Efectos del déficit hídrico sobre variables hídrico-funcionales en Eucalyptus grandis e híbridos interespecíficos

Afforestation with Eucalyptus species occupies over a million hectares in Uruguay, with E. grandis being one of the most cultivated species. The increasing frequency of drought and heat waves in the region raises the need to evaluate hybrids with red gums (E. camaldulensis and E. tereticornis) since they are known to sustain gas exchange and growth even under severe drought conditions. Hybrids with E. urophylla are suitable for humid-subtropical regions. This study aimed to compare the effects of water restriction (WR) on plant water status, hydraulics, and growth of E. grandis (one clone; GG), E. grandis × E. camaldulensis (one clone; GC), E. grandis × E. tereticornis (one clone; GT), and E. grandis × E. urophylla (two clones; GU1 and GU2). Two drought-stress cycles were applied to six-month rooted cuttings from mid-spring to early fall under greenhouse environmental conditions. Predawn (Ψpd) and midday (Ψmd) leaf water potential, relative leaf water content (RWC), stomatal conductance (gs), and plant height and diameter were measured across each cycle. Daily fluctuation of Ψ was calculated as ΔΨ = Ψpd - Ψmd. Pressure-volume curves were performed to calculate the elastic modulus (Ɛ) and the osmotic potential at turgor loss (Ψπ₀) and full turgor (Ψπ_t). Specific (k_S) and leaf-specific (k_L) branch hydraulic conductivity, specific leaf area (SLA), and chlorophyll content (SPAD) were measured at the end of the second drought-stress cycle. Percentage loss of hydraulic conductivity (PLC) was calculated after removing the xylem embolism. Red-gum hybrids (GC and GT) had higher cavitation (PLC) under drought, as a consequence of maintaining high ΔΨ to sustain transpiration and carbon fixation. They showed elastic adjustment in WR, and osmotic adjustment was observed in the E. grandis clone (GG). GT clone showed a three-fold increase in cavitation and had 1.5 times stomatal opening (gs) than the most drought-sensitive clone (GG), exhibiting the lowest reduction (17%) in diameter growth under WR. GC hybrid attained the highest height at the end of the study (40% higher than GG) and GU clones reached the highest diameter. GT and GU2 increased by 25% the SLA in WR and GC clone did not show difference. GC and GT had higher chlorophyll content in WR, suggesting an “hormetic” response. Correlations among functional variables are explored, and the water supply capacity to the foliage among clones is discussed to better understand drought resistance strategies and growth performance of the different taxa.