Seasonal Variations In Environmental Conditions Research Articles

Seasonal benefits of farmland pond management for birds

ABSTRACTCapsule: There is seasonal variation in the benefits that birds can take from restored farmland ponds.Aims: To evaluate season-specific benefits of farmland pond restoration for local bird communities.Methods: Bird communities were recorded at unmanaged overgrown and managed open-canopy farmland ponds over the breeding, post-breeding and winter seasons. Results were compared and related to seasonal variation in environmental conditions of within-pond and marginal habitats to identify predictors of local bird communities.Results: Bird communities at managed open-canopy ponds showed a higher abundance and species richness over all seasons and displayed pronounced seasonal shifts in composition. Warblers and other specialised bird species were frequently observed at open-canopy sites over the breeding and post-breeding seasons but were generally absent from overgrown ponds. While pond management and landscape connectivity had a consistent positive influence on bird communities over all seasons, the importance of other predictors such as bramble area varied seasonally.Conclusions: Our study highlights a key role of pond management for farmland bird conservation. In addition, the identified seasonal predictors of bird assemblages provide valuable lessons for the design of agri-environment prescriptions for farmland ponds, highlighting the importance of bramble-dominated patches and pond marginal habitat over the breeding season and of a strong connectivity between pond margins and surrounding semi-natural habitats throughout the year.

Seasonal dynamics of phytoplankton morphological characters and driving factors in tropical reservoirs: A case study from Gaozhou Reservoir

体积、比表面积和最大轴性长度是浮游植物主要的形态性状，反映浮游植物资源竞争和反牧食能力.群落中物种的性状分布会随着环境条件的季节改变而变化，热带水库环境条件的季节性变化小，可能导致群落形态性状变化不显著.本文以热带大型水库——高州水库为研究对象，分析浮游植物形态性状季节动态及关键影响因子.高州水库浮游植物以丝状和单细胞藻类为主，群落水平的平均细胞体积在108.52~753.25 μm³之间，平均比表面积在0.93~2.08 μm^-1之间，平均最大轴性长度在5.21~17.44 μm之间，均有明显的季节特征.浮游植物群落平均细胞体积、最大轴性长度与总氮浓度呈负相关，与水温呈正相关；平均比表面积与硝态氮浓度呈负相关.粘质长孢藻（Dolichospermum mucosa）和光角星鼓藻（Staurastrum muticum）是高州水库浮游植物优势种，其形态性状均具有明显的时空差异，表现出明显的形态可塑性.粘质长孢藻的平均细胞体积、最大轴性长度与总氮浓度呈正相关，与水温呈负相关；平均比表面积与总氮浓度呈负相关，与水温呈正相关.光角星鼓藻的平均细胞体积、最大轴性长度与正磷酸盐浓度呈正相关.总体上高州水库浮游植物在群落和种群水平形态性状均有明显的季节差异，夏季以大细胞为主，其他季节以小细胞种类为主，水温、氮和磷的可利用性是导致浮游植物形态性状季节差异的关键因子.;Volume, specific surface area and the longest axial linear dimension are main morphological characters of phytoplankton. These characters reflect the ability of phytoplankton in competing for resources and resisting grazing. The morphological characters of cells change with the seasonal environmental conditions. It was assumed that limited seasonal changes occurred on phytoplankton cells morphological characters in community, due to the small seasonal variation of environmental conditions in tropical reservoirs. To test this assumption, the seasonal dynamic of phytoplankton morphological characters and the affecting factors in large tropical reservoir (Gaozhou Reservoir)were analyzed. The phytoplankton community was dominated by filamentous species and unicellular algae in Gaozhou Reservoir. In community level, the average cell volume was 108.52-753.25 μm³, the average cell specific surface area was 0.93-2.08 μm^-1, the average cell longest axial linear dimension was 5.21-17.44 μm, and the three morphological characters all showed seasonal dynamics. The average cell volume and the average cell longest axial linear dimension were correlated negatively with total nitrogen, and positively with temperature, the average cell specific surface area was correlated negatively with nitrate nitrogen. Dolichospermum mucosa and Staurastrum muticum were the dominant phytoplankton species in Gaozhou Reservoir, and they both showed morphological plasticity and seasonal dynamics in the morphological characters. The average cell volume and the average cell longest axial linear dimension of D. mucosa were correlated positively with total nitrogen, and negatively with temperature. The average cell specific surface area of D. mucosa was correlated negatively with total nitrogen, and positively with temperature. The average cell volume and the average cell longest axial linear dimension of S. muticum were correlated positively with soluble reactive phosphate. In conclusion, the morphological characters of phytoplankton in community and species were different with seasonal dynamics in Gaozhou Reservoir. The large cells dominated phytoplankton community in summer, but small cells in other season. Temperature, the availability of nitrogen and phosphorus were the primary factors to explain the morphological variation of phytoplankton.

