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As the critical ecological engineers, biological soil crusts (biocrusts) are considered to play essential roles in improving substrate conditions during ecological rehabilitation processes. Physical disturbance, however, often leads to the degradation of biocrusts, and it remains unclear how the physical disturbance affects biocrust microorganisms and their related metabolism. In this study, the photosynthetic biomass (indicated by chlorophyll a), nutrients, enzyme activities, and bacterial communities of biocrusts were investigated in a gold mine tailing of Central China to evaluate the impact of physical disturbance on biocrusts during the rehabilitation process of gold mine tailings. The results show that physical disturbance significantly reduced the photosynthetic biomass, nutrient contents (organic carbon, ammonium nitrogen, nitrate nitrogen, and total phosphorus), and enzyme activities (β-glucosidase, sucrase, nitrogenase, neutral phosphatase, and urease) of biocrusts in the mine tailings. Furthermore, 16S rDNA sequencing showed that physical disturbance strongly changed the composition, structure, and interactions of the bacterial community, leading to a shift from a cyanobacteria dominated community to a heterotrophic bacteria (proteobacteria, actinobacteria, and acidobacteria) dominated community and a more complex bacterial network (higher complexity, nodes, and edges). Altogether, our results show that the biocrusts dominated by cyanobacteria could also develop in the tailings of humid region, and the dominants (e.g., Microcoleus) were the same as those from dryland biocrusts; nevertheless, physical disturbance significantly reduced cyanobacterial relative abundance in biocrusts. Based on our findings, we propose the future work on cyanobacterial inoculation (e.g., Microcoleus), which is expected to promote substrate metabolism and accumulation, ultimately accelerating the development of biocrusts and the subsequent ecological restoration of tailings.

BACKGROUND With the rapid development of society, a large amount of wastewater and pesticides enter the water bodies globally, posing a threat to both the environment and the health of people and other living things. In this paper, an algal strain Scenedesmus sp. was isolated from a municipal wastewater treatment plant (WWTP); its interaction effect with wastewater bacteria on the removal of IMI and conventional pollutants in municipal wastewater was evaluated. RESULTS In this study, an algae‐bacteria system was constructed with municipal wastewater, with the aim of exploring the removal effects and mechanisms of the consortium system on Imidacloprid (IMI, 20 mg L−1 and 60 mg L−1) and conventional nutrients from municipal wastewater. The results showed that no IMI was removed under 20 μmol m−2 s−1. However, under 60 μmol m−2 s−1, more than 90% of IMI was removed in the algae‐wastewater group (AWG) with Scenedesmus sp.; this value is much higher than the 50.4% (20 mg L−1) and 36.1% (60 mg L−1) achieved by the wastewater group (WG) without Scenedesmus sp. Meanwhile, the removal efficiency of nitrogen was 82.3% (20 mg L−1) and 71.9% (60 mg L−1) in AWG, both of which are higher than the 73.4% and 59.1% in WG, respectively. Moreover, Scenedesmus sp. TXH has a strong resistance to IMI and 4 degradation products (including IMI‐urea, 4(5)‐hydroxy‐IMI, Nitrosimine, and a substance with m/z of 176) were found in AWG. CONCLUSION Using consortium to treat municipal wastewater containing IMI is an effective and safe way. © 2022 Society of Chemical Industry (SCI).

BackgroundRecently, it has been found that nitrogen (N) deposition could strongly affect the spatial pattern of biocrusts by reducing their cover. However, as the key cementing materials in the formation and stabilization of biocrusts, little has been known about the response of exopolysaccharides (EPS) excreted by cyanobacteria in biocrusts to N deposition. MethodThree N sources nitrate nitrogen (NN), ammonia nitrogen (AN), urea nitrogen (UN) with three gradients (2 mg/g, 4 mg/g, 8 mg/g) were set to evaluate the effects of N addition on the growth of biocrusts. ResultsOur results showed that AN and UN (2-4 mg/g) both strongly decreased the cyanobacterial biomass in biocrusts, indicated by chlorophyll-a and 16s rDNA gene copy-number. The results also suggested that although medium and high NN (4-8 mg/g) inhibited the growth of dominant cyanobacteria (Microcoleus vaginatus) in biocrusts, they promoted other cyanobacterial growth. High-throughput sequencing results suggested N increased the α-biodiversity of biocrusts, and bacterial community shifted from more Cyanobacteria to more Proteobacteria and Actinobacteria, especially driven by AN and UN. Notably, EPS was signi cantly reduced after high-N addition, and the co-reduction of cyanobacterial biomass and EPS would affect the stabilization of early-stage biocrusts. Meanwhile, the reduced proportion of Rhamnose and Fucose in EPSs may further reduce the adhesion of EPS to soil. ConclusionThese ndings improve our understanding of biocrusts' responses to N deposition. Considering the importance of cyanobacteria and EPS in biocrusts, cyanobacterial biocrust coverage may face more serious challenges with the continuous increasing N deposition in drylands.

