Global fine-resolution data on springtail abundance and community structure.

Springtails (Collembola) inhabit soils from the Arctic to the Antarctic and comprise an estimated ~32% of all terrestrial arthropods on Earth. Here, we present a global, spatially-explicit database on springtail communities that includes 249,912 occurrences from 44,999 samples and 2,990 sites. These data are mainly raw sample-level records at the species level collected predominantly from private archives of the authors that were quality-controlled and taxonomically-standardised. Despite covering all continents, most of the sample-level data come from the European continent (82.5% of all samples) and represent four habitats: woodlands (57.4%), grasslands (14.0%), agrosystems (13.7%) and scrublands (9.0%). We included sampling by soil layers, and across seasons and years, representing temporal and spatial within-site variation in springtail communities. We also provided data use and sharing guidelines and R code to facilitate the use of the database by other researchers. This data paper describes a static version of the database at the publication date, but the database will be further expanded to include underrepresented regions and linked with trait data.

Globally invariant metabolism but density-diversity mismatch in springtails.

Soil life supports the functioning and biodiversity of terrestrial ecosystems. Springtails (Collembola) are among the most abundant soil arthropods regulating soil fertility and flow of energy through above- and belowground food webs. However, the global distribution of springtail diversity and density, and how these relate to energy fluxes remains unknown. Here, using a global dataset representing 2470 sites, we estimate the total soil springtail biomass at 27.5 megatons carbon, which is threefold higher than wild terrestrial vertebrates, and record peak densities up to 2 million individuals per square meter in the tundra. Despite a 20-fold biomass difference between the tundra and the tropics, springtail energy use (community metabolism) remains similar across the latitudinal gradient, owing to the changes in temperature with latitude. Neither springtail density nor community metabolism is predicted by local species richness, which is high in the tropics, but comparably high in some temperate forests and even tundra. Changes in springtail activity may emerge from latitudinal gradients in temperature, predation and resource limitation in soil communities. Contrasting relationships of biomass, diversity and activity of springtail communities with temperature suggest that climate warming will alter fundamental soil biodiversity metrics in different directions, potentially restructuring terrestrial food webs and affecting soil functioning.

Intensive grassland management disrupts below-ground multi-trophic resource transfer in response to drought.

Modification of soil food webs by land management may alter the response of ecosystem processes to climate extremes, but empirical support is limited and the mechanisms involved remain unclear. Here we quantify how grassland management modifies the transfer of recent photosynthates and soil nitrogen through plants and soil food webs during a post-drought period in a controlled field experiment, using in situ 13C and 15N pulse-labelling in intensively and extensively managed fields. We show that intensive management decrease plant carbon (C) capture and its transfer through components of food webs and soil respiration compared to extensive management. We observe a legacy effect of drought on C transfer pathways mainly in intensively managed grasslands, by increasing plant C assimilation and 13C released as soil CO2 efflux but decreasing its transfer to roots, bacteria and Collembola. Our work provides insight into the interactive effects of grassland management and drought on C transfer pathways, and highlights that capture and rapid transfer of photosynthates through multi-trophic networks are key for maintaining grassland resistance to drought.

Drought decreases incorporation of recent plant photosynthate into soil food webs regardless of their trophic complexity.

Theory suggests that more complex food webs promote stability and can buffer the effects of perturbations, such as drought, on soil organisms and ecosystem functions. Here, we tested experimentally how soil food web trophic complexity modulates the response to drought of soil functions related to carbon cycling and the capture and transfer below-ground of recent photosynthate by plants. We constructed experimental systems comprising soil communities with one, two or three trophic levels (microorganisms, detritivores and predators) and subjected them to drought. We investigated how food web trophic complexity in interaction with drought influenced litter decomposition, soil CO2 efflux, mycorrhizal colonization, fungal production, microbial communities and soil fauna biomass. Plants were pulse-labelled after the drought with 13 C-CO2 to quantify the capture of recent photosynthate and its transfer below-ground. Overall, our results show that drought and soil food web trophic complexity do not interact to affect soil functions and microbial community composition, but act independently, with an overall stronger effect of drought. After drought, the net uptake of 13 C by plants was reduced and its retention in plant biomass was greater, leading to a strong decrease in carbon transfer below-ground. Although food web trophic complexity influenced the biomass of Collembola and fungal hyphal length, 13 C enrichment and the net transfer of carbon from plant shoots to microbes and soil CO2 efflux were not affected significantly by varying the number of trophic groups. Our results indicate that drought has a strong effect on above-ground-below-ground linkages by reducing the flow of recent photosynthate. Our results emphasize the sensitivity of the critical pathway of recent photosynthate transfer from plants to soil organisms to a drought perturbation, and show that these effects may not be mitigated by the trophic complexity of soil communities, at least at the level manipulated in this experiment.

Allelochemicals of Pinus halepensis as drivers of biodiversity in Mediterranean open mosaic habitats during the colonization stage of secondary succession.

The Mediterranean region is recognized as a global biodiversity hotspot. However, over the last 50 years or so, the cessation of traditional farming has given way to strong afforestation at the expense of open habitats. Pinus halepensis Miller, known to synthesize a wide range of secondary metabolites, is a pioneer expansionist species colonizing abandoned agricultural land that present high species richness. Here, laboratory bioassays were used to study the potential impact of P. halepensis on plant diversity through allelopathy, and the role of microorganisms in these interactions. Germination and growth of 12 target species naturally present in fallow farmlands were tested according to concentration of aqueous extracts obtained from shoots of young pines (aged about 5 years), with or without the presence of soil microorganisms (autoclaved or natural soil). Under the highest concentrations and autoclaved soil, more than 80 % of target species were germination and/or growth-inhibited, and only two species were non-sensitive. Under more natural conditions (lower extracts concentrations and natural soil with microorganisms), only 50 % of species were still inhibited, one was non-sensitive, and five were stimulated. Thus, microorganisms alter the expression of allelochemicals released into the ecosystem, which highlights their key role in chemical plant-plant interactions. The results of allelopathic experiments conducted in the lab are consistent with the community patterns observed in the field. These findings suggest that allelopathy is likely to shape vegetation composition and participate to the control of biodiversity in Mediterranean open mosaic habitats.