Relationship between Ecosystem Carbon Fluxes and Canopy Radiometric Temperature Using Infrared Thermometry in a Ryegrass Ecosystem

Using the closed chamber technique daily changes of net ecosystem carbon dioxide (CO
₂
) exchange (NEE) and ecosystem respiration (R
_e
) were determined in a ryegrass ecosystem on eight separated days at half hour interval from morning to afternoon in Taiyuan basin, Shanxi province of China. The gross primary production (GPP) was calculated as the difference of NEE and R
_e
. The objective of the study was to examine the relationship between ecosystem C fluxes and canopy temperature (T
_c
), air temperature (T
_a
) and soil temperature (T
_s
), and finally to explore the possibility that T
_c
could substitute T
_a
or T
_s
for estimate of ecosystem carbon fluxes. The results showed on diurnal scales that the coefficients of determination of both NEE and GPP with T
_c
were significantly higher than those of the GPP and NEE with T
_a
, and that the R
_e
was also closely related with both T
_a
and T
_c
on all measurement dates, but that significant correlation of R
_e
with T
_s
existed only on 7 out of 8 measurement dates. The determination coefficients between R
_e
and T
_s
were lower than those between R
_e
and both T
_a
and T
_c
on diurnal scales. These results suggested that at plot scale T
_c
also is a good factor for ecosystem carbon fluxes estimate as both T
_a
and T
_s
factors. This gives some implications for linking remotely sensed infrared temperature of canopy to ecosystem carbon flux estimate. However, further experiments at ecosystem scale are still needed.