Leaf ¹³C and ¹⁵N composition shedding light on easing drought stress through partial K substitution by Na in...

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.