Journal Article

Responses of Vegetation and Ecosystem CO sub(2) Exchange to 9Years of Nutrient Addition at Mer Bleue Bog

Moore, Tim R, Juutinen, Sari, Bubier, Jill L

2010

Overview

Anthropogenic nitrogen (N) loading has the potential to affect plant community structure and function, and the carbon dioxide (CO sub(2)) sink of peatlands. Our aim is to study how vegetation changes, induced by nutrient input, affect the CO sub(2) exchange of a nutrient-limited bog. We conducted 9- and 4-year fertilization experiments at Mer Bleue bog, where we applied N addition levels of 1.6, 3.2, and 6.4gNm super(-2) super(-1), upon a background deposition of about 0.8gNm super(-2)a super(-1), with or without phosphorus and potassium (PK). Only the treatments 3.2 and 6.4gNm super(-2)a super(-1) with PK significantly affected CO sub(2) fluxes. These treatments shifted the Sphagnum moss and dwarf shrub community to taller dwarf shrub thickets without moss, and the CO sub(2) responses depended on the phase of vegetation transition. Overall, compared to the large observed changes in the vegetation, the changes in CO sub(2) fluxes were small. Following Sphagnum loss after 5years, maximum ecosystem photosynthesis (Pg sub(max)) and net CO sub(2) exchange (NEE sub(max)) were lowered (-19 and -46%, respectively) in the highest NPK treatment. In the following years, while shrub height increased, the vascular foliar biomass did not fully compensate for the loss of moss biomass; yet, by year 8 there were no significant differences in Pg sub(max) and NEE sub(max) between the nutrient and the control treatments. At the same time, an increase (24-32%) in ecosystem respiration (ER) became evident. Trends in the N-only experiment resembled those in the older NPK experiment by the fourth year. The increasing ER with increasing vascular plant and decreasing Sphagnum moss biomass across the experimental plots suggest that high N deposition may lessen the CO sub(2) sink of a bog.

• Subject: Sphagnum