Abstract

Predicting Eucalyptus plantation productivity in the face of climate change is a key challenge for intensively managed forest plantations around the world. Forest industry tree improvement and advanced silvicultural programs are charged with maximizing forest production but face challenging selection choices where Eucalyptus genotypes may be sensitive to genetic x environment interactions (GxE). Our study investigated the importance of GXE interactions by measuring the early (establishment to 2.6 years old) cumulative growth response of 30 selected genotypes of Eucalyptus giobulus, E. niter's, E. badjensis, E. stnithii, E. niter's x giobulus and E. camnieltdensis x giobulus hybrid seedlings established across contrasting water availability conditions (High vs Low Irrigation). We compared the same genotypes at a low vapor pressure deficit (VPD) and clayey soil (North site) and a high VPD sandy soil (South site) in order to evaluate the stability of these genotypes across environmental gradients and thus evaluate the importance of genetic versus environmental impacts on growth. Stand growth was evaluated at 2.6 years when leaf area index (LAI) reached canopy closure in order to estimate a growth efficiency relationship (GE) with current annual increment (CAI). As expected, irrigation increased cumulative growth and LAI for all texas, except for E. smithii at the North site. Genotypes showed large significant differences of performance within and across sites under each irrigation treatment. However, a strong relationship between North and South cumulative volume at age 2.6 years was observed for irrigated genotypes but not for non-irrigated genotypes. This suggests that a large GxE interaction may be expected under low water resource availability conditions associated with strong effects in ranking change of evaluated taxas and genotypes. Comparing taxas with at least two genotypes or more in our experiment, GE increased under High Irrigation for all taxas across sites. However, E. nitens x globules hybrids showed small differences between High vs Low Irrigation treatments GE relationships compared to E. nitens and E. globulus genotypes. Our results suggest the need for strategic allocation of genotypes to contrasting drought risk environments and the need to assess our understanding of how particular genotypes interact with water stress conditions.