Changes In Species Dominance Research Articles

A-233 Wastewater-based surveillance for SARS-CoV-2 Subvariants using the Nanopore Sequencing in South Korea

Abstract Background Genomic tools to identify and characterize SARS-CoV-2 and its various subvariants were adapted from clinical settings. Wastewater-based surveillance (WBS) has since been recognized as tool of transformative potential, providing real-time objective, comprehensive data on the prevalence and distribution of the target pathogen across the space and time. We conducted wastewater-based epidemiology (WBE) at sewage treatment plants to find a more efficient mutation monitoring method, and respond to pre-existing infectious diseases. Methods In our study, domestic sewage collected every weeks from 6 sewage treatment plants in urban region from June 2023 to November 2023 was used to concentrate and isolate viruses using wastewater ultra nucleic acid isolation kits with virus enrichment kits. Positive samples confirmed were subjected to SARS-CoV-2 whole genome sequencing (WGS) using GridION (Oxford Nanopore Technologies). The experimental data was aligned through Epi2me, analyzed using Nextclade, that was compared with KCDC official reports and our monitoring results (total 780 cases) ongoing at SCL. Results Various mutations were identified at each collection time, occurring new subvariants over time. The mutations (orf1a:A690V, S:F456L) sequentially confirmed from the sample collected on Aug. 23rd are specific mutations of XBB.1.9.2 and EG.5. In addition, the mutations orf1b: D54N, S:L455F, which were sequentially confirmed from the sample collected on Sep. 6th, are HK.3, a descendent lineage of EG.5, and FLip variants, which show growth advantage, were confirmed. Furthermore, the detection rate of FLip variants detected from Sep.6th gradually increased from 17% to 67% (Fig.1). Taken together, we confirmed the similarity between monthly detected mutations and changes in dominant species over time by comparing with ‘monthly COVID-19 mutation trends’ and ‘HK.3 dominance announcement by KCDC’(Fig.2). Conclusions WBS would be a useful tool for proactively responding to infectious diseases including COVID-19 by exploring new mutations and predicting changes in dominant species.

Growth and physiological metabolic regulation mechanisms of the dominant plant Leymus secalinus in alpine meadow under nitrogen deposition

Nitrogen (N) deposition is an important pathway that affects the growth and development of alpine grassland plants. Under N deposition, Leymus secalinus has become the most dominant species in the alpine meadow of the Qinghai-Tibetan Plateau. However, its adaptive mechanisms to N deposition are still unknown. Therefore, we analyzed the physiological indices of Leymus secalinus under different N deposition levels (CK, 0 kg N ha−1 yr−1; N1, 8 kg N ha−1 yr−1; N3, 40 kg N ha−1 yr−1; N5, 72 kg N ha−1 yr−1) and focused on its growth and metabolism. The results indicated that the leaf carbon (C), N, amino acid (AA), and photosynthetic pigment contents in Leymus secalinus were significantly increased under N deposition, its endogenous hormone levels were regulated and the activities of N metabolism-related enzymes were enhanced. Metabolomics analysis further showed that the metabolites changed significantly and were mostly enriched in the amino acid metabolic pathway. Among them, glutamine and aspartic acid played key roles in N deposition for dominant growth of Leymus secalinus by regulating N and amino acid metabolism. These analyses unveiled the physiological and biochemical changes of dominant species in response to N deposition, identifying critical metabolites involved in this process. Furthermore, these findings provide substantial evidence explaining the ecological phenomenon of Leymus secalinus emerging as a dominant species under N deposition, serving as a data reference for understanding the physiological response and adaptation to N deposition in alpine grassland plants.

Two grasses differ in their absorptive root physiological traits and rooting depth under drought in an alpine steppe.

