Strategies for restoring the structure and function of lichen‐moss biocrust communities

Cyanobacterial and moss biocrusts shape soil nematode community in dryland mountain ecosystems with increasing aridity

Soil nematodes are the most abundant animals on Earth and play critical roles in regulating numerous ecosystem processes, from enhancing primary productivity to mineralizing multiple nutrients. In dryland soils, a rich community of microphyte organisms (biocrusts) provide critical habitats for soil nematodes, but their presence is being threatened by increasing aridity induced by global climate change. Despite its importance, how types of biocrusts and aridity index influence soil nematode community in dryland mountain ecosystems remains largely unknown. To fill these knowledge gaps, we conducted a field survey with contrasting aridity indexes (0.2, 0.4, and 0.6) and three types of biocrusts (cyanobacterial, cyanobacterial-moss mixed, and moss crusts) in the topsoil (0-5 cm) from the northern Chinese Loess Plateau. We found that the abundance (number of individuals per gram of soil), richness (number of Operational Taxonomic Units; OTUs), and diversity (number of different species) of soil nematodes were remarkably higher under biocrusts than in bare soils, regardless of aridity index and types of biocrusts. Our results also showed that the same variables had the highest values in moss crusts compared to cyanobacterial and cyanobacterial-moss mixed crusts. Structural equation modelling further revealed that biocrust types and traits (i.e., biocrust thickness, chlorophyll content, shear force, and penetration resistance) are the most important factors associated with both nematode abundance and richness. Together, our findings indicate that biocrusts, especially moss cover, and less stressful aridity conditions favor soil nematodes community in dryland mountain regions. Such knowledge is critical for anticipating the distribution of these animals under climate change scenarios and, ultimately, the numerous ecosystem services supported by soil nematodes.

Protist Diversity Responses to Experimental N Deposition in Biological Crusts of a Semiarid Mediterranean Ecosystem

Biological soil crusts (BSC) are associations of different macro and microorganisms and aggregated soil particles located on the surface of soils in many different habitats. BSC harbour a diverse and complex community of ciliates and testate amoebae. These phagotrophic protists play an important role in C and N recycling in soil ecosystems but have not been frequently studied in BSC. In this context, the effects of three increasing N inputs on ciliates and testate amoebae in crusts from a semi-arid Mediterranean ecosystem were evaluated. A field experiment with artificial N-deposition was designed to mimic the effects caused by anthropogenic N depositions. The results have shown that the protist populations of these semi-arid Mediterranean environments have lower species richness than other soil environments. The increase in N produces a net loss of diversity in the populations studied and shifts in the community structure. It has also been shown that some ciliates and testate amoebae, due to their population responses to increased N concentrations, could potentially be used as bio-indicators of N contamination in these BSCs.

Biocrust Amendments to Topsoils Facilitate Biocrust Restoration in a Post-mining Arid Environment

Soil cryptogamic biocrusts provide many ecological functions in arid zone ecosystems, though their natural reestablishment in disturbed areas is slow. Accelerating reestablishment of biocrusts may facilitate the establishment of vascular plant communities within the timeframes of restoration targets (typically 5–15 years). One technique is to inoculate the soil surface using slurries of biocrust material harvested from another site. However, this is destructive to donor sites, and hence the potential to dilute slurries will govern the feasibility of this practice at large spatial scales. We conducted a replicated experiment on a disturbed mine site to test the individual and combined effects of two strategies for accelerating soil cryptogamic biocrust reestablishment: (1) slurry inoculation using biocrust material harvested from native vegetation; and (2) the use of psyllium husk powder as a source of mucilage to bind the soil surface, and to potentially provide a more cohesive substrate for biocrust development. The experiment comprised 90 experimental plots across six treatments, including different dilutions of the biocrust slurries and treatments with and without psyllium. Over 20 months, the reestablishing crust was dominated by cyanobacteria (including Tolypothrix distorta and Oculatella atacamensis), and these established more rapidly in the inoculated treatments than in the control treatments. The inoculated treatments also maintained this cover of cyanobacteria better through prolonged adverse conditions. The dilute biocrust slurry, at 1:100 of the biocrust in the remnant vegetation, performed as well as the 1:10 slurry, suggesting that strong dilution of biocrust slurry may improve the feasibility of using this technique at larger spatial scales. Psyllium husk powder did not improve biocrust development but helped to maintain a soil physical crust through hot, dry, and windy conditions, and so the potential longer-term advantages of psyllium need to be tested.

Ecology and responses to climate change of biocrust-forming mosses in drylands

Interest in understanding the role of biocrusts as ecosystem engineers in drylands has substantially increased during the past two decades. Mosses are a major component of biocrusts and dominate their late successional stages. In general, their impacts on most ecosystem functions are greater than those of early-stage biocrust constituents. However, it is common to find contradictory results regarding how moss interactions with different biotic and abiotic factors affect ecosystem processes. This review aims to (i) describe the adaptations and environmental constraints of biocrust-forming mosses in drylands, (ii) identify their primary ecological roles in these ecosystems, and (iii) synthesize their responses to climate change. We emphasize the importance of interactions between specific functional traits of mosses (e.g. height, radiation reflectance, morphology, and shoot densities) and both the environment (e.g. climate, topography, and soil properties) and other organisms to understand their ecological roles and responses to climate change. We also highlight key areas that should be researched in the future to fill essential gaps in our understanding of the ecology and the responses to ongoing climate change of biocrust-forming mosses. These include a better understanding of intra- and interspecific interactions and mechanisms driving mosses' carbon balance during desiccation-rehydration cycles.