Biocrust Species Research Articles

Hyperspectral Imaging Predicts Differences in Carbon and Nitrogen Status Among Representative Biocrust Functional Groups of the Colorado Plateau

AbstractBiological soil crusts (biocrusts) are widespread soil photosynthetic communities covering about 12% of Earth's land surface, and play crucial roles in terrestrial carbon (C) and nitrogen (N) cycles, yet scalable quantifications of biocrusts and their biogeochemical contributions are notably lacking. While remote sensing has enormous potential to assess, scale, and contextualize biocrusts and their functions, the applicability of hyperspectral data in predicting C‐ and N‐related biocrust traits remains largely unexplored. We address this issue by evaluating the potential of in situ hyperspectral data to predict C and N across a range of biocrust species and different environmental conditions. We found that in situ hyperspectral reflectance measurements can be used to predict biocrust tissue C/N ratios and N concentrations with relatively high accuracy but to a lesser extent for potential biocrust N2 fixation rates. Critical wavelength domains included the visible region of the spectrum from roughly 490–600 nm, which most effectively captured variations in biocrust tissue C, and the shortwave infrared region from 1,150 to 1,350 nm and 1,550–1,650 nm, which most effectively captured biocrust tissue N and N2 fixation potential. Finally, we provide evidence that multi‐ and hyperspectral missions with targeted band placement, such as the proposed 26‐band Landsat Next, could be effective in predicting biocrust traits. This work provides a critical step in understanding how to apply data from new and upcoming satellite missions to the monitoring of biocrusts.

Impact of biocrust on soil nitrogen maintenance and microbial composition in citrus orchards under varying urea application rates

Biocrust communities and their effects on soil nitrogen (N) content in natural drylands have been extensively studied. However, their significance in citrus orchards, which are typically managed with N fertilizer, remains unclear. To address this, an investigation was conducted in a citrus orchard subjected to varying levels of urea application (0 %, 70 %, and 100 % of the local N fertilizer application) over three years. The study focused on biocrust communities dominated by bryophytes, examining their community and individual characteristics, and comparing the properties and microbial communities of soils with and without biocrust cover. The results showed that biocrust had the highest percent coverage (56.1 %) in the plot with 70 % local N fertilizer application. Dicranella heteromalla was the dominant biocrust species across all treatments, exhibiting greener and longer leaves with 70 % local N fertilizer application. Biocrust cover significantly (P < 0.01) influenced soil total nitrogen content, soil water content, soil total carbon content, and soil dissolved organic carbon content. In contrast, fertilizer application had non-significant effects on the physicochemical properties of soils, regardless of biocrust cover. A notable difference in bacterial phyla composition was observed between soils with and without biocrust cover (PERMANOVA, P = 0.001), although fertilization did not significantly affect the bacterial diversity index. Additionally, biocrust cover significantly (P < 0.01) influenced predicted soil bacterial functional groups, including ureolysis and nitrogen fixation, while fertilizer application had a weaker impact on these bacterial functional groups. In conclusion, nitrogen application altered the community and dominant species characteristics of biocrust but did not overshadow the effects of biocrust on soil N dynamics. In the citrus orchard with varying levels of urea application, biocrust played a crucial role in soil water retention, N maintenance, and predicted microbial ecological functions related to N cycling.

Limited range shifting in biocrusts despite climate warming: A 25‐year resurvey

Abstract The ranges of many species globally have already shifted to maintain climatic equilibrium in the face of climate change. Biocrusts—soil surface dwelling communities of lichens, bryophytes and microbes—play important functional roles in many ecosystems, particularly in drylands. Compared to better studied animal and plant taxa, dryland biocrusts have different establishment requirements and have never been assessed for historical range shifts. Here, we revisited the sites (N = 204) of a 25‐year‐old biocrust survey across a large area (400,000 km2) of drylands in south‐eastern Australia. We used quadratic models to quantify changes in the climate niches of 15 lichen, eight moss and five liverwort taxa, as well as biocrust cover and richness. Our models showed that the observed climatic niches of most taxa have become hotter and drier in the past quarter century, yet the responses of the vast majority of taxa are consistent with remaining in the same geographic space. A similar pattern was observed at the community level, where the peak of biocrust cover and richness now occurs in a hotter, drier environment. Notable exceptions were the liverwort Riccia lamellosa and lichens in the genera Cladonia and Xanthoparmelia, which showed signs of contraction at their arid range edges. Unlike more mobile taxa, most biocrust species have yet to shift geographically and may already be lagging behind the pace of climate change. One explanation for the mortality lag is that long‐term climate variability in the system is extensive, which may have selected for the ability to withstand multi‐year warm periods as long as there is an eventual return to milder conditions. However, no forecasts of future climate include a return to milder conditions, suggesting there will be an eventual loss of ecosystem multifunctionality at the contracting front. Expansion lags are most likely due to delays in the mortality of competing vascular plants. Synthesis: Our study provides a valuable contribution to the knowledge of range shifts in understudied taxa and highlights a future need to promote the expansion of biocrusts to maintain the provision of ecosystem functions and services across their range.

