The diversity and coevolution of Rubisco and CO2 concentrating mechanisms in marine macrophytes.

The kinetic properties of Rubisco, the most important carbon-fixing enzyme, have been assessed in a small fraction of the estimated existing biodiversity of photosynthetic organisms. Until recently, one of the most significant gaps of knowledge in Rubisco kinetics was marine macrophytes, an ecologically relevant group including brown (Ochrophyta), red (Rhodophyta) and green (Chlorophyta) macroalgae and seagrasses (Streptophyta). These organisms express various Rubisco types and predominantly possess CO2 -concentrating mechanisms (CCMs), which facilitate the use of bicarbonate for photosynthesis. Since bicarbonate is the most abundant form of dissolved inorganic carbon in seawater, CCMs allow marine macrophytes to overcome the slow gas diffusion and low CO2 availability in this environment. The present review aims to compile and integrate recent findings on the biochemical diversity of Rubisco and CCMs in the main groups of marine macrophytes. The Rubisco kinetic data provided demonstrate a more relaxed relationship among catalytic parameters than previously reported, uncovering a variability in Rubisco catalysis that has been hidden by a bias in the literature towards terrestrial vascular plants. The compiled data indicate the existence of convergent evolution between Rubisco and biophysical CCMs across the polyphyletic groups of marine macrophytes and suggest a potential role for oxygen in shaping such relationship.

Effects of nutrient enrichment on freshwater macrophyte and invertebrate abundance: A meta-analysis.

External nutrient loading can cause large changes in freshwater ecosystems. Many local field and laboratory experiments have investigated ecological responses to nutrient addition. However, these findings are difficult to generalize, as the responses observed may depend on the local context and the resulting nutrient concentrations in the receiving water bodies. In this research, we combined and analysed data from 131 experimental studies containing 3054 treatment-control abundance ratios to assess the responses of freshwater taxa along a gradient of elevated nutrient concentrations. We carried out a systematic literature search in order to identify studies that report the abundance of invertebrate, macrophyte, and fish taxa in relation to the addition of nitrogen, phosphorus, or both. Next, we established mixed-effect meta-regression models to relate the biotic responses to the concentration gradients of both nutrients. We quantified the responses based on various abundance-based metrics. We found no responses to the mere addition of nutrients, apart from an overall increase of total invertebrate abundance. However, when we considered the gradients of N and P enrichment, we found responses to both nutrients for all abundance metrics. Abundance tended to increase at low levels of N enrichment, yet decreased at the high end of the concentration gradient (1-10 mg/L, depending on the P concentration). Responses to increasing P concentrations were mostly positive. For fish, we found too few data to perform a meaningful analysis. The results of our research highlight the need to consider the level of nutrient enrichment rather than the mere addition of nutrients in order to better understand broad-scale responses of freshwater biota to eutrophication, as a key step to identify effective conservation strategies for freshwater ecosystems.

The abundance of comammox bacteria was higher than that of ammonia-oxidizing archaea and bacteria in rhizosphere of emergent macrophytes in a typical shallow lake riparian.

Complete ammonia oxidation (comammox) bacteria can complete the whole nitrification process independently, which not only challenges the classical two-step nitrification theory but also updates long-held perspective of microbial ecological relationship in nitrification process. Although comammox bacteria have been found in many ecosystems in recent years, there is still a lack of research on the comammox process in rhizosphere of emergent macrophytes in lakeshore zone. Sediment samples were collected in this study from rhizosphere, far-rhizosphere, and non-rhizosphere of emergent macrophytes along the shore of Lake Liangzi, a shallow lake. The diversity of comammox bacteria and amoA gene abundance of comammox bacteria, ammonia-oxidizing archaea (AOA), and ammonia-oxidizing bacteria (AOB) in these samples were measured. The results showed that comammox bacteria widely existed in the rhizosphere of emergent macrophytes and fell into clade A.1, clade A.2, and clade B, and clade A was the predominant community in all sampling sites. The abundance of comammox amoA gene (6.52 × 106-2.45 × 108 copies g-1 dry sediment) was higher than that of AOB amoA gene (6.58 × 104-3.58 × 106 copies g-1 dry sediment), and four orders of magnitude higher than that of AOA amoA gene (7.24 × 102-6.89 × 103 copies g-1 dry sediment), suggesting that the rhizosphere of emergent macrophytes is more favorable for the growth of comammox bacteria than that of AOB and AOA. Our study indicated that the comammox bacteria may play important roles in ammonia-oxidizing processes in all different rhizosphere regions.

