The objective of this dissertation is to clarify the role of a relatively large
Hungarian biosphere region in the carbon cycle. This is accomplished by determining
the Net Ecosystem carbon dioxide Exchange (NEE) of an active agricultural region
and a small grassland area in Hegyhátsál (western Hungary) using the
eddy covariance (EC) technique. NEE is determined as the sum of the CO
EC flux at 82 m and the rate of change of CO storage below the measuring
level for the regional scale system. NEE of the grassland is determined directly
from the carbon dioxide fluxes measured at 3 m. The temperature dependence of
nighttime ecosystem respitation and photosynthetically active photon flux density
(PPFD) dependence of daytime NEE is analyzed. The missing measurement intervals
are filled with the modified CO flux data determined from the parallel
profile measurements or with data calculated from the temperature and light
dependences. Maximum values of carbon dioxide uptake reached 1.5 mg CO m
s
(34.1 
mol m s) during summertime, and soil
decomposition resulted in net carbon dioxide loss during wintertime. The agricultural
region sequestered 134 gC m in 1997, 146 gC m in 1998,
and 92 gC m in 1999. The grassland sequestered 86 gC m
in 1999 and 247 gC m in 2000. The year-round NEE values are comparable
with results from boreal environment, temperate croplands or in some cases with
results from temperate deciduous forests. More scientific data are needed to
understand the behaviour of the ecosystem and to constrain the results.