Biological Soil Crust Cover Research Articles

Do topographic changes tell us about variability in aeolian sediment transport and dune mobility? Analysis of monthly to decadal surface changes in a partially vegetated and biocrust covered dunefield

Vegetation and biological soil crust (biocrust) cover can have a stabilizing effect on dunes by fixing sediment in-place and increasing surface roughness, thus limiting dune mobility, sediment transport, and erosion. These biological effects influence rates of aeolian activity and thus surficial changes, though variability in wind and sediment supply may obscure these topographic effects. In this study, we compare monthly measures of sediment transport and decadal estimates of dune mobility to repeat topographic changes measured as a net volume change in sediment storage (difference in volume between all positive and negative topographic changes) and total volume change (absolute summed volume of all positive and negative changes) for areas of bare, vegetated, and biocrusted sand within a dunefield with limited sediment supply and unimodal winds. We found that monthly net volume changes normalized by area were similar between bare sand and sand with at least 20 % vegetation cover. However, total volume change was significantly greater for bare sand and correlated with monthly sediment flux estimates (R2 = 0.46), though the relationship was significantly improved by including monthly changes in surface roughness (R2 = 0.8). Longer-term decadal trends in topographic change showed larger total volume changes with the greatest decreases in vegetation canopy cover. Additionally, decadal total volume changes strongly correlated with estimates of dune mobility (R2 = 0.99). We also found that increased total volume changes did not necessarily signal increased net volume changes for all land cover types. Specifically, increases in total volume change for bare sand resulted in near equal or lower net volume changes, as both positive (deposition) and negative (erosion) change increased with sediment transport. Conversely, less mobile land covers, such as biocrust covered sand, increased in erosion without significant increases in total volume change, demonstrating that more stable surfaces might exhibit a larger topographic change imbalance than mobile sediment surfaces under the same conditions. This study highlights the importance of considering multiple measures of topographic change for interpreting sediment mobility, transport, and availability. Additionally, we hypothesize a novel framework for remote sensing-based empirical studies aimed at interpreting aeolian landscape evolution resulting from climate change effects on weather as well as biological controls such as vegetation and biocrusts.

Hydrological heterogeneity and the plant colonization of recently deglaciated terrain

ABSTRACT Climate change accelerates glacier retreat, leading to extensive exposure of sediment to light and ecological succession. Succession has traditionally been studied as a chronosequence, where vegetation development is directly correlated with time since glacier retreat or distance from the retreating glacier margin. More recent work has challenged this model, arguing that succession seems to be mainly influenced by heterogeneous conditions at the local scale. The aim of this study was to identify the factors influencing the local-scale establishment of plant communities following glacier recession. Vascular plants and their cover were inventoried in 100 plots (1 m2) for a thirty-year-old alluvial plain in front of the Otemma glacier (Swiss Alps). Depth to water table, distance to the glacial main river and to the nearest channel, sediment size, moss, lichen, and biological soil crust cover were measured. Results showed that proglacial margins develop hydrological heterogeneity over a small scale, reflected in the four observed plant communities. These range from the dry Sempervivum-dominated community, on gravel-rich sediments with a deep water table, to the Trifolium-dominated community, close to secondary channels, with the highest plant cover and species richness and incorporating grassland species. Heterogeneity in water availability exerted a critical control on vegetation development.

An advanced coverage estimation method to quantify biological soil crust coverage using Sentinel-2 imagery in desert and sandy land of China

ABSTRACT Monitoring the distribution and area change of biological soil crusts (BSCs) can enhance our understanding of the interactions between nonvascular plants and the environment in drylands. However, using only pixel-based binary classification methods results in large-area estimation errors at large scales. The lack of available calculation methods for directly measuring BSC coverage using multispectral satellite images makes it challenging to obtain BSC area data for further studies at large scales. To address these issues, this study developed feature space conceptual models for desert and sandy land based on the characteristics of BSC in drylands. The desert feature space comprised the normalized difference vegetation index (NDVI) combined with the brightness index (BI), encompassing moss, lichen, and non-BSC. The sandy land feature space relied on the biological soil crust index (BSCI) and the NDVI, including vegetation, mixed BSCs and sandy soil. Using Sentinel-2 satellite imagery and a spectral unmixing model, the abundance of BSCs was quantified in four BSC growth areas located in the Gurbantunggut Desert and Mu Us Sandy Land of China. Validation of the method indicated that the root mean square error (RMSE) of the BSC coverage estimation results was 10% and 8% in desert and sandy land, respectively (estimation accuracies of 79% and 81%, respectively). This demonstrated that the proposed method can effectively estimate BSC coverage at a subpixel scale. The resulting BSC coverage data can provide the possibility to evaluate the functions of regional ecosystems.

