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Plant recruitment interactions (i.e., what recruits under what) shape the composition, diversity, and structure of plant communities. Despite the huge body of knowledge on the mechanisms underlying recruitment interactions among species, we still know little about the structure of the recruitment networks emerging in ecological communities. Modeling and analyzing the community-level structure of plant recruitment interactions as a complex network can provide relevant information on ecological and evolutionary processes acting both at the species and ecosystem levels. We report a data set containing 143 plant recruitment networks in 23 countries across five continents, including temperate and tropical ecosystems. Each network identifies the species under which another species recruits. All networks report the number of recruits (i.e., individuals) per species. The data set includes >850,000 recruiting individuals involved in 118,411 paired interactions among 3318 vascular plant species across the globe. The cover of canopy species and open ground is also provided. Three sampling protocols were used: (1) The Recruitment Network (RN) protocol (106 networks) focuses on interactions among established plants ("canopy species") and plants in their early stages of recruitment ("recruit species"). A series of plots was delimited within a locality, and all the individuals recruiting and their canopy species were identified; (2) The paired Canopy-Open (pCO) protocol (26 networks) consists in locating a potential canopy plant and identifying recruiting individuals under the canopy and in a nearby open space of the same area; (3) The Georeferenced plot (GP) protocol (11 networks) consists in using information from georeferenced individual plants in large plots to infer canopy-recruit interactions. Some networks incorporate data for both herbs and woody species, whereas others focus exclusively on woody species. The location of each study site, geographical coordinates, country

El Real Jardín Botánico (RJB) ocupa un lugar muy prominente en la ciencia botánica y de los hongos, y es un centro de excelencia del Consejo Superior de Investigaciones Científicas (CSIC) que lleva a cabo una investigación multidisciplinar en 5 de los 6 reinos de organismos eucariotas del árbol de la vida. Las investigaciones del RJB se enfocan en comprender la sistemática y evolución de la diversidad de organismos de estos 5 reinos, desde sus genes, las especies y los ecosistemas de los que forman parte. El RJB desarrolla líneas de investigación frontera enfocadas desde la sistemática y florística de plantas vasculares, la biodiversidad, biogeografía y sistemática molecular de hongos, hasta la biología evolutiva de plantas y sus patrones, procesos y mecanismos, la colonización y evolución en islas oceánicas, y la biodiversidad escondida, ahondando en el estudio de su ecología, evolución y conservación. El RJB está situado en un lugar privilegiado de Madrid, junto a la Glorieta de Atocha, y ha de sobrevivir a las nuevas como son el cambio global, incluido el cambio climático y la contaminación atmosférica. En este artículo se hace referencia a los objetivos y las actividades que desarrolla este importante centro de investigación botánica

Atmospheric nitrogen (N) inputs in the Mediterranean Basin are projected to increase due to fossil fuel combustion, fertilizer use, and the exacerbation of agricultural production processes. Although increasing N deposition is recognized as a major threat to ecosystem functioning, little is known about how local environmental conditions modulate ecosystem function response to N addition, particularly in the context of Mediterranean-Basin ecosystems. Here, we assess how N addition affects important ecosystem properties associated with litter decomposition, soil physical-chemical properties, soil extracellular enzymatic activity and microbial abundance across three long-term N addition experimental sites in the Mediterranean Basin. Sites were located in El Regajal (Madrid, Spain), Capo Caccia (Alghero, Italy), and Arrábida (Lisbon, Portugal) and are all representative of Mediterranean shrublands. No common pattern for litter decomposition process or other studied variables emerged among the control plots of the studied sites. Nitrogen supply only affected soil pH, a major driver of decomposition, in two out of three experimental sites. Moreover, when we explored the role of N addition and soil pH in controlling litter decay, we found that the effects of these factors were site-dependent. Our results point out to local ecosystem features modulating N addition effects in controlling litter decomposition rates in Mediterranean ecosystems, suggesting that the responses of soil functioning to N deposition are site-dependent. These findings provide further knowledge to understand contrasting ecosystem responses to N additions based on a single field experiments.

