Seasonal Temperature Fluctuations Research Articles

Species-specific differences and temperature-dependence of Na+/K+-ATPase in freshwater mussels Anodonta anatina and Unio tumidus (Bivalvia: Unionidae)

The predicted global warming of surface waters can be challenging to aquatic ectotherms like freshwater mussels. Especially animals in northern temperate latitudes may face and physiologically acclimate to significant stress from seasonal temperature fluctuations. Na+/K+-ATPase enzyme is one of the key mechanisms that allow mussels to cope with changing water temperatures. This enzyme plays a major role in osmoregulation, energy control, ion balance, metabolite transport and electrical excitability. Here, we experimentally studied the effects of temperature on Na+/K+-ATPase activity of gills in two freshwater mussel species, Anodonta anatina and Unio tumidus. The study animals were acclimated to three ambient temperatures (+4, +14, +24 °C) and Na+/K+-ATPase activity was measured at those temperatures for each acclimation group. Both species had their highest gill Na+/K+-ATPase activity at the highest acclimation temperature. Na+/K+-ATPase activity of gills exhibited species-specific differences, where it was higher in A. anatina than U. tumidus in all test groups at all test temperatures. Temperature dependence of Na+/K+-ATPase was confirmed in both species, being highest at temperatures between +4 and + 14 °C when Q10 values in the acclimation groups varied between 5.06 and 6.71. Our results underline the importance of Na+/K+-ATPase of gills for the freshwater mussels in warming waters. Because Na+/K+-ATPase is the driving force behind ciliary motion, our results also suggest that in warming waters A. anatina may be more tolerate at sustaining vigorous ciliary action (associated with elevated respiration rates and filter-feeding) than U. tumidus. Overall, our results indicate great flexibility of the mussel's physiological system as response to changing conditions.

Soil salinity regulates spatial-temporal heterogeneity of seed germination and seedbank persistence of an annual diaspore-trimorphic halophyte in northern China

Background and aimsSeed heteromorphism is a plant strategy that an individual plant produces two or more distinct types of diaspores, which have diverse morphology, dispersal ability, ecological functions and different effects on plant life history traits. The aim of this study was to test the effects of seasonal soil salinity and burial depth on the dynamics of dormancy/germination and persistence/depletion of buried trimorphic diaspores of a desert annual halophyte Atriplex centralasiatica.MethodsWe investigated the effects of salinity and seasonal fluctuations of temperature on germination, recovery of germination and mortality of types A, B, C diaspores of A. centralasiatica in the laboratory and buried diaspores in situ at four soil salinities and three depths. Diaspores were collected monthly from the seedbank from December 2016 to November 2018, and the number of viable diaspores remaining (not depleted) and their germinability were determined.ResultsNon-dormant type A diaspores were depleted in the low salinity “window” in the first year. Dormant diaspore types B and C germinated to high percentages at 0.3 and 0.1 mol L-1 soil salinity, respectively. High salinity and shallow burial delayed depletion of diaspore types B and C. High salinity delayed depletion time of the three diaspore types and delayed dormancy release of types B and C diaspores from autumn to spring. Soil salinity modified the response of diaspores in the seedbank by delaying seed dormancy release in autum and winter and by providing a low-salt concentration window for germination of non-dormant diaspores in spring and early summer.ConclusionsBuried trimorphic diaspores of annual desert halophyte A. centralasiatica exhibited diverse dormancy/germination behavior in respond to seasonal soil salinity fluctuation. Prolonging persistence of the seedbank and delaying depletion of diaspores under salt stress in situ primarily is due to inhibition of dormancy-break. The differences in dormancy/germination and seed persistence in the soil seedbank may be a bet-hadging strategy adapted to stressful temporal and spatial heterogeneity, and allows A. centralasiatica to persist in the unpredictable cold desert enevironment.

Strong acclimation effect of temperature and humidity on heat tolerance of the Arctic collembolan Megaphorura arctica.

