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The objective was to know the effect of amendments and mulch (pine woodchips) on three planted autochthonous species in two substrates six years after the beginning of the restoration. But because this kind of mulch contained pine cones, pine seedlings appeared after the first year of the restoration; new objectives were added to the initial one: to know if organic amendments influence pine growth among planted vegetation, and if there were competition among planted species, opportunistic species and pines. Essential soil parameters, plant cover and diversity and pine growth were measured and statistically processed with correlation analyses, ANOVA and Detrended Correspondence Analysis. Six years after restoration organic amendments, applied all over the plots contributed significantly to explain the differences on the tested variables. The combined effects of the two substrates and the two organic amendments effectively enhanced soil properties recovery, but they also facilitated the establishment and entry of new species in addition to planted vegetation, driving a differential plant development. The number of pines, as well as their coverage, depended on the interaction between the amendment and the substrate: a) only one amendment favoured the pines and b) the way the amendment works depended on the substrate. Planted vegetation cover and total plant cover from amended plots doubled that of control plots. Results indicate the potential suitability of organic amendments, pine chips mulch and derived opportunistic species for restoring post-mining areas.

Many dryland soils absorb atmospheric CO2 at night. Despite the relatively small annual carbon (C) uptake, ranging locally from 1 to 10 g C m-2, it may have large-scale effects, as drylands cover almost 45% of the Earth’s land surface. This process might contribute to the global missing C sink of 3.1 ± 0.9 Pg C year-1. As dryland soils have high inorganic C contents compared to organic C, mechanisms of the nocturnal CO2 uptake likely involve both biotic and abiotic processes that are tightly coupled to water availability. Biological soil crusts (hereafter, biocrusts) cover about 30% of global drylands and provide favourable physico-chemical hotspots for this C exchange mechanism. In this study, we present a mechanistic model of inorganic C binding that is enhanced by the activity of biocrust communities. The model results show good agreement with field measurements of the soil-atmosphere CO2 exchange dynamics under contrasting conditions of water availability and temperature in the Tabernas Desert (Spain). We further show that inorganic C sequestration rates at night vary, depending on the successional stages of biocrusts. Our findings have the potential to substantially improve the often-overlooked processes of dryland systems in the global C cycle. By unravelling the mechanisms occurring along the succession of biocrusts, this study highlights the roles of soil biological agents in mitigating CO2 emissions in a drier future.

Many industries and agriculture generate huge amounts of wastes either mineral, organic or both, with environmental impact. Some of these residues have the potential to become Technosols when mixed in proper proportions. Degraded terrestrial ecosystems, especially sloping land, show very shallow or no soil left which makes restoration very difficult. Covering such degraded surfaces with Technosols might be a possible solution. The purpose of this paper is to show how some combinations and proportions of residues, mainly sludge from the ornamental stone industry and compost from green residues, become useful Technosols for landscape restoration. We tested in the laboratory twelve different combinations of that sludge, organic compost and other materials, as experimental Technosols. The three best combinations were tested in the field in (3 × 2 m) experimental plots at the open air on a 30° slope. We planted autochthonous species and survival and growth monitored for 1 year. The essential soil physical and chemical properties were also monitored as well as their hydrological behavior by means of repeated rainfall simulations. Treatments with artificial stone sludge up to 70% and slabs were able to provide substrates with physical and chemical properties relatively similar to those of natural soils in arid-semiarid environments like those from SE Spain. Higher content of organic matter and better physical properties were found in the Technosols. No clear differences between types of treatments were detected. Although runoff was slightly higher in Technosols than in natural soils, the treatment with the highest compost content (15%), presented the lowest erodibility, similar to natural soils in the area. None of the tested Technosols produced dangerous leachates exceeding the maximum values recommended by the European legislation. Technosols also increased plant growth of Rosmarinus officinalis and Thymus vulgaris. These results confirm that the tested Technosols can be used for the restoration of degraded soils and, in areas affected by earthworks, as road taluses.

The process of water vapor adsorption (WVA) by soil (i.e. water vapor movement from atmosphere to soil, forming liquid water on soil particles) is likely a substantial contributor to the water cycle in drylands. However, several gaps remain in our knowledge of WVA: (1) continuous in situ estimates of WVA are still very scarce; (2) the underlying mechanisms involved in its temporal patterns are still not well constrained, and (3) the understanding of its coupling with the carbon cycle and ecosystem processes remains at an incipient stage.Here, we aimed to (1) identify periods of WVA and improve the understanding of the underlying mechanisms involved in its temporal patterns by using the gradient method (GM); (2) characterize a potential coupling between water vapor and CO2 fluxes, especially expected in drylands due to the water-limitation of ecosystem processes. In particular, we assumed that the nocturnal soil CO2 uptake increasingly reported in those environments (including at our study site) could come from WVA enhancing reactions with CaCO3; (3) explore the effect of soil properties and biocrusts ecological succession on fluxes.To this end, in the Tabernas Desert (Almería, Spain), we measured continuously during ca. 2 years the relative humidity and CO2 molar fraction in soil and atmosphere, in association with below- and aboveground variables, in microsites representative of the biocrusts ecological succession. We estimated water vapor and CO2 fluxes with the GM, and cumulative fluxes over the study. Then, we used linear and non-linear statistical modelling to explain relationships between variables.Our main findings are (1) WVA during hot and dry periods, and a new insight into the micrometeorological conditions triggering those fluxes; (2) a diel coupling between water vapor and CO2 fluxes (including the uptake of both gases by soil at night) and between cumulative fluxes, well predicted by our models; and (3) cumulative CO2 influxes increasing with specific surface area in early succession stages, thus mitigating CO2 emissions. We suggest that the GM is a suitable approach to monitor WVA in-situ since it offers several advantages such as providing direct low-cost measurements of water vapor fluxes with good spatio-temporal resolution and low soil disturbance. Over a year, the WVA represented between ca. 0.2% and 2.8% of the precipitation amount, depending on the microsite and the diffusion model that was used to estimate the fluxes.Therefore, WVA constituted a non-negligible input of liquid water in this dryland. In particular, during summer drought, as WVA was the main water source, it probably maintained ecosystem processes such as microbial activity and mineral reactions. We propose that the nocturnal CO2 uptake reported in this dryland may arise from (i) WVA enhancing geochemical reactions involving CaCO3 and/or biological dark CO2 fixation; (ii) the co-adsorption of CO2. Further research is now needed to (1) disentangle those processes; (2) monitor soil water vapor and CO2 uptake by soils as those sinks could grow with climate change; (3) improve the accuracy of the water vapor fluxes estimated with the GM, for example by calibrating the GM with lysimeters.

