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This article is an editorial that discusses the development and ecological functions of biological soil crusts (biocrusts). Biocrusts are composed of microorganisms and play important roles in soil stabilization, microbial diversity, and ecosystem development. The editorial emphasizes the need for further research on biocrust communities and their impact on landscape-scale outcomes. It also highlights the ecological functions of biocrusts, such as reducing erosion and influencing biogeochemical cycles. The article concludes by discussing the importance of understanding biocrusts for ecological restoration and land management strategies. Another document provides a list of references for articles related to biological soil crusts, covering topics such as land degradation neutrality, ecological restoration, and the impact of biocrusts on microbial communities. The articles also explore the composition and response of biocrusts to climate change and physical disturbance, as well as their effects on soil properties and metabolic response to hydration. [Extracted from the article]

Biological soil crusts (biocrusts) are complex communities of micro‐ and macro‐organisms dwelling at the soil surface in dryland regions worldwide, which contribute to important ecological functions in these areas. Biocrusts may reach different developmental stages, associated to autogenic succession of specific phototrophic organisms. However, notwithstanding the large amount of existing literature, little is known regarding the relationship between biocrust stages of development and soil nutrient dynamics. In this opinion paper, we specifically focused on soil nitrogen, and compared the total nitrogen content and potential nitrogenase activity of different developmental types of biocrust (‐covered) soils. Based on published reports, we looked at a possible relationship between nitrogen content at the soil surface and biocrust development, discussing the potential mechanisms leading to the observed soil nitrogen content heterogeneity. The results showed that a higher nitrogen content remained associated to the presence of moss‐dominated biocrusts, and this biocrust morphotype was characterized by a lower potential nitrogenase activity compared to the cyanobacteria‐ and/or lichen‐dominated biocrusts. We hypothesized that these seemingly contradictory findings might be attributed to three potential mechanisms: nitrogen inheritance, nutrient retention and nutrient transfer, which we hereby examined one by one. Altogether, our opinion supports the theory of biocrust succession from incipient cyanobacteria‐dominated stages to more 'mature' stages dominated by mosses. We stress how the heterogeneous distribution of soil nitrogen, which is closely related with biocrust development and community types, eventually affects regional and even global nitrogen dynamic and storage. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Summary: Biocrusts provide numerous ecological functions in drylands. Recovering biocrusts via cyanobacterial inoculation recently gathered interest for ecological restoration, yet it still lacks long‐term experiments to unravel biocrust community dynamics. To examine how cyanobacterial inoculants influenced local microbial community and biocrust development, we observed a 2 km2 (Qubqi Desert, China) inoculation experiment after 10 and 15 years, following biocrust formation. Our results revealed that biocrust development was in line with ecological regime shift, providing evidence for biocrust community succession, from cyanobacteria‐ to moss‐dominated types. Associated with biocrust development, microbial communities differed significantly with less specialists compared to shifting sands. Cyanobacterial community analysis showed that Microcoleus vaginatus and Scytonema javanicum are an ideal inoculating model, as they were still dominating the community after 15 years since inoculation, while other nitrogen‐fixing cyanobacteria occurred profusely with biocrust development. Biocrust community composition combined with thickness, Chl‐a and exopolysaccharide measurements revealed the large variation of cyanobacterial ecological functions along biocrust development, suggesting a main function shift: from carbon fixation associated with exopolysaccharide secretion in bare sandy soils to nitrogen fixation in developed biocrusts. This large‐scale field study verifies that cyanobacterial inoculation accelerates biocrust development and forwards succession, shaping the biocrust community composition over a long time. [ABSTRACT FROM AUTHOR]

Summary: Cyanobacteria, as key biocrust components, provide a variety of ecosystem functions in drylands. In this study, to identify whether a cyanobacterial community shift is involved in biocrust succession and whether this is linked to altered ecological functions, we investigated cyanobacterial composition, total carbon and nitrogen contents of biocrusts in the Gurbantunggut Desert. Our findings showed that the biocrust cyanobacteria in the Gurbantunggut desert were mostly filamentous, coexisting with abundant unicellular colonial Chroococcidiopsis. Heterocystous Nostoc, Scytonema and Tolypothrix always represented the majority of biocrust nitrogen‐fixing organisms, comprising an average of 92% of the nifH gene reads. Community analysis showed a clear shift in prokaryotic community composition associated with biocrust succession from cyanobacteria‐ to lichen‐ and moss‐dominated biocrusts, and filamentous non‐nitrogen‐fixing cyanobacteria‐dominated communities were gradually replaced by nitrogen‐fixing and unicellular colonial communities. Along the succession, there were concomitant reductions in cyanobacterial relative abundance, whereas Chl‐a, total carbon and nitrogen contents increased. Concurrently, distinct carbon and nitrogen stores shifts occurred, implying that the main ecological contribution of cyanobacteria in biocrusts changes from carbon‐ to nitrogen‐fixation along with the succession. Our results suggest that any activity that reverses biocrust succession will influence cyanobacterial community composition and eventually lead to large reductions in soil carbon and nitrogen stores. [ABSTRACT FROM AUTHOR]

