Drylands are characterized by a high spatiotemporal heterogeneity, which complicates the development of remote sensing applications for these regions. Biological soil crusts are among the key phenomena driving this heterogeneity. Biocrusts are living communities composed of photoautotrophic organisms (cyanobacteria, algae, lichens, and bryophytes) in intimate association with heterotrophic microorganisms and covering the soil surface across global drylands. Biocrusts modify surface reflectance through specific absorption features arising from insulation-protective and photosynthetic pigments. These features have been used to develop local applications for biocrust mapping and monitoring, but their extrapolation, especially to the global scale, remains difficult because the biocrust reflectance interacts with the underlying soil signal. Moreover, the currently available biocrust spectral datasets do not capture the great variety of biocrust communities and their diverse spectral signals. Furthermore, these data are often collected without standardized protocols, which hampers data comparison, transferability and the development of standard procedures for mapping and monitoring.To overcome this limitation, we developed a standard protocol to build the first consistent biocrust spectral library, which aims to support new biocrust mapping and monitoring efforts. that aims at supporting new biocrust mapping and monitoring actions. Spectra of 354 samples representing different biocrust communities from around the world were recorded in the laboratory under dry and wet conditions under controlled illumination intensity in the lab. The library includes a reflectance spectrum, a continuum removal spectrum, albedo, and a set of narrow- and broad-band spectral indices commonly applied for vegetation, soil, and characterization. We also used associated metadata, including general descriptors of habitats, location and sampling time information, and physicochemical variables related to biocrusts development and functioning. The latter facilitates the quantification of some key functional traits for comparison with remote sensing products (e.g., photosynthetic pigments, organic matter, stability, surface roughness, EPS concentration). Spectra and physicochemical features of the underlying soil are also included, as they are known to significantly influence the response of biocrust organisms. Overall, this spectral library encompasses a wide range of biocrust functional types from global drylands but further input from currently not well-covered geographic regions is still welcome.Awknoledgment:CRUST R-Forze (PID2021-127631NA-I00) project funded by MICIU/AEI /10.13039/501100011033 and FEDER, UE; Support for Encouraging Research Consolidation (CNS2024-154916) funded by MICIU/AEI /10.13039/501100011033 and UE NextGenerationEU/PRTR. ERC was supported by the Ramon y Cajal Fellowship (RYC2020-030762-I) founded by MICIU/AEI/10.13039/501100011033 and El FSE invierte en tu future.

With climate change and population growth threatening food security, farmers urgently need sustainable tools to grow crops in harsher conditions. Our research aims to demonstrate the potential of a natural extract from Nostoc commune—a cyanobacterium isolated from arid biocrusts—as a biostimulant capable of enhancing crop growth and improving plant survival under drought and saline conditions, thereby offering an eco-friendly solution for agriculture in challenging environments. We conducted two complementary trials using tomato (Solanum lycopersicum cv. MicroTom) and lettuce (Lactuca sativa var. longifolia) as model species. The first trial systematically evaluated optimal hydrolysate concentrations for enhancing both seed germination and vegetative growth, comparing different application methods (foliar spraying versus seed soaking). Building on these results, the second trial specifically tested the biostimulant's efficacy in protecting plants against drought and salinity stress under controlled environmental conditions. Our findings demonstrate that N. commune hydrolysate significantly enhanced plant development and stress resilience in both crop species. In lettuce, treatment increased leaf number by 19.7

