The effects of winter stress on Sphagnum species with contrasting macro- and microdistributions

Figures & data

Table 1. Summaries of biogeographic element, continental-oceanic affinity (Hill et al. 2007) and centre of microtopographic position (Flatberg 2013) for Sphagnum species used in the experiments. Which experiment it is used in and the materials origin is also given: Kulflyten (K), Ryggmossen (Ry), Römossen (Rö) and Wildmoor (W).

Species	Expt.^origin	Microtopography	Biogeographic element, oceanity
S. fuscum (Schimp.) H.Klinggr.	1^Ry; 2–5^K	High hummock	Boreo-arctic /Continental
S. rubellum Wilson	1^W; 2–5^K	Low hummock	Boreo-temperate /Oceanic-suboceanic
S. magellanicum Brid.	1^W; 2^K	Lawn-low hummock	Boreal montane /Widespread
S. papillosum Lindb.	1^W; 2^K	Lawn	Boreo-temperate /Oceanic-suboceanic
S. balticum (Russow) C.E.O.Jensen	1^Ry; 2–5^K	Lawn	Boreo-arctic /Continental
S. tenellum (Brid.) Brid.	2–5^K	Lawn	Boreo-temperate /Suboceanic
S. lindbergii Schimp.	1^Rö; 2–5^K	Pool-Carpet	Boreo-arctic /Continental
S. cuspidatum Ehrh. ex Hoffm.	1^Ry; 2–5^K	Pool-carpet	Boreo-temperate /Oceanic-widespread
S. majus (Russow) C.E.O.Jensen	2^K	Pool-carpet	Boreal montane /Continental

Table 2. Summary of the experimental design. Hardening treatments are designed to test different ways in which freezing tolerance can be induced. Winter treatments are different winter conditions.

	Hardening treatment	Winter treatment	Recovery and responses
Expt. 1 Testing tolerance to different levels and durations of freezing in unhardened plants	None	20, 5, −5, −10°C, 1, 7, 14, 26 d	(1) Fv/Fm 24 h after freezing (2) Growth rate after freezing
Expt. 2 Testing if different durations of low night temperature can induce frost tolerance	Day + 5, night −1°C, for 0–34 d	−5°C, dark, 48 h	Fv/Fm 24 h after freezing
Expt. 3 Testing if different day length and night temperature can induce frost tolerance.	Factorial combinations of 30 d with day length (6 or 12 h) ×night temp (−1 or 5°C).	48 h at 5, −5, −10 or −18°C	(1) Fv/Fm 24 h after freezing (2) Growth rate after freezing (3) Survival 0–28 days after freezing
Expt. 4 Testing if submergence affects freezing tolerance	As Expt. 3	48 h at −5°C, submerged or not (the non-submerged are the same experimental units as −5°C in Expt. 3)	As Expt. 3
Expt. 5 Testing the effect of a cold dark period (simulating winter under snow)	As Expt. 3	1 month at 0°C in darkness	As Expt. 3

Figure 1. Experiment 2: Maximal PSII efficiency (F_v/F_m) during the acquisition of frost tolerance in Sphagnum. Points are means with standard errors of F_v/F_m from the results of all species.

Figure 2. Hourly temperature readings of the loggers at the highest and lowest mean heights above the water table at Kulflyten (A) and Ryggmossen (B). Daily temperature extrema, means and standard errors for July (C) and December (D) at Kulflyten and Ryggmossen per logger.

Figure 3. Experiment 1: Effect of duration and degree of freezing on the maximal PSII efficiency (F_v/F_m) of unhardened shoots of Sphagnum. Points are means with standard errors.

Figure 4. Experiment 1: Effect of duration and degree of freezing on the growth rate (mm d⁻¹) of unhardened shoots of Sphagnum. Points are means with standard errors.

Figure 5. Experiment 2: Acquisition of frost tolerance in Sphagnum by low night temperature. Radius of the circle is proportional to the area of effect, which is an integrated measure of effect and time to quantify a samples ability to return to 95% of the pre-treatment F_v/F_m value (cf. Figure 1).

Figure 6. Experiment 3: Effects of hardening and winter treatments on the maximal PSII efficiency (F_v/F_m) in Sphagnum. The hardening treatments were factorial combinations of day length (6 or 12 h) and night temperature (−1 or 5°C). Winter temperature treatments comprised 5, −5, −10 and −18°C. Sphagnum treatment temperatures were maintained for 48 h. Points are means with standard errors.

Figure 7. Experiment 3: Effects of hardening and winter treatments on Sphagnum survival. The hardening treatments were factorial combinations of day length (6 or 12 h) and night temperature (−1 or 5°C). Winter temperature treatments shown are for 5 and −18°C. Individual stems were assessed for death at 1, 7, 14, 21 and 28 d after treatment. Points are the proportion of living shoots, error bars are 95% confidence interval.

Hill MO, Preston CD, Bosanquet SDS, Roy DB. 2007. BRYOATT: attributes of British and Irish mosses, liverworts and hornworts. Huntingdon: Centre for Ecology and Hydrology.

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Flatberg K. 2013. Norges torvmoser. Oslo, Norway: Akademika Forlag.

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