Biomass and abiotic variables change in phytotelmic environment in the tank-bromeliad Nidularium longiflorum Ule in tropical forest

Abstract Aim Phytotelm plays an important role in plant growth and ecosystem functioning, but this natural aquatic microcosm is poorly known. We evaluated the seasonal (dry and rainy seasons) and spatial variations (forest trail and stream sites) of the phytotelm in Nidularium longiflorum, bromeliad that occurs in the Atlantic Forest. Methods Abiotic and biotic variables were measured in tank-bromeliad phytotelms. The biomass was analyzed by ash-free dry mass and chlorophyll-a concentration. Results Abiotic variables measured in the phytotelmic environment of bromeliads varied between sampling sites and seasons. Temperature, electrical conductivity and total nitrogen values were significantly different between seasons and sites. Chlorophyll-a and ash-free dry mass (organic matter) in phytotelm were significantly different between sampling sites. Eleven genera of algae in the phytotelm were identified. PCA axis 1 ordination evidenced the seasonal variation of environmental conditions. Conclusions Our findings suggest that environmental and micro-environmental conditions do not favor the development of algal community in the phytotelm. Biomass and abiotic variables in phytotelm of Nidularium longiflorum change seasonally, however biomass accumulation was strongly influenced by site characteristics.

Seasonal and Site Differences in Phorid Parasitoidism Rates of Leaf-Cutting Ants.

Interspecific interactions are influenced by several environmental factors that may affect spatial and temporal dynamics. Seasonal variations in environmental conditions and differences among sites may affect the intensity of interactions and the abundance of interacting species. In this study, we describe the variability in parasitoids of Atta ants among sites and seasons over a year. More specifically, we studied parasitoidism of Atta sexdens Linnaeus and Atta laevigata Smith nests at a site with native cerrado vegetation and a Eucalyptus monoculture in dry and rainy seasons. Of the 45,147 workers collected, 1,020 (2.2%) were parasitized. We found five parasitoid species of A. sexdens and four species of A. laevigata. The two species of leaf-cutting ants shared similar parasitoid communities, but the infection rate was higher in A. laevigata (5.3%) compared with A. sexdens (0.8%). Parasitoidism rates of A. laevigata increased in the rainy season, but the rate for A. sexdens was consistently low in both seasons. The identity of the host species and the season, therefore, appear to interact to influence the rate of parasitoidism in these leaf-cutting ant species.

Trophic Ecology of Two Sympatric Frogs with Contrasting Morphology and Habitat Use in a Subtropical Wetland

Abstract Frog diets are influenced by multiple factors, including morphological constraints, habitat use, and seasonal variation in environmental conditions and food availability. This study combined stomach content analysis (SCA), stable isotope analysis (SIA), and estimates of prey availability to investigate the influence of body size and microhabitat use on seasonal variation of the trophic ecology of two sympatric hylids (Pseudis minuta and Scinax squalirostris). We evaluated two hypotheses: (1) the species with larger body and mouth sizes or broader use of microhabitats will have greater diet breadth, and (2) regardless of differences in morphological traits and microhabitat use, diet breadth of both species will be greater during the warmer of two periods. Pseudis minuta exhibited larger body size and mouth width and revealed broader use of microhabitats (mostly within and near major water bodies), whereas S. squalirostris had smaller body size and mouth gape and was found exclusively within or nea...