Absorptive root traits play important roles in acquisition of water and nutrients from soil by plants. Despite numerous reports on the changes in species dominance under long-term drought in grassland community, few studies have specifically investigated absorptive root traits of these dominant species in grasslands, especially in the alpine grasslands. Here, two grass species (Leymus secalinus and Stipa purpurea) differing in their responses to drought were selected from an alpine steppe. A series of absorptive root traits were examined under drought in a 3-year glasshouse experiment. We found that drought had no effects on root morphological and architectural traits, whereas root physiological traits and rooting depth differed in their responses to drought. Specifically, drought significantly reduced root respiration and enhanced organ carbon (C) exudation rate, carboxylate exudation rate, acid phosphatase activity and rooting depth of L. secalinus. Particularly, L. secalinus released more citrate into the rhizosphere under drought than S. purpurea. In contrast, these root traits of S. purpurea remained relatively unchanged in response to the drought. These differential responses would render L. secalinus more competitive in acquisition of nutrients and water, thus contributing to its dominance in the community under drought. Moreover, root respiration was negatively correlated with organic C exudation rate, carboxylate exudation rate and acid phosphatase activity, indicating a tradeoff between root respiration and root exudates to acquire nutrients and water by optimizing C allocation under drought. Additionally, all root traits exhibited two independent dimensions in root economic space (RES) for both species under drought. These results indicate that the plant species with great capacity to acquire water and nutrients in soil by optimizing C allocation under drought will be dominant in the community of the alpine grasslands. These findings provide an important insight into species re-ordering under drought on the Tibetan Plateau.

Light competition drives species replacement during secondary tropical forest succession

Light competition is thought to drive successional shifts in species dominance in closed vegetations, but few studies have assessed this for species-rich and vertically structured tropical forests. We analyzed how light competition drives species replacement during succession, and how cross-species variation in light competition strategies is determined by underlying species traits. To do so, we used chronosequence approach in which we compared 14 Mexican tropical secondary rainforest stands that differ in age (8–32 year-old). For each tree, height and stem diameter were monitored for 2 years to calculate relative biomass growth rate (RGR, the aboveground biomass gain per unit aboveground tree biomass per year). For each stand, 3D light profiles were measured to estimate individuals’ light interception to calculate light interception efficiency (LIE, intercepted light per unit biomass per year) and light use efficiency (LUE, biomass growth per intercepted light). Throughout succession, species with higher RGR attained higher changes in species dominance and thus increased their dominance over time. Both light competition strategies (LIE and LUE) increased RGR. In early succession, a high LIE and its associated traits (large crown leaf mass and low wood density) are more important for RGR. During succession, forest structure builds up, leading to lower understory light levels. In later succession, a high LUE and its associated traits (high wood density and leaf mass per area) become more important for RGR. Therefore, successional changes in relative importance of light competition strategies drive shifts in species dominance during tropical rainforest succession.

Dynamic causes contribute to the increasing trend of red tides in the east China sea during 2020–2022

Red tide is a marine phenomenon caused by the excessive growth of microscopic algae in the ocean. This study aims to analyze the development trends of red tides in the past 20 years and the dynamic external causes that induce red tides based on existing satellite remote sensing and numerical simulation data. And the changes in dominant species of red tides in different seasons are analyzed. The results show significant temperature fluctuations within the week before the red tide occurs, with an average increase of 1.42 °C. In contrast, the change in salinity is relatively small. Meanwhile, ocean fronts are areas in the ocean where different water masses meet and form boundaries. The average strength of ocean fronts increased by 3.7%, indicating enhanced ocean mixing over a short period of time. Under the combined influence of these factors, the probability of a red tide outbreak in the East China Sea increases rapidly. Therefore, this study has important reference value for further research on the causes of red tides and their response to ocean dynamic changes.

