Seasonal Variations In Environmental Conditions Research Articles

The role of nitrogen and iron biogeochemical cycles in the production and export of dissolved organic matter in agricultural headwater catchments

Abstract. To better understand the seasonal variations in environmental conditions regulating dissolved organic matter (DOM) export in agricultural headwater catchments, we combined the monitoring of nitrate, iron, soluble phosphorus, and DOM concentration (as dissolved organic carbon; DOC) and composition (3D fluorescence) in soil and stream waters at regular intervals during 1 hydrological year. We installed 17 zero-tension lysimeters in organic-rich top soil horizons (15 cm below the surface) in the riparian area of a well-monitored agricultural catchment in French Brittany and collected them at a fortnightly frequency from October 2022 to June 2023. We observed a large increase in DOC concentrations in soil waters during the high-flow period linked to the establishment of Fe-reducing conditions and the subsequent release of DOM. We also noted that the timing and the spatial variability in Fe(II) biodissolution in soils was regulated by nitrate from agricultural origin and the heterogeneity of water flow paths at the hillslope scale. Contrary to our current understanding of DOM export in headwater catchments, these results lead us to consider the winter high-flow period as an active phase of both DOM production and export.

Has COVID-19 Lockdown Affected C and N Level and Isotope Composition in Urban Soils and Plant Leaves?

This study aimed to evaluate how seasonal variations in environmental conditions and atmospheric NO 2 impact C and N cycle in an urban environment by determining their elemental concentration and isotopic composition (δ 13 C, δ 15 N) at spatial scale (urban and peri-urban sites) and species level (evergreen plants). Leaves and soil across the medium-sized city of Pisa were collected over 1 year including COVID-19 lockdown, taking advantage of the unprecedented containment measures causing a substantial NO 2 drop. The enrichment in heavier isotopes of organic matter in urban soil was most likely due to the long-term contribution of both δ 15 N-enriched depositions and greater C and N cycling rates in comparison with peri-urban soil. Leaf δ 15 N represented a valuable proxy of the urbanization degree depending on microclimate and N inputs from atmospheric NO 2 . Leaf δ 13 C showed a seasonal trend linked to plant functional types, with significant differences between sites and species. Differently from Nerium oleander and Pittosporum tobira , Quercus ilex showed a positive correlation between δ 13 C and NO 2 , highlighting the positive effect of N deposition on its intrinsic water-use efficiency. Moreover, the lockdown-induced NO 2 reduction was reflected in a decreasing trend of leaf N concentration and change in intrinsic water-use efficiency depending on the plant species and urbanization degree. Q. ilex showed the best adaptability to the more NO 2 -polluted site, being able to uptake and immobilize high amounts of 15 N-enriched atmospheric depositions into its leaves without toxic effects. Overall, these results must be considered in urban greening programs to improve air quality in NO 2 -polluted areas.

A Review of Wrky Transcription Factors in The Regulation of Abiotic and Biotic Stress in Cotton (Gossypium Spp.)

Cotton is an important economic crop that is grown in over 100 countries throughout the world. It provides the textile industry raw materials, cottonseed oil for cooking, and edible and protein-rich oil cake remnants for farm animals. Abiotic and biotic stressors limit its production, which is strongly reliant on climatic circumstances. Cotton plants have several built-in mechanisms for dealing with abiotic and biotic stress. These defense systems are controlled by changes in the expression of stress-responsive genes. Several stress response-related genes have been discovered, including WRKY transcription elements. WRKY proteins bind to the W box (TGACC (A/T)) in the promoter regions of genes to activate or reduce the expression of downstream genes, which regulates the stress response. It also works with other transcription factors to control the defense responses of the plant. The function of WRKY transcription factors in cotton was briefly discussed in this review in terms of drought, salinity, temperature, and oxidative and biotic stress reactions. In conclusion, WRKY genes are thought to be important components of gene regulatory networks involved in plant stress responses and developmental plasticity in response to seasonal variations in environmental conditions and pathogenic infections.