Vapor condensation, whether due to dew or fog, may add a stable and important source of water to deserts. This was also extensively assessed in the Negev, regarded as a dew desert. Dew deserts necessitate a large reservoir of vapor, and are therefore confined to near oceans or seas. Yet, examples of such deserts are scarce. Here we try to assess whether the Tabernas Desert in SE Spain can be regarded as a dew desert, and may therefore facilitate the growth of certain organisms that otherwise would not survive the dry season. We analyze some of the abiotic conditions of four relatively dry months (June, July, August, September) in the Tabernas and Negev deserts (with the Negev taken as an example of a dew desert) during 2003–2012. The analysis showed substantially lower values of relative humidity (by 10–13%) in the Tabernas in comparison to the Negev, with RH ≥95% being on average only 0.9–1.1 days a month in the Tabernas in comparison to 9.7–13.9 days in the Negev. Our findings imply that the Tabernas Desert cannot be regarded as a dew desert, suggesting that rain will be the main factor responsible for the food web chain in the Tabernas.

Ongoing global warming and alterations in rainfall patterns driven by climate change are known to have large impacts on biogeochemical cycles, particularly on drylands. In addition, the global increase in atmospheric nitrogen (N) deposition can destabilize primary productivity in terrestrial ecosystems, and phosphorus (P) may become the most limiting nutrient in many terrestrial ecosystems. However, the impacts of climate change on soil P pools in drylands remain poorly understood. Furthermore, it is unknown whether biocrusts, a major biotic component of drylands worldwide, modulate such impacts. Here we used two long-term (8-10 years) experiments conducted in Central (Aranjuez) and SE (Sorbas) Spain to test how a ~2.5°C warming, a ~30% rainfall reduction and biocrust cover affected topsoil (0-1 cm) P pools (non-occluded P, organic P, calcium bound P, occluded P and total P). Warming significantly increased most P pools-except occluded P-in Aranjuez, whereas only augmented non-occluded P in Sorbas. The rainfall reduction treatment had no effect on the soil P pools at any experimental site. Biocrusts increased most soil P pools and conferred resistance to simulated warming for major P pools at both sites, and to rainfall reduction for non-occluded and occluded P in Aranjuez. Synthesis. Our findings provide novel insights on the responses of soil P pools to warming and rainfall reduction, and highlight the importance of biocrusts as modulators of these responses in dryland ecosystems. Our results suggest that the observed negative impacts of warming on dryland biocrust communities will decrease their capacity to buffer changes in topsoil P driven by climate change., Departamento de Sistemas Físicos, Químicos y Naturales

Biological soil crusts (biocrusts) have been reported to play a considerable role in the global carbon budget through CO2 uptake by photosynthesis. However, it is still unclear if ecosystems dominated by biocrusts are net carbon sinks. That is mainly because so far, most research have focused on characterizing photosynthesis ex-situ, neglecting the underlying soil component, and particularly the in-situ spatio-temporal variability of soil CO2 fluxes, which can be substantial. Moreover, it is still unknown how those CO2 fluxes evolve during the ecological succession of biocrusts and which are the biophysical and geochemical factors that control them. Therefore, this research aimed to (1) identify those factors and (2) describe and explain the evolution of annual cumulative soil CO2 fluxes over ecological succession in a dryland.To this end, we conducted continuous measurements over 2 years of the topsoil CO2 molar fraction (χs) in association with below- and aboveground microclimatic variables in 21 locations representative of the ecological succession of biocrusts, characterized by 5 stages: (1) physical depositional crust; (2) incipient cyanobacteria; (3) mature cyanobacteria; (4) lichen community dominated by Squamarina lentigera and Diploschistes diacapsis and (5) lichen community of Lepraria isidiata. Those measurements were also conducted under plants (Macrochloa tenacissima, Salsola genistoides, and Lygeum spartum). Using spatio-temporal statistics, an explanatory model of χs dynamics was calibrated on the first year of data and cross-validated to test prediction on the second year. An explanatory model of annual cumulative fluxes was also developed.The biocrust type, soil water content (ϑ) and temperature (Ts) and interactions between those variables explained and predicted efficiently the χs dynamics. Among those factors, the effect of ϑ was preponderant and dependent on Ts and antecedent soil moisture conditions. The magnitude of the ϑ effect tended to increase in late successional stages, producing greater CO2 emissions, most likely as a result of progressive soil organic carbon accumulation resulting in greater substrate availability for microbial respiration, and higher porosity enhancing CO2 diffusion. The calcite content (and potentially indirectly the pH through a buffering effect of CaCO3) also played a role in explaining annual cumulative CO2 fluxes. Those fluxes were particularly mitigated where CaCO3 was abundant, apparently due to a substantial nocturnal uptake of atmospheric CO2 by soil (influx) throughout the study. The cumulative annual influx represented up to 115% of the cumulative annual efflux, generating a net annual carbon uptake by soil in some locations. Influxes have been increasingly reported recently from drylands soils, which are now regarded as potential carbon sinks. Those influxes have been attributed to different abiotic processes which are still debated. In this ecosystem, in the light of our observations, we assume that a geochemical process of CO2 dissolution in soil water followed by CaCO3 dissolution that consumes CO2 might be involved. If this assumption could be verified, this geochemical process consuming CO2 would need to be separated from biocrust photosynthesis and respiration, when measuring soil surface CO2 fluxes, to not overestimate and underestimate respectively the biotic contribution to the global carbon budget.

This study was started in the context of the research projects PECOS (REN2003-04570/GLO) and PREVEA (CGL2007-63258/BOS) , both funded by the Spanish National Plan for RD&I and by the European ERDF Funds (European Regional Development Fund) , and continued during the project SCIN (Soil Crust In-terNational, PRI-PIMBDV-2011-0874, European project of ERA-NET BIODIVERSA, the Spanish team being funded by the Spanish Ministry of Economy and Competitiveness) . The work was finally supported and culminated by the DINCOS project (CGL2016-78075-P, Spanish State Programme for Scientific Research) and by the European ERDF Funds (Euro-pean Regional Development Fund) . Consuelo Rubio's partici-pation was possible thanks to the contract as a doctoral student FPU18/00035. Dr. Javier Barbero advised us on mathemati-cal issues. Special thanks: This research was kindly facilitated by the Viciana brothers, landowners of the El Cautivo field site., The runoff coefficient (RC) is widely used despite requiring to know the effective contributing area, which cannot be known a priori. In a previous work, we defined runoff length (RL), which is difficult to measure. This work aimed to define the minimum RL (mRL), a quantitative and easy proxy of RL, for use in a pilot study on biocrusts in the Tabernas Desert, Spain. We show that RC decreases according to a hyperbola when the contributing area increases, the independent variable being the length of the effective contributing area and its coefficient involving the effects of rainfall and surface features and antecedent conditions. We defined the mRL as the length of the effective contributing area making RC = 1, which is calculated regardless of the area. We studied mRL from three biocrust types and 1411 events clustered in seven categories. The mRL increased with rain volume and intensity, catchment area and slope, whereas plant cover and biocrust succession (with one exception) had a negative effect. Depending on the plot, mRL reached up 3.3–4.0 m on cyanobacterial biocrust, 2.2–7.5 m on the most widespread lichens, and 1.0–1.5 m on late-successional lichens. We discuss the relationships of mRL with other runoff-related parameters., Spanish National Plan for RDI REN2003-04570/GLO CGL2007-63258/BOS, European ERDF Funds (European Regional Development Fund), Spanish Government PRI-PIMBDV-2011-0874, DINCOS project (Spanish State Programme for Scientific Research) CGL2016-78075-P, European ERDF Funds (Euro-pean Regional Development Fund) FPU18/00035