Distribution of Macrozoobenthos of Flowing Water Bodies by Altitudinal Belts of the Nakhchivan Autonomous Republic

Spatial distribution, species structure and ecological indicators of macrozoobenthos of flowing water bodies by altitude belts of Nakhchivan Autonomous Republic were studied. Macrobenthos fauna of the rivers of the region is formed in psammoreophilic, phytoreophilic and peloreophilic biocenoses with a great advantage of lithoreophilic biocenosis. The lithoreophilic biocenosis of rivers of the mountain and high-mountain belts is characterized by extensive area and abundance of species diversity. The core of the lithoreophilic biocenosis is composed of populations of rheophilic organisms such as moths, mayflies, vernal pools and simulids; its usual inhabitants are also rheophilic larvae of chironomids of the genus Polypedilum, Endochironomus, Eukiefferiella, Cricotopus and Orthocladius. The family composition of the fauna was found to be relatively stable along the rivers. Differences in the species composition of macrobenthos fauna, change of dominant species in biocenoses are related to biological features of the main species, anthropic and anthropogenic impacts, as well as different time of research. The species composition of macrozoobenthos of the rivers of the autonomous republic decreases from the source to the mouth.

Effects of Nitrogen on the Bacterial Microbiome Community of Oocystis borgei, an Alga Widely Used in Marine Aquaculture

In order to investigate the effects of various nitrogen (ammonium) concentrations on the epibiotic bacterial community associated with Oocystis borgei, a metabarcoding sequencing method was employed. The 16S rDNA sequencing and bioinformatic analysis were conducted on cultures of O. borgei that were grown on four different nitrogen element concentrations (2.5, 10, 50, and 100 mg/L), and the differences in the epibiotic bacterial community and functions of O. borgei among different nitrogen concentrations were compared. The results showed that the chlorophyll a content of O. borgei increased with increasing nitrogen concentrations. A total of 43 operational taxonomic units (OTUs) were obtained from the four groups, which were categorized into 7 phyla, 9 classes, 18 orders, 21 families, and 26 genera. Winogradskyella was the dominant genus in the groups with 2.5 and 100 mg/L nitrogen, while Marinobacter and Winogradskyella were relatively abundant in the groups with 50 and 100 mg/L nitrogen. Functional analysis using PICRUST2 showed that the three most abundant gene functions were carbohydrate metabolism, amino acid transport and metabolism, ribosomal structure and biogenesis, and energy production and conversion. BugBase phenotypic analysis revealed that there were no significant differences in phenotypes between the groups with 2.5 and 10 mg/L nitrogen, while the group with 50 mg/L nitrogen exhibited higher abundance in aerobicity, biofilm formation, mobile genetic elements, and stress tolerance phenotypes. Most of the bacteria in this work belonged to the aerobic types. A redundancy analysis (RDA) of environmental factors demonstrated that nitrogen concentration showed a positive correlation with species changes in the groups with 10 and 50 mg/L nitrogen; chlorophyll a exhibited a positive correlation with species changes in the groups with 50 and 100 mg/L nitrogen. Nitrogen concentration significantly influenced the epibiotic bacterial community associated with O. borgei, leading to changes in dominant species and community structure. This study provides important references for understanding the functional characteristics of the epiphytic microbial community of O. borgei and the exploration of specific microorganisms.

Effects of dominant plant species change on soil multifunctionality in alpine meadows of the three-river source region

Alpine meadows are an important ecosystem in the Three-River Source Region of the Qinghai-Tibet Plateau. The dominant plant species in alpine meadows undergo changes during degradation that may directly or indirectly influence soil functionality. In this study, the effects of variations in the dominant plant species on soil physicochemical properties and multifunctionality were analyzed. Quadrats with different dominant plant species were classified as CY (for Cyperaceae), CGF (for Cyperaceae-Gramineae-Forbs), and FB (for Forbs). The results showed that, for all cases, there were significant correlations among TN (Total Nitrogen), SOC (Soil Organic Carbon), TP (Total Phosphorus), soil water, and bulk density, whereas TK (Total Kalium) showed no clear correlations with other properties. The most significant correlation between plant community characteristics and soil physicochemical properties was found in CGF because of the higher biodiversity and intensity of intermediate competition. Species with absolute dominance had stable positive or negative effects on soil multifunctionality at almost all thresholds. The effects of Cyperaceae decreasing and Forbs increasing on soil multifunctionality were nonlinear. Turning points of important values of Cyperaceae (∼0.38 and 0.66) and Forbs (∼0.34 and 0.69) were observed in dominant species changes. The different effects of Cyperaceae and Forbs on soil multifunctionality before and after the turning point indicate that the effect of plant communities on soil multifunctionality depends more on the interactions between species that remain rather than those that depart. The results of this study can guide efforts to maximize both plant communities and soil multifunctionality for the protection and restoration of alpine meadows.