The successional ecology of nitrogen cycling in biocrusts and the linkages to ecosystem processes remains unclear. To explore this, four successional stages of natural biocrust with five batches of repeated sampling and three developmental stages of simulated biocrust were studied using relative and absolute quantified multi-omics methods. A consistent pattern across all biocrust was found where ammonium assimilation, mineralization, dissimilatory nitrite to ammonium (DNiRA), and assimilatory nitrate to ammonium were abundant, while denitrification medium, N-fixation, and ammonia oxidation were low. Mathematic analysis showed that the nitrogen cycle in natural biocrust was driven by dissolved organic N and NO3–. pH and SO42– were the strongest variables affecting denitrification, while C:(N:P) was the strongest variable affecting N-fixation, DNiRA, nitrite oxidation, and dissimilatory nitrate to nitrite. Furthermore, N-fixation and DNiRA were closely related to elemental stoichiometry and redox balance, while assimilatory nitrite to ammonium (ANiRA) and mineralization were related to hydrological cycles. Together with the absolute quantification and network models, our results suggest that responsive ANiRA and mineralization decreased during biocrust succession; whereas central respiratory DNiRA, the final step of denitrification, and the complexity and interaction of the whole nitrogen cycle network increased. Therefore, our study stresses the changing environmental functions in the biocrust N-cycle, which are succession-dependent. [ABSTRACT FROM AUTHOR]

As an important successional stage and main type of biological soil crusts (BSCs) in Shapotou region of China (southeastern edge of Tengger Desert), lichen soil crusts (LSCs) often suffer from many stresses, such as desiccation and excess light intensity. In this study, the chlorophyll fluorescence and CO2 exchange in the rehydrated LSCs were detected under a series of photosynthetically active radiation (PAR) gradients to study the photosynthetic acclimation of LSCs. The results showed that although desiccation leaded to the loss of photosynthetic activity in LSCs, the fluorescence parameters including Fo, Fv and Fv/Fm of LSCs could be well recovered after rehydration. After the recovery of photosynthetic activity, the effective photosynthetic efficiency ΦPSII detected by Imaging PAM had declined to nearly 0 within both the lichen thallus upper and lower layers when the PAR increased to 200 μE m-2 s-1, however the net photosynthesis detected by the CO2 gas analyzer in the LSCs still appeared when the PAR increased to 1000 μE m-2 s-1. Our results indicate that LSCs acclimating to high PAR, on the one hand is ascribed to the special structure in crust lichens, making the incident light into the lichen thallus be weakened; on the other hand the massive accumulation of photosynthetic pigments in LSCs also provides a protective barrier for the photosynthetic organisms against radiation damage. Furthermore, the excessive light energy absorbed by crust lichens is also possibly dissipated by the increasing non-photochemical quenching, therefore to some extent providing some protection for LSCs. [ABSTRACT FROM AUTHOR]

Abstract: Lichen soil crusts (LSCs) are an important stage during the development of biological soil crusts (BSCs). The photosynthetic characteristics of this stage are determined by both of the symbiotic and free-living cyanobacteria and algae in the crusts. In this study, the recovery rate, extent, pattern of chlorophyll fluorescence and CO2 exchange in LSCs were detected after rehydration under different water contents (5%, 20% and 40%). The results showed that original fluorescence (Fo) of each group increased dramatically after rehydration and then reached a plateau to steady state; however both maximum quantum efficiency of PS II photochemistry (Fv/Fm) and the ratio of variable fluorescence at different recovery time to the maximal value during the recovery period (Fv/FvMax) showed a similar and corresponding “three steps” recovery pattern. At the end of experiment, Fv/Fm of 20% water content group recovered to the highest level (0.45), although no obvious difference in the Fv/Fm was found among the three water content groups within the first 4 h. Additionally, after the rehydration CO2 release from LSCs (under the light) gradually decreased, and the organic carbon accumulation first occurred in 40% water content group, in which a higher CO2 assimilation rate was also observed. The obvious inconsistency between chlorophyll fluorescence detection and CO2 exchange analysis is considered to be the result of the special structure and photosynthetic characteristics of LSCs. [Copyright &y& Elsevier]