Biocrust diversity enhances dryland saline soil multifunctionality

AbstractBiocrusts are multifaceted communities including mosses, lichens, and cyanobacteria that are crucial for sustaining soil functions in drylands. Most studies on biocrust functions to date have focused on biocrust cover and development, largely in non‐saline soils, and we know very little about the importance of biocrust diversity for maintaining multifunctionality in saline dryland soils. We assessed the direct and indirect linkages between biocrust richness, soil texture and salinity and soil multifunctionality by measuring 13 variables characterizing soil biological, nutrient and hydrological functions across 32 plots in a salinized dryland in northeastern Iran. We assessed the species richness of biocrust patches and characterized soil functions in bare soils. Overall, biocrust species richness declined with soil clay content and soil salinity, whereas soil salinity increased with soil clay content. Structural equation modeling showed a strong positive association between biocrust species richness and all measured dryland soil functions (soil biological, nutrient, and hydrological functions), but soil hydrological function declined with soil salinity. Overall, dryland soil multifunctionality was positively associated with biocrust species richness but negatively associated with soil clay content. Biocrust species richness likely enhances soil multifunctionality via the distinct roles of species and biocrust functional groups in providing carbon and nutrient inputs, creating favourable microsites, enhancing infiltration, and facilitating soil microbial colonization in saline dryland soils. Overall, our findings highlight a key role for biocrust diversity in facilitating and maintaining soil multifunctionality in drylands affected by soil salinity.

Selecting phototrophic species of native biocrusts in arid and semi-arid regions

Background: Biological soil crusts (BSCs) that are able to produce sticky extracellular polymeric substances (EPS) play an important role in the formation of soil aggregates, thereby, reducing soil erosion. In this study, experiments were undertaken to identify biocrust species that produce EPS, in order to combat desertification in the Sejzi desert of Iran. Methods: A biocrust distribution map of Sejzi plain was prepared using Landsat 8 OLI images, then, various sampling points were selected. Some physicochemical parameters of samples from lichen-dominated and non-biocrusted areas were measured. The relationship between soil parameters and biocrusts presence was confirmed based on the Pearson’s correlation coefficient and principal component analysis (PCA) method. The type of chemical compounds in the soil content were determined via Fourier transform infrared spectroscopy (FTIR), including polysaccharides. To estimate the degradability of polysaccharides, each soil sample was placed under defined UV-B radiation for 24, 48, and 72 hours at three replications. Results: There was no significant correlation between moss and lichen species with the amount of EPS (%) values and various occurring cyanolichen species in three biocrusted soil samples, which included Collema coccophorum, Collema tenax, Peccania terricola, and Placidium squamulosum. It was speculated that these polysaccharides were produced by the photobiotic partners (microalgae or cyanobacteria) and secreted to the soil. Conclusion: According to the results, the cyanobacteria species of biocrusted samples might have high potential to combat desertification and soil stabilization in Sejzi desert.

