README ====== Dataset title: Increasing susceptibility to priming of soil N mineralisation across a Subarctic tundra-forest ecotone under N fertilisation Recommended Citation: Rzepczynska, A., & Hicks, L. (2026). Data for: Increasing susceptibility to priming of soil N mineralisation across a Subarctic tundra-forest ecotone under N fertilisation (Version 1) [Dataset]. Lund University. https://doi.org/10.5878/61fv-xa43 See the Researchdata.se catalogue entry for this dataset - accessible via the DOI link above - for complete metadata, including the dataset description, contact information and information about how to obtain the dataset. Responsible organization: Department of Biology, Lund University Description: Soil parameters and soil microbial responses measured in samples collected along a vegetation gradient in the Swedish Subarctic. Microbial responses to laboratory priming experiment, where glucose addition simulated pronounced inputs of rhizosphere-derived organic matter under shrub encroachment in a warmer climate. License: Creative Commons Attribution 4.0 International (CC BY 4.0) Essential information for dataset reuse. ---------------------------------------- Field experiment was located along a Subarctic vegetation gradient (ecotone) near Abisko, northern Sweden. Four different sites were selected along the same mountain slope [tundra heath (tundra), shrub tundra (shrub), treeline and birch forest (forest)] according to vegetation characteristics. A nutrient addition experiment was established across the ecotone in June 2021. Fertilisation treatments included: control (Con; 6 L water m-2 year-1), nitrogen (N; 10 g N + 6 L water m-2 y-1), phosphorus (P; 10 g P + 6 L water m-2 y-1) and were established in 1 m x 1 m squares, replicated in four blocks at each site, with each block separated by at least 10 m. Soils were sampled at the end of the growing season in August 2022, approximately two months after the second fertilisation treatment. Soils were transported to a laboratory and stored at 4 oC until further analyses SOM was measured through loss on ignition (600 oC for 12h). Soil C and N content were measured with a C:N analyser. Soil pH and electrical conductivity were measured in a 1:5 soil:water (w:v) extraction using a pH meter and a conductivity meter. Inorganic nutrient availability was determined by mixing 10 g of fresh weight (fwt) soil with 50 mL ddH2O before shaking and filtering, followed by measurement of extractable ammonium (NH4+-N), nitrate (NO3--N) and phosphate (PO43--P) with a continuous flow analyser. Soil C mineralisation rates were determined by weighing soil into 20 mL glass vials and by measuring the headspace CO2 concentration with thermal conductivity detector after 24 h incubation. Gross N mineralisation rates were determined using the 15N pool-dilution method. Bacterial growth rates were measured using the 3H-leucine incorporation method. Fungal growth rates were determined using the 14C-acetate-in-ergosterol incorporation method. Resulting incorporation rates were converted to bacterial and fungal C production using established conversion factors. Gross ecosystem productivity across the ecotone was determined by measuring CO2 fluxes in the field in August 2023, using Li-COR LI-8100. Net Ecosystem Exchange (NEE), which captures the net CO2 flux from both photosynthesis and ecosystem respiration (ER), was measured under ambient light conditions by mounting a transparent polycarbonate chamber on a permanently installed PVC cyllinder (⌀20 cm). Then, the chamber was lifted and air above the collar was allowed to mix, after which a dark chamber was mounted to measure ER. Gross Ecosystem Productivity (GEP) was calculated by summing NEE and ER. Priming experiment: For each soil, two 60 g fwt soil subsamples were weighed into 250 mL transparent polypropylene microcosms with air-tight lids, with one microcosm receiving 13C-labelled glucose (3.75 atom% enrichment) to simulate rhizosphere inputs, and the other receiving water as a control (n=96 incubations in total). For the 13C-glucose addition, soils received 1000 µg glucose g-1 fwt soil (equivalent to 400 µg C g-1 fwt). Glucose was dissolved in distilled water and applied as 10 µL solution g-1 fwt, after which it was mixed into the soil. For the control, soils received 10 µL distilled water g-1 fwt soil instead of glucose solution. All microcosms were then incubated at 18 oC for 7 days. Measurements of soil C mineralisation, soil N mineralisation and microbial growth were carried out by subsampling from each microcosm over time (measurements taken after 4 h (T1), 24 h (T2), 48 h (T3), 72 h (T4) and 172 h (T5) in order to capture the dynamics following the labile C addition). Additional subsamples were collected at T5 for measurement of microbial biomass and community structure by phospholipid fatty acid (PLFA) analysis, to screen for differences among soils and treatments. Datafile descriptions ---------------------- (1) Soil properties and biogeochemical rates at T1.csv - values of soil physicochemical