Abstract: In order to estimate the biomass of photoautotrophic organisms in biological soil crusts (BSCs), based on the extraction and determination of phytoplanktonic chlorophyll-a (Chl-a) in aquatic ecosystems, this paper comparatively studied the Chl-a extraction efficiencies in ethanol, acetone, N, N -dimethyl -formamide (DMF) and dimethyl sulphoxide (DMSO) from algae, lichen, and moss crusts, analyzed the effects of dominant organisms or development degree of BSCs, mass of sample, and soil characteristics on the extraction efficiency. The results showed that the extraction efficiencies of different organic solvents were significantly different, and such efficiencies declined with the increase of mass of sample. DMSO resulted in the greatest extraction efficiency, but was not suitable for lichen crusts; DMF strongly underestimated the Chl-a content of man-made crusts relative to the other extractants, and was particularly affected by interfering pigments from the well-developed crusts. Generally, the extraction efficiency of ethanol was greater than that of acetone, and ethanol method showed the greatest stability compared with other 3 solvents. In addition, Chl-a content showed an increasing trend with the succession of BSCs when it was expressed on an areal basis. On the basis of this and related experiments we suggest Chl-a content of BSCs be extracted by ethanol and expressed on an areal basis. [Copyright &y& Elsevier]

• Both room and low temperature storage didn't cause a major change in biocrust community. • Distinct microbial communities could be clearly identified using one month-stored biocrusts. • Biocrust development had little influence on the selection of sample storage methods. • Dry sample storage provides an effective method for microbial preservation of biocrusts. Microbial communities within biocrusts fulfill important ecological functions, particularly in dryland environments. Identifying the optimal conditions for transporting and storing biocrusts is essential to preserve and accurately analyze their microbial communities. However, the effectiveness of these preservation methods remains poorly understood. In this study, we collected dry biocrusts at different developmental stages (shifting sand, cyanobacteria-dominated, and moss-dominated) from the Qbuqi Desert in northern China. We examined the effects of different storage conditions, i.e. at room temperature (25 ± 2 °C) and low temperature (4 °C and −80 °C) over one month on the microbial community characteristics, including species composition, abundance and diversity. Our findings demonstrated that microbial community differences among the biocrust developmental stages were maintained even after one month of storage at room temperature. Compared to the control (analyzed immediately after sampling), storing biocrusts at 25 °C and 4 °C did not significantly alter biocrust assemblages, whereas storage at −80 °C increased the estimated gene copy number of Proteobacteria in cyanobacteria-dominated biocrusts. Furthermore, our results suggest that biocrust developmental stage and microbial community composition had minimal impact on the effectiveness of different storage methods, though caution should be kept for the prokaryotic communities. Overall, we recommend storing dry-collected biocrusts at room temperature as an effective and economic method for preserving microbial communities, particularly for DNA-based microbial studies from dryland soils with frequent monitoring of biocrust development at remote areas. [ABSTRACT FROM AUTHOR]

Realizing the reasonable allocation of resources is possible to solve the dual problems of resources and environment. Therefore, in this study desert cyanobacterium Scytonema javanicum was cultivated in artificial synthetic wastewater to explore the feasibility of nutrient transferring from wastewater to desert. After inoculation, S. javanicum grew well in the wastewater; nitrogen and phosphorus were gradually removed from the wastewater. In general, cyanobacterial biomass, exopolysaccharide content, COD, nitrogen and phosphorus contents were all significantly affected by the cultivation time, wastewater dilution treatment and their interaction ( P < 0.001). Comprehensively considering the producing period, biomass accumulation and nutrient removal efficiency, cultivation time of cyanobacterium S. javanicum in the synthetic wastewater should be controlled around 20 days, with wastewater dilution ratio at 1:1. Conclusively, desert cyanobacterium S. javanicum is a promising species for nutrient transferring from wastewater to desert, and its maximum biomass yield could reach 3.91 mg Chl- a L −1 in the synthetic wastewater. [ABSTRACT FROM AUTHOR]