Nutrient input and carbon and microbial dynamics in an ombrotrophic bog

Slow rates of plant production and decomposition in ombrotrophic bogs are believed to be partially the result of low nutrient availability. To test the effect of nutrient availability on decomposition, carbon dioxide ( CO2) flux dynamics, microbial biomass, and nutrients, we added nitrogen ( N) with phosphorus ( P) and potassium ( K), to prevent limitation of the latter 2 nutrients, over 2 growing seasons to plots at Mer Bleue peatland, Ontario, Canada. After the first growing season, increasing N fertilization ( with constant P and K) decreased in vitro CO2 production potential and increased microbial biomass measured with a chloroform fumigation- extraction technique in the upper peat profile, while by the end of the second season, CO2 production potential was increased in response to N plus PK treatment, presumably due to more easily decomposable newly formed plant material. In situ CO2 fluxes measured using chamber-techniques over the second year corroborated this presumption, with greater photosynthetic CO2 uptake and ecosystem respiration ( ER) during high N plus PK treatments. The more efficient microbial community, with slower CO2 production potential and larger biomass, after the first year was characterized by larger fungal biomass measured with signature phospholipid fatty acids. The majority of N was likely quickly sequestered by the vegetation and transferred to dissolved organic forms and microbial biomass in the upper parts of the peat profile, while additional P relative to controls was distributed throughout the profile, implying that the vegetation at the site was N limited. However, in situ CO2 flux data suggested the possibility of P or NPK limitation. We hypothesize that nutrient deposition may lead to enhanced C uptake by altering the microbial community and decomposition, however this pattern disappears through subsequent changes in the vegetation and production of more readily decomposable plant tissues.