The structure and role of the “petola” microbial mat in sea salt production of the Sečovlje (Slovenia)

Microbial mats are commonly observed in estuaries and in salt marshes but they only rarely represent a significant surface involved in salt production. In the Sečovlje salt works in Northern Adriatic, a microbial mat known as the “petola” covers the bottom of salt crystallising pans, highly influencing salt composition and salt production processes. Throughout the year the petola is subjected to numerous co-varying factors that drive changes in its structure and the microbial community. Seasonal modifications were investigated via various methods (cryo-HRSEM, XRD, elemental analysis, carbohydrate content, bacterial community structure). This study provides knowledge on microbial mat compositional characteristics and functional roles in response to seasonal variation in environmental conditions. The in situ characterisation (close-to its natural hydrated state) of the three-dimensional microstructure provides precise information about dominating filamentous cyanobacterium Coleofasciculus chthonoplastes and extracellular polymer secretion (EPS) organisation. This is the first study to address how microbial mat composition and structure, especially 3D EPS network (and microbial diversity), affects the salt production processes within a hypersaline environment.

To share or not to share? Phytoplankton species coexistence puzzle in a competition model incorporating multiple resource-limitation and synthesizing unit concepts

The predictions of the competitive exclusion principle about the number of coexisting species not exceeding the number of limiting resources in equilibrium constitute an ecological puzzle for phytoplankton ecosystems. Here we present a synthesizing unit (SU) based competition model taking co-limitation into account, which is the extension of the competition model developed by Dutta et al. (2014).The study aims at understanding the mechanisms of violation of competitive exclusion principle for phytoplankton species with seasonal environmental forcing when multiple resource limitation is taken into account and species growth is formulated based on SU. We also explore the role of changing environmental conditions on species coexistence on a seasonal and a decadal time scale by linking the model forcing to the Helgoland Roads Time Series data sets. For the first time, based on the Helgoland Roads data, we are able to find a realistic parameterization for the phytoplankton competition model where growth is formulated using SU concept. Our study confirms that more species than limiting resources can coexist with seasonal variations of environmental conditions. This supersaturation is related to periodic changes in species’ biomass, variation in interspecific competition and niche configuration, nonlinear functional response and the position of resource supply within the convex hull of species’ resource uptake rate. Changes in environmental conditions within realistic ranges do not prevent the coexistence of species rather it slightly changes species’ biomass and turnover time. This study also confirms that our model with SU based species growth performs better than species competition model where multiple resource limitation is formulated based on the product of several Monod functions. Our study has created a new avenue for phytoplankton coexistence research and the results might be helpful to answer the complex questions on species diversity maintenance in nature.

Seasonal Variation and Sexual Shape Dimorphism in Wings of the Neotropical HairstreakStrymon davara(Lycaenidae, Theclinae, Eumaeini)

The northern valleys of the Atacama Desert in Chile have minimal seasonal variations of temperature, which enable continuous growth of many plants and their associated phytophagous insects. This is the case in the Neotropical hairstreak Strymon davara (Lepidoptera, Lycaenidae, Theclinae, Eumaeini), whose larvae are able to develop throughout the year on the inflorescences of their only host plant, Althernanthera halimifolia (Amaranthaceae). Although minimal, environmental seasonal variations could have some effect on the development of highly sensitive organisms. The first geometric morphometrics study of the wings of S. davara was intended to test for seasonal changes in the morphology. The same tools were used to assess for wing sexual dimorphism in this Neotropical hairstreak. Fifteen and 14 landmarks were selected on the fore and hindwings, respectively, of male and female adults collected in winter and summer in the Azapa Valley, northern Chile. The principal component analysis of wing shape shows that the variation was mainly distinguished by sexual dimorphism at the first dimension (PC1) and mostly by season at the second dimension (PC2). This variation might be a plastic response to subtle seasonal variation in environmental conditions and due to sexual niche divergence and behavior of male and female butterflies.

Influence of the seasonal variation of environmental conditions on biogas upgrading in an outdoors pilot scale high rate algal pond

The influence of the daily and seasonal variations of environmental conditions on the quality of the upgraded biogas was evaluated in an outdoors pilot scale high rate algal pond (HRAP) interconnected to an external absorption column (AC) via a conical settler. The high alkalinity in the cultivation broth resulted in a constant biomethane composition during the day regardless of the monitored month, while the high algal-bacterial activity during spring and summer boosted a superior biomethane quality. CO2 concentrations in the upgraded biogas ranged from 0.1% in May to 11.6% in December, while a complete H2S removal was always achieved regardless of the month. A limited N2 and O2 stripping from the scrubbing cultivation broth was recorded in the upgraded biogas at a recycling liquid/biogas ratio in the AC of 1. Finally, CH4 concentration in the upgraded biogas ranged from 85.6% in December to 99.6% in August.

