This work aimed to investigate the partial K-replacement by Na supply to alleviate drought-induced stress in Eucalyptus species. Plant growth, leaf gas exchange parameters, water relations, oxidative stress (H₂O₂ and MDA content), chlorophyll concentration, carbon (C) and nitrogen (N) isotopic leaf composition (δ¹³C and δ¹⁵N) were analyzed. Drought tolerant E. urophylla and E. camaldulensis showed positive responses to the partial K substitution by Na, with similar dry mass yields, stomatal density and total stomatal pore area relative to the well K-supplied plants under both water conditions, suggesting that 50% of the K requirements is pressing for physiological functions that is poorly substituted by Na. Furthermore, E. urophylla and E. camaldulensis up-regulated leaf gas exchanges, leading to enhanced long-term water use efficiency (WUE_L). Moreover, the partial K substitution by Na had no effects on plants H₂O₂, MDA, δ¹³C and δ¹⁵N, confirming that Na, to a certain extent, can effectively replace K in plants metabolism. Otherwise, the drought-sensitive E. saligna species was negatively affected by partial K replacement by Na, decreasing plants dry mass, even with up-regulated leaf gas exchange parameters. The exclusive Na-supplied plants showed K-deficient symptoms and lower growth, WUE_L, and δ¹³C, besides higher Na accumulation, δ¹⁵N, H₂O₂ and MDA content.

The objective of this work was to evaluate the losses in the process, survival, uniformity and growth during an entire short rotation of a clonal planting of Eucalyptus grandis x Eucalyptus urophylla in Brazil as a function of the different morphological characteristics of the seedlings considered a proxy of seedling quality. Seedlings were classified in descending order of quality by the following treatments: A > B > C. Treatment D was composed of prime seedlings 180 days old in the nursery. Treatment A and B experienced a mortality rate of 3% 30 days after planting, while seedlings C and D showed a mortality rate of 8%. Throughout the entire planting process, treatment C had the highest total losses of 24%, which was 15% higher than the average of the other three treatments. The quality of seedlings, as determined by the IQD, positively correlated with stem diameter, leaf biomass, and PH50 at 60 days of age. However, these relationships lost significance at later ages, and the DQI could not explain the variation in volume and stand uniformity (PV50) along the rotation. Despite early differences, from 36 to 64 months, only old seedlings (Treat. D) showed a difference in wood volume to the other treatments.