Changes in Phyto- and Zooplankton under the Climatic Shifts and Anthropogenic Load (Lake Baikal, Russia)

The hydro-chemical data collected today and structural and quantitative parameters of phyto- and zooplankton from Maloe More Strait, Lake Baikal, were analysed. Comparison of current and earlier observations revealed recent alterations in phyto- and zooplankton functions analogous to other areas of Lake Baikal. Major reconstructions in phytoplankton were registered in spring: violation in cycles of annual growth maxima of large-cell Baikalian diatoms and changes in dominant species. Dramatic abundance of rotifers caused the increase by an order of magnitude in pelagic zooplankton numbers in 2019–2020. In 2021, all of these groups were suppressed under intensive diatom vegetation. In the Mukhor bay, such changes were related to a sharp increase of rotifer numbers until 2021. In 2021, we observed decline in plankton abundance, meanwhile the relative proportion of taxonomic groups did not change with dominance of rotifers.

Change in the faunal composition of mosquitoes (Diptera: Culicidae) along a heterogeneous landscape gradient in the Brazilian Amazon.

This study aimed to evaluate the influence of different anthropic landscape profiles on the diversity and distribution of mosquito species in a rural settlement of the Brazilian Amazon. Eight field collections were conducted at 18 sampling points interspersed throughout 2020-2021. Plastic containers, bamboo internodes, and tires were used as traps to capture immature mosquitoes in three distinct habitats: forest, forest edge, and peridomicile. A total of 15,547 individuals, distributed in 26 species of culicids, were collected. The most abundant species were Culex urichii (8,376 specimens), Culex (Melanoconion) (2,473 specimens), and Aedes albopictus (1,252 specimens). Forest habitat showed the highest abundance, and forest edge showed the highest species richness. Different types of environments influenced both the abundance and richness of mosquitoes. The species composition was also significantly different between the analyzed sites, mainly between forest and peridomicile environments. The change in species dominance could largely explain this change in mosquito community composition. Haemagogus janthinomys, an important sylvatic arbovirus vector, was found in peridomicile habitats and Ae. albopictus, a vector associated with human environments, was found in forest habitats, thus providing evidence of species spillover. Our results indicated that landscape changes affect mosquito communities, influencing their richness and abundance. These changes may have implications for future arboviral outbreaks in this rural settlement due to the possible establishment of sylvatic vector species in anthropic environments.

Opposite response of N2O emissions in different seasons to warming and precipitation addition on a temperate steppe

