Development Of Biological Soil Crusts Research Articles

Dam construction accelerated the development of biological soil crusts in degraded soil patches in the Lhasa River basin, Qinghai-Tibetan Plateau

The Lhasa River Basin currently faces severe land degradation. In recent years, several dams have been built on the main stream, whereas, their impact on land desertification remains less elucidated. Herein, we investigated variances of soil properties and microbial communities in biological soil crusts (BSCs) along the valley area of Lhasa River and the mountain slope (altitude gradient) in reservoir area after five years of dam construction. Soil nutrient and water contents, enzyme activities, and N-cycle related functional gene copies significantly increased in reservoir-affected areas and decreased with the increase of mountain slope altitude and the distance away from the reservoir, which were usually degraded soil patches; similarly, the relative abundance of bacteria, fungi and moss in BSCs significantly increased in reservoir-affected areas, whilst that of cyanobacteria was higher in degraded soil patches. The linear and structural equation models also showed that dam construction altered water distribution status of soil surface, which enhanced soil properties, N-cycle and increased the relative abundance of moss of BSCs, and successfully accelerated the development and succession of BSCs in degraded soil. This study firstly reported that dam construction could accelerate the succession process of degraded soil in the reservoir affected area and thus a reference for ecological restoration of desertification soil of the Lhasa River Basin in QTP.

Role of an arbuscular mycorrhizal fungus in vegetation restoration as indicated by bacterial diversity and microbial metabolic limitation in soil underlying moss biocrusts

Arbuscular mycorrhizal (AM) fungi contribute to the revegetation of degraded ecosystems such as coal mining areas and may indirectly affect the development of biological soil crusts (biocrusts). However, bacterial diversity and microbial nutrient cycling in the soil underlying biocrusts are seldom considered when assessing ecological restoration effects. Bacterial community composition was quantified and compared using 16S rRNA gene sequencing, metabolic limitation of microbes via extracellular enzymatic stoichiometry and their association with carbon use efficiency (CUE) in soil underlying moss biocrusts in vegetated areas inoculated with an AM fungus or uninoculated and in uninoculated unvegetated areas. The AM fungal inoculum significantly influenced bacterial community composition and diversity, extracellular enzyme activities and CUE in soil underlying moss biocrusts mainly by affecting soil nutrients. Correlation analysis revealed that Actinobacteria, Armatimonadetes, Bacteroidetes, Chlorobi, Cyanobacteria, Saccharibacteria, and Verrucomicrobia were positively correlated with soil nutrients carbon (C), nitrogen (N) and phosphorus (P). A vector analysis of extracellular enzyme activity indicates that soil microbial communities underlying moss biocrusts were limited by P but microbial communities in areas inoculated with the AM fungus had the lowest relative P limitation. The alleviation of microbial P limitation increased the microbial CUE and bacterial phylum community and alpha diversity, leading to an increase in subsoil C content underlying moss biocrusts. This indicates that microbial communities in soil underlying moss biocrusts under in restoration areas containing the AM fungus were more stable under environmental stress, and the inclusion of AM fungal inoculation may be recommended as the preferred option for ecosystem restoration in arid and semi-arid coal mining areas.

Bacterial carbonic anhydrase-induced carbonates mitigate soil erosion in biological soil crusts

Soil erosion is a significant environmental issue worldwide, particularly in island regions where land resources are exceedingly scarce. Biological soil crusts play a crucial role in mitigating soil erosion, yet the precise effect and mechanism of biological soil crusts against erosion remain ambiguous. In this study, biological soil crusts at various developmental stages from a tropical coral island in the South China Sea were chosen to investigate the role of carbonic anhydrase in mitigating erosion. A cohesive strength meter, real-time quantitative PCR, and 16S rRNA gene high-throughput sequencing were employed to assess variations in soil antiscouribility as well as bacterial abundance and composition during the formation and development of biological soil crusts. Scanning electron microscopy was utilized to detect carbonates induced by bacterial carbonic anhydrase and elucidate their role in the solidification of sand particles. The findings indicate that the formation and development of biological soil crusts significantly enhance anti-scouribility. Comparison to those of bare coral sand, the shear stress increased from 0.35 to 1.11 N/m2 in the dark biocrusts. Moreover, significantly elevated carbonic anhydrase activity was observed in biological soil crusts, demonstrating a positive correlation with antiscouribility. In addition, there was a significant increase in bacterial abundance within the biological soil crusts. The enrichment of Cyanobacteriales and Chloroflexales potentially contributed to the increased carbonic anhydrase activity and antiscouribility. Furthermore, three cyanobacterial strains with carbonic anhydrase activity were isolated from biological soil crusts and subsequently confirmed to enhance sand solidification through microbial carbonate precipitation. This study presents initial evidence for the role of microbial carbonic anhydrase in enhancing the antiscouribility of biological soil crusts during their formation and development. These findings offer novel insights into the functional and mechanistic dimensions underlying the mitigation of soil erosion facilitated by biological soil crusts, which are valuable for implementing sustainable biorestoration and environmental management technologies to prevent soil erosion.

