The oxygen isotopic signature of soil- and plant-derived sulphate is controlled by fertilizer type and water source

Uptake patterns for nitrogen and sulfur source by aquatic plants and various nitrogen acquisition strategies: Affected by mining activities

Understanding the nitrogen and sulfur uptake strategies of mine plants, including sources and preferences for nitrogen forms (ammonium nitrogen (NH4+) vs nitrate nitrogen (NO3-)), is critical to improving understanding of the role of plants in participating in the biogeochemical cycles of nitrogen and sulfur in mining areas. In this study, the stable N and S isotopic compositions of two species of aquatic plants (calamus and reed) in Linhuan mining area were analyzed to determine their absorption strategies for different nitrogen and sulfur sources. The results showed that river water was the largest source of nitrogen and sulfur, contributing 54.6% and 53.9% respectively. NO3- is the main form of nitrogen uptake by reed and calamus, followed by NH4+. In order to adapt to the change of nitrogen form in the environment, reed and calamus tend to absorb and utilize NO3- to maintain their absorption of nitrogen. Mine effluents from mining activities provide at least 12.9% and 16.8% sulfate to reed and calamus respectively, and the effect of mine effluents on reed and calamus sulfur has been underestimated. This study reveals the key factors controlling plant isotope composition, and the use of nitrogen and sulfur isotope composition of aquatic plants can help quantify the level of influence of mining activities, and understand the biogeochemical cycle of nitrogen and sulfur in mining areas.

Tracing sulfate sources and transformations of surface water using multiple isotopes in a mining-rural-urban agglomeration area

Rapid urbanization and mining activities are exacerbating sulfate (SO42-) pollution in surface water, and the information on its sources and transformations is crucial for understanding the sulphur cycle in mining areas. In this study, the SO42- in the surface water of Huaibei mining area were monitored and the main sources of pollution and biogeochemical processes were identified using stable isotopes (δD, δ18O-H2O, δ34S-SO42- and δ18O-SO42-) and water chemistry. The results demonstrated the SO42- content in the Huihe River and Linhuan subsidence water area (SWA) is higher than that in other rivers and SWAs, which exceeded the environmental quality standard of surface water. The SO42- content of different rivers and SWAs showed seasonal differences, and the dry season was higher than the wet season. In addition, the SO42- in Tuohe River and Suihe River is primarily caused by urban sewage and agriculture activities, while in Zhonghu and Shuoxihu SWA is mainly contributed by natural evaporate dissolution. Notably, the input of SO42- in the Huihe River and Linhuan SWA caused by mining activities cannot be disregarded. The aerobic environment and isotopic fractionation of surface water indicate that sulfide oxidation is not the major cause of SO42- formation. This work has revealed the multiple sources and transformation mechanisms of SO42-, and provided a reference for the development of comprehensive management and effective remediation strategies of SO42- contamination in surface water around mining areas.

Stable Isotope Fractionation of Metals and Metalloids in Plants: A Review

This work critically reviews stable isotope fractionation of essential (B, Mg, K, Ca, Fe, Ni, Cu, Zn, Mo), beneficial (Si), and non-essential (Cd, Tl) metals and metalloids in plants. The review (i) provides basic principles and methodologies for non-traditional isotope analyses, (ii) compiles isotope fractionation for uptake and translocation for each element and connects them to physiological processes, and (iii) interlinks knowledge from different elements to identify common and contrasting drivers of isotope fractionation. Different biological and physico-chemical processes drive isotope fractionation in plants. During uptake, Ca and Mg fractionate through root apoplast adsorption, Si through diffusion during membrane passage, Fe and Cu through reduction prior to membrane transport in strategy I plants, and Zn, Cu, and Cd through membrane transport. During translocation and utilization, isotopes fractionate through precipitation into insoluble forms, such as phytoliths (Si) or oxalate (Ca), structural binding to cell walls (Ca), and membrane transport and binding to soluble organic ligands (Zn, Cd). These processes can lead to similar (Cu, Fe) and opposing (Ca vs. Mg, Zn vs. Cd) isotope fractionation patterns of chemically similar elements in plants. Isotope fractionation in plants is influenced by biotic factors, such as phenological stages and plant genetics, as well as abiotic factors. Different nutrient supply induced shifts in isotope fractionation patterns for Mg, Cu, and Zn, suggesting that isotope process tracing can be used as a tool to detect and quantify different uptake pathways in response to abiotic stresses. However, the interpretation of isotope fractionation in plants is challenging because many isotope fractionation factors associated with specific processes are unknown and experiments are often exploratory. To overcome these limitations, fundamental geochemical research should expand the database of isotope fractionation factors and disentangle kinetic and equilibrium fractionation. In addition, plant growth studies should further shift toward hypothesis-driven experiments, for example, by integrating contrasting nutrient supplies, using established model plants, genetic approaches, and by combining isotope analyses with complementary speciation techniques. To fully exploit the potential of isotope process tracing in plants, the interdisciplinary expertise of plant and isotope geochemical scientists is required.