Analysis of diversity and function of epiphytic bacterial communities associated with macrophytes using a metagenomic approach.

Epiphytic bacteria constitute a vital component of aquatic ecosystems, pivotal in regulating elemental cycling. Despite their significance, the diversity and functions of epiphytic bacterial communities adhering to various submerged macrophytes remain largely unexplored. In this study, we employed a metagenomic approach to investigate the diversity and function of epiphytic bacterial communities associated with six submerged macrophytes: Ceratophyllum demersum, Hydrilla verticillata, Myriophyllum verticillatum, Potamogeton lucens, Stuckenia pectinata, and Najas marina. The results revealed that the predominant epiphytic bacterial species for each plant type included Pseudomonas spp., Microbacterium spp., and Stenotrophomonas rhizophila. Multiple comparisons and linear discriminant analysis effect size indicated a significant divergence in the community composition of epiphytic bacteria among the six submerged macrophytes, with 0.3-1% of species uniquely identified. Epiphytic bacterial richness associated with S. pectinata significantly differed from that of both C. demersum and H. verticillata, although no significant differences were observed in diversity and evenness. Functionally, notable variations were observed in the relative abundances of genes associated with carbon, nitrogen, and phosphorus cycling within epiphytic bacterial communities on the submerged macrophyte hosts. Among these communities, H. verticillata exhibited enrichment in genes related to the 3-hydroxypropionate bicycle and nitrogen assimilation, translocation, and denitrification. Conversely, M. verticillatum showcased enrichment in genes linked to the reductive citric acid cycle (Arnon-Buchanan cycle), reductive pentose phosphate cycle (Calvin cycle), polyphosphate degradation, and organic nitrogen metabolism. In summary, our findings offer valuable insights into the diversity and function of epiphytic bacteria on submerged macrophyte leaves, shedding light on their roles in lake ecosystems.

Eutrophication driven macrophyte-derived organic matter decomposition to methane emission relates to co-metabolism effect in freshwater sediments.

Lakes and wetlands play pivotal roles in global organic matter storage, receiving significant inputs of organic material. However, the co-metabolic processes governing the decomposition of these organic materials and their impact on greenhouse gas emissions remain inadequately understood. This study aims to assess the effects of mixed decomposition involving macrophytes and cyanobacteria on carbon emissions. A series of microcosms was established to investigate the decomposition of macrophyte residues and algae over a period of 216 days. A two-component kinetic model was utilized to estimate methane (CH4) production rates. Gas isotope technology was employed to discern the contributions of CH4 produced by macrophyte residues or algae. Quantitative PCR and analysis of 16S rRNA gene amplicons were employed to assess changes in functional genes and microbial communities. There were significant differences in the cumulative carbon release from the decomposition of different plant types due to the addition of carbon sources. After adding algae, the cumulative emission of CH4 increased significantly. The δ13C-CH4 partitioning indicated that CH4 originated exclusively from the fresh organic carbon of macrophyte residues, while it shifted to algae source after adding algae. The synergistic effect of the mixed decomposition on the CH4 emissions was greater than the sum of the individual decompositions. The microbial community richness was higher in the single plant residue treatment compared to the mixed treatment with algae addition, while microbial evenness in the sediment increased steadily in each treatment. Our findings emphasize the pronounced co-metabolic effect observed during the mixed decomposition of macrophytes and cyanobacteria.

Epiphytic microorganisms of submerged macrophytes effectively contribute to nitrogen removal.