Dune Blowouts as Microbial Hotspots and the Changes of Overall Microbial Activity and Photosynthetic Biomass Along with Succession of Biological Soil Crusts

Biological soil crust (BSC) constitutes a consortium of cyanobacteria, algae, lichen, mosses, and heterotrophic microorganisms, forming a miniature ecosystem within the uppermost soil layer. The biomass of different organisms forming BSC and their activity changes along with succession. Previous studies focused primarily on BSC in hyper-arid/arid regions, whereas the ecophysiology of BSC in temperate climates is still not well recognized. In order to determine changes in overall microbial activity and photosynthetic biomass in BSC at different stages of the succession of inland sandy grasslands, we analyzed dehydrogenase activity and determined the content of photosynthetic pigments. We also compared these parameters between BSC developed on the dune ridges and aeolian blowouts in the initial stage of succession. Our study revealed a significant increase in both photosynthetic biomass and overall microbial activity in BSC as the succession of inland shifting sands progresses. We found that chl a concentration in BSC could be considered a useful quantitative indicator of both the presence of photoautotrophs and the degree of soil crust development in warm-summer humid continental climates. The photosynthetic biomass was closely related to increased microbial activity in BSC, which suggests that photoautotrophs constitute a major BSC component. Dune blowouts constitute environmental niches facilitating the development of BSC, compared to dune ridges. High biomass of microorganisms in the dune blowouts may be associated with a high amount of organic material and more favorable moisture conditions. We conclude that deflation fields are key places for keeping a mosaic of habitats in the area of shifting sands and can be a reservoir of microorganisms supporting further settlement of dune slopes by BSC.

Microbial Architects of the Cold Deserts: A Comprehensive Research of Biological Soil Crusts in the High-Altitudinal Cold Deserts of the Western Himalayas

Our research has focused on Biological Soil Crusts (BSCs) in the Western Himalayas, specifically in Tibetan Plateau and Karakoram (Ladakh, India) along the elevation gradient spanning a range of 4300–6000 m a.s.l. where habitats like cold deserts, steppes, alpine and subnival vegetation, as well as primary successional stages behind retreating glaciers are present. These regions are characterised by extensive development of BSCs, with cyanobacteria as the dominant component. BSCs are of great significance for the sustainability and development of ecosystems of arid regions worldwide. Their activity is limited to brief periods when precipitation or dew hydrates microbial cells, enabling metabolic activity. Despite the crucial role played by these phototrophic microbial communities in arid and semi-arid ecosystems worldwide, remote mountain regions like the Tibetian Tibetan Plateau and Karakoram have received limited attention in this regard. More than 15 years long research allowed us to determine several critical aspects of BSCs’ activity and performance: We conducted laboratory and in-situ experiments Fig. 1 to assess the potential photosynthetic and heterotrophic activity of BSCs from high-altitude cold deserts. The experiments involved measuring the production and consumption of CO2 and O2 by BSCs under various temperature and moisture conditions, as well as light intensity. By manipulating these factors, we could differentiate the activities of heterotrophs and autotrophs within the BSCs. The results of these experiments were then analysed in the context of soil nutrient stoichiometry, phylogenetic structure, and microbial community biomass. Using these data, we developed a mechanistic mathematical model to predict the overall metabolic activity of BSCs in response to the major climatic drivers: temperature and moisture. This knowledge could help us to predict the reaction of BSC to climatic changes and reveal if the arid areas in Western Himalayas will act as CO2 sources or sink. We further investigated the composition and content of pigments in microbial soil communities across various habitats along the elevation gradient in the Tibetan Plateau (Rehakova and Capkova 2019). Soil microbes have evolved complex metabolic strategies, such as producing photoprotective and photosynthetic pigments, to survive the environmental stress caused by high UV radiation, fluctuating temperatures, and drought. We also examined the effects of environmental factors such as altitude, mountain range, and soil physico-chemical parameters on the composition and biovolume of phototrophs which dominate the BSc in the studied region (Řeháková 2011, Janatková and Řeháková 2013). This was accomplished through multivariate redundancy analysis and variance partitioning. Interestingly, the phylogenetic diversity and morphotypes’ composition were similar between the Karakoram and Tibetan Plateau (Čapková 2015). Our investigation represents the first recorded assessment of the phylogenetic diversity of cyanobacterial communities within biological soil crusts in the Western Himalayas, specifically at altitudes exceeding 5000 m. We conducted laboratory and in-situ experiments Fig. 1 to assess the potential photosynthetic and heterotrophic activity of BSCs from high-altitude cold deserts. The experiments involved measuring the production and consumption of CO2 and O2 by BSCs under various temperature and moisture conditions, as well as light intensity. By manipulating these factors, we could differentiate the activities of heterotrophs and autotrophs within the BSCs. The results of these experiments were then analysed in the context of soil nutrient stoichiometry, phylogenetic structure, and microbial community biomass. Using these data, we developed a mechanistic mathematical model to predict the overall metabolic activity of BSCs in response to the major climatic drivers: temperature and moisture. This knowledge could help us to predict the reaction of BSC to climatic changes and reveal if the arid areas in Western Himalayas will act as CO2 sources or sink. We further investigated the composition and content of pigments in microbial soil communities across various habitats along the elevation gradient in the Tibetan Plateau (Rehakova and Capkova 2019). Soil microbes have evolved complex metabolic strategies, such as producing photoprotective and photosynthetic pigments, to survive the environmental stress caused by high UV radiation, fluctuating temperatures, and drought. We also examined the effects of environmental factors such as altitude, mountain range, and soil physico-chemical parameters on the composition and biovolume of phototrophs which dominate the BSc in the studied region (Řeháková 2011, Janatková and Řeháková 2013). This was accomplished through multivariate redundancy analysis and variance partitioning. Interestingly, the phylogenetic diversity and morphotypes’ composition were similar between the Karakoram and Tibetan Plateau (Čapková 2015). Our investigation represents the first recorded assessment of the phylogenetic diversity of cyanobacterial communities within biological soil crusts in the Western Himalayas, specifically at altitudes exceeding 5000 m.

