Putative roles of bacteria in the carbon and nitrogen cycles in a tropical peat swamp forest

Novel adaptive activated sludge process leverages flow fluctuations for simultaneous nitrification and denitrification in rural sewage treatment

The fluctuating characteristics of rural sewage flow pose a significant challenge for wastewater treatment plants, leading to poor effluent quality. This study establishes a novel adaptive activated sludge (AAS) process specifically designed to address this challenge. By dynamically adjusting to fluctuating water flow in situ, the AAS maintains system stability and promotes efficient pollutant removal. The core strategy of AAS leverages the inherent dissolved oxygen (DO) variations caused by flow fluctuations to establish an alternating anoxic-aerobic environment within the system. This alternating operation mode fosters the growth of aerobic denitrifiers, enabling the simultaneous nitrification and denitrification (SND) process. Over a 284-day operational period, the AAS achieved consistently high removal efficiencies, reaching 94 % for COD and 62.8 % for TN. Metagenomics sequencing revealed HN-AD bacteria as the dominant population, with the characteristic nap gene exhibiting a high relative abundance of 0.008 %, 0.010 %, 0.014 %, and 0.015 % in the anaerobic, anoxic, dynamic, and oxic zones, respectively. Overall, the AAS process demonstrates efficient pollutant removal and low-carbon treatment of rural sewage by transforming the disadvantage of flow fluctuation into an advantage for robust DO regulation. Thus, AAS offers a promising model for SND in rural sewage treatment.

Exploring different methodological approaches to unlock paleobiodiversity in peat profiles using ancient DNA

Natural and human-induced environmental changes deeply affected terrestrial ecosystems throughout the Holocene. Paleoenvironmental reconstructions provide information about the past and allow us to predict/model future scenarios. Among potential records, peat bogs are widely used because they present a precise stratigraphy and act as natural archives of highly diverse organic remains. Over the decades, several techniques have been developed to identify debris occurring in peat, including their morphological description. However, this is strongly constrained by the researcher's ability to distinguish residues at the species level, which typically requires many years of experience. In addition, potential contamination hampers using these techniques to obtain information from organisms such as fungi or bacteria. Environmental DNA metabarcoding and shotgun metagenome sequencing could represent a solution to detect specific groups of organisms without any a priori knowledge of their characteristics and/or to identify organisms that have rarely been considered in previous investigations. Moreover, shotgun metagenomics may allow the identification of bacteria and fungi (including both yeast and filamentous life forms), ensuring discrimination between ancient and modern organisms through the study of deamination/damage patterns. In the present review, we aim to i) present the state-of-the-art methodologies in paleoecological and paleoclimatic studies focusing on peat core analyses, proposing alternative approaches to the classical morphological identification of plant residues, and ii) suggest biomolecular approaches that will allow the use of proxies such as invertebrates, fungi, and bacteria, which are rarely employed in paleoenvironmental reconstructions.

CH4 and N2 O emissions from smallholder agricultural systems on tropical peatlands in Southeast Asia

There are limited data for greenhouse gas (GHG) emissions from smallholder agricultural systems in tropical peatlands, with data for non-CO2 emissions from human-influenced tropical peatlands particularly scarce. The aim of this study was to quantify soil CH4 and N2 O fluxes from smallholder agricultural systems on tropical peatlands in Southeast Asia and assess their environmental controls. The study was carried out in four regions in Malaysia and Indonesia. CH4 and N2 O fluxes and environmental parameters were measured in cropland, oil palm plantation, tree plantation and forest. Annual CH4 emissions (in kg CH4 ha-1  year-1 ) were: 70.7 ± 29.5, 2.1 ± 1.2, 2.1 ± 0.6 and 6.2 ± 1.9 at the forest, tree plantation, oil palm and cropland land-use classes, respectively. Annual N2 O emissions (in kg N2 O ha-1  year-1 ) were: 6.5 ± 2.8, 3.2 ± 1.2, 21.9 ± 11.4 and 33.6 ± 7.3 in the same order as above, respectively. Annual CH4 emissions were strongly determined by water table depth (WTD) and increased exponentially when annual WTD was above -25 cm. In contrast, annual N2 O emissions were strongly correlated with mean total dissolved nitrogen (TDN) in soil water, following a sigmoidal relationship, up to an apparent threshold of 10 mg N L-1 beyond which TDN seemingly ceased to be limiting for N2 O production. The new emissions data for CH4 and N2 O presented here should help to develop more robust country level 'emission factors' for the quantification of national GHG inventory reporting. The impact of TDN on N2 O emissions suggests that soil nutrient status strongly impacts emissions, and therefore, policies which reduce N-fertilisation inputs might contribute to emissions mitigation from agricultural peat landscapes. However, the most important policy intervention for reducing emissions is one that reduces the conversion of peat swamp forest to agriculture on peatlands in the first place.

Encephalartos natalensis, Their Nutrient-Cycling Microbes and Enzymes: A Story of Successful Trade-Offs

