What are the main drivers affecting the pattern of bryophyte life history traits at two contrasting spoil heaps?

Abstract

In this paper we analysed the relationship between chemical elements (Hg, Cu, Pb, Zn, Ni, Co, As, Cd, Cr, Fe, Al, Ba, Mn, P, Ca, Mg, K and Na) recorded in the upper soil (10 cm from surface) in each relevé plot, 11 environmental variables (coverage of tree, shrub, herbaceous and bryophyte layers, elevation, slope, proportion of rocks, soil depth, soil temperature, soil moisture and soil pH) and bryophyte life history traits at two spoil heaps with different mineralogical composition in Central Slovakia (Hg-spoil heap Veľká Studňa and Cu-spoil heap Podlipa). Vegetation composition and environmental data were sampled by stratified random sampling in defined physiognomic vegetation types. The results of the Principal Component Analysis (PCA) revealed that at both spoil heaps, bryophyte functional traits were mostly arranged along the successional gradient, which may also be interpreted as a moisture gradient. The results of the Redundancy Analysis (RDA) showed that at both heaps, the statistically most significant environmental variables explained a similar portion of the overall variability (20.6% at Veľká Studňa and 21.3% at Podlipa). Similarly to the PCA analysis, the proportion of rocks and the coverage of tree layer had the most significant effect on the functional traits of bryophytes at both sites. Other significant factors included soil temperature and coverage of herbaceous layer for the Hg-spoil heap, and elevation for the Cu-spoil heap. Our results also suggest that the acrocarpous (i.e. erect) mosses are more metal-tolerant than pleurocarpous (i.e. prostrate). Analysis by bryophyte traits seems to be an appropriate approach to analyse successional processes and factors that influence them in various habitat types, inculding spoil heaps.