The extent and severity of dryland degradation, coupled with future expansion under climate change, make their restoration both urgent and challenging. In these regions, biocrusts play a pivotal role in stabilizing soil surfaces and improving nutrient cycling, and biocrust-forming cyanobacteria inoculation has emerged as a promising restoration approach. However, field inocula often fail to establish due to harsh environmental conditions, prompting the development of habitat amelioration. This study evaluated the effect of native plant-based environmental stress reduction (ESR) strategies, including a Plantago ovata-based stabilizer, Macrochloa tenacissima litter, and a commercial M. tenacissima mesh, combined with cyanobacteria inoculation and biocrust fragments, on biocrust formation, soil properties, and native bacterial communities at two semiarid sites in SE Spain (Las Amoladeras and El Cautivo). ESR strategies enhanced inoculum survival and soil fertility. After 24 months, the M. tenacissima mesh significantly increased chlorophyll a gain in El Cautivo (381% higher than inoculation alone), while the P. ovata stabilizer performed better at Las Amoladeras (167% increase). ESR strategies also increased soil organic carbon (SOC), especially when combined with inoculation at El Cautivo. Introduction of biocrust fragments increased chlorophyll and SOC in the soil adjacent to the fragment, with stronger effects observed under M. tenacissima mesh cover. No significant changes in soil microbial composition were observed at the phylum level, and only slight variations occurred at the family level. Our results support the use of ESR strategies to promote biocrust recovery and enhance soil fertility without altering native soil communities and highlight the importance of tailoring ESR strategies to site-specific conditions to maximize restoration success.

Ecological restoration in drylands can be enhanced by understanding the composition and spatial distribution patterns of natural ecosystems, shaped by landscape geomorphology, species' microhabitat requirements and resource availability. This study aims to develop a precision restoration framework using UAV based data and statistical models, identify suitable microhabitats for native species in degraded areas based on reference ecosystems, and generate suitability and probability maps to guide species reintroduction. We selected an abandoned semi-arid quarry as a case study and identified five native plant species from a nearby natural reference ecosystem to replicate its ecological conditions. High-resolution orthoimages and Digital Elevation Models (DEMs) were obtained, and topographic attributes were calculated to model species' spatial distribution and topographical suitability. The resulting models were then used to generate suitability and probability maps to apply in a restoration site, revealing that species' spatial distributions are strongly influenced by topographically induced microhabitats, with effects varying among species. The distribution models predicted species presence with AUC values exceeding 0.90, identifying insolation, hillslope position, and runoff-related variables as key drivers of species distribution. This methodology enables more precise and efficient ecological restoration planning in arid zones by optimizing species selection and placement to enhance reintroduction success and survival rates.

IntroductionDrylands are subject to multiple overlapping stresses, including high temperatures, drought, and salinity, along with soils that are low in organic matter and nitrogen. Hence, both agricultural practices and natural regeneration in these areas are hindered by poor plant establishment and growth. The use of plant growth-promoting (PGP) microorganisms has recently emerged as a promising strategy to enhance plant performance under these harsh conditions.MethodsIn this context, the aim of this work was to isolate and screen the PGP properties of cyanobacteria and heterotrophic bacteria from biocrusts in arid soils, representing a highly unexplored niche of microorganisms with potential application in agriculture and ecological restoration. We determined key PGP traits, including phosphate and potassium solubilization, growth under nitrogen-free conditions, siderophore and auxin production, as well as protease, lipase, DNase, amylase, catalase, and cytochrome-C-oxidase activities.ResultsOur results showed that, among the cyanobacteria analyzed, Nostoc commune CANT2, isolated from the province of Almería (Spain), exhibited the highest number of PGP properties, followed by N. commune AB55 (southern Sardinia, Italy) and Trichocoleus cf. desertorum CAU7 (Almería). Both strains AB55 and CANT2 are characterized by their production of exopolysaccharides (EPS). Regarding the heterotrophic bacterial strains, those with the best PGP properties were identified as Peribacillus frigoritolerans and Bacillus atrophaeus by 16S rRNA gene sequencing. Seed biopriming experiments with the model plant Triticum aestivum showed that application of N. commune CANT2, either alone or in combination with P. frigoritolerans 1E, enhanced vigor indices by up to 58% compared to the control.DiscussionThese findings highlight the potential of combined microbial consortia with PGP activities as candidates for the development of biostimulants, offering a sustainable approach to improve plant growth and resilience in dryland agriculture.

