Effects of planting method and nitrogen addition on Sphagnum growth in microcosm wetlands

In this study, we propose a method to create a Sphagnum wetland in an urban ecosystem by collecting basic information about Sphagnum growth and decomposition. We constructed six groups of Sphagnum microcosms (1 m × 1 m) with three replicates. A factorial design with two planting methods (capitulum without stem and capitulum with stem) and three levels of nitrogen addition (0, 2, and 6 g N m^-2 year^-1) were prepared. Changes in length, dry mass, and decomposition rates of Sphagnum were monitored over a growing season. The effect of N concentration on production varied for the different planting methods. Production of Sphagnum increased with N concentration in the capitulum without the stem treatment (-D) than in the with stem treatment (+D). Adding N affected the decomposition rate in both with and without stem treatments. Decomposition rate increased with added nitrogen. Planting without stems (-D) was an effective design for a high production and low decomposition of Sphagnum. Net primary production was 187-260 g m^-2year^-1 for dry mass and 15.5- 26.5 mm year^-1 for length, whereas decomposition rates were 10.9-14.7 % mass loss per year. These values are comparable to those from natural bogs. The overall results indicate that constructing Sphagnum wetlands can be successfully employed as a greening technology in urban ecosystems, even in mid-latitudes.