Submerged macrophytes play important roles in nutrient cycling and are widely used in ecological restoration to alleviate eutrophication and improve water quality in lakes. Epiphytic microbial communities on leaves of submerged macrophytes might promote nitrogen cycling, but the mechanisms and quantification of their contributions remain unclear. Here, four types of field zones with different nutrient levels and submerged macrophytes, eutrophic + Vallisneria natans (EV), eutrophic + V. natans + Hydrilla verticillata, mesotrophic + V. natans + H. verticillata, and eutrophic without macrophytes were selected to investigate the microbial communities that involved in nitrification and denitrification. The alpha diversity of bacterial community was higher in the phyllosphere than in the water, and that of H. verticillata was higher compared to V. natans. Bacterial community structures differed significantly between the four zones. The highest relative abundance of dominant bacterioplankton genera involved in nitrification and denitrification was observed in the EV zone. Similarly, the alpha diversity of the epiphytic ammonia-oxidizing archaea and nosZI-type denitrifiers were highest in the EV zone. Consist with the diversity patterns, the potential denitrification rates were higher in the phyllosphere than those in the water. Higher potential denitrification rates in the phyllosphere were also found in H. verticillata than those in V. natans. Anammox was not detected in all samples. Nutrient loads, especially nitrogen concentrations were important factors influencing potential nitrification, denitrification rates, and bacterial communities, especially for the epiphytic nosZI-type taxa. Overall, we observed that the phyllosphere harbors more microbes and promotes higher denitrification rates compared to water, and epiphytic bacterial communities are shaped by nitrogen nutrients and macrophyte species, indicating that epiphytic microorganisms of submerged macrophytes can effectively contribute to the N removal in shallow lakes.

Contrasting plant-induced changes in heavy metals dynamics: Implications for phytoremediation strategies in estuarine wetlands.

Wetland plants play a crucial role in regulating soil geochemistry, influencing heavy metal (HM) speciation, bioavailability, and uptake, thus impacting phytoremediation potential. We hypothesized that variations in HM biogeochemistry within estuarine soils are controlled by distinct estuarine plant species. We evaluated the soils (pH, redox potential, rhizosphere pH, HM total concentration, and geochemical fractionation), plant parts (shoot and root), and iron plaques of three plants growing in an estuary affected by Fe-rich mine tailings. Though the integration of multiple plant and soil analysis, this work emphasizes the importance of considering geochemical pools of HM for predicting their fate. Apart from the predominance of HM associated with Fe oxides, Typha domingensis accumulated the highest Cr and Ni contents in their shoots (> 100 mg kg-1). In contrast, Hibiscus tiliaceus accumulated more Cu and Pb in their roots (> 50 mg kg-1). The differences in rhizosphere soil conditions and root bioturbation explained the different potentials between the plants by altering the soil dynamics and HM's bioavailability, ultimately affecting their uptake. This study suggests that Eleocharis acutangula is not suitable for phytoextraction or phytostabilization, whereas Typha domingensis shows potential for Cr and Ni phytoextraction. In addition, we first showed Hibiscus tiliaceus as a promising wood species for Cu and Pb phytostabilization.

A pilot-scale assessment of five common weeds in the sustainable treatment of sewage utilizing SHEFROL®, with prospects of a closed-loop biorefinery.