AbstractClimate change is an important issue that affects both global warming and precipitation, and the main cause is increased N2O emissions. Temperature and moisture are key factors in grassland ecosystem's response to climate change, and they can affect N2O fluxes. To clarify the impacts of warming and precipitation changes on N2O fluxes, an experiment was conducted in a semiarid steppe in Inner Mongolia, China over a nine‐year period (2011–2019). Plant productivity and soil nutrient dynamics were examined concurrently from 2017 to 2019, and N2O fluxes were monitored in response to different treatment conditions: control (C), warming (W), precipitation addition (P), and warming and precipitation addition (WP). The results showed that N2O emissions in the growing season were higher than those in the nongrowing season. Warming and precipitation addition had no significant effect on N2O fluxes compared with ambient conditions. Compared with P treatment, warming increased N2O flux in nongrowing season and decreased it in growing season. N2O flux was positively correlated with soil temperature and moisture (p < 0.05). Warming had a significant positive effect on soil NH4+‐N, whereas additional precipitation had a large positive effect on soil total nitrogen and soil nitrate nitrogen. With the WP treatment, soil microbial biomass nitrogen (MBN) and soil microbial biomass carbon (MBC) increased by 53.8% and 41.9%, respectively. The decrease in N2O emissions during the growing season in the W treatment compared with the P treatment may be largely attributed to the greater dominance of Leymus chinensis. The results highlight that changes in species dominance play an important role in regulating N2O emissions, and that the N2O fluxes in the nongrowing season account for a large proportion of the changes in N2O fluxes. Therefore, The warming effects on N2O emissions during nongrowing seasons should be further investigated.

Invasion and interaction determine population composition in an open evolving ecological system.

It is well-known that interactions between species determine the population composition in an ecosystem. Conventional studies have focused on fixed population structures to reveal how interactions shape population compositions. However, interaction structures are not fixed but change over time due to invasions. Thus, invasion and interaction play an important role in shaping communities. Despite its importance, however, the interplay between invasion and interaction has not been well explored. Here, we investigate how invasion affects the population composition with interactions in open evolving ecological systems considering generalized Lotka-Volterra-type dynamics. Our results show that the system has two distinct regimes. One is characterized by low diversity with abrupt changes of dominant species in time, appearing when the interaction between species is strong and invasion slowly occurs. On the other hand, frequent invasions can induce higher diversity with slow changes in abundances despite strong interactions. It is because invasion happens before the system reaches its equilibrium, which drags the system from its equilibrium all the time. All species have similar abundances in this regime, which implies that fast invasion induces regime shift. Therefore, whether invasion or interaction dominates determines the population composition.

The reciprocal changes in dominant species with complete metabolic functions explain the decoupling phenomenon of microbial taxonomic and functional composition in a grassland.

The decoupling of microbial functional and taxonomic components refers to the phenomenon that a drastic change in microbial taxonomic composition leads to no or only a gentle change in functional composition. Although many studies have identified this phenomenon, the mechanisms underlying it are still unclear. Here we demonstrate, using metagenomics data from a steppe grassland soil under different grazing and phosphorus addition treatments, that there is no "decoupling" in the variation of taxonomic and metabolic functional composition of the microbial community within functional groups at species level. In contrast, the high consistency and complementarity between the abundance and functional gene diversity of two dominant species made metabolic functions unaffected by grazing and phosphorus addition. This complementarity between the two dominant species shapes a bistability pattern that differs from functional redundancy in that only two species cannot form observable redundancy in a large microbial community. In other words, the "monopoly" of metabolic functions by the two most abundant species leads to the disappearance of functional redundancy. Our findings imply that for soil microbial communities, the impact of species identity on metabolic functions is much greater than that of species diversity, and it is more important to monitor the dynamics of key dominant microorganisms for accurately predicting the changes in the metabolic functions of the ecosystems.

Characterization of algal community composition and structure from the nearshore environment, Lake Tahoe (United States).