Shrubs have a greater influence on the nonstructural carbohydrates of desert mosses along precipitation decreased

Biological soil crusts and the mosaic distribution of vascular plants have become an important landscape feature on the desert surface owing to limited water. The desert shrub, as one of the best-known vascular plants, exerts a notable influence on multiple facets, encompassing the growth and development of biological soil crusts as well as the coverage, biomass, physiology, and biochemical properties of mosses. Therefore, to comprehend how plants react and adapt to drought conditions, it is necessary to investigate the concentration and allocation patterns of nonstructural carbohydrates (NSCs). Nevertheless, the phenomenon still remains unclear whether the influence of shrubs on biological soil crusts follows any pattern concerning the alteration in precipitation gradients on a broader spatial scale. In this investigation, Syntrichia caninervis was gathered from two distinct microenvironments within the Gurbantunggut Desert spanning the gradient of natural precipitation. The aim was to examine the reaction of NSCs within S. caninervis to the presence of shrubs under varying precipitation circumstances. The amount of total NSCs and their components in S. caninervis were determined by the shrub effect, mean annual precipitation (MAP), and mean annual temperature (MAT). The presence of shrubs led to a remarkable rise in the content of fructose, starch, and total NSCs in S. caninervis, but a decline in the ratio of soluble sugar to starch. Nonetheless, variations were observed in the overall NSCs content, the individual constituents of NSCs, and the proportion of soluble sugars to starch within S. caninervis across diverse microenvironments and sampling locations. The content of total NSC and its components, as well as the ratio of soluble sugar to starch, substantially increased with a decrease in MAP (negative correlation) in S. caninervis. Conversely, they significantly decreased as MAT decreased (positive correlation). With the amplifying MAP, the disparities in these parameters (total NSC content, its components, and the ratio of soluble sugar to starch) between two distinct microhabitats diminished gradually, whereas these disparities progressively intensified with rising mean annual temperature (MAT). The outcomes derived from the structural equation model (SEM) underscored the direct and indirect influence of climate and the presence of shrubs influenced the content of NSCs directly or indirectly by enhancing soil nutrients. As a conclusion, the impact of shrub presence, followed by mean annual precipitation (MAP), had the most notable effect on NSCs in S. caninervis. Consequently, despite the observed spatial pattern in NSCs content, shrubs emerged as the most critical factor, in speaking of their effect continuous raising with the declining MAP. These findings provide new insights into the mechanisms of NSCs distribution and stress resistance in desert moss in different microhabitats.

Native microalgae and Bacillus XZM remediate arsenic-contaminated soil by forming biological soil crusts