Relative efficacy of five common weeds-of the kind that are either rooted in soil or which freely float over water-was assessed in rapid, effective and sustainable treatment of sewage at pilot plant scale in the recently developed and patented SHEFROL® bioreactors. The plants were utilized in a unit of capacity 12,000 liters/day (LPD) which, after two years of use, was enlarged to handle 40,000 LPD of sewage. It was then further expanded after an year to treat 57,000 LPD. All the five weeds, of which none has previously been tested in a pilot-scale SHEFROL, were able to foster highly efficient primary treatment (in terms of suspended and total solids) and secondary treatment (in terms of BOD and COD) to levels exceeding 85% in most cases. Additionally, the weeds also helped in achieving significant tertiary treatment. At different hydraulic retention times, and at steady state, the five weeds achieved treatment of BOD, COD, suspended solids, nitrogen, phosphorous, copper, nickel, zinc, and manganese in the ranges, 80-95, 79-91, 82-95, 61-71, 51-73, 37-43, 30-38, 39-47, and 27-35%, respectively. It all occurred in a single process step and without the use of any machine or chemical. This made the system not only simple and inexpensive to install but also to maintain. Over continuous long-term operation for four years, the system was seen to be very robust as it was able to handle wide variations in the volumes and characteristics of sewage, as well as absorb shock loads without compromising the reactor performance. The sustainability of the system can be further enhanced by upgrading it to a circular biorefinery. Energy sources in the form of volatile fatty acids (VFAs) can be extracted from the weeds removed from SHEFROL and then the weeds can be converted into organic fertilizer using high-rate vermireactors recently developed by the authors.

A novel and inexpensive, yet very efficient sewage treatment system is presented.The versatility and robustness of the system has been assessed at pilot plant scale for several years.The long-term continuous studies establish the efficacy of five common weeds­not hitherto explored at pilot plant level­which can serve as the main bioagent(s) in the sewage treatment system.The system has the potential of being transformed in to a closed-loop-no-waste biorefinery.

Evolution and distribution of antibiotic resistance genes in submerged macrophytes and biofilm systems: From seasonal monitoring to mesocosm experiments.

The aquatic ecosystem has been extensively investigated as a hotspot for the spread of antibiotic resistance genes (ARGs); yet, the evolution and distribution of ARGs profiles in submerged macrophytes biofilms and surrounding water remained unclear. In this study, the dynamic distribution and seasonal variations of microbial communities and ARGs profiles were investigated, alongside their assembly processes and mutual interactions. Bacitracin and multidrug resistance genes were predominant, constituting more than 60% of the total ARGs abundance. The deterministic processes (<65%), influenced by the physicochemical properties of the river environment, governed the assembly and composition of ARGs profiles, exhibiting significant seasonal variation. The peak diversity (21 types) and abundance (0.316 copy ratios) of ARGs were detected during the summer. Proteobacteria and Actinobacteria were the dominant bacterial phyla, accounting for 38.41-85.50% and 4.03-27.09% of the microbial community, respectively. Furthermore, Proteobacteria, especially genera such as Acinetobacter, Burkholderia, and Pseudomonas, with various resistance sequences, were the primary carriers of multiple ARGs. Notably, the genetic exchanges between biofilms and surrounding water facilitated the further propagation of high-risk ARGs, posing greater ecological risks. Redundancy analysis indicated that the total nitrogen and temperature in water determined the fate of pathogenic-resistant species. These findings provided theoretical support for the mitigation of ARGs contamination in aquatic environments.

Effects of herbivorous fish on shallow lake ecosystems increase at moderate nutrient conditions.

Submerged macrophytes are vital in shallow lakes, as they provide critical ecosystem functions and services and can stabilize the clear-water conditions by various mechanisms. Nutrient enrichment reduces the resilience of macrophyte dominance in shallow lakes, thereby making them susceptible to shifts towards phytoplankton dominance following perturbations. Here, we conducted a mesocosm experiment to examine the individual and combined effects of nutrient enrichment and the addition of grass carp (Ctenopharyngodon idella) on the abundance of submerged macrophytes, epiphyton, and phytoplankton. We hypothesized that moderate nutrient enrichment facilitates macrophyte abundance, but also phytoplankton abundance after macrophyte removal by herbivorous fish. Our data showed that herbivory by grass carp could trigger a shift from macrophytes to algal dominance in mesocosms with moderate nutrient concentrations, but not in those with low nutrient concentrations. Moderate nutrient enrichment alone promoted submerged macrophyte growth, whereas the introduction of grass carp induced a collapse of submerged macrophytes regardless of nutrient conditions. Moreover, the introduction of grass carp showed more negative effects on light conditions of the water column in mesocosms with moderate nutrient concentrations compared to those with low nutrient concentrations. A recovery of submerged macrophytes might thus be limited by low light availability in lakes with moderate nutrient conditions suffering grass carp perturbation. Our results suggest that submerged macrophyte-dominated shallow lakes with moderate nutrient conditions are vulnerable to perturbation by herbivorous fish such as grass carp. In turn, managing the abundance of herbivores in these lakes can support the dominance of macrophytes and associated clear water conditions.

