Effect of chilling on CO2 gas-exchange in Carica papaya L and Carica quercifolia (A St Hil) Solms

The CO2 gas exchange of Carica papaya and C. quercifolia was studied under different chilling treatments. after 4 d in a low temperature regime (15 degrees C day/5 degrees C night) photosynthesis reduction was more pronounced in C. papaya (15 % of control ar 25/15 degrees C) than in C. quercifolia (42 % of control). Stomatal conductance reduction was similar in both species (25-30 % of the control), indicating that CO2 fixation was more affected in C. papaya, which showed higher intercellular CO2 levels under stress. Photosynthesis versus intercellular CO2-response curves under non stressing conditions were very similar in both species, but differed significantly after 4 d in the 15/5 degrees C regime. Under these conditions, gas-phase and mesophyll resistances increased 300 % or more in C. papaya leaves. C. quercifolia exhibited a similar increase in gasphase resistance, bur mesophyll resistance increased only 80 %. The photosynthetic apparatus of C. papaya revealed no capacity to acclimate to low temperatures and a slow recovery after chilling. On the contrary, C. quercifolia apparatus was capable of fast recovery and is able to acclimate and function normally in low temperature regimes.