Biological soil crusts (BSCs) are a useful tool for immobilization of metal(loid)s in mining areas. Yet, the typical functional microorganisms involved in promoting the fast development of BSCs and their impacts on arsenic(As) contaminated soil remain unverified. In this study, As-contaminated soil was inoculated with indigenous Chlorella thermophila SM01 (C. thermophila SM01), Leptolyngbya sp. XZMQ, isolated from BSCs in high As-contaminated areas and plant growth-promoting (PGP) bacteria (Bacillus XZM) to construct BSCs in different manners. After 45 days of ex-situ culture experiment, Leptolyngbya sp. XZMQ and bacteria could form obvious BSCs. Compared to single-inoculated microalgae, the co-inoculation of Leptolyngbya sp. XZMQ and Bacillus XZM increased soil pH and water content by 10% and 26%, respectively, while decreasing soil EC and density by 19% and 14%, respectively. The soil catalase, alkaline phosphatase, sucrase, and urease activities were also increased by 30.53%, 96.24%, 154.19%, and 272.17%, respectively. The co-inoculation of Leptolyngbya sp. XZMQ and Bacillus XZM drove the formation of BSCs by producing large amounts of extracellular polymeric substances (EPS). The three-dimensional fluorescence spectroscopy (3D-EEM) analysis showed that induced BSCs increased As immobilization by enhancing the contents of tryptophan and tyrosine substances, fulvic acid, and humic acid in EPS. The presence of the –NH2 and –COOH functional groups in tryptophan residues were determined using Fourier Transform Infrared Spectroscopy (FTIR). X-Ray Diffraction (XRD) analysis showed that there were iron (hydrogen) oxides in BSCs, which could form ternary complexes with humic acid and As, thereby increasing the adsorption of As. Therefore, BSCs formed by co-inoculation of Leptolyngbya sp. XZMQ and Bacillus XZM increased the immobilization of As, thereby reducing the content of soluble As in the environment. In summary, our findings innovatively provided a new method for the remediation of As-contaminated soil in mining areas.

Morphology and distribution of biological soil crusts and their potential role in soil-forming processes under dry high-altitude periglacial conditions (Eastern Pamir, Tajikistan)

Under demanding climatic conditions that limit the development of vascular vegetation, biological soil crusts (BSCs) drive the processes of soil formation and nutrient sequestration. Though BSCs were studied in glacier forelands worldwide, the high-altitude areas with a combination of glaciation/deglaciation and arid or hyperarid climate remain almost unstudied in this respect. Therefore, we provided the first data on BSCs from a glacier foreland in the E Pamir. These characteristics can be crucial for assessing BSC's role in soil-forming processes in dry, high-altitude periglacial environments. During our research, we assessed (1) BSCs’ morphology and distribution; (2) microbial biomass and nutrient retention patterns in morphologically differentiated BSC types, (3) C, N and P accumulation in BSCs biomass in comparison to sub-crust soils; (4) sub-crust soils enrichment in C, N and P in comparison to bare soils and soils under vascular plants; (5) potential origin and transformation degree of organic matter accumulated by BSCs. Our study showed that the distribution and development of BSCs were noticeably restricted, probably due to low temperatures, aridity and intense periglacial processes, resulting in continuous soil surface remodeling. Thus, poorly developed BSCs were the dominating biologically active soil cover type and, thus, most likely the main biological soil-forming factor in the foreland. BSCs accumulated C, N and P in their biomass and enriched their sub-crust soils in these nutrients. The average enrichment observed for soils under advanced crusts was similar to those obtained for soils under vascular plants. In all types of the studied samples, including bare soils, n-alkanes of vascular plant origin dominated, indicating mixing and uniform distribution of organic matter. Over the course of aridification projected for the Pamir Mountains, the BSCs could potentially become the most important player in the accumulation of soil nutrients in this area. However, due to the dominance of the simplest BSC type, soil formation in the Uisu Glacier foreland will be relatively slow.

Biological soil crust development affects bacterial communities in the Caragana microphylla community in alpine sandy areas.

Biological soil crusts (BSCs) constitute a substantial portion of primary production in dryland ecosystems. They successionally mature to deliver a series of ecosystem services. Bacteria, as an important community in BSCs, play critical roles in maintaining the structure and functions of BSCs. However, the process by which bacterial diversity and community are altered with BSC development is not fully understood. In this study, amplicons sequencing was used to investigate bacterial diversity and community compositions across five developmental stages of BSCs (bare sand, microbial crusts, algae crusts, lichen crusts, and moss crusts) and their relationship with environmental variables in the Gonghe basin sandy land in Qinghai-Tibet Plateau, northwestern China. The results showed that Proteobacteria, Actinobacteria, Cyanobacteria, Acidobacteria, Bacteroidetes, and Firmicutes were predominant in different developmental stages of BSCs, accounting for more than 77% of the total relative abundance. The phyla of Acidobacteria and Bacteroidetes were abundant in this region. With BSC development, bacterial diversity significantly increased, and the taxonomic community composition significantly altered. The relative abundance of copiotrophic bacteria, such as Actinobacteria, Acidobacteria, Bacteroidetes, Verrucomicrobia, Planctomycetes, and Gemmatimonadetes significantly increased, whereas the relative abundance of oligotrophic bacteria, such as Proteobacteria and Firmicutes significantly decreased. The relative abundance of Cyanobacteria in the algae crusts was significantly higher than that in the other developmental stages (p < 0.05). Variations in bacterial composition suggested that the potential ecological functions of the bacterial community were altered with BSC development. The functions varied from enhancing soil surface stability by promoting soil particle cementation in the early stages to promoting material circulation of the ecosystem by fixing carbon and nitrogen and decomposing litter in the later stages of BSC development. Bacterial community is a sensitive index of water and nutrient alterations during BSC development. SWC, pH value, TC, TOC, TN, NO3 -, TP and soil texture were the primary environmental variables that promoted changes in the bacterial community composition of BSCs.

