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1. Overlooked biocrust impacts on surface soil thermal properties: Evidence from heat‐pulse sensing on large volume samples

   https://doi.org/10.1111/ejss.70004  

   Chen, Junru; Xiao, Bo; Heitman, Joshua (September 2024, European Journal of Soil Science)

   Abstract Biocrusts are a critical surface cover in global drylands, but knowledge about their influences on surface soil thermal properties are still lacking because it is quite challenging to make accurate thermal property measurements for biocrust layers, which are only millimetres thick. In this study, we repacked biocrust layers (moss‐ and cyanobacteria‐dominated, respectively) that had the same material as the original intact biocrusts but was more homogeneous and thicker. The thermal conductivity (λ), heat capacity (C) and thermal diffusivity (k) of the repacked and intact biocrusts were measured by the heat pulse (HP) technique at different mass water contents (θ_m) and mass ratios (W_t), and the differences between repacked and intact biocrusts were analysed. Our results show that biocrusts substantially alter the thermal properties of the soil surface. The averageλof moss (0.37 W m⁻¹ K⁻¹) and cyanobacteria biocrusts (0.90 W m⁻¹ K⁻¹) were reduced by 63.0% and 10.3% compared with bare soil (1.00 W m⁻¹ K⁻¹), respectively. Edge effects including heat loss and water evaporation caused theλandkof the biocrusts to be underestimated, but theCto be overestimated. The differences in thermal properties were significant (p <0.001), except for the differences in thermal conductivity between repacked and intact cyanobacteria biocrusts, which were not significant (p = 0.379). Specifically, in the volumetric water content (θ_v) range of 0 to 20%, theλandkof the repacked moss biocrusts were underestimated by 59.1% and 61.8%, respectively, and theCwas overestimated by 23.9% compared with the intact moss biocrusts. Theλandkof the repacked cyanobacteria biocrusts were underestimated by 15.8% and 79.2%, respectively, and theCwas overestimated by 34.8% compared with the intact cyanobacteria biocrusts at theθ_vrange of 0 to 30%. Typically, this difference increased as theθ_vrises between repacked and intact biocrusts. Our new measurements provide evidence that the thermal properties of biocrusts were previously misjudged due to the measurement limitations imposed by their limited thickness when measured in situ. Biocrusts are likely more significant in regulating soil heat and temperature in drylands than was previously assumed. 

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2. Soil-atmosphere fluxes of CO2, CH4, and N2O across an experimentally-grown, successional gradient of biocrust community types

   https://doi.org/10.3389/fmicb.2022.979825  

   Richardson, Andrew D; Kong, Gary V; Taylor, Katrina M; Le_Moine, James M; Bowker, Matthew A; Barber, Jarrett J; Basler, David; Carbone, Mariah S; Hayer, Michaela; Koch, George W; et al (September 2022, Frontiers in Microbiology)

   Biological soil crusts (biocrusts) are critical components of dryland and other ecosystems worldwide, and are increasingly recognized as novel model ecosystems from which more general principles of ecology can be elucidated. Biocrusts are often diverse communities, comprised of both eukaryotic and prokaryotic organisms with a range of metabolic lifestyles that enable the fixation of atmospheric carbon and nitrogen. However, how the function of these biocrust communities varies with succession is incompletely characterized, especially in comparison to more familiar terrestrial ecosystem types such as forests. We conducted a greenhouse experiment to investigate how community composition and soil-atmosphere trace gas fluxes of CO₂, CH₄, and N₂O varied from early-successional light cyanobacterial biocrusts to mid-successional dark cyanobacteria biocrusts and late-successional moss-lichen biocrusts and as biocrusts of each successional stage matured. Cover type richness increased as biocrusts developed, and richness was generally highest in the late-successional moss-lichen biocrusts. Microbial community composition varied in relation to successional stage, but microbial diversity did not differ significantly among stages. Net photosynthetic uptake of CO₂by each biocrust type also increased as biocrusts developed but tended to be moderately greater (by up to ≈25%) for the mid-successional dark cyanobacteria biocrusts than the light cyanobacterial biocrusts or the moss-lichen biocrusts. Rates of soil C accumulation were highest for the dark cyanobacteria biocrusts and light cyanobacteria biocrusts, and lowest for the moss-lichen biocrusts and bare soil controls. Biocrust CH₄and N₂O fluxes were not consistently distinguishable from the same fluxes measured from bare soil controls; the measured rates were also substantially lower than have been reported in previous biocrust studies. Our experiment, which uniquely used greenhouse-grown biocrusts to manipulate community composition and accelerate biocrust development, shows how biocrust function varies along a dynamic gradient of biocrust successional stages. 

