Abstract: Climate change poses a significant threat to agricultural production in the tropics, yet
relatively little research has been carried out to understand its impact on mature tropical tree
crops. This research aims to understand the genotypic variation in growth and photosynthesis
in mature cacao trees in response to elevated CO2 and water deficit. Six genotypes were grown
under greenhouse conditions at ambient (ca. 437 ppm) and elevated CO2 (ca. 724 ppm) and under
well-watered and water deficit conditions for 23 months. Leaf- and canopy-level photosynthesis,
water-use efficiency, and vegetative growth increased significantly in response to elevated CO2. Water
deficit had a significant negative effect on many photosynthetic parameters and significantly reduced
biomass production. The negative effect of water deficit on quantum efficiency was alleviated
by elevated CO2. Genotypic variation was observed in several parameters including stomatal
conductance, stomatal density and index, quantum efficiency, and biomass production, indicating
the potential to develop more climate-change-resilient genotypes that can cope with predicted future
climate change conditions. Elevated CO2 reduced some of the negative effects of water deficit through
changes in water-use efficiency and light utilisation and reduced the negative impact of water deficit
on biomass accumulation, but this was genotype-specific.
Black, Emily, Ewan Pinnington, Caroline Wainwright, Fiona M Lahive, Tristan Quaife, Richard P. Allan, Peter Cook, Andrew Daymond, Paul Hadley, Patrick CMcGuire, Anne Verhoef and Pier Luigi Vidale