Soil fungi, microbes, microfauna, nitrogen fixation, hydrology, erosion, global change

Biological soil crusts (biocrusts) are widely distributed throughout the world, and cover approximately 12% of the terrestrial surface. Biocrusts are composed of cyanobacteria, algae, lichens, mosses, and a great diversity of other microorganisms, which bind soil particles together to form a layer of biological-soil matrix on the soil surface typically of several millimetres thickness. They are important sites of regional and global microbial diversity and perform multiple ecological functions (multifunctionality). During the evolution of terrestrial life on earth, biocrusts are regarded as the main colonising photosynthetic organisms before the advent of vascular vegetation. They not only represent the early stages of terrestrial ecosystems, but also facilitate the ecosystem’s development and succession. Therefore, biocrusts are recognised as ecological engineers in the natural development of ecosystems and for the restoration of degraded terrestrial ecosystems. The development of biocrusts is highly heterogeneous, which is reflected on both temporal and spatial scales, and this heterogeneity is still clearly visible even in a small scale. However, up to now, only limited knowledge is acquired on biocrust temporal and spatial organisation. In particular there still is a large knowledge gap regarding the various biocrust communities under different developmental states and their related physiological metabolisms and ecological functions. Therefore, in-depth studies of these issues will undoubtedly further promote our understanding of the heterogeneous development of biocrusts, as well as their ecological multifunctionality in terrestrial ecosystems. The relevant contributions are expected to provide a scientific basis for the management of biocrusts and technology development (e.g. cyanobacteria-induced biocrust technology) for ecological restoration and the promotion of soil health.

This volume summarizes our current understanding of biological soil crusts (biocrusts), which are omnipresent in dryland regions. Since they cover the soil surface, they influence, or even control, all surface exchange processes. Being one of the oldest terrestrial communities, biocrusts comprise a high diversity of cyanobacteria, algae, lichens and bryophytes together with uncounted bacteria, and fungi. The authors show that biocrusts are an integral part of dryland ecosystems, stabilizing soils, influencing plant germination and growth, and playing a key role in carbon, nitrogen and water cycling. Initial attempts have been made to use biocrusts as models in ecological theory. On the other hand, biocrusts are endangered by local disruptions and global change, highlighting the need for enhanced recovery methods. This book offers a comprehensive overview of the fascinating field of biocrust research, making it indispensable not only for scientists in this area, but also for land managers, policy makers, and anyone interested in the environment.

Biological soil crusts (biocrusts) are topsoil communities of organisms that contribute to soil fertility and erosion resistance in drylands. Anthropogenic disturbances can quickly damage these communities and their natural recovery can take decades. With the development of accelerated restoration strategies in mind, I studied physiological mechanisms controlling the establishment of cyanobacteria in biocrusts, since these photoautotrophs are not just the biocrust pioneer organisms, but also largely responsible for improving key soil attributes such as physical stability, nutrient content, water retention and albedo. I started by determining the cyanobacterial community composition of a variety of biocrust types from deserts in the Southwestern US. I then isolated a large number of cyanobacterial strains from these locations, pedigreed them based on their 16SrRNA gene sequences, and selective representatives that matched the most abundant cyanobacterial field populations. I then developed methodologies for large-scale growth of the selected isolates to produce location-specific and genetically autochthonous inoculum for restoration. I also developed and tested viable methodologies to physiologically harden this inoculum and improve its survival under harsh field conditions. My tests proved that in most cases good viability of the inoculum could be attained under field-like conditions. In parallel, I used molecular ecology approaches to show that the biocrust pioneer, Microcoleus vaginatus, shapes its surrounding heterotrophic microbiome, enriching for a compositionally-differentiated "cyanosphere" that concentrates the nitrogen-fixing function. I proposed that a mutualism based on carbon for nitrogen exchange between M. vaginatus and its cyanosphere creates a consortium that constitutes the true pioneer community enabling the colonization of nitrogen-poor, bare soils. Using the right mixture of photosynthetic and diazotrophic cultures will thus likely help in soil restoration. Additionally, using physiological assays and molecular meta-analyses, I demonstrated that the largest contributors to N2-fixation in late successional biocrusts (three genera of heterocystous cyanobacteria) partition their niche along temperature gradients, and that this can explain their geographic patterns of dominance within biocrusts worldwide. This finding can improve restoration strategies by incorporating climate-matched physiological types in inoculum formulations. In all, this dissertation resulted in the establishment of a comprehensive "cyanobacterial biocrust nursery", that includes a culture collection containing 101 strains, isolation and cultivation methods, inoculum design strategies as well as field conditioning protocols. It constitutes a new interdisciplinary application of microbiology in restoration ecology.

In biological soil crusts (biocrusts)--communities of mosses, lichens, cyanobacteria, and heterotrophs living at the soil surface-- fundamental components of drylands worldwide, and destruction of biocrusts dramatically alters biogeochemical processes, hydrology, surface energy balance, and vegetation cover are present. Though 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, in this paper 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, these results suggest that multiple aspects of climate change will affect biocrusts to the same degree as physical disturbance. Finally, 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.