Hydrochemistry, water table depth and related distribution patterns of vascular plants in a mixed mire

The hydrological and floristic variation within a mire vegetation is mostly controlled by three ecological gradients: nutrient availability, acidity-alkalinity, and water table depth. The objectives of this study were: (a) to analyse the hydrochemistry of a mixed mire in relation to different habitat conditions; (b) to evaluate the patterns of vascular plant composition in relation to nutrient availability, acidity-alkainity, and water table depth, and to partition the pure effects of these gradients. Within a mixed mire, we sampled 36 smalling a growing season. Water chemistry proved to be significantly different between the various vegetation types. Two biological systems could be identified according to hydrochemistry and vascular plant composition: (1) several fen vegetation types lacking raised Sphagnum structures where the water chemistry reflected groundwater properties; (2) bog Sphagnum-dominated vegetation, where the convex shape of the mire surface prevented mixing with the groundwater. The results of the partitioning indicated that the acidity-alkalinity gradient was more important in controlling the patterns of plant distribution than water table depth. © 2008 Società Botanica Italiana.