Encephalartos spp. establish symbioses with nitrogen (N)-fixing bacteria that contribute to soil nutrition and improve plant growth. Despite the Encephalartos mutualistic symbioses with N-fixing bacteria, the identity of other bacteria and their contribution to soil fertility and ecosystem functioning is not well understood. Due to Encephalartos spp. being threatened in the wild, this limited information presents a challenge in developing comprehensive conservation and management strategies for these cycad species. Therefore, this study identified the nutrient-cycling bacteria in Encephalartos natalensis coralloid roots, rhizosphere, and non-rhizosphere soils. Additionally, the soil characteristics and soil enzyme activities of the rhizosphere and non-rhizosphere soils were assayed. The coralloid roots, rhizosphere, and non-rhizosphere soils of E. natalensis were collected from a population of >500 E. natalensis in a disturbed savanna woodland at Edendale in KwaZulu-Natal (South Africa) for nutrient analysis, bacterial identification, and enzyme activity assays. Nutrient-cycling bacteria such as Lysinibacillus xylanilyticus; Paraburkholderia sabiae, and Novosphingobium barchaimii were identified in the coralloid roots, rhizosphere, and non-rhizosphere soils of E. natalensis. Phosphorus (P) cycling (alkaline and acid phosphatase) and N cycling (β-(D)-Glucosaminidase and nitrate reductase) enzyme activities showed a positive correlation with soil extractable P and total N concentrations in the rhizosphere and non-rhizosphere soils of E. natalensis. The positive correlation between soil enzymes and soil nutrients demonstrates that the identified nutrient-cycling bacteria in E. natalensis coralloid roots, rhizosphere, and non-rhizosphere soils and associated enzymes assayed may contribute to soil nutrient bioavailability of E. natalensis plants growing in acidic and nutrient-poor savanna woodland ecosystems.

Effects of Pb-, Cd-resistant bacterium Pantoea sp. on growth, heavy metal uptake and bacterial communities in oligotrophic growth substrates of Lolium multiflorum Lam

Phosphate-solubilizing bacteria (PSB) can accelerate phytoremediation, especially in those fertilized soils. However, PSB function in oligotrophic growth substrates remains poorly studied. In this study, we isolated lead (Pb)- and cadmium (Cd)-resistant PSB from contaminated sandy soil at an abandoned lubricant plant. The isolated Pantoea sp. PP4 (PP4 hereafter) can produce organic acid and IAA (Indole-3-acetic acid) and dissolve up to 238 mg/L of inorganic phosphate Ca2(PO4)3, exhibiting biosorption capability for Pb and bioprecipitation for Pb and Cd. In the sand pot experiment, inoculation of PP4 increased the accumulation of Pb and Cd in Lolium multiflorum Lam. by 28.9% and 95.5%, respectively, and increased the available phosphorous in oligotrophic river sand by 30.8% (P < 0.05). Meanwhile, the growth of Lolium multiflorum Lam. was also stimulated, resulting in 89.2%, 57.1%, 184.6%, and 28.5% increase in fresh weight, dry weight, root length, and shoot length, respectively. NMDS analysis showed that the bacterial communities in river sand were more clustered after inoculation with PP4. These results indicated that the application of Pantoea sp. PP4 can facilitate the phytoremediation of Pb and Cd in oligotrophic growth substrates, forming a convergent bacterial community. Our findings highlighted the importance of identifying ideal PSB to improve phytoremediation efficiency in oligotrophic environments.

Effects of conservation tillage strategies on soil physicochemical indicators and N2O emission under spring wheat monocropping system conditions

As one of the important greenhouse gas, nitrous oxide (N₂O) has attracted much attention globally under climate change context. Agricultural practices are the main sources of greenhouse gas emissions. Nevertheless, scarcity of literature is available on the effects of different tillage measures on soil N₂O emission under spring wheat (Triticum aestivum L.) ecosystem in the semi-arid area of the Loess Plateau. The main objective of the experimental study was to explore the influence of conservation tillage techniques on soil physicochemical properties, nitrous oxide emission and yield in the Northern semi-arid Dingxi region of China. Four treatments viz., conventional tillage (CT), no tillage (NT), straw mulch with conventional tillage (TS) and stubble-return with no-till (NTS) were evaluated under randomized complete block design with three replications. Our results depicted that compared with conventional tillage, bulk density and water content of topsoil was increased and soil pH value was reduced under conservation tillage techniques. Conservation tillage NT, TS and NTS increased organic carbon, TN, MBN and NH₄⁺-N and reduced the accumulation of NO₃^–N. Additionally, although the N₂O emission under NT, TS and NTS was 8.95, 41.90 and 21.05% respectively higher than under T treatment, the corresponding wheat yield was 15.40, 31.97 and 63.21% higher than T treatment. Moreover, correlation analysis showed that soil moisture and temperature were the most significant factors affecting soil N₂O emission. The NTS treatment pointedly increased crop yield without significantly increasing soil N₂O emission. Consequently, based on economic and environmental benefits and considering N₂O emission and crop yield, we suggest that NTS technique is the best conservation tillage strategy in the semi-arid environmental zone of the Loess Plateau of Dingxi China.

Effect of petroleum hydrocarbon pollution levels on the soil microecosystem and ecological function

Petroleum hydrocarbon pollution is a global problem. However, the effects of different petroleum pollution levels on soil microbial communities and ecological functions are still not clear. In this study, we analyzed the changes in microbial community structures and carbon and nitrogen transformation functions in oil-contaminated soils at different concentrations by chemical analysis, high-throughput sequencing techniques, cooccurrence networks, and KEGG database comparison functional gene annotation. The results showed that heavy petroleum concentrations (petroleum concentrations greater than 20,000 mg kg^-1) significantly decreased soil microbial diversity (p = 0.01), soil microbiome network complexity, species coexistence patterns, and prokaryotic carbon and nitrogen fixation genes. In medium petroleum contamination (petroleum concentrations of between 4000 mg kg^-1 and 20,000 mg kg^-1), microbial diversity (p > 0.05) and carbon and nitrogen transformation genes showed no evident change but promoted species coexistence patterns. Heavy petroleum contamination increased the Proteobacteria phylum abundance by 3.91%-57.01%, while medium petroleum contamination increased the Actinobacteria phylum abundance by 1.69%-0.26%. The results suggested that petroleum concentrations played a significant role in shifting soil microbial community structures, ecological functions, and species diversities.