A direct comparison of methods for assessing the threat from emerging infectious diseases in seasonally varying environments

Seasonal variations in environmental conditions lead to changing infectious disease epidemic risks at different times of year. The probability that early cases initiate a major epidemic depends on the season in which the pathogen enters the population. The instantaneous epidemic risk (IER) can be tracked. This quantity is straightforward to calculate, and corresponds to the probability of a major epidemic starting from a single case introduced at time t=t0, assuming that environmental conditions remain identical from that time onwards (i.e. for all t≥t0). However, the threat when a pathogen enters the population in fact depends on changes in environmental conditions occurring within the timescale of the initial phase of the outbreak. For that reason, we compare the IER with a different metric: the case epidemic risk (CER). The CER corresponds to the probability of a major epidemic starting from a single case entering the population at time t=t0, accounting for changes in environmental conditions after that time. We show how the IER and CER can be calculated using different epidemiological models (the stochastic Susceptible-Infectious-Removed model and a stochastic host-vector model that is parameterised using temperature data for Miami) in which transmission parameter values vary temporally. While the IER is always easy to calculate numerically, the adaptable method we provide for calculating the CER for the host-vector model can also be applied easily and solved using widely available software tools. In line with previous research, we demonstrate that, if a pathogen is likely to either invade the population or fade out on a fast timescale compared to changes in environmental conditions, the IER closely matches the CER. However, if this is not the case, the IER and the CER can be significantly different, and so the CER should be used. This demonstrates the need to consider future changes in environmental conditions carefully when assessing the risk posed by emerging pathogens.

Real time side-by-side experimental validation of energy and comfort performance of a zero net energy retrofit package for small commercial buildings

Making buildings zero-net energy (ZNE) is one of the major strategies for achieving carbon emission reduction goals. For this strategy to be successful, it entails a very significant reduction in energy use – 50% or more. In small commercial buildings, however, owners and building management teams usually have limited resources for identifying, analyzing, and procuring appropriate retrofit measures for reducing such use. An approach to overcome this limitation is the development of bundles of energy efficiency measures that can be presented to building owners/operators as a comprehensive package. The research presented in this paper focuses on an experimental evaluation of the impacts of a retrofit package developed for small office buildings in California. Performing this evaluation in a full-scale whole-building integrated systems test facility allowed a side-by-side evaluation in real time, against a reference case, of the impact of the retrofit package not only on energy use but also on visual and thermal comfort. The retrofit package evaluated is comprised of a combination of HVAC, lighting (including daylighting), and plug load measures. The evaluation occurred at different times of the year in order to account for seasonal variations in environmental conditions, including solar angles and weather. The experimental facility allowed testing for two different façade orientations: south and west. Results show that the proposed ZNE retrofit package can save significant amounts of energy for small commercial buildings. During cooling-prevalent periods, total energy savings were 65% for south orientation and 68% for west orientation; during heating-prevalent periods total energy savings were 22% for south orientation and 25% for west orientation. Measurements indicate that the ZNE retrofit package resulted in small but not very significant changes in comfort levels for building occupants.

Stage-dependent niche segregation: insights from a multi-dimensional approach of two sympatric sibling seabirds

Niche theory predicts that to reduce competition for the same resource, sympatric ecologically similar species should exploit divergent niches and segregate in one or more dimensions. Seasonal variations in environmental conditions and energy requirements can influence the mechanisms and the degree of niche segregation. However, studies have overlooked the multi-dimensional aspect of niche segregation over the whole annual cycle, and key facets of species co-existence still remain ambiguous. The present study provides insights into the niche use and partitioning of two morphologically and ecologically similar seabirds, the common (CDP, Pelecanoides urinatrix) and the South Georgian diving petrel (SGDP, Pelecanoides georgicus). Using phenology, at-sea distribution, diving behavior and isotopic data (during the incubation, chick-rearing and non-breeding periods), we show that the degree of partitioning was highly stage-dependent. During the breeding season, the greater niche segregation during chick-rearing than incubation supported the hypothesis that resource partitioning increases during energetically demanding periods. During the post breeding period, while species-specific latitudinal differences were expected (species specific water mass preference), CDP and SGDP also migrated in divergent directions. This segregation in migration area may not be only a response to the selective pressure arising from competition avoidance between sympatric species, but instead, could reflect past evolutionary divergence. Such stage-dependent and context-dependent niche segregation demonstrates the importance of integrative approaches combining techniques from different fields, throughout the entire annual cycle, to better understand the co-existence of ecologically similar species. This is particularly relevant in order to fully understand the short and long-term effects of ongoing environmental changes on species distributions and communities.This work demonstrates the need of integrative multi-dimensional approaches combining concepts and techniques from different fields to understand the mechanism and causal factors of niche segregation.