Environmental impacts of photovoltaic power plants in northwest China

In the past decade, approximately 17 % of the world's photovoltaic capacity has been installed in China, especially in the northwestern desert areas. The impacts of the construction and operation of large-scale photovoltaic power plants (PPPs) on local ecological environments have become urgent scientific issues in regional environmental protection decision-making. To quantitatively evaluate the local environmental impacts of the construction and operation of PPPs in the desert oasis region, thermal infrared and multispectral sensors mounted on unmanned aerial vehicles (UAVs) as well as X-ray fluorescence spectrometers and soil sensors were used in this study to monitor a large PPP in Northwest China. We found that the construction and operation of PPPs can promote biological soil crust development and vegetation growth and can thus improve the soil texture and nutrition. However, the Ca, S and Cl concentrations were found to be 3, 5 and 1.7 times higher inside the PPP area than outside the PPP area, respectively. In addition, the soil salinization is also more severe inside the PPP area. In future studies, it is essential to further elucidate the impacts of PPP operations and agricultural on desert ecosystems.

Effect of crevice density on biological soil crust development on rock cut slope in mountainous regions, Sichuan, China

BackgroundThe rock cut slope (RCS) could cause damage to regional ecological functions and landscapes and requires recovery. Biological soil crusts (BSCs) are pioneer and dominant colonizers during the initial recovery stage. To accelerate the natural recovery of RCS, the development process and influencing agents of BSC should be revealed. Thus, the area index of crevices (IR), BSC coverage (COV) and biomass (BM), soil weight (SW), and major soil nutrients [organic carbon (OC), total nitrogen (TN) and total phosphorus (TP)] content, collected from 164 quadrats on 13 RCSs in the mountainous area of west Sichuan Province, China, were measured, to explore the effect of crevice of RCS on BSC development.ResultsSoil OC, TN and TP on RCSs ranged from 18.61 to 123.03 g kg−1, 0.96 to 6.02 g kg−1 and 0.52 to 2.46 g kg−1, respectively, and were approximately to or higher than those on natural slopes. The OC, TN and TP contents in soils elevated unsystematically with recovery time of RCSs. BSCs on RCS distributed along crevices generally and firstly. During the first 13 years of natural recovery, COV, BM and SW ranged from 6.5 to 28.2%, 14.43 to 67.25 g m−2, and 127.69 to 1277.74 g m−2, respectively. COV, BM and SW increased linearly with IR on RCSs. The positive correlation between COV and BM and IR was insignificantly impacted by bedrock, slope aspect and altitude within the recovery time less than 13 years. COV and BM on RCSs increased significantly when the recovery time is more than 27 years.ConclusionsCrevice on RCSs could be a major environmental factor which is conducive to BSC development and soil accumulation through creating a space for water and soil particle. Furthermore, with the increase of recovery time of RCSs, BSCs may grow and reach a stable state with the promotion of soil nutrients, plant growth and microbial activity. These results provide a development process of BSC that from inside to outside the crevices on RCSs. In the areas with stable rock strata and a low risk of geological disasters, purposeful improvement in crevice density on RCS may effectively accelerate BSC development.

Variations in organic carbon mineralization of the biological soil crusts following revegetation in the Tengger Desert, North China

Revegetation is an effective measure to combat desertification worldwide, which parallelly facilitates the colonization and development of biological soil crusts (BSCs), and thereby affecting C cycles of BSCs in desert regions. However, knowledge about soil organic carbon (SOC) mineralization of BSCs and the involved mechanisms during long-term revegetation process in desert is rather limited. In this study, SOC mineralization rates of the mobile sand dune (MSD) and the BSCs in revegetated sites along chronosequence in the Tengger Desert were investigated, and the relationships between the SOC mineralization and the characteristics of vegetation and BSCs, soil properties and incubation temperature (T) and soil water content (SWC) were analyzed. The results showed that SOC mineralization rate of the BSCs and the corresponding subsoils was significantly greater than those of the MSD, and it increased considerably with increasing site age, regardless of the T, SWC, soil layer and sampling time (p < 0.001). The maximum instantaneous mineralization rates (MIR), cumulative CO2-C release (CCR) and the potentially mineralizable SOC (C0) of BSCs and subsoils were 1.29–12.63, 3.67–23.16 and 3.78–23.41 times, and 0.16–2.26, 0.12–1.84 and 0.17–1.26 times greater than those of the MSD, respectively; while the proportion of C0 to total SOC (C0/SOC) decreased by 31–88 % and 24–72 % in comparison with MSD, respectively. The mineralization rate increased with T and SWC, and the temperature sensitivity of BSCs increased with site age, indicating that the loss of SOC would be accelerated with the succession of BSCs upon the future global change. The variation magnitude of SOC mineralization was largely dependent on revegetation-induced changes in the properties of BSCs and the incubation T and SWC, and their interactions. The C:N, pH, and the activities of POD and PPO and DOC, and the coverage of moss-dominated crusts, SOC, C:N, the content of clay and silt and AYL activity were the main factors affecting SOC mineralization of BSCs and the subsoils, respectively. These results indicated that multiple factors that co-varied with the succession of BSCs led to variable SOC mineralization. Our findings suggested that planting xerophytic shrubs in desert drives the development and the SOC mineralization of BSCs, but decreased SOC loss due to mineralization, leading to SOC sequestration.

