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1. Beneficial Cyanosphere Heterotrophs Accelerate Establishment of Cyanobacterial Biocrust

   https://doi.org/10.1128/AEM.01236-21  

   Nelson, Corey; Garcia-Pichel, Ferran (September 2021, Applied and Environmental Microbiology)

   Stams, Alfons J. (Ed.)

   ABSTRACT Biological soil crusts (biocrusts) are communities of microbes that inhabit the surface of arid soils and provide essential services to dryland ecosystems. While resistant to extreme environmental conditions, biocrusts are susceptible to anthropogenic disturbances that can deprive ecosystems of these valuable services for decades. Until recently, culture-based efforts to produce inoculum for cyanobacterial biocrust restoration in the southwestern United States focused on producing and inoculating the most abundant primary producers and biocrust pioneers, Microcoleus vaginatus and members of the family Coleofasciculaceae (also called Microcoleus steenstrupii complex). The discovery that a unique microbial community characterized by diazotrophs, known as the cyanosphere, is intimately associated with M. vaginatus suggests a symbiotic division of labor in which nutrients are traded between phototrophs and heterotrophs. To probe the potential use of such cyanosphere members in the restoration of biocrusts, we performed coinoculations of soil substrates with cyanosphere constituents. This resulted in cyanobacterial growth that was more rapid than that seen for inoculations with the cyanobacterium alone. Additionally, we found that the mere addition of beneficial heterotrophs enhanced the formation of a cohesive biocrust without the need for additional phototrophic biomass within native soils that contain trace amounts of biocrust cyanobacteria. Our findings support the hitherto-unknown role of beneficial heterotrophic bacteria in the establishment and growth of biocrusts and allow us to make recommendations concerning biocrust restoration efforts based on the presence of remnant biocrust communities in disturbed areas. Future biocrust restoration efforts should consider cyanobacteria and their beneficial heterotrophic community as inoculants. IMPORTANCE The advancement of biocrust restoration methods for cyanobacterial biocrusts has been largely achieved through trial and error. Successes and failures could not always be traced back to particular factors. The investigation and application of foundational microbial interactions existing within biocrust communities constitute a crucial step toward informed and repeatable biocrust restoration methods. 

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2. Improving field success of biocrust rehabilitation materials: hardening the organisms or softening the environment?

   https://doi.org/10.1111/rec.12965  

   Bowker, Matthew A.; Antoninka, Anita J.; Chuckran, Peter F. (July 2019, Restoration Ecology)

   Drylands are a widely degraded biome characterized by low productivity and high abiotic stress. Biological soil crust (biocrust) inoculants hold promise as a rehabilitation material in drylands, useful for boosting ecosystem functions including stabilization of eroding soil surfaces. However, biocrust materials cultivated ex situ by humans inconsistently establish under field conditions. We tested two approaches aimed at improving field establishment of biocrust inoculum: exposing the organisms within the inoculum to abiotic stress in an attempt to harden them, and applying habitat ameliorations intended to reduce the stressfulness of the environment. We hypothesized that both approaches in concert would lead to the most consistent field establishment of biocrusts. Overall, addition of biocrust inoculum did enhance biocrust establishment over the 1.5‐year duration of the study but did not result in full recovery. Generally, hardened biocrust inoculum performed no better than inoculum that was not hardened, although one indicator (chlorophylla) was enhanced by addition of hardened inoculum in some circumstances. Temporary irrigation was initially an effective habitat amelioration but had no effect on biocrust establishment by 1.5 years. In contrast, application of jute net to the soil surface promoted biocrust establishment both in synergy with and in the absence of inoculum addition. We hypothesize that jute net stabilizes the soil surface, reduces abiotic stress, and enhances resource availability, overcoming barriers to establishment of biocrusts. Currently, there is broad support for the efficacy of habitat amelioration approaches in biocrust rehabilitation, but effective hardening techniques remain elusive. 