Habitat Associations of Overwintering Bats in Managed Pine Forest Landscapes

Research Highlights: Seasonal variation in environmental conditions coinciding with reproductive and energetic demands might result in seasonal differences in species-specific habitat use. We studied a winter assemblage of insectivorous bats and found that species acted as habitat generalists during winter compared to expectations based on the summer active season. Background and Objectives: In temperate regions, seasonal fluctuations in resource availability might restructure local bat assemblages. Initially perceived to only hibernate or migrate to avoid adverse winter conditions, temperate insectivorous bats appear to also employ intermediate overwintering strategies, as a growing body of literature suggests that winter activity is quite prevalent and even common in some lower latitude areas. However, to date, most studies have exclusively assessed habitat associations during summer. Because habitat use during summer is strongly influenced by reproduction, we hypothesized that habitat associations might differ during the non-reproductive winter period. We used acoustic monitoring to assess the habitat associations of bats across a managed pine landscape in the southeastern United States. Materials and Methods: During the winters of 2018 and 2019, we deployed acoustic detectors at 72 unique locations to monitor bat activity and characterized vegetation conditions at two scales (microhabitat and landscape). We used linear mixed models to characterize species-specific activity patterns associated with different vegetation conditions. Results: We found little evidence of different activity patterns during winter. The activity of three species (hoary bat: Lasiurus cinereus; southeastern myotis: Myotis austroriparius; and tricolored bat: Perimyotis subflavus) was not related to vegetation variables and only modest relationships were evident for four other species/groups (big brown bat: Eptesicus fuscus; eastern red bat: L. borealis; Seminole bat: L. seminolus; evening bat: Nycticeius humeralis; and Brazilian free-tailed bat: Tadarida brasiliensis). Conclusions: During winter, the bats in our study were active across the landscape in various cover types, suggesting that they do not exhibit the same habitat associations as in summer. Therefore, seasonal differences in distributions and habitat associations of bat populations need to be considered so that effective management strategies can be devised that help conserve bats year round.

Daily and seasonal time partitioning in surface activity of Porcellioalbinus (Isopoda, Oniscidea) in the arid region of Zarat (Gabes, Tunisia).

The terrestrial isopod Porcellioalbinus is a burrowing species, dwelling in the desert of south Tunisia. Field studies were carried out in the coastal area of Zarat, Tunisia, to examine the surface activity rhythm of P.albinus in relation to daily and seasonal variations in environmental conditions. The activity of P.albinus was followed once a month, from November 2012 through October 2013. Hourly capture frequency was compared across the different seasons of the year. Porcellioalbinus is a strictly nocturnal species showing a nycthemeral rhythm regulated by the rhythmic and natural variations of the duration of the dark period. A positive correlation is observed between the circadian rhythm of the locomotor activity of the species and the duration of the dark period outside its burrow, P.albinus has a single daily activity peak. Individuals concentrated their activity in the first part of the night in winter and in the second part in summer. This peak is more spread out in spring and autumn. The differences in the activity rhythm of P.albinus between different seasons may be determined by two important factors, namely temperature and the length of the dark period.

Seasonal and Spatial Variations in Synechococcus Abundance and Diversity Throughout the Gullmar Fjord, Swedish Skagerrak.