Tissue chemistry of biocrust species along an aridity gradient and comparison to vascular plant leaves

Abstract Biocrusts are an extensive autotrophic groundcover but are regularly excluded from ecosystem models. One rationale for their exclusion is that their contributions to C and N cycles are negligible in comparison to vascular plants. Here we estimated the magnitude of the biocrust contribution to nutrient cycling in functional terms, comparing tissue chemistry and stoichiometry per ground area with vascular plants per leaf area. We quantified tissue C, N, P and a range of micronutrients in 21 abundant biocrust taxa from an aridity gradient spanning 500 km of Australian drylands. The C, N and P tissue chemistry of biocrust species and vascular plant leaves occupied a similar range, both as ratios and per area. This implies that in functional terms, biocrusts could be considered as a single layer of leaf area spread out across the ground and added to Leaf Area Index (LAI) measurements accordingly. Within biocrust species, the C:N ratio significantly declined with increasing aridity, which was entirely driven by carbon. This finding demonstrates a key functional difference between vascular leaves and biocrusts: C:N ratios in vascular plants are lower in drier environments due to elevated levels of N‐rich photosynthetic machinery relating to a trade‐off in water‐use regulation, while C:N ratios in biocrusts decline with aridity most likely due to carbon shortages relating to their inability to regular water loss (poikilohydry). As global drylands become drier with climate change, our findings suggest that biocrust tissue carbon stocks will decline gradually until the point where carbon budgets become negative and standing biomass is no longer viable. A free Plain Language Summary can be found within the Supporting Information of this article.

Measuring reflectance of tiny organisms: The promise of species level biocrust remote sensing

Abstract To understand how ecological communities will respond to global change we need new tools and datasets on species across large spatial and temporal scales. Hyperspectral reflectance ‘spectra’ capture a promising set of traits that show potential to be scaled up in time and space via remote sensing. Thus far, spectra have been shown to distinguish the taxa and trait responses of a substantial number of species within a plethora of vascular plant communities, but not yet for biological soil crust communities (biocrusts). Here, we assess if spectra can be applied to identify biocrust species and their trait variation. We collected biocrust specimens across an aridity gradient spanning 650 km within drylands of Eastern Australia and acquired their spectra, over 12,700 spectral readings, with a high‐resolution radiospectrometer. A machine learning method (random forests) was used to assess how well the spectra of biocrust specimens could distinguish their species and broader structural and chemical traits. Spectra were able to differentiate a substantial number of biocrust species (35) with considerable accuracy (~78.5%). Furthermore, spectral features related to chemical traits were found to primarily drive species spectral differences. Synthesis. Our findings establish that biocrust species hold unique and detectable spectral responses, providing an important basis for remote sensing applications on biocrust species and their trait responses across dryland systems.

Contribution of biological soil crusts to soil organic matter composition and stability in temperate forests

Biological soil crusts (biocrusts) play an important role in the biogeochemical C-, N- and P-cycles but there is limited knowledge about their effect on the composition and stability of organic matter (OM) in soil. In pine and beech dominated temperate forests, the different compartments of biocrust, crust-adhering soil and crust-free soil were analysed by pyrolysis field ionization mass spectrometry (Py-FIMS) and C K-edge X-ray absorption near edge structure (XANES) spectroscopy. Phototrophic biocrust communities had been determined morphologically. Predominant tree species affected OM composition and stability but an overriding effect of biocrust organisms was observed. In biocrusts, the OM mineralization potential was high due to a high carbohydrate/ketone ratio and a high proportion of the fatty acid C22:0. A high proportion of free fatty acids in combination with a high carbohydrate proportion was identified as a relative marker for biocrusts and additional high proportions of lignin dimers were specific for samples under pine. In biocrust under pine, OM in soil compartments was characterized by large proportions of long-chain aliphatics from plant cuticular material. In A-horizon substrate under beech, OM compound classes were not affected by phototrophic species richness, suggesting functional redundancy of these biocrust organisms with regard to OM composition. In contrast to A-horizon substrate, OM in C-horizon substrate was characterized by a higher proportion of easily decomposable material. Under pine, forest management intensity (SMI) affected OM by stand age and density due to effects on phototrophic biocrust species. We conclude that compartment, vegetation, horizon substrate and SMI affected OM composition and stability, and biocrusts hence contributed to soil OM diversity in forest ecosystems.

