Freshwater Biology最新文献

1. Environmental conditions undergo considerable variation with increasing elevation, where high elevations can detrimentally affect plant growth and distribution. Ranunculus bungei, a widespread aquatic plant in the Tibetan Plateau, successfully thrives across a wide range of elevations. This study aims to clarify the photosynthetic and structural adaptability of R. bungei to varying elevations.

2. The study conducted in situ experiments with R. bungei across 18 elevation gradients (2923 m–4906 m) to analyse pigment content, HCO₃⁻ utilisation, CAM metabolism and leaf structure. It also examined environmental factors to investigate how the CO₂ concentrating mechanisms (CCMs) and leaf structure of R. bungei respond to elevation-driven varying environment.

3. A significant decline in Chlorophyll a, Chlorophyll a/b, and carotenoid content occurs with increasing elevation, indicating an adaptive response to mitigate potential oxidative stress associated with harsh conditions at higher elevations. Ranunculus bungei exhibits CAM metabolism at elevations below 3010 m; however, both CAM activity and HCO₃⁻ utilisation decrease with rising elevation. Key environmental factors influencing CAM activity include elevation, water temperature and CO₂ concentration. R. bungei leaf thickness responded nonlinearly to elevation, showing initial decreases followed by increases past the inflection elevation. A significant positive correlation exists between the ratio of air space area to leaf lobe area and the proportion of total inorganic carbon to alkalinity (C_T/Alk) in pH-drift experiments, indicating that R. bungei can adjust its air space according to the availability of inorganic carbon sources.

4. Elevation variations significantly affect the CCMs and anatomy of R. bungei on the Tibetan Plateau. These findings enhance our understanding of the plasticity of CCMs and the ecological adaptability of R. bungei, allowing for predictions about the species' responses to future climate scenarios.

1. Overwintering cells play a crucial role in Microcystis blooms; however, the mechanisms underlying this process are not yet fully understood. In this study, we investigated the response mechanism of Microcystis aeruginosa to a gradual temperature decline (GTD) by simulating temperature shifts from autumn to winter.
2. Here, the difference of the growth, cell viability, chlorophyll fluorescence, and oxidative stress between GTD group and direct low-temperature treatment (DLT) group were compared. We also determined the trade-offs between defensive and active strategies for coping with GTD treatment by conducting metabolomics and transcriptomic analysis.
3. Our findings revealed that the growth of M. aeruginosa cells subjected to gradual temperature decline decreased significantly; however, they were able to recover rapidly once normal conditions were restored. Following the gradual decrease in temperature, several genes associated with photosynthesis, carbohydrate metabolism, oxidative phosphorylation and peptidoglycan biosynthesis in M. aeruginosa were downregulated. In contrast, genes involved in microcystin production—specifically, mcyB-G, mcyI and mcyJ—and those related to the methionine salvage pathway were upregulated compared with those in cells subjected to direct low-temperature treatment (DLT). Significant enrichment of metabolites such as L-proline, γ-aminobutyric acid (GABA), maltitol, nerol and panose was observed in the GTD group compared with the DLT group.
4. This study integrated physiological, metabolite and transcriptomic data to characterise cold-induced changes in M. aeruginosa. Our findings demonstrate that the energy requirements of M. aeruginosa cells can be reduced by downregulating energy and carbohydrate metabolism. Additionally, M. aeruginosa cells can regulate metabolites, including microcystin and the methionine salvage pathway, to survive cold stress. These results vividly underscore the remarkable physiological plasticity of M. aeruginosa in adapting to incremental environmental alterations. This adaptability not only provides valuable insights into the survival mechanisms of this species but also has significant implications for understanding the ecological dynamics of cyanobacterial blooms in changing environments, providing new insights into the mechanisms underlying seasonal cyanobacterial blooms and the pivotal roles of signalling and microcystin regulation.

1. The latitudinal diversity gradient is one of the most striking biogeographical patterns on Earth and typically reveals increases in species richness from the poles towards the tropics. However, the latitudinal diversity patterns vary among taxa, ecosystems and scales. In freshwater, the patterns are particularly obscure, partially owing to limited geographical and taxonomical scope, as well as unclear controls of sampling effort.
2. Here, we compiled data from a diverse group of benthic macroinvertebrates derived from standardised offshore surveys of 485 shallow freshwater lakes spread across the northern hemisphere to elucidate how diversity patterns at multiple spatial scales vary with latitude. At each scale, we calculated multiple effort-controlled measures emphasising different aspects of biodiversity.
3. Contrary to our expectations, we found no evidence of a latitudinal gradient for any metric of diversity at small (local, α-) or large (regional, γ-) scales, nor any pattern of β-diversity among the lakes.
4. Our results therefore provide some of the broadest evidence to date of a lack of latitudinal diversity gradient in offshore benthic macroinvertebrates in freshwater shallow lakes. Understanding this null relationship, and its contrast with many terrestrial and marine patterns, will require a concerted effort towards data compilation and comparative analyses.