Effects of Dietary Selenium and Oxidized Fish Oils on Intestinal Lipid Metabolism and Antioxidant Responses of Yellow Catfish Pelteobagrus fulvidraco.

Currently, the effect of selenium and oxidized fish oil interactions on the intestinal lipid metabolism and antioxidant responses of fish remains unknown. Herein, yellow catfish Pelteobagrus fulvidraco (weight: 3.99 ± 0.01 g) were used as experimental animals and were fed four diets: an adequate amount of selenium (0.25 mg kg-1) with fresh fish oil (A-Se+FFO), an adequate amount of selenium with oxidized fish oil (A-Se+OFO), a high amount of selenium (0.50 mg kg-1) with fresh fish oil (H-Se+FFO), and a high amount of selenium with oxidized fish oil (H-Se+OFO). The feeding experiment was conducted for 10 weeks. The results showed that selenium supplementation alleviated the intestinal tissue damage and reduced the lipid accumulation that was induced by oxidized fish oils. Meanwhile, we also found that 0.50 mg kg-1 selenium reduced the oxidative stress that is caused by oxidized fish oils through increasing the GSH and the activity and mRNA expression of antioxidant enzymes. Dietary selenium and oxidized fish oils also affected the mRNA expression of intestinal selenoproteins including selenow2a, selenop2, and selenot2. Mechanistically, Se and oxidized eicosapentaenoic acid (oxEPA) influenced the GSH content by affecting the DNA binding ability of activating transcription factor (ATF) 3 to the slc7a11 promoter. For the first time, our results suggested that selenium alleviated the oxidized fish oil-induced intestinal lipid deposition and the oxidative stress of the fish. We also elucidated the novel mechanism of selenium increasing the GSH content by affecting the interaction of ATF3 and the slc7a11 promoter.

Phosphorus alleviation of nitrogen-suppressed methane sink in global grasslands.

Grassland ecosystems account for more than 10% of the global CH4 sink in soils. A 4-year field experiment found that addition of P alone did not affect CH4 uptake and experimental addition of N alone significantly suppressed CH4 uptake, whereas concurrent N and P additions suppressed CH4 uptake to a lesser degree. A meta-analysis including 382 data points in global grasslands corroborated these findings. Global extrapolation with an empirical modelling approach estimated that contemporary N addition suppresses CH4 sink in global grassland by 11.4% and concurrent N and P deposition alleviates this suppression to 5.8%. The P alleviation of N-suppressed CH4 sink is primarily attributed to substrate competition, defined as the competition between ammonium and CH4 for the methane mono-oxygenase enzyme. The N and P impacts on CH4 uptake indicate that projected increases in N and P depositions might substantially affect CH4 uptake and alter the global CH4 cycle.

Influence of nitrogen additions on litter decomposition, nutrient dynamics, and enzymatic activity of two plant species in a peatland in Northeast China.

Nitrogen (N) availability affects litter decomposition and nutrient dynamics, especially in N-limited ecosystems. We investigated the response of litter decomposition to N additions in Eriophorum vaginatum and Vaccinium uliginosum peatlands. These two species dominate peatlands in Northeast China. In 2012, mesh bags containing senesced leaf litter of Eriophorum vaginatum and Vaccinium uliginosum were placed in N addition plots and sprayed monthly for two years with NH4NO3 solution at dose rates of 0, 6, 12, and 24gNm-2year-1 (CK, N1, N2 and N3, respectively). Mass loss, N and phosphorus (P) content, and enzymatic activity were measured over time as litter decomposed. In the control plots, V. uliginosum litter decomposed faster than E. vaginatum litter. N1, N2, and N3 treatments increased the mass losses of V. uliginosum litter by 6%, 9%, and 4% respectively, when compared with control. No significant influence of N additions was found on the decomposition of E. vaginatum litter. However, N and P content in E. vaginatum litter and V. uliginosum litter significantly increased with N additions. Moreover, N additions significantly promoted invertase and ß-glucosidase activity in E. vaginatum and V. uliginosum litter. However, only in V. uliginosum litter was polyphenol oxidase activity significantly enhanced. Our results showed that initial litter quality and polyphenol oxidase activity influence the response of plant litter to N additions in peatland ecosystems. Increased N availability may change peatland soil N and P cycling by enhancing N and P immobilization during litter decomposition.

Responses of plant nutrient resorption to phosphorus addition in freshwater marsh of Northeast China.

Anthropogenic activities have increased phosphorus (P) inputs to most aquatic and terrestrial ecosystems. However, the relationship between plant nutrient resorption and P availability is still unclear, and much less is known about the underlying mechanisms. Here, we used a multi-level P addition experiment (0, 1.2, 4.8, and 9.6 g P m(-2) year(-1)) to assess the effect of P enrichment on nutrient resorption at plant organ, species, and community levels in a freshwater marsh of Northeast China. The response of nutrient resorption to P addition generally did not vary with addition rates. Moreover, nutrient resorption exhibited similar responses to P addition across the three hierarchical levels. Specifically, P addition decreased nitrogen (N) resorption proficiency, P resorption efficiency and proficiency, but did not impact N resorption efficiency. In addition, P resorption efficiency and proficiency were linearly related to the ratio of inorganic P to organic P and organic P fraction in mature plant organs, respectively. Our findings suggest that the allocation pattern of plant P between inorganic and organic P fractions is an underlying mechanism controlling P resorption processes, and that P enrichment could strongly influence plant-mediated biogeochemical cycles through altered nutrient resorption in the freshwater wetlands of Northeast China.

Impacts of mire reclamation on dynamics of dissolved nutrients in fluvial systems in the Sanjiang Plain, Northeast China.

As an important nutrient reservoir, the mires in the Sanjiang Plain of Northeast China have been suffering from large-scale agriculture reclamation since the 1960s. The effects of the long-term reclamation on the dynamics of the dissolved nutrients in fluvial systems are revealed through surveying the export concentrations of dissolved nitrogen and phosphorus in the natural mire, degraded mire and drainage ditches during the growing seasons in 2009 and 2010. The results show that the mean concentrations of total dissolved nitrogen (TDN, 2.03 ± 0.355 mg l(-1)) are much higher in natural mire than in degraded mire (1.15 ± 0.247 mg l(-1)) and ditches (1.03 ± 0.231 mg l(-1)), and the fraction lessened is primarily the organic part of nitrogen. It indicates that the long-term mire reclamation has led to a significant reduction in TDN concentrations in the surface fluvial system, and has changed the dominant nitrogen components from organic to inorganic formation. In comparison, the concentrations of total dissolved phosphorus (TDP) have no significant difference between natural mire and degraded mire or ditches, which demonstrates that mire reclamation has no impact on TDP export dynamics in the fluvial system. The seasonal dynamics of TDN are strongly correlated to dissolved organic carbon at almost all the sample sites, and mire reclamation does not alter the C : N ratio in the fluvial system, but lowers N : P ratio remarkably. The long-term reclamation exerts distinctly different effects on the export dynamics of TDN and TDP in the fluvial system in the Sanjiang Plain. Specific goals and methods ought to be determined if ecological management and recovery measures are to be carried out.