In terms of monitoring wind turbine performance, the power curve plays a key role and it is a valuable indicator of the wind turbine’s condition as it allows the identification of anomalies related to production. On the other hand, by calculating a typical reference curve of the machine, it is possible to calculate losses and estimate its performance. A suitable model that characterises the power curve can benefit the estimated production of a wind turbine or wind farm. The most widely used models to characterise power curves are based on 2-variable models (wind speed and power). The power curve is affected by different exogenous variables (such as temperature, wind direction or turbulence intensity) that must be taken into account in the characterisation of the power curve. Consequently, the working conditions of the wind turbine are different depending on the site, and multivariable models that can take these variables into account are required. Currently new models and alternatives are emerging. This study will evaluate the performance of multivariate models based on Gaussian mixture copula model (GMCM), Regressive artificial neural Networks (ANN) and Bayesian artificial neural networks (BANN) in terms of power curve characterisation and power estimation. The results will be compared to the most common methods such as the manufacturer power curve and historical power curve, which is generated using the the bins method. Taking advantage of the benefits of neural networks (NN), particular types of NN have been considered to provide the value of uncertainty in the estimation of power.

Data preprocessing is the initial and utmost critical phase of wind resource assessment and wind power curve performance analysis. Without ensuring high quality and site representative data availability, an evaluation for the wind resource potential of a wind farm site means investment decision making involving a great deal of uncertainty. The current practice in the field is to use fix rules and via data scanning by manual labouring of data field experts. Although rule-based (if-else, interval-based) prefiltering applications can be found in some commercial software, and these rules are also limited for addressing the needed preprocessing requirements fully. Therefore, this process is time consuming and causes inefficient resource allocation considering the manual scanning process performed by data scientists & experts. In this study, reviewed data by experts are used as data with correct labels, and then efficient classifiers are generated by applying machine learning algorithms to unfiltered and filtered data. It is reported that tree-based classifiers are performing better.

Individual plant species form so-called resource islands in the barren semiarid landscape, whereby many soil properties are enhanced including soil structure. Within the soil structure, mostly studied as soil aggregates, microaggregates (During two sampling campaigns in spring 2017 and 2018, soil samples were taken over a distance gradient from two major semiarid grassland plant species in Southern Spain, the legume shrub Anthyllis cytisoides and the grass tussock Macrochloa tenacissima, to the surrounding bare soil. While topsoil was sampled in five distances to the plant during the first sampling campaign, the second one focused stronger on the root influence, hence rhizoplane and rhizosphere were sampled. Additionally, two sites with different parent materials were chosen to scale the effect of EPS on soil aggregation in the presence of inorganic binding agents (here carbonates). Total community DNA and EPS were extracted, followed by quantification of EPS-saccharides and bacterial abundance, as well as examination of the prokaryotic community composition by Illumina amplicon sequencing of the 16S rRNA genes. Further, the particle size distribution of (micro)aggregates in water was determined, with and without ultrasound treatment, as a measure of soil aggregate size distribution and stability.Based on the first sampling campaign, we found that the overall prokaryotic community composition differed between the two sites, but not between plant species. Interdependencies between the community composition and EPS content were revealed, whereby soil organic matter (SOM) seems to be a regulating factor as increasing SOM contents resulted in more EPS-saccharides. Soil microaggregation in the topsoil was enhanced by the plant canopy, especially at the edge of Macrochloa tussocks. Contrary to the expectation that increasing inorganic C contents would diminish the importance of EPS, the parent material richest in inorganic C results in a significant effect of EPS-saccharides on microaggregation.First results of the second sampling campaign indicate that even in the rhizoplane and rhizosphere, parent material had a dominating influence on the prokaryotic community composition. As EPS-saccharide contents and soil aggregation followed a similar decreasing trend with distance to the roots and canopy cover, interdependencies are expected.From the outcomes until now, we can conclude that the availability of decomposable OM influences the prokaryotic community composition and thereby triggers EPS production, whereas large contents of polyvalent cations from carbonates promote the stabilizing effect of EPS on microaggregates.

© 2020 by the authors., Arid and semi-arid ecosystems are characterized by patchy vegetation and variable resource availability. The interplant spaces of these ecosystems are very often covered by cyanobacteria-dominated biocrusts, which are the primary colonizers of terrestrial ecosystems and key in facilitating the succession of other biocrust organisms and plants. Cyanobacterial biocrusts regulate the horizontal and vertical fluxes of water, carbon and nutrients into and from the soil and play crucial hydrological, geomorphological and ecological roles in these ecosystems. In this paper, we analyze the influence of cyanobacterial biocrusts on water balance components (infiltration-runoff, evaporation, soil moisture and non-rainfall water inputs (NRWIs)) in representative semiarid ecosystems in southeastern Spain. The influence of cyanobacterial biocrusts, in two stages of their development, on runoff-infiltration was studied by rainfall simulation and in field plots under natural rainfall at different spatial scales. Results showed that cover, exopolysaccharide content, roughness, organic carbon, total nitrogen, available water holding capacity, aggregate stability, and other properties increased with the development of the cyanobacterial biocrust. Due to the effects on these soil properties, runoff generation was lower in well-developed than in incipient-cyanobacterial biocrusts under both simulated and natural rainfall and on different spatial scales. Runoff yield decreased at coarser spatial scales due to re-infiltration along the hillslope, thus decreasing hydrological connectivity. Soil moisture monitoring at 0.03 m depth revealed higher moisture content and slower soil water loss in plots covered by cyanobacterial biocrusts compared to bare soils. Non-rainfall water inputs were also higher under well-developed cyanobacterial biocrusts than in bare soils. Disturbance of cyanobacterial biocrusts seriously affected the water balance by increasing runoff, decreasing soil moisture and accelerating soil water loss, at the same time that led to a very significant increase in sediment yield. The recovery of biocrust cover after disturbance can be relatively fast, but its growth rate is strongly conditioned by microclimate. The results of this paper show the important influence of cyanobacterial biocrust in modulating the different processes supporting the capacity of these ecosystems to provide key services such as water regulation or erosion control, and also the important impacts of their anthropic disturbance., This work has been supported by several research projects: REBIOARID (RTI2018-101921-B-I00), DINCOS (CGL2016-78075-P) projects, founded by the Spanish National Plan for Research and the European Union ERDF and the BIOCOST project Supported by Biodiversity Foundation of the Ministry for the Ecological Transition., Publisher’s version

