characterized by methanogens, Thermoplasmatales or Group I.1b Thaumarchaeota, which suggests that the former two may contribute to the crenarchaeol pool. Last, when samples containing enhanced abundance of Thermoplasmatales and methanogens were considered, crenarchaeol was observed to correlate positively with Thermoplasmatales and archaeol, respectively. Collectively, our data suggest that the crenarchaeol production is mainly derived from Thaumarchaeota and partly associated with uncultured representatives of Thermoplasmatales and archaeol-producing methanogens in soil environments that may be in favor of their growth. Our finding supports the notion that Thaumarchaeota may not be the sole source of crenarchaeol in the natural environment, which may have implication for the evolution of lipid synthesis among different types of archaea.

Effect of enhanced UV-B radiation on methane emission in a paddy field and rice root exudation of low-molecular-weight organic acids

A local rice variety, "Baijiaolaojing", was grown in a paddy field in the Yuanyang rice terraces under ambient and supplemental levels of ultraviolet-B (UV-B, 280-315 nm) radiation. The effects of enhanced UV-B radiation (5 and 10 kJ m(-2) d(-1)) on methane emissions in the paddy field were evaluated using a closed-chamber gas chromatography-based system, and the contents of low-molecular-weight organic acids (LMWOAs) in root exudates were determined by high-performance liquid chromatography (HPLC). Peaks in methane emissions in the paddy field were detected at 60, 80 and 100 days after rice transplantation. The highest level of cumulative methane emissions occurred at the tillering stage, followed by the jointing-booting and maturity stages. The lowest level was found at the flowering stage. The enhanced UV-B radiation did not change the seasonal variation in methane emissions in the paddy field; however, it induced a significant increase in the flux of methane emissions at the jointing-booting and maturity stages, as well as a significant increase in the cumulative flux of methane emissions throughout the growth period. In addition, the enhanced UV-B radiation caused an increase in the contents of oxalic acid and succinic acid and a decrease in the contents of tartaric acid and malic acid in rice root exudates. Furthermore, a significant positive correlation (r = 0.725, p < 0.01) was found between the content of oxalic acid and the methane emissions in the paddy field. The results indicated that enhanced UV-B radiation promoted methane emissions in the paddy field, which was closely associated with its impact on the exudation of LMWOAs by rice roots.

Exotic Spartina alterniflora invasion alters ecosystem-atmosphere exchange of CH4 and N2O and carbon sequestration in a coastal salt marsh in China

Coastal salt marshes are sensitive to global climate change and may play an important role in mitigating global warming. To evaluate the impacts of Spartina alterniflora invasion on global warming potential (GWP) in Chinese coastal areas, we measured CH4 and N2O fluxes and soil organic carbon sequestration rates along a transect of coastal wetlands in Jiangsu province, China, including open water; bare tidal flat; and invasive S. alterniflora, native Suaeda salsa, and Phragmites australis marshes. Annual CH4 emissions were estimated as 2.81, 4.16, 4.88, 10.79, and 16.98 kg CH4 ha(-1) for open water, bare tidal flat, and P. australis, S. salsa, and S. alterniflora marshes, respectively, indicating that S. alterniflora invasion increased CH4 emissions by 57-505%. In contrast, negative N2O fluxes were found to be significantly and negatively correlated (P < 0.001) with net ecosystem CO2 exchange during the growing season in S. alterniflora and P. australis marshes. Annual N2O emissions were 0.24, 0.38, and 0.56 kg N2O ha(-1) in open water, bare tidal flat and S. salsa marsh, respectively, compared with -0.51 kg N2O ha(-1) for S. alterniflora marsh and -0.25 kg N2O ha(-1) for P. australis marsh. The carbon sequestration rate of S. alterniflora marsh amounted to 3.16 Mg C ha(-1) yr(-1) in the top 100 cm soil profile, a value that was 2.63- to 8.78-fold higher than in native plant marshes. The estimated GWP was 1.78, -0.60, -4.09, and -1.14 Mg CO2 eq ha(-1) yr(-1) in open water, bare tidal flat, P. australis marsh and S. salsa marsh, respectively, but dropped to -11.30 Mg CO2 eq ha(-1) yr(-1) in S. alterniflora marsh. Our results indicate that although S. alterniflora invasion stimulates CH4 emissions, it can efficiently mitigate increases in atmospheric CO2 and N2O along the coast of China.