The picophytoplankton Synechococcus is a globally abundant autotroph that contributes significantly to primary production in the oceans and coastal areas. These cyanobacteria constitute a diverse genus of organisms that have developed independent niche spaces throughout aquatic environments. Here, we use the 16S V3–V4 rRNA gene region and flow cytometry to explore the diversity of Synechococcus within the picophytoplankton community in the Gullmar Fjord, on the west coast of Sweden. We conducted a station-based 1-year time series and two transect studies of the fjord. Our analysis revealed that within the large number of Synechococcus amplicon sequence variants (ASVs; 239 in total), prevalent ASVs phylogenetically clustered with clade representatives in both marine subcluster 5.1 and 5.2. The near-surface composition of ASVs shifted from spring to summer, when a 5.1 subcluster dominated community developed along with elevated Synechococcus abundances up to 9.3 × 104 cells ml–1. This seasonal dominance by subcluster 5.1 was observed over the length of the fjord (25 km), where shifts in community composition were associated with increasing depth. Unexpectedly, the community shift was not associated with changes in salinity. Synechococcus abundance dynamics also differed from that of the photosynthetic picoeukaryote community. These results highlight how seasonal variations in environmental conditions influence the dynamics of Synechococcus clades in a high latitude threshold fjord.

Long-term trends and seasonal variations in environmental conditions in Sesoko Island, Okinawa, Japan

Long-term trends and seasonal variations in environmental conditions in Sesoko Island, Okinawa, Japan

Improving phenotyping in winter barley cultivars towards waterlogging tolerance by combining field trials under natural conditions with controlled growth condition experiments

Additional rainfall in Northern Europe due to global climate change is increasing the incidences of field flooding. Flooding causes hypoxic stress that results in a reduced capacity for photosynthesis, reduction in nutrient availability and uptake, increased production of toxic metabolites by anaerobic bacteria in the soil, and ultimately yield losses and crop death. To overcome hypoxic environmental conditions, new cultivars need to be bred and tested for waterlogging tolerance. We scored 403 winter barley cultivars from the ‘Association Genetics of UK Elite Barley’ (AGOUEB) population, taking advantage of the phenotypic changes associated with hypoxic stress. This enabled us to identify an initial set of waterlogging sensitive and tolerant cultivars. Comparative analysis of a subset of 65 cultivars exposed to waterlogging stress under field and growth cabinet environments showed variability in scores due to varying sensitivity to waterlogging over multi-season field trials. In field trials, we observed waterlogging damage resulting in reductions in biomass, grain yield and crop height. However, the effects varied between seasons and the severity of waterlogging due to differences in the topography of the field and the amount of rainfall. To overcome the seasonal variations in environmental conditions in multi-season field trials, we developed in parallel, an enhanced phenotyping method by complementing field experiments with phenotyping under controlled growth conditions. The phenotyping scoring method allows for the grouping of cultivars by sensitivity and tolerance to waterlogging, with limited variance between cultivars scored in the field and controlled conditions. Together, these two complementary approaches maximise the data available to breeders, allowing for the reliable selection of more tolerant cultivars able to grow under flooding conditions.

Gill Histopathology as a Biomarker for Discriminating Seasonal Variations in Water Quality

Histopathological alterations in various fish organs have a pronounced value in aquatic toxicology and are widely used in environmental monitoring. The aim of this study was to evaluate whether histopathological alterations in fish gills can discriminate seasonal variations in environmental conditions within the same aquatic ecosystem, and if so, which alterations contributed the most to seasonal differentiation. Microscopic examination of common bream Abramis brama gills displayed various alterations in gill structure, including epithelial hypertrophy, hyperplasia, mucous and chloride cell alterations, epithelial lifting, necrosis, hyperemia and aneurism. These alterations were subsequently quantified by a semi-quantitative analysis in order to detect differences in the intensity of the mentioned alterations. Epithelial hypertrophy, hyperplasia, epithelial lifting and necrosis varied significantly between seasons with only necrosis being significantly higher in the first season. Discriminant canonical analysis displayed that epithelial hyperplasia, mucous cell alterations, epithelial lifting and necrosis contributed the most to discrimination between seasons. Overall, this study demonstrates that histopathological biomarkers in fish gills can be used in discriminating seasonal variations in water quality within the same aquatic ecosystem.