The availability of metallic nutrients in dryland soils, many of which are essential for the metabolism of soil organisms and vascular plants, may be altered due to climate change-driven increases in aridity. Biocrusts, soil surface communities dominated by lichens, bryophytes and cyanobacteria, are ecosystem engineers known to exert critical functions in dryland ecosystems. However, their role in regulating metallic nutrient availability under climate change is uncertain. Here, we evaluated whether well-developed biocrusts modulate metallic nutrient availability in response to 7 years of experimental warming and rainfall reduction in a Mediterranean dryland located in southeastern Spain. We found increases in the availability of K, Mg, Zn and Na under warming and rainfall exclusion. However, the presence of a well-developed biocrust cover buffered these effects, most likely because its constituents can uptake significant quantities of available metallic nutrients. Our findings suggest that biocrusts, a biotic community prevalent in drylands, exert an important role in preserving and protecting metallic nutrients in dryland soils from leaching and erosion. Therefore, we highlight the need to protect them to mitigate undesired effects of soil degradation driven by climate change in this globally expanding biome., Eduardo Moreno-Jiménez et al. experimentally manipulate rainfall and temperature in a Mediterranean dryland to explore the association of biocrusts with essential metallic nutrients. They find that biocrusts—communities of lichens, bryophytes and cyanobacteria on the soil surface—can buffer against the effects of warming and reduced rainfall on metallic nutrient availability.

Catchment asymmetry is a fairly frequent phenomenon on a global scale but the main causes leading to its formation are still not well understood. Where the intervention of structural or tectonic causes is not relevant, asymmetry seems to result from differential erosion between opposite slopes that flow into the same channel, which is frequently associated with contrasted biocrust and/or vegetation covers. Biocrusts are known to be important surface stabilizing agents. However, their geomorphological consequences at the landscape scale are little known. In this study we combined field measurements with digital elevation models and image analysis to determine whether catchment asymmetry in the Tabernas Desert (semi-arid SE of Spain) is a local or general phenomenon, and to explore the main factors determining asymmetry occurrence, magnitude and direction. We pay special attention to the role of biocrusts. We found that catchment asymmetry is a very common phenomenon in the area; only 25% of the catchments are symmetrical, while approximately 40% present asymmetry with the relatively shady hillslope having a lower gradient, and 35% with that hillslope being the steeper. Solar radiation reaching the soil, surface area and channel gradient in the considered catchment stretch, as well as the total catchment area upstream from the lower point of the considered stretch were the main abiotic factors controlling the formation of the asymmetry. Microclimatic differentiation due to differences in radiation input caused by the uneven topography favoured the relative stabilization of the shadier hillslope and its colonization by biocrusts and later by plants. The effect of the biocrusts and vegetation protection against water erosion on shadier hillslopes is often stronger than that of the set of abiotic factors and gives rise to asymmetries with lower gradients in the shady hillslope by promoting lateral displacement of the channel. We hypothesised that the opposite pattern, with the sunnier hillslope having a lower gradient, occurs when abiotic factors control the development of asymmetry formation. In these conditions, the effect of biocrusts and plants would act in the opposite direction. We propose a conceptual model of feedbacks generating catchment asymmetry, with biocrust playing a crucial role.

The original publication is available at: publicaciones.unirioja.es/revistas/cig, [EN]A combination of high temporal variability and spatial heterogeneity of rainfall, soil surfaces, and plant cover is the cause of the complex hydrological response in arid/semiarid regions. Under these premises, long-term monitoring is necessary to capture drivers controlling the response of these areas and to be able to model and predict their reaction. A succinct, up-to-date review of the databases and results produced by two representative micro-catchments in the most arid extreme of Europe, Almería (SE Spain), is presented with the aim to show how the different precipitation patterns, during a 20-year period, influence the hydrological behavior on different lithologies and soil surfaces. The problems encountered about the functioning of these experimental stations, including the generation and maintenance of long-term databases, is also reviewed., [ES]Una combinación de elevadas variabilidades, espacial y temporal, en precipitación, superficies del suelo y vegetación es la causa de la compleja respuesta hidrológica en las regiones áridas-semiáridas. Bajo esta premisa es necesario un seguimiento a largo plazo para conocer los factores que controlan las respuestas hidrológicas de estas regiones, poder modelizarlas y predecirlas. Se presenta una breve revisión actualizada de las bases de datos y de los resultados obtenidos en dos microcuencas representativas del semiárido almeriense, en el SE peninsular, con la finalidad de mostrar cómo diferentes patrones de precipitación influyen en el comportamiento hidrológico en diferentes litologías y superficies del suelo, en un período de unos 20 años. Además, se repasan los problemas encontrados respecto al funcionamiento y mantenimiento de estas microcuencas y en las bases de datos generadas., field installations, data gathering, and personnel: MEDALUS (contract no. EV5VCT92- 0128), financed by the EEC European Union; PROHIDRADE (AMB95-0986), PROGESED (HID97-0581), EPOHIDRO (HID98-1056), PROHISEM (REN2001- 2268-C02-01), CANOA (CGL2004-04919-C02-01), PROBASE (CGL2006-11619/ HID), BACARCOS (CGL2011-29429), RESUCI (CGL2014-59946-R), DINCOS (CGL2016-78075-P), financed by the Spanish I+D program; COSTRAS (RNM 3614) financed by Junta de Andalucía; and RESEL (network of Spanish field stations measuring soil erosion), supported by the General Directorate for Nature Conservancy of the Spanish Ministry of Agriculture and Environment.

Biocrusts are an important drylands landscape component, which enriches the upper millimeters of the soil with organic matter and initiates biogeochemical cycles. However, little is known about the influence of biocrusts on soil bacterial community structure and diversity. Different biocrust types representing a successional gradient were studied. This gradient, from the earliest to the latest successional stages, consisted of an incipient cyanobacterial biocrust

© The Author(s)., We examined the variations in microfungal communities from different surface types (cyanobacterial crusts, lichen-dominated crusts, and noncrusted bare surface) at two different positions—north-oriented slope and sun-exposed plain in the Tabernas Desert, Spain. A total of 77 species from 46 genera was isolated using the soil dilution plate method. The studied mycobiota, similar to the majority of desert mycobiotas, was dominated by melanin-containing species. However, in the Tabernas crusts, unlike the studied crusts of the Negev Desert (Israel) and the Tengger Desert (China), melanized fungi with large multicellular spores were much less abundantly represented, while the thermotolerant group, Aspergillus spp., remarkably contributed to the communities’ structure. Density of microfungal isolates positively correlated with chlorophyll content indicating possible significant influence of organic matter content on fungal biomass. The variations in crust composition, biomass, and the position of habitats were accompanied by the variations in microfungal community structure, diversity level, and isolate densities, with the communities at the plain sun-exposed position being much less variable than the communities at the north-oriented position. The study shows that microclimatic and edaphic factors play an essential role in the development of crust and noncrust microfungal communities, and their structure can be a sensitive indicator of changing environmental conditions at a microscale., To CSIC Agency (Spain) for support.