Photoperiodic cues regulate phenological carry‐over effects in an herbivorous insect

AbstractTo maximise their fitness, organisms need to synchronise their phenology with the seasonal variation in environmental conditions. Most phenological traits are affected by environmental abiotic cues such as photoperiod, temperature and rainfall. When individuals with complex life cycles fail to match one of the stages with the favourable environment, the negative conditions experienced may lead to carry‐over effects and, thus, influence fitness in subsequent stages.In the winter moth, an herbivorous insect with an annual life cycle, timing of egg‐hatching in spring is strongly influenced by temperature and varies from year to year. To investigate whether the phenological variation in egg‐hatching date affects subsequent stages, we analysed data on egg‐hatching date and adult catching date (considered here to be a proxy for adult eclosion date) from our long‐term study (1994–2014). Furthermore, we experimentally manipulated the photoperiod experienced by newly hatched larvae and recorded the phenology of their subsequent life cycle stages.In the long‐term field study, we found that the timing of winter moth egg‐hatching in spring varied strongly from year to year. Interestingly, however, the timing of adult eclosion date in winter showed little inter‐annual variation. In line with these findings, our experimental data showed that the winter moth shortened the duration of their pupal development when they experienced a late spring photoperiod as a larva, and prolonged pupal development when experiencing early spring photoperiod. The effects of the larval photoperiodic treatments persisted during egg development in the following generation.The results show that a phenological shift that occurs during an early life stage is partially compensated during subsequent stages and suggest that the mechanism underlying this compensation is mediated by photoperiod. Winter moths regulated their phenology in such a way that the variation in the egg‐hatching stage was not carried over to the next life cycle stages. This has strong effects on fitness as it (1) ensures the synchronisation of adult eclosion during the mating period and (2) is likely to reduce potentially negative fitness consequences of phenological mismatches in egg‐hatching in the following generation. Overall, these findings stress the importance of understanding phenological carry‐over effects to forecast the impact of global change in species with complex life cycles.Aplain language summaryis available for this article.

Coccolithophore diversity and dynamics at a coastal site in the Gulf of Trieste (northern Adriatic Sea)

Two years-data (May 2011–February 2013) obtained from a monthly sampling carried out at the coastal long term Ecological Research station C1-LTER in the Gulf of Trieste (northern Adriatic Sea) were analysed to describe the seasonal dynamics and diversity of coccolithophore assemblages and to assess their relationship with environmental forcing.Coccolithophores represented 10.7% of the total Utermöhl phytoplankton that were mainly dominated by small (<10 μm) flagellates and diatoms (62.2% and 24.8% of total abundances, respectively). Coccolithophore abundances obtained by polarized light microscopy analysis ranged from 0.2 to 35.3 · 104 coccospheres L−1 with a mean value of 5.2 · 104 coccospheres L−1. A marked seasonal pattern was observed with a main peak in December–February (2.5–31.5 · 104 coccospheres L−1), in correspondence of the winter mixing, mainly due to Emiliania huxleyi, and a secondary peak in May–June (0.7–15.0 · 104 coccospheres L−1), coinciding with the increase of the light intensity and the beginning of the seasonal stratification, dominated by holococcolithophores and small Syracosphaera species. The most abundant taxa were E. huxleyi and holococcolithophores, followed by Acanthoica quattrospina, Syracosphaera species and other minor species. Statistical analyses recognized four distinct groups, corresponding to seasonal variations of environmental conditions. Considering the two years, some species displayed a recurrent seasonal pattern highlighting possible species-specific ecological requirements, while others showed an interannual variability probably due to local factors.