Implications of overlooked seasonal growth dynamics in tropical fisheries assessment: A test case of an oyster (Crassostrea tulipa) fishery in the Densu Delta, Ghana

Tropical fish stocks are perceived not to exhibit seasonality in growth. For this reason the standard von Bertalanffy growth function (VBGF) has been used widely to fit the growth of tropical fish populations compared to the seasonally-oscillating VBGF (soVBGF), which is seldom used in tropical fisheries. To advocate for the use of the soVBGF in assessment of tropical fish stocks, this study compared the outputs of the two methods using ELEFAN_GA_boot on oysters from the Densu Delta, Ghana. Sampling of mangrove oyster, Crassostrea tulipa covered a period of 12 months and the data were analysed for VBGF growth parameters and its prediction models. The intensity of growth oscillation showed that C. tulipa exhibited seasonal growth (C = 0.50), and the soVBGF fitted the growth of the oyster better than the standard VBGF method. Estimates of some of the stock parameters (t50,tmax, Fcur, Ecur and Ycur) were comparatively higher for the standard VBGF than the soVBGF approach. In both approaches, the oysters were underexploited (Ecur < Emsy). However, unlike the soVBGF method where Fcur < F0.5, the standard method indicated that Fcur > F0.5. In view of the disparities, studies which adopt standard VBGF on tropical stocks that exhibit seasonality would likely generate comparatively higher outputs for relevant biological reference points, which may ultimately mislead management decisions. Given the sedentary nature of oysters which could render the organisms more susceptible to seasonal variations in environmental conditions to show seasonality as observed in this study, we recommend further works on tropical shell- and finfishes to corroborate the current findings or otherwise.

Dam promotes downriver functional homogenization of phytoplankton in a transitional river-reservoir system in Amazon

Dams disrupt the longitudinal gradient and decrease the natural connectivity of lotic systems and change the physical, chemical, and biological compartments of the river environment. Here, we investigated the effects of damming and seasonal variation in environmental conditions and richness, density, taxonomic and functional beta diversity patterns of phytoplankton, through dry and rainy seasons (of 2011 and 2012), among four zones (upriver, reservoir, dam, downriver) of the Tucurui dam (Tocantins River sub-basin, eastern Amazon, Brazil). Species were quantified and classified into three functional traits (size class, floating, life form) used to estimate functional beta diversity. We showed that water transparency was higher in the dam, and dry periods presented higher total phosphorus. Our results also demonstrated that the dam promotes species turnover between zones and seasonal periods and that the functional morphological groups respond to local limnological conditions. However, the dam led to a reduction in functional beta diversity—functional homogenization—of phytoplankton species, mainly downstream. We demonstrated that the dam is promoting unfavorable conditions and reducing the environmental heterogeneity, leading to a significant loss of functional traits variation between phytoplankton communities, which compromises the ecosystem processes provided by phytoplankton.

The Genomic Capabilities of Microbial Communities Track Seasonal Variation in Environmental Conditions of Arctic Lagoons.

In contrast to temperate systems, Arctic lagoons that span the Alaska Beaufort Sea coast face extreme seasonality. Nine months of ice cover up to ∼1.7 m thick is followed by a spring thaw that introduces an enormous pulse of freshwater, nutrients, and organic matter into these lagoons over a relatively brief 2–3 week period. Prokaryotic communities link these subsidies to lagoon food webs through nutrient uptake, heterotrophic production, and other biogeochemical processes, but little is known about how the genomic capabilities of these communities respond to seasonal variability. Replicate water samples from two lagoons and one coastal site near Kaktovik, AK were collected in April (full ice cover), June (ice break up), and August (open water) to represent winter, spring, and summer, respectively. Samples were size fractionated to distinguish free-living and particle-attached microbial communities. Multivariate analysis of metagenomes indicated that seasonal variability in gene abundances was greater than variability between size fractions and sites, and that June differed significantly from the other months. Spring (June) gene abundances reflected the high input of watershed-sourced nutrients and organic matter via spring thaw, featuring indicator genes for denitrification possibly linked to greater organic carbon availability, and genes for processing phytoplankton-derived organic matter associated with spring blooms. Summer featured fewer indicator genes, but had increased abundances of anoxygenic photosynthesis genes, possibly associated with elevated light availability. Winter (April) gene abundances suggested low energy inputs and autotrophic bacterial metabolism, featuring indicator genes for chemoautotrophic carbon fixation, methane metabolism, and nitrification. Winter indicator genes for nitrification belonged to Thaumarchaeota and Nitrosomonadales, suggesting these organisms play an important role in oxidizing ammonium during the under-ice period. This study shows that high latitude estuarine microbial assemblages shift metabolic capabilities as they change phylogenetic composition between these extreme seasons, providing evidence that these communities may be resilient to large hydrological events in a rapidly changing Arctic.