A shift in habitat use patterns of brown trout (Salmo trutta): A behavioural response to macrophyte removal.

Mass development of macrophytes is an increasing problem worldwide and they are frequently removed where they are in conflict with local waterway users. Yet, macrophytes can provide important refuge and nursery habitats for fish. Little is known about the consequences of macrophyte removal for fish behavioural space use and habitat selection. We hypothesised that macrophyte removal would affect brown trout (Salmo trutta) movement during the partial removal of the aquatic plant Juncus bulbosus (L.) in an oligotrophic impounded Norwegian river.We tagged 94 brown trout and tracked them using passive acoustic telemetry for 10 months and mapped the cover of J. bulbosus. Trout behavioural patterns were quantified as space use (utilisation areas 50% and 95%) which was linked to habitat use and selection for J. bulbosus. Removal of J. bulbosus influenced space use of brown trout by reducing the core utilisation area by 22%. Habitat use and selection were likewise influenced by removal with increased use and selection of areas with low J. bulbosus cover (<25%) with corresponding reduction in high J. bulbosus cover (>25-75%). Finally, diurnal differences in space use and habitat use were found, with 19% larger utilisation areas at night and higher use of areas with low J. bulbosus during daytime. Yet, all effect sizes were relatively small compared to the size of the study area. This research provides a detailed case study on the effects of macrophyte removal on fish behavioural patterns in a section of a large Norwegian river with macrophyte mass development. We found no large effects of removal on trout behaviour but noted an increased use of areas with low macrophyte cover. This research is relevant for water managers and policy makers of freshwater conservation and provides a template for using acoustic telemetry to study the effects of macrophyte removal on fish.

Decline of seagrass (Posidonia oceanica) production over two decades in the face of warming of the Eastern Mediterranean Sea.

The response of Posidonia oceanica meadows to global warming of the Eastern Mediterranean Sea, where the increase in sea surface temperature (SST) is particularly severe, is poorly investigated. Here, we reconstructed the long-term P. oceanica production in 60 meadows along the Greek Seas over two decades (1997-2018), using lepidochronology. We determined the effect of warming on production by reconstructing the annual and maximum (i.e. August) SST, considering the role of other production drivers related to water quality (i.e. Chla, suspended particulate matter, Secchi depth). Grand mean (±SE) production across all sites and the study period was 48 ± 1.1 mg DW per shoot yr-1 . Production over the last two decades followed a trajectory of decrease, which was related to the concurrent increase in annual SST and SSTaug . Annual SST > 20°C and SSTaug > 26.5°C was related to production decline (GAMM, P < 0.05), while the rest of the tested factors did not help explain the production pattern. Our results indicate a persistent and increasing threat for Eastern Mediterranean meadows, drawing attention to management authorities, highlighting the necessity of reducing local impacts to enhance the resilience of seagrass meadows to global change threats.

Eutrophication decreases ecological resilience by reducing species diversity and altering functional traits of submerged macrophytes.

Positive feedback is key to producing alternative stable states and largely determines ecological resilience in response to external perturbations. Understanding the positive feedback mechanisms in macrophyte-dominated lakes is crucial for resilience-based management and restoration. Based on the field investigation of submerged macrophyte communities in 35 lakes in China, we found that morphological complexity (MC) and morphological plasticity (MP) are correlated with the stoichiometric homeostasis of phosphorus (HP ) and are related to ecosystem structure, functioning, and stability. We also found that the positive feedback strength of lakes dominated by macrophytes is biomass- and diversity-dependent. Eutrophication can decrease the community biomass by decreasing community MC, MP, and HP and the species diversity through low-light availability, ultimately decreasing the positive feedback strength and resilience of clear water states. We argue that functional traits and species diversity should be considered to build more resilient ecosystems in future changing environment scenarios.

