Effect of Aquaculture Reclamation on Sediment Nitrates Reduction Processes in Mangrove Wetland

Mangrove wetland recovery enhances soil carbon sequestration capacity of soil aggregates and microbial network stability in southeastern China

Mangrove wetlands are highly productive ecosystems in tropical and subtropical coastal zones, play crucial roles in water purification, biodiversity maintenance, and carbon sequestration. Recent years have seen the implementation of pond return initiatives, which have facilitated the gradual recovery of mangrove areas in China. However, the implications of these initiatives for soil aggregate stability, microbial community structure, and network interactions remain unclear. This study assesses the impacts of converting ponds to mangroves-both in natural and artificially restored settings-on soil aggregate stability and microbial networks at typical mangrove restoration sites along China's southeastern coast. Our observations confirmed our hypothesis that pond-to-mangrove conversions resulted in an increase in the proportion of large aggregates (>0.25 mm), improved soil aggregate structural stability, and increased carbon sequestration. However, mangrove recovery led to a decrease in the abundance and diversity of soil fungi communities. In terms of co-occurrence networks, naturally restored mangrove wetlands exhibited more nodes and edges. The naturally recovered mangrove wetlands demonstrated a higher level of community symbiosis compared to those that were manually restored. Conversely, bacterial networks showed a different pattern, with significant shifts in key taxa related to carbon sequestration functions. For instance, the proportion of bacterial Desulfobacterota and fungi Basidiomycota in natural recovery mangrove increased by 15.03 % and 7.82 %, respectively, compared with that in aquaculture ponds. Soil fungi and bacteria communities, as well as carbon sequestration by aggregates, were all positively correlated with soil total carbon content (P < 0.05). Both bacterial and fungal communities contributed to soil aggregate stability. Our study highlights the complex relationships between soil microbial communities, aggregate stability, and the carbon cycle before and after land-use changes. These findings underscore the potential benefits of restoring mangrove wetlands, as such efforts can enhance carbon storage capacity and significantly contribute to climate change mitigation.

Effects of vegetation cover and aquaculture pollution on viral assemblages in mangroves sediments

Mangrove forests, a critical coastal ecosystem, face numerous anthropogenic threats, particularly from aquaculture activities. Despite the acknowledged significance of viruses in local and global biogeochemical cycles, there is limited knowledge regarding the community structure, genomic diversity, and ecological roles of viruses in mangrove forests ecosystems, especially regarding their responses to aquaculture. In this study, we identified 17,755 viral operational taxonomic units (vOTUs) from nine sediments viromes across three distinct ecological regions of the mangrove forests ecosystem: mangrove, bare flat, and aquaculture regions. Viral assemblages varied among three regions, and the pathogenic viruses associated with marine animals, such as the white spot syndrome virus (WSSV) from Nimaviridae, were identified in this study. The relative abundance of Nimaviridae in the bare flat region was higher than in other regions. Furthermore, viruses in distinct mangrove forests sediments regions have adapted to their environments by adopting distinct survival strategies and encoding various auxiliary metabolic genes involved in carbon metabolism and antibiotic resistance. These adaptations may have profound impacts on biogeochemical cycles. This study provides the first insights into the effects of vegetation cover and aquaculture on the community structure and ecological roles of viruses in mangrove forests sediments. These findings are crucial for understanding the risks posed by anthropogenic threats to mangrove forests ecosystems and informing effective management strategies.

Denitrification dominates dissimilatory nitrate reduction across global natural ecosystems

Denitrification, anaerobic ammonium oxidation (anammox), and dissimilatory nitrate reduction to ammonium (DNRA) are three competing processes of microbial nitrate reduction that determine the degree of ecosystem nitrogen (N) loss versus recycling. However, the global patterns and drivers of relative contributions of these N cycling processes to soil or sediment nitrate reduction remain unknown, limiting our understanding of the global N balance and management. Here, we compiled a global dataset of 1570 observations from a wide range of terrestrial and aquatic ecosystems. We found that denitrification contributed up to 66.1% of total nitrate reduction globally, being significantly greater in estuarine and coastal ecosystems. Anammox and DNRA could account for 12.7% and 21.2% of total nitrate reduction, respectively. The contribution of denitrification to nitrate reduction increased with longitude, while the contribution of anammox and DNRA decreased. The local environmental factors controlling the relative contributions of the three N cycling processes to nitrate reduction included the concentrations of soil organic carbon, ammonium, nitrate, and ferrous iron. Our results underline the dominant role of denitrification over anammox and DNRA in ecosystem nitrate transformation, which is crucial to improving the current global soil N cycle model and achieving sustainable N management.