Limited effects of six years of fertilization on carbon mineralization dynamics in a Minnesota fen

Peatlands, including fens, are important ecosystems in the context of the global carbon cycle. Future climate change and other anthropogenic activities are likely to increase nutrient loading in many peatland ecosystems and a better understanding of the effects of these nutrients on peatland carbon cycling is necessary. We investigated the effects of six years of nitrogen and phosphorus fertilization, along with liming, on carbon mineralization dynamics in an intermediate fen in northern Minnesota. Specifically, we measured CO2 and CH4 emission from intact peat cores, as well as CH4 production and CH4 consumption at multiple depths in short-term laboratory incubations. Despite increased nitrogen and phosphorus availability in the upper 5 cm of peat, increased pH, and clear shifts in the vegetation community, fertilization and liming had limited effects on microbial carbon cycling in this fen. Liming reduced the net flux of CO2 approximately 3-fold compared to the control treatment, but liming had no effect on CH4 emissions from intact cores. There were no nutrient effects on CO2 or CH4 emissions from intact cores. In all treatments, rates of CH4 production increased with depth and rates of CH4 consumption were highest near the in situ water-table level. However, nutrient and liming had no effect on rates of CH4 production or CH4 consumption at any depth. Our results suggest that over at least the intermediate term, the microbial communities responsible for soil carbon cycling in this peatland are tolerant to wide ranges of nutrient concentrations and pH levels and may be relatively insensitive to future anthropogenic nutrient stress.