Acidifying surface water and water level management promote Sphagnum health for peatland restoration and paludiculture

Sphagnum -dominated peatlands play a vital role in carbon storage worldwide. However, large areas are strongly degraded due to land-use change. Success of Sphagnum introduction for bog restoration or paludiculture in former agricultural areas largely depends on local surface water for irrigation and to obtain stable water levels, especially during drought events. However, this water is often unsuitable for Sphagnum , especially in a drained and intensively-used landscape due to high bicarbonate concentrations, known to be toxic to Sphagnum . As such, removing bicarbonate from surface water through artificial acidification using hydrochloric acid (HCl) and/or water level management to mitigate bicarbonate toxicity may be an effective method to initiate a vital Sphagnum cover, but this has not yet been experimentally demonstrated. We therefore performed a five-week laboratory experiment in which Sphagnum palustre was exposed to surface water from two drained peat landscapes with high bicarbonate concentrations, which differed in ion- and nutrient concentrations, and one artificial rainwater control. We applied the following treatments: acidified (pH 4.0) or non-acidified water, and moss capitula were placed either above or below the water surface. Our experiment revealed that Sphagnum survived in all emergent treatments regardless of the ion concentration. Sphagnum submerged in non-acidified water became chlorotic and had lower capitulum potassium levels, but accumulated calcium and magnesium. Sphagnum remained vital when submerged in acidified conditions and had higher capitulum potassium levels. This study highlights that acidification of bicarbonate-rich surface water mitigates bicarbonate toxicity even when surface water is high in ion concentrations. We further show that emergent capitula in bicarbonate-rich water does not lead to chlorosis after five weeks. This suggests artificial acidification of surface water or application of bicarbonate-rich irrigation water with emergent capitula are measures to overcome drought periods in Sphagnum restoration or paludiculture projects when acidic surface water is unavailable.