Biocrust as one of multiple stable states in global drylands

Abstract

Biocrusts cover ~30% of global drylands with a prominent role in the biogeochemical cycles. Theoretically, biocrusts, vascular plants, and bare soil can represent multiple stable states in drylands. However, no empirical evidence for the existence of a biocrust stable state has been reported. Here, using a global drylands dataset, we found that biocrusts form an alternative stable state (biocrust cover, ~80%; vascular cover, ≤10%) besides bare soil (both biocrust and vascular cover, ≤10%) and vascular plants (vascular cover, >50%; biocrust cover, ~5%). The pattern of multiple stable states associated with biocrusts differs from the classic fold bifurcation, and values of the aridity index in the range of 0 to 0.6 define a bistable region where multiple stable states coexist. This study empirically demonstrates the existence and thresholds of multiple stable states associated with biocrusts along climatic gradients and thus may greatly contribute to conservation and restoration of global drylands.

Biogeography of global drylands

“…(2018) (diamonds) and Chen et al . (2020 ) (circles). See additional methodological details in Supporting Information Notes S6 and Fig.…”

Biological Soil Crust Bacterial Communities Vary Along Climatic and Shrub Cover Gradients Within a Sagebrush Steppe Ecosystem

“…Projected climatic changes in temperature and precipitation in the study site may directly or indirectly influence BSC communities and their ecosystem functions. Because biocrusts contribute to a large fraction of terrestrial biological N fixation and drive dryland emissions of reactive nitrogen (NO and HONO; Weber et al, 2015;Belnap et al, 2016;Barger et al, 2016;Chen et al, 2020), future research employing multi-omics and direct measurements of N metabolic rates will be required to fully delineate N cycling-related functional shifts in BSC communities with climatic change.…”

“…Drylands are characterized by low precipitation and limited vegetation (Belnap and Lange, 2003;Huang et al, 2016). These ecosystems cover over 35% of terrestrial landmass (Kuske et al, 2012), and are commonly colonized by biological soil crusts (BSCs; Chen et al, 2020). BSCs are a soil-surface community of mosses, lichens, liverworts, algae, archaea, cyanobacteria, and other bacteria.…”

“…BSC communities perform vital ecological functions (Belnap et al, 2016;Bowker et al, 2018), including reducing nutrient loss by runoff (Barger et al, 2006), decreasing erosion by wind (Belnap and Lange, 2003), fixing carbon (C) and nitrogen (N; Belnap, 2003;Belnap and Lange, 2003), facilitating vascular plant establishment (Belnap, 2003;Coe et al, 2014), and decreasing soil surface albedo (Belnap and Lange, 2003;Kuske et al, 2012). Despite their importance in the ecosystem structure and function in drylands, current understanding of how BSC communities respond to changing climatic conditions and environmental disturbances is still incomplete (Belnap, 2002;Belnap and Lange, 2003;Yeager et al, 2004;Kuske et al, 2012;Chen et al, 2020). Addressing these knowledge gaps may be particularly important in environments whose winter precipitation is primarily snow, as these areas are likely to undergo pronounced climate changes, with declines in precipitation amount and shifts in precipitation phase (Nayak et al, 2010;Seyfried et al, 2011;Flerchinger et al, 2019).…”

“…Following disturbance, BSC recovery can take over 1,000 years, depending on soil characteristics, severity of disturbance, and climate (Belnap, 2002). Thus, understanding how BSC bacterial communities, particularly taxonomic and functional compositions involved in N 2 fixation, vary with disturbance and climatic changes is vital to the management of these systems (Belnap et al, 2016;Steven et al, 2018;Chen et al, 2020;Velasco Ayuso et al, 2020).…”