The effectiveness of weed control in a threatened plant community: A grassland case study

Habitat loss due to altered land use has resulted in the fragmentation of remnant grasslands, resulting in an increase in the edge to area ratio and a subsequent rise in the risk of weed invasion. Restoration in threatened remnant grasslands focus on spot-spraying high threat herbaceous weeds with herbicides (i.e. weed control) as a dominant management action, but there is limited knowledge about the ecological outcomes of weed control effectiveness in these systems.In this study, we conducted a Before-After-Control-Impact analysis over three years using 32 linear grassland remnants to test whether weed control can improve grassland condition. Our predictions were that weed control would: (i) reduce the cover and health of pervasive exotic perennial grasses (i.e. target weeds), (ii) increase the cover of native plants by removing competition from target weeds, and (iii) not affect native plant richness as any recolonization will likely be from species already occurring in the area of sampling. We also predicted that weed control would shift the cover of ground layer attributes towards levels more appropriate for a grassland in good condition.Our results show that short-term weed control can be effective in reducing the cover and health of target weeds with minimal effects on native vascular plants. Changes in bare ground and litter cover following weed control were dynamic and complementary. A reduction in soil crust cover after two consecutive weed control treatments could lead to altered survival and recruitment dynamics of native grassland plants.Effective weed control requires actions that limit subsequent re-invasion by target weeds and promote a microenvironment suitable for native species to re-colonise. Our findings suggest a need to assess (i) if changes in ground layer cover post herbicide application affects native vegetation recruitment, and (ii) if other management activities, such as burning (in combination with, or independent of, weed control), are effective in controlling weeds while promoting better outcomes for ground layer cover (i.e. biological soil crust does not decrease) and native species (i.e. cover increases). If a strategy that eliminates target weeds while maintaining biological soil crust cover and increasing native cover can be identified, it will greatly improve the long-term restoration of these highly threatened grasslands.

Droughting a megadrought: ecological consequences of a decade of experimental drought atop aridification on the Colorado Plateau.

Global dryland vegetation communities will likely change as ongoing drought conditions shift regional climates towards a more arid future. Additional aridification of drylands can impact plant and ground cover, biogeochemical cycles, and plant-soil feedbacks, yet how and when these crucial ecosystem components will respond to drought intensification requires further investigation. Using a long-term precipitation reduction experiment (35% reduction) conducted across the Colorado Plateau and spanning ten years into a 20+ year regional megadrought, we explored how vegetation cover, soil conditions, and growing season nitrogen (N) availability are impacted by drying climate conditions. We observed large declines for all dominant plant functional types (C3 and C4 grasses and C3 and C4 shrubs) across measurement period, both in the drought treatment and control plots, likely due to ongoing regional megadrought conditions. In experimental drought plots, we observed less plant cover, less biological soil crust cover, warmer and drier soil conditions, and more soil resin-extractable N compared to the control plots. Observed increases in soil N availability were best explained by a negative correlation with plant cover regardless of treatment, suggesting that declines in vegetation N uptake may be driving increases in available soil N. However, in ecosystems experiencing long-term aridification, increased N availability may ultimately result in N losses if soil moisture is consistently too dry to support plant and microbial N immobilization and ecosystem recovery. These results show dramatic, worrisome declines in plant cover with long-term drought. Additionally, this study highlights that more plant cover losses are possible with further drought intensification, and underscore that, in addition to large drought effects on aboveground communities, drying trends drive significant changes to critical soil resources such as N availability, all of which could have long-term ecosystem impacts for drylands.