Long‐term influence of nitrogen, plant growth regulators, and iron sulfate on annual bluegrass populations and turfgrass quality on a golf green

AbstractAnnual bluegrass (ABG, Poa annua L.) is often considered an undesirable species on golf courses in many regions of the United States. However, the long‐term effect of the cultural and chemical management practices of ABG control is not sufficiently investigated. The objective of this study was to determine the long‐term effect of N, Fe sulfate, and plant growth regulators (PGRs) on ABG populations in a creeping bentgrass (CBG, Agrostis stolonifera L.) golf green. The study was established on a mixed stand of ‘L‐93′ CBG (∼75%) and ABG (∼25%) and managed as a putting green in University Park, PA, from 2012 to 2018. Treatments included ammonium sulfate (24 and 147 kg ha−1 yr−1), Fe sulfate (0, 12, or 49 kg FeSO4 ha−1 application−1), and the PGRs trinexapac‐ethyl (TE, 0.043 kg a.i. ha−1 application−1), flurprimidol (FL, 0.28 kg a.i. ha−1 application−1) and a nontreated control. Treatments were initiated in late April or early May each year and reapplied where required every 3 wk for nine applications annually. In general, ABG populations were lowest under lower N rates and with applications of FL. The long‐term effect of FeSO4 was minimal. In the first year of this study (2012), turfgrass quality was reduced, but quality levels generally increased in subsequent years. Although low N and FL may reduce ABG and high N and TE may increase ABG, seasonal variations in environmental conditions may reduce the efficacy of these treatments.

Quantifying the influence of shoreface shape on coastal responses to sea level rise

The coastal zone is a very dynamic region, constantly seeking to reach a state of equilibrium due to variations in the external forces. The shallow zone along the inner continental shelf known as the shoreface, can be divided into the upper and lower shoreface. While the former responds to processes operating across time spans ranging from that of a single event, such as storm, through to seasonal variations in environmental conditions, the latter evolution's occurs in geological scale, more in response to mean trends in environmental conditions (decades to millennia). These zones are connected via sedimentary exchanges, by a transition zone that adapts to changes imposed from behaviors and displacements of the upper and lower shoreface, such as upward profile displacement with sea level rise, aeolian transport, alongshore transport gradient, cross-shore transport. To analyze the influence of shoreface morphology variations on coastal response to mean sea level rise (MSLR), computer simulations were performed using synthetic shoreface profiles with variable shoreface shape parameter (‘m’) values. The random shoreface translation model (RanSTM) was used to simulate coastal response through variations in the shape of shoreface profiles. The ‘m’ value was changed in the upper and lower shoreface separately, to check the sensitivity of coastal response (in this case, shoreline recession distance) as a function of morphological change in each of the two zones. In addition, the variations of ‘m’ were analyzed with a variable and a fixed transition zone length (in order to isolate effects of a variable ‘m’). The simulations indicated that changes in ‘m’ on the upper shoreface have minimal influence on shoreline recession distance, especially when the transition zone remained constant. Conversely, profiles with higher ‘m’ values in the lower shoreface exhibited greater shoreline recession. It was also observed that, a longer transition zone produced a higher shoreline recession. Profiles adjusted with ‘m’ values of 0.66 and 0.4 in both shoreface zones had the highest and lowest shoreline recession distances (141.4 and 203.7 m), respectively. Sensitivity tests have shown that an increase of only 0.02 units in ‘m’ in the lower shoreface had a strong positive correlation (r = 0.97, p < 0.01) with increased shoreline recession. The results obtained in this study demonstrate the control that lower shoreface shape variations have on coastal response during MSLR. Critically, even small variations in shoreface shape parameter, such as those that occur along adjacent coastal sectors, and due to climate change effects may have implications for management and adaptation on a regional scale.