Hillslope geodiversity effects on properties and composition of biological soil crusts in drylands

AbstractBiological soil crusts (biocrusts) play important roles in ecosystem functioning and are considered ecosystem engineers: stabilizing the soil surface, preventing soil erosion, changing soil surface hydrology, and enriching the soil with carbon and nitrogen. The link between geodiversity and biodiversity incorporates physical aspects from geology, geomorphology and pedology. We aimed to assess the effects of hillslope geodiversity on the cover, composition and biophysiological properties of biological soil crusts (biocrusts) in a dryland ecosystem. The geodiversity of the hillslope is determined by the stone cover on the ground surface, the content, stones in the soil profile, and the soil depth. It is known from the scientific literature that geodiversity affects biodiversity; thus, we hypothesized that the hillslope type may affect biocrust properties that develop on these hillslopes. The results indicate that the mean covers of biocrust types in the homogeneous (low geodiversity) hillslopes were 60.6% cyanobacterial crusts and 39.4% biocrusts composed of cyanobacteria, moss and lichens, whereas those of the heterogeneous (high geodiversity) hillslopes were 81.6% cyanobacterial crusts and 18.4% biocrusts composed of cyanobacteria, moss and lichens. It was concluded that geodiversity enhances the growth of biocrust species that require higher soil moisture. The results imply that wherever restoration activities are planned, and especially in drylands, the geodiversity of the area should be taken into account.Highlights Geodiversity expressed by the degree of stoniness impacts ecosystem functioning and soil properties Geodiversity impacts the biocrust's cover and composition Geodiversity enhances the growth of biocrusts that require high soil moisture Chlorophyll a, b and a + b in biocrusts are increased in heterogeneous hillslopes

Role of shrubs in the community assembly of biocrusts: the biotic and abiotic influences along a biocrust succession gradient

In water-limited areas, shrubs influence biological soil crust (biocrust) composition and diversity via soil microenvironment alterations and through modifying biotic interactions amongst biocrust taxa. However, the relative contributions of shrubs to biocrust succession and assembly via the biotic and abiotic influences are poorly known. The community composition of biocrusts and soil properties in the interspace and beneath the dominant shrub (Artemisia ordosica) along a biocrust succession sequence were investigated. Biocrust interspecific interactions at a small scale (within shrub) were evaluated based on the co-occurrence pattern using null models. A hypothetical multigroup structural equation model (SEM) was proposed to evaluate the influence of multiple variables on the biocrust richness and to investigate the path variance between successional stages. Along the biocrust succession, shrubs significantly increased the size of bare soil gap by 489%, decreased lichens by 43% and increased soil organic matter by 13%. In years 18, 31and 37, the paths in SEM explained 59% of the variation in richness, only the effect of abiotic amelioration was significant (0.62). In years 54 and 62, the shrubs had direct (0.37) and indirect effect (0.10) via species interaction to biocrust richness. Shrubs directly and indirectly affected the community assembly of biocrusts. Biocrust species interactions are an important driver of biocrust diversity and primarily affect late succession. The increasing influences of shrubs suggests a close relationship between shrub and biocrust components in arid or semiarid ecosystems, with shrubs playing an important role in regulating biocrust assembly and maintaining biocrust richness.

Species-specific effects of biocrust-forming lichens on soil properties under simulated climate change are driven by functional traits.

Biocrusts are key drivers of ecosystem functioning in drylands, yet our understanding of how climate change will affect the chemistry of biocrust-forming species and their impacts on carbon (C) and nitrogen (N) cycling is still very limited. Using a manipulative experiment conducted with common biocrust-forming lichens with distinct morphology and chemistry (Buellia zoharyi, Diploschistes diacapsis, Psora decipiens and Squamarina lentigera), we evaluated changes in lichen total and isotopic C and N and several soil C and N variables after 50months of simulated warming and rainfall reduction. Climate change treatments reduced δ13 C and the C:N ratio in B.zoharyi, and increased δ15 N in S.lentigera. Lichens had species-specific effects on soil dissolved organic N (DON), , β-glucosidase and acid phosphatase activity regardless of climate change treatments, while these treatments changed how lichens affected several soil properties regardless of biocrust species. Changes in thallus δ13 C, N and C:N drove species-specific effects on dissolved organic nitrogen (DON), , β-glucosidase and acid phosphatase activity. Our findings indicate that warmer and drier conditions will alter the chemistry of biocrust-forming lichens, affecting soil nutrient cycling, and emphasize their key role as modulators of climate change impacts in dryland soils.

