No abstract

The structure and function of the soil microbiome of urban greenspaces remain largely undetermined. We conducted a global field survey in urban greenspaces and neighboring natural ecosystems across 56 cities from six continents, and found that urban soils are important hotspots for soil bacterial, protist and functional gene diversity, but support highly homogenized microbial communities worldwide. Urban greenspaces had a greater proportion of fast-growing bacteria, algae, amoebae, and fungal pathogens, but a lower proportion of ectomycorrhizal fungi than natural ecosystems. These urban ecosystems also showed higher proportions of genes associated with human pathogens, greenhouse gas emissions, faster nutrient cycling, and more intense abiotic stress than natural environments. City affluence, management practices, and climate were fundamental drivers of urban soil communities. Our work paves the way toward a more comprehensive global-scale perspective on urban greenspaces, which is integral to managing the health of these ecosystems and the well-being of human populations.

Aim: Cyanobacteria have shaped the history of life on Earth and continue to play important roles as carbon and nitrogen fixers in terrestrial ecosystems. However, their global distribution and ecological preferences remain poorly understood, particularly for two recently discovered non-photosynthetic cyanobacterial classes (Sericytochromatia and Melainabacteria). Location: Two hundred and thirty-seven locations across six continents encompassing multiple climates (arid, temperate, tropical, continental and polar) and vegetation types (forests, grasslands and shrublands). Time period: Sampling was carried out between 2003 and 2015. Major taxa studied: Photosynthetic and non-photosynthetic cyanobacterial taxa. Methods: We conducted a field survey and used co-occurrence network analysis and structural equation modelling to evaluate the distribution and environmental preferences of soil cyanobacteria across the globe. These ecological preferences were used to create a global atlas (predictive distribution maps) of soil cyanobacteria. Results: Network analyses identified three major groups of cyanobacterial taxa, which resembled the three main cyanobacterial classes: the photosynthetic Oxyphotobacteria-dominated cluster, which were prevalent in arid and semi-arid areas, and the non-photosynthetic Sericytochromatia-and Melainabacteria-dominated Ministry of Economy and Competitiveness (BIOMOD project, ref.

Soil carbon losses to the atmosphere through soil respiration are expected to rise with ongoing temperature increases, but available evidence from mesic biomes suggests that such response disappears after a few years of experimental warming. However, there is lack of empirical basis for these temporal dynamics in soil respiration responses, and for the mechanisms underlying them, in drylands, which collectively form the largest biome on Earth and store 32% of the global soil organic carbon pool. We coupled data from a ten-year warming experiment in a biocrust-dominated dryland ecosystem with laboratory incubations to confront 0-2 years (short-term hereafter) vs. 8-10 years (longer-term hereafter) soil respiration responses to warming. Our results showed that increased soil respiration rates with short-term warming observed in areas with high biocrust cover returned to control levels in the longer-term. Warming-induced increases in soil temperature were the main driver of the short-term soil respiration responses, whereas longer-term soil respiration responses to warming were primarily driven by thermal acclimation and warming-induced reductions in biocrust cover. Our results highlight the importance of evaluating short and longer-term soil respiration responses to warming as a mean to reduce the uncertainty in predicting the soil carbon-climate feedback in drylands.

Cyanobacteria are a key constituent of biocrusts, communities dominated by lichens, mosses and associated microorganisms, which are prevalent in drylands worldwide and that largely determine their functioning. Despite their importance, there are large gaps in our knowledge of the composition and diversity of cyanobacteria associated with biocrusts, particularly in areas such as the Mediterranean Basin. We studied the diversity of these cyanobacteria in a gypsiferous grassland from Central Spain using both morphological identification after cultivation and genetic analyses with the 16S rRNA gene. Nine different morphotypes were observed, eight corresponding to filamentous, and one to unicellular cyanobacteria. We found cyanobacterial genera typical of biocrust communities, such as and, and N-fixing cyanobacteria such as and. Genetic information allowed us to identify cultures belonging to recently described genera such as , and . We also describe two new phylotypes of and , which are key genera contributing to ecosystem functioning in biocrust-dominated ecosystems worldwide.