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Biological soil crusts (biocrusts)—communities of mosses, lichens, cyanobacteria, and heterotrophs living at the soil surface—are fundamental components of drylands worldwide, and destruction of biocrusts dramatically alters biogeochemical processes, hydrology, surface energy balance, and vegetation cover. Although there has been long-standing concern over impacts of physical disturbances on biocrusts (e.g., trampling by livestock, damage from vehicles), there is increasing concern over the potential for climate change to alter biocrust community structure. Using long-term data from the Colorado Plateau, we examined the effects of 10 y of experimental warming and altered precipitation (in full-factorial design) on biocrust communities and compared the effects of altered climate with those of long-term physical disturbance (>10 y of replicated human trampling). Surprisingly, altered climate and physical disturbance treatments had similar effects on biocrust community structure. Warming, altered precipitation frequency [an increase of small (1.2 mm) summer rainfall events], and physical disturbance from trampling all promoted early successional community states marked by dramatic declines in moss cover and increases in cyanobacteria cover, with more variable effects on lichens. Although the pace of community change varied significantly among treatments, our results suggest that multiple aspects of climate change will affect biocrusts to the same degree as physical disturbance. This is particularly disconcerting in the context of warming, as temperatures for drylands are projected to increase beyond those imposed as treatments in our study.

Background and aimsKarst rocky desertification (KRD), a land degradation form which is widespread but unique to karst ecosystems, has become an ecological disaster in southwest China. Biocrusts play crucial roles in many ecological processes of the degraded ecosystems. However, little is known about the effects of biocrusts on soil properties and soil microbial communities in the progression of KRD. MethodsWe sampled soil beneath moss biocrusts and bare soil in four grades of KRD (none, light, moderate, and severe) to compare soil nutrients, soil microbial diversity, community composition, structure, and networks across the range of KRD progression.ResultsMoss biocrusts had a positive effect on all soil nutrients and buffered the negative effects of KRD progression compared to bare soil. Moss biocrusts significantly increased soil microbial richness but had little contribution to diversity and community composition. Both soil bacterial and fungal communities were significantly correlated with total and available phosphorus, total potassium, soil temperature, slope, and altitude. Soil bacterial and fungal communities showed different sensitivities and strategies in face of environmental degradation in KRD-affected ecosystems.ConclusionsMoss biocrust restoration could be used as a supplementary method in promoting ecological restoration in areas undergoing KRD due to their positive effects on soil nutrients and soil microbial richness. Our findings filled a knowledge gap pertaining to the microbial ecology of biocrust in regions experiencing KRD.

Future climates will alter the frequency and size of rain events in drylands, potentially affecting soil microbes that generate carbon feedbacks to climate, but field tests are rare. Topsoils in drylands are commonly colonized by biological soil crusts (biocrusts), photosynthesis-based communities that provide services ranging from soil fertilization to stabilization against erosion. We quantified responses of biocrust microbial communities to 12 years of altered rainfall regimes, with 60 mm of additional rain per year delivered either as small (5 mm) weekly rains or large (20 mm) monthly rains during the summer monsoon season. Rain addition promoted microbial diversity, suppressed the dominant cyanobacterium, Microcoleus vaginatus, and enhanced nitrogen-fixing taxa, but did not consistently increase microbial biomass. The addition of many small rain events increased microbial biomass, whereas few, large events did not. These results alter the physiological paradigm that biocrusts are most limited by the amount of rainfall and instead predict that regimes enriched in small rain events will boost cyanobacterial biocrusts and enhance their beneficial services to drylands.

Background and aims Biocrusts are communities of cyanobacteria, mosses, and/or lichens found in drylands worldwide. Biocrusts are proposed to enhance soil fertility and productivity, but simultaneously act as a barrier to the invasive grass, Bromus tectorum, in western North America. Both biocrusts and B. tectorum are sensitive to climate change drivers, yet how their responses might interact to affect dryland ecosystems is unclear. Methods Using mesocosms with bare soil versus biocrust cover, we germinated B. tectorum seeds collected from warmed, warmed + watered, and ambient temperature plots within a long-term climate change experiment on the Colorado Plateau, USA. We characterized biocrust influences on soil fertility and grass germination, morphology, and chemistry. Results Biocrusts increased soil fertility and B. tectorum biomass, specific leaf area (SLA), and root:shoot ratios. Germination rates were unaffected by mesocosm cover-type. Biocrusts delayed germination timing while also interacting with the warmed treatment to advance, and with the warmed + watered treatment to delay germination. Conclusions Biocrusts promoted B. tectorum growth, likely through positive influence on soil fertility which was elevated in biocrust mesocosms, and interacted with seed treatment-provenance to affect germination. Understanding how anticipated losses of biocrusts will affect invasion dynamics will require further investigation of how plant plasticity/adaptation to specific climate drivers interact with soil and biocrust properties.

