The Response of Estuarine Ammonia-Oxidizing Communities to Constant and Fluctuating Salinity Regimes

Seasonal and anthropogenic influences on bacterioplankton communities: ecological impacts in the coastal waters of Qinhuangdao, Northern China

Marine bacterioplankton play a crucial role in the cycling of carbon, nitrogen, and phosphorus in coastal waters. And the impact of environmental factors on bacterial community structure and ecological functions is a dynamic ongoing process. To systematically assess the relationship between environmental changes and bacterioplankton communities, this study delved into the spatiotemporal distribution and predicted metabolic characteristics of bacterioplankton communities at two estuarine beaches in Northern China. Coastal water samples were collected regularly in spring, summer, and autumn, and were analyzed in combination with environmental parameters and bacterioplankton community. Results indicated significant seasonal variations in bacterioplankton communities as Bacteroidetes and Actinobacteria were enriched in spring, Cyanobacteria proliferated in summer. While Pseudomonadota and microorganisms associated with organic matter decomposition prevailed in autumn, closely linked to seasonal variation of temperature, light and nutrients such as nitrogen and phosphorus. Particularly in summer, increased tourism activities and riverine inputs significantly raised nutrient levels, promoting the proliferation of specific photosynthetic microorganisms, potentially linked to the occurrence of phytoplankton blooms. Spearman correlation analysis further revealed significant correlations between bacterioplankton communities and environmental factors such as salinity, chlorophyll a, and total dissolved phosphorus (TDP). Additionally, the metabolic features of the spring bacterioplankton community were primarily characterized by enhanced activities in the prokaryotic carbon fixation pathways, reflecting rapid adaptation to increased light and temperature, as well as significant contributions to primary productivity. In summer, the bacterial communities were involved in enhanced glycolysis and biosynthetic pathways, reflecting high energy metabolism and responses to increased light and biomass. In autumn, microorganisms adapted to the accelerated decomposition of organic matter and the seasonal changes in environmental conditions through enhanced amino acid metabolism and material cycling pathways. These findings demonstrate that seasonal changes and human activities significantly influence the structure and function of bacterioplankton communities by altering nutrient dynamics and physical environmental conditions. This study provides important scientific insights into the marine biological responses under global change.

Salt marsh nitrogen cycling: where land meets sea

Salt marshes sit at the terrestrial-aquatic interface of oceans around the world. Unique features of salt marshes that differentiate them from their upland or offshore counterparts include high rates of primary production from vascular plants and saturated saline soils that lead to sharp redox gradients and a diversity of electron acceptors and donors. Moreover, the dynamic nature of root oxygen loss and tidal forcing leads to unique biogeochemical conditions that promote nitrogen cycling. Here, we highlight recent advances in our understanding of key nitrogen cycling processes in salt marshes and discuss areas where additional research is needed to better predict how salt marsh N cycling will respond to future environmental change.

Stochastic factors drive dynamics of ammonia-oxidizing archaeal and bacterial communities in aquaculture pond sediment

Ammonia-oxidizing archaea (AOA) and bacteria (AOB) play an important role in nitrification, which is essential in the global nitrogen cycle. However, their dynamics and the underlying community processes in agricultural ecosystems under disturbance remain largely unknown. In this study we examined the spatiotemporal dynamics of AOA and AOB communities and analyzed their community processes in the sediment of aquaculture ponds across three different areas in China. We found some significant temporal changes in AOA and AOB community diversity and abundances, but no temporal changes in community composition, despite the significant variations in sediment properties between different sampling times. Nevertheless, significant differences were found for AOA and AOB communities between different areas. Distinct area-specific taxa were detected, and they were found to be important in determining the response of AOA and AOB communities to environmental factors. In addition, geographic distance was found to be significantly correlated with AOA and AOB community composition, which demonstrates that dispersal limitation could significantly contribute to the variations in AOA and AOB communities, and stochastic processes were found to be important in structuring AOA/AOB communities in aquaculture ponds. Taken together, our study indicates that the dynamics of AOA and AOB are based on their community characteristics in aquaculture pond sediment. Our results, for the first time, provide evidence for the dynamics of AOA and AOB communities being driven by stochastic factors in a disturbed environment, and might also be of use in the management of the aquaculture environment.