Search

Core subcommunity represents the less diversity but high abundance, while indicative subcommunity is highly diverse but low abundance in soils. The core subcommunity fundamentally maintains ecosystem stability, while the indicative plays important roles in vital ecosystem functions and is more sensitive to environmental change. However, their environmental driving factors and responses to human disturbances remain less defined. Herein, we explored the patterns of core and indicative soil microbes and their responses to animal grazing in dry grasslands across the Tibetan Plateau, using the Illumina sequencing of 16S rRNA gene. The results revealed that the core subcommunity diversity and richness were lower than the indicative in soils. The indicative subcommunity diversity exhibited substantially stronger correlations with nutrient-associated factors than the core diversity, including soil organic carbon, nitrogen and plant biomass. The core and indicative microbial subcommunities both strongly varied with grassland ecosystems, while the latter was also significantly influenced by grazing. The variation partitioning analysis revealed that indicative microbial subcommunity was explained less by environmental factors than core subcommunity (34.5% vs 73.0%), but more influenced by grazing (2.6% vs 0.1%). Our findings demonstrated that the indicative microbes were particularly sensitive to soil nutrient-associated factors and human disturbances in alpine dry grasslands.

The occurrence of harmful algae blooms has been increasing in large lakes worldwide. The mechanism of heavy metals mobilization in sediments during algae blooms is not well understood. As a major pollutant in the sediments of Taihu Lake, cobalt (Co) has been selected to study heavy metal mobilization during algae blooms. Rhizon and HR-Peeper sampling techniques have been used for in situ investigation and indoor simulation experiments to collect information on dissolved Co, manganese (Mn), and UV absorbance at 254 nm (UV254) in sediments. Excitation–emission matrix (EEM) was combined with parallel factor (PARAFAC) to determine the change of dissolved organic matter (DOM) components during algae blooms. The chemical morphology of Co in pore water was analyzed by visual MINTEQ model. The Stern–Volmer model was used to characterize the stability of different DOM components and Co(II). Algae blooms significantly increased the dissolved Co concentration in sediments. The release of Co was closely related to DOM in the algae bloom sediments, which was reflected by the similar distribution and significant positive correlation between the dissolved Co and DOM in pore water, during both in situ and laboratory simulation algae blooms experiments. On the other hand, the saturation of oxygen in the sediment–water interface (SWI) rapidly decreased from 100 to 0% during algae blooms, resulting in high mobilization of Co and reduction of Mn oxides in sediments. This was supported by the simultaneous increase of dissolved Co and Mn and significant positive correlation between dissolved Co and Mn in the simulation aerobic–anaerobic sediments. The transformation of most Co(II) into DOM-Co(II) complexes, as calculated by the Visual MINTEQ model, further demonstrated that the mobilization of Co was mainly controlled by the DOM content in the sediments during algae blooms. Further studies revealed that tyrosine-like substance released by algae played a major role in their complexation with Co, possibly due to their relatively high content and high stability after binding Co. The mobilization of Co in sediments during algae blooms was mainly controlled by DOM through complexation, reflected by the observation that dissolved Co concentration and UV254 increased simultaneously and had significant positive correlation during in situ monitoring and indoor simulations experiments. More than 80% of dissolved Co in the pore water during algae blooms was DOM-Co complexes, supporting this conclusion. It was further observed that tyrosine-like substances played an important role in Co complexation.

Lake eutrophication and algal blooms may result in the mortality of macrozoobenthos. However, it is still not clear how macrozoobenthos decomposition affect phosphorus (P) mobility in sediments. High-resolution dialysis (HR-Peeper) and the diffusive gradients in thin films (DGT) technique were used in this study to assess the dissolved organic matter (DOM), dissolved/DGT-labile iron (Fe), P, and sulfur (S(–II)) profiles at a millimeter resolution. The decomposition of Bellamya aeruginosa significantly increased the internal loading of sediments P. The Fe(III) and sulfate were reduced under anaerobic conditions and promoted P desorption from sediments. This was supported by the significant increase in DGT-labile S(–II) and dissolved/DGT-labile P, Fe(II) and the significant positive correlation between Fe and P on day 8. The simultaneous increase in DOM and soluble reactive phosphorus (SRP) and the significant positive relationship between these factors were observed during the decomposition of B. aeruginosa. This suggested that complexation of DOM with metals may promotes the release of P from sediments.

Eutrophication and metal pollution are global environmental problems. The risk of metal pollution is high in the eutrophic lakes because of high mobility of metal in sediments. However, the mechanism of cadmium (Cd) mobility in sediments is still unclear. Here we study the mobilization of Cd in sediments from the eutrophic Lake Taihu via monthly field monitoring of mobile Cd using diffusive gradient in thin films (DGT) and high resolution dialysis (HR-Peeper) techniques. We found a high mobility of Cd in sediments in February and March, resulting from reductive dissolution of Mn oxide mediation by high microbial activities, as shown by the similarities in distribution patterns of DGT-labile Cd and Mn. A two orders of magnitude increase in dissolved Cd concentrations (about 28 μg L−1) was observed in May and June, with dissolved Cd concentrations in overlying water about 110 times higher than the criteria continuous concentration set by Environmental Protection Agency. Hourly changes were found to coincide and correlate between dissolved Cd and dissolved organic matter (DOM) under simulated anaerobic conditions, strongly suggesting that the sudden outbreak of Cd pollution observed in the field resulted from the complexation of DOM with Cd in sediments. This was further supported by the NICA-Donnan model that more than 71% of dissolved Cd in the pore water in May and June was present as Cd-DOM complexes. Three components of DOM including humic-, tryptophan-, and tyrosine-like components in the sediments in June was identified using the fluorescence excitation emission matrix-parallel factor analysis. We found that Cd was stable complexed with tyrosine-like component. The Fourier transform infrared and two-dimensional correlation spectroscopy further revealed that Cd was bound to phenolic O H, alkene C C, alcoholic C O, aromatic C H, and alkene CH groups. Our study effectively promotes the understanding of Cd mobilization in sediments and highlights the risk of sudden Cd pollution events in the eutrophic lakes.