Since the Japanese system started to provide data in March 1999, the missing data at the beginning of the year was filled using the empirical NEE-t function. During the growing period, the empirical NEE-PPFD function was used to patch the missing daytime data. Unfortunately, there were two months during 2000 when no data was measured at all due to data acquisition failure (June and July). During this period, the empirical NEE-PPFD and NEE-t relationships were used to fill data gaps.
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Figure shows the temporal variation of daily net CO
exchange during 1999 and 2000 as a function of time. The figure is comparable
with the measured net values of the 82 m system (fig.
).
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Figure shows the temporal cycle of carbon NEE, R
and GPP for the local, 3 m system. The most striking feature of the plot compared
to fig.
is the enhanced rates of photosynthesis and ecosystem
respiration. Yearly cycles in 1999 (the only year when both measuring system
was operative) are similar both in NEE, GPP and respiration. Maximum daily NEE
sums were higher as measured by the 82 m system.
Other interesting feature is the negative NEE during November and December, 2000. This is caused by an unusual warm period which supported carbon sequestration by the small scale vegetation.
Finally, yearly sums of carbon NEE, GPP and R presented in table
. There is a huge difference between carbon NEE calculated
during 1999 and 2000. NEE measured in 1999 by the 82 m system and the 3 m system
are very close. Since there are no more years available yet to compare yearly
sums for the two systems, we may not conclude that the two systems measure the
same NEE. Further data are needed to clarify the behaviour of the local scale
during 2000.
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