Changes in leaf physiology for eucalyptus genotypes with increase in integral water stress and its consequence for initial growth in central Chile

Limited information exists on how small changes in soil water affect the physiological responses of eucalyptus and their relationship with productivity. This experiment evaluated physiological traits during decreased soil water and compared them with growth and water stress integral (WSI) of 22 eucalyptus genotypes with 1.5 years old. The experiment was conducted in sandy soil with low water holding capacity in Chile. Selected genotypes were Eucalyptus globulus, E. nitens, and E. nitens x E. globulus hybrids (E. gloni). Seasonal predawn leaf water potential (psi(pd)) was evaluated under well-irrigated conditions and after 40 days without irrigation. Subsequently, two sampling instances were considered for analysis, well-irrigated conditions M-0 (470 days after planting) and 40 days without irrigation M-final (510 days after planting). During that period, we measured midday leaf water potential (psi(pd)), leaf area index (LAI), diurnal changes in photosynthesis (A(n)) and stomatal conductance (g(s)). The broad range of WSI among genotypes indicated contrasting levels of accumulated water stress during early development. In fact, E. globulus presented 30% more water stress than E. nitens, and genotypes with the highest WSI showed the lowest growth. Between M-0 and M-final, there was a reduction in A(n) and g(s) in the morning and midday with small changes in the afternoon, and consequently, values of the intrinsic water use efficiency (iWUE) increased. The psi(pd) showed small changes and we observed a large LAI increment for all genotypes. Changes in iWUE were more pronounced for genotypes with lower WSI, which suggested that these genotypes with lower accumulated water stress were more sensitive to changes in soil water, such as E. gloni genotypes allowing them to maintain high productivity.