Soil biocrusts (communities of cyanobacteria, algae, mosses, lichens, and heterotrophs living at the soil surface) are fundamental components of dryland ecosystems worldwide. There is increasing concern over the potential for increasing nitrogen (N) inputs to affect biocrusts. This is of special concern in Mediterranean Basin drylands that face the threat of increased N inputs however, the effect on biocrusts remains poorly studied. We evaluated the potential effects of increased N inputs on biocrust structure and functioning in surrounding Mediterranean shrublands in the seventh year of a N-manipulation field experiment. We tracked the N-driven changes in biotope (changes in bare soil and in the non-legume and the legume occupation areas, and the percentage of radiation intercepted by plant canopies), evaluated biocrust functional traits (based on pigments) and measured biocrust functioning in terms of C and N cycling, soil fertility (macro and micronutrients) and biodiversity, and integrated these multiple soil functions simultaneously (i.e. soil multifunctionality) Biocrust pigment concentration was significantly influenced by both plant legacy and N input. Biocrust pigments revealed a clear functional shift from: i) biocrusts dominated by photosynthetically inactive cyanobacteria that fix N and are mostly committed to photoprotection at the expense of N-containing pigments under low N inputs; into ii) biocrusts more evenly composed of prokaryotes and eukaryotes, which are more photosynthetically active, but less committed to photoprotection and N fixation under exposure to increased N inputs. The N-driven functional and structural changes in biocrusts resulted in trade-offs in biocrust functioning and processes (only N fixation was affected) and an overall improvement in biocrust multifunctionality. By itself, biocrust pigment evenness accounted for ~50% of the observed variation in biocrust multifunctionality. The biocrust pigment functional approach we adopted

Soil nitrogen (N) availability is a key driver of soil-atmosphere greenhouse gas (GHG) exchange, yet we are far from understanding how increases in N deposition due to human activities will influence the net soil-atmosphere fluxes of the three most important GHGs: nitrous oxide (NO), methane (CH) and carbon dioxide (CO). We simulated four levels of N deposition (10, 20 and 50 kg N ha yr, plus unfertilised control) to evaluate their effects on NO, CH and CO soil fluxes in a semiarid shrubland in central Spain. After 8 years of experimental fertilisation, increasing N availability led to a consistent increase in NO emissions, likely due to simultaneous increases in soil microbial nitrification and/or denitrification processes. However, only intermediate levels of N fertilisation reduced CH uptake, while increasing N fertilisation had no effects on CO fluxes, suggesting complex interactions between N deposition loads and GHG fluxes. Our study provides novel insight into the responses of GHGs to N deposition in drylands, forecasting increases in NO emissions, and decreases in CH uptake rates, with likely consequences to the on-going climate change.

Although anthropogenic nitrogen (N) deposition has been identified as a major threat to biodiversity and ecosystem functioning in Mediterranean environments, little is known on the role of soil properties and microbial attributes in mediating the response of soil organic matter (SOM) decomposition to N inputs. Here, we used Structural Equation Modeling (SEM) to evaluate the direct and indirect effects of N inputs on SOM decomposition rates across different N loads and three Mediterranean semi-arid ecosystems. Our SEM showed that soil ammonium availability decreases soil pH leading to a reduction of the fungi/bacteria ratio and to an increase in soil enzymatic activity, whereas it also has a negative direct and mayor effect on soil decomposition rate. This increase in soil enzymatic activity, which was conditioned not only by soil pH but also by the fungi/bacteria ratio and inorganic N content, had a positive direct effect on the soil decomposition rate. Together, our results suggest that changes in soil properties and microbial attributes linked to N additions can affect the SOM decomposition rates across three regions from the Mediterranean Basin. These findings improve our understanding of the links between soil chemical properties, microbial communities and function in Mediterranean ecosystems, especially in the context of anthropogenic N enrichment.