Este artículo contiene 16 páginas, 6 figuras, 2 tablas., Soil degradation by water is a serious environmental problem worldwide, with specific climatic factors being the major causes. We investigated the relationships between synoptic atmospheric patterns (i.e. weather types, WTs) and runoff, erosion and sediment yield throughout the Mediterranean basin by analyzing a large database of natural rainfall events at 68 research sites in 9 countries. Principal Component Analysis (PCA) was used to identify spatial relationships of the different WTs including three hydro-sedimentary variables: rainfall, runoff, and sediment yield (SY, used to refer to both soil erosion measured at plot scale and sediment yield registered at catchment scale). The results indicated 4 spatial classes of rainfall and runoff: (a) northern sites dependent on North (N) and North West (NW) flows; (b) eastern sites dependent on E and NE flows; (c) southern sites dependent on S and SE flows; and, finally, (d) western sites dependent on W and SW flows. Conversely, three spatial classes are identified for SY characterized by: (a) N and NE flows in northern sites (b) E flows in eastern sites, and (c) Wand SW flows in western sites. Most of the rainfall, runoff and SY occurred during a small number of daily events, and just a few WTs accounted for large percentages of the total. Our results confirm that characterization by WT improves understanding of the general conditions under which runoff and SY occur, and provides useful information for understanding the spatial variability of runoff, and SY throughout the Mediterranean basin. The approach used here could be useful to aid of the design of regional water management and soil conservation measures., This research was supported by projects funded by the MINECOFEDER: CGL2014-52135-C3-3-R, CGL2014-59946-R, CGL2015-65569- R, CGL2015-64284-C2-2-R, and PCIN-2017-061/AEI. When this manuscript was first submitted Estela Nadal-Romero and Damià Vericat received a “Ramón y Cajal” postdoctoral contract (RYC-2013-14371 and RYC‐2010‐06264, Spanish Ministry of Economy and Competitiveness, MEC). Damià Vericat is now a Serra Húnter Fellow at the University of Lleida. María Fernández-Raga received a “José Castillejo” postdoctoral grant (Spanish Ministry of Education, Culture and Sports). Carla Ferreira was supported by a post-doctoral research grant from the Portuguese Science and Technology Foundation (SFRH/ BPD/120093/2016). Mariano Moreno-de las Heras received a Juan de la Cierva postdoctoral contract (IJCI-2015-26463) from the MEC. José Andrés López-Tarazón received a Vicenç Mut postdoctoral fellowship from the Autonomous Balearic Government (CAIB PD/038/2016). José Andrés López-Tarazón and Ramon Batalla also acknowledge the Secretariat for Universities and Research of the Department of the Economy and Knowledge of the Autonomous Government of Catalonia for supporting the Consolidated Research Group 2014 SGR 645 (RIUSFluvial Dynamics Research Group), and the CERCA Programme. This paper has benefited from the Lab and Field Data Pool created within the framework of the COST action CONNECTEUR (ES1306).

We studied the effect of plant canopy on the distribution of microfungi through 0−30-cm soil profiles under canopies of three plant species and in their adjacent interspace at sun-exposed plain and north-facing slope in the Tabernas Desert, Spain. Using the soil dilution plate method, 142 species from 68 genera were isolated. Melanin-containing fungi dominated in the topsoil layers because of high temperatures and dryness. By contrast, light-colored fungi generating a high amount of small thin-walled conidia substantially increased their abundance in the deeper soil layers – thermotolerant Aspergillus spp. in the 1−5-cm layers and mesophilic Penicillium spp. in the 10−20-cm layers. The significant increase in density of microfungal isolates at 1−10 cm-depth could be associated with the deposition of conidia of aspergilli and penicillii caused by shallow water infiltration in the fine-grained soil and their survival at these depths due to more appropriate edaphic conditions (mainly higher water availability and root concentration). Generally, the effect of plant canopy on microfungal communities was only weakly expressed in higher variations of isolate densities and species richness through the profiles, and in reduced abundance of melanized species with protective multicellular spore morphology in the topsoil layers; at the same time, soil depth strongly influenced all community characteristics. The study highlights the remarkable role of edaphic factors (temperature, water regime, and soil texture) in the distribution of microfungi through soil depth in semi-arid areas.

Understanding how drylands respond to ongoing environmental change is extremely important for global sustainability. In this review, we discuss how biotic attributes, climate, grazing pressure, land cover change, and nitrogen deposition affect the functioning of drylands at multiple spatial scales. Our synthesis highlights the importance of biotic attributes (e.g., species richness) in maintaining fundamental ecosystem processes such as primary productivity, illustrates how nitrogen deposition and grazing pressure are impacting ecosystem functioning in drylands worldwide, and highlights the importance of the traits of woody species as drivers of their expansion in former grasslands. We also emphasize the role of attributes such as species richness and abundance in controlling the responses of ecosystem functioning to climate change. This knowledge is essential to guide conservation and restoration efforts in drylands, as biotic attributes can be actively managed at the local scale to increase ecosystem resilience to global change.

Wind turbine component’s failure prognosis allows wind farm owners to apply predictive maintenance techniques to their fleets. This permits optimal scheduling of the maintenance actions considering the best time to stop the turbines and perform those actions. Determining the health status of a turbine’s component typically requires verifying a wide number of variables that should be monitored simultaneously. The scope of this study is the investigation and the selection of an effective combination of variables and smoothing and forecasting methodologies for obtaining a wind turbine gearbox health status indicator, in order to interpret clearly the remaining lifetime of the gearbox. The proposed methodology is based on Gaussian Mixture Copula Model (GMCM) models combined with the smoothing treatment and the forecasting model to define the health index of the wind turbine gearbox. Then, the resulting index is tested using various warning and critical thresholds. These thresholds should be chosen adequately in order to indicate appropriate inspection visit and preventive maintenance intervention date. Then, the best combination found, for the studied cases, was 50% and 70% for warning and critical respectively. This combination ensures that the developed procedure is capable of providing long enough time window for maintenance decision making.

Several studies have predicted changes in precipitation patterns affecting both rain quantity and its temporal distribution for the Mediterranean Basin. This three-year study was performed to determine the physiological response of Macrochloa tenacissima, a dominant species in the western Mediterranean grasslands, to these changes. A rainfall manipulation experiment was therefore conducted to test the interaction of two factors: quantity (Q) and frequency (F) of rainfall, both at three levels (100%, 75% and 50% of natural rainfall). A mobile transparent polycarbonate rain-out shelter was designed to cover experimental plots of M. tenacissima when it rained, and then treatments were implemented by watering. Reductions in Q and F caused seasonal down-regulation of net photosynthesis (A) and stomatal conductance (gs), but the first variable showed greater resistance to change. At the annual scale, only the reductions of F had negative effects on A rates, but without causing significant changes to gs. The decrease in Q and F had opposite effects on intrinsic water-use efficiency (IWUE), enhancing and diminishing it, respectively. However, the response to Q was stronger, even exceeding the range of natural interannual variability. Rainfall Q and F reduction did not decrease Fv/Fm, as compared to ambient conditions. In conclusion, although the responses to the simulated rainfall patterns did not surpass the current seasonal oscillations of M. tenacissima's physiological parameters, they caused a down-regulation of its gas exchange and increased its water-use efficiency.

