Influence of environmental factors on the sap flux density of mango trees under rain-fed cropping systems in West Africa

Xylem sap flux density (Fd) was measured, on a 43-year-old (mature) and three 4-year-old (young) mango (Mangifera indica L.) trees, using Granier-type probes. The relative influences of environmental variables were examined under well-watered condition. Circumferential variation in Fd was also investigated by placing sensors on the north, south-west and south-east sides of the mature tree. Sap flux density lagged solar radiation (Rs) by 30 min and led vapour pressure deficit (De) also by 30 min in the young trees whereas Fd lagged Rs by 60 min in the mature tree. However, the canopy of mature tree seems better coupled with the diurnal course of De as time lag between the paired series was zero. Maximum Fd occurred at 1330 h in the mature tree and 1130 h in the young trees. Significant (P 0.98). However, Fd from the south-west side of the 43-year-old tree was 4.2% and 18.3% higher on a typically bright and partially clouded days while Fd from south-east side was lower with about 4.4% and 1.1%, respectively, compared with Fd on the north. This indicates the possibility of transpiration enhancement in response to wind advection from the nearby village in the south-west direction. Identification of the relative influence of these environmental factors on sap flow may provide basis for an in-depth analysis of the control of transpiration in rain-fed mango trees both under plantation and agroforestry systems in West Africa.