This paper aimed to study the effect of diurnal and seasonal variation of the environmental factors on the sap flow density (SFD) and leaf water potential (Ψl) in the east and west side of the canopy of 'Valencia' sweet orange trees under field conditions, with no irrigation system. Were evaluated three plants, whose planting rows were north-south oriented. The evaluations were performed during one day in each season of the year: summer, autumn, winter and spring. The values of water potential measured at predawn ranged from -0,31 MPa, in the day 12/10/05, to -1,1 MPa, in the day 08/30/05, however there was no significant difference between the east and west sides of the canopy. At the afternoon, leaves at the west side showed smaller (p<0,05) water potential than the ones at east position, with values varying between -0,95 (12/10/05) and -1,89 MPa (08/30/05). The largest air evaporative demand that is verified at afternoon induces to a larger water deficit in the west side of the canopy independent of the time of the year and, in consequence, larger SFD in well-watered plants under conditions of days completely sunny. Under water deficit conditions (low values of Ψl), the west side of the plants is more sensible to that condition, showing reduction of SFD.
Citrus sinensis; stem heat balance method; transpiration