Spectral determinants of biological soil crusts in the Gurbantungut Desert

ABSTRACT As thick crustal layers form on dryland surfaces, they affect the spectral information that is originally dominated by sand or rock. The spectral characteristics of organic matter replace the mineral elements as prominent features. In this case, the growth patterns and spectral characteristics of biological soil crusts (BSCs) can be observed. Satellite spectral data have been used for BSC spatial information extraction. However, the dynamic changes in BSCs can affect the spectra. Two aspects are involved here: moisture change and BSC growth. When these changes are superimposed with BSC succession, they lead to an increase in spectral complexity. This study explored three BSC types, including algal crust, lichen and moss, and discussed their spectra. By selecting BSC samples at different succession states and by combining coverage and simulated precipitation, the response of the spectra to BSC coverage and the spectral characteristics of BSCs under dry and wet conditions were measured and analysed. In addition, the spectral index variations caused by coverage and moisture of three types of BSCs were discussed, where the spectral indices include the normalized difference vegetation index (NDVI), brightness index (BI), crust index (CI), and biological soil crust index (BSCI). The results showed that the succession, moisture and growth of BSCs were the main factors affecting their spectra. BSC types can be distinguished in a particular climatic context to determine the degree of BSC succession. Precipitation in the monitoring areas needs to be considered to avoid the effects of dry and wet BSC variations on remote sensing monitoring. The coverage of different types of BSCs in mixed pixels can be determined by multiple indices. The results of this study will provide a basis for monitoring BSCs using satellite spectral information to guide regional ecological management.

Las comunidades criptógamas como potenciales indicadores de recuperación post-fuego en el pedemonte

Among the disturbances affecting terrestrial ecosystems, fire is one of the most important in the Monte ecoregion of Argentina. In the foothills, recurrent fires generate changes in the composition of the vegetation and the physiognomy of the landscape, without knowledge of the effects of fire on cryptogams. Cryptogams include biological soil crusts (BSC), corticolous and saxicolous lichens, and mosses. These communities are crucial in degraded ecosystems and in arid zones by fixing nitrogen and stabilizing the soil. Furthermore, some of the organisms of BSC develop quite slowly and are sensitive to disturbances, which makes them potentially useful as indicators of disturbance or recovery. In this work, we evaluate the cover and frequency of functional types of cryptogams, as well as the environmental factors that favor their development in sites with different fire histories, in order to identify potential indicators of post-fire recovery. We found that saxicolous and corticolous lichen frequency, BSC cover and cyanobacterial-dominated BSC frequency varied as a function of post-fire recovery time. Their cover and frequency were also affected by the cover of vascular plants, bare soil, rocks and mounds generated by animals. These variations in abundance can be used as indicators of the success of passive ecological restoration strategies. Corticolous and saxicolous lichens may function as indicators of post-fire recovery as they are only present on sites with +40 years since the latest fire and showed a greater response than vascular plants. On the other hand, CBS dominated by cyanobacteria —being more abundant in sites with recent fires— would be good indicators of more recent soil recovery processes. The wide distribution of BSC dominated by mosses, and the development of cyanobacteria in recently disturbed places, highlight the potential of these two groups of organisms to actively and more quickly restore arid ecosystems degraded by fires.

BSC (biological soil crust) Method for soil erosion control and vegetation recovery: Case studies in Japan

The biological soil crust (BSC) is a naturally occurring vegetation layer in the topsoil that is composed of a diverse array of microscopic living organisms such as cyanobacteria, green algae, lichen, liverworts, moss, micro-fungi, and other bacteria. BSC cover is well recognized for mitigating soil erosion caused by wind forces and overland flow. By forming a sheet-like soil microbe community, BSC cover can bind loose soil particles, stabilize and protect soil surfaces. This article reviews the applications of human-induced BSC, namely BSC Method, that was developed by the Japanese company Nippon Koei Co. Ltd. The BSC Method utilizes an algal species called BSC-1. We also discussed the BSC projects undertaken by Nippon Koei Co. Ltd between 2016 and 2021. BSC Method has been demonstrated to be effective in preventing and controlling soil erosion and regenerating vegetation; this method is simple, eco-friendly, and inexpensive.

Small effects of livestock grazing intensification on diversity, abundance, and composition in a dryland plant community.

Livestock grazing is a globally important land use and has the potential to significantly influence plant community structure and ecosystem function, yet several critical knowledge gaps remain on the direction and magnitude of grazing impacts. Furthermore, much of our understanding of the long-term effects on plant community composition and structure are based on grazer exclusion experiments, which explicitly avoid characterizing effects along grazing intensity gradients. We sampled big sagebrush plant communities using 68 plots located along grazing intensity gradients to determine how grazing intensity influences multiple aspects of plant community structure over time. This was accomplished by sampling plant communities at different distances from 17 artificial watering sources, using distance from water and cow dung density as proxies for grazing intensity at individual plots. Total vegetation cover and total grass cover were negatively related to grazing intensity, and cover of annual forbs, exotic cover, and exotic richness were positively related to grazing intensity. In contrast, species richness and composition, bunchgrass biomass, shrub density and size, percentage cover of bare ground, litter, and biological soil crusts did not vary along our grazing intensity gradients, in spite of our expectations to the contrary. Our results suggest that the effects of livestock grazing over multiple decades (mean=46 years) in our sites are relatively small, especially for native perennial species, and that the big sagebrush plant communities we sampled are somewhat resistant to livestock grazing. Collectively, our findings are consistent with existing evidence that indicates the stability of the big sagebrush plant functional type composition under current grazing management regimes.