Periphyton assemblages from the nearshore environment of the west (California) side of Lake Tahoe, were analyzed to determine their taxonomic composition and community structure across habitats and seasons. Lake Tahoe is the second deepest lake in the US and an iconic oligotrophic subalpine lake with remarkable transparency. It has experienced offshore cultural eutrophication since the 1960s with observations of nuisance nearshore algal growth since the mid 2000s attributed to anthropogenic stressors. Samplings from November 2019-September 2020 provide useful snapshots against which older monitoring may be contextualized. A voucher flora, complete with descriptions, photo-documentation and referencing to species concepts employed, was created as a method of providing reproducible identification and enumeration of algal species, and more seamless reconciliation of detailed taxonomic data with future monitoring projects. The eulittoral zone (0-2 m) is seasonally dominated by elongate araphid (Synedra, Ulnaria) and stalked or entubed diatoms (Gomphonema, Cymbella, Encyonema). The sublittoral zone (>2 m) is dominated by a nitrogen-fixing Epithemia-cyanobacteria assemblage with less seasonal changes in dominance and composition that expanded to impinge on the 2 m depths of the eulittoral zone in the Fall. Sublittoral epipsammic samples, despite their proximity to rocks, had a very distinct diatom composition and high species dominance, similar to what was seen in the Fall eulittoral samples, with high numbers of Staurosirella chains and small biraphid diatoms. The deeper samples at 30 and 50 m contained high numbers of live Epithemia, and indicate a thriving sublittoral assemblage at these greater depths, but with less biomass. The 2019-20 data show many of the same diatom taxa observed in the 1970's and 1980's but with changes in species dominance. Notably, there was less of the green alga Mougeotia, when compared to the 1970's data, and a higher dominance by nitrogen fixing Epithemia in the sublittoral zone, persisting year-round. These new data show roughly double the algal species biodiversity that had been documented previously in the Lake Tahoe nearshore, and is largely attributed to the methods employed. Adopting these new methods in future monitoring efforts should improve harmonization of taxonomic data and help advance our knowledge of the contributions to nearshore cultural eutrophication.

Response of the plant–soil system to desertification in the Hulun Buir Sandy Land, China

AbstractIn this study, the vegetation and soils of different desertification landscapes (sandy grassland, and fixed, semi‐fixed, semi‐mobile, and mobile dunes) in the Hulun Buir Sandy Land were examined to quantify the impacts of desertification on plants, soils, and microbes, and the key limiting factors of restoration. Desertification caused soil quality to decline and led to an imbalance of nitrogen (N) and phosphorus (P) supplies (N:P ratios decreased significantly from 3.55–1.8, p < 0.05). Desertification did not change the stoichiometric relationships among plant carbon (C), N, and P at a community level, but promoted redistribution of nutrients from roots to aboveground tissues. The aboveground biomass N and P increased by 9.8% and 39.3%, respectively from grassland to mobile dunes, but these of the underground biomass decreased by 26.1% and 37.7%, respectively. N limitation (plant N:P < 10) occurred at the community level. Desertification led to the change of dominant species from perennial herbs to annual psammophytes, and plant diversity (from 1.15–0.79) and productivity (from 880.6 to 128.6 g m−2) first increased slightly (p > 0.05) and then decreased sharply (p < 0.05) with increasing desertification, but with no significant (p > 0.05) change of the microbial community. Redundancy analysis showed that the main environmental drivers were the soil N:P (with an explanation of 29.6%), followed by pH, electrical conductivity, and the soil's fine particles (with a total explanation of 24.3%). Based on these results, three reference frames were proposed for the restoration of the near‐original vegetation community.

Multi-proxy record of ocean-climate variability during the last two millennia on the Mackenzie Shelf, Beaufort Sea