Dual community assembly processes in dryland biocrust communities

Abstract Biocrusts are critical components of drylands where they regulate a wide range of ecosystem functions, however, their response to the world‐wide phenomenon of shrub encroachment and to livestock grazing, the most extensive land use in drylands, is not well studied. Grazing by livestock and increases in shrub cover could influence biocrust communities directly via trampling or shading, or indirectly, by altering biotic interactions amongst biocrust taxa. The extent of these changes in biocrust cover, diversity and composition are poorly known. We used linear models and structural equation modelling to examine the direct effects of grazing and shrubs on biocrust community composition and the indirect effects mediated by changes in species interactions. Biocrust richness and cover increased with increasing shrub cover at the site level. This pattern occurred despite the negative response we found (lower cover and richness) under shrub patches versus open areas, which was consistent irrespective of the grazing level. Functional diversity and evenness were similar between shrubs and open at low grazing intensity, but at high grazing functional diversity was greater in the open. Competition between biocrust species was an important driver of their community assembly irrespective of shrub cover, grazing intensity or patch type. Structural equation models showed that the effects of grazing and shrub cover on functional evenness, functional diversity and richness were controlled by biotic interactions within the shrub microsites. In the open, however, these effects were either direct or mediated by changes in cover. Biocrust cover, species richness and functional diversity increase with shrub cover at the site scale, despite the negative effects at the microsite level. We demonstrate here that drivers of community assembly differ markedly at small spatial scales. Though biocrust communities were directly driven by environmental filtering in the open, biotic interactions played a fundamental role in their assembly when growing beneath shrubs. A free plain language summary can be found within the Supporting Information of this article.

Grazing Disturbance Promotes Exotic Annual Grasses by Degrading Soil Biocrust Communities

Exotic invasive plants threaten ecosystem integrity, and their success depends on a combination of abiotic factors, disturbances, and interactions with existing communities. In dryland ecosystems, soil biocrusts (communities of lichens, bryophytes, and microorganisms) can limit favorable microsites needed for invasive species establishment, but the relative importance of biocrusts for landscape-scale invasion patterns remains poorly understood. We examine effects of livestock grazing in habitats at high risk for invasion to test the hypothesis that disturbance indirectly favors exotic annual grasses by reducing biocrust cover. We present some of the first evidence that biocrusts increase site resistance to invasion at a landscape scale and mediate the effects of disturbance. Biocrust species richness, which is reduced by livestock grazing, also appears to promote native perennial grasses. Short mosses, as a functional group, appear to be particularly valuable for preventing invasion by exotic annual grasses. Our study suggests that maintaining biocrust communities with high cover, species richness, and cover of short mosses can increase resistance to invasion. These results highlight the potential of soil surface communities to mediate invasion dynamics and suggest promising avenues for restoration in dryland ecosystems.

Grazing disturbance promotes exotic annual grasses by degrading soil biocrust communities.

Exotic invasive plants threaten ecosystem integrity, and their success depends on a combination of abiotic factors, disturbances, and interactions with existing communities. In dryland ecosystems, soil biocrusts (communities of lichens, bryophytes, and microorganisms) can limit favorable microsites needed for invasive species establishment, but the relative importance of biocrusts for landscape-scale invasion patterns remains poorly understood. We examine effects of livestock grazing in habitats at high risk for invasion to test the hypothesis that disturbance indirectly favors exotic annual grasses by reducing biocrust cover. We present some of the first evidence that biocrusts increase site resistance to invasion at a landscape scale and mediate the effects of disturbance. Biocrust species richness, which is reduced by livestock grazing, also appears to promote native perennial grasses. Short mosses, as a functional group, appear to be particularly valuable for preventing invasion by exotic annual grasses. Our study suggests that maintaining biocrust communities with high cover, species richness, and cover of short mosses can increase resistance to invasion. These results highlight the potential of soil surface communities to mediate invasion dynamics and suggest promising avenues for restoration in dryland ecosystems.

The influence of climatic legacies on the distribution of dryland biocrust communities.