Vegetative growth and belowground expansion from transplanted low‐arctic tundra turfs

Whole‐turf transplantation is a restoration method used to restore plant communities within disturbed arctic environments. Transplant expansion and restoration success is often determined based on aboveground characteristics, and to our knowledge, this is the first investigation of belowground expansion from transplanted turfs. In this growth chamber experiment, turfs harvested from undisturbed tundra near Rankin Inlet, Nunavut, Canada, were exposed to fertilized and unfertilized substrates to determine the effect of adjacent nutrient‐enrichment on plant community composition within the turfs and substrates, as well as above and belowground biomass and expansion. Next‐generation sequencing was used to determine the species identity of expanding roots. Our results show that fertilization of substrates surrounding tundra transplants did not alter the community composition of the turfs, but did increase biomass and expansion, as well as biological soil crust cover on the adjacent substrate. Belowground biomass far exceeded aboveground, revealing the importance of evaluating belowground roots and rhizomes that dominate the vegetative biomass within arctic ecosystems. Investigation of belowground development is likely to provide holistic interpretations of restoration success and should not be ignored in future transplantation studies.

Global cycling and climate effects of aeolian dust controlled by biological soil crusts

Biological soil crusts (biocrusts) cover ~12% of the global land surface. They are formed by an intimate association between soil particles, photoautotrophic and heterotrophic organisms, and they effectively stabilize the soil surface of drylands. Quantitative information on the impact of biocrusts on the global cycling and climate effects of aeolian dust, however, is not available. Here, we combine the currently limited experimental data with a global climate model to investigate the effects of biocrusts on regional and global dust cycling under current and future conditions. We estimate that biocrusts reduce the global atmospheric dust emissions by ~60%, preventing the release of ~0.7 Pg dust per year. Until 2070, biocrust coverage is expected to be severely reduced by climate change and land-use intensification. The biocrust loss will cause an increased dust burden, leading to a reduction of the global radiation budget of around 0.12 to 0.22 W m−2, corresponding to about 50% of the total direct forcing of anthropogenic aerosols. This biocrust control on dust cycling and its climate impacts have important implications for human health, biogeochemical cycling and the functioning of the ecosystems, and thus should be considered in the modelling, mitigation and management of global change.

Spatial cover and carbon fluxes of urbanized Sonoran Desert biological soil crusts

Biological soil crusts (BSC) are important contributors to nutrient cycling in arid environments such as the Sonoran Desert. BSC at an urban (University Indian Ruins) and at a non-urban site (Santa Rita Experimental Range) were compared to determine if their structure or function was influenced by proximity to an urban environment. The Step Point method was used in the field to determine ground cover; which was found to be similar between sites. However, the spatial distribution of the BSCs was significantly different, such that more BSCs were found under plants at the non-urban site (P < 0.05). Relative gross photosynthesis was measured in the lab by addition of a watering event. Gross photosynthesis was found to be higher in the non-urban BSCs (P < 0.001), indicating lowered productivity in urban BSCs due to effects caused by proximity to urban environments. This study provides evidence that BSCs at urbanized sites are affected functionally, and therefore may be contributing differently to carbon and nitrogen cycling in these ecosystems.