The Arctic is a highly variable environment in which extreme daily and seasonal temperature fluctuations can occur. With climate change, an increase in the occurrence of extreme high temperatures and drought events is expected. While the effects of cold and dehydration stress on polar arthropods are well studied in combination, little is known about how these species respond to the combined effects of heat and dehydration stress. In this paper, we investigated how the heat tolerance of the Arctic collembola Megaphorura arctica is affected by combinations of different temperature and humidity acclimation regimes under controlled laboratory conditions. The effect of acclimation temperature was complex and highly dependent on both acclimation time and temperature, and was found to have a positive, negative or no effect depending on experimental conditions. Further, we found marked effects of the interaction between temperature and humidity on heat tolerance, with lower humidity severely decreasing heat tolerance when the acclimation temperature was increased. This effect was more pronounced with increasing acclimation time. Lastly, the effect of acclimation on heat tolerance under a fluctuating temperature regime was dependent on acclimation temperature and time, as well as humidity levels. Together, these results show that thermal acclimation alone has moderate or no effect on heat tolerance, but that drought events, likely to be more frequent in the future, in combination with high temperature stress can have large negative impacts on heat tolerance of some Arctic arthropods.

Temporal and Spatial Dynamics of Vibrio harveyi: An Environmental Parameter Correlation Investigation in a 4-Metre-Deep Dicentrarchus labrax Aquaculture Tank.

Nowadays, European seabass (Dicentrarchus labrax) aquaculture is undergoing a significant expansion. Nevertheless, the aquaculture industry is plagued by vibriosis. The spatial and temporal dynamics of Vibrio harveyi were studied on a European seabass farm in northern France during seven months of 2022. Concrete specimens were suspended and water was pumped from different depths (0.3 m, 2.15 m and 4 m deep), providing insights into the biofilm and planktonic V. harveyi dynamics. The abundances of V. harveyi, in the biofilm and free-living forms, were positively correlated. The water parameters revealed seasonal fluctuations in temperature, pH, and salinity, with no significant differences observed across the water column. Quantification of V. harveyi revealed no significant differences between depths, but seasonality, with peak abundances observed in August, correlated with temperature increases. Principal component analysis identified temperature as a primary driver, but also additional parameters, such as salinity and pH. Vibriosis occurred during the sampling period, providing valuable insights into the conditions before, during, and after the outbreaks. This study underscores the importance of understanding V. harveyi behaviour in aquaculture, particularly in the context of global warming, for effective disease management and sustainable practices.

Shark critical life stage vulnerability to monthly temperature variations under climate change

In a 10-month experimental study, we assessed the combined impact of warming and acidification on critical life stages of small-spotted catshark (Scyliorhinus canicula). Using recently developed frameworks, we disentangled individual and group responses to two climate scenarios projected for 2100 (SSP2-4.5: Middle of the road and SSP5-8.5: Fossil-fueled Development). Seasonal temperature fluctuations revealed the acute vulnerability of embryos to summer temperatures, with hatching success ranging from 82% for the control and SSP2-4.5 treatments to only 11% for the SSP5-8.5 treatment. The death of embryos was preceded by distinct individual growth trajectories between the treatments, and also revealed inter-individual variations within treatments. Embryos with the lowest hatching success had lower yolk consumption rates, and growth rates associated with a lower energy assimilation, and almost all of them failed to transition to internal gills. Within 6 months after hatching, no additional mortality was observed due to cooler temperatures.

Study on the estradiol degradation gene expression and resistance mechanism of Rhodococcus R-001 under low-temperature stress

Estradiol (E2), an endocrine disruptor, acts by mimicking or interfering with the normal physiological functions of natural hormones within organisms, leading to issues such as endocrine system disruption. Notably, seasonal fluctuations in environmental temperature may influence the degradation speed of estradiol (E2) in the natural environment, intensifying its potential health and ecological risks. Therefore, this study aims to explore how bacteria can degrade E2 under low-temperature conditions, unveiling their resistance mechanisms, with the goal of developing new strategies to mitigate the threat of E2 to health and ecological safety. In this paper, we found that Rhodococcus equi DSSKP-R-001 (R-001) can efficiently degrade E2 at 30 °C and 10 °C. Six genes in R-001 were shown to be involved in E2 degradation by heterologous expression at 30 °C. Among them, 17β-HSD, KstD2, and KstD3, were also involved in E2 degradation at 10 °C; KstD was not previously known to degrade E2. RNA-seq was used to characterize differentially expressed genes (DEGs) to explore the stress response of R-001 to low-temperature environments to elucidate the strain's adaptation mechanism. At the low temperature, R-001 cells changed from a round spherical shape to a long rod or irregular shape with elevated unsaturated fatty acids and were consistent with the corresponding genetic changes. Many differentially expressed genes linked to the cold stress response were observed. R-001 was found to upregulate genes encoding cold shock proteins, fatty acid metabolism proteins, the ABC transport system, DNA damage repair, energy metabolism and transcriptional regulators. In this study, we demonstrated six E2 degradation genes in R-001 and found for the first time that E2 degradation genes have different expression characteristics at 30 °C and 10 °C. Linking R-001 to cold acclimation provides new insights and a mechanistic basis for the simultaneous degradation of E2 under cold stress in Rhodococcus adaptation.

