Growth and Physiological Parameters of Cacao Influenced by Soil Moisture, and Photosynthetic Photon Flux Density.

Cacao (Theobroma cacao) is  native to the under-story of the evergreen rain forest of the Amazon basin. Growth, development  and physiological processes of cacao grown under agroforestry systems are largely influenced by the level of photosynthetic photon flux density (PPFD) received at the canopy level and the status of  soil moisture. However  influence of these environmental variables on growth and physiological traits of cacao have not  been fully explored.  Climatically controlled greenhouse was adapted to evaluate the effects of levels of PPFD and soil  moisture content on growth and physiological traits  of cacao. At all the levels of soil moisture, reduction of PPFD from 500 µmol m^-2s^-1 (adequate) to 200 µmol m^-2s^-1 (high shade) reduced the growth (biomass accumulation of shoot and root, root length) and physiological traits (total transpirations water use efficiency, net assimilation rates and net photosynthesis). Reduction of soil moisture potentials from 33 to 100 kPa reduced growth and physiological traits and further increase of soil moisture potentials to 300 kPa slightly increased these parameters but further increase in soil moisture potential reduced all the growth and physiological traits. Cacao appears to be very sensitive to high shade (low PPFD) and low soil moisture (high moisture potentials),