Moderate Grazing During the Off-Season (Fall-Winter) Reduces Exotic Annual Grasses in Sagebrush-Bunchgrass Steppe

Exotic annual grass invasion and dominance of sagebrush-bunchgrass steppe is a concern because it decreases biodiversity and promotes frequent wildfires. Management is needed to reduce exotic annual grasses to prevent sagebrush-bunchgrass communities from transitioning to annual grasslands. Grazing during the off season (fall-winter) has shown promise at reducing exotic annual grasses, but it has not been evaluated in plant communities dominated by sagebrush and native bunchgrasses. We compared moderate grazing during the off season with not grazing in five Wyoming big sagebrush (Artemisia tridentata ssp. wyomingensis [Beetle & A. Young] S.L. Welsh)−bunchgrass communities in the northern Great Basin. Treatments were applied annually for 10 yr (2009−2010 through 2018−2019). Plant community characteristics were measured after treatments had been applied from 6 to 10 yr. Off-season grazing reduced exotic annual grass density and cover. After a decade, annual grass cover was twofold greater in ungrazed areas. Sandberg bluegrass (Poa secunda J. Presl) density increased with off-season grazing, but large bunchgrass density was similar between off-season grazed and ungrazed areas. Perennial and annual forb density and cover were similar between off-season grazed and ungrazed treatments. Biological soil crust cover was also similar between off-season grazed and ungrazed areas. The results of this study provide strong evidence that off-season grazing has application for managing exotic annual grasses in sagebrush-bunchgrass steppe. Considering the vast scope of the exotic annual grass problem, properly applied grazing may be the most cost-efficient tool to mediate the impacts of annual grass invasion.

Response of biocrust nitrogenase activity to the variation of rainfall regime in the Tengger Desert, northern China

In arid desert regions, a large proportion of the ground surface is covered by specialized organisms such as cyanobacteria and mosses that form biological soil crusts (BSCs), which have multifunctionality in the ecosystem via stabilizing soil and fixing nitrogen (N) and carbon (C). Climate change, especially variations in rainfall will alter BSC species composition, cover and biomass, shaping the N-fixation of BSCs. Although BSCs are main contributors of N in desert ecosystems, it is not clear how nitrogenase activity (NA) of BSCs responds to changes in rainfall amount and frequency to function in the N-cycle. To address this important knowledge gap, based on long-term rainfall monitoring and predicted scenarios, we designed five levels of rainfall amount ranging from decreased by 50% to increased by 50%, and five rainfall frequencies ranging from increased by 100% to decreased by 80%, to simulate the potential variation of rainfall using rainout shelters. The NA of bare soil and cyanobacteria- and moss-dominated crust soil (three soil types) was determined by acetylene reduction assay. The soil water content (SWC), oxidable C and microbial biomass C and N were also determined. The NA of the three soil types was positively correlated with their SWC when rainfall amount decreased. In the case of increased rainfall frequency, NA of bare soil and moss-dominated crust was positively correlated with SWC, but negatively correlated for cyanobacteria-dominated crust. However, with increased rainfall amount combined with decreased rainfall frequency, there was no significant relationship between NA and SWC. In addition, NA of BSC was higher than that of bare soil with increased rainfall amount combined with decreased rainfall frequency, while that of bare soil was higher than that of BSC for decreased rainfall amount combined with increased rainfall frequency. In the case of increased frequency combined with decreased rainfall amount, the NA was higher for moss-dominated than cyanobacteria-dominated crust, but higher for cyanobacteria-dominated than moss-dominated crust for reduced rainfall frequency combined with increased rainfall amount. Meanwhile, NA of both bare soil and moss-dominated crust was correlated with microbial biomass C; and NA of cyanobacteria-dominated crust was positively correlated with SWC as well as oxidable C. Our findings indicated that future changes in rainfall regime will strongly affect NA of BSCs and bare soil in arid desert regions, and consequently change the soil fertility and net primary production.

Combined impact of moss crust coverage rates and distribution patterns on wind erosion using beryllium-7 measurements

Although biological soil crusts (BSCs) provide considerable control over wind erosion in arid and semiarid regions, understanding of BSCs coverage rates and distribution patterns impacts on wind erosion is remain limited, which further causes poor quantification of BSCs factors in wind erosion prediction models. This study estimated wind erosion affected by moss crust coverage rates and distribution patterns using the weighting approach and beryllium-7 measurements through wind tunnel experiments, and screened factors that significantly influence wind erosion based on landscape metrics and multiple linear regression. Results showed that both moss crust coverage and distribution pattern significantly affected wind erosion and deposition. When moss crust coverage increased from 10% to 80%, average erosion rates in bare soil areas of trays almost all decreased logarithmically from 623.0 to 27.4 g m−2 min−1, while the average deposition rates in moss crust covered areas decreased from −21.7 to −16.7 g m−2 min−1. Moss crust located at the middle area of trays (SCS) showed better overall erosion control effects, while moss crust located at downwind of sand (SC) showed better sediment trapping effects compared to other distribution patterns when moss crust coverage was the same. The SCS and SC patterns decreased wind erosion and deposition rates reached up to 81.9% and 38.0%, respectively. Moreover, wind erosion rates when arranged moss crust parallel to the wind direction resulted in significantly higher soil erosion (i.e., by a factor up to 7.3) compared to that of perpendicular to the wind direction. Stepwise regression showed that only wind velocity and moss crust coverage were included in the linear regression equation with a relatively low R2 value (R2 = 0.35), but excluded other landscape metrics. This is indicated the importance of developing composite indices and their associative algorithms should be considered when quantifying spatial distribution impacts of BSCs on wind erosion.