parameters and biogeochemical rates measured in the laboratory, and gross ecosystem productivity measured in the field in August 2023. Columns: Site - one of the four sites across the ecotone (categorical values: Tundra, Shrub, Treeline, Forest) Field treatment - fertilisation treatment (categorical values: Con, N, P) Block - field block (categorical values: 1, 2, 3, 4) SOM - soil organic matter (g g-1 dwt) (numerical values) C:N ratio SOM - carbon to nitrogen ratio of bulk soil organic matter (numerical values) (unitless) pH - soil pH (numerical values) (unitless) EC - electric conductivity (numerical values) (µS cm-1) F/B growth ratio - ratio of fungal growth rate to bacterial growth rate (numerical values) (unitless) Microbial CUE - microbial carbon use efficiency (numerical values) (unitless) Total inorganic N - sum of concentrations of water-extractable NH4+-N and NO3--N (numerical values) (µg N g-1 SOM) PO4-P - concentrations of water-extractable PO4-P (numerical values) (µg PO4-P g-1 SOM) Gross Ecosystem productivity (numerical values) (µmol CO2 m-2 s-1) Soil C mineralisation rate (numerical values) (µg CO2-C g-1 SOM h-1) Gross N mineralisation rate (numerical values) (µg NH4-N g-1 SOM h-1) Ratio of soil C mineralisation to soil N mineralisation (numerical values) (unitless) (2) Priming of soil C mineralisation.csv - Responses of soil C mineralisation in a laboratory-incubation priming experiment measured at five timepoints on soils collected across the fertilised Subarctic ecotone. Columns: Site - one of the four sites across the ecotone (categorical values: Tundra, Shrub, Treeline, Forest) Field treatment - fertilisation treatment (categorical values: Con, N, P) Block - field block (categorical values: 1, 2, 3, 4) Timepoint - timepoint of measurement corresponding to incubation times: 4 h, 24 h, 48 h, 96 h, 172 h (categorical values: 1, 2, 3, 4, 5) Laboratory treatment - in the priming experiment (categorical values: CONTROL = soil samples with water addition only; GLUCOSE = soil samples amended with glucose) Fraction - source of respired CO2 (categorical values: SOM-derived, Glucose-derived) Soil C mineralisation rate (numerical values) (µg CO2-C g-1 SOM h-1) (3) Priming of soil N mineralisation.csv - Responses of soil N mineralisation (gross N mineralisation rates) in a laboratory-incubation priming experiment measured at five timepoints on soils collected across the fertilised Subarctic ecotone. Columns: Site - one of the four sites across the ecotone (categorical values: Tundra, Shrub, Treeline, Forest) Field treatment - fertilisation treatment (categorical values: Con, N, P) Block - field block (categorical values: 1, 3, 4); block 2 was not measured Timepoint - timepoint of measurement corresponding to incubation times: 4 h, 24 h, 48 h, 72 h, 96 h, 172 h (categorical values: 1, 2, 3, 4, 5) Laboratory treatment - in the priming experiment (categorical values: CONTROL = soil samples with water addition only; GLUCOSE = soil samples amended with glucose) Gross N mineralisation (numerical values) (µg NH4-N g-1 SOM h-1) (4) Priming of microbial growth.csv - Responses of microbial growth rates in a laboratory-incubation priming experiment measured at five timepoints on soils collected across the fertilised Subarctic ecotone. Columns: Site - one of the four sites across the ecotone (categorical values: Tundra, Shrub, Treeline, Forest) Field treatment - fertilisation treatment (categorical values: Con, N, P) Block - field block (categorical values: 1, 2, 3, 4) Timepoint - timepoint of measurement corresponding to incubation times: 4 h, 24 h, 48 h, 72 h, 96 h, 172 h (categorical values: 1, 2, 3, 4, 5) Laboratory treatment - in the priming experiment (categorical values: CONTROL = soil samples with water addition only; GLUCOSE = soil samples amended with glucose) Microbial growth rate - sum of bacterial and fungal growth rate (numerical values) (µg C g-1 SOM h-1) Fungal-to-bacterial growth ratio - ratio of fungal growth rate to bacterial growth rate (numerical values) (unitless) (5) Microbial biomass.csv - microbial biomass measured after 172 h incubation in the laboratory on soils collected across the fertilised Subarctic ecotone. Columns: Site - one of the four sites across the ecotone (categorical values: Tundra, Shrub, Treeline, Forest) Field treatment - fertilisation treatment (categorical values: Con, N, P) Block - field block (categorical values: 1, 2, 3, 4) Laboratory treatment - in the priming experiment (categorical values: CONTROL = soil samples with water addition only; GLUCOSE = soil samples amended with glucose) Total PLFA concentration (numerical values) (nmol g-1 SOM) Microbial biomass C - sum of bacterial and fungal biomass C (numerical values) (mg C g-1 SOM) fungal-to-bacterial biomass C ratio - ratio of fungal biomass C to bacterial biomass C (numerical values) (unitless) NOTE: Soil from three out of four blocks were used in the measurements of gross N mineralisation rates. Values indicated as "not measured" mark the soils that were not used in the analyses.