Research in global change ecology relies heavily on global climatic grids derived from estimates of air temperature in open areas at around 2 m above the ground. These climatic grids thus fail to reflect conditions below vegetation canopies and near the ground surface, where critical ecosystem functions are controlled and most terrestrial species reside. Here we provide global maps of soil temperature and bioclimatic variables at a 1-km² resolution for 0-5 and 5-15 cm depth. These maps were created by calculating the difference (i.e., offset) between in-situ soil temperature measurements, based on time series from over 1200 1-km² pixels (summarized from 8500 unique temperature sensors) across all of the world's major terrestrial biomes, and coarse-grained air temperature estimates from ERA5-Land (an atmospheric reanalysis by the European Centre for Medium-Range Weather Forecasts). We show that mean annual soil temperature differs markedly from the corresponding 2 m gridded air temperature, by up to 10°C (mean = 3.0 ± 2.1°C), with substantial variation across biomes and seasons. Over the year, soils in cold and/or dry biomes are substantially warmer (3.6 ± 2.3°C warmer than gridded air temperature), whereas soils in warm and humid environments are on average slightly cooler (0.7 ± 2.3°C cooler). The observed substantial and biome-specific offsets underpin that the projected impacts of climate and climate change on biodiversity and ecosystem functioning are inaccurately assessed when air rather than soil temperature is used, especially in cold environments. The global soil-related bioclimatic variables provided here are an important step forward for any application in ecology and related disciplines. Nevertheless, we highlight the need to fill remaining global gaps by collecting more in-situ measurements of microclimate conditions to further enhance the spatiotemporal resolution of global soil temperature products for ecological applications.
Research in environmental science relies heavily on global climatic grids derived from estimates of air temperature at around 2 meter above ground1-3. These climatic grids however fail to reflect conditions near and below the soil surface, where critical ecosystem functions such as soil carbon storage are controlled and most biodiversity resides4-8. By using soil temperature time series from over 8500 locations across all of the world’s terrestrial biomes4, we derived global maps of soil temperature-related variables at 1 km resolution for the 0–5 and 5–15 cm depth horizons. Based on these maps, we show that mean annual soil temperature differs markedly from the corresponding 2 m gridded air temperature, by up to 10°C, with substantial variation across biomes and seasons. Soils in cold and/or dry biomes are annually substantially warmer (3.6°C ± 2.3°C) than gridded air temperature, whereas soils in warm and humid environments are slightly cooler (0.7 ± 2.3°C). As a result, annual soil temperature varies less (by 17%) across the globe than air temperature. The effect of macroclimatic conditions on the difference between soil and air temperature highlights the importance of considering that macroclimate warming may not result in the same level of soil temperature warming. Similarly, changes in precipitation could alter the relationship between soil and air temperature, with implications for soil-atmosphere feedbacks9. Our results underpin that the impacts of climate and climate change on biodiversity and ecosystem functioning are inaccurately assessed when air rather than soil temperature is used, especially in cold environments.
AimPredicting the potential for climate change to disrupt host–microbe symbioses requires basic knowledge of the biogeography of these consortia. In plants, fungal symbionts can ameliorate the abiotic stressors that accompany climate warming and thus could influence plants under a changing climate. Forecasting future plant–microbe interactions first requires knowledge of current fungal symbiont distributions, which are poorly resolved relative to the distributions of plants.LocationWe used meta‐analysis to summarize the biogeographic distributions of plant‐fungal symbionts in mountain ecosystems worldwide, because these ecosystems are likely to be among the first to experience climate change‐induced range shifts.MethodsWe analysed 374 records from 53 publications to identify general trends, pinpoint areas in need of greater study and develop reporting guidelines to facilitate future syntheses.ResultsElevational patterns varied strongly among fungal and plant functional groups. Fungal diversity and abundance increased with altitude for the ectomycorrhizal fungi. However, arbuscular mycorrhizal fungi and localized foliar endophytes declined in either abundance or diversity with altitude. In shrubs, fungal abundance increased with elevation, but in C3 grasses, fungal abundance declined with elevation. Altitudinal patterns in fungal composition were stronger than gradients in fungal abundance or diversity, suggesting that species turnover contributes more to elevational gradients in fungal symbionts than does variation in abundance or richness. Plant functional groups were overrepresented by C3 grasses and trees, with surprisingly few data on sedges or shrubs, despite their ecological dominance in mountain ecosystems. Similarly, epichloae, ericoid mycorrhizal fungi and root endophytes were understudied relative to other fungal groups.Main ConclusionsMeta‐analysis revealed broad biogeographic patterns in plant‐fungal symbiont abundance, diversity and composition that inform predictions of future distributions.
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