A 2,000 year-long oceanographic history, in sub-centennial resolution, from a Canadian Beaufort Sea continental shelf site (60meters water depth) near the Mackenzie River outlet is reconstructed from ostracode and foraminifera faunal assemblages, shell stable isotopes (delta 18O, delta 13C) and sediment biogenic silica. The chronology of three sediment cores making up the composite section was established using 137Cs and 210Pb dating for the most recent 150 years and combined with linear interpolation of radiocarbon dates from bivalve shells and foraminifera tests.Continuous centimeter-sampling of the multicore and high-resolution sampling of a gravity and piston core yielded a time-averaged faunal record of every approximately 40 years from 0 to 1850 CE and every approximately 24 years from 1850 to 2013 CE. Proxy records were consistent with temperature oscillations and related changes in organic carbon cycling associated with the Medieval Climate Anomaly (MCA) and the Little Ice Age (LIA). Abundance changes in dominant microfossil species, such as the ostracode Paracyprideis pseudopunctillata and agglutinated foraminifers Spiroplectammina biformis and S. earlandi, are used as indicators of less saline, and possibly corrosive/turbid bottom conditions associated with the MCA (approximately 800 to 1200 CE) and the most recent approximately 60 years (1950–2013). During these periods, pronounced fluctuations in these species suggest that prolonged seasonal sea-ice melting, changes in riverine inputs and sediment dynamics affected the benthic environment. Taxa analyzed for stable oxygen isotope composition of carbonates show the lowest delta 18O values during intervals within the MCA and the highest during the late LIA, which is consistent with a 1 degree to 2 degree C cooling of bottom waters. Faunal and isotopic changes during the cooler LIA (1300 to 1850 CE) are most apparent at approximately 1500 to 1850 CE and are particularly pronounced during 1850 to approximately 1900 CE, with an approximate 0.5 per mil increase in delta 18O values of carbonates from median values in the analyzed taxa. This very cold 50-year period suggests that enhanced summer sea ice suppressed productivity,which is indicated by low sediment biogenic silica values and lower delta 13C values in analyzed species. From 1900CE to present, declines in calcareous faunal assemblages and changes in dominant species (Cassidulina reniforme and P. pseudopunctillata) are associated with less hospitable bottom waters, indicated by a peak in agglutinated foraminifera from 1950 to 1990 CE.

Ontogenetic trait variability and nitrogen stoichiometric homeostasis explained high stability of Artemisia frigida-dominated grassland

The degraded grassland is characterized by changes in dominant species and decreased soil resource supply capacity, limiting community foraging by carbon capturing and/or resource absorption. In this study, we used a manipulative greenhouse experiment to explore the plant trait variations of three species representing three degradation succession stages in the Inner Mongolian grassland of China. We examined variability in key trait values during early, middle and late growing stages and assessed the nitrogen stoichiometric homeostasis (HN) of different plant organs growing on loamy (undegraded) and sandy (degraded) soils. The results showed that plant root length (RL) shifted significantly from the early to middle stage, where Artemisia frigida presented the longest RL, and Setaria viridis had the shortest RL. Leyums chinensis exhibited the largest root-shoot ratio (RSR) with a well-developed rhizome, while A. frigida had smaller but variable RSR which increased 1.57–2.15 times, changing from the resource acquisition to the resource conservation strategy from the early to late stage. The shoot nitrogen content (SNC) and root nitrogen content (RNC) decreased over the growing season. No obvious differences were observed between plant traits of L. chinensis or A. frigida when growing on loamy or sandy soils, despite the fact that the nutrient supply in loamy soil was better. Shoot HN showed higher values for plants growing on loamy soils than on sandy soils. The degradation indicator species A. frigida presented the highest shoot HN under sandy soil and held relatively stable root HN for both soils (6.71 vs 6.00), indicating a higher adaptability to sandy soils. Our results explained the occurrence of the stable degraded grassland dominated by A. frigida and could shed light on methods for its restoration.

Surface copepod assemblages in shallow coastal waters off northeastern Yucatan Peninsula influenced by the Yucatan upwelling

