Limited effects of shade on physiological performances of cocoa (Theobroma cacao L.) under elevated temperature

Mensah Eric Opoku, Asare Richard, Vaast Philippe, Amoatey Christiana A., Markussen Bo, Owusu Kwadwo, Asitoakor Bismark Kwesi, Ræbild Anders. 2022. Limited effects of shade on physiological performances of cocoa (Theobroma cacao L.) under elevated temperature. Environmental and Experimental Botany, 201 : p. 104983.

Résumé : Shade is one of the recommended management solutions to mitigate the effects of heat stress, which is a major challenge for cocoa production globally. Nevertheless, there are limited studies to verify this hypothesis. Here, we evaluate the effects of heat and shade on cocoa physiology using experimental plots with six-month old potted seedlings in a randomized complete block design. Infrared heaters were applied for one month to increase leaf temperatures by an average of 5–7 °C (heat treatment) compared with no heat (unheated treatments), and shaded plants were placed under a shade net removing 60% of the light compared with no shade (sun treatments). Plants under heat treatments in sun and in shade showed severe reduction in photosynthesis. Measurements of chlorophyll fluorescence and photosynthetic light response curves indicated that heat caused damages at photosystem II and additionally resulted in lower rates of maximal photosynthesis. Temperature optima for photosynthesis were at 31–33 °C with only small differences between treatments, and as light saturation was reached at low PAR levels of 325 – 380 μmol m-2 s-1 in shade and 427 – 521 μmol m-2 s-1 in sun, ambient rates of photosynthesis were comparable between sun and shade treatments. Heat treatments resulted in decreased concentrations of chlorophyll and changed pigment composition, reduced specific leaf areas, and plant biomass. While shade may benefit cocoa seedlings, our results indicate that the positive effects may not be sufficient to counteract the negative effects of increased temperatures on cocoa physiology.

Mots-clés Agrovoc : Theobroma cacao, photosynthèse, ombrage, expérimentation en pot, traitement thermique, température, thermogénèse, biomasse, Coffea arabica, surface foliaire, stress thermique, fluorescence, agroforesterie, altitude

Mots-clés libres : Cocoa, Shade, Heat, Climate, Photosynthesis, Chlorophyll fluorescence

Agences de financement hors UE : Ministry of Foreign Affairs of Denmark

Projets sur financement : (DNK) Climate Smart Cocoa Systems for Ghana

Auteurs et affiliations

• Mensah Eric Opoku, University of Ghana (GHA) - auteur correspondant
• Asare Richard, IITA (GHA)
• Vaast Philippe, CIRAD-DGDRS (COL)
• Amoatey Christiana A., University of Ghana (GHA)
• Markussen Bo, UCPH (DNK)
• Owusu Kwadwo, University of Ghana (GHA)
• Asitoakor Bismark Kwesi, University of Ghana (GHA)
• Ræbild Anders, UCPH (DNK)

Source : Cirad-Agritrop (https://agritrop.cirad.fr/606429/)

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