The influence of climatic legacies on the distribution of dryland biocrust communities

Biocrusts protect the Great Wall of China from erosion

The Great Wall of China, one of the most emblematic and historical structures built by humankind throughout all of history, is suffering from rain and wind erosion and is largely colonized by biocrusts. However, how biocrusts influence the conservation and longevity of this structure is virtually unknown. Here, we conducted an extensive biocrust survey across the Great Wall and found that biocrusts cover 67% of the studied sections. Biocrusts enhance the mechanical stability and reduce the erodibility of the Great Wall. Compared with bare rammed earth, the biocrust-covered sections exhibited reduced porosity, water-holding capacity, erodibility, and salinity by 2 to 48%, while increasing compressive strength, penetration resistance, shear strength, and aggregate stability by 37 to 321%. We further found that the protective function of biocrusts mainly depended on biocrust features, climatic conditions, and structure types. Our work highlights the fundamental importance of biocrusts as a nature-based intervention to the conservation of the Great Wall, protecting this monumental heritage from erosion.

Cyanobacterial community composition and their functional shifts associated with biocrust succession in the Gurbantunggut Desert

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.

Cyanobacterial persistence and influence on microbial community dynamics over 15 years in induced biocrusts

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.

Resistance, Resilience, and Recovery of Dryland Soil Bacterial Communities Across Multiple Disturbances

Dryland ecosystems are sensitive to perturbations and generally slow to recover post disturbance. The microorganisms residing in dryland soils are especially important as they contribute to soil structure and nutrient cycling. Disturbance can have particularly strong effects on dryland soil structure and function, yet the natural resistance and recovery of the microbial components of dryland soils has not been well documented. In this study, the recovery of surface soil bacterial communities from multiple physical and environmental disturbances is assessed. Samples were collected from three field sites in the vicinity of Moab, UT, United States, 6 to 7 years after physical and climate disturbance manipulations had been terminated, allowing for the assessment of community recovery. Additionally, samples were collected in a transect that included three habitat patches: the canopy zone soils under the dominant shrubs, the interspace soils that are colonized by biological soil crusts, and edge soils at the plot borders. Field site and habitat patch were significant factors structuring the bacterial communities, illustrating that sites and habitats harbored unique soil microbiomes. Across the different sites and disturbance treatments, there was evidence of significant bacterial community recovery, as bacterial biomass and diversity were not significantly different than control plots. There was, however, a small number of 16S rRNA gene amplicon sequence variants that distinguished particular treatments, suggesting that legacy effects of the disturbances still remained. Taken together, these data suggest that dryland bacterial communities may possess a previously unappreciated potential to recover within years of the original disturbance.

The response of dust emission sources to climate change: Current and future simulation for southwest of Iran

This study recognizes present dust emission sources (DESs) and their future projections in the southwest of Iran (2050 and 2070) through simulations performed by distribution models. The sites observation, raster dataset of climate layers and statistical models in the MaxEnt software were used to predict the current and future dust coverage and distribution, and their response to climate change using representative concentration pathways (RCPs) scenarios of +2.6, +4.5, +6.0, and +8.5 W m^-2 projections. Statistical machine learning analysis show that 40.8% of the study area covering 25,810 km² are susceptible to emit dust at the present time, and its projections will increase up to 28,839, 26,002, 26,071 and 26,124 km² for RCP scenarios of +2.6, +4.5, +6.0, and +8.5 W m^-2, respectively, by the year 2070. Temperature and precipitation assessments show that the most effective parameters determine future changes in DES coverage and distribution. The area under the curve (AUC) for DESs was 0.919, and results of Jackknife analyses show high sensitivity of dust sources to climate variables. The results illustrate that the present DESs are mainly driven by a combination of temperature, precipitation and land-use management, and the effects of nature are comparable to the anthropogenic activities, as humans continue to shape the DESs through energy, water and land use. The predicted increase of DESs may substantially worsen dust storms in the future, thereby affecting the functioning of ecosystems as well as human health. The outcomes of this study may support biocrust restoration technologies as a suitable option in sustainable management of arid lands and dust emission sources.