PARENT SESSION
Contributed Oral Session 164: Wetland Chemistry
Friday, August 12, 8:00 AM - 11:30 AM, Meeting Room 520 C, Level 5, Palais des congrès de Montréal

Different responses of vascular plants and mosses to nutrient addition in a mire: a matter of scale?

Hotes, Stefan^*,1, ¹ The University of Tokyo, Tokyo, Japan

ABSTRACT- Nutrient availability is a major determinant of species composition and vegetation structure in wetlands. Nutrient enrichment is, therefore, an important factor driving numerous ecosystem processes including plant succession. The effects of eutrophication have been studied in particular under the aspect of anthropogenic inputs into wetland ecosystems, but there are also natural events that have the potential to increase nutrient availability. The research that is presented here was carried out as part of a study on the effects of volcanic ash deposition on mire vegetation in Hokkaido, northern Japan. A full factorial experiment with N, P and K fertilizers (25 kg/ha each) was conducted in a Carex middendorffii - Sphagnum papillosum lawn community at Sarobetsu Mire in northern Hokkaido. Each combination of nutrients was applied to 1 m² plots and replicated six times. The response of vascular plants was measured as dry weight of above-ground parts, and Sphagnum growth was determined by the "cranked wire method". Nutrient concentrations in tissues of Carex middendorffii and Sphagnum papillosum were also measured. Above-ground vascular plant biomass indicated fertilization effects and a co-limitation of phosphorus and nitrogen with a stronger response to phosphorus. Sphagnum growth, on the other hand, did not show the expected outcome. Growth rates were similar or higher in the control plots than in plots treated with fertilizer. Repeated measurements in the same plots one year after fertilization yielded similar differences between most treatments, although on a lower level. Possible reasons for this pattern are presented, including processes that work on different spatial and temporal scales. Implications for vegetation dynamics in mires and methods to study Spagnum growth are discussed.

Key words: nutrient limitation, mire, field experiment, scale effects