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Fluxes of CO2 above a plantation of Eucalyptus in southeast Brazil |
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| Authors: | Osvaldo MR Cabral John HC Gash Humberto R RochaClaire Marsden Marcos AV LigoHelber C Freitas Jonatan D TatschEduardo Gomes |
| Institution: | a Embrapa Meio Ambiente, C.P. 69, CEP 13820-000, Jaguariúna SP, Brazil b Universidade de São Paulo, R. Matão 1226 CEP 05508-090, São Paulo, SP, Brazil c Centre for Ecology and Hydrology, Wallingford OX10 8BB, United Kingdom d VU University Amsterdam, Amsterdam 1081 HV, The Netherlands e CIRAD, Persyst, UPR80, s/c UMR Eco&Sols, 2 Place Viala, Montpellier, France |
| Abstract: | Eddy-covariance measurements of net ecosystem exchange of CO2 (NEE) and estimates of gross ecosystem productivity (GEP) and ecosystem respiration (RE) were obtained in a 2-4 year old Eucalyptus plantation during two years with very different winter rainfall. In the first (drier) year the annual NEE, GEP and RE were lower than the sums in the second (normal) year, and conversely the total respiratory costs of assimilated carbon were higher in the dry year than in the normal year.Although the net primary production (NPP) in the first year was 23% lower than that of the second year, the decrease in the carbon use efficiency (CUE = NPP/GEP) was 11% and autotrophic respiration utilized more resources in the first, dry year than in the second, normal year. The time variations in NEE were followed by NPP, because in these young Eucalyptus plantations NEE is very largely dominated by NPP, and heterotrophic respiration plays only a relatively minor role.During the dry season a pronounced hysteresis was observed in the relationship between NEE and photosynthetically active radiation, and NEE fluxes were inversely proportional to humidity saturation deficit values greater than 0.8 kPa. Nighttime fluxes of CO2 during calm conditions when the friction velocity (u*) was below the threshold (0.25 m s−1) were estimated based on a Q10 temperature-dependence relationship adjusted separately for different classes of soil moisture content, which regulated the temperature sensitivity of ecosystem respiration. |
| Keywords: | CO2 fluxes Eddy covariance Eucalyptus plantation Ecosystem respiration Water deficit |
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