Predicting the distribution of biocrust species, mosses, lichens and liverworts associated with surface soils is difficult, but climatic legacies (changes in climate over the last 20k years) can improve our prediction of the distribution of biocrust species. To provide empirical support for this hypothesis, we used a combination of network analyses and structural equation modelling to identify the role of climatic legacies in predicting the distribution of ecological clusters formed by species of mosses, lichens and liverworts using data from 282 large sites distributed across 0.6 million km2 of eastern Australia. Two ecological clusters contained 87% of the 120 moss, lichen and liverwort species. Both clusters contained lichen, moss and liverwort species, but were dominated by different families. Sites where the air temperature increased the most over 20kyears (positive temperature legacies) were associated with reductions in the relative abundance of species from the lichen (Peltulaceae and Teloschistaceae) and moss (Bryaceae) families (Cluster A species), greater groundstorey plant cover and lower soil pH. Sites where precipitation has increased over the past 20kyears (positive precipitation legacy) were associated with increases in the relative abundance of lichen (Cladoniaceae, Lecideaceae and Thelotremataceae) and moss (Pottiaceae) families (Cluster B species) and lower levels of soil pH. Sites where temperatures have increased the most in the past 20kyears suppressed the negative effects of plant cover on Cluster B by reducing plant cover. Increased intensity of grazing suppressed the negative effect of soil pH and the positive effect of soil carbon, on the relative abundance of Cluster B taxa. Finally, increasing temperature and precipitation legacies reduced the negative effect of soil pH on Cluster B. Understanding of the importance of climatic legacies improves our ability to predict how biocrust assemblies might respond to ongoing global environmental change associated with increasing land use intensification, increasing temperature and reduced rainfall.

Insolation and disturbance history drive biocrust biodiversity in Western Montana rangelands

Background and AimsBiological soil crust (biocrust) communities, though common and important in the intermountain west, have received little research attention. There are gaps in understanding what influences biocrust species’ abundance and distributions in this ecoregion. Climatic, edaphic, topographic, and biotic forces, in addition to anthropogenic disturbance can all influence the biocrust.MethodsWe determined the relative influence of several possible environmental filters in biocrust communities of western Montana (USA) grasslands at two spatial scales. The larger scale exploited strong topographically-dictated climatic variation across >60km2, while the smaller scale focused on differences among distinct microsites within ~700m2 plots.ResultsWe detected a total of 96 biocrust taxa, mostly lichens. Biocrust richness at each site ranged from 0 to 39 species, averaging 14 species. Insolation, aspect, and disturbance history were the strongest predictors of biocrust richness, abundance, and species turnover across the landscape; soil texture was influential for some biocrust community properties. Steep, north-facing slopes that receive longer periods of shade harbored higher diversity and cover of biocrust than south-facing sites. At a small scale, interspaces among native herbaceous communities supported the greatest diversity of biocrust species, but microsites under shrub canopies supported the greatest cover.ConclusionsWe found that, among the variables investigated, tillage, insolation, soil texture and the associated vegetation community were the most important drivers of biocrust abundance and species richness. This study can inform the practice of restoration and conservation, and also guide future work to improve predictions of biocrust properties.

Fungal loop transfer of nitrogen depends on biocrust constituents and nitrogen form

Abstract. Besides performing multiple ecosystem services individually and collectively, biocrust constituents may also create biological networks connecting spatially and temporally distinct processes. In the fungal loop hypothesis rainfall variability allows fungi to act as conduits and reservoirs, translocating resources between soils and host plants. To evaluate the extent to which biocrust species composition and nitrogen (N) form influence loops, we created a minor, localized rainfall event containing 15NH4+ and 15NO3-. We then measured the resulting δ15N in the surrounding dry cyanobacteria- and lichen-dominated crusts and grass, Achnatherum hymenoides, after 24 h. We also estimated the biomass of fungal constituents using quantitative PCR and characterized fungal communities by sequencing the 18S rRNA gene. We found evidence for the initiation of fungal loops in cyanobacteria-dominated crusts where 15N, from 15NH4+, moved 40 mm h−1 in biocrust soils with the δ15N of crusts decreasing as the radial distance from the water addition increased (linear mixed effects model (LMEM)): R2=0.67, F2,12=11, P=0.002). In cyanobacteria crusts, δ15N, from 15NH4+, was diluted as Ascomycota biomass increased (LMEM: R2=0.63, F2,8=6.8, P=0.02), Ascomycota accounted for 82 % (±2.8) of all fungal sequences, and one order, Pleosporales, comprised 66 % (±6.9) of Ascomycota. The seeming lack of loops in moss-dominated crusts may stem from the relatively large moss biomass effectively absorbing and holding N from our minor wet deposition event. The substantial movement of 15NH4+ may indicate a fungal preference for the reduced N form during amino acid transformation and translocation. We found a marginally significant enrichment of δ15N in A. hymenoides leaves but only in cyanobacteria biocrusts translocating 15N, offering evidence of links between biocrust constituents and higher plants. Our results suggest that minor rainfall events may initiate fungal loops potentially allowing constituents, like dark septate Pleosporales, to rapidly translocate N from NH4+ over NO3- through biocrust networks.