Organic amendments and microbial inoculants are widely applied to improve soil properties. However, their combined application remains underexplored in both soil restoration and sustainable agriculture. This study explores the synergistic potential of paper waste and biocrust-forming cyanobacteria as a combined strategy to enhance soil functions in drylands. Specifically, we assessed (i) whether paper waste can support long-term cyanobacterial survival and establishment in soil, and (ii) the effects of their combined application on soil functions and microbial community structure. In a mesocosm experiment, two forms of paper waste, shredded paper and paper pulp, were applied alone or with a native cyanobacterial consortium to natural and agricultural soils. Results showed that cyanobacteria remained viable on paper waste for three months. Redundancy Analysis (RDA) revealed strong association between treatments and shifts in key indicators of soil functions. The combination of paper waste and cyanobacteria significantly improved SOC (up to 979 %), total nitrogen (30 %), aggregate stability (500 %), and water retention (86 %), compared to untreated soil. A complementary field experiment confirmed this synergism and revealed partial inoculum transfer to the underlying soil, resulting in increased chlorophyll-a, aggregate stability and nitrogen concentration. Functional potential predictions of microbial communities (PICRUSt2 and FungalTraits) indicated that microbial taxa most strongly related to nutrient changes following amendment were linked to nutrient cycling pathways, particularly carbon and nitrogen metabolism. Despite functional shifts, occurring mainly in the paper layer, overall soil microbial diversity and nutrient balance were preserved, supporting this strategy as a sustainable tool for enhancing key soil functions in drylands.

The highly diverse equatorial dry forests are among the most threatened ecosystems on Earth due to the alarming rates of deforestation, and are currently classified as "critically endangered" according to IUCN criteria. Understanding the causes of its deforestation and its impacts on local communities is essential for its management and conservation. In this study, we used public information in geographic information systems (GISs) from 1990–2020 together with remote sensing data and local expert knowledge to assess the drivers of deforestation and the provision of regulatory ecosystem services (ESs) through the Nature’s Contributions to People (NCP) framework in the Arenillas and Zarumilla watersheds (Province of El Oro, Ecuador). Our results clearly identify the expansion of agricultural and rangelands as the main driver of deforestation, especially starting in 2000. The reduction in area of equatorial dry forest by more than 42,224.45 ha implies a broad reduction of carbon storage and water regulation, and increased erosion. As a consequence, the ESs associated with air quality regulation (NCP3), control of harmful organisms (NCP10), climate regulation (NCP4), pollination (NCP2) and habitat maintenance (NCP1) all declined over the study period. The protected areas in the study region were insufficient to stop this trend and preserve ESs. More precisely, one of the two protected areas in the region, BP-Tahuín, presented levels of provision of services similar to non-protected areas. Our study highlights the urgency to identify alternative conservation measures, which respond to social needs and valorize regulatory services to stop deforestation due to agricultural and rangeland expansion.

Water scarcity poses a significant life constraint in global drylands that determines species adaptations and mosaic of exposed bare areas and vegetation patches. Runoff‐water redistribution resulting from this spatial configuration has been suggested as a key process controlling water availability for vegetation and ecosystem functioning. However, the potential of this process to ameliorate the negative impacts of aridification in drylands remains unclear, and there is no empirical evidence of its relevance on natural ecosystems under different levels of aridity and disturbance regimes. To address this gap, we analysed temporal series of the normalized vegetation index (NDVI, a proxy of vegetation functioning) along a regional aridity–disturbance gradient under current and future climatic conditions. We found that mean NDVI increases in areas of runoff water accumulation (calculated using a water redistribution index) until a certain threshold, above which vegetation patches are not able to retain extra runoff water. Once thresholds were identified, we analysed the role of water redistribution on vegetation dynamics by analysing temporal series of monthly NDVI in a space–for–time substitution approach. The obtained results provided further evidence of the runoff water redistribution on vegetation, triggering a positive feedback between water accumulation and vegetation growth. Results obtained by the combination of the obtained model with climatic data from the 6th IPCC report suggest that this feedback could ameliorate the expected negative effects of aridification in drylands. However, this effect is partially counterbalanced in scenarios of high human disturbance and in areas where vegetation is not able to trap and retain the extra amount of resources given by runoff. Overall, our results provide empirical evidence of the relevance of runoff redistribution as a key process linking vegetation patterns to climate resistance in drylands that underscores its importance in the analysis and modelling of drylands' responses to aridification.

