Freshwater Biology最新文献

1. Freshwater mussels (Bivalvia: Unionida) are among the most imperilled freshwater taxa. Yet, there is a lack of basic life history information for mussels, including data on their growth and longevity. These data help inform conservation efforts, as they can indicate whether species or populations may be vulnerable to decline and inform which species may be best adapted to certain habitats. We aimed to quantify growth and longevity in five mussel species from four river systems in the southeastern United States and test whether growth was related to stream flow. We also interpreted our findings in the context of life history theory.
2. To model mussel growth and longevity, we cut radial thick sections from the shells of mussels and used high-resolution photography to image the shells. We identified annual growth rings (annuli) and used von Bertalanffy growth models to estimate growth rate (K) and maximum age (A_max) across 13 mussel populations. We then used biochronological methods to remove age-related variation in annual growth in each shell. We tested whether annual growth was correlated with stream flow using discharge-based statistics.
3. We found substantial variation in K and A_max among species and among populations of the same species. K was negatively related to A_max. We did not find consistent correlations between annual growth and stream flow.
4. Our estimates of K and A_max align with previous studies on closely related species and populations. They also match the eco-evolutionary prediction that growth rate and longevity are negatively related. Life history theory predicts that short-lived species with higher growth rates should be better adapted to environments with cyclical disturbance regimes, whereas longer-lived species with low growth rates should be better adapted to stable environments. The lack of correlation between annual growth and stream flow suggests that mussel growth may be limited by other factors in our study system.
5. While some species seem to have relatively narrow ranges for growth and longevity, other species show wide variation among populations. This highlights the need for species- and population-specific conservation efforts. Fundamental life history information can be integrated with other species traits to predict how freshwater taxa may respond to ecological threats.

1. Overwintering is a crucial stage in the seasonal cycle of Microcystis, which is often overlooked as a state of “suspended animation”. With global warming and increasing heatwaves, temperature rise during the overwintering phase causes earlier recruitment or blooms. However, the impact of elevated overwinter temperatures on the growth of toxic Microcystis aeruginosa remains poorly understood.
2. This study aimed to elucidate the physiological, metabolic and molecular mechanisms at different overwintering temperatures (4°C, 6°C, 4°C → 6°C → 8°C, 6°C → 8°C) by cellular growth, photosynthetic effect, metabolic products, enzyme activities and transcriptomic analysis.
3. Elevated overwinter temperatures (4°C → 6°C → 8°C, 6°C → 8°C) significantly promoted the growth of M. aeruginosa. Photosynthetic activity responded rapidly, reaching its peak at the 9°C–16°C temperature range.
4. Elevated overwinter temperatures also enhanced the secretion of microcystins and extracellular polymeric substances. These temperatures favoured the expression of rbcL and mcyB genes associated with photosynthetic and microcystin production, with significant activation of RuBisCO and FBA enzymes during recruitment. Furthermore, transcriptomic analysis revealed 321 genes with significant differential expression under elevated overwinter temperatures, including 156 up-regulated and 165 down-regulated genes.
5. The interaction network highlighted proteins with the highest connectivity, comprising ribosomal proteins and RNA polymerase proteins, triggering processes related to oxidative phosphorylation and photosynthesis.
6. This study sheds light on the intricate interplay of temperatures with the physiological and molecular dynamics of M. aeruginosa during overwintering, offering valuable insights into the effects of global warming on algae growth in the future.

1. Nutrient cycling and organic matter transformations in aquatic systems are primarily performed by microorganisms but are further facilitated through the mixing of sediment by macroinvertebrates. Despite known impacts of macroinvertebrates on the biogeochemistry and microbial community of sediments, the impact of macroinvertebrates and their microbiome on the water column of freshwater systems has been understudied.
2. A microcosm approach was used to study the short-term effects that freshwater bivalves, Corbicula fluminea, and crayfish, Procambarus vioscai paynei, have on the microbial community in the surrounding water column. The activity of microbial enzymes involved in the breakdown of organic carbon (β-glucosidase), phosphate (phosphatase), and carbon and nitrogen (N-acetylglucosaminidase) were assayed, and the bacterial community in the water column and other system components was characterised using Illumina 16S rRNA gene sequencing.
3. Crayfish and bivalves both significantly altered the structure and function of the bacterial community in the water column. Crayfish stimulated microbial enzyme activity to a greater extent than bivalves, whereas bivalves at higher densities increased water column enzyme activity more than when they were at lower densities.
4. The external microbiomes of macroinvertebrates were not a significant source of bacterial populations to the bacterial communities of vegetation or the water column, but macroinvertebrate presence was associated with an increased abundance of certain bacterial taxa in the water column, such as Comamonadaceae and Chitinophagaceae.
5. These results demonstrate that, even in the short term, macroinvertebrates can impact biogeochemical processes in the water column of freshwater ecosystems, potentially by influencing the bacterial community.
6. This study contributes to a deeper understanding of the relationships between macroinvertebrates and microbial communities in their environment, with specific implications for processes in the water column, a component that is frequently overlooked in terms of macroinvertebrate effects. Considering interactions between all components of freshwater ecosystems is crucial to understanding their functioning, especially in the face of escalating environmental pressures.

1. The trophic state of water significantly affects the structure of bacterial communities in sediments. The direct and indirect impacts of trophic state, along with trophic-induced changes in the properties of organic matter, on the composition and distribution of bacteria in sediments, remain largely unknown.

2. We collected surface sediments from 21 sites across five areas of Lake Taihu, the third largest freshwater lake in China. These sites represented a range of trophic states from mesotrophic to moderately eutrophic. We investigated how trophic state influences bacterial composition and distribution in the surface sediments of Lake Taihu.

3. Proteobacteria, Firmicutes and Bacteroidetes were the most abundant phyla identified in the DNA sequences of surface sediments from the sampling sites in Lake Taihu, regardless of the water trophic state. The relative abundance of Proteobacteria and Firmicutes in the surface sediments increased with trophic level index (TLI) of the water column. In contrast, the relative abundance of Bacteroidetes, Acidobacteria and Fibrinobacteria decreased with increasing TLI. The α-biodiversity of the sediment bacterial community in Lake Taihu did not vary significantly among different water trophic states. However, surface sediments from sites with varied trophic states exhibited different groups of bacteria that were either specifically present or in higher relative abundance.

4. Several factors influenced the sediment bacterial communities in Lake Taihu, including sediment total nitrogen, sediment total phosphorus, sediment organic carbon, δ¹³C and trophic state. However, the primary influencing factors varied between sites and trophic states. For mesotrophic states, sediment organic carbon was the most important factor, while for moderately eutrophic states, trophic state was the most significant factor.

5. Our findings provide evidence for both the direct and indirect influences of water trophic state on the composition and distribution of bacteria in sediments.