Effects of climate change and land use intensification on regional biological soil crust cover and composition in southern Africa

Biological soil crusts (biocrusts) form a regular and relevant feature in drylands, as they stabilize the soil, fix nutrients, and influence water cycling. However, biocrust forming organisms have been shown to be dramatically vulnerable to climate and land use change occurring in these regions.In this study, we used Normalized Difference Vegetation Index (NDVI) data of biocrust-dominated pixels (NDVIbiocrust) obtained from hyperspectral and LANDSAT-7 data to analyse biocrust development over time and to forecast future NDVIbiocrust development under different climate change and livestock density scenarios in southern Africa. We validated these results by analysing the occurrence and composition of biocrusts along a mesoclimatic gradient within the study region.Our results show that NDVIbiocrust, which reached maximum values of 0.2 and 0.4 in drier and wetter years, respectively, mainly depended on water availability. A predicted decrease in rainfall events according to all future climate scenarios combined with increased temperatures suggested a pronounced decrease in NDVIbiocrust by the end of the 21st century caused by reduced biocrust coverage. Livestock trampling had similar effects and exacerbated the negative impacts of climate change on biocrust coverage and composition. Data assessed in the field concurred with these results, as reduced biocrust cover and a shift from well-developed to early stages of biocrust development were observed along a gradient of decreasing precipitation and increasing temperatures and livestock density.Our study demonstrates the suitability of multi-temporal series of historical satellite images combined with high-resolution mapping data and Earth system models to identify climate change patterns and their effects on biocrust and vegetation patterns at regional scales.

Coverage and Rainfall Response of Biological Soil Crusts Using Multi-Temporal Sentinel-2 Data in a Central European Temperate Dry Acid Grassland

Biological soil crusts (BSCs) are thin microbiological vegetation layers that naturally develop in unfavorable higher plant conditions (i.e., low precipitation rates and high temperatures) in global drylands. They consist of poikilohydric organisms capable of adjusting their metabolic activities depending on the water availability. However, they, and with them, their ecosystem functions, are endangered by climate change and land-use intensification. Remote sensing (RS)-based studies estimated the BSC cover in global drylands through various multispectral indices, and few of them correlated the BSCs’ activity response to rainfall. However, the allocation of BSCs is not limited to drylands only as there are areas beyond where smaller patches have developed under intense human impact and frequent disturbance. Yet, those areas were not addressed in RS-based studies, raising the question of whether the methods developed in extensive drylands can be transferred easily. Our temperate climate study area, the ‘Lieberoser Heide’ in northeastern Germany, is home to the country’s largest BSC-covered area. We applied a Random Forest (RF) classification model incorporating multispectral Sentinel-2 (S2) data, indices derived from them, and topographic information to spatiotemporally map the BSC cover for the first time in Central Europe. We further monitored the BSC response to rainfall events over a period of around five years (June 2015 to end of December 2020). Therefore, we combined datasets of gridded NDVI as a measure of photosynthetic activity with daily precipitation data and conducted a change detection analysis. With an overall accuracy of 98.9%, our classification proved satisfactory. Detected changes in BSC activity between dry and wet conditions were found to be significant. Our study emphasizes a high transferability of established methods from extensive drylands to BSC-covered areas in the temperate climate. Therefore, we consider our study to provide essential impulses so that RS-based biocrust mapping in the future will be applied beyond the global drylands.

