Nutrient enrichment drives the sediment microbial communities in Chinese mitten crab Eriocheir sinensis culture.

Microbial communities play a critical role in aquaculture ecosystems. To identify the influence of sediment nutrient levels on microbial communities, sediment and water samples were collected from Chinese mitten crab Eriocheir sinensis culture ponds with different nutrient enrichment levels. Relevant physicochemical properties were measured, and 16 S rRNA gene sequencing was applied to identify relevant bacterial communities in the sediments. The results showed that the diversity and composition of microbial communities in sediments with different levels of nutrient enrichment varied considerably. Proteobacteria was the most abundant phylum in all samples, followed by Bacteroidetes, and Desulfobacterota with relative abundances of 23.5-40.9%, 9.8-21.5%, and 9.6-18.1%, respectively. Notably, total nitrogen (TN), organic matter (OM), and pH were important factors driving sediment bacterial community aggregation, the TN concentration explaining 61.5% of the microbial community variation. This study highlights that long-term culture activities alter the degree of sediment nutrient enrichment, which in turn affects microbial community composition and may ultimately have an impact on culture efficiency.

How do inundation provoke the release of phosphorus in soil-originated sediment due to nitrogen reduction after reclaiming lake from polder.

Different N and P fractions in microcosm incubation experiment was measured using high-resolution in-situ Peeper and DGT techniques combining with sequential extraction procedure. The results showed the synchronous desorption and release of PO43-, S2- and Fe2+ from the solid soil-originated sediment. This trend indicated that the significant reduction of Fe-P and SO42- occurred in the pore water during the inundation. The concentrations of PO43- in the overlying water and pore water increased to more than 0.1 and 0.2 mg/L at the beginning of the incubation experiment. Decreased NO3-concentrations from more than 1.5 mg/L to less than 0.5 mg/L combining with increasing NH4+ concentrations from less than 1 mg/L to more than 5 mg/L suggested the remarkable NO3- reduction via dissimilatory nitrate reduction to ammonia (DNRA) pathway over time. High NH4+ concentrations in the pore water aggravated the release of Fe2+ through reduction of Fe(III)-P as electric acceptors under anaerobic conditions. This process further stimulated the remarkable releasing of labile PO43- from the solid phase to the solution and potential diffusion into overlying water. Additionally, high S2- concentration at deeper layer indicated the reduction and releasing of S2- from oxidation states, which can stimulated the NO3- reduction and the accumulation of NH4+ in the pore water. This process can also provoke the reduction of Fe-P as electric acceptors following the release of labile PO43- into pore water. Generally, inundation potentially facilitate the desorption of labile P and attention should be paid during the reclaiming lake from polder.

A molting chemical cue (N-acetylglucosamine-6-phosphate) contributes to cannibalism of Chinese mitten crab Eriocheir sinensis.

Under high-density culture, cannibalism occurs frequently during the molting of the Chinese mitten crabs Eriocheir sinensis, resulting in a large reduction in production. We found that the leakage of molting fluid from sexually immature crabs informs conspecifics that they are in a molting process. This hypothesis was verified through metabolomics analyses combined with behavioral experiments. The GlcNAc-6-P was identified as a molting biomarker from the differential metabolites by non-targeted metabolomics. In addition, we found that the concentration of GlcNAc-6-P in the molting fluid was significantly higher than other molting metabolites at different molting stages, reaching 5.84 µmol L-1, indicating that the molting fluid was the source of GlcNAc-6-P. Moreover, the behavioral experiments showed that crabs were actively approached to high concentrations of GlcNAc-6-P (1 µmol L-1), but had no obvious choice tendency at different concentrations of UTP, 20-HE and low concentrations of GlcNAc-6-P (0.1 µmol L-1, 0.01 µmol L-1) compared with the control groups. In conclusion, that E. sinensis by sensing the concentration change of GlcNAc-6-P can locate the source of GlcNAc-6-P release and actively approach the high concentration GlcNAc-6-P area and attack the molting crab, causing cannibalism. Blocking the reception pathway of molting chemical cues in E. sinensis, thereby preventing the perception of signals originating from conspecifics' molting in the vicinity, could lead to a reduction in cannibalistic behavior and an increase in overall production. Additionally, this method presents a prospective solution for addressing cannibalism in other crustacean species where such behavior is prevalent.

