Testing inter-regional variation in pH niches of fen mosses

Abstract

Question: Mosses are important ecosystem engineers in mires. Their pH optima and tolerances presented in the literature differ between regions, even though the high dispersal ability of mosses should prevent local adaptations. Nutrient availability is sometimes suggested as a reason for local niche differentiation. Are patterns in moss niche diversification, optima and tolerance with respect to pH consistent between regions differing in nutrient availability and abundance of calcareous bedrock? Location: Western Carpathians (Slovakia, a predominantly calcareous P- and K-poor region), Bohemian Massif (Czech Republic, a predominantly crystalline, P- and K-rich region). Methods: Analyses of an original stratified data set and a large database using species response curves. Results: Although the above two regions differ in abundance of calcareous fens, species pH optima (either original or adjusted according to calcium level) were consistent between the regions and data sets. Calcium-tolerant peat mosses (Sphagnum warnstorfii, S. contortum, S. teres) showed an optimum at pH 6 and rather narrow niches. Sphagnum fallax was the most acidophilous, and both S. palustre and S. flexuosum had rather wide intermediate niches. The pH amplitudes were largely consistent between the regions (especially when adjusted pH was used), but S. fallax and Aulacomnium palustre exhibited wider niches in the Bohemian Massif. Despite no significant difference in niche optimum and width, some more nutrient demanding and more generalist species occurred at higher frequency in specific parts of the pH gradient in the Bohemian Massif, while some fen specialists showed the opposite pattern. Conclusions: The small stratified data set and the database data set yielded rather consistent results regarding fen moss niches in the Bohemian Massif and the Western Carpathians. The consistency in pH niches corresponds to the lack of large-scale genetic differentiation in moss species. The observed inter-regional differences in species response curves may thus reflect an increased frequency of competitively strong species in certain parts of the pH/Ca gradient in the nutrient-richer Bohemian Massif rather than genetically conditioned niche shifts. Expansion of these species was probably triggered by potassium enrichment that took place in the 1970s-1980s. Inter-regional differences in species response curves were observed in both data sets, but in the large database data set they were more frequently statistically significant.