Developmental characteristics of biological soil crusts and their effects on soil water infiltration on karst slope

Biological soil crusts (BSCs), as a pioneer for vegetation restoration and crucial component of surface landscape, greatly affect land surface process. To explore the development of BSCs and its effects on soil water infiltration in karst region, we investigated the development of BSCs and analyzed the infiltration processes with different BSCs coverages (0, 28%, 40%, 70%, 97%) and rainfall intensities (42 and 132 mm·h-1) in simulating rainfall experiments on a typical karst slope. The results showed that there were significant differences in the development of BSCs for different land use types, whereas the spatial variation of BSCs development on the slope was not obvious under the same land use type. Compared to the bare plot, the presence of BSCs significantly increased surface roughness, the initial runoff generation time, and soil water infiltration. In the cases of light (42 mm·h-1) and intensive (132 mm·h-1) rainfall, the initial infiltration rate of BSCs covered plots were 1.7-1.9 times and 1.2-1.9 times as that of bare plot, while the average infiltration rate in BSCs covered plots were 2.5-3.0 times and 1.4-3.3 times as that of bare plot, respectively. The BSCs coverage was significantly positively correlated with the initial runoff production time. The critical values of facilitating infiltration of BSCs coverage were between 65% and 70% under the test rainfall intensities. For heavy rainfall events, the inhibiting effects of BSCs on surface runoff were weakened. Horton model was the most reliable one for describing the infiltration process on karst slope with BSCs, followed by Kostiakov model and Philip model. In conclusion, the spatial variability of BSCs development on the karst slope was higher. The presence of BSCs had a significant effect on soil permeability in karst region.

Effects of covering sand with different soil substrates on the formation and development of artificial biocrusts in a natural desert environment

In recent years, artificial biological soil crusts (BSCs)—i.e., the inoculation of soil with cyanobacteria—have become one of the most promising biotechnological strategies for preventing soil erosion and restoring soil functionality in degraded drylands. In order to use this biotechnology on a large scale, researchers must explore methods that enable rapid and largescale propagation of soil inoculum, as well as testing methods for developing artificial BSCs in the field. To help do this, we tested the effects of four soil substrates on the development of artificial BSCs in the Tengger Desert. Each soil substrate was collected from a different area in Zhongwei city in northern China and had different particle sizes and nutrient contents. We measured artificial BSCs characteristics according to the coverage, thickness, and wind erosion resistance of the BSCs analyzed. After 12 months, incubated artificial BSC coverage in incubated soils rose from 6% to 20%, and thickness rose from 2.94 to 4.06 mm. Incubated BSC coverage was positively correlated with fine material content (i.e., soil particle size less than 0.10 mm). There was also a positive relationship between coverage and soil organic matter, total nitrogen, and total phosphorus. Artificial BSC inoculation significantly improved soil resistance to wind erosion. These findings indicate that soil substrates improve BSC recovery rate over sand substrates by enhancing sand surface stabilization, increasing initial silt and clay content and nutrient content, especially soil organic matter content. Considering the scarcity of soil resources and the advantages of reusing soil resources, we suggest that left-over soils dredged from irrigation channels and abandoned farmlands can be used as substrate for the propagation of BSC inoculum.

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

Numerous studies have examined bacterial communities in biological soil crusts (BSCs) associated with warm arid to semiarid ecosystems. Few, however, have examined bacterial communities in BSCs associated with cold steppe ecosystems, which often span a wide range of climate conditions and are sensitive to trends predicted by relevant climate models. Here, we utilized Illumina sequencing to examine BSC bacterial communities with respect to climatic gradients (elevation), land management practices (grazing vs. non-grazing), and shrub/intershrub patches in a cold sagebrush steppe ecosystem in southwestern Idaho, United States. Particular attention was paid to shifts in bacterial community structure and composition. BSC bacterial communities, including keystone N-fixing taxa, shifted dramatically with both elevation and shrub-canopy microclimates within elevational zones. BSC cover and BSC cyanobacteria abundance were much higher at lower elevation (warmer and drier) sites and in intershrub areas. Shrub-understory BSCs were significantly associated with several non-cyanobacteria diazotrophic genera, including Mesorhizobium and Allorhizobium-Neorhizobium-Pararhizobium-Rhizobium. High elevation (wetter and colder) sites had distinct, highly diverse, but low-cover BSC communities that were significantly indicated by non-cyanobacterial diazotrophic taxa including families in the order Rhizobiales and the family Frankiaceae. Abiotic soil characteristics, especially pH and ammonium, varied with both elevation and shrub/intershrub level, and were strongly associated with BSC community composition. Functional inference using the PICRUSt pipeline identified shifts in putative N-fixing taxa with respect to both the elevational gradient and the presence/absence of shrub canopy cover. These results add to current understanding of biocrust microbial ecology in cold steppe, serving as a baseline for future mechanistic research.