Drylands are characterised by spatially discontinuous vegetation coverage. Consequently, during most rainfalls, runoff is generated in open areas and redistributed to vegetation. This transfer of water and nutrients from source to sink areas has been identified as a key ecohydrological process modulating drylands functioning. However, there are only a few experimental studies assessing the role of runoff redistribution on vegetation, and none of them evaluate its effect on determining the response of vegetation patches to aridification. In this study, we conducted a 3-year runoff exclusion experiment on 8 study sites consisting of Macrochloa tenacissima steppes distributed along two aridity gradients with contrasting lithologies in SE Spain. The aim was to assess the effect of runoff redistribution on vegetation and underlying soil communities as aridity increases, and to determine the influence of lithology on this response. For that, we compared a set of plants (photosynthetic activity, leaf chlorophyll content and green biomass production) and soil (microbial activity and composition) traits measured during different field campaigns on plants receiving run-on with the same variables measured on plants where run-on was excluded. Our findings demonstrate that run-on increases plant green biomass during wet periods with control plants showing a gain of the green biomass fraction higher than run-on excluded plants (difference between control and excluded plants is about similar to 10 % of the total AGB in both gradients). By altering green biomass accumulation, run-on exclusion also shapes soil microbial communities (similar to 20 % of the aridity dependent ASVs are affected by run-on exclusion) and ameliorates the negative effects of drought on the activity and biomass of soil microorganisms (the decrease of SIR values between time 1 and 2 is 17 % lower in control than on run-on excluded plants), but it does not affect photosynthetic rate and chlorophyll concentration. This is due to the poikilohydric behaviour of M. tenacissima and the contrasting timing in the response of the measured variables to water pulses. Vegetation photosynthetic rates respond to short-term water availability, while green biomass and its indirect effect on the soil microbial communities results from a delayed response to the different rainfalls during the growing season. The effects of run-on were lower than expected and did not vary along aridity gradients, probably due to the unusual drought conditions and the atypical rainfalls during the studied period. During the last years, only a few large rainfalls were registered, causing soil moisture saturation under both excluded and control plants. Under these conditions, resources provided by runoff to control plants is diminished, thus lessening their competitive position compared to excluded plots. Long-term monitoring is necessary to evaluate the response of vegetation and the underlying soil to resource supply through runoff water with increasing aridity.

Restoration of drylands is crucial to reverse global land degradation because these areas cover around 40% of the Earth surface and host one third of the world population. Restoration efforts are often unsuccessful in drylands and alternative approaches need to be developed, i.e., biocrust-based restoration, to promote plant growth and increase soil fertility and stability. In this research, we cultured several biocrust-forming organisms to inoculate them on degraded soils. We designed a more effective inoculum based on biocrust-forming heterotrophic bacteria with plant growth promotion properties (PGP) and key enzymatic activities. We hypothesised that inoculation of native seeds with a consortium of selected heterotrophic bacteria would enhance seed germination and establishment. We sampled incipient and developed biocrusts from three study sites located in semi-arid areas from SE Spain, and isolated 48 bacterial strains. We performed a screening within the bacterial collection to find those strains with key PGP properties and enzymatic activities. Specifically, we analysed their capacity to fix N2, solubilize P and K, produce biofilms, auxins and siderophores, and the extracellular activity of DNAse, amylase, protease, catalase, and lipase. Then, we assessed the best performing bacterial strains for co-culturing to avoid possible antagonistic effects and identified them by sequencing the 16S rRNA gene. The next step of this project will focus on assessing the effects of seed pelleting with the best-performing consortium on germination and establishment of native plants.