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3. Do soil inoculants accelerate dryland restoration? A simultaneous assessment of biocrusts and mycorrhizal fungi

   https://doi.org/10.1111/rec.13088  

   Chaudhary, V. Bala; Akland, Kristine; Johnson, Nancy C.; Bowker, Matthew A. (January 2020, Restoration Ecology)

   Biological soil crusts (biocrusts) and arbuscular mycorrhizal (AM) fungi are communities of soil organisms often targeted to assist in the achievement of multiple ecological restoration goals. In drylands, benefits conferred from biocrust and AM fungal inoculation, such as improved native plant establishment and soil stabilization, have primarily been studied separately. However, comparisons between these two types of soil inoculants and investigations into potential synergies between them, particularly at the plant community scale, are needed to inform on‐the‐ground management practices in drylands. We conducted two full‐factorial experiments—one in greenhouse mesocosms and one in field plots—to test the effects of AM fungal inoculation, biocrust inoculation, and their interaction on multiple measures of dryland restoration success. Biocrust inoculation promoted soil stabilization and plant drought tolerance, but had mixed effects on native plant diversity (positive in greenhouse, neutral in field) and productivity (negative in greenhouse, neutral in field). In greenhouse mesocosms, biocrust inoculation reduced plant biomass, which was antagonistic to % root length colonized by AM fungi. Inoculation with native or commercial AM fungi did not influence plant establishment, drought tolerance, or soil stabilization in either study, and few synergistic effects of simultaneous inoculation of AM fungi and biocrusts were observed. These results suggest that, depending on the condition of existing soil communities, inoculation with AM fungi may not be necessary to promote dryland restoration goals, while inoculation with salvaged biocrust inoculation may be beneficial in some contexts. 

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4. Biocrusts mediate a new mechanism for land degradation under a changing climate

   https://doi.org/10.1038/s41558-021-01249-6  

   Phillips, M. L.; McNellis, B. E.; Howell, A.; Lauria, C. M.; Belnap, J.; Reed, S. C. (January 2022, Nature Climate Change)

   Global concerns for desertification have focused on the slow recovery of extensive and expanding drylands following disturbance, which may be exacerbated by climate change. Biological soil crusts (biocrusts) are photosynthetic soil communities found in drylands worldwide, which are central to the stability and resilience of dryland ecosystems, but vulnerable to global change. Here we use multiple decade-long experiments to investigate the consequences of climate and land-use change on biocrusts and soil stability. Biocrusts recovered rapidly under ambient temperatures but warming interacted with the precipitation disturbance to halt recovery. Moreover, warming alone caused losses of mosses, lichens and soil stability. Our results present a new mechanism contributing to land degradation in drylands whereby warming drives a state shift in biocrust communities, which degrades soil stability. The synergistic effects of climate and land-use change co-occur globally and our results support projections of increased desertification and lowered dryland resilience under warming. 

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5. Responses of Biocrust and Associated Soil Bacteria to Novel Climates Are Not Tightly Coupled

   https://doi.org/10.3389/fmicb.2022.821860  

   Antoninka, Anita; Chuckran, Peter F.; Mau, Rebecca L.; Slate, Mandy L.; Mishler, Brent D.; Oliver, Melvin J.; Coe, Kirsten K.; Stark, Llo R.; Fisher, Kirsten M.; Bowker, Matthew A. (April 2022, Frontiers in Microbiology)

   Climate change is expanding drylands even as land use practices degrade them. Representing ∼40% of Earth’s terrestrial surface, drylands rely on biological soil crusts (biocrusts) for key ecosystem functions including soil stability, biogeochemical cycling, and water capture. Understanding how biocrusts adapt to climate change is critical to understanding how dryland ecosystems will function with altered climate. We investigated the sensitivity of biocrusts to experimentally imposed novel climates to track changes in productivity and stability under both warming and cooling scenarios. We established three common gardens along an elevational-climate gradient on the Colorado Plateau. Mature biocrusts were collected from each site and reciprocally transplanted intact. Over 20 months we monitored visible species composition and cover, chlorophyll a, and the composition of soil bacterial communities using high throughput sequencing. We hypothesized that biocrusts replanted at their home site would show local preference, and biocrusts transplanted to novel environments would maintain higher cover and stability at elevations higher than their origin, compared to at elevations lower than their origin. We expected responses of the visible biocrust cover and soil bacterial components of the biocrust community to be coupled, with later successional taxa showing higher sensitivity to novel environments. Only high elevation sourced biocrusts maintained higher biocrust cover and community stability at their site of origin. Biocrusts from all sources had higher cover and stability in the high elevation garden. Later successional taxa decreased cover in low elevation gardens, suggesting successional reversal with warming. Visible community composition was influenced by both source and transplant environment. In contrast, soil bacterial community composition was not influenced by transplant environments but retained fidelity to the source. Thus, responses of the visible and soil bacterial components of the biocrust community were not coupled. Synthesis: Our results suggest biocrust communities are sensitive to climate change, and loss of species and function can be expected, while associated soil bacteria may be buffered against rapid change. 

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