Understanding soil–plant–microbe inter- and intra- interactions are essential for ensuring proper soil health, quality, and soil-mediated ecosystem services (e.g., nutrient cycling) required for human–plant–animal life. Intensive and unsustainable farming practices can decrease soil microbial biodiversity, fertility, and quality leading to soil degradation, impaired nutrient cycling, and the incapability of soil to support plant growth. Under such a context, soil biological fertility can appear as a regenerative component that has the potential to harmonize and improve soil’s physical, chemical, and biological parameters. This study defines and discusses the microbiome in the rhizosphere, microbial nutrient cycling, and biological soil crusts as the major components of soil biological fertility, and explores the answers to the following questions: (i) how does the rhizosphere promote plant growth, development, and nutrient cycling through soil microorganisms (e.g., bacteria, fungi)? (ii) How can soil microorganisms regulate macronutrient cycling and facilitate biocrust formation? This review reveals that soil biological fertility is crucial for increasing crop resilience and productivity as well as sustainability in agriculture. Additionally, the reintroduction of plant growth promoting rhizobacteria, a quantitative estimation of the root exudate’s composition, identifying the spatiotemporal dynamics of potassium solubilizing bacteria and establishing biological soil crusts in agricultural lands remain the major tasks for improving soil biological fertility and the transition towards regenerative agriculture.

Biocrusts determine soil stability and resiliency, with a special role played by oxygenic photoautotrophic microorganisms in these communities. We evaluated temporal and geographic trends in studies focused on these microorganisms in biocrusts. Two databases were surveyed to obtain scientific articles published from 1998 to 2020 containing the terms ‘biocrusts,’ ‘algae,’ and ‘cyanobacteria.’ Although interest in biocrusts has increased recently, their ecological importance is still little explored. The scientific articles that mentioned a species list of cyanobacteria and/or algae revealed a very heterogeneous geographic distribution of research. Biocrusts have not been explored in many regions and knowledge in the tropics, where these communities showed high species richness, is limited. Geographic gaps were detected and more detailed studies are needed, mainly where biocrust communities are threatened by anthropogenic impacts. Aiming to address these knowledge gaps, we assembled a taxonomic list of all algae and cyanobacteria found in these articles, including information on their occurrence and ecology. This review is an updated global taxonomic survey of biocrusts, which importantly reveals their high species richness of oxygenic photoautotrophic microorganisms. We believe this database will be useful to future research by providing valuable taxonomic and biogeographic information regarding algae and cyanobacteria in biocrusts.

Soil inoculation with cyanobacteria (cyanobacterization) is a biotechnological method widely studied to improve soil quality and productivity. During their growth on soil, cyanobacteria excrete exopolysaccharides (EPSs) which glue trichomes to soil particles, in a three-dimensional extracellular polymeric matrix. EPS productivity is an important screening parameter to select proficient inoculants and is affected by growth conditions and abiotic stresses. In this study, we evaluated the capability of the cyanobacterium Schizothrix cf. delicatissima AMPL0116 to form biocrusts when inoculated in sand microcosms under stressing conditions, and the characteristics of the synthesized polymeric matrix. In parallel, we evaluated the characteristics of exopolysaccharidic exudates of the strain when grown in liquid culture, under optimal growth setting. Our results pointed out at significant differences of the exopolymers produced in the two conditions in terms of monosaccharidic composition and molecular weight distribution, and proved the capability of S. cf. delicatissima AMPL0116 to form stable bioaggregates on sandy soils.

Escalating global concerns about soil degradation, driven by erosion, salinization, compaction, pollution, and organic matter loss, highlights the critical need for sustainable remediation. Biocrusts—complex communities of cyanobacteria, algae, lichens, bryophytes, and fungi—play a pivotal role in soil stabilization, erosion prevention, and nutrient cycling. This study presents recent advancements in biocrust application for soil management and restoration, focusing on artificial biocrusts as a nature-based solution biotechnology. It emphasizes their effectiveness in enhancing soil quality, biodiversity, and ecosystem functionality. Researchers are leveraging these microbial communities to develop strategies that improve soil health and rehabilitate degraded landscapes. The review concludes that biocrusts are a viable strategy for boosting soil resilience and enhancing soil health against environmental stressors. It recommends future research on their long-term ecological impacts and methods to enhance their functionality.

Background and AimsBiocrusts are found on soil surface resulting from an association between soil particles and microorganisms. Photoautotrophic cyanobacteria and microalgae are pioneers on biocrusts formation, promoting soil stability, nutrients availability and water retention, leading to the development of other communities. This work aimed at isolating and characterizing cyanobacteria/microalgae from biocrusts (Central Portugal) and to assess their potential as plant biostimulants, as well as obtaining an insight into their mechanism(s) of action.MethodsMicroorganisms were isolated through successive spread plating/serial dilutions and characterized using genetical analysis/morphological traits. An initial screening was performed using exudates from each microorganism and two plant species, Arabidopsis thaliana and Lolium multiflorum. Subsequently, the selected microorganisms were tested as a consortium in hydroponic systems. Biometric and biochemical parameters were evaluated for both plant species.ResultsThe consortium microorganisms belong to genera often found in soils/biocrusts: Trichocoleus, Nodosilinea, Microcoleus (filamentous cyanobacteria), Nostoc (diazotrophic heterocystous cyanobacteria), and Klebsormidium (filamentous microalga), and some of them have the capacity to produce phytohormones and/or siderophores. The consortium showed biostimulant potential in hydroponic cultures, promoting plant growth and enhancing physiological productivity related parameters. Stress related parameters revealed that the microorganisms did not lead to a stressful situation. However, a significant increase in proline was observed, endorsing a role of this molecule in this process.ConclusionThis study contributes to the knowledge on the biodiversity of cyanobacteria and microalgae from Portuguese soils and highlights their potential as biostimulants, constituting a step forward towards understanding the molecular mechanisms behind this effect.

Abstract 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. 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, and easily migrated up to biocrust surface after hydration. 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. Two living forms of Microcoleus vaginatus playing distinct ecological roles in the biocrust formation process.