Commercial chambers for in vivo gas exchange are usually designed to measure on vascular plants, but not on cryptogams and other organisms forming biological soil crusts (BSCs). We have therefore designed two versions of a chamber with different volumes for determining CO2 exchange with a portable photosynthesis system, for three main purposes: (1) to measure in situ CO2 exchange on soils covered by BSCs with minimal physical and microenvironmental disturbance; (2) to acquire CO2-exchange measurements comparable with the most widely employed systems and methodologies; and (3) to monitor CO2 exchange over time. Different configurations were tested in the two versions of the chamber and fluxes were compared to those measured by four reference commercial chambers: three attached to two respirometers, and a conifer chamber attached to a portable photosynthesis system. Most comparisons were done on biologically crusted soil samples. When using devices in a closed system, fluxes were higher and the relationships to the reference chambers were weaker. Nevertheless, high correlations between our chamber operating in open system and measurements of commercial respiration and photosynthetic chambers were found in all cases (R 2 > 0.9), indicating the suitability of the chamber designed for in situ measurements of CO2 gas exchange on BSCs.

Differences in vegetation pattern between slope aspects in semiarid environments are well known, with shaded aspects presenting a higher biomass. The micrometeorological and soil conditions involved in non-rainfall water inputs (NRWI), comprising dew and water vapour adsorption (WVA) were compared between two contrasted slopes and different environmental conditions (wet and dry periods). Changes in natural soil surfaces were measured using automated microlysimeters, and the partial contributions of dew and WVA to the total NRWI were clarified. Dew amounts were higher on the northeast facing slope and were directly related to dew durations. Differences in dew deposition between slopes were mainly driven by insolation patterns, which controlled the surface temperatures, the soil water content and, in turn, dew duration. Apart from spatial variation in microclimate, WVA deposition was higher in the southwest facing slope due to its higher clay content and electric conductivity and because of its lower soil water content. Water vapour adsorption was directly governed by the relative humidity amplitude in summer (with dry soil) but not in winter. A significant amount of water evaporation was satisfied by NRWI, reaching 100% in dry periods and being WVA the main input.

This study was undertaken in the context of the research projects PECOS (REN2003-04570/GLO) and PREVEA (CGL2007-63258/BOS), both funded by the Spanish National Plan for RD&I and by the European ERDF Funds (European Regional Development Fund), as well as the projects COSTRAS (Excellence project RNM-3614) funded by the Junta de Andalucia (Autonomous Government of Andalusia, Spain), and SCIN (Soil Crust Inter-National, PRI-PIMBDV-2011-0874, European project of ERA-NET BIODIVERSA, the Spanish team being funded by the Spanish Ministry of Economy and Competitiveness)

Objective We investigated the temporal variation of soil bulk density (BD) in a semiarid Macrochloa tenacissima grassland where BD plays a key role in the soil–plant feedback mechanisms that are responsible for the patchy distribution of vegetation. Methods We used the core method to analyse the soil BD in two experimental sites in microsites that were representative of the spatial heterogeneity of soils and vegetation. The study was performed over two years, in winter (three times) and summer (twice). We studied the changes in BD in relation to the rainfall and to the soil properties that describe or affect the soil structural conditions, such as soil moisture, particle-size, clay mineralogy, the contents of various organic carbon fractions and certain microaggregation indices. Results We found a consistent temporal variation in BD, which was lower in winter (1.22 ± 0.02 g/cm 3 , average ± SEM) than in summer (1.33 ± 0.02 g/cm 3 ) and depended on the rainfall in the weeks before sampling. The greatest change was observed during the first year of study, when the wettest winter and the driest summer occurred. The variation of BD was most pronounced in the mounds developed under senescent plants (+ 16.7% average increase from winter to summer), intermediate under adult plants and in the residual mounds (+ 8.9%) and was weak in the soils of the bare areas or under young plants (+ 5.1%). This implies that the microtopography should get steeper in winter and flatter in summer. The largest changes in BD were correlated with variables representing organic matter and its action in adhering soil particles. Conclusion We observed consistent temporal variations in BD that were spatially heterogeneous and related to wet conditions in the soils studied. Research is needed to establish the mechanisms responsible for the changes in BD, which may include greater activity of roots and fauna during the wet season and the enrichment in labile organic fractions that are hygroscopic and can bind soil particles into temporary aggregates. Practice implications Spatially heterogeneous temporal variation in BD must be taken into account in inventories of soil nutrients, water or carbon. Moreover, it implies an increased porosity under vegetated patches just when the soil receives the most rainfall, resulting in a positive feedback of plant growth and mound formation. This mechanism might be added to those already described for plant–soil feedbacks in dry lands.

Finalizado FONDECYT FONDECYT

In drylands, water erosion can be a process with important economic and ecological implications, and is very dependent on the soil surface cover. There is broad agreement that biocrusts protect the soil from erosion in a wide range of circumstances. However, there is little information available on the effect of rain and biocrust types on this protective capacity and there is particularly very little knowledge on the erosive effects of runoff on biocrusts, which are expected to be larger in larger drainage areas, on the resistance of biocrusts to the combined effect of raindrops plus runoff flow and on the solute mobilisation by runoff in biocrusts. To answer these questions, we performed 96 rainfall-simulation in situ factorial experiments, including two biocrust types (cyanobacteria and lichens), three rain types (42, 63 and 77 mm h−1, always 20 min rain), four plot lengths (1, 2, 3 and 4 m long) and four replicates. In each experiment, runoff volume was measured and a runoff sample was taken to determine (i) the amount of dry matter in runoff, (ii) the amount of organic matter among the dry matter, (iii) the electrical conductivity, pH and alkalinity in runoff water. The main findings were: biocrusts strongly protected soil against water erosion, even under the most erosive conditions, and the protection increased with the successional development. Biocrusts were very resistant to the impact of raindrops and also to runoff flow, although an emergent hypothesis arose: under the most erosive conditions, a threshold of erodibility could be reached at the cyanobacterial biocrust. The lichen crust also protected the soil against the removal of soil soluble substances. The development of a biocrust could change the chemical composition of the solutes in runoff.