Soil contamination by heavy metals represents an important environmental and public health problem of global concern. Biocrust-forming cyanobacteria offer promise for heavy metal immobilisation in contaminated soils due to their unique characteristics, including their ability to grow in contaminated soils and produce exopolysaccharides (EPS). However, limited research has analysed the representativeness of cyanobacteria in metalcontaminated soils. Additionally, there is a lack of studies examining how cyanobacteria adaptation to specific environments can impact their metal-binding capacity. To address this research gap, we conducted a study analysing the bacterial communities of cyanobacteria-dominated biocrusts in a contaminated area from South Sardinia (Italy). Additionally, by using two distinct approaches, we isolated three Nostoc commune strains from cyanobacteria-dominated biocrust and we also evaluated their potential to immobilise heavy metals. The first isolation method involved acclimatizing biocrust samples in liquid medium while, in the second method, biocrust samples were directly seeded onto agar plates. The microbial community analysis revealed Cyanobacteria, Bacteroidota, Proteobacteria, and Actinobacteria as the predominant groups, with cyanobacteria representing between 13.3 % and 26.0 % of the total community. Despite belonging to the same species, these strains exhibited different growth rates (1.1 -2.2 g L -1 of biomass) and capacities for EPS production (400 -1786 mg L -1 ). The three strains demonstrated a notable ability for metal immobilisation, removing up to 88.9 % of Cu, 86.2 % of Pb, and 45.3 % of Zn from liquid medium. Cyanobacteria EPS production showed a strong correlation with the removal of Cu, indicating its role in facilitating metal immobilisation. Furthermore, differences in Pb immobilisation (40 -86.2 %) suggest possible environmental adaptation mechanisms of the strains. This study highlights the promising application of N. commune strains for metal immobilisation in soils, offering a potential bioremediation tool to combat the adverse effects of soil contamination and promote environmental sustainability.

Low restoration success in degraded drylands has promoted research efforts towards recovery of pioneer components of these ecosystems such as biocrusts. Biocrusts can stabilize soils and improve nutrient cycling to assist vegetation establishment, but their natural recovery following a disturbance may be very slow. Soil inoculation with biocrust-forming components such as cyanobacteria is widely spread to foster biocrust formation. However, the growth of induced biocrust can be constrained under field conditions due to the harsh environmental conditions in drylands. Thus, strategies to reduce abiotic stresses have to be explored to improve cyanobacteria survival and growth. In this study, we performed an outdoor experiment to analyze the effect of plant-based ameliorating strategies in combination with cyanobacteria inoculum on biocrust formation and improvement of degraded arid soil properties. These ameliorants consisted of a plant mesh made of Macrochloa tenacissima and a Plantago ovata-based stabilizer. Application of ameliorating treatments improved cyanobacteria growth (higher chlorophyll a content, lower albedo and higher NDVI) compared to the application of cyanobacteria inoculum alone. Inoculated soils showed higher aggregate stability than non-inoculated ones, but the highest soil stability was found in the soils treated with P. ovata and was also significantly increased in the soils covered by the M. tenacissima mesh compared to uncovered soils. Both the mesh and the P. ovata stabilizer increased soil organic carbon content by up to 10% and 172%, respectively, compared to soils without habitat amelioration. Microbial community composition was similar between control and inoculated soils and between the mesh covered and uncovered soils, indicating that neither cyanobacteria inoculation nor the vegetal mesh had negative effects on the native soil community. In contrast, the soil with the P. ovata stabilizer alone displayed a different composition, with up to 95% of the bacteria's relative abundance represented by Firmicutes. This effect needs to be considered when applying this stabilizer to prevent a potential alteration of the indigenous soil microbial community. This study indicates the viability of using plant-based ameliorating strategies to optimize the establishment and growth of cyanobacteria inoculum and maximize their effects on soil properties, thus contributing to advancing in the application of nature-based solutions for the restoration of degraded dryland ecosystems.

A significant fraction of Earth's ecosystems undergoes periodic wet-dry alternating transitional states. These globally distributed water-driven transitional ecosystems, such as intermittent rivers and coastal shorelines, have traditionally been studied as two distinct entities, whereas they constitute a single, interconnected meta-ecosystem. This has resulted in a poor conceptual and empirical understanding of water-driven transitional ecosystems. Here, we develop a conceptual framework that places the temporal availability of water as the core driver of biodiversity and functional patterns of transitional ecosystems at the global scale. Biological covers (e.g., aquatic biofilms and biocrusts) serve as an excellent model system thriving in both aquatic and terrestrial states, where their succession underscores the intricate interplay between these two states. The duration, frequency, and rate of change of wet-dry cycles impose distinct plausible scenarios where different types of biological covers can occur depending on their desiccation/hydration resistance traits. This implies that the distinct eco-evolutionary potential of biological covers, represented by their trait profiles, would support different functions while maintaining similar multifunctionality levels. By embracing multiple alternating transitional states as interconnected entities, our approach can help to better understand and manage global change impacts on biodiversity and multifunctionality in water-driven transitional ecosystems, while providing new avenues for interdisciplinary studies. Our framework proposes that water-driven transitional ecosystems experience periodic shifts between aquatic and terrestrial states within a single interconnected meta-ecosystem, driven by temporal water availability. Biological covers like aquatic biofilms and biocrusts play a central role, undergoing successional dynamics in response to wet-dry transitions, impacting biodiversity and ecosystem functioning. These impacts, especially considering the risk to become a stable dry ecosystem under the global change context, pose threats to the contribution of water-driven transitional ecosystems to global biogeochemical cycles, climatic stability, and human welfare.image

