Differential photosynthetic and survival responses to soil drought in two evergreen Nothofagus species

Abstract

We asked if differences in distribution between Nothofagus nitida and N. dombeyi were associated with differences in drought tolerance. Survival, gas exchange and chlorophyll fluorescence were measured on seedlings subjected to a gradual drought. At a predawn leaf water potential (ψm) of 2.7 MPa, survival of N. nitida was 50%, compared to 100% in N. dombeyi. Under well-watered conditions, the two species displayed similar stomatal conductance (gw) and transpiration (E), but net photosynthesis (A) and instantaneous water-use efficiency (WUEi) were slightly higher in N. nitida. A, E and gw declined in N. nitida along the gradual drought but increased in N. dombeyi at a ψm between 1.5 and 2.5 MPa, and declined then drastically at a ψm below