Impact of seasonal forcing on reactive ecological systems

Our focus is on the short-term dynamics of reactive ecological systems which are stable in the long term. In these systems, perturbations can exhibit significant transient amplifications before asymptotically decaying. This peculiar behavior has attracted increasing attention. However, reactive systems have so far been investigated assuming that external environmental characteristics remain constant, although environmental conditions (e.g., temperature, moisture, water availability, etc.) can undergo substantial changes due to seasonal cycles. In order to fill this gap, we propose applying the adjoint non-modal analysis to study the impact of seasonal variations of environmental conditions on reactive systems. This tool allows the transient dynamics of a perturbation affecting non-autonomous ecological systems to be described. To show the potential of this approach, a seasonally forced prey-predator model with a Holling II type functional response is studied as an exemplifying case. We demonstrate that seasonalities can greatly affect the transient dynamics of the system.

Erasing day/night differences in light intensity and spectrum affect biodiversity and the health of mammals by confusing the circadian clock

The beneficial effect of sunlight on all forms of life has been well-known to human cultures worldwide throughout history. However, the importance of darkness for survival, successful reproduction and the overall fitness of all organisms is fully appreciated only by physiologists and environmental biologists. Seasonal variations in environmental conditions (i.e., rainfall, temperature, barometric pressure, food availability) significantly affect reproduction and survival but they are of little predictive value. In contrast, daily fluctuations in light levels and the light spectrum are less dramatic in their impact on life, but were highly predictable throughout evolution. Natural selection has thus favored a strategy of monitoring a day’s length as a predictor of changes in external conditions by the development of the molecular circadian clock, which is sensitive to changes in light/darkness during the day and night. Well-synchronized circadian clockwork ensures that behavioral and physiological processes fluctuate with the daily solar cycle and programs the seasonal changes in physiology via the transduction of the photoperiod into hormonal messages. During the last two decades, energy-efficient lighting technology has shifted from “yellow” high-pressure sodium vapor lamps to new “white” light-emitting diodes (LEDs). As a consequence, nighttime light pollution increased, and the sharp difference between day and night has been erased in many parts of the world, which threatens animal ecology and human health. Studies on humans, laboratory mammals and wildlife suggest that the physiological costs of living under artificial light at night (ALAN) may be due to the disruption of circadian and circannual timing. This overview summarizes the recent findings on the effect of the blurred day/night difference on the circadian clock, nighttime melatonin secretion and photoperiodic changes in mammals and suggests that the gradual decline of fitness due to the increasing ALAN measured in the human population may contribute to the changes in mammalian biodiversity in nature.

Annual egg production rates of calanoid copepod species on the continental shelf of the Eastern Tropical Pacific off Mexico

We provide the first estimations of calanoid copepod egg production rates (EPR) in the Eastern Tropical Pacific over an annual cycle (January–December 2011). Gravid females were collected twice monthly and incubated for 12 h without food to estimate EPR, weight-specific fecundity (Gf), spawning success (SS, percentage of females to spawn out of the total species incubated per month and season) and egg hatching success (EHS). This study reports the average EPR of 10 species and the monthly EPR and Gf of four planktonic calanoid copepods (Centropages furcatus, Temora discaudata, Pontellina sobrina, and Nannocalanus minor) that spawned with enough frequency to infer their seasonal reproductive patterns. These species showed distinct seasonal reproductive strategies. Most copepod species spawned sporadically with large EPR variability, while three copepod species reproduced throughout the year (C. furcatus, T. discaudata and P. sobrina) and N. minor spawned only during the mixed period (Feb–May). The four species had relatively similar average EPR (C. furcatus 16, T. discaudata 18, P. sobrina 13, and N. minor 12 eggs fem−1 day−1). These are the first EPR estimations of P. sobrina and its previously known reproductive period is expanded. A Canonical Correspondence Analysis (CCA) was used to analyze EPR and species abundance of all calanoid copepods (40 spp.) collected throughout the time series in relation to temperature, salinity, mixed layer depth (MLD), dissolved oxygen, and chlorophyll a (Chl-a) concentrations to identify the variables that best explained the copepod abundance variability. Temperature, Chl-a, and salinity had the strongest effect on the biological variables, linked to seasonal and episodic upwelling-downwelling processes in the surveyed area. As a result of moderate upwelling events and seasonal variation of environmental conditions, it appears relatively few species are capable of maintaining continuous reproduction under the relatively higher temperatures and strong fluctuations of food availability that exist in this coastal habitat of the Eastern Tropical Pacific.

