Species Replacement in the Bryophyte Layer in Mires: The Role of Water Type, Nutrient Supply and Interspecific Interactions

Abstract

1 Four bryophyte species, Scorpidium scorpioides (characteristic of mineral-rich, nutrient-poor fens), Sphagnum subnitens (mineral-poor, nutrient-poor), Calliergonella cuspidata (mineral-rich, nutrient-rich) and Sphagnum squarrosum (mineral-poor, nutrient-rich), were cultivated to study whether their mutual replacement was regulated by abiotic conditions or whether interspecific interactions played a major role. 2 Water type may contribute to the replacement of some rich-fen species by Sphagnum spp. Growth of Calliergonella cuspidata was best in (mineral-rich) groundwater and reduced in (mineral-poor) rain water, whereas growth of Sphagnum subnitens was much better in rain water than in groundwater. Scorpidium scorpioides and Sphagnum squarrosum, however, performed well in both water types. 3 Nutrient enrichment may also explain species replacements to some extent. As expected, Sphagnum squarrosum was clearly stimulated by nutrient supply, while S. subnitens did not respond. However, S. scorpioides showed increased rather than decreased growth rates and C. cuspidata was not affected by nutrient supply. 4 Interspecific interactions played a role in all replacement series. Generally, mixed culture stimulated growth of the species whose natural environment was simulated and/or reduced growth of the other species, suggesting that competitive interactions are involved. However, interactions between S. scorpioides and S. subnitens appear to counteract the observed succession. 5 The different species responses may lead to different rates of succession in nutrientpoor ('slow succession') and nutrient-rich fens ('rapid succession').