Daily sap flow rate as an indicator of drought avoidance mechanisms in five Mediterranean perennial species in semi-arid southeastern Spain

Abstract

Daily sap flow rate was determined in five Mediterranean species (Pinus halepensis, Quercus coccifera, Pistacia lentiscus, Erica multiflora, and Stipa tenacissima) under two slope aspects (north- and south-facing) in a semi-arid area (Alicante, SE Spain). Sap flow velocity was measured in January, May, August and October of two consecutive years (1998 and 1999) using the stem heat balance (SHB) method. Our results have demonstrated the effects of global radiation (R g), vapour pressure deficit (VPD) on the sap flow velocity per unit of leaf area. Mean daily sap flow rates (Q md) showed values between 0.001 and 0.202 g H2O cm−2 leaf area day−1. Q md values were higher on the south-facing slope than on the north-facing slope. In most species, the Q md was higher in 1998 than in 1999 due to the higher soil water content, temperature and VPD in 1998. In all five species, a decrease in predawn leaf water potential was accompanied by a decrease in mean daily sap flow rates; nevertheless, the responses of the five species to water deficit conditions were different. In this context, we have linked the drought avoidance mechanisms of the different species through the combined use of daily sap flow rate and predawn leaf water potential under different water deficit conditions. We conclude that Pinus halepensis, Pistacia lentiscus and Erica multiflora show water-savers mechanisms to cope with drought, while Quercus coccifera and Stipa tenacissima show water-spenders mechanisms.