Lakeshore residential development as a driver of aquatic habitat and littoral fish communities: A cross-system study.

Lakeshore riparian habitats have undergone intensive residential development in many parts of the world. Lakeshore residential development (LRD) is associated with aquatic habitat loss/alteration, including altered macrophyte communities and reduced coarse woody habitat. Yet habitat-mediated and other generalized effects of LRD on lake biotic communities are not well understood. We used two approaches to examine the relationships among LRD, habitat, and fish community in a set of 57 northern Wisconsin lakes. First, we examined how LRD affected aquatic habitat using mixed linear effects models. Second, we evaluated how LRD affected fish abundance and community structure at both whole-lake and site-level spatial scales using generalized linear mixed-effects models. We found that LRD did not have a significant relationship with the total abundance (all species combined) of fish at either scale. However, there were significant species-specific responses to LRD at the whole-lake scale. Species abundances varied across the LRD gradient, with bluegill (Lepomis macrochirus) and mimic shiners (Notropis volucellus) responding positively along the gradient and walleye (Sander vitreus) having the most negative response. We also quantified site-level habitat associations for each fish species. We found that habitat associations did not inform a species' overall response to LRD, as illustrated by species with similar responses to LRD having vastly different habitat associations. Finally, even with the inclusion of littoral habitat information in models, LRD still had significant effects on species abundances, reflecting a role of LRD in shaping littoral fish communities independent of our measure of littoral habitat alteration. Our results indicated that LRD altered littoral fish communities at the whole-lake scale through both habitat and non-habitat-mediated drivers.

Temporal Succession of Bacterial Community Structure, Co-occurrence Patterns, and Community Assembly Process in Epiphytic Biofilms of Submerged Plants in a Plateau Lake.

In shallow macrophytic lakes, epiphytic biofilms are formed on the surface of submerged plant stems and leaves because of algae and bacterial accumulation. Epiphytic biofilms significantly impact the health of the host vegetation and the biogeochemical cycling of lake elements. However, community diversity, species interactions, and community assembly mechanisms in epiphytic bacterial communities (EBCs) of plants during different growth periods are not well understood. We investigated the successional dynamics, co-occurrence patterns, and community assembly processes of epiphytic biofilm bacterial communities of submerged plants, Najas marina and Potamogeton lucens, from July to November 2020. The results showed a significant seasonal variation in EBC diversity and richness. Community diversity and richness increased from July to November, and the temperature was the most important driving factor for predicting seasonal changes in EBC community structure. Co-occurrence network analysis revealed that the average degree and graph density of the network increased from July to November, indicating that the complexity of the EBC network increased. The bacterial community co-occurrence network was limited by temperature, pH, and transparency. The phylogeny-based null model analysis showed that deterministic processes dominated the microbial community assembly in different periods, increasing their contribution. In addition, we found that as the dominance of deterministic processes increased, the microbial co-occurrence links increased, and the potential interrelationships between species became stronger. Thus, the findings provide insights into the seasonal variability of EBC assemblage and co-occurrence patterns in lacustrine ecosystems.

Using explainable machine learning methods to evaluate vulnerability and restoration potential of ecosystem state transitions.

Ecosystem state transitions can be ecologically devastating or be a restoration success. State transitions are common within aquatic systems worldwide, especially considering human-mediated changes to land use and water use. We created a transferable conceptual framework to enable multiscale assessments of state resilience and early warnings of state transitions that can inform strategic restorations and avoid ecosystem collapse. The conceptual framework integrated machine learning predictions with ecosystem state concepts (e.g., state classification, gradients of vulnerability, and recovery potential leading to state transitions) and was devised to investigate possible environmental drivers. As an application of the framework, we generated prediction probabilities of submersed aquatic vegetation (SAV) presence at nearly 10,000 sites in the Upper Mississippi River (United States). Then, we used an interpretability method to explain model predictions to gain insights into possible environmental drivers and thresholds or linear responses of SAV presence and absence. Model accuracy was 89% without spatial bias. Average water depth, suspended solids, substrate, and distance to nearest SAV were the best predictors and likely environmental drivers of SAV habitat suitability. These environmental drivers exhibited nonlinear, threshold-type responses for SAV. All the results are also presented in an online dashboard to explore results at many spatial scales. The habitat suitability model outputs and prediction explanations from many spatial scales (4 m to 400 km of river reach) can inform research and restoration planning.