Identity of plant, lichen and moss species connects with microbial abundance and soil functioning in Maritime Antarctica.

We lack studies evaluating how the identity of plant, lichen and moss species relates to microbial abundance and soil functioning on Antarctica. If species identity is associated with soil functioning, distributional changes of key species, linked to climate change, could significantly affect Antarctic soil functioning. We evaluated how the identity of six Antarctic plant, lichen and moss species relates to a range of soil attributes (C, N and P cycling), microbial abundance and structure in Livingston Island, Maritime Antarctica. We used an effect size metric to predict the association between species (vs. bare soil) and the measured soil attributes. We observed species-specific effects of the plant and biocrust species on soil attributes and microbial abundance. Phenols, phosphatase and β-D-cellobiosidase activities were the most important attributes characterizing the observed patterns. We found that the evaluated species positively correlated with soil nutrient availability and microbial abundance vs. bare soil. We provide evidence, from a comparative study, that plant and biocrust identity is associated with different levels of soil functioning and microbial abundance in Maritime Antarctica. Our results suggest that changes in the spatial distribution of these species linked to climate change could potentially entail changes in the functioning of Antarctic terrestrial ecosystems.

Lichen-biocrust diversity in a fragmented dryland: Fine scale factors are better predictors than landscape structure

Biological soil crusts (or biocrusts) are widespread, diverse and important components of drylands sometimes threatened by global change drivers. However, their response to fragmentation processes is poorly known. The aim of this study was to assess the effects of changing landscape structure, given by land use change and the presence of linear infrastructure (e.g., roads), on the cover and diversity of lichen-biocrusts. We also evaluated the influence of several subrogates of fragment quality, such as soil properties, vascular plant community structure and topography. Biocrust cover and diversity were measured in 50 remnants of a Mediterranean shrubland. The fragments varied in size, connectivity and distance to a road, but also in plant and soil attributes, topography and fragment history. We applied general linear and mixed models to assess the effects of environmental variables on biocrust communities. Biocrust cover, richness and species composition were mostly unresponsive to changes in landscape structure, while connectivity and distance to the road decreased species diversity. Soil properties better explained the variation in biocrust cover and diversity. Changes in plant community and biocrust community composition were coupled. We also identified several biocrust species with strong capacity to reflect landscape structure. Our findings suggest that landscape structure needs to be evaluated jointly with other environmental factors to fully understand the consequences of fragmentation processes on biocrust communities and the subsequent implications for their functional role in drylands.

Nitrogen deposition reduces the cover of biocrust-forming lichens and soil pigment content in a semiarid Mediterranean shrubland.

Biocrusts are key drivers of the structure and functioning of drylands and are very sensitive to disturbance, including atmospheric nitrogen (N) deposition. We studied the impacts of simulated N deposition on biocrust community composition and soil photosynthetic and photoprotective pigment content after fiveyears of N application in a European semiarid Mediterranean shrubland. The experiment consisted in six experimental blocks with four plots, each receiving 0, 10, 20, or 50kg NH4NO3-Nha-1year-1+6-7kg Nha-1year-1 background. After 5years of N application, total lichen cover decreased up to 50% compared to control conditions and these changes were only clearly evident when evaluated from a temporal perspective (i.e. as the percentage of change from the first survey in 2008 to the last survey in 2012). In contrast, moss cover did not change in response to N, suggesting that biocrust community alterations operate via species- and functional group-specific effects. Interestingly, between-year variations in biocrust cover tracked variations in autumnal precipitation, showing that these communities are more dynamic than previously thought. Biocrust species alterations in response to N were, however, often secondary when compared to the role ofecologically relevant drivers such as soil pH and shrub cover, which greatly determined the composition and inter-annual dynamics of the biocrust community. Similarly, cyanobacterial abundance and soil pigment concentration were greatly determined by biotic and abiotic interactions, soil pH for pigments, and organic matter content and shrub cover for cyanobacteria. Biocrusts, and particularly the lichen component, are highly sensitive to N deposition and their responses to pollutant N can be best understood when evaluated from a temporal and multivariate perspective, including impacts mediated by interactions with biotic and abiotic drivers.