Growth, phytochemical concentration, nutrient uptake, and water consumption of butterhead lettuce in response to hydroponic system design and growing season

Two hydroponic system designs (nutrient film technique: NFT, and deep water culture: DWC) were set up in a climate-controlled greenhouse to compare growth, nutrients and water uptake patterns, yield and quality of lettuce (Lactuca sativa cv. Butterhead) during fall (October through November) and summer (July-August) growing conditions. The research was conducted with four system replicates for each hydroponic design and each system contained nine lettuce plants. Plant photosynthetic properties, growth parameters, and irrigation solution nutrient concentrations were measured weekly. At the end of the production cycle, plants were harvested for leaf area, fresh and dry yield of shoots and roots, nutritional and phytochemical concentrations. In the study, DWC system had better water quality properties than NFT including less seasonal water temperature fluctuation, which supported lettuce with better photosynthetic rates, growth rate and fresh yield in fall. Tipburn symptoms were only observed in summer, and NFT grown lettuce had significantly lower shoot calcium and magnesium concentrations than DWC in both fall and summer seasons, which led to more severe tip burn symptom in summer. In addition, better water quality in DWC also benefited lettuce with higher antioxidant concentrations than NFT, which included 9.4 % higher vitamin C in fall, 34.6 % higher total carotenoids in fall, 40.6 % higher non-acidified phenols in fall, as well as 12.9 % higher total chlorophyll in summer. Although there were marginal differences in fresh yield, most types of mineral nutrients and antioxidants between DWC and NFT, DWC performed better than NFT with less tipburn in summer as well as increased yield, total carotenoids, vitamin C and non-acidified phenols in fall.

The effects of temperature on plasticity, shape symmetry and seasonal variation in the freshwater benthic green microalga Micrasterias thomasiana

AbstractDesmids are usually abundant in shallow peatland pools. In these localities, water temperature is closely linked to seasonal fluctuations in air temperature, so with increasing temperature extremes in temperate ecosystems, these microalgae are exposed to conditions of high-temperature stress. We investigated whether the shape, size, and growth rates of Micrasterias thomasiana, a frequently occurring species, are associated with varying temperatures in cultures and natural populations. The research was based on parallel analysis of clonal populations in temperature levels from 13 to 33 °C as well as cells from natural populations collected during the season. The effects of high temperature on morphological plasticity and fluctuating asymmetry in the shape of cellular parts were investigated by the landmark-based geometric morphometrics. The results showed that variation among individuals and fluctuating asymmetry between the lateral lobes of Micrasterias cells increased at 29 °C and in natural samples taken in July and October. In parallel, the size of semicells growing at temperatures above 25 °C decreased compared to those grown at lower temperatures. However, the temperature effects on shape and size were not directly related to the growth rates. The overall bilateral asymmetry between semicell halves did not change in relation to varying temperatures. In general, the results showed that morphological variation in natural populations of M. thomasiana reflected seasonal cycles and corresponded to plasticity associated with temperature changes in clonal cultures. It might therefore be possible to use these phenotypic markers as indicators of thermal stress in natural populations inhabiting shallow pools in peatlands.

Water mass exchange in triangle seas of the Java-Makassar-Flores (JMF): A modeling study

The ocean dynamics of the marginal seas in the Java-Makassar-Flores (JMF) Triangle seas facilitates the seasonal exchange of water masses between Java, Makassar, and Flores, which influences the occurrence of small pelagic fish. This research investigates seasonal fluctuations in sea currents, seawater temperature, salinity, and phytoplankton primary production (PPN and PPD) based on validated model output datasets from NEMO and PISCES from the INDESO simulation (2008–2015). The model demonstrated seasonal exchanges of the top 50 m of water masses in the area, where the eastward monsoon current transported freshwater (salinity<31 psμ) from the Java Sea to southern Makassar and Flores. This northwest monsoon produced a much fresher water in the southern region of Makassar and western region of Flores. During the southeast monsoon, the surface component of the Makassar throughflow, which transports saline water (salinity >34 PSU) into the Java Sea, pushes fresh Java waters westward. Seasonal salinity changes and PPN/PPD in the shelf region of southern Kalimantan correlated with substantial small pelagic fishing.

