Abstract:
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 ºC (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 chlo rophyll fluorescence and photosynthetic light response curves indicated that heat caused damages at photo system II and additionally resulted in lower rates of maximal photosynthesis. Temperature optima for
photosynthesis were at 31–33 ºC 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.