Early successional changes in biological soil crust community assembly and nutrient capture in mining impacted landscapes

Biological soil crusts (BSCs) are communities of bryophytes, lichens, bacteria, and fungi and are the primary colonizing communities in early successional landscapes. In early ecosystem development BSCs often improve the physical and chemical conditions while also promoting soil microbial communities. Although BSCs are considered ecosystem engineers in many early successional environments, the links between BSC functional processes and their developmental stage are unclear, especially in landscapes recovering from anthropogenic disturbances. In this study we examined natural BSC development over a 30-year chronosequence on two mining impacted landscapes in both boreal and arctic regions of Canada. Using High Throughput Sequencing (HTS), we found similar ubiquitous ruderal bryophytes and bacteria species common at both study areas, but significant differences in lichen and fungal community structure between the two locations. In addition, community assembly of BSC macro (bryophytes and lichens) and micro (bacteria and fungi)-phyla changed over the first 30 years of recovery at both mine sites, however, these changes were unique to each study location. We observed nutrient accumulation in the crust layer but did not find clear trends in available nutrients or gas flux over time. Instead, changes in our functional measurements were associated with colonization by specific BSC species. Further, the bacterial community at both mines seemed to be responding to changes in the bryophyte communities as they developed over time. This suggests that the establishment of bryophyte communities in early succession may be driving micro-phyla BSC community composition. A holistic view of BSCs as they develop over time in relation to their functional abilities needs further investigation, and this study provides insight into these interactions. This knowledge will improve both our understanding of early stage BSC development and our ability to develop restoration techniques to effectively restore landscapes disturbed by anthropogenic activities.

The Effects of Biochar on Microbial Community Composition in and Beneath Biological Soil Crusts in a Pinus massoniana Lamb. Plantation

Biological soil crusts (BSCs) hold promise for reducing soil erosion in subtropical forest plantations, and microorganisms profoundly affect the formation and development of BSCs. The effects of biochar as a soil conditioner on the diversity and structure of soil microbial communities in BSCs are largely unknown. Therefore, our aim was to determine how biochar might improve microbial community composition and BSC function. Herein, a field experiment was conducted in a P. massoniana plantation; the addition of biochar was the treatment, and no biochar addition was the control (CK). Soil microbial communities associated with moss BSCs (in and beneath BSCs) with and without the addition of biochar were analyzed by Illumina sequencing technology. The results showed that Acidobacteria (28.35%), Proteobacteria (22.53%), Actinobacteria (17.41%), and Chloroflexi (16.74%) were the dominant bacterial phyla, whereas Basidiomycota (70.00%) and Ascomycota (22.76%) were the dominant fungal phyla in BSCs. The soil bacterial and fungal OTU number and richness in BSCs were higher than those beneath BSCs. The relative abundances of Acidobacteria, Chloroflexi, and Basidiomycota were higher in BSCs than beneath BSCs, whereas the relative abundances of Actinobacteria, Firmicutes, Ascomycota, and Chytridiomycota showed the opposite trend. Beneath BSCs, biochar addition increased the soil bacterial OTU number and richness (ACE index and Chao1) but decreased the soil fungal OTU number and richness. Biochar had little effect on soil microbial community structures in BSCs; however, beneath BSCs, it significantly increased the relative abundances of Acidobacteria, Chloroflexi, and Basidiomycota and significantly decreased the relative abundances of Actinobacteria, Firmicutes, Ascomycota, and Chytridiomycota. Biochar-induced changes in soil microbial communities were related to soil environmental factors, especially urease activity, organic matter content, pH, total nitrogen content, and sucrase activity. We demonstrated the different effects of biochar on soil microbial communities in and beneath the BSCs of subtropical forest plantations; these findings provided new insights into soil stabilization with BSCs below the forest canopy in subtropical regions.