Topography influences diurnal and seasonal microclimate fluctuations in hilly terrain environments of coastal California.

Understanding the topographic basis for microclimatic variation remains fundamental to predicting the site level effects of warming air temperatures. Quantifying diurnal fluctuation and seasonal extremes in relation to topography offers insight into the potential relationship between site level conditions and changes in regional climate. The present study investigated an annual understory temperature regime for 50 sites distributed across a topographically diverse area (>12 km2) comprised of mixed evergreen-deciduous woodland vegetation typical of California coastal ranges. We investigated the effect of topography and tree cover on site-to-site variation in near-surface temperatures using a combination of multiple linear regression and multivariate techniques. Sites in topographically depressed areas (e.g., valley bottoms) exhibited larger seasonal and diurnal variation. Elevation (at 10 m resolution) was found to be the primary driver of daily and seasonal variations, in addition to hillslope position, canopy cover and northness. The elevation effect on seasonal mean temperatures was inverted, reflecting large-scale cold-air pooling in the study region, with elevated minimum and mean temperature at higher elevations. Additionally, several of our sites showed considerable buffering (dampened diurnal and seasonal temperature fluctuations) compared to average regional conditions measured at an on-site weather station. Results from this study help inform efforts to extrapolate temperature records across large landscapes and have the potential to improve our ecological understanding of fine-scale seasonal climate variation in coastal range environments.

Diurnal temperature fluctuations improve predictions of developmental rates in the spruce bark beetle Ips typographus

AbstractThe European spruce bark beetle Ips typographus is a widespread pest in Norway spruce-dominated forests in Eurasia. Predicting its phenology and voltinism is crucial to plan forest management measures and to mitigate mass outbreaks. Current phenology models are based on constant temperatures inferred from laboratory experiments; however, insect life cycles under natural conditions are rather driven by diurnal and seasonal temperature fluctuations. Therefore, phenology models based on fluctuating temperatures would reflect field conditions more realistically and might thus improve model predictions. In a laboratory experiment, we investigated the development of I. typographus, applying mean temperatures between 3 and 35 °C and diurnal temperature oscillations of up to ± 15 °C. Subsequently, we calibrated developmental rate models and applied them to climate data, in order to assess the effect of temperature fluctuations on voltinism under field conditions. Our results showed that diurnal temperature oscillations significantly affected developmental rates. Compared to constant temperatures, development was faster at temperature oscillations falling below the lower developmental threshold, and slower at temperature oscillations exceeding the developmental optimum. Furthermore, short exposures to suboptimal temperatures affected I. typographus less than expected from constant conditions. Natural temperature fluctuations thus accelerate development under cool, shaded conditions, whilst slowing it under hot, sun-exposed conditions, thereby ultimately affecting voltinism. Our findings highlight the importance to account for diurnal temperature fluctuations for more accurate predictions of developmental rates of I. typographus in natural thermal environments, and provide the fundament for improving current phenology models to support effective bark beetle management in a warming climate.

Interhemispheric propagation of seasonal sea surface temperature fluctuations over the western Pacific in CMIP6

AbstractInterannual sea surface temperature (SST) variability in the western Pacific is a critical research topic in climate change, as it can significantly impact regional and global weather patterns. Previous observational studies have shown that SST in the southwestern Pacific (SWP) can effectively serve as a precursor signal for SST in the western tropical Pacific (WTP). In this study, we evaluate and compare the modelling capabilities of 32 CMIP6 models to simulate the relationship between SWP and WTP SST. The results indicate that while some CMIP6 models can simulate the spatial connection and physical processes between the SWP and WTP, there are significant intermodel differences. Specifically, the models that best simulate the cross‐equatorial propagation of SWP SST anomalies are those that accurately simulate the cross‐equatorial wind anomalies induced by SWP SST anomalies, highlighting the key role of wind‐evaporation‐SST feedback in SST propagation. Further analysis reveals that the intermodel spread in cross‐equatorial SST propagation is attributable to model biases in simulating climatological SST and wind speed. Models with warm climatological equatorial SST and strong wind speeds provide favourable conditions for the cross‐equatorial propagation of SWP‐related SST anomalies towards the north. Warm SST and strong inter‐season wind speeds near the equator facilitate the northward propagation of the SWP warm signal, leading to increased warming in the WTP.