The Tabernas desert occupies an area of about 150 km2 and contains one of the best-preserved badlands in the Mediterranean. Besides its many geological interests, the area has unique ecological features like rare endemic plant species and biocrusts. Part of the area has no specific protection for its many geofeatures. In recent years, because the high number of annual hours of sunshine, the area is attracting solar power plants from large companies, which might jeopardize the future of this unique landscape. The purpose of this paper is to assess the geotourist and conservation merits of the area to be included in a future Geopark. The assessment is based on known indicators evaluating the scientific, educational, and geotourist values of the Tabernas badlands. We also provide notorious, well-documented geofeatures as well as the major threats in this area. In addition to the badlands, the Tabernas desert contains nine inventoried sites of geological interest and five in its close vicinity. In addition, Cabo de Gata UNESCO Geopark is located 60 km from this site. The area has been the subject of over 150 international scientific papers in recent decades. Since the 60 s, the Tabernas Desert has attracted the attention of many moviemakers, especially the "western type". Three "western villages" remain as tourist attractions. Recurrent movies, TV series, commercials, and landscape photographers show their permanent interest. There are many reasons for the protection of this environment for future generations though only two are mentioned here: (1) the dominant lithology, flysch-type sedimentary rocks and gypsiferous marls provide a profusion of notorious geomorphic features though prone to occasional, localized high erosion rates; (2) the high cover of fragile biocrusts carpet and protect from erosion about one-third of the unprotected area. Allowed activities should be those related to sightseeing and educational tourism. Present adventure tourism and some sports activities lack regulation and could be a threat to the future.

In drylands, extreme environmental conditions pose a challenge for restoration, especially on a large scale. Direct seeding is the most cost-effective approach to restore large areas, but it requires improvements to enhance seedling survival and establishment. For this purpose, biopriming seeds with cyanobacteria is promising due to their plant growth-promoting properties. We evaluated the effect of seed biopriming with native biocrust-forming cyanobacteria on seed germination and radicle length of four native plant species, two perennials (Macrochloa tenacissima and Thymus hyemalis) and two annuals (Plantago ovata and Stipa capensis), chosen for their ubiquity in Mediterranean drylands. Treatments included seed biopriming with cyanobacteria inoculants (biomass + exudate), seed priming only with the cyanobacterial exudate, and controls (BG11 culture medium and distilled water). Biopriming effect was assessed individually for four native biocrust-forming cyanobacteria species: Nostoc commune, Tolypothrix distorta, Trichocoleus desertorum, and Leptolyngbya frigida. Seed biopriming showed no effect on germination with similar rates among treatments (on average, 45 ± 12.6

The biocontrol potential of three native soil cyanobacteria from biological soil crusts (Nostoc commune, Scytonema hyalinum, and Tolypothrix distorta) was tested by means of in vitro mycelial growth inhibition assays for eighteen cyanobacteria-based products against three phytopathogenic soilborne fungi (Phytophthora capsici, Pythium aphanidermatum, and Fusarium oxysporum f. sp. radicis-cucumerinum). Three cyanobacteria-based production factors were considered: (i) cyanobacterium strain, (ii) cyanobacterial culture growth phase, and (iii) different post-harvest treatments: raw cultures, cyanobacterial filtrates, and cyanobacterial extracts. Results showed that any of the factors considered are key points for successfully inhibiting fungal growth. N. commune showed the highest growth inhibition rates for the three phytopathogens; stationary phase treatments produced higher inhibition percentages than logarithmic ones; and all the post-harvest treatments of N. commune at the stationary phase inhibited the growth of P. capsici, up to 77.7%. Thus, N. commune products were tested in planta against P. capsici, but none of the products showed efficacy in delaying the onset nor reducing the damage due to P. capsici, demonstrating the complexity of the in planta assay’s success and encouraging further research to design an appropriate scaling up methodology.

