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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]

In dryland regions, biological soil crusts (BSCs) have numerous important ecosystem functions. Crust species and functions are, however, highly spatially heterogeneous and remain poorly understood at a range of scales. In this study, chlorophyll fluorescence imaging was used to quantify millimeter-scale patterns in the distribution and activity of photosynthetic organisms in BSCs of different successional stages (including cyanobacterial, lichen, moss three main successional stages and three intermixed transitional stages) from the Tengger Desert, China. Chlorophyll fluorescence images derived from the Imaging PAM (Pulse Amplitude Modulation) showed that with the succession from cyanobacterial to lichen and to moss crusts, crust photosynthetic efficiency (including the maximum and effective photosynthetic efficiency, respectively) and fluorescence coverage increased significantly (P < 0.05), and that increasing photosynthetically active radiation (PAR) reduced the effective photosynthetic efficiency (Yield). The distribution of photosynthetic organisms in crusts determined Fv/Fm (ratio of variable fluorescence to maximum fluorescence) frequency pattern, although the photosynthetic heterogeneity (SHI index) was not significantly different (P > 0.05) between cyanobacterial and moss crusts, and showed a unimodal pattern of Fv/Fm values. In contrast, photosynthetic heterogeneity was significantly higher in lichen, cyanobacteria-moss and lichen-moss crusts (P < 0.05), with a bimodal pattern of Fv/Fm values. Point pattern analysis showed that the distribution pattern of chlorophyll fluorescence varied at different spatial scales and also among the different crust types. These new results provide a detailed (millimeter-scale) insight into crust photosynthetic mechanisms and spatial distribution patterns associated with their community types. Collectively, this information provides an improved theoretical basis for crust maintenance and management in dryland regions. [ABSTRACT FROM AUTHOR]

With the continuing consumption of resources and increasingly prominent environmental issues, microalgal resource utilization has received extensive attention. In this study, based on the microalgal investigation in desert biological soil crusts (BSCs) using pyrosequencing technology, the cultivated crust microalgae were further isolated in order to obtain high quality microalgae for resource utilization. The results showed that with crust development and succession, microalgal diversity gradually decreased, including the number of operational taxonomic units (OTUs) and genus, although Microcoleus always was the dominant genera. Pyrosequencing obtained 630 OTUs of cyanobacteria, 25 OTUs of green algae and 9 OTUs of diatom; however, part of cultivated microalgae still could not yet be detected due to the DNA extraction preferences and errors caused by PCR amplification. After isolation, four strains were purified and cultivated, including two filamentous cyanobacteria Microcoleus vaginatus BSC-06 and Scytonema javanicum BSC-39, and two unicellular green algae Chlorella sp. BSC-24 and Monoraphidium dybowskii BSC-81. The two green algae grew fast (>250 mg L -1  d -1 ), and achieved high lipid productivity up to 75–85 mg L -1  d -1 , with lipid content of 28.7–39.0%, thus was considered as promising feedstock for biodiesel production. In addition, the two crust cyanobacteria could be used to construct artificial cyanobacterial soil crusts in desertification control, although their biomass accumulation was not as high as that in the green algae. Ultimately, combining biodiesel production with desertification control would not only improve desert environments, but also provide ideal places for the local microalgal resource exploitation, further promoting desert socioeconomic development. [ABSTRACT FROM AUTHOR]

Non-rainfall water (NRW), as the most frequent water source of drylands, is significantly boosted by biocrusts. However, the mechanism of biocrustal promotion and utilization of NRW have been little studied. In this paper, the NRW accumulation patterns, photosynthetic activities and CO 2 exchange of different biocrusts (2 cyanobacteria crusts-ACs, 1 cyanolichen crust-LC1, 1 green algae lichen crust-LC2, and 1 moss crust-MC) under NRW were studied through in situ mesocosm experiments in the Hobq Desert of China during the autumns of 2014 and 2015. Structural equation models showed that crustal properties feedback affected the degree of meteorological parameters on NRW accumulation, in which the effect of surface temperature gradually decreased with the development of biocrusts while that of subsoil temperature and light intensity increased. As for the sources, ca. 50% of NRW in ACs derived from subsoil but more than 78% from atmosphere in LCs and MC, and this pattern was obviously influenced by the recovery degree of photosynthetic activity. But the diel maximum NRW (NRW max ) were mainly determined by crust thickness, photoautotroph biomass and other properties. During NRW accumulation, the recovery of photosynthetic activity in ACs was the earliest, followed by that of LC2 and MC, LC1 never recovered. Whereas, the initial CO 2 exchange of ACs and MC were often earlier than that of LC2, and the minimum diel NRW max required by ACs, LC2, and MC to maintain carbon balance were ca. 0.08, 0.17, and 0.20 mm, respectively. Thus we proposed the application boundary of inoculation-based technology in drylands is the areas where the diel NRW max exceed or equal 0.08 mm and carbon input under NRW last more than 2 h during NRW-abundant seasons. [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]

