Wetter is better: rewetting of minerotrophic peatlands increases plant production and moves them towards carbon sinks

Abstract

<p>In their natural state peatlands are effective carbon sinks as more biomass is produced than decomposed under the prevalent anoxic conditions. Draining peatlands results in release of the stored carbon. Rewetting may or may not restore the original carbon sink. Patterns of plant production and decomposition in rewetted peatlands and how they compare to the drained state remain largely unexplored.</p><p>We measured annual above- and belowground biomass production and decomposition in three different drained and rewetted peatland types: alder forest, percolation fen and coastal fen. We also used standard material (green and rooibos tea) to compare decomposition between the sites, regardless of the decomposability of the local plant material.</p><p>Rewetted sites had higher root and shoot production in the percolation fen, and higher root production in the coastal fen but similar root and leaf production in the alder forest (excluding woody biomass). Decomposition rates were similar in drained and rewetted sites, only in the percolation fen and alder forest aboveground litter decomposed faster in the drained sites. The rewetted percolation fen and the two coastal sites have the highest projected potential for organic matter accumulation due to high production and low decomposition rates. Roots accounted for 23–66% of total biomass production, and the importance of belowground biomass, rather than aboveground biomass, for organic matter accumulation increased with time. This highlights the significance of roots as main peat forming element in these graminoid-dominated fen peatlands and their crucial role in carbon cycling. Notably, increased production compensated for loss by decomposition even during the exceptionally dry year 2018.</p><p>Rewetted sites generally had a more productive plant community compared to drained sites, only tree stem biomass increment was higher in the drained alder forest site. High biomass production supported the peatlands’ function as carbon sink even during a dry year and roots were more important than shoots in establishing this sink, especially in the graminoid dominated sites. Rewetted peatlands may cope better with the extreme weather conditions that will occur more frequently in the future, emphasizing the case for rewetting those systems</p>