Effects of moss biocrusts on soil-microbe-ectoenzyme stoichiometric characteristics in a subtropical area

The formation and development of biological soil crusts (biocrusts) potentially affect the cycles and stoichiometric characteristics of soil carbon (C), nitrogen (N), and phosphorus (P). However, it is still unclear how soil microbes adapt to such changes. In this study, we examined the effects of moss-dominated biocrusts coverage (0, 1%-20%, 20%-40%, 40%-60%, 60%-80%, and 80%-100%) on soil physicochemical properties, soil microbial biomass, and ectoenzyme activities [β-1, 4-glucosidase (BG), β-1, 4-N-acetyl glucosidase (NAG), acid phosphatase (AP)] in two soil layers (0-5 and 5-10 cm) in the Three Gorges Reservoir area, as well as the covariations of soil-microbe-ectoenzyme C:N:P stoichiometry. The results showed that biocrust development significantly increased soil clay content, water stable aggregates, soil C, N, P contents, and significantly decreased soil bulk density and sand content. Microbial biomass C, N, P and ectoenzyme activities were significantly increased with increasing biocrust coverage. Soil depth did not affect soil physicochemical properties and C:N:P, but significantly affected microbial biomass, ectoenzyme activities, BG:AP and NAG:AP. Soil C, N and P contents were significantly positively correlated with microbial biomass and ectoenzyme activities, negatively correlated with BG:NAG, while positively correlated with NAG:AP, but had no significant correlation with microbial biomass C:N:P. There was no significant correlation between soil-microbe and microbial-ectoenzyme C:N:P. BG:NAG:AP decreased gradually with the increase of C:N:P stoichiometric imbalance between microbe and soil. This study indicated that the microbial metabolism was co-limited by N and P and with stronger P limitation. Microbes could maintain homeostasis by adjusting their own biomass and ectoenzyme C:N:P to adapt to changes in soil ecological stoichiometry driven by biocrust development.

Bryophyte diversity and microhabitat characteristics of bryophyte-dominated biological soil crusts development in water-wind erosion crisscross region of the northern Loess Plateau, China

Microhabitat factors play an important role in regulating bryophyte species distribution and the development of bryophyte-dominated biological soil crusts (hereafter bryophyte crusts). We investigated the distribution and development of bryophytes in eight microhabitats in the water-wind erosion crisscross region of the Loess Pla-teau. We used the line intercept transects to explore and quantify the influencing pathways of microhabitat factors on bryophyte diversity and analyzed the influencing pathways of plant cover, slope aspect, and slope gradient by using structural equation model to quantify influencing coefficients. Our results showed that: 1) The Patrick, Shannon, Pielou, and Simpson indcies of bryophytes under plant canopy were 63.4%, 66.6%, 91.0%, and 68.3% lower than that without plant canopy, respectively, while the thickness, biomass, and chlorophyll content of bryophyte crusts were 0.5, 0.2, and 1.3 times higher than that without plant canopy, respectively. 2) The Patrick, Shannon, Pielou, and Simpson indexes of bryophytes on the north slope were 0.6, 0.9, 5.6, and 0.9 times higher than those on the south slope, while the thickness, biomass, and chlorophyll content of bryophyte crusts were 0.3, 0.3, and 0.6 times higher than those on the south slope, respectively. 3) As the slope increasing from 14° to 34°, the Patrick, Shannon, Pielou, and Simpson indexes of bryophyte were decreased by 59.8%, 84.1%, 57.3% and 68.0%, and the thickness, biomass, and chlorophyll content of bryophyte crusts were decreased by 15.2%, 25.0%, and 16.5%, respectively. 4) The importance of the three microhabitat factors on bryophyte diversity and the development of bryophyte crusts followed an order of plant canopy cover > slope aspect > slope gradient. The primary influencing pathway varied among the microhabitat factors. In conclusion, plant cover, slope aspect, and slope gradient significantly affected the distribution of bryophytes species and developmental level of bryophyte crusts through direct and indirect pathways. Therefore, full consideration should be given to microhabitat conditions when using bryophyte crusts to control desertification.

Microbial metal homeostasis of biological soil crusts as a mechanism for promoting soil restoration during desert revegetation

The main characteristic of a desert ecosystem is a low content of water and nutrients, which reduces the rate of the biogeochemical cycle. In such a seemingly slow metabolism ecosystem, little attention has been paid to microbial metal homeostasis and its relationship with biogeochemical processes and soil properties. Here, we studied the microbial functional genes associated with metal homeostasis from five measurements (17y, 30y, 44y, 53y and 61y) during a 61-year development of biological soil crusts (BSCs) in the revegetation of the Tengger Desert. The aim was to determine the effect of metal homeostasis on biogeochemical cycle and soil properties in a desert ecosystem. Among the microbial functional genes detected by GeoChip 5.0 in BSC samples of different ages, the total signal intensity of iron (Fe) and nickel (Ni) metabolism genes was the highest in the ranking of the top 17 metals. Moreover, Proteobacteria and Actinobacteria were the major source groups at the phylum level of all metal metabolism genes. Almost all genes involved in metal homeostasis had the potential to function as transporters or redox catalyzers. Fe metabolism genes were the main nodes (ten of the top 50 genes) and the zinc (Zn) transporter gene znuC had the most connections (21) in the correlation network of metal genes. Metal metabolism was the focus (11 of the top 30 nodes) for the biogeochemical cycle and other metabolic processes. It had the closest relationship with stress responses, the carbon (C) cycle, and virulence, in that order, and a relatively weak relationship with the nitrogen (N) cycle. Metal homeostasis showed a close positive relationship with soil physiochemical (48.7% explanation) and biological properties (51.4% explanation) compared with C and N cycling (35.2% and 19.8% explanation, respectively). Due to the promotion of soil nutrient and microbial activity in BSCs, metal homeostasis may be regarded as a potential mechanism for soil restoration during desert revegetation. This study unravels the importance of metal homeostasis in the regulation of soil quality and underscores the need for future studies that take a holistic view on biogeochemical cycles mediated by metal homeostasis in soil ecosystems.

