Eucalyptus, the