Assessment of interspecific variations in the reproductive patterns of co-existing female mullet species inhabiting intertidal mudflats of Indian Sundarbans

Mullets are considered as the most abundant and important species with respect to the local fisheries of the Indian Sundarbans. Being economically important, their natural population stock is of much priority for which their reproductive biology needs to be clearly understood followed by the projected trends in recruitment pattern. The study was concentrated towards female specimens as the male specimens were significantly lower in number. The purpose of the study was to investigate and highlight the seasonal pattern of the reproductive cycle through analysis of morpho-gonadal parameters, percentage frequency of maturity stages and flow-cytometric records of ovarian cells of female mullet species, which has not been reported in any other studies till date. The study was conducted in mangrove eco-region situated at the central part of Indian Sundarbans in the main estuarine network of Matla River and Bidya River from April 2015 to January 2018. Results suggested that the prominent peaks of reproductive parameters are indicative of the spawning time for Osteomugil cunnesius during pre-monsoon season (February–May) and in post-monsoon season (October–January) for Chelon parsia and Planiliza subviridis. Seasonal variation of environmental conditions indicated an influence on timing and duration of the reproductive mechanisms of mullets. Evidences suggested temporal segregation of reproductive maturation among the three mullet species with similar feeding niches. The present study highlights an inter-specific reproductive expression of three co-existing female mullets to avoid the struggle for food resources necessary for reproductive maturity to ensure recruitment success under favourable environmental conditions in estuarine intertidal mudflats of Indian Sundarbans.

Individual variation in parental tradeoffs between the number and size of offspring at the pre‐ and post‐natal stages

Life‐history theory predicts that parents refer to the resources they hold to determine their breeding strategy. In multi‐brooded species, it is hypothesized that single‐brooded parents produce larger clutches and raise offspring with a brood survival strategy, whereas multi‐brooded parents only do this under good breeding conditions. Under poor conditions, they produce smaller clutches and raise offspring with a brood reduction strategy. We tested this hypothesis in the Brown‐cheeked Laughing Thrush Trochalopteron henrici, which can breed twice a year on the Tibetan Plateau, by investigating the life‐history traits and provisioning behaviours of single‐ and double‐brooded parents. Single‐brooded parents laid larger clutches of smaller eggs and produced more and larger fledglings than double‐brooded parents in their first brood. Double‐brooded parents produced smaller clutches of larger eggs but fledged larger nestlings in their first brood than in their second brood. As single‐brooded parents only need to raise one brood a year, then producing and raising as many offspring as possible (i.e. the brood survival strategy in a large brood) can maximize their reproductive success. For double‐brooded parents, producing and raising fewer offspring in the first brood (i.e. the brood survival strategy in a small brood) can ensure their nesting success during a short breeding cycle. Additionally, producing more offspring but raising larger nestlings in the second brood (i.e. the brood reduction strategy in a large brood) can select for offspring of higher quality within the brood. Our findings indicate that different tradeoffs between single‐ and double‐brooded parents in egg‐laying and nestling‐raising may be an adaptation to the seasonal variation in environmental conditions.

Bacterial succession in oil-contaminated soil under phytoremediation with poplars.

Petroleum hydrocarbons (PHCs) continue to be among the most common pollutants in soil worldwide. Phytoremediation has become a sustainable way of dealing with PHC contamination. We conducted the off-site phytoremediation of PHC-polluted soil from an oil tanker truck accident, where poplars were used for the phytoremediation of the oil-polluted soil in a boreal climate during a seven-year treatment. The succession of bacterial communities over the entire phytoremediation process was monitored using microbial ecological tools relying on high-throughput 16S rRNA gene sequencing. Upon the successful depletion of PHCs from soil, endophytic communities were analyzed in order to assess the complete plant-associated microbiome after the ecological recovery. The rhizosphere-associated soil exhibited different bacterial dynamics than unplanted soil, but both soils experienced succession of bacteria over time, with diversity being negatively correlated with PHC concentration. In the relatively short growing season in North Europe, seasonal variations in environmental conditions were identified that contributed to the dynamics of bacterial communities. Overall, our study proved that phytoremediation using poplar trees can be used to assist in the removal of PHCs from soils in boreal climate conditions and provides new insight into the succession patterns of bacterial communities associated with these plants.