On the temperature sensitivity of near-surface seismic wave speeds: application to the Groningen region, the Netherlands

SUMMARY Subsurface temperature measurements play a crucial role, for instance, in optimizing geothermal power plants and monitoring heat-storage systems. Previous studies have demonstrated that time-lapse variations in temperature can be correlated with variations in seismic wave speeds, offering the potential for temperature monitoring via seismic surveys. However, an apparent discrepancy has emerged between field and laboratory experiments. Field studies predominantly report positive correlations between temperature and seismic wave speeds, while laboratory experiments often show anticorrelations. This inconsistency underscores the need for a more comprehensive, physics-based understanding of temperature-induced wave speed changes. In this study, we strive to bridge the gap between field and laboratory findings by examining several mechanisms governing temperature-induced seismic wave speed changes, namely the intrinsic temperature dependency of elastic parameters and thermally induced elasticity. We present a physics-based modelling approach to identify the primary mechanisms responsible for temperature-induced seismic wave speed changes. By considering several end-member models, we find that intrinsic temperature dependency of elastic parameters (negative correlation) compete with thermal pressure effects (positive correlation). The precise initial and boundary conditions and physical parameters of the system under consideration will determine the weight of both effects. Temperature-related dilatation does not seem to play an important role. We apply our approach to loosely consolidated sediments in the shallow subsurface of the Groningen region, where subsurface temperature fluctuations are driven by seasonal atmospheric temperature fluctuations roughly between −5 and $30\, ^\circ$C. For these models, we predict seasonal temperature-induced changes in body-wave speeds of up to 8 per cent in the first few metres of the subsurface, high-frequency (above 2 Hz) surface wave phase velocity variations in the range of 1–2 per cent, and relative changes in site amplification on the order of 4 per cent. These findings contribute to a more comprehensive understanding of the intricate relationship between temperature and near-surface seismic properties, offering insights for applications as subsurface temperature monitoring systems.

Freezing and Thawing of Enclosing Structures and Foundation Soils Taking into Account the Effects of Solar Energy: Part 1. Theoretical Foundations of Freezing Wet Soils

The temperature and humidity state of the foundations and foundations in the climatic conditions of the Russian Federation is decisive in their design,it affects the bearing capacity, operational reliability, and durability of the foundations and the entire building. When designing foundations and foundations, they solve a set of tasks that are subordinated to one idea, so that the soil (base) he carried the load from the building or structure proposed to him, and the foundation structure itself would ensure reliable operation of the building or structure for the entire life cycle, since the foundations belong to permanent structures, and their repair is associated with large material costs. Existing modern calculation methods assume that the heat transfer process is stationary and do not consider real processes – seasonal and daily fluctuations in outdoor air temperature, heating on and off modes, temperature changes in the depth of the soil, wet structures due to accidents of heating plants, the absence (or destruction) of a blind area, etc. Freezing of soils, as a rule, occurs in autumn-winter period, when the soil is saturated with moisture. Thawing of the soil occurs in the spring-summer period. These processes are non-stationary in nature, which is influenced by many factors, including solar radiation. The work is devoted to modelling and calculation of these real processes. The process of freezing and thawing of the foundation soils is influenced by many factors: the composition of the soil, water, ice, snow, solar radiation, fluctuations in outdoor temperature. The paper provides general information about some of the physical properties of water, ice, and snow, necessary for understanding the processes under consideration.

Diurnal temperature variation impacts energetics but not reproductive effort across seasons in a temperate dung beetle.