Water is a limiting resource for dryland vegetation, and vegetation biomass, composition, and phenology are directly dependent on highly variable water availability and close linkages between water availability and vegetation dynamics that characterized arid and semiarid ecosystems. Dryland perennial vegetation commonly forms isolated patches interspersed with bare soil areas that usually exhibit high runoff rates, while vegetated areas act as runoff sinks, re-infiltrating most of this run-on. Thus, dryland ecosystems usually act as complex ecohydrologically coupled systems in which water and sediment redistribution from bare areas controls ecosystem functioning and increases vegetation productivity. In the present study, we analyze the response of Macrochloa tenacissima to run-on exclusion during two years in a semiarid ecosystem located in Almeria (SE Spain). To do this, we established eight experimental plots, including one plant of M. tenacissima per plot. For four of them, run-on from upstream areas was excluded, whereas the rest of plots were maintained as control open plots (receiving runoff from upstream interplant spaces). All the plants were scanned by using a terrestrial laser scanner, and we measured their spectral response, at the beginning and the end of the experiment. From the plant point clouds, we estimated total above ground biomass per plant and total photosynthetically active biomass. Also, we periodically monitored plant phenology and productivity, measuring leaf photosynthesis on the different plants and their spectral response. In addition, we continuously monitored soil water content at two depths and soil CO2 molar fraction. The results showed that plants receiving run-on showed more photosynthetically active biomass and net C uptake rates than plants under run-on exclusion treatment. The observed differences between treatments increase with time and were especially accentuated after rainfalls, when the differences in water availability were more pronounced. Our findings highlight the important role that the supply of water from run-on plays for dryland vegetation. In this sense, any alteration on unvegetated spaces may also have an important effect on vegetation productivity, like those pushed by the alteration in precipitation pattern, reducing vegetation biomass and their capacity to respond to water pulses.

Context Macrochloa tenacissima (L.) Kunth (= Stipa tenacissima L.), also defined as Alpha grass steppes, form the main dryland ecosystems throughout the Mediterranean region. Recent studies suggest that ongoing climate change will lead to a sequence of changes in them, including modifications in the composition of vegetation and reduction in vegetation cover and biomass, which will diminish plant-derived organic inputs into the soil. These changes are expected to affect the spatial arrangement of vegetation and the ecosystem’s water-nutrient balance, as well as the microbial populations in the underlying soil. In addition, the lithological legacy affecting soil hydrological properties might modulate the effects of aridity. Objectives With this study, we wanted to evaluate the interactive effects of the lithological legacy on soil water availability and aridification on vegetation cover, spatial structure, and composition, and on soil microbial biomass. Methods We combined field data, including plant composition and soil physicochemical and biological properties, with unmanned aerial vehicle (UAV) images collected at eight study sites along two different altitudinal-aridity gradients with contrasting lithologies in a space-for-time substitution approach to explain the role of lithological legacies on soil properties in aridification. High-resolution UAV images were used to determine the vegetation cover and three spatial metrics related with the hydrological connectivity within the study areas. Soil microbial biomass was estimated using the substrate-induced respiration method. Results Aridification was critical to explaining changes in vegetation coverage, diversity, richness, and spatial distribution, reducing plant cover, and promoting dominance of small round isolated vegetation patches. By modulating soil physicochemical properties, lithology interacted with aridity controlling the variations in plant composition and the changes in soil microbial biomass along the altitudinal aridity gradients. This may have also affected nutrient cycling, thus determining the response of the ecosystem to aridification. Conclusion According to our results, the effect of the lithology legacy on soil properties interacts with aridity, determining the response of M. tenacissima steppes to aridification, as it modifies water availability on soil and plant composition, leading to differences in microbial biomass. Thus, both factors should be considered in the development of management strategies aimed for reducing and mitigating the negative impacts of climate change and aridification in drylands.