Soils are being degraded at an alarming rate and thereby also crucial ecosystem goods and services. Nitrogen (N) enrichment is a major driver of this degradation. While the negative impacts of N enrichment on vegetation are well known globally, those on various ecological interactions, and on ecosystem functioning, remain largely unknown. Because Mediterranean ecosystems are N limited, they are good model systems for evaluating how N enrichment impacts not only vegetation but also ecological partnerships and ecosystem functioning. Using a 7-year N-manipulation (dose and form) field experiment running in a Mediterranean Basin maquis located in a region with naturally low ambient N deposition (<4 kg N ha−1 y−1), we assessed the impacts of the N additions on (i) the dominant plant species (photosynthetic N-use efficiency); (ii) plant–soil ecological partnerships with ectomycorrhiza and N-fixing bacteria; and (iii) ecosystem degradation (plant–soil cover, biological mineral weathering and soil N fixation). N additions significantly disrupted plant–soil cover, plant–soil biotic interactions, and ecosystem functioning compared with ambient N deposition conditions. However, the higher the ammonium dose (alone or with nitrate), the more drastic these disruptions were. We report a critical threshold at 20–40 kg ammonium ha−1 y−1 whereby severe ecosystem degradation can be expected. These observations are critical to help explain the mechanisms behind ecosystem degradation, to describe the collective loss of organisms and multifunction in the landscape, and to predict potential fragmentation of Mediterranean maquis under conditions of unrelieved N enrichment.

Increased atmospheric nitrogen (N) deposition is known to alter ecosystem carbon source-sink dynamics through changes in soil CO2 fluxes. However, a limited number of experiments have been conducted to assess the effects of realistic N deposition in the Mediterranean Basin, and none of them have explored the effects of N addition on soil respiration (R s ). To fill this gap, we assessed the effects of N supply on R s dynamics in the following two Mediterranean sites: Capo Caccia (Italy), where 30kgha-1year-1 was supplied for 3years, and El Regajal (Spain), where plots were treated with 10, 20, or 50kg Nha-1year-1 for 8years. Results show a complex, non-linear response of soil respiration (R s ) to N additions with R s overall increasing at Capo Caccia and decreasing at El Regajal. This suggests that the response of R s to N addition depends on dose and duration of N supply, and the existence of a threshold above which the N introduced in the ecosystem can affect the ecosystem's functioning. Soil cover and seasonality of precipitations also play a key role in determining the effects of N on R s as shown by the different responses observed across seasons and in bare soil vs. the soil under canopy of the dominant species. These results show how increasing rates of N addition may influence soil C dynamics in semiarid ecosystems in the Mediterranean Basin and represent a valuable contribution for the understanding and the protection of Mediterranean ecosystems.

Nitrogen (N) deposition due to anthropogenic pollution is a major driver of the global biodiversity loss. We studied the effect of experimental N and phosphorus (P) fertilization (0, 10, 20, and 50 kg N ha¿1 year¿1 and 14 kg P ha¿1 year¿1 over the background deposition levels) on plant cover dynamics of a rosemary (Rosmarinus officinalis L.) shrubland after 8 years of nutrient addition in a semiarid Mediterranean ecosystem from Central Spain. We specifically aimed at testing whether N deposition has the potential to influence the observed expanding trend of woody vegetation into areas dominated by grassland, biological soil crusts, and bare soil. Our results show that N addition loads above 10 kg N ha¿1 year¿1 reverted the cover dynamics of shrubs. Under N addition conditions, N was no longer a limiting nutrient and other elements, especially P and calcium, determined the seasonal growth of young twigs. Interestingly, N fertilization did not inhibit the growth of young shoots; our estimates point to a reduced rosemary leaf lifespan that is driving individuals to death. This may be triggered by long-term accumulation of N compounds in leaves, suggesting the need to consider the old organs and tissues in long-lived perennial plants, where N toxicity effects could be more mediated by accumulation processes. Shrublands are a widely distributed ecosystem type in biodiverse Mediterranean landscapes, where shrubs play a key role as nurse plants. Therefore, the disappearance of shrublands may accelerate the biodiversity loss associated with other global change drivers, hamper the recruitment of seedlings of woody species, and, as a consequence, accelerate desertification.