Effects of elevated carbon dioxide and increased nitrogen deposition on bog vegetation in the Netherlands

Abstract

Summary 1We studied the effects of elevated atmospheric CO 2 and increased N deposition on the plant species composition of a Sphagnum -dominated bog ecosystem in the Netherlands. Large peat monoliths (surface area 1 m 2 , depth 0.6 m) with intact bog vegetation were kept outdoors in large containers and were exposed to elevated CO 2 or increased N deposition for three growing seasons. Elevated CO 2 conditions (target concentration 560 µ mol CO 2 mol -1 ) were created using MiniFACE technology. In a separate experiment, N deposition was increased by 5 g N m -2 year -1 by adding dissolved NH 4 NO 3 at 3 week intervals during the growing season. 2 Elevated atmospheric CO 2 increased height growth of Sphagnum magellanicum , the dominant Sphagnum species, in the second and third growing seasons. Vascular plant biomass was not significantly affected by elevated CO 2 , but growth of species growing close to the moss surface was influenced negatively by the increased Sphagnum height growth. Elevated CO 2 did not change allocation to below-ground plant parts. 3 Adding N increased above-ground vascular plant biomass. The shallow-rooted species Vaccinium oxycoccus responded most to the increased N deposition. Sphagnum growth was significantly reduced in the third growing season. This reduction was likely the result of the increased vascular plant cover, given the observed negative relation between vascular plant cover and Sphagnum growth. 4 The observed shifts in species composition as a result of species-specific responses to treatments, and interactions between peat mosses and vascular plants will have important consequences for the sequestration of carbon in the bog ecosystem.

The multi-annual carbon budget of a peat-covered catchment

“…Decreases in atmospheric deposition of sulphur have been associated with increased losses of dissolved organic carbon (DOC) Clark et al, 2005). Increased N deposition would lead to increased litter production (Aerts et al, 1992), enhances the release of carbon from roots to the soil (Cortufo and Gorissen, 1997); favours the vascular plants over mosses (Heijmans et al, 2001) and may inhibit CH 4 oxidation (Steudler et al, 1989). In addition, management practices in peatlands have not necessarily been conducive to carbon storage.…”

Dwarf shrubs are stronger competitors than graminoid species at high nutrient supply in peat bogs

“…Consequently, a higher amount of soil nitrogen (N) and phosphorus (P) will become available for the vegetation. Several studies showed that the enhanced nutrient availability in bog ecosystems causes an increase in vascular plant cover Heijmans et al 2001;Limpens et al 2003;Wiedermann et al 2007;Gerdol et al 2008), while it negatively affects Sphagnum biomass Chapin et al 2004;Bubier et al 2007;Wiedermann et al 2007). The expansion of vascular plants in bog systems caused by enhanced mineralization rates might cause the same positive feedback as described by Lamers et al (2000) for N deposition.…”

Sphagnum can ‘filter’ N deposition, but effects on the plant and pore water depend on the N form

“…However, there are 58 limits to the capacity of this filter; as atmospheric N deposition increases the Sphagnum and often greatly exceeds 20 mg g -1 (Heijmans et al, 2001). N addition (40-80 kg N ha -1 84 yr -1 for up to 4 years) also increased mineral N concentrations in pore water (Limpens et 85 al., 2003;Limpens et al, 2004;.…”