Seasonal, Sex- and Plant Size-Related Effects on Photoinhibition and Photoprotection in the Dioecious Mediterranean Dwarf Palm, Chamaerops humilis.

In Mediterranean-type ecosystems plants are exposed to several adverse environmental conditions throughout the year, ranging from drought stress during the warm and dry summers to chilling stress due to the typical drop in temperatures during winters. Here we evaluated the ecophysiological response, in terms of photoinhibition and photoprotection, of the dioecious Mediterranean palm, Chamaerops humilis to seasonal variations in environmental conditions. Furthermore, we considered as well the influence of plant size, maturity, and sexual dimorphism. Results showed evidence of winter photoinhibition, with a marked decrease of the Fv/Fm ratio below 0.7 between January and March, which was coincident with the lowest temperatures. During this period, the de-epoxidation state of the xanthophyll cycle and zeaxanthin levels increased, which might serve as a photoprotection mechanism, owing the full recovery from winter photoinhibition during spring. Furthermore, mature plants showed lower chlorophyll levels and higher β-carotene levels per unit of chlorophyll than juvenile plants, and females displayed lower leaf water contents and higher photoinhibition than males during summer, probably due to increased reproductive effort of females. However, neither low temperatures during winter nor reproductive events in females during the summer led to irreversible damage to the photosynthetic apparatus. We conclude that (i) the Mediterranean dwarf palm, C. humilis, suffers from photoinhibition during winter, but this is transient and does not lead to irreversible damage, and (ii) females from this plant species are more sensitive than males to photoinhibition during reproductive events.

Seasonal changes in water quality and fisheries of Tanbi Wetland National Park

This research was aimed at studying seasonal changes in water quality of Tanbi Wetland National Park (TWNP) and how these interact with the different land use types to influence fish assemblage. Physicochemical properties were measured in situ with a portable YSI multiprobe watermeter and fish sampling was done using a seine net of 100×4 m. To assess nutrient (nitrogen and phosphorus) input and chlorophyll a concentration (chl-a) in TWNP, spectrophotometry (fluorescence method) was applied. Subjecting the main water variables to a Principal Components Analysis (PCA) indicated a strong correlation between water temperature and pH, phosphate and pH, as well as water temperature and phosphate. A further Multidimensional Scaling (MDS) of the environmental variables indicated salinity as the main water variable influencing fish species richness in TWNP. Except at the settlement and agricultural zones, changes in fish assemblage appear not to be influenced by the specific land use types. As judged from a three-decade time series of rainfall and atmospheric temperatures, seasonal variations in environmental conditions have intensified and are negatively influencing fish assemblage in TWNP.

Sequencing and characterization of a multi-organ Arctic charr transcriptome: A toolbox for investigating polymorphism and seasonal life in a high Arctic fish

The Arctic charr (Salvelinus alpinus L.) inhabits fresh water ecosystems of the high North. The species has developed a strong phenotypic plasticity and variability in life history characteristics which has made this species an attractive model for investigations on phenotype plasticity, morph formation and ecological speciation. Further, the extreme seasonal variations in environmental conditions (e.g. food availability) in the high North induce seasonal changes in phenotype, which require precise timing mechanisms and physiological preparations. Individual gating of life-history strategies (e.g. formation of resident and sea-migrating morphs) and transitions (e.g. maturation) depends on conditional traits (size/energy status) at specific assessment time windows, and complex neuroendocrine regulation, which so far is poorly understood. In the absence of a reference genome, and in order to facilitate the investigation of the complex biological mechanisms of this unique fish model, the present study reveals a reference transcriptome for the Arctic charr. Using Roche 454 GS FLX+, we targeted various organs being either at the crossroads of many key pathways (neuroendocrine, metabolic, behavioral), of different ontological origins or displaying complementary physiological functions. The assemblage yielded 34,690 contigs greater than 1000bp with an average length (1690bp) and annotation rate (52%) within the range, or even higher, than what has been previously obtained with other teleost de novo transcriptomes. We dramatically improve the publically available transcript data on this species that may indeed be useful for various disciplines, from basic research to applied aspects related to conservation issues and aquaculture.

