Water table depth, experimental warming, and reduced precipitation impact on litter decomposition in a temperate Sphagnum-peatland

Highlights: • Tea Bags Index method was used to assess the litter decomposition in Sphagnum peatland. • Water table depth controls the litter decomposition processes in Sphagnum peatland. • Warming and rainfall reduction do not deviate the litter decomposition processes. • Open Top Chambers instead to warm they cool down the peat temperature. The Tea Bag Index (TBI) method was used to estimate the litter decomposition rate in peatland exposed for climate manipulation (increased temperature and reduced precipitation) at two contrasting sites differing in water table depth (WTD) dynamics. To manipulate climate on peatland, the prototyped Open Top Chambers (OTC) and automated rain-out shelters were used. OTCs increased daytime air temperatures by ~1.7 °C at the driest plots exposed for an increase of air temperature and reduced precipitation, while the increase of the average daily air temperature was lower than 0.9 °C. However, OTCs cooled down the peat temperature even by 0.8 °C and this effect was most pronounced for daytime rather than night-time conditions. The precipitation amount was reduced by 26%. The tea bags were buried at 8 cm depth for 83 and 172 days starting from the 19th of April 2019. Our observation proved that although decomposition rates were dependent on temperature, WTD and its fluctuations are the main factors controlling the rates of litter decomposition in waterlogged ecosystems like ours. At waterlogged Sphagnum-dominated peatlands, the interrelation between different environmental factors may mitigate the impact of warming and reduced precipitation on litter decomposition.