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3. The pervasive and multifaceted influence of biocrusts on water in the world's drylands

   https://doi.org/10.1111/gcb.15232  

   Eldridge, David J.; Reed, Sasha; Travers, Samantha K.; Bowker, Matthew A.; Maestre, Fernando T.; Ding, Jingyi; Havrilla, Caroline; Rodriguez‐Caballero, Emilio; Barger, Nichole; Weber, Bettina; et al (July 2020, Global Change Biology)

   Abstract The capture and use of water are critically important in drylands, which collectively constitute Earth's largest biome. Drylands will likely experience lower and more unreliable rainfall as climatic conditions change over the next century. Dryland soils support a rich community of microphytic organisms (biocrusts), which are critically important because they regulate the delivery and retention of water. Yet despite their hydrological significance, a global synthesis of their effects on hydrology is lacking. We synthesized 2,997 observations from 109 publications to explore how biocrusts affected five hydrological processes (times to ponding and runoff, early [sorptivity] and final [infiltration] stages of water flow into soil, and the rate or volume of runoff) and two hydrological outcomes (moisture storage, sediment production). We found that increasing biocrust cover reduced the time for water to pond on the surface (−40%) and commence runoff (−33%), and reduced infiltration (−34%) and sediment production (−68%). Greater biocrust cover had no significant effect on sorptivity or runoff rate/amount, but increased moisture storage (+14%). Infiltration declined most (−56%) at fine scales, and moisture storage was greatest (+36%) at large scales. Effects of biocrust type (cyanobacteria, lichen, moss, mixed), soil texture (sand, loam, clay), and climatic zone (arid, semiarid, dry subhumid) were nuanced. Our synthesis provides novel insights into the magnitude, processes, and contexts of biocrust effects in drylands. This information is critical to improve our capacity to manage dwindling dryland water supplies as Earth becomes hotter and drier. 

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4. 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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5. Cover and frequency of biological soil crust community types, moss species, vascular plants, and abiotic land surface features, on gypsum & non-gypsum soils from the Chihuahuan and Mojave Deserts in 2023

   https://doi.org/10.6073/pasta/488c8b229fed3e872a57a9125986e5a8  

   Gobbie, Katelyn G; Drenovsky, Rebecca E; Pietrasiak, Nicole (January 2024, Environmental Data Initiative)

   This dataset contains raw and calculated percent cover and frequency data for biological soil crust (hereafter biocrust) functional groups, vascular plant functional groups, and abiotic land surface features on and off gypsum soils in the northern Chihuahuan and eastern Mojave Deserts. Abundance data were obtained from 20 study sites total, 10 located on soils derived from gypsum parent material and 10 located on soils derived from non-gypsum parent materials. Sites were grouped into 10 pairs, in which every gypsum site was partnered with a non-gypsum site located in the same region. Apart from soil type, partnered-site characteristics (topography, climate, elevation, slope, aspect, and presence of biocrusts) were held relatively constant. At each site, cover and frequency assessments were made using the line-point intercept method (LPI) and frequency quadrats (1.0 m^2), respectively. Biocrust functional groups included the following crusts: lichen, moss, incipient algal, light algal, dark algal, unknown photosynthetic crust, and vagrant cyanobacteria. Vascular plant categories included: perennial forbs, perennial graminoids, annual forbs, annual graminoids, subshrub, shrub, Yucca, and cacti. Abiotic land surface features included: woody litter, herbaceous litter, bare soil, rock, bedrock, and animal feces. Moss crusts identified within cover and frequency analyses were sampled, and classified to species level via microscopy. The resulting percent cover and frequency data was used to understand differences in biocrust and moss species abundance and diversity on and off gypsum soils; furthermore, how biocrust and moss species abundance was associated with the measured environmental variables. Soil physical and chemical data from this study can be accessed at knb-lter-jrn.210616002. This study and dataset are complete. 

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