Drylands are ecohydrologically-coupled ecosystems whose functioning depends on the interplay between hydrological connectivity between runoff source areas and the capacity of vegetation to retain water fluxes and associated resources. In this study we present a new easily applicable methodology for the ecohydrological characterization of dryland ecosystem functioning grounded in the balance between these two strongly interrelated processes using easily obtainable remote sensing data (e.g. UAV and SENTINEL-2 images), the BalanCR method (Balance between Connectivity and potential Water Retention Capacity). This methodology was first tested on synthetic hillslopes representing different configurations of the patchy and heterogenic distribution of vegetation in drylands. The analysis of these synthetic vegetation spatial patterns involving different vegetation patch densities, sizes, and fractional coverage values showed that BalanCR properly characterizes the expected ecohydrological interactions between potential conditions of runoff connectivity and water retention by plants operating in drylands. In a second step, we applied the BalanCR method on four semiarid hillslopes along an altitudinal aridity gradient covered by Mediterranean alpha steppes at very detailed spatial resolution (0.2 m) and at medium resolution (10 m). The obtained results were validated based on soil moisture data and vegetation greening and clearly recognized the four study sites as functional ecosystems, with very low water resource losses, and a pattern of increasing water redistribution processes as vegetation coverage declines. However, the sensitivity of methodology depends on the resolution of the input data (vegetation map and Digital Elevation Model; DEM), and the expected positive effect of small vegetation structures (vegetation patches smaller than the pixel size) on water redistribution is underestimated. Even in this case, the functionality and connectivity of the analyzed sites is correctly characterized as ecosystems showed similar values of both components for the methodology BalanC (hydrological connectivity component) and BalanR (potential water retention capacity component) than those obtained at very detailed scale, with a similar pattern of water allocation values in response to increased aridity. Thus, the proposed metric represents a promising tool for the proper evaluation of dryland conditions and to incorporate hillslope processes in climate change models, which is one of the main gaps to better understand the drylands response upon ongoing climate change.

Biocrusts are ecosystem engineers in drylands and structure the landscape through their ecohydrological effects. They regulate soil infiltration and evaporation but also surface water redistribution, providing important resources for vascular vegetation. Spatially-explicit ecohydrological models are useful tools to explore such ecohydrological mechanisms, but biocrusts have rarely been included in them. We contribute to closing this gap and assess how biocrusts shape spatio-temporal water fluxes and availability in a dryland landscape and how landscape hydrology is affected by climate-change induced shifts in the biocrust community. We extended the spatially-explicit, process-based ecohydrological dryland model EcoHyD by a biocrust layer which modifies water in- and outputs from the soil and affects surface runoff. The model was parameterized for a dryland hillslope in South-East Spain using field and literature data. We assessed the effect of biocrusts on landscape-scale soil moisture distribution, plant-available water and the hydrological processes behind it. To quantify the biocrust effects, we ran the model with and without biocrusts for a wet and dry year. Finally, we compared the effect of incipient and well-developed cyanobacteria- and lichen biocrusts on surface hydrology to evaluate possible paths forward if biocrust communities change due to climate change. Our model reproduced the runoff source-sink patterns typical of the landscape. The spatial differentiation of soil moisture in deeper layers matched the observed distribution of vascular vegetation. Biocrusts in the model led to higher water availability overall and in vegetated areas of the landscape and that this positive effect in part also held for a dry year. Compared to bare soil and incipient biocrusts, well-developed biocrusts protected the soil from evaporation thus preserving soil moisture despite lower infiltration while at the same time redistributing water toward downhill vegetation. Biocrust cover is vital for water redistribution and plant-available water but potential changes of biocrust composition and cover can reduce their ability of being a water source and sustaining dryland vegetation. The process-based model used in this study is a promising tool to further quantify and assess long-term scenarios of climate change and how it affects ecohydrological feedbacks that shape and stabilize dryland landscapes.