DOI: 10.5061/dryad.79cnp5j2q
title: Data from: Frost damage measured by electrolyte leakage in subarctic bryophytes increases with climate warming

description: 1. Observed climate change in northern high latitudes is strongest in
 winter, but still relatively little is known about the effects of winter
 climate change on tundra ecosystems. Ongoing changes in winter climate and
 snow cover will change the intensity, duration, and frequency of frost
 events. Bryophytes form a major component of northern ecosystems but their
 responses to winter climate changes are largely unknown. 2. Here, we
 studied how changes in overall winter climate and snow regime affect frost
 damage in three common bryophyte taxa that differ in desiccation tolerance
 in a subarctic tundra ecosystem. We used a snow manipulation experiment
 where bryophyte cores were transplanted from just above the treeline to
 similar elevation (i.e., current cold climate) and lower elevation (i.e.,
 near-future warmer climate scenario) in Abisko, Sweden. Here we measured
 frost damage in shoots of Ptilidium ciliare, Hylocomium splendens and
 Sphagnum fuscum with the relative electrolyte leakage (REL) method, during
 late winter and spring in two consecutive years. We hypothesized that
 frost damage would be lower in a milder climate (low site), higher under
 reduced snow cover, and that taxa from moister habitats with assumed low
 desiccation tolerance would be more sensitive to lower temperature and
 thinner snow cover than those from drier and more exposed habitats. 3.
 Contrary to our expectations, frost damage was highest at low elevation,
 while the effect of snow treatment differed across sites and taxa. At the
 high site, frost damage was reduced under snow addition in the taxon with
 the assumed lowest desiccation tolerance, S. fuscum. Surprisingly, frost
 damage increased with mean temperature in the bryophyte core of the
 preceding 14 days leading up to REL measurements and decreased with higher
 frost degree sums, i.e., was highest in the milder climate at the low
 site. 4. Synthesis. Our results imply that climate warming in late winter
 and spring increases frost damage in bryophytes. Given the high abundance
 of bryophytes in tundra ecosystems, higher frost damage could alter the
 appearance and functioning of the tundra landscape, although the short and
 long-term effects on bryophyte fitness remain to be studied.
description: We used a snow manipulation experiment where bryophyte
 cores were transplanted from just above the treeline to similar elevation
 (i.e., current cold climate) and lower elevation (i.e., near-future warmer
 climate scenario) in Abisko, Sweden. For full details on the experimental
 design, see the corresponding publication in Journal of Ecology (Van
 Zuijlen et al. 2023).<br>
 Sampling and frost damage
 assessment To capture periods when bryophytes may
 be more vulnerable to freezing, we sampled multiple times after snowmelt
 (i.e., when all plots had melted out at least partially), and across two
 consecutive years to increase the generality of our
 findings. In 2015 sampling took place on May 10
 and 27 at the low site and on May 11 and 29 at the high site. In 2016, we
 sampled on May 2, 11 and 16 and June 1 at the low site and on May 3, 10
 and 17 and June 2 at the high site. At each sampling occasion, we
 collected bryophyte shoots from each species in each plot. Five living
 (i.e., healthy looking) individual shoots of approximately 2.5 cm length
 were selected randomly from each core, at a minimum of 5 cm distance from
 the core edge. After sampling, bryophyte shoots were stored at 4 °C
 overnight until the REL assay was started the following
 day.<br><br>For REL estimation, each sample,
 consisting of 5 shoots, was soaked in 16 ml of 0.1% (v/v) Triton X-100
 (VWR chemicals) for 24 hours at 20 °C to allow electrolyte leakage to
 equilibrate, after which we measured initial conductivity (SevenCompact
 S230, Mettler-Toledo AG, Switzerland). We then placed the samples in a
 water bath at 97 °C for one hour, with the purpose to lyse all cells.
 Final conductivity was measured after another 24 hours at 20 °C. Along
 with each batch of 45 samples (one sampling moment of one site), three
 blank samples, consisting of 16 ml of 0.1% (v/v) Triton X-100, were taken
 of which the mean initial and mean final conductivity was calculated. REL
 was then calculated as (initial conductivity – initial blank conductivity)
 / (final conductivity – final blank conductivity). 
 Bryophyte
 performance To assess the impact of snow and
 elevation on growth as a measure of actual fitness of the bryophytes, we
 tied cotton threads around two <em>H. splendens</em> and three
 <em>P. ciliare</em> shoots. Shoot growth was not measured on
 <em>S. fuscum</em> as shoots were not strong enough to
 withstand this handling. Distance from thread to tip was measured at the
 beginning and end of the growing season of 2014 and the difference was
 calculated to represent shoot length growth. For each plot, the shoot with
 the highest growth was used to assess growth response. This was done to
 avoid counting growth of shoots that were potentially affected by the
 measurement, i.e., tying a thread around the moss shoot may disturb or
 even kill the shoot. In this way, we were more likely to be assessing
 actual treatment responses.  Microclimate in
 the bryophyte cores In spring 2015
 temperature (°C) and moisture (volumetric water content (VWC), in
 m<sup>3</sup>m<sup>-3</sup>) in the bryophyte
 cores were measured hourly (5TM sensors and ECH2O Em50 loggers, Decagon
 Devices Inc., WA, USA). Sensors were placed vertically in bryophyte cores
 so that measurements were taken at 0–5 cm depth (integrated) from the
 bryophyte surface and down. Sensors were placed in four out of five blocks
 in all bryophyte species and snow treatments at both sites. In spring
 2016, bryophyte core temperature was measured as in 2015 (but using
 Tinytags, Plus2 TGP‐4017 external sensors, Gemini Co., UK; and ECH2O Em50
 loggers, Decagon Devices Inc., WA, USA) and in <em>H.
