摘要：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 (H
2O
2 and MDA content), chlorophyll concentration, carbon (C) and nitrogen (N) isotopic leaf composition (δ
13C and δ
15N) 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 H
2O
2, MDA, δ
13C and δ
15N, 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 δ
13C, besides higher Na accumulation, δ
15N, H
2O
2 and MDA content.
