Water relations in almond trees under moderate water deficits

Abstract

The responses of almond trees 'Guara' to different levels of water deficits were investigated. Three irrigation treatments as well as a rainfed treatment were applied in the field to 5-year-old trees during the summer of 2013. Plant water status was monitored by measurement of stem water potential at midday (Ψx), leaf gas-exchange was measured with a photosynthesis analyzer (IRGA) and stomatal conductance with a steady-state leaf porometer. Ψx of well-watered trees was near -0.9 MPa and always higher than -1.0 MPa. In the case of trees irrigated with amounts of water below full crop requirements, Ψx decreased down to -1.5 MPa, and simultaneously, a gradual decrease in stomatal conductance was observed. The close correlation between stomatal conductance (gs) and CO2 assimilation (A) pointed toward the stomatal limitation of CO2 assimilation in almond. Then although the stomatal closure will reduce photosynthesis, the fact that that closure occurs gradually as stress progresses will permit some rate of CO2 assimilation by the plant. The value of -1.0 MPa could be considered a reference threshold in full irrigation programming to ensure maximum stomatal conductance of 'Guara' almond trees. That high value showed the sensibility of this cultivar to water stress.