Unmanned aerial vehicle image biological soil crust recognition based on UNet++

ABSTRACT Biological soil crust is an important feature of desert ecosystem composition and surface landscape. Determining the role of biological soil crust in the energy flow and logistics cycle in the desert ecosystem is one of the frontier areas of ecological restoration in arid and semi-arid areas. Obtaining biological soil crust information from drone images is an efficient, fast, and low-cost method. However, due to the scattered and uneven growth of biological soil crusts and the complexity of the field environment, it is difficult to accurately extract biological soil crusts. In view of this, this study used the improved UNet++ model to extract biological soil crusts based on UAV image data. Firstly, the optimal Epoch, Backbone, and Loss function are selected and trained based on the network structure of UNet++ model. Then, the improved UNet++ model proposed in this paper, which takes ResNeXt as the Backbone and Soft Cross-Entropy Loss+Dice Loss as the Loss Function, is obtained. Finally, the test results of UNet++, U-Net, LinkNet, FPN, and PSPNet are compared with the improved UNet++ model in this paper. The results showed that the improved UNet++ model had the best segmentation effect, and the precision, recall, F1-Score, and IoU were 0.9788, 0.9501, 0.9495, and 0.9309, respectively. UAV image biological soil crust recognition based on the improved UNet++ model in this paper can obtain high-precision extraction results, provide good data support for studying the development of biological soil crusts in arid areas, and provide a new method for precise segmentation of different features in arid areas. In particular, it is of great significance to evaluate the governance effect of ecological restoration projects.

Impact of Environmental Factors on the Formation and Development of Biological Soil Crusts in Lime Concrete Materials of Building Facades

Microbial colonization leads to the formation of biological soil crusts (BSCs) on the surface of architecture, which causes the deterioration of construction materials. However, little information is available on the formation of BSCs on lime concrete materials of early architecture. In this study, the variances of microbial communities, physicochemical properties, and surrounding environmental factors of the lime concrete facades from the early architecture of Wuhan University were investigated. It was found that the surface of lime concrete materials was internally porous and permeable, embedded with biofilms of cyanobacteria, mosses, bacteria, and fungi. Redundancy analysis (RDA) analysis showed that the abundances of photoautotrophic microorganisms depended on light intensity and moisture content of construction materials, while that of heterotrophic microorganisms depended on total nitrogen (TN) and NO3−-N content. The deposition of total carbon (TC), NH4+-N, and total organic carbon (TOC) was mainly generated by photoautotrophic microorganisms. The lime concrete surface of early architecture allowed internal growth of microorganisms and excretion of metabolites, which promoted the biodeterioration of lime concrete materials.

Dynamics of phoD- and gcd-Harboring Microbial Communities Across an Age Sequence of Biological Soil Crusts Under Sand-Fixation Plantation.

Biological soil crusts (BSCs) are important for restoring vegetation and improving soil fertility in arid or semiarid desertified land. However, studies on the contribution of BSC microbes to phosphorus (P) transformation remains limited. The microbial diversity involved in P transformation and its dynamic along BSC development should be examined to further understand the microbial regulatory mechanism of the P-cycling process. This paper investigates the soil properties, P fractions, and potential of P transformation across a chronosequence (0-, 8-, 20-, and 35-year) of the BSC under Caragana microphylla plantation on the moving sand dunes in Horqin Grassland, China. An abundance of phoD and gcd genes was detected, and the diversities and structures of phoD- and gcd-haboring microbial communities were illustrated via high-throughput sequencing. Soil nutrient content, activity of alkaline phosphomonoesterase, potential of organic P (OP) mineralization, and the abundance of phoD and gcd genes all linearly increased along with BSC age. The microbial quantity and species diversity of the phoD community were greater than those of gcd. BSC development increased the availability of inorganic P (IP) fractions, and both NaHCO3-Pi and NaOH-Pi were positively correlated with the abundance of the two genes and the activity of alkaline phosphomonoesterase. The phyla of Actinobacteria, Planctomycetes, and Proteobacteria and the family of Streptomycetaceae were the most dominant taxa in the phoD community, Proteobacteria was the dominant phylum in the gcd community in BSC soils, and Rhizobium and Planctomyces were the most dominant genera. The dominant taxa quantitatively responded to soil property improvement, but the basic compositions and dominant taxa did not change along with BSC development. The structures of phoD and gcd communities were linked to soil properties, and pH available K, and total K tend to be the direct determining factors.