Métodos de aprendizaje automático para evaluar la vulnerabilidad y el potencial de restauración de las transiciones de estados de los ecosistemas Resumen Las transiciones de estado de los ecosistemas pueden tener consecuencias ecológicas graves o ser un éxito de restauración. Estas transiciones son comunes en los sistemas acuáticos, especialmente si consideramos los cambios mediados por humanos en el uso del suelo y del agua. Generamos un marco conceptual transferible para permitir las evaluaciones multiescalares de la resiliencia del estado y las alertas tempranas de la transición de estado que sirvan para guiar las restauraciones estratégicas y evitar el colapso del ecosistema. Este marco integró predicciones de aprendizaje automático a los conceptos de estado del ecosistema (p. ej.: clasificación del estado, gradientes de vulnerabilidad y potencial de restauración que lleve a transiciones de estado) y fue diseñado para investigar los posibles factores ambientales. Para aplicar el marco, generamos probabilidades de predicción de la presencia de vegetación acuática sumergida (VAS) en casi 10,000 sitios del Alto Río Mississippi en los Estados Unidos. Después usamos un método de interpretabilidad para explicar las predicciones del modelo y obtener información de los posibles factores ambientales y umbrales o respuestas lineales de la presencia y ausencia de la VAS. La precisión del modelo fue de 89% sin sesgo espacial. Los mejores pronosticadores y probables factores ambientales de la idoneidad de hábitat de la VAS fueron la profundidad promedio del agua, los sólidos suspendidos, el sustrato y la distancia a la VAS más cercana. Estos factores ambientales exhibieron respuestas no lineales de tipo umbral para la VAS. Todos los resultados también están presentados en un tablero virtual para explorar los resultados a varias escalas espaciales. Los resultados del modelo de idoneidad de hábitat y las explicaciones de las predicciones de varias de las escalas espaciales (4 m-400 km de alcance del río) pueden guiar la investigación y la planeación de la restauración.

Seasonal Differences and Grazing Pressure Alter the Fate of Gold Nanoparticles in a Microcosm Experiment.

Gold nanoparticles (AuNPs) are used as models to track and predict NP fates and effects in ecosystems. Previous work found that aquatic macrophytes and their associated biofilm primarily drove the fate of AuNPs within aquatic ecosystems and that seasonality was an important abiotic factor in the fate of AuNPs. Therefore, the present work aims to study if grazers, by feeding on these interfaces, modify the AuNP fate and if this is altered by seasonal fluctuations. Microcosms were dosed with 44.8 µg/L of AuNP weekly for 4 weeks and maintained in environmental chambers simulating Spring and Fall light and temperature conditions. We discovered that seasonal changes and the presence of grazers significantly altered the fate of Au. Higher temperatures in the warmer season increased dissolved organic carbon (DOC) content in the water column, leading to stabilization of Au in the water column. Additionally, snail grazing on biofilm growing on the Egeria densa surface led to a transfer of Au from macrophytes to the organic matter above the sediments. These results demonstrate that climate and grazers significantly impacted the fate of Au from AuNPs, highlighting the role that grazers might have in a large and biologically more complex ecosystem.

Responses of sediment nitrogen forms and bacterial communities to different aquatic nitrogen conditions in three submerged macrophyte-type ecological treatment systems.

