Implications of CO2 pooling on ?13C of ecosystem respiration and leaves in Amazonian forest
Résumé
The carbon isotope of a leaf (?13Cleaf) is generally more negative in riparian zones than in areas with low soil moisture content or rainfall input. In Central Amazonia, the small-scale topography is composed of plateaus and valleys, with plateaus generally being drier than the valley edges in the dry season. The nocturnal accumulation of CO2 is higher in the valleys than on the plateaus in the dry season. The CO2 stored in the valleys takes longer to be released than that on the plateaus, and sometimes the atmospheric CO2 concentration (ca) does not drop to the same level as on the plateaus at any time during the day. Samples of sunlit leaves and atmospheric air were collected along a topographical gradient to test whether the ?13Cleaf of sunlit leaves and the carbon isotope ratio of ecosystem respired CO2 (?13CR) may be more negative in the valley than those on the plateau.
The ?13Cleaf was significantly more negative in the valley than on the plateau. Factors considered to be driving the observed variability in ?13Cleaf were: leaf nitrogen concentration, leaf mass per unit area (LMA), soil moisture availability, more negative carbon isotope ratio of atmospheric CO2 (?13Ca) in the valleys during daytime hours, and leaf discrimination (?leaf). The observed pattern of ?13Cleaf suggests that water-use efficiency (WUE) may be higher on the plateaus than in the valleys. The ;13CR was more negative in the valleys than on the plateaus on some nights, whereas in others it was not. It is likely that lateral drainage of CO2 enriched in 13C from upslope areas might have happened when the nights were less stable. Biotic factors such as soil CO2 efflux (Rsoil) and the responses of plants to environmental variables such as vapor pressure deficit (D) may also play a role.
The ?13Cleaf was significantly more negative in the valley than on the plateau. Factors considered to be driving the observed variability in ?13Cleaf were: leaf nitrogen concentration, leaf mass per unit area (LMA), soil moisture availability, more negative carbon isotope ratio of atmospheric CO2 (?13Ca) in the valleys during daytime hours, and leaf discrimination (?leaf). The observed pattern of ?13Cleaf suggests that water-use efficiency (WUE) may be higher on the plateaus than in the valleys. The ;13CR was more negative in the valleys than on the plateaus on some nights, whereas in others it was not. It is likely that lateral drainage of CO2 enriched in 13C from upslope areas might have happened when the nights were less stable. Biotic factors such as soil CO2 efflux (Rsoil) and the responses of plants to environmental variables such as vapor pressure deficit (D) may also play a role.
Origine : Accord explicite pour ce dépôt
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