Dissimilatory nitrate reduction to ammonium (DNRA) potentially facilitates the accumulation of phosphorus in lake water from sediment.

Nitrogen (N) and phosphorus (P) are crucial nutrients for eutrophication in the lacustrine ecosystem and attract the attention worldwide. However, the interaction between them need further clarification. This study aimed to assess the influence of dissimilatory nitrate reduction to ammonia (DNRA) on the cycle of P in lacustrine sediment. Different fractions of N and P in the pore water were measured using high-resolution in-situ measurement techniques, HR-Peeper and DGT, coupling with sequential extraction for solid sediment from a shallow freshwater lake. The results showed that elevated nitrate (NO3-) reduction via DNRA rather than denitrification was verified at deeper sediment layer, suggesting the generation of inorganic ammonia (NH4+) as electron donor under anaerobic episodes. High abundance of DNRA bacteria (nrfA gene) obtained using high-throughput sequencing analysis were detected at upper layer and responsible for the accumulation of NH4+ in the sediment coupling with chemolithoautotrophic metabolism. Additionally, significant desorption of ionic ferrous iron (Fe2+) and dissolved reactive phosphate (DRP) from solid phase and the enrichment in the solution was simultaneously detected. Higher concentration of solid Fe bound P (Fe-P) at deeper layer indicated the potential re-oxidation of Fe2+ as electron donor during DNRA process and sorption of DRP toward the Fe-containing minerals. However, obvious evidence of desorption proved by DGT indicated that higher NH4+ concentrations favored the reduction of Fe(III) oxy(hydr)oxides and the desorption of DRP into the pore water and diffusion toward the overlying water. Finally, noteworthy S2- release from solid sediment was speculated to stimulate the DNRA and facilitated the accumulation of NH4+ in the solution, which further induced the enrichment of DRP in water from the solid phase. Overall, DNRA potentially facilitates the accumulation of P in lake water, and the synchronous control of N and P is important for the eutrophication management and restoration of lake eutrophication.

Water-level fluctuations regulate the availability and diffusion kinetics process of phosphorus at lake water-sediment interface.

Sequential extraction and in-situ diffusive gradients in thin films (DGT) techniques were used to determine phosphorus (P) fractions and high-resolution 2D fluxes of labile PDGT, Fe2+DGT, and S2-DGT in sediment systems. The diffusion fluxes were subsequently calculated for different scenarios. Dynamic diffusion parameters between solid sediment and solution were also fitted using the DIFS (DGT-induced fluxes in sediments) model. The results suggested that Fe-bound P (Fe-P) was the dominant pool which contributed to the resupply potential of P in the water-sediment continuum. Significant upward decreases of labile PDGT, Fe2+DGT, and S2-DGT fluxes were detected in pristine and incubated microcosms. This dominance indicated the more obvious immobilization of labile P via oxidation of both Fe2+ and S2- in oxidic conditions. Additionally, these labile analytes in the microcosms obviously decreased after a 30-day incubation period, indicating that water-level fluctuations can significantly regulate adsorption-desorption processes of the P bound to Fe-containing minerals within a short time. Higher concentrations of labile PDGT, Fe2+DGT, and S2-DGT were measured at the shallow lake region where more drastic water-level variation occurred. This demonstrates that frequent adsorption-desorption of phosphate from the sediment particles to the aqueous solution can result in looser binding on the solid sediment surface and easier desorption in aerobic conditions via the regulation of water levels. Higher R values fitted with DIFS model suggested that more significant desorption and replenishment effect of labile P to the aqueous solution would occur in lake regions with more dramatic water-level variations. Finally, a significant positive correlation between S2-DGT and Fe2+DGT in the sediment indicated that the S2- oxidization under the conditions of low water-level can trigger the reduction of Fe(III) and subsequent release of active P. In general, speaking, frequent water-level fluctuations in the lake over time facilitated the formation and retention of the Fe(II) phase in the sediment, and desorption of Fe coupled P into the aqueous solution when the water level was high.