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

Abstract

Xylem sap flux density (<em>Fd</em>) was measured, on a 43-year-old (mature) and three 4-year-old (young) mango (<em>Mangifera indica </em>L.) trees, using Granier-type probes. The relative influences of environmental variables were examined under well-watered condition. Circumferential variation in <em>Fd</em> 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 (<em>Rs</em>) by 30 min and led vapour pressure deficit (<em>De</em>) also by 30 min in the young trees whereas <em>Fd</em> lagged <em>Rs</em> by 60 min in the mature tree. However, the canopy of mature tree seems better coupled with the diurnal course of <em>De</em> as time lag between the paired series was zero. Maximum <em>Fd</em> occurred at 1330 h in the mature tree and 1130 h in the young trees. Significant (<em>P</em><0.001) correlation was between most of the environmental factors and <em>Fd</em> for mango tree. No systematic differences in <em>Fd</em> were found between the north and other aspects (sides) of the mature tree. Instead they had close relation with each other (<em>r²></em> 0.98). However, <em>Fd</em> 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 <em>Fd</em> from south-east side was lower with about 4.4% and 1.1%, respectively, compared with <em>Fd</em> 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.