Estimating the canopy architecture and photosynthesis of coffea Arabica L. Plants cultivated under long-term elevated air CO2 concentration

Climate forecasts suggest that [CO
₂
] in the atmosphere will continue to increase, stimulated by anthropogenic actions. Artificial facilities are available to study the physiological responses of plants to high air [CO
₂
], such as Free-Air-CO
₂
-Enrichment (FACE) systems. The structural and ecophysiological responses to elevated air [CO
₂
] in tree species are contradictory, due to species-dependent responses and relatively short-term experiments. After long-term cultivation (four years) under elevated air [CO
₂
], we studied structural and photosynthetic acclimation of Arabica coffee trees (Coffea Arabica L.), with significant changes in leaf area along the vertical profile, number of metamers, leaf and whole-plant photosynthesis. We evaluated the responses of plant leaf area, total number of metamers, leaf and whole-plant photosynthesis along the plant vertical profile to elevated air [CO
₂
], trying to reveal the acclimation of both plant structure and photosynthesis and its relevance for overall photoassimilate production during the reduced growth period. Coffee plants were grown under two [CO
₂
] conditions since transplantation of coffee seedlings to the field: actual (~390 μL CO
₂
L
^-1
) and elevated (actual + ~200 μL CO
₂
L
^-1
). Plants were codified following the VPlants methodology and computational modules of CoffePlant3D software, to obtain coffee mock-ups. The plants were separated in three 50 cm-thick layers in vertical profile. Leaf photosynthetic light response curves were determined under actual and elevated air [CO
₂
]. Under elevated air [CO
₂
]: 1) the tree leaf area was strongly reduced and this was associated with the occurrence of coffee leaf rust disease, significantly diminishing the area of the lowest and the upper plant layers; 2) leaf photosynthesis presented decreases in light compensation point and increases in the light-saturated photosynthetic rate; 3) the leaf scale photosynthesis was increased about three to four folds in the middle and upper plant layers and slightly in the lowest plant layer; and 4) the negative impact of leaf area reduction was mitigated by high whole-plant photosynthesis during the dry tropical winter conditions. The possible response pattern of Arabica coffee plants growth under the complex scenarios of long term elevated air [CO
₂
] integrated structural and functional modifications and mitigated the negative impacts of leaf loss and winter water deficit through the leaf and whole-plant photosynthesis. So, after four years under FACE conditions, Arabica coffee trees are still responsive to elevated air [CO
₂
] at leaf or plant scales.