Summary Non-vegetated areas in arid and semiarid ecosystems are usually covered by biological soil crusts (BSCs), which modify many surface properties and reduce soil erosion at local spatial scales. Nevertheless, runoff generated in these areas could increase downstream erosion, or on the contrary, supply water to downslope plants, which act as surface obstructions slowing down runoff, trapping sediments and thus reducing water erosion. However, their buffer capacity might be overwhelmed during some torrential rains, increasing catchment connectivity and modifying the hydrological behavior and subsequent water erosion measured at the catchment outlet. To progress in the knowledge of the effect of the interactions between BSCs and vegetation on runoff generation and water erosion at catchment scale, the long term hydrological response of semiarid badlands with an important cover of BSCs has been studied. This effect has been analyzed using piecewise regression analysis to find any possible break point in the runoff response of the catchment to rainfall, attributable to variations in the hydrological connectivity of the catchment. Once we found this break point, we used it to divide the database in two sub-databases, and we built two structural equation models (SEM) to identify the main hydrological drivers controlling runoff generation and water erosion at sub-datasets, corresponding with different stages of catchment connection. Our results show that during low magnitude rainfall events, runoff and erosion measured at the catchment outlet come essentially from physically crusted areas directly connected to the channel network and are controlled by rainfall intensity, whereas runoff generated in areas with BSCs is reinfiltrated downstream into local vegetation patches. However, during high-magnitude events, vegetated buffers are saturated, connecting areas covered by BSCs with the channel network and increasing the catchment efficiency in exporting water out of the system. Nevertheless, water and sediments connectivity is not always linked, and most sediments measured during both low and high-magnitude events are almost exclusively supplied by physically crusted areas, whereas, BSCs areas rarely yield sediments. The differences in the hydrological behavior of the catchment under low and high-magnitude rainfall events were found to be controlled by the interactions between source and vegetated areas, which in last turn control the hydrological connectivity at catchment scale.

The Soil Crust International project aims to better understand the functioning of biological soil crust environments (BSC) in Europe in order to understand the importance of these ecosystems. The final objective of this project is to inform and strengthen protection strategies for these types of habitats in the frame of the European Union. To achieve this, four different soil crust regions have been chosen in Europe following latitudinal and altitudinal gradients. The work presented here is based on the simultaneous monitoring of gas exchange, chlorophyll fluorescence and microclimate of the most abundant BSC in one of these four locations, the Tabernas badlands, Almeria, SE Spain, one of the driest regions in Europe. The five BSC types monitored are dominated by the lichen species Squamarina cartilaginea, Diploschistes diacapsis, Toninia albilabra and Psora decipiens and by the moss Didymodon rigidulus. We aim to understand the conditions in which the BSC are metabolically active in order to get a better knowledge about the contribution of the BSC to the carbon budget of the ecosystem. Our first results after nearly 1 year of chlorophyll fluorescence and microclimatic monitoring linked to gas exchange data during typical activity days obtained in the field suggest similar physiological performance between the different BSC types studied. BSC were active under suboptimal conditions, and activity duration was not different whether measured by chlorophyll a fluorescence or CO2 gas exchange, a relationship that will be the basis of a productivity model.

Here we report details of the European research initiative “Soil Crust International” (SCIN) focusing on the biodiversity of biological soil crusts (BSC, composed of bacteria, algae, lichens, and bryophytes) and on functional aspects in their specific environment. Known as the so-called “colored soil lichen community” (Bunte Erdflechtengesellschaft), these BSCs occur all over Europe, extending into subtropical and arid regions. Our goal is to study the uniqueness of these BSCs on the regional scale and investigate how this community can cope with large macroclimatic differences. One of the major aims of this project is to develop biodiversity conservation and sustainable management strategies for European BSCs. To achieve this, we established a latitudinal transect from the Great Alvar of Öland, Sweden in the north over Gössenheim, Central Germany and Hochtor in the Hohe Tauern National Park, Austria down to the badlands of Tabernas, Spain in the south. The transect stretches over 20° latitude and 2,300 m in altitude, including natural (Hochtor, Tabernas) and semi-natural sites that require maintenance such as by grazing activities (Öland, Gössenheim). At all four sites BSC coverage exceeded 30 % of the referring landscape, with the alpine site (Hochtor) reaching the highest cyanobacterial cover and the two semi-natural sites (Öland, Gössenheim) the highest bryophyte cover. Although BSCs of the four European sites share a common set of bacteria, algae (including cyanobacteria) lichens and bryophytes, first results indicate not only climate specific additions of species, but also genetic/phenotypic uniqueness of species between the four sites. While macroclimatic conditions are rather different, microclimatic conditions and partly soil properties seem fairly homogeneous between the four sites, with the exception of water availability. Continuous activity monitoring of photosystem II revealed the BSCs of the Spanish site as the least active in terms of photosynthetic active periods. Electronic supplementary material The online version of this article (doi:10.1007/s10531-014-0645-2) contains supplementary material, which is available to authorized users.

28 páginas, 6 figuras, 2 tablas.- The definitive version is available on: http://www.sciencedirect.com/science/article/pii/S0341816213001252, [EN] Small-scale portable rainfall simulators are an essential research tool for investigating the process dynamics of soil erosion and surface hydrology. There is no standardisation of rainfall simulation and such rainfall simulators differ in design, rainfall intensities, rain spectra and research questions, which impede drawing a meaningful comparison between results. Nevertheless, these data become progressively important for soil erosion assessment and therefore, the basis for decision-makers in application-oriented erosion protection. The artificially generated rainfall of the simulators used at the Universities Basel, La Rioja, Malaga, Trier, Tübingen, Valencia, Wageningen, Zaragoza, and at different CSIC (Spanish Scientific Research Council) institutes (Almeria, Cordoba, Granada, Murcia and Zaragoza) was measured with the same methods (Laser Precipitation Monitor for drop spectra and rain collectors for spatial distribution). Data are very beneficial for improvements of simulators and comparison of simulators and results. Furthermore, they can be used for comparative studies, e.g. with measured natural rainfall spectra. A broad range of rainfall data was measured (e.g. intensity: 37–360 mm h− 1; Christiansen Coefficient for spatial rainfall distribution: 61–98%; median volumetric drop diameter: 0.375–6.5 mm; mean kinetic energy expenditure: 25–1322 J m− 2 h− 1; mean kinetic energy per unit area and unit depth of rainfall: 0.77–50 J m− 2 mm− 1). Similarities among the simulators could be found e.g. concerning drop size distributions (maximum drop numbers are reached within the smallest drop classes < 1 mm) and low fall velocities of bigger drops due to a general physical restriction. The comparison represents a good data-base for improvements and provides a consistent picture of the different parameters of the simulators that were tested., The research for this study was funded by the Deutsche Forschungsgemeinschaft (DFG) project number Ri-835/6-1. We would like to thank the anonymous reviewers for their remarks.

