Direct and interaction-mediated effects of environmental changes on peatland bryophytes

Abstract

Ecosystem processes of northern peatlands are largely governed by the vitality and species composition in the bryophyte layer, and may be affected by global warming and eutrophication. In a factorial experiment in northeast China, we tested the effects of raised levels of nitrogen (0, 1 and 2 g m(-2) year(-1)), phosphorus (0, 0.1 and 0.2 g m(-2) year(-1)) and temperature (ambient and +3°C) on Polytrichum strictum, Sphagnum magellanicum and S. palustre, to see if the effects could be altered by inter-specific interactions. In all species, growth declined with nitrogen addition and increased with phosphorus addition, but only P. strictum responded to raised temperature with increased production of side-shoots (branching). In Sphagnum, growth and branching changed in the same direction, but in Polytrichum, the two responses were uncoupled: with nitrogen addition there was a decrease in growth (smaller than in Sphagnum) but an increase in branching; with phosphorus addition growth increased but branching was unaffected. There were no two-way interactions among the P, N and T treatments. With increasing temperature, our results indicate that S. palustre should decrease relative to P. strictum (Polytrichum increased its branching and had a negative neighbor effect on S. palustre). With a slight increase in phosphorus availability, the increase in length growth and production of side-shoots in P. strictum and S. magellanicum may give them a competitive superiority over S. palustre. The negative response in Sphagnum to nitrogen could favor the expansion of vascular plants, but P. strictum may endure thanks to its increased branching.

Performance of four mosses in a reciprocal transplant experiment: implications for peatland succession in NE China

“…Like S. fuscum, P. strictum did not show any habitat effect on the three measures of growth. Given its strong competitive advantage in the former study (Bu et al, 2011), and its negative effect on growth of S. palustre and S. magellanicum in this study, P. strictum could be classified as a stress tolerant competitor (Grime et al, 1990). This could be the reason why it can be a pioneer plant in peatland restoration (Groeneveld et al, 2007).…”

“…This could explain why P. strictum showed the highest vigour in the S. fuscum habitat which has the most compact colonies and a good water holding-ability, and also why the performance of S. fuscum was independent of habitat. Given the excellent health of the non-transplanted shoots, the low vigour levels of the transplanted P. strictum may result from physiological damage by transplanting in the dry early summer in the Changbai Mountains; it grew well in a transplant experiment started nearly two months later in the season (Bu et al, 2011). Niche segregation of peatland mosses in ecological gradients such as pH or HWT may relate to their life history strategy.…”

“…This could be the reason why it can be a pioneer plant in peatland restoration (Groeneveld et al, 2007). Low vigour levels and a negative habitat effect when transplanted to P. strictum hummocks indicate a weaker competitive ability in both S. palustre and S. magellanicum (Bu et al, 2011). S. magellanicum, however, grew best in S. palustre habitat with high vigour levels and biomass production, indicating its competitive superiority over S. palustre (cf.…”

“…Our previous experiments showed that phosphorus addition increased growth and branching of Sphagnum but had no effect on side-shoot production in P. strictum (Bu et al, 2011). Rich base cation concentration in water suppresses Sphagnum subnitens Russ.…”

“…Additionally, many peatlands without strong anthropogenic disturbance have a reduced density and growth of Sphagnum and an increase of other mosses such as P. strictum (Lang et al, 1999;Bu et al, 2005). The ecological amplitude and interactions of these other species with Sphagnum need to be thoroughly studied (Kooijman and Bakker 1995;Mulligan & Gignac, 2001Bu et al, 2011), since their expansion will alter the ecosystem functions of peatlands (Mitchell et al, 2002).…”