Gas-exchange response and survival of young Eucalyptus spp commercial genotypes under water stress

Abstract

In the last decades, breeding programs for Eucalyptus species in Chile have mainly focused on increasing productivity and adaptation. However, little is known about how droughts and climate change may influence physiological responses that determine tree growth. Evaluating leaf-level physiology may be important to predict survival of eucalyptus genotypes under severe water stress. This study assessed net photosynthesis (A_N), stomatal conductance (g_s), transpiration (E) and instantaneous water use efficiency (WUE_i) in Eucalyptus globulus, E. nitens, E. badjensis, E. smithii and E. globulus x E. nitens and E. camaldulensis x E. globulus hybrids genotypes under increasing water stress conditions. Survival of each genotype was related to the observed physiological responses at -0.03 MPa, -1.5 MPa and -2.5 MPa soil water potentials. Higher plant survival was observed on genotypes with reduced water loss due to stomatal adjustment under water deficit, and on genotypes that could maintain initial photosynthetic rates under increased
water deficit despite reductions in stomatal conductance. A negative relationship between plant survival and gas-exchange parameters suggests that photosynthesis rate, under high water availability (-0.03 MPa) and moderate water deficit (-1.5 MPa), may be a useful indicator for early selection of genotypes at sites under water limitations.