Growth-limiting nutrients in Sphagnum-dominated bogs subject to low and high atmospheric nitrogen supply

• Published in: The Journal of ecology Vol. 80; no. 1; pp. 131 - 140
• Main Authors: Aerts, R, Wallen, B, Malmer, N
• Format: Journal Article
• Language: English
• Published: 01.01.1992
• Subjects: biomass production; bogs; deposition; mosses and liverworts; nitrogen; nutrient availability; nutrient-nutrient interactions; ombrotrophic bogs; peatlands; phosphorus; Sweden
• ISSN: 0022-0477; 1365-2745
• DOI: 10.2307/2261070

1. The effects of increased nitrogen or phosphorus supply on the productivity of Sphagnum-dominated ombrotrophic bogs in northern and southern Sweden were studied. Atmospheric nitrogen deposition in southern Sweden (high-N site) exceeds that in northern Sweden (low-N site) by about tenfold. 2. Vertical height growth of the Sphagnum carpet was measured by the cranked-wire method. Length growth of individuals was measured by autoradiography after labelling with 14CO2. The results of both methods were significantly correlated, but the cranked-wire data were systematically lower. 3. Productivity of Sphagnum at the low-N site increased almost fourfold after additional nitrogen supply (4 g N m-2 year-1), but no increase was found after additional phosphorus supply (0.4 g P m-2 year-1). At the high-N site, phosphorus supply caused an almost threefold productivity increase, but nitrogen supply did not result in any productivity increase. Thus, in an area with a high atmospheric nitrogen supply, plant productivity is P-limited instead of N-limited. 4. At an intermediate nitrogen supply (2 g N m-2 year-1) the recovery of the supplied nitrogen in the Sphagnum carpet was not different for both sites (60% and 69%, respectively). However, at a high nitrogen supply (4 g N m-2 year-1) nitrogen recovery at the low-N site significantly exceeded that at the high-N site (73% and 47%, respectively). At the low-N site, the supplied phosphorus was not recovered, but at the high-N site the phosphorus recovery was 85% (intermediate phosphorus supply) and 100% (high phosphorus supply), respectively. 5. It is suggested that a high atmospheric nitrogen supply may affect the carbon balance of ombrotrophic bogs, because productivity is under these circumstances not N-limited, but decomposition is probably increased by high loads of nitrogen. In the end, this may turn these C-accumulating systems into C-emitting systems.