Spatiotemporal assembly and functional composition of planktonic microeukaryotic communities along productivity gradients in a subtropical lake.

Microeukaryotes play crucial roles in the microbial loop of freshwater ecosystems, functioning both as primary producers and bacterivorous consumers. However, understanding the assembly of microeukaryotic communities and their functional composition in freshwater lake ecosystems across diverse environmental gradients remains limited. Here, we utilized amplicon sequencing of 18S rRNA gene and multivariate statistical analyses to examine the spatiotemporal and biogeographical patterns of microeukaryotes in water columns (at depths of 0.5, 5, and 10 m) within a subtropical lake in eastern China, covering a 40 km distance during spring and autumn of 2022. Our results revealed that complex and diverse microeukaryotic communities were dominated by Chlorophyta (mainly Chlorophyceae), Fungi, Alveolata, Stramenopiles, and Cryptophyta lineages. Species richness was higher in autumn than in spring, forming significant hump-shaped relationships with chlorophyll a concentration (Chl-a, an indicator of phytoplankton biomass). Microeukaryotic communities exhibited significant seasonality and distance-decay patterns. By contrast, the effect of vertical depth was negligible. Stochastic processes mainly influenced the assembly of microeukaryotic communities, explaining 63, 67, and 55% of community variation for spring, autumn, and both seasons combined, respectively. Trait-based functional analysis revealed the prevalence of heterotrophic and phototrophic microeukaryotic plankton with a trade-off along N:P ratio, Chl-a, and dissolved oxygen (DO) gradients. Similarly, the mixotrophic proportions were significantly and positively correlated with Chl-a and DO concentrations. Overall, our findings may provide useful insights into the assembly patterns of microeukaryotes in lake ecosystem and how their functions respond to environmental changes.

Assessment of the effectiveness of a field-scale combined ecological treatment system at removing water pollutants, after optimization using a system dynamic model: a case study of rural inland ponds in China.

Field-scale combined ecological treatment systems (FCETS) are designed to remove nutrients from aquaculture wastewater in ponds according to the characteristics of the nutrients present. We designed and established a numerical model based on the system dynamic (SD) method, to optimize the parameters of FCETS. Results showed that the mean removal rates of TSS, TN, NO3--N, NH4+-N, TP, DP, and CODMn ranged from 83.3 to 125.8%, 41.1 to 49.1%, 44.8 to 56.2%, 49.3 to 55.6%, 80.0 to 88.2%, 52.6 to 65.0%, and 52.0 to 61.5%, respectively. The SD model provided satisfactory estimates of water quality at the outlet throughout both the validation and calibration periods. In addition, we conducted a sensitivity analysis to determine the key parameters of the SD model. This also involved optimization of the N and P removal capacity of FCETS, and their corresponding discharge (Q), and concentration (C) at the inlet. This made it possible to use R and MATLAB to simulate seasonal differences in the removal of N and P. Our results indicate that a FCETS can be used to efficiently remove nutrients from rural wastewater in ponds. In addition, we demonstrated that the SD-based numerical model is a useful management support tool to ensure that decisions are made which result in the stable operation of a FCETS. This illustrates that contamination-free aquaculture from rural inland ponds is a feasible goal.

Isolation and characterization of 20 polymorphic microsatellites loci for Xenocypris davidi based on high-throughput sequencing.

Xenocypris davidi is one of the most economically important freshwater fish in China. However, few molecular markers have been reported for this species, impeding in-depth population genetic, dispersal, and gene flow studies. In the present study, a batch of novel polymorphic microsatellites from the genome of X. davidi were isolated and characterized using high-throughput sequencing. A total of 20 microsatellite markers were isolated. Analysis of 33 individuals revealed an average of 7.35 alleles per locus, ranging from 3 to 18. The observed and expected heterozygosities ranged from 0.3 to 1 and from 0.426 to 0.93, respectively. Only one tested locus significantly deviated from Hardy-Weinberg equilibrium. 18 microsatellite loci were highly polymorphic (PIC > 0.5). These newly isolated microsatellite markers would be useful to study the population genetics and stock management of X. davidi.

Acute toxicity of cypermethrin on the juvenile of red claw crayfish Cherax quadricarinatus.

In order to assess the toxicity of Cypermethrin (CYP), the 50% lethal concentration (LC50) of CYP on the juvenile of Cherax quadricarinatus is assessed. Meanwhile, the transcription level and the content in the antioxidant and biotransformation enzymes in hepatopancreas and immune enzymes in the serum of C. quadricarinatus exposed to CYP (0.1, 1, 10 and 100 ng·L-1) for 96 h were analyzed to reveal the CYP toxicity and detoxification mechanism. 24, 48, 72, 96 h LC50 were 1305.14, 424.52, 287.10 and 215.99 ng·L-1, respectively. There was no significant change of the content of enzymes at low concentration (0.16 ng·L-1). The fast increase of SOD and CAT content was observed at early stage (24 h), subsequent decreased at later stage of trail at medium concentration (0.32 and 0.63 ng·L-1). However, high concentration (1.25 ng·L-1) of CYP significantly inhibited SOD and CAT content. There was a significant increase in the level of MDA, PC and the content of GPx, EROD, CarE, GST at medium and high concentration after 72 h and 96 h exposure. The Na+-K+-ATPase, PO, ALK content decreased at medium and high concentration, especially at the 72-h and the 96-h exposure. The transcription was altered similarly to enzyme content, but the transcriptional response was generally more immediate than enzymatic response. Heat shock protein (hsp70) and multidrug resistance-associated protein 2 (abcc2) genes were up-regulated.