Community patterns of vascular plants, mosses and testate amoebae along the bog-fen gradient reveal different responses of aboveground and belowground communities to ecological gradients

Vegetation responses to environmental gradients in peatlands are well documented but little is known about how these patterns compare with those of soil organisms. We studied the vegetation, testate amoebae, and abiotic variables (depth of the water table – DWT, pH, electrical conductivity, Ca and Mg concentrations of water extracted from mosses) along the bog to extremely rich fen gradient in sub-alpine peatlands of Engadine (Swiss Alps). Testate amoeba diversity was correlated to that of mosses but not of vascular plants. Diversity peaked in rich fens for testate amoebae and in extremely rich fens for mosses, while it was lowest in bogs for testate amoebae and mosses but in the extremely rich fen for vascular plants. Multiple factor (MFA) and redundancy (RDA) analyses revealed a stronger correlation of testate amoebae than of vegetation to water table and hydrochemical variables and relatively strong correlation between testate amoeba and moss community data. In RDA hydrochemical variables explained a higher proportion of the testate amoeba and moss data than DWT. Abiotic variables explained a higher percentage of the species data for testate amoebae (30.3%, or 19.5% for binary data) than for mosses (13.4%) and vascular plants (10%). These results show that 1) above-ground and below-ground communities respond differently to ecological gradients in peatlands, 2) testate amoebae are more strongly related than vascular plants to the abiotic factors at the mire surface. These differences are related to vertical trophic gradients and associated niche differentiation.