Temperature varies on multiple timescales and ectotherms must adjust to these changes to survive. These adjustments may lead to energetic trade-offs between self-maintenance and reproductive investment. However, we know little about how diurnal and seasonal temperature changes impact energy allocation. Here we used a combination of empirical data and modeling of both thermoregulatory behaviors and body temperature to examine potential energetic trade-offs in the dung beetle Onthophagus taurus. Beginning in March 2020, universities and laboratories were officially closed due to the COVID-19 pandemic. We thus performed experiments at a private residence near Knoxville, Tennessee, USA, leveraging the heating, ventilation and air conditioning of the home to manipulate temperature and compare beetle responses to stable indoor temperatures versus variable outdoor temperatures. We collected O. taurus beetles in the early-, mid-, and late-breeding seasons to examine energetics and reproductive output in relation to diurnal and seasonal temperature fluctuations. We recorded the mass of field fresh beetles before and after a 24-h fast and used the resulting change in mass as a proxy for energetic costs of self-maintenance across seasons. To understand the impacts of diurnal fluctuations on energy allocation, we held beetles either indoors or outdoors for 14-day acclimation trials, fed them cow dung, and recorded mass change and reproductive output. Utilizing biophysical models, we integrated individual-level biophysical characteristics, microhabitat-specific performance, respirometry data, and thermoregulatory behaviors to predict temperature-induced changes to the allocation of energy toward survival and reproduction. During 24 h of outdoor fasting, we found that beetles experiencing reduced temperature variation lost more mass than those experiencing greater temperature variation, and this was not affected by season. By contrast, during the 14-day acclimation trials, we found that beetles experiencing reduced temperature variation (i.e., indoors) gained more mass than those experiencing greater temperature variation (i.e., outdoors). This effect may have been driven by shifts in the metabolism of the beetles during acclimation to increased temperature variation. Despite the negative relationship between temperature variation and energetic reserves, the only significant predictor of reproductive output was mean temperature. Taken together, we find that diurnal temperature fluctuations are important for driving energetics, but not reproductive output.

The Spatial and Temporal Variability of the Blue–Green Spatial Structures of the South Dongting Lake Wetland Areas Amidst Climate Change, including Its Relationship with Meteorological Factors

In recent years, the water level of the Dongting Lake (DTL) has been continuously low, and the wetland area and landscape pattern have changed significantly. Considering the obvious spatial heterogeneity of water regime changes in different waters of the DTL, this paper takes two core areas of the South Dongting Lake Nature Reserve (SDLNR) as study areas and analyzes the spatial distribution characteristics of the wetland blue–green landscape patterns by using remote sensing image data and hydrological and meteorological data. The multi-scale correlation between runoff, precipitation, temperature, and evapotranspiration in the SDLNR was studied via cross-wavelet transform analysis. The results show the following: (1) The change in the blue–green spatial patterns in different regions in different periods is inconsistent, and this inconsistency is related to the topography, climate, and human activities in each region; (2) there are seasonal fluctuations in precipitation, air temperature, and evapotranspiration in the SDLNR. Among them, the annual mean temperature shows a rising trend and passes the significance test with 95% confidence, while the annual mean precipitation and annual mean evapotranspiration show no significant change trend; and (3) our Pearson correlation analysis and cross-wavelet change results show that precipitation and temperature are strongly correlated with runoff, with a resonance period of 8–16 months, while the correlation between evapotranspiration and runoff is not significant. We recommend that policymakers establish an effective early warning system and make plans to store water through micro-terrain transformation in possible climate change treatments and strategies.

Influence of season on the microbial population dynamics of activated sludge.

This review discusses critically how seasonal changes might affect the community composition and dynamics of activated sludge wastewater treatment plants (WWTP), and examines the factors thought more generally to control microbial community assembly, including the role of taxa-time relationships and stochastic and deterministic influences. The review also questions the differences in protocols used in these studies, which make any subsequent attempts at data comparisons problematic. These include bacterial DNA extraction and PCR methodologies, 16S rRNA sequencing and especially its depth, and subsequent statistical analyses of the data, which together often fail to reveal seasonal dynamic community shifts. Suggestions are given as to how experimental protocols need to be improved and standardized, and especially the requirement to examine bacterial populations at the species level. This review looks critically at what is known currently about seasonal influences on key members of this community, including viruses, the bacteria responsible for nitrogen and phosphorus removal and those causing bulking and foaming. The data show many of these species exhibit replicative seasonal abundances over several years, but not under all conditions, illustrating how complex these community dynamics are. Fungal and protozoal/metazoal seasonal community dynamics, less studied, are also discussed. The current data suggest that seasonal temperature fluctuations are responsible for most of seasonal community dynamics by selectively favouring or otherwise individual populations. However, more longer term studies carried out under much stricter controlled conditions are required.

