Microtopography-Induced Differentiation of Moss Synusiae in Wet Grasslands Covering a Karst Plain in Central Italy (Pian Grande, Central Apennines)

This study examines the relationships between the occurrence of epigeic moss assemblages in different grasslands and the microhabitats (pits, dolines, brooks and mounds) occurring in a karst, almost flat basin. The bryophytes tend to form specific synusiae in grassland communities that cover particular microhabitats differentiated on the basis of microtopography. Except for pits and mounds, all other microhabitats are clearly distinguishable in terms of bryophyte composition. The most discriminant species between the moss synusiae of dolines, brooks and pits are Drepanocladus aduncus, Fontinalis antipyretica and Polytrichum commune, respectively. The mounds have no differential species and are poorly distinguished from pits based only on the low cover of Polytrichum commune. A combined soil acidity-moisture gradient determined by both land microtopography and surface water runoff is responsible for the good compositional distinctiveness of dolines and brooks from pits and mounds. A relatively broad section of this gradient is occupied by the niche of Calliergonella cuspidata, which could be the indicator of a different synusia occurring in microhabitats with ecological conditions intermediate between dolines and brooks. A weaker gradient of soil organic matter content accounts for the distinction of pits from dolines and brooks in the species multidimensional space. Overall, there is a good Agreement between the structure of epigeic bryophyte assemblages and the corresponding type of vascular plant communities developed in the same karst habitat, which supports the hypothesis of their dependence and the methodological approach of integrated releve´s in phytocoenosis sampling.