Seasonal variation in reproductive parameters of the squat lobster Pleuroncodes monodon from a South Pacific population

Pleuroncodes monodon from the Chilean coast has seasonal reproduction. During the seasonal period, females and their eggs are exposed to seasonal variation in environmental conditions. In P. monodon populations inhabiting the Southern Pacific coast near Concepción, Chile, we quantified late summer (February–March 2014) and late winter (August–September 2014) seasonal variations in female reproductive parameters (carapace length, fecundity, reproductive output (RO), ash weight, organic content) as well as eggs parameters (length, volume, dry weight, organic content). There was conspicuous seasonal variation in the main reproductive parameters of this species. During the summer, the number of eggs and organic content of females were higher than winter, whereas RO was slightly higher in winter than in summer. Significant variation in the size and biomass of the eggs was also found between seasons. For example, eggs laid in summer were smaller, had a lower measured dry mass, and had a lower organic content than eggs laid in winter. Seasonal variations in the fecundity and size of the eggs have implications for fishery models, which can be used to estimate the relative contribution of different cohorts to recruitment and stability of adult benthic populations.

The bacterial community inhabiting temperate deciduous forests is vertically stratified and undergoes seasonal dynamics

Bacterial communities living in forest soils contribute to the decomposition of organic matter and the recycling of nutrients in these ecosystems and form one of the most diverse habitats on Earth. Unfortunately, due to difficulty in culturing soil bacteria, the understanding of their ecology is still limited. In the case of temperate deciduous forests, soil microbial communities face large seasonal variations in environmental conditions, such as temperature or moisture. Moreover, the supply of nutrients also differs due to seasonal processes, such as the allocation of photosynthates into soil by the roots of primary producers or the seasonal input of fresh litter. The aim of this study was to reveal how the bacterial community responds to these seasonal processes in the litter and soil of a Quercus petraea forest. Bacterial communities from litter and from the organic and mineral horizons of soil were analyzed during the four seasons of the year by 16S rRNA gene pyrosequencing. The results revealed that the composition of the bacterial community is horizon specific. The litter horizon had a higher relative abundance of Proteobacteria and Bacteroidetes than soil, while the organic and mineral horizons had a higher abundance of Acidobacteria, Firmicutes and Actinobacteria than litter. Moreover, the bacterial community was significantly affected by seasonality in all horizons. Bacterial communities in the litter showed significant differences between the vegetation season (May and July) and the autumn and winter seasons (October, February). In mineral soil, bacterial community composition was specific in the summer, when it was significantly different from all other seasons, with a larger number of taxa described as rhizosphere and mycorrhizosphere inhabitants. The results indicate that litter decomposition is the main driver of bacterial community composition in litter horizon. In contrast to reports on fungal communities, bacterial community composition in mineral soil responds to the seasonal peaks of rhizodeposition in the summer.

Ecophysiological response to seasonal variations in water availability in the arborescent, endemic plant Vellozia gigantea.

The physiological response of plants growing in their natural habitat is strongly determined by seasonal variations in environmental conditions and the interaction of abiotic and biotic stresses. Here, leaf water and nutrient contents, changes in cellular redox state and endogenous levels of stress-related phytohormones (abscisic acid (ABA), salicylic acid and jasmonates) were examined during the rainy and dry season in Vellozia gigantea, an endemic species growing at high elevations in the rupestrian fields of the Espinhaço Range in Brazil. Enhanced stomatal closure and increased ABA levels during the dry season were associated with an efficient control of leaf water content. Moreover, reductions in 12-oxo-phytodienoic acid (OPDA) levels during the dry season were observed, while levels of other jasmonates, such as jasmonic acid and jasmonoyl-isoleucine, were not affected. Changes in ABA and OPDA levels correlated with endogenous concentrations of iron and silicon, hydrogen peroxide, and vitamin E, thus indicating complex interactions between water and nutrient contents, changes in cellular redox state and endogenous hormone concentrations. Results also suggested crosstalk between activation of mechanisms for drought stress tolerance (as mediated by ABA) and biotic stress resistance (mediated by jasmonates), in which vitamin E levels may serve as a control point. It is concluded that, aside from a tight ABA-associated regulation of stomatal closure during the dry season, crosstalk between activation of abiotic and biotic defences, and nutrient accumulation in leaves may be important modulators of plant stress responses in plants growing in their natural habitat.