Title: The effect of hydrology and temperature on the competition between Sphagnum species in Raised Bogs

Primary Researcher: Bjorn Robroek
Email address: b.j.m.robroek@uu.nl
Submitted on: May 22, 2003

Start date: 01 May 2003
End date: 30 April 2007

Introduction:

Sphagnum species are the key species in the ecology of raised bog systems. They have an impact on the hydrochemistry of the bog system by their capacity to exchange cations for hydrogen ions. They regulate the hydrological conditions at the bog surface to a high extent. Their morphology and their growth form in dense carpets or lawns provide a large number of intracellular and extracellular spaces which result in a high waterholding capacity of the moss layer in bogs (Clymo, 1983). Recent studies have shown that the living peatmoss layer together with the top peat layer consisting of poorly decomposed Sphagnum remains - the so-called acrotelm - play a crucial role in the overall hydrology of raised bog systems (van der Schaaf, 1999: van der Schaaf, in press).

Raised bogs usually show a microtopographical variation in pools, hollows, lawns and hummocks. Different Sphagnum species occupy the different microtopographical niches. Species such as Sphagnum cuspidatum and S. auriculatum are more or less restricted to the pools; S. capillifolium and S. imbricatum can form hummocks of more than 0.5 m in height; S. papillosum, S. magellanicum and S. fuscum take intermediate positions.

Palaeobotanical records show that the contribution of each species to the overall Sphagnum cover of a bog can change in time as a response to the changes in climatic conditions (e.g. Middeldorp, 1986; Svensson, 1988; van der Molen & Hoekstra, 1989; Mauquoi et al., 2001). Relatively dry periods favour the hummock species; in wetter periods the pool and hollow species tend to dominate. Studies in Irish raised bog systems have shown that recent changes in the bog's surface hydrology as a result of drainage and burning have led to changes in the relative cover of the different Sphagnum species (Kelly et al., 1995). Changes in the species composition of the moss layer in bogs can also result from increased N-deposition (e.g. Press et al., 1986: Lütke Twenhöven, 1992a).

Considerable research has been carried out into the habitat conditions of Sphagnum species and there is a good knowledge of hydrological and trophic regimes at which the different species usually occur (e.g. Kelly, 1993; Aggenbach & Jalink, 1998). However, this information is not sufficient to accurately interpret past changes in the species composition of the moss layer in response to changes in hydrological or trophic conditions or to predict future responses to such changes. A good understanding of the way in which the different species compete for water and nutrients is also required.

Sphagnum species have - to a varying degree - the capacity to influence their environment. Certain morphological features and specific growth form characteristics enable peatmosses in different degrees to influence the rate of evapotranspiration (Clymo, 1983; Clymo & Hayward, 1982). Studies presently carried out at Wageningen University indicate that the different species furthermore show a variation in uptake of nutrients and abilities to transport nutrients to the capitulum. This variation in morphology and physiology has a bearing on the competitive ability of the different species.

Some research has been conducted with respect to competition between Sphagnum species (Luken, 1985; Rydin, 1987; Lütke Twenhöven, 1992b; Rydin, 1993a, b) but no systematic study has been carried out involving all the important species of raised bogs and comprehending both competition for water and for nutrients.

This project will study the competition between Sphagnum cuspidatum, S. papillosum, S. magellanicum, S. capillifolium, S. fuscum, S. imbricatum and S. recurvum. (the prominent species of European raised bogs) under different hydrological conditions and at different trophic levels. We will investigate how changes in these environmental factors will affect the performance of the different species and which morphological and/or physiological features of the plants have a bearing on their competitive abilities. Experiments will be carried out both under controlled conditions in the glasshouse and in the field.

There are indications that temperatures of more than 20 degrees during the growth season negatively affect at least some of the species (Streefkerk & Casparie, 1989; Schouten et al., 1992; Heijmans, 2000). It is not clear whether this is due to increased evaporation pressure or to susceptibility to high temperatures. Therefore, controlled experiments will also be carried out at different temperatures. The outcome is of importance for the assessment of the effect of climatic change on the vegetation of raised bogs.

Aim:

The objective of this project is to determine the competetive performance of the most important Sphagnum species of raised bogs under different hydrological and conditions and different (micro-)temperature zones. Mixes of species will be grown in greenhouse experiments under controlled conditions and transplantation experiments will be carried out in bogs in Ireland and Estonia (which represent a gradient from oceanic influenced climate to a more land influenced climate).

Research:

In the proposed study we will attempt to answer the following questions:

1. What is the competitive performance of the most important Sphagnum species of European raised bogs at different hydrological and trophic conditions? How do changes in these conditions affect the species composition of the bog`s moss layer?

2. What morphological and/or physiological features in the moss plant play a role in competition (morphological features, growth form: horizontal extension or lateral branching, differences in capacity to form extracellular capillary pathways, allotoxines)?

3. Does the sociability with which the species occur in the moss layer affect the competitive strength?

4. How and why do changes in temperature during the growth season affect the performance of the different species?

Web page

http://www.dow.wau.nl/natcons/NP/Start.htm

External funding

Yes

External Funding Sponsors

Staatsbosbeheer (State Forestry Service)