DOI: 10.5061/dryad.b5mkkwhkf
title: Dataset for: Heat wave-induced microbial thermal trait adaptation and its reversal in the Subarctic

description: Climate change predictions suggest that arctic and subarctic ecosystems
 will be particularly affected by rising temperatures and extreme weather
 events, including severe heat waves. Temperature is one of the most
 important environmental factors controlling and regulating microbial
 decomposition in soils; therefore, it is critical to understand its impact
 on soil microorganisms and their feedback to climate warming. We conducted
 a warming experiment in a subarctic birch forest in North Sweden to test
 the effects of summer heat waves on the thermal trait distributions that
 define the temperature dependencies for microbial growth and respiration.
 We also determined the microbial temperature dependences 10 and 12 months
 after the heat wave simulation had ended to investigate the persistence of
 the thermal trait shifts. As a result of warming, the bacterial growth
 temperature dependence shifted to become warm-adapted, with a similar
 trend for fungal growth. For respiration, there was no shift in the
 temperature dependence. The shifts in thermal traits were not accompanied
 by changes in α- or β-diversity of the microbial community. Warming
 increased the fungal-to-bacterial growth ratio by 33% and decreased the
 microbial carbon use efficiency (CUE) by 35%, and both these effects were
 caused by the reduction in moisture the warming treatments caused, while
 there was no evidence that substrate depletion had altered microbial
 processes. The warm-shifted bacterial thermal traits were partially
 restored within one winter but only fully recovered to match ambient
 conditions after one year. To conclude, summer heat waves in the Subarctic
 resulted in (i) shifts in microbial thermal trait distributions; (ii)
 lower microbial process rates caused by decreased moisture, not substrate
 depletion; and (iii) no detectable link between the microbial thermal
 trait shifts and community composition changes. 
description: In brief, soil and field characteristics: We measured gravimetric soil moisture (105°C for
 24 h) and SOM content through loss on ignition (550°C for 12 h). Soil pH
 and electrical conductivity (EC) were determined in a 1:5 (w:v) soil:water
 extraction. Soil total carbon (TC) and total nitrogen (TN) were measured
 using Dumas dry combustion by a C/N 144 elemental analyzer (VarioMAX CN,
 Elementar, Germany). The normalized difference vegetation index (NDVI) as
 a proxy for plant productivity, the fraction of photosynthetically active
 radiation (fPAR), and the leaf area index (LAI; the projected area of
 leaves over the unit of measured ground area; m<sup>2</sup>
 m<sup>-2</sup>) were determined with NDVI meter
 (SpectroSense2+, Skye, UK). The
 temperature and moisture data were collected by using data loggers (TMS-4 29cm, TOMST®, Czech Republic)
 with 15 min resolution. The <em>in situ</em> soil (-8 cm),
 surface (0 cm), air (+15 cm) temperatures, and volumetric soil moisture
 (between 0 and -14 cm) were monitored.
 Bacterial growth, fungal
 growth, and respiration were determined at ten different screening
 temperatures from 0 to 45°C in 5°C intervals. Bacterial growth was
 determined by radioactively labeled <sup>3</sup>H-Leucine
 (Leu) incorporation into extracted bacteria from 0.5 g of fresh soils.
 Fungal growth was measured in 0.5 g of fresh soils using
 <sup>14</sup>C-acetate (Ace)-in-ergosterol incorporation
 method. Microbial respiration was measured by a gas chromatograph equipped
 with a methanizer and flame ionization detector.
description: # Dataset for Heat wave-induced microbial thermal trait adaptation and its
 reversal in the Subarctic
 [https://doi.org/10.5061/dryad.b5mkkwhkf](https://doi.org/10.5061/dryad.b5mkkwhkf) We conducted a field warming experiment to test the effects of summer heat waves on microbial temperature traits. The field warming experiment included 4 independent blocks, and each block included 2 control and warmed plots. The dataset includes the field and soil characteristics (August 2020), *in situ* temperature and moisture measurements (between June 2020 and August 2020), as well as bacterial growth, fungal growth, and respiration rates in C unit (μg C g<sup>-1</sup> SOM h<sup>-1</sup>) measured at different time points (August 2020, June 2021, August 2021). The warming treatments started in mid-June and ran until mid-August, covering the growing season of 2020. In mid-August 2020, the IR heaters were removed after two months of warming, and the plots were left without warming treatment under ambient conditions. Then, after one winter (in June 2021) and one entire annual cycle (in August 2021), the plots were sampled again to investigate if any warming legacy remained in the microbial community temperature relationships. Files included contain all data from the article (DOI), organised as follows: 1\. This file includes the soil and field characteristics: water content \(WC\) \(g H<sub>2</sub>O g<sup>-1</sup> dwt), soil organic matter (g SOM g<sup>-1</sup> dwt), soil pH, soil electrical conductivity (µS cm<sup>-1</sup>), water holding capacity (g H<sub>2</sub>O g<sup>-1</sup> dwt), total carbon (g C g<sup>-1</sup> dwt), total nitrogen (g N g<sup>-1</sup> dwt), NDVI (normalized difference vegetation index), fPAR (the fraction of photosynthetically active radiation), LAI (the projected area of leaves over the unit of measured ground area). 2\. Soil temperature \(°C\) \(\-8 cm\) measured with 15 min resolution 3\. Soil volumetric moisture \(cm<sup>3</sup> cm<sup>-3</sup>) (0 and -14 cm) with 15 min resolution 4\. Surface temperature \(°C\) \(0 cm\) measured with 15 min resolution 5\. Air temperature \(°C\) \(\+15 cm\) measured with 15 min resolution 6\. Microbial rates \(bacterial growth\, fungal growth\, and respiration data\) \(µg C g<sup>-1</sup> SOM h<sup>-1</sup>) measured in August 2020 7\. Microbial rates \(bacterial growth\, fungal growth\, and respiration data\) \(µg C g<sup>-1</sup> SOM h<sup>-1</sup>) measured in June 2021 8\. Microbial rates \(bacterial growth\, fungal growth\, and respiration data\) \(µg C g<sup>-1</sup> SOM h<sup>-1</sup>) measured in August 2021 9\. Microbial rates \(bacterial growth\, fungal growth\, and respiration data\) \(µg C g<sup>-1</sup> SOM h<sup>-1</sup>) measured at 20°C at field moisture and 50% WHC 10\. Carbon use efficiency and fungal\-to\-bacterial growth ratio measured in August 2020 ## Description of the data and file structure The 4 independent blocks are called BLOCK1, BLOCK2, BLOCK3, BLOCK4. Each block includes 2 control and 2 warmed plots. For BLOCK1: CONTROL1, WARMING1, CONTROL2, WARMING2. For BLOCK2: CONTROL3, WARMING3, CONTROL4, WARMING4. For BLOCK3: CONTROL5, WARMING5, CONTROL6, WARMING6. For BLOCK4: CONTROL7, WARMING7, CONTROL8, WARMING8. Prior to the statistical analysis, we combined field technical replicates into means per block, ending with one control and one warming treatment per block. In files including 2-10, in all columns, “NA” (Not Available) values are used to signify instances where the data could not be obtained or recorded. To see how the data was used and analyzed, see Materials & Methods and Results section of the connected article, DOI: 10.1111/GCB.17032. ## Sharing/Access information The sequencing data that support the findings are available on European Nucleotide Archive with the primary accession number PRJEB54006 ([http://www.ebi.ac.uk/ena/data/view/PRJEB54006](http://www.ebi.ac.uk/ena/data/view/PRJEB54006)).