 splendens</em> cores only, and only in three out of five blocks,
 from mid-April until the beginning of June. All data were checked visually
 for discrepancies; untenable moisture values (i.e. VWC&lt;0 and
 VWC&gt;1) and bryophyte core moisture values measured when the soil
 was frozen (i.e. concurrent temperature ≤0°C) were removed. We further
 removed unreliable data from one
 control plot (showing exceptionally high temperatures right at the start
 of the spring snow treatments).<br><br>After data
 cleaning, we calculated the following microclimate variables: average
 daily mean temperature; absolute minimum temperature; no. of diurnal
 freeze-thaw cycles (if temperature reaches below and above 0°C in one
 calendar day); number of frost days (daily average temperature &lt;
 0°C); frost degree sums (the absolute value of the sum of daily minimum
 temperatures below 0°C; i.e. higher values correspond to more frost); and
 finally mean moisture content. We calculated these variables over the
 entire experimental period in 2015, that is April 16 to and including May
 26, i.e., right after the start of the spring snow treatments and just
 before the final REL sampling in 2015. In addition, for each REL sampling
 occasion in 2015 and 2016, we calculated all the same microclimate
 variables over the 14 days leading up to sampling, as well as an
 additional variable for each measurement date that is the number of days
 since the last diurnal freeze-thaw cycle.
 Frost damage in unmanipulated bryophyte
 shoots To assess the REL of healthy,
 non-transplanted bryophytes in spring, shoots <em>of H.
 splendens</em> and <em>P. ciliare</em> were collected on
 the 28th of April 2016 just before snowmelt, from a half-open birch forest
 close to the low site. For each moss species, shoots were sampled from one
 site with thin snow cover (7-10 cm) and one site with thick snow cover
 (53-40 cm). For each snow regime and species, 6 samples containing 5
 shoots each of about 5 cm length were collected. The samples were
 consistently subjected to +5 °C for 144 h with alternating tubular
 lighting every 12 h in environmental test chambers (MLR-350, Sanyo
 Electric Biomedical Co., Ltd., Japan) before REL measurements were taken
 following the same protocol as described above for bryophytes exposed to
 experimental treatments in the field common
 gardens. 
description: # Data from: Frost damage measured by electrolyte leakage in subarctic
 bryophytes increases with climate warming
 [https://doi.org/10.5061/dryad.79cnp5j2q](https://doi.org/10.5061/dryad.79cnp5j2q) The dataset include relative electrolyte leakage (REL) values for three subarctic bryophyte taxa, microclimate variables calculated from hourly measurements taken inside the bryophyte cores, and maximum shoot growth per bryophyte core from a snow manipulation field experiment in Abisko, Sweden. In addition, REL values of unmanipulated bryophyte shoots are included. ## File list * vanzuijlen\_et\_al\_2023\_rel.txt * vanzuijlen\_et\_al\_2023\_clim\_exp.txt * vanzuijlen\_et\_al\_2023\_clim\_rel.txt * vanzuijlen\_et\_al\_2023\_shootgrowth.txt * vanzuijlen\_et\_al\_2023\_unm\_rel.txt ## File and variable descriptions vanzuijlen\_et\_al\_2023\_rel.txt - This file contains the REL values for the bryophyte cores within the snow manipulation field experiment. There are two elevational sites ("site": "low" and "high"), ten blocks ("block": numbered 1-10, five at each site), three snow treatments ("snowtreat": "addition", "control", and "reduction"), three bryophyte taxa ("species": "Hyl.spl" (*Hylocomium splendens*), "Pti.cil" (*Ptilidium ciliare*), and "Sph.fus" (*Sphagnum fuscum*). REL was measured on several occasions during late winter/spring in two years (year: 2015 and 2016) a total of six times (time: numbered 1-6, 1-2 in 2015 and 3-6 in 2016). vanzuijlen\_et\_al\_2023\_clim\_exp.txt - This file contains microclimate variables calculated from hourly measurements taken inside the bryophyte cores from April 16 to and including May 26, 2015. The variables for the experimental design are the same as in vanzuijlen\_et\_al\_2023\_rel.txt as described above. The microclimate variables are: average daily mean temperature ("meanT"); absolute minimum temperature ("minT"); no. of diurnal freeze-thaw cycles ("dft"); number of frost days ("frdays"); frost degree sums ("fdsums"), and mean moisture content ("meanVWC"). Note that this file contains data only for 2015. vanzuijlen\_et\_al\_2023\_clim\_rel.txt - This file contains microclimate variables calculated over the 14 days leading up to each REL sampling in 2015 and 2016, as well as the corresponding REL values. The variables for the experimental design and the REL values are the same as in vanzuijlen\_et\_al\_2023\_rel.txt. The microclimate variables are the same as in vanzuijlen\_et\_al\_2023\_clim\_exp.txt, but calculated over different time periods. In addition, the file contains an additional variable: the number of days since the last diurnal freeze-thaw cycle ("tdft"). Note that not every REL value from vanzuijlen\_et\_al\_2023\_rel.txt has corresponding microclimate data. vanzuijlen\_et\_al\_2023\_shootgrowth.txt - This file contains maximum shoot growth values (in millimeters, "max\_shoot\_growth\_mm") per bryophyte core, measured during summer 2014. The variables for the experimental design are the same as described above for vanzuijlen\_et\_al\_2023\_rel.txt. vanzuijlen\_et\_al\_2023\_unm\_rel.txt - This file contains REL values for unmanipulated shoots of *H. splendens* ("Hyl.spl") and *P. ciliare* ("Pti.cil"), sampled from a site with thin and thick snow cover ("snow\_regime" and snow thickness in centimeters: "snow\_thickness\_cm").