Differential leaf gas exchange responses to salinity and drought in the mangrove tree Avicecennia germinans (Avicenniaceae)

Abstract

Leaf gas exchange was assessed in Avicennia germinans L. grown under different NaCl concentrations (0-40‰), after salt-relief, and then during drought. Stomatal conductance (gs) and net photosynthetic rate (Pn) decreased with increasing NaCl concentration, and intrinsic water use efficiency (Pn/gs) increased. Under desalinization Pn/gsdeclined. Thus, gsdid not change in plants grown at low NaCl concentration (10‰), but increased up to 30-32% at higher NaCl concentration (20-40‰). However, Pnwas only slightly enhanced (10-15%). Under drought, Pndecreased by as much as 46% in plants grown at low NaCl concentration (10‰) and by 22% at high NaCl concentration (40‰). Thus, Pn/gsdecreased and water use efficiency was lower during drought compared to estimates prior to salt-relief.