Ombrotrophic hummock species are stress-tolerant plants that occurred at sites with high stress and low disturbance (i.e., at the old end of the chronosequence). Hollow species are competitive plants that occurred at sites with low stress and low disturbance (i.e., in the wet depressions in the middle and at the old end of the chronosequence). fimbriatum is a ruderal plant that occurred at the first sites along the chronosequence, which were characterized by low stress but high disturbance. Our study divided the species into three groups pioneer species, hollow species, and ombrotrophic hummock formers. Mosses at the young and old ends of the chronosequence showed indications of downregulation, measured as a low ratio between variable and maximum fluorescence ( F v/ F m).
In agreement with our hypothesis, increase in biomass and CO 2 exchange rate of Sphagnum mosses decreased along the successional gradient, following the tactics of more intensely studied vascular plants. We quantified the rates of increase in biomass and length of different Sphagnum species in relation to their CO 2 assimilation rates, their photosynthetic light reaction efficiencies, and their physiological states, as measured by the chlorophyll fluorescence method. To address this hypothesis, we studied links between the growth and related ecophysiological processes of Sphagnum mosses from a time-since-initiation chronosequence of five wetlands. We hypothesized that moss species follow the known vascular plant growth strategy along the successional gradient (i.e., decrease in production and maximal photosynthesis while succession proceeds).
Their ecophysiology is known to be related to the water level, but very little is currently known about the successional trend in Sphagnum. Sphagnum mosses are widespread in areas where mires exist and constitute a globally important carbon sink.
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