[Display omitted] • Biocrust cyanobacteria efficiently transferred over 90% of nutrients from the wastewater. • S. javanicum exhibited 13.4- to 17.9-fold higher biomass, while M. vaginatus produced 28.4–81.3 % more EPS. • The presence of indigenous microbes in the wastewater did not affect cyanobacterial performance. • A robust nutrient recycling strategy from wastewater to desert was developed. Wastewater is rich in nutrients, while desert regions often suffer from severe nutrient shortages, potentially leading to eutrophication and desertification in respective landscapes. Cyanobacterial cultivation emerges as a promising solution by extracting nutrients from wastewater and transferring them to deserts using cyanobacteria-induced biocrust technology. In this study, two biocrust inducing cyanobacteria, Microcoleus vaginatus and Scytonema javanicum were cultivated in synthetic and municipal wastewater, respectively, to assess their capabilities of nutrient removal and biocrust induction. Both cyanobacteria demonstrated effective removal of nitrogen and phosphorus from either synthetic or municipal wastewater, achieving removal rates exceeding 90 %. Sterilization experiments on the municipal wastewater confirmed that indigenous microorganisms did not influence cyanobacterial performance, though the two cyanobacteira exhibited contrasting growth and metabolic behaviors. Specifically, S. javanicum achieved higher biomass accumulation, reaching up to 6.05 ± 0.87 mg Chl- a L−1, whereas M. vaginatus produced more exopolysaccharides, up to 40.98 ± 2.96 mg L−1 in the municipal wastewater. The cyanobacteria harvested from the municipal wastewater effectively promoted biocrust formation, validating the feasibility of transferring nutrients from wastewater to deserts through cyanobacteria-induced biocrusts. Considering their varied growth behaviors, our findings advocate for the use of a combination of diverse cyanobacteria strains to optimize cultivation and inoculation technologies. [ABSTRACT FROM AUTHOR]

Cyanobacterial inoculation is a promising technology that can induce biocrust development, for stabilizing degraded soils in dryland environments. However, it is challenging to grow cyanobacteria in dry, saline soils, which limits the application of this technology. In this study, NaCl was added into field-collected induced biocrusts to investigate how salt affects the biocrust community. This fundamental knowledge improves our assessment of microbial salinity preference and adaptation, and can guide researchers to select the appropriate cyanobacterial inoculants for saline soil restoration. The results showed that the biocrusts induced by inoculating Microcoleus vaginatus and Scytonema javanicum could survive 1.0% salinity, although both salt and drought stresses significantly inhibited microbial biomass and metabolism (P < 0.05), and salinity led to an obvious shift in microbial community structure. Compared to salt stress, drought seems to provide a vital ecological protection for the biocrusts, allowing them to be active only under relative low salinity after hydration. In the induced biocrusts, cyanobacteria were always the dominant organisms (even 18 years since inoculation), whereas under elevated salinity, cyanobacterial communities with lower relative abundance had a higher survival percentage of M. steenstrupii and Phormidium sp. Altogether, our results showed that both prokaryotic and eukaryotic communities have obvious salinity preference in the cyanobacteria-induced biocrusts. These results suggest that cyanobacterial inoculation strategies can be adapted in response to the soil salinity conditions. Furthermore, a combined inoculation of M. steenstrupii and Phormidium sp. appears to be favorable approach that is expected to improve cyanobacterial inoculation technology in saline soils. [Display omitted] • M. vaginatus and S. javanicum effectively promoted biocrust formation and development. • Both biocrust prokaryotic and eukaryotic communities have obvious salinity preference. • Drought provides vital ecological protection for biocrust microorganisms against salt stress. • M. steenstrupii and Phormidium sp have the relative higher salt tolerance capacity. • An alternative approach for improving cyanobacteria inoculation for saline soils is suggested. [ABSTRACT FROM AUTHOR]

• Biocrust hydration led to a large and immediate increase in soil CO 2 flux. • Hydration initiates photosynthesis in some, but not all biocrusts. • Biocrusts are highly spatially variable at both landscape and small scales. Soil biocrusts, formed from communities of microbes and their extracellular products are a common feature of dryland soil surfaces. Biocrust organisms are only intermittently metabolically active, but due to their ubiquity they make a significant contribution to the carbon cycle. Quantification of the controls and insights into the interlinked process of photosynthesis and respiration are essential to enhancing our understanding of the carbon cycle in the world's drylands. Yet, there have been relatively few field studies investigating controls on both biocrust photosynthesis and respiration. We undertook field-based experiments at two dune sites during the dry season in Diamantina National Park in Queensland, Australia to determine how biocrust hydration and illumination affect soil CO 2 flux and photosynthesis. Static chambers and an infra-red gas analyser were used to quantify soil CO 2 flux, and a fluorometer and a CFImager were used to determine a range of photosynthetic parameters in the field and laboratory respectively. When dry, biocrust photosynthetic activity was not detected and soil CO 2 flux was very low irrespective of biocrust cover. Hydration led to a large and immediate increase in CO 2 flux, which was more pronounced in the presence of biocrusts and on the dune with thinner biocrusts. Hydration also initiated the onset of photosynthesis in some biocrusts, which was greatest under low light conditions and sustained with further hydration. There were only infrequent periods of net CO 2 uptake to the soil, occurring when CO 2 uptake due to photosynthetic activity was less than background soil CO 2 flux. Chlorophyll fluorescence imaging indicated biocrust spatial heterogeneity was evident at the cm scale where microtopography creates a myriad of environments for different crust organisms. Our findings demonstrate that biocrusts are highly spatially heterogenetic at both landscape and small scale, which suggests the maintenance of biocrust spatial diversity is likely to be key to imparting resilience to changing climate and disturbance. As well as reaffirming the importance of biocrusts for the carbon cycle in dryland dune soils the study demonstrates that biocrust respiration and photosynthesis respond differently to hydration and shading. This adds an unpredictability to the distribution of soil carbon stocks and the gaseous exchanges of CO 2 between the surface and atmosphere. Future changes to precipitation and increased temperatures are likely to reduce soil moisture across much of the Australian interior and consequently biocrusts may experience a decline in biomass, structure, and function which could have significant repercussions beyond carbon stocks. [ABSTRACT FROM AUTHOR]