Long-term water level draw-down affects functional plant trait composition of northern peatlands

Anna M. Laine, Aino Korrensalo, Nicola A.K. Kokkonen and Eeva-Stiina Tuittila

Water level draw-down induced vegetation change in the bog and fen sites in Lakkasuo. Image credits Nicola Kokkonen.
Water level draw-down induced vegetation change in the bog and fen sites in Lakkasuo. Image credits Nicola Kokkonen.

Peatlands form a significant soil carbon storage, but due to drying caused by climate change the rate of carbon accumulation may decrease. The carbon that accumulates into peat is fixed from the atmosphere by vegetation in photosynthesis. To predict carbon accumulation in the future it is therefore necessary to understand how vegetation responds to climate change.
Plant properties such as plant height or specific leaf area (leaf area per unit dry mass), also called functional traits, are directly linked to ecosystem functions like carbon accumulation. Therefore, traits provide a useful tool for forecasting how the effect of climate change on vegetation could impact carbon accumulation. In peatlands, drying is known to have a stronger impact than warming itself, yet the responses of peatlands with different nutrient status seem to differ.
Here we studied how a 15-year-long water-level drawdown (WLD) impacts functional traits of vascular plants and mosses in peatland types of different nutrient status, namely rich fens, poor fens and bogs. We discovered the traits of both vascular plants and Sphagnum mosses vary between species, but in the latter the traits of the same species showed higher variability than those of vascular plants. This variability makes Sphagnum species more flexible and allows them to survive in changing environmental conditions.
Secondly, we observed that plants growing in different peatland types manifested different strategies with their traits. Fens supported plants with a productive growth strategy, while bogs had plants with a slow-growing, stress tolerant strategy. In addition, the WLD experiment strengthened the traits typical of the peatland type. In rich fen after WLD the productive strategy was even more pronounced, with taller plants and higher specific leaf area, while in the bog, WLD further enhanced those properties of mosses that allow them to remain moist under drier conditions.
Thirdly, we found that the way the vegetation modulated its strategy defined the mechanism of peatland response to WLD. The shift in fens towards more a productive strategy increased photosynthetic capacity, while the same did not happen in bogs. It seems evident that fens and bogs adapt differently to WLD and this should be considered when predicting the effects of climate change on peatland carbon cycling.

Read the research in full here

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