Dryland ecosystems account for ca. 27% of global soil organic carbon (C) reserves, yet it is largely unknown how cli- mate change will impact C cycling and storage in these areas. In drylands, soil C concentrates at the surface, making it particularly sensitive to the activity of organisms inhabiting the soil uppermost levels, such as communities domi- nated by lichens, mosses, bacteria and fungi (biocrusts). We conducted a full factorial warming and rainfall exclusion experiment at two semiarid sites in Spain to show how an average increase of air temperature of 2-3 °C promoted a drastic reduction in biocrust cover (ca. 44% in 4 years). Warming significantly increased soil CO2 efflux, and reduced soil net CO2 uptake, in biocrust-dominated microsites. Losses of biocrust cover with warming through time were par- alleled by increases in recalcitrant C sources, such as aromatic compounds, and in the abundance of fungi relative to bacteria. The dramatic reduction in biocrust cover with warming will lessen the capacity of drylands to sequester atmospheric CO2. This decrease may act synergistically with other warming-induced effects, such as the increase in soil CO2 efflux and the changes in microbial communities to alter C cycling in drylands, and to reduce soil C stocks in the mid to long term.

El área acarcavada, o malpaís, de mayor extensión del sudeste peninsular, en el sub-desierto de Tabernas, Almería, es un mosaico de teselas en donde se encuentran concentradas muchas de las formas de erosión de la mayoría de paisajes fluviales, y muy en especial los de zonas áridas. Un clima Mediterráneo semiárido, cercano a su extremo más árido, y una particular litología sobre una alternancia de margas yesíferas y calcarenitas explican la enorme variedad de geoformas de este paisaje. Si bien la geomorfología de la zona sugiere elevadas tasas de erosión, las particulares condiciones climáticas, con escasez de eventos de elevada intensidad y/o magnitud impiden que la erosión sea elevada. Se explican sucintamente los principales procesos geomorfológicos que han configurado este malpaís: desde la meteorización de la principal roca madre, la marga yesífera, pasando por la formación de regolitos, suelos y sus costras superficiales y un conjunto muy particular de comunidades vegetales que conviven con los procesos erosivos y las peculiares condiciones climáticas, los grupos de factores ecológicos más importantes y típicos de la zona.

Summary The interplant soil surfaces in most arid and semiarid ecosystems are covered by biological soil crusts (BSCs). These crusts regulate water inputs and losses through soils and play major roles in local hydrological regimes. In recent years, the role of BSCs in infiltration and runoff has gained increasing importance and better knowledge of their effects on these processes has been acquired. However, the role of BSCs in other important components of the water balance, such as evaporation or soil moisture has hardly been studied, so their effects on these processes remain unknown. The aim of this study was to explore the influence of BSCs on soil moisture regimes in the top layer of the soil in two semiarid ecosystems in SE Spain with different particle-size distributions. At both study sites, soil moisture was monitored at 0.03 and 0.10 m under two types of BSCs, a cyanobacteria-dominated BSC and a lichen-dominated BSC, and in adjacent soils where they had been removed. Our results showed that during wet soil periods, removal of BSCs led to decreased soil moisture, especially in the upper layer (0.03 m), compared to soils covered by BSCs. Decrease in soil moisture was more noticeable after removal of lichens than cyanobacterial BSCs, and more so in fine than in coarse-textured soils. Soil water loss was also generally faster in soils with no BSCs than in soils covered by them. However, no difference was found in soil moisture under either crusted or scalped soils during soil drying periods. The type of BSC influenced soil moisture differently depending on soil water content. During wet soil periods, soil water loss was faster and soil moisture lower under cyanobacterial than under lichen BSCs. On the contrary, during soil drying periods, soils covered by lichens lost water faster and showed lower moisture than those covered by cyanobacteria. Our results show the major role of the presence of BSCs, as well as the types, in soil water content in semiarid ecosystems.

The typical patchy structure of dryland vegetation is a result of soil–plant feedbacks occurring in water-limited areas. The resilience of dryland ecosystems depends largely on the persistence of fertility islands associated with vegetated patches, which determines the efficiency of the vegetation regarding recolonising the gaps that result from disturbances. In this study, we investigated the mechanisms underlying soil–plant interactions throughout the process of the growth and senescence of alpha grass ( Macrochloa tenacissima ) and the subsequent disintegration of islands of fertility and microtopography formed during the process at two nearby alpha grass communities exhibiting different degrees of development. The life cycle of alpha grass and the rise and disintegration of the underlying microrelief were accompanied by feedback changes in the content of soil C fractions presenting different times of cycling and incorporation to the soil, the collection of particles from splash erosion, redistribution phenomena related to particles of different sizes, and erosion of the most easily erodible materials. Despite their ecological and geographical proximity, the study sites differ with respect to the persistence, after plant death, of fertility islands, which almost disappear in one case, while they remain in the other, constituting a resource for the growth of new plants and resulting in greater development and resilience in the community. A subtle erodibility threshold emerges as a cause of the considerable differences in vegetation between the two sites.

Biological soil crusts (BSCs) cover non-vegetated areas in most arid and semiarid ecosystems. BSCs play a crucial role in the redistribution of water and sediments and, ultimately, in the maintenance of ecosystem function. The effects of BSCs on water infiltration are complex. BSCs increase porosity and micro-topography, thus enhancing infiltration, but, at the same time, they can increase runoff by the secretion of hydrophobic compounds and clogging of soil pores upon wetting. BSCs confer stability on soil surfaces, reducing soil detachment locally; however, they can also increase runoff, which may increase sediment yield. Although the key role of BSCs in controlling infiltration–runoff and erosion is commonly accepted, conflicting evidence has been reported concerning the influence of BSCs on runoff generation. Very little is known about the relative importance of different BSC features such as cover, composition, roughness, or water repellency, and the interactions of these attributes in runoff and erosion. Because BSC characteristics can affect water flows and erosion both directly and indirectly, we examined the direct and indirect effects of different BSC features on runoff and erosion in a semiarid ecosystem under conditions of natural rainfall. We built structural equation models to determine the relative importance of BSC cover and type and their derived surface attributes controlling runoff and soil erosion. Our results show that the hydrological response of BSCs varies depending on rainfall properties, which, in turn, determine the process governing overland flow generation. During intense rainfalls, runoff is controlled not only by rainfall intensity but also by BSC cover, which exerts a strong direct and indirect influence on infiltration and surface hydrophobicity. Surface hydrophobicity was especially high for lichen BSCs, thus masking the positive effect of lichen crust on infiltration, and explaining the lower infiltration rates recorded on lichen than on cyanobacterial BSCs. Under low intensity, rainfall volume exerts a stronger effect than rainfall intensity, and BSC features play a secondary role in runoff generation, reducing runoff through their effect on surface micro-topography. Under these conditions, lichen BSCs presented higher infiltration rates than cyanobacterial BSCs. Our results highlight the significant protective effect against erosion exerted by BSCs at the plot scale, enhancing surface stability and reducing sediment yield in both high- and low-magnitude rainfall events.