The seasonal variability of the Yucatan upwelling is known to exert a definite influence on environmental and biological conditions over the Yucatan Shelf. The present study is the first to analyze the variability of surface mesoplanktonic copepods in coastal waters off northeastern Yucatan Peninsula. Copepod samples and environmental parameters were obtained monthly in surface waters (∼1 m depth) at twelve sampling sites (<20 m depth). The sampling period included the upwelling season (April–September: Up) and representative months of non-upwelling (November–December: NUp). Differences in copepod assemblage attributes (abundance, species composition and diversity) and environmental parameters were analyzed among sampling sites, months, and seasons. Forty-two copepod species were recorded. Paracalanus quasimodo, a coastal euryhaline species, was widely dominant throughout the study period (relative abundance: 54%, frequency of occurrence: 94%). Univariate and multivariate statistical analyses indicated that copepod assemblages and environmental parameters remained spatially homogeneous but varied significantly over time. Two copepod assemblages were found concerning temporal changes in dominant species, its numerical and relative abundance, diversity and contrasting assemblage–environment​ relationships. The first assemblage occurred in the Up season, with a clear dominance of P. quasimodo (known as a coastal upwelling indicator species), high total copepod abundance, low diversity, and evenness, and positively influenced by high dissolved inorganic nutrients and chlorophyl-a concentrations. The second assemblage, present in the NUp season, also showed a dominance of P. quasimodo but with reduced relative abundance and increased of indicator species of oligotrophic waters, such as Clausocalanus furcatus and Farranula gracilis, low total copepod abundance, high diversity, and evenness, and positively influenced by salinity. The present results reinforce previous conclusions about the major influence that the Yucatan upwelling exerts on diverse marine biota off northeastern Yucatan Peninsula, improving the knowledge about the influence of local environmental parameters linked with upwelling variability to structuring the copepod assemblages.

Increasing fish diversity of Chicago's waterways

Descriptions of shifts in biodiversity across time are desired for urban freshwater systems to better study ecosystem change and causal mechanisms. I document changes in fish diversity within the Chicago Area Waterways across 35 years using a battery of diversity metrics calculated on both abundance and biomass data. Has diversity of Chicago's waterways changed over 35 years and if so, do different diversity metrics exhibit different trends or breakpoints in trends? Diversity of the fish assemblage increased across the three decades of study. Breakpoint analysis suggested that trends across the timeseries were nonlinear. Changes in dominant species influenced behavior of less traditional metrics, whereas Margalef's Richness, Shannon-Weiner, and Gini-Simpson appeared more robust. Increases in richness and taxonomic diversity combined with decreases in species dominance suggest an ecosystem of increasing quality. The fish community of the Chicago Area Waterway System is more diverse both in abundance as well as biomass (i.e., energy flows) in the late 2010's than it was in the late 1980's. Although external factors related to wastewater treatment increased water quality and likely led to these assemblage-level changes breakpoint analysis did not allow verification of causal mechanisms.

Synanthropization and species diversityof floodplain ecosystems of the Ob-Irtysh basin, Russia

Currently, the phytocenoses of the Irtysh floodplain are experiencing intense anthropogenic pressures due to the intensive development of the oil and gas industry, as well as the urbanization of the territory. This paper focuses on the structure and species composition of the 27 studied areas in the floodplain ecosystems of the Ob-Irtysh basin. As a result of the research, we found 111 species of vascular plants from 33 families in plant communities. The areas belong to meadows and forest vegetation are represented by (1) birch forests (33%), (2) pine forests (10%), (3) fir forests (8%), (4) aspen forests (4%) and (5) associations of meadows (45%). Furthermore, we conducted a comparative analysis of the studied phytocenoses according to the Drude scale. To determine the anthropogenic transformation of the flora and individual plant communities, we determined the synanthropization index (the ratio of synanthropic species to the total number of species). In the synanthropic flora fraction, we distinguished 45 species belonging to 12 families, with the most multispecies being Apiaceae, Scrophulariaceae, Compositeae, Ranunculaceae, Poaceae, Fabaceae, Plantaginaceae. The synanthropization index of the studied phytocenoses ranges from 6.6% to 81.2%. The largest number of synanthropic species occurs in meadow associations, the content of synanthropes is greater than 50%, the structure is becoming more superficial, and the productivity and stability of plant communities are changing. The study of the horizontal structure of grass stands of meadow phytocenoses makes it possible to find the variability of different years, the change of dominant species and the stability of the species composition. Currently, researchers are paying considerable attention to the analysis of the structure of the herbage, since its study is of great theoretical and practical importance in clarifying phytocenotic relations.