S12 - Session O1 - Relationship between daily intercepted radiation and tree transpiration in pear

Authors: Inigo Auzmendi *, Merce Mata, Jesus del Campo, Gerardo Lopez, Joan Girona, Jordi Marsal

Intercepted radiation can be used as a basis for scheduling irrigation in some fruit tree species. For example, daily transpiration (T d ) was linearly related to daily intercepted photosynthetically active radiation (IPAR d ) in apple canopies. The T d /IPAR d ratio, termed transpiratory radiation use efficiency (TRUE), was relatively constant before harvest. Therefore, intercepted radiation and a constant TRUE can be used to estimate the amount of water required for irrigation in apple trees before harvest, serving as a basis for automating irrigation with light sensors. This can improve the efficiency of water use, which is becoming a paramount factor to maintain productivity and sustainability in some world areas, such as the Mediterranean region and some parts of Australia. Having said that, it is not known yet whether TRUE is also constant for other fruit tree species. For example, whole pear tree transpiration data are scarce, and there are not many works that point out a constant TRUE for this species. To test this hypothesis, we measured whole-day values of intercepted radiation and transpiration in 'Conference' pear trees growing in a large weighing lysimeter 13 times over the season in Mediterranean conditions. Effect of vapour pressure deficit (VPD) on TRUE was also considered. Before harvest T d correlated linearly with IPAR d , as was observed in apple and in a pear study in Australia. However, our work showed that TRUE was not constant within the season. It increased from spring to midsummer and decreased afterwards, while TRUE was linearly correlated with daily mean VPD. In conclusion, intercepted radiation and a constant TRUE alone are not considered adequate as a basis for irrigation scheduling in 'Conference' pears grown in Mediterranean conditions.