Uptake of Soil-Derived Carbon into Plants: Implications for Disposal of Nuclear Waste

Tritium and Carbon-14 Contamination Reshaping the Microbial Community Structure, Metabolic Network, and Element Cycle in the Seawater Environment

The potential ecological risks caused by entering radioactive wastewater containing tritium and carbon-14 into the sea require careful evaluation. This study simulated seawater's tritium and carbon-14 pollution and analyzed the effects on the seawater and sediment microenvironments. Tritium and carbon-14 pollution primarily altered nitrogen and phosphorus metabolism in the seawater environment. Analysis by 16S rRNA sequencing showed changes in the relative abundance of microorganisms involved in carbon, nitrogen, and phosphorus metabolism and organic matter degradation in response to tritium and carbon-14 exposure. Metabonomics and metagenomic analysis showed that tritium and carbon-14 exposure interfered with gene expression involving nucleotide and amino acid metabolites, in agreement with the results seen for microbial community structure. Tritium and carbon-14 exposure also modulated the abundance of functional genes involved in carbohydrate, phosphorus, sulfur, and nitrogen metabolic pathways in sediments. Tritium and carbon-14 pollution in seawater adversely affected microbial diversity, metabolic processes, and the abundance of nutrient-cycling genes. These results provide valuable information for further evaluating the risks of tritium and carbon-14 in marine environments.

Effects of marine biofertilisation on Celtic bean carbon, nitrogen and sulphur isotopes: Implications for reconstructing past diet and farming practices

RATIONALE

The application of fertilisers to crops can be monitored and assessed using stable isotope ratios. However, the application of marine biofertilisers (e.g., fish, macroalgae/seaweed) on crop stable isotope ratios has been rarely studied, despite widespread archaeological and historical evidence for the use of marine resources as a soil amendment.

METHODS

A heritage variety of Celtic bean, similar in size and shape to archaeobotanical macrofossils of Vicia faba L., was grown in three 1 × 0.5 m outdoor plots under three soil conditions: natural soil (control); natural soil mixed with macroalgae (seaweed); and 15 cm of natural soil placed on a layer of fish carcasses (Atlantic cod). These experiments were performed over two growing seasons in the same plots. At the end of each growing season, the plants were sampled, measured and analysed for carbon, nitrogen and sulphur stable isotope ratios (δ¹³ C, δ¹⁵ N, δ³⁴ S).

RESULTS

The bean plants freely uptake the newly bioavailable nutrients (nitrogen and sulphur) and incorporate a marine isotopic ratio into all tissues. The bean δ¹⁵ N values ranged between 0.8‰ and 1.0‰ in the control experiment compared with 2‰ to 3‰ in the macroalgae crop and 8‰ to 17‰ in the cod fish experiment. Their δ³⁴ S values ranged between 5‰ and 7‰ in the control compared with 15‰ to 16‰ in the macroalgae crop and 9‰ to 12‰ in the cod fish crop. The beans became more ¹³ C-depleted (δ¹³ C values: 1-1.5‰ lower) due to crop management practices.

CONCLUSIONS

Humans and animals consuming plants grown with marine biofertilisers will incorporate a marine signature. Isotopic enrichment in nitrogen and sulphur using marine resources has significant implications when reconstructing diets and farming practices in archaeological populations.

Content of soil-derived carbon in soil biota and fauna living near soil surface: Implications for radioactive waste

¹⁴C is known as one of the radionuclides that have potential to be released into the biosphere from radioactive waste repositories and taken up by organisms. In this study, we used a novel approach to investigate the proportion of soil organic carbon (SOC) in invertebrates and microbial biomass. The study was conducted on a peatland site after the end of peat extraction. There was a large difference in the isotopic abundance of ¹⁴C between the 8000-year-old peat and air. We used a two-pool isotope mixing model to reveal the fraction of soil-derived C in the organisms and in dissolved organic carbon in soil water. The contribution of soil-derived C was found to be highest in microbial biomass (61%) and earthworms (22%). Some contribution of soil-derived C was detected in fungus gnats (2%), but not in other insects or in spiders. These findings are important for developing evidence-based radioecological models based on correct understanding of the relative contributions of atmospheric C vs. SOC in organisms.