Weather Factors in Different Growing Periods Determine Inter-Annual Change in Growth of Four Sphagnum Species: Evidence from an Eight-Year Study

The growth of peat mosses is crucial for carbon uptake and storage in high latitude peatlands. Nevertheless, little is known on how variation in specific weather conditions affect Sphagnum functional traits and productivity. Using data from an eight-year study in a mire complex in the southern taiga of Western Siberia, we investigated how a suite of within-season weather conditions relates to Sphagnum growth. We collected weather data, and data on functional traits (length increment, increment biomass, capitulum numerical density and capitulum biomass) and net primary productivity of four Sphagnum species growing in raised bogs and poor fens. Overall, the most important factors were those related moisture conditions. Growing season averages of weather variables (e.g., precipitation and mean temperature) were often as good predictors of Sphagnum functional traits and productivity as early or late seasonal averages, but not necessarily for the same variables. The most sensitive traits to weather fluctuation were length increment (for S. magellanicum agg., S. angustifolium, S. fallax ) and numerical density (for S. fuscum ). Primary productivity of S. fuscum and S. magellanicum agg. were the highest under warm and wet conditions with S. fuscum being less sensitive to the weather; productivity of S. angustifolium increased under cool and wet conditions; and productivity of S. fallax was the highest under dry weather. Diversity in interspecific response to weather fluctuations may result in high peatland resistance towards environmental variability, and thereby maintaining a stable Sphagnum productivity in time across the mire complex.