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

Charles Campbell,Håkan Rydin

doi:10.1080/03736687.2019.1626167

Charles Campbell, Håkan Rydin

Open Access

https://doi.org/10.1080/03736687.2019.1626167

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Abstract

ABSTRACTIntroduction. Sphagnum L. forms much of the ground cover in northern peatlands. Different species show affinities for bioclimatic regions in Europe (oceanic/continental; northern/southern) and species-specific tolerance of winter conditions can be a factor explaining their distribution.Methods. We focussed on low temperature in a series of experiments and tested (1) the innate ability of a selection of Sphagnum species to tolerate low temperature in relation to their micro-topographic (wetness) and geographical (climate) distribution; (2) the rate of cold tolerance acquisition; and (3) the ability of species to survive a range of low temperature once cold hardened.Key results. Our experiments showed that maximal PSII efficiency (Fv/Fm, chlorophyll fluorescence), growth rates and survival were all negatively affected by sub-zero temperatures. Environmental conditions associated with the onset of winter (colder nights and shorter days) triggered the acquisition of cold tolerance in Sphagnum.Conclusions. The results were not unequivocal, but species associated with colder climates were generally more tolerant of sub-zero conditions. Species associated with the wettest and driest ends of the wetness gradient were more consistent in their responses than those in between, with wetter-dwelling species being less sensitive to sub-zero temperature than species found in drier microhabitats. Overall, our results suggest that adaptation to winter conditions contribute to the current distribution patterns of Sphagnum species.

Highlights

Sphagnum L. forms much of the ground cover in northern peatlands
We focussed on low temperature in a series of experiments and tested (1) the innate ability of a selection of Sphagnum species to tolerate low temperature in relation to their microtopographic and geographical distribution; (2) the rate of cold tolerance acquisition; and (3) the ability of species to survive a range of low temperature once cold hardened
Our experiments showed that maximal photosystem II (PSII) efficiency (Fv/Fm, chlorophyll fluorescence), growth rates and survival were all negatively affected by sub-zero temperatures

Summary

Introduction

Sphagnum L. forms much of the ground cover in northern peatlands. Different species show affinities for bioclimatic regions in Europe (oceanic/continental; northern/ southern) and species-specific tolerance of winter conditions can be a factor explaining their distribution. The results were not unequivocal, but species associated with colder climates were generally more tolerant of sub-zero conditions. Sphagnum L. forms much of the ground cover of boreal and temperate mires (Wieder and Vitt 2006; Rydin and Jeglum 2013). Kyrkjeeide et al (2016a, 2016b) found evidence for frequent longdistance gene flow, and detected barriers in the form of wind direction, mountains and oceans. This matches patterns observed in other bryophyte genera where local environmental filtering of regional spore rain dictates the assemblage, rather than the species composition of local sources (Hassel and Söderström 2005; Hylander 2009). For several plant species there is evidence that low temperature is more likely to limit distribution than high temperature (Woodward 1990; Rochefort et al 1994; Vetaas 2002; Woodward et al 2004)

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