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Fungal-mediated extracellular reactive oxygen species (ROS) are essential for biogeochemical cycles of carbon, nitrogen, and contaminants in terrestrial environments. These ROS levels may be modulated by iron nanoparticles that possess intrinsic peroxidase (POD)-like activity (nanozymes). However, it remains largely undescribed how fungi modulate the POD-like activity of the iron nanoparticles with various crystallinities and crystal facets. Using well-controlled fungal-mineral cultivation experiments, here, we showed that fungi possessed a robust defect engineering strategy to modulate the POD-like activity of the attached iron minerals by decreasing the catalytic activity of poorly ordered ferrihydrite but enhancing that of well-crystallized hematite. The dynamics of POD-like activity were found to reside in molecular trade-offs between lattice oxygen and oxygen vacancies in the iron nanoparticles, which may be located in a cytoprotective fungal exoskeleton. Together, our findings unveil coupled POD-like activity and oxygen redox dynamics during fungal-mineral interactions, which increase the understanding of the catalytic mechanisms of POD-like nanozymes and microbial-mediated biogeochemical cycles of nutrient elements as well as the attenuation of contaminants in terrestrial environments.

Snow serves as a vital scavenging mechanism to gas-phase and particle-phase organic nitrogen substances in the atmosphere, providing a significant link between land-atmosphere flux of nitrogen in the surface-earth system. Here, we used optical instruments (UV-vis and excitation-emission matrix fluorescence) and a Fourier transform ion cyclotron resonance mass spectrometer (FT-ICR MS) to elucidate the molecular composition and potential precursors of snow samples collected simultaneously at four megacities in North China. The elemental O/N ratio (≥3), together with the preference in the negative ionization mode, indicates that the one and two nitrogen atom-containing organics (CHON1 and CHON2) in snow were largely in the oxidized form (as organic nitrates, -ONO2). This study assumed that scavenging of particle-phase and gas-phase organic nitrates might be significant sources of CHON in precipitation. A gas-phase oxidation process and a particle-phase hydrolysis process, at a molecular level, were used to trace the potential precursors of CHON. Results show that more than half of the snow CHON molecules may be related to the oxidized and hydrolyzed processes of atmospheric organics. Potential formation processes of atmospheric organics on a molecular level provide a new concept to better understand the sources and scavenging mechanisms of organic nitrogen species in the atmosphere.

Nitrate pollution of the karstic groundwater is an increasingly serious problem with the development of Guiyang, the capital city of Guizhou Province, southwest China. The higher content of NO3- in groundwater compared to surface water during both summer and winter seasons indicates that the karstic groundwater system cannot easily recover once contaminated with nitrate. In order to assess the sources and conversion of nitrate in the groundwater of Guiyang, we analyzed the major ions, delta(15)N-NH4+, delta(15)N-NO3-, and delta(18)O-NO3- in surface and groundwater samples collected during both summer and winter seasons. The results show that nitrate is the major dominant species of nitrogen in most water samples and there is a big variation of nitrate sources in groundwater between winter and summer season, due to fast response of groundwater to rain or surface water in the karst area. Combined with information on NO3- /Cl-, the variations of the isotope values of nitrate in the groundwater show a mixing process of multiple sources of nitrate, especially in the summer season. Chemical fertilizer and nitrification of nitrogen-containing organic materials contribute nitrate to suburban groundwater, while the sewage effluents and denitrification mainly control the nitrate distribution in urban groundwater.

O acidification is typically caused by production of carbonic acid (H2CO3) through the dissolution of increasing atmospheric CO2, which adds to CO2 plus DIC (dissolved CO2, H2CO3, HCO3 −, and CO3 2−) produced in seawater by several processes including biological ones (primary production followed by respiration). Acidification can decrease the saturation states of carbonate minerals, which may considerably endanger the dynamics, structure and biodiversity of coral reefs and other marine calcifying organisms. The consequence is the decline in the early development stages of shellfish, coral reefs, or other marine calcifiers, with impacts on fertilization, sexual reproduction, cleavage, larval settlement, survival and growth, finally causing a substantial population decline. Decline in shellfish or coral reefs, which form the foundation of marine ecosystems, would markedly affect the whole food webs and marine population dynamics. Despite the apparent straightforwardness of such a scenario, the actual determination of the impact of atmospheric CO2 on seawater pH is a difficult task. This happens primarily because of the relatively small pH changes, unless very long time spans are taken into account. Moreover, pH modifications can also take place at a local scale because of several possible confounding factors, of which we will show the potential role of superoxide chemistry. Among additional causes for seawater pH variation, one is the acidification connected with eutrophication phenomena that have increased worldwide since the last few decades. Indeed, changes in land-use practices can induce the release of high amounts of nutrients and terrestrial organic matter (OM) to coastal seawaters, including dissolved OM (DOM) and particulate OM (POM). The transformation of organic P and N into phosphate and nitrate because of microbial or photochemical processes can cause a significant decrease of the alkalinity of coastal seawater and, therefore, a decrease in pH. Another possibility (although limited in space and time) is the elevated production of CO2 and DIC during harmful algal blooms, which can significantly alter the pH of seawater as long as they are operational. Eutrophication phenomena and algal blooms can both be enhanced by global warming, which causes an increase of surface seawater temperature and leads to a longer summer stratification period. In warm, sunlit surface seawater the photochemical and biological processes that are involved in the degradation of DOM and POM can be strongly enhanced, leading to increased production of CO2 and of anionic species that decrease the alkalinity of seawater. The third possible issue is connected with atmospheric acid rain, most notably involving HNO3 and H2SO4 that can directly lower the seawater pH. All such processes are usually limited to the coastal areas that are most affected by eutrophication phenomena, while acid rains are not expected to have a comparatively important impact on the pH of the open ocean. Within this context, an additional factor of potential importance is represented by the chemistry of superoxide. The radical ion O2 −• is produced by various sources including extracellular generation by heterotrophic bacteria that are commonly detected in lakes, soil, hydrothermal vents, marine sediments, estuaries, and oceans. Rates of superoxide production normalized to the proportion of metabolically active cells are found to vary between 0.02 ± 0.02 amol cell−1 hour−1 (mean ± standard error) and 19.4 ± 5.2 amol cell−1 hour−1. Such production rates could lead to an alteration of seawater pH because of H consumption upon dismutation of superoxide (2 O2 −• + 2H → H2O2 + O2). The latter process is catalyzed by redox-active metals such as Cu(I/II) and Fe(II/ III) and possibly (but still controversially) by organic compounds with redox-capable moieties. With a biological generation rate of O2 −• prudentially assumed to be 0.2 pmol dm−3 s−1, which is only 10% of that reported by Diaz et al., based on superoxide dismutation alone one can have a H consumption rate of ∼6 μmol dm−3 year−1. A simplified seawater model shows that the process would be able to compensate for an acidification rate of 0.1−0.3 pH units year−1 Viewpoint