Resumo

RADA, F. et al. Water relations and gas exchange in Theobroma cacao var. Guasare under periods of water deficit. Rev. Fac. Agron. [online]. 2005, vol.22, n.2, pp.112-120. ISSN 0378-7818.

Water relations and gas exchange of Theobroma cacao var. Guasare under periods of water deficit were evaluated. Microclimatic characteristics (air temperature, relative humidity and photosynthetically active radiation), leaf gas exchange (stomatal conductance, transpiration and CO₂ assimilation rates) and leaf water potential were measured throughout the day in plants subjected to 3, 12 and 25 days without water. Pressure-volume curves were used to determine osmotic potential at turgor loss. A significant decrease in stomatal conductance was observed as water stress increased. As a consequence, gas exchange characteristics were also affected. An evident osmotic adjustment was recorded in plants subjected to 3 and 12 days without water, while no additional adjustment occurred 25 days later. Water use efficiency increased as water availability decreased. CO₂ assimilation rates decreased 25% in severely stressed plants, while water loss was reduced in 39% indicating that stomatal closure affects water loss to a greater degree.

Palavras-chave : criollo type; water stress; CO₂ assimilation; stomatal conductance; osmotic adjustment.