Double nitrite autotrophic shunt processes enable highly efficient nitrogen removal in Anammox-mediated biotechnology for seasonal temperature fluctuation tolerance

Anammox, an energy-efficient bioprocess, is gaining growing attention. However, its widespread adoption confronts challenges due to residual nitrate and unstable nitrite supply, especially during seasonal temperature fluctuations. To address this, we developed an innovative Anammox-mediate biotechnology, incorporating a double nitrite autotrophic shunt: partial nitrification (PN/A) and sulfur-driven partial denitrification (SPDN/A). Remarkably, a nitrogen removal efficiency was realized over 183 days, encompassing a significant seasonal temperature decrease (from 25.3℃ to 13.2℃). Functional gene analysis revealed Anammox spontaneously downregulated functional gene expression to allocate core metabolic energy for essential cellular processes towards temperature plunge condition. Interestingly, as seasonal temperature decreased, nitrogen removal contribution of Anammox in SPDN/A exhibited a noticeable upward tendency from 66.4 % to 86.7 %. Enriched Thiobacillus and decreased NO2− reductase gene expression in SPDN/A ensured sustainable nitrite supply for Anammox process, promoting superiority of Candidatus Kuenenia to 7.3 %. However, Anammox groups decreased significantly in PN/A. Divergence in responses towards temperature fluctuation credibly concluded Anammox’s correlation with temperature is not necessarily positive or parallel. Instead, stable provision of NO2− is primary determinant. Comprehensive analysis, integrating functional gene transcription, microbiota synergetic interactions, and kinetics underscores PN/A–SPDN/A’s potential for reliable nitrogen removal, offering a sustainable solution subject to seasonal temperature fluctuation.

Temporal differentiation in the adaptation of functional bacteria to low-temperature stress in partial denitrification and anammox system

Despite reliable nitrite supply through partial denitrification, the adaptation of denitrifying bacteria to low temperatures remains elusive in partial denitrification and anammox (PDA) systems. Here, temporal differentiations of the structure, activity, and relevant cold-adaptation mechanism of functional bacteria were investigated in a lab-scale PDA bioreactor at decreased temperature. Although distinct denitrifying bacteria dominated after low-temperature stress, both short- and long-term stresses exerted differential selectivity towards the species with close phylogenetic distance. Species Azonexus sp.149 showed high superiority over Azonexus sp.384 under short-term stress, and long-term stress improved the adaptation of Aquabacterium sp.93 instead of Aquabacterium sp.184. The elevated transcription of nitrite reductase genes suggested that several denitrifying bacteria (e.g., Azonexus sp.149) could compete with anammox bacteria for nitrite. Species Rivicola pingtungensis and Azonexus sp.149 could adapt through various adaptation pathways, such as the two-component system, cold shock protein (CSP), membrane alternation, and electron transport chain. By contrast, species Zoogloea sp.273 and Aquabacterium sp.93 mainly depended on the CSP and oxidative stress response. This study largely deepens our understanding of the performance deterioration in PDA systems during cold shock and provides several references for efficient adaptation to seasonal temperature fluctuation.

Impact of environmental variables on the distribution of phytoplankton communities in the Southern Yellow Sea

To gain a comprehensive understanding of the seasonal variation in the structure of phytoplankton communities in the Southern Yellow Sea (SYS), two research expeditions were conducted from 12 to 24 in April 2019, and from 12 to 22 in October of 2019. During the spring season, the phytoplankton community within the SYS was primarily comprised of diatoms and dinoflagellates, while in autumn, diatoms and cyanobacteria dominated. Thalassiosira rotula and Paralia sulcata were the dominant species in both seasons. In spring, P. sulcata displayed no obvious correlation with any environmental parameter, while in autumn, it exhibited negative correlations with environmental factors. According to the cluster and multidimensional scaling analyses, the phytoplankton community was stratified into three distinct ecological provinces in the SYS: the Western Yellow Sea, the Yellow Sea basin, and the southern coastal region. The phytoplankton community composition was predominantly affected by seasonal fluctuations in temperature and nutrient levels. Notably, the Yellow Sea basin exhibited the lowest phytoplankton abundance, largely because of the impact of the Yellow Sea Cold Water Mass. Furthermore, the presence of cyanobacteria, particularly prevalent in the Yellow Sea basin, may have been facilitated by transport mechanisms associated with the Kuroshio current. Aggregated boosted tree (ABT) and Generalized Additive models (GAM) suggested that temperature, DIN, salinity, and DIP were significant parameters of phytoplankton abundance in SYS. Additionally, the N:P nutrient ratio was a key parameter in governing the structure of phytoplankton communities during both seasons.