Background Recently, it has been found that nitrogen (N) deposition could strongly affect the spatial pattern of biocrusts by reducing their cover. However, as the key cementing materials in the formation and stabilization of biocrusts, little has been known about the response of exopolysaccharides (EPS) excreted by cyanobacteria in biocrusts to N deposition. Method Three N sources nitrate nitrogen (NN), ammonia nitrogen (AN), urea nitrogen (UN) with three gradients (2 mg/g, 4 mg/g, 8 mg/g) were set to evaluate the effects of N addition on the growth of biocrusts. Results Our results showed that AN and UN (2–4 mg/g) both strongly decreased the cyanobacterial biomass in biocrusts, indicated by chlorophyll-a and 16s rDNA gene copy-number. The results also suggested that although medium and high NN (4–8 mg/g) inhibited the growth of dominant cyanobacteria (Microcoleus vaginatus) in biocrusts, they promoted other cyanobacterial growth. High-throughput sequencing results suggested N increased the α-biodiversity of biocrusts, and bacterial community shifted from more Cyanobacteria to more Proteobacteria and Actinobacteria, especially driven by AN and UN. Notably, EPS was significantly reduced after high-N addition, and the co-reduction of cyanobacterial biomass and EPS would affect the stabilization of early-stage biocrusts. Meanwhile, the reduced proportion of Rhamnose and Fucose in EPSs may further reduce the adhesion of EPS to soil. Conclusion These findings improve our understanding of biocrusts' responses to N deposition. Considering the importance of cyanobacteria and EPS in biocrusts, cyanobacterial biocrust coverage may face more serious challenges with the continuous increasing N deposition in drylands.

Microcoleus vaginatus has been regarded as the important contributor for biocrust formation and ecological services. However, little is known about its living forms in biocrusts, and whether the living form is related to biocrust structure and ecological functions. Therefore, in this study, natural biocrusts collected from the Gurbantunggut Desert were divided into different aggregate/grain fractions, aiming at investigating the living forms of M. vaginatus in biocrusts at fine scale, and exploring its roles in aggregate structure and ecological functions of biocrusts. The results showed that two distinct living forms of M. vaginatus had been identified from the biocrusts. The non-bundling M. vaginatus was mainly distributed in the fractions of > 0.5 mm, forming aggregate structure by cementing sand particles firmly; while the bundling M. vaginatus, distributed mainly among the free sand particles with diameter < 0.5 mm, hardly bound soil particles to form aggregate structure. Furthermore, the aggregate structure formed by non-bundling M. vaginatus supported a higher biomass, nutrient contents, and enzyme activities. Altogether, our results suggest that the strong migrating ability of bundling M. vaginatus contributes to the environmental adaptation and light resource acquirement, while non-bundling M. vaginatus acts as the constructor of the aggregate structure in biocrusts.

Cyanobacterial exopolysaccharides (EPS) accumulated during microalgal cultivation have significant application potential in antioxidation, pharmaceutical products, and so on. Inoculation concentration strongly affects the cultivation cost, biomass, and EPS accumulation. In this study, a high‐EPS‐excreted desert cyanobacterium Microcoleus vaginatus was isolated, and the effects of inoculation concentration on biomass, photosynthetic activity, and EPS accumulation were explored. The results showed that the original fluorescence (Fo) provided a good indication to cyanobacterial biomass, when Chl‐a concentration was lower than 10 mg L−1. Inoculation concentration significantly affected cyanobacterial biomass and EPS concentration (P < 0.001), whereas did not affect photosynthetic activity (Fv/Fm; P > 0.05). The two fractions of EPS, capsular exopolysaccharides (CPS) and released exopolysaccharides (RPS) were strongly affect by inoculation concentration. Other than forming thick sheath (CPS) surrounded the filaments, M. vaginatus excreted higher proportions of RPS to culture medium, and the ratio of RPS to CPS ranged from 1.08 to 1.58 depending on the inoculation concentration. Additionally, although the biomass and EPS accumulation increased with inoculation concentration, the increasing inoculation concentration did not bring to the proportionate increase of the final biomass and EPS yield. Altogether, comprehensively considering the EPS yield and productivity, inoculation concentration of 0.04 mg Chl‐a L−1 is recommended for M. vaginatus to produce EPS, with an EPS yield of 94.32 mg L−1 and EPS productivity of 184.86 mg (mg Chl‐a)−1 L−1 d−1 at the end of experiment.