Ecological treatment system (ETS) has been recognized as a promising technology for mitigating agricultural non-point pollution, whereas it remains to be seen how nitrogen (N) forms and bacterial communities in ETS sediments respond to different aquatic N conditions. Therefore, a four-month microcosm experiment was conducted to investigate the effects of three aquatic N conditions (2 mg/L NH4+-N, 2 mg/L NO3--N and 1 mg/L NH4+-N + 1 mg/L NO3--N) on sediment N forms and bacterial communities in three ETSs vegetated by Potamogeton malaianus, Vallisneria natans and artificial aquatic plant, respectively. Through analysis of four transferable N fractions, the valence states of N in ion-exchange and weak acid extractable fractions were found to be mainly determined by aquatic N conditions, while significant N accumulation was observed only in strong oxidant extractable and strong alkali extractable fractions. Sediment N profiles were primarily influenced by time and plant types, with N condition having secondary effect, while sediment bacterial community structures experienced a significant shift over time and were slightly influenced by plant types. Sediment functional genes related to N fixation, nitrification, assimilable nitrate reduction, dissimilatory nitrite reduction (DNRA) and denitrification were substantially enriched in month 4, and the bacterial co-occurrence network exhibited less complexity but more stability under NO3- condition compared to others. Furthermore, certain sediment N fractions were found to have strong relationships with specific sediment bacteria, such as nitrifiers, denitrifiers and DNRA bacteria. Our findings highlight the significant influence of aquatic N condition in submerged macrophyte-type ETSs on sediment N forms and bacterial communities.

Response of dissolved organic matter (DOM) and microbial community to submerged macrophytes restoration in lakes: A review.

Microorganisms play a crucial role in the biogeochemical processes of Dissolved Organic Matter (DOM), and the properties of DOM also significantly influence changes in microbial community characteristics. This interdependent relationship is vital for the flow of matter and energy within aquatic ecosystems. The presence, growth state, and community characteristics of submerged macrophytes determine the susceptibility of lakes to eutrophication, and restoring a healthy submerged macrophyte community is an effective way to address this issue. However, the transition from eutrophic lakes dominated by planktic algae to medium or low trophic lakes dominated by submerged macrophytes involves significant changes. Changes in aquatic vegetation have greatly affected the source, composition, and bioavailability of DOM. The adsorption and fixation functions of submerged macrophytes determine the migration and storage of DOM and other substances from water to sediment. Submerged macrophytes regulate the characteristics and distribution of microbial communities by controlling the distribution of carbon sources and nutrients in the lake. They further affect the characteristics of the microbial community in the lake environment through their unique epiphytic microorganisms. The unique process of submerged macrophyte recession or restoration can alter the DOM-microbial interaction pattern in lakes through its dual effects on DOM and microbial commu-----nities, ultimately changing the stability of carbon and mineralization pathways in lakes, such as the release of methane and other greenhouse gases. This review provides a fresh perspective on the dynamic changes of DOM and the role of the microbiome in the future of lake ecosystems.

Influence of seasonal variation to the population growth and ecophysiology of Typha domingensis (Typhaceae).

Precipitation is an important climatic element that defines the hydrological regime, and its seasonal variation produces annual dry and wet periods in some areas. This seasonality changes wetland environments and leverages the growth dynamics of macrophytes present, including Typha domingensis Pers. This study aimed to evaluate the influence of seasonal variation on the growth, anatomy and ecophysiology of T. domingensis in a natural wetland. Biometric, anatomical and ecophysiological traits of T. domingensis were evaluated over one year at four-month intervals. Reductions in photosynthesis were evidenced at the end of the wet periods and during the dry periods, and these reductions were associated with thinner palisade parenchymas. Increased stomatal indexes and densities as well as thinner epidermis observed at the beginning dry periods can be associated with higher transpiration rates during this period. The plants maintained their water contents during the dry periods, which may be related to the storage of water in leaf trabecular parenchyma, as this is the first time that results indicate the function of this tissue as a seasonal aquiferous parenchyma. In addition, increasing proportions of aerenchymas were evident during the wet periods, which may be related to a compensation mechanism for soil waterlogging. Therefore, the growth, anatomy and ecophysiology of T. domingensis plants change throughout the year to adjust to both the dry and wet periods, providing conditions for the survival of the plants and modulating population growth.