title: Sphagnum establishment in alkaline fens: Importance of weather and water chemistry.
abstract: Sphagnum expansion to alkaline fens has accelerated during the last decades in Europe, leading to changes in diversity, habitat distributions and carbon storage. The causes are still not clearly understood and involve an interplay between climate change, hydrology, nutrient supply and Sphagnum physiology. We conducted a 4-year field experiment in eight fens in Central European highlands and assessed survival and establishment of individual apical shoot fragments of S. flexuosum, S. warnstorfii and S. squarrosum transplanted along the microtopographical gradient. In a laboratory experiment, we tested combined effects of desiccation and high calcium bicarbonate concentration on Sphagnum survival. We found that in unflooded positions, living shoots of Sphagnum and brown mosses lowered [Ca2+] and pH in their capillary water, in contrast to dead fragments; yet without differences between species. Survival and expansion of Sphagnum fragments, which did not die of acute calcium toxicity during first weeks/months, was negatively affected by dry weather and alkaline water chemistry, reflecting Sphagnum intolerance to desiccation and to combined high [Ca2+] and pH. Shoot fragments expanded to patches only when precipitation was high. Interestingly, non-toxic concentration of calcium bicarbonate reduced desiccation damage in Sphagnum, probably through protection of membranes or other cell components. This mechanism would facilitate Sphagnum survival in elevated, frequently desiccated microhabitats of calcareous fens such as brown-moss hummocks. However, since water-retaining capacity of few Sphagnum shoots is insufficient to change water chemistry in its surroundings, surface acidification may occur only once the environment (e.g. sufficient humidity) enabled expansion to larger mats. Then, the retained rainwater together with hardly decomposable Sphagnum litter would separate mire surface from groundwater, speeding up successional shift towards poor fens. Sphagnum expansion to alkaline fens is therefore more likely in humid regions.
authors.affiliation: Institute of Botany, Czech Academy of Sciences, Department of Functional Ecology, Dukelská 135, CZ-379 82 Třeboň, Czech Republic; Faculty of Science, University of South Bohemia, Branišovská 1760, CZ-370 05 České Budějovice, Czech Republic. Electronic address: vicherova.e@gmail.com.
authors.forename: Eliška
authors.initials: E
authors.lastname: Vicherová
authors.affiliation: Faculty of Science, Masaryk University, Department of Botany and Zoology, Kotlářská 2, CZ-611 37 Brno, Czech Republic. Electronic address: hajek@sci.muni.cz.
authors.forename: Michal
authors.initials: M
authors.lastname: Hájek
authors.affiliation: Faculty of Science, University of South Bohemia, Branišovská 1760, CZ-370 05 České Budějovice, Czech Republic. Electronic address: petrsm@jcu.cz.
authors.forename: Petr
authors.initials: P
authors.lastname: Šmilauer
authors.affiliation: Institute of Botany, Czech Academy of Sciences, Department of Functional Ecology, Dukelská 135, CZ-379 82 Třeboň, Czech Republic; Faculty of Science, University of South Bohemia, Branišovská 1760, CZ-370 05 České Budějovice, Czech Republic. Electronic address: tomas.hajek@prf.jcu.cz.
authors.forename: Tomáš
authors.initials: T
authors.lastname: Hájek
mesh_terms: D000468:Alkalies; D057231:Climate Change; D005060:Europe; D006863:Hydrogen-Ion Concentration; D044003:Sphagnopsida / Q000254:growth & development*; D014867:Water / Q000737:chemistry*; D014887:Weather
chemical_list: D000468:Alkalies; D014867:Water
keywords: Calcium tolerance; Climate humidity; Competition; Desiccation; Fen succession; Sphagnum transplants