Mires and Peat (Jun 2015)
Effects of shading on relative competitive advantage of three species of Sphagnum
Abstract
(1) Sphagnum is an important genus of bryophytes holding 10–15 % of the terrestrial carbon stock. With climate change a drier surface may increase the abundance of vascular plants on peatlands, so shading of Sphagnum may increase. Here we describe growth cabinet experiments to reveal the effects of shading on interactions among mixtures of three species: S. capillifolium, S. palustre (hummock species), and S. fallax (a hollow species). We measured the six traits: growth in length, growth as increase in dry mass, side-shoot production, nitrogen and carbon proportion of the capitulum dry mass, and C:N ratio in the capitulum. (2) Shading had no effect on biomass production or side-shoot production but increased height increment in all three species. It also increased the C and N proportions of total dry mass but decreased C:N ratio in the capitula. (3) Neighbours of a different species reduced biomass and side-shoot production in the two hummock species but had no effect on the hollow species. (4) All three species showed interaction between shading and neighbour in two or more plant traits. S. fallax showed competitive advantage over S. palustre in no-shading treatments and over S. capillifolium in moderate shading treatments. In addition, under deep shading, S. fallax showed a competitive advantage over both hummock species. A clear competitive hierarchy S. fallax＞S. capillifolium＞S. palustre emerged which was consistent with the hierarchy of side-shoot production. (5) The results suggest that all the species appear to tolerate deep shade (for a few months at least). In a shaded environment, especially under deeply shaded conditions, S. fallax retains its dominance in hollow habitats (if water availability is guaranteed) by virtue of its advantage in side-shoot production. (6) If shading increases then the abundance of different Sphagnum species is likely to change.
