N deposition affects N availability in interstitial water, growth of Sphagnum and invasion of vascular plants in bog vegetation

Abstract

Summary• We studied the effects of N deposition on shrub-moss competition and the establishment and growth of invasive Betula pubescens and Molinia caerulea in intact bog vegetation removed from a site subject to 40 kg N ha − 1 yr − 1 .• Mesocosms with and without introduced Betula seedlings and Molinia sprouts were kept under a roof and received an equivalent of 0, 40 and 80 kg N ha − 1 yr − 1 for two growing seasons.• N concentration in both interstitial water and Sphagnum decreased when N input ceased and increased when N input was doubled. Molinia biomass was positively related to the inorganic N concentration in the interstitial water. Adding N increased production of Molinia and prolonged survival of Betula seedlings in the first year. Sphagnum height increment showed a hump-shaped relationship with light interception by vascular plants.• N deposition encouraged vascular plants to grow by enhancing N availability in the rhizosphere. Water table level and the availability of P were found to be important in explaining species-specific responses to N deposition. The underlying mechanisms and the reversibility of N effects are discussed.

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

“…Consequently, R. alba might be less dependent on the applied nutrients for its growth and therefore did not show a response to the added N and P. The N:P ratio in the leaves, however, differed among the nutrient treatments, suggesting that R. alba did use the nutrients to some extent. Studies of Heijmans et al (2002); Limpens et al (2003) found an increase in R. alba biomass after N fertilization in intact bog vegetation. Interestingly, both studies determined the increase in this species during the second growing season of the study.…”

“…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.…”

Atmospheric nitrogen deposition promotes carbon loss from peat bogs

“…However, Sphagnum productivity has only been shown to respond positively to atmospheric N deposition until a critical threshold of Ϸ1 g of N⅐m Ϫ2 ⅐yr Ϫ1 , beyond which productivity is reported to decrease (30,(33)(34)(35). Moreover, increased N deposition may also give a competitive advantage to vascular plants (30,36) whose litter is more easily decomposed (37). However, as Sphagnum remains the dominant peat-building component of European bogs, our findings indicate that high chronic N additions have the potential to promote peatland C release in gaseous and aqueous forms.…”

Linking habitat modification to catastrophic shifts and vegetation patterns in bogs

“…The pivotal environmental variables determining growth of Sphagnum and vascular plants in bogs are temperature, light availability, nutrient availability, pH, and the level of the water table (Malmer 1962;Clymo 1970;Ivanov 1981;Clymo and Hayward 1982;Ingram 1983;Hayward and Clymo 1983;Backéus 1985;Rydin and McDonald 1985;Wallén et al 1988;Økland 1990;Alexandrov and Logofet 1994;Belyea 1996;Gunnarsson and Rydin 1998;Frankl and Schmeidl 2000;Limpens et al 2003;Nungesser 2003). The physiological characteristics of both Sphagnum and vascular plants drive ecosystem processes that change the pivotal environmental variables of bog ecosystems in a way that favors their own functional group, but disfavors the other functional group (Fig.…”