Climate change sensitively concerns peatlands as ecosystems which represent significant stores of soil carbon globally. Differences in the carbon balance of peatlands seem to be long-term variations of carbon accumulation that appears in climate change but also it is particularly useful to study the short-term seasonal ecological function of small mires located in the frontier zone of Sphagnum-dominated peat bogs in the plains of Europe. The aim of the study is to provide a seasonal overview of functional physiological mechanisms of a unique and isolated peat moss dominated area in Hungary. Net ecosystem exchange (NEE) of carbon dioxide, Normalized Difference Vegetation Index (NDVI values), chlorophyll fluorescence parameter (Fv/Fm) of dominant Sphagnum and vascular plant species were measured seasonally in two Hungarian Sphagnum dominated mires under in situ field conditions. NEE ranged from -1.08 to -2.89 μmol m^–2 s^–1 in the spring and autumn but fell to 0.68 to –2.52 μmol m^–2 s^–1 (a negative value indicates ecosystem uptake) under higher light flux density (PPFD of 1100 μ mol m^–2 s^–1) during the summer period. NDVI values showed the highest rates in summer (between 0.756-0.882) and the lowest rates were measured in spring (between 0.426-0.612) in all investigated microhabitats. The maximal photochemical activity (Fv/Fm) of the dominated species reflected the seasonal and microclimatic adaptation; showed lower values in spring and autumn (0.505-0.847) while these parameters are characterized by higher values (0.8-0.857) in all dominated species in summer. Our study shows that functional differences can also exist within relatively small mire not only seasonally but also depending on microsites or types of plant communities. These results contribute to our understanding of dynamic changes of peatlands, mire ecosystem functioning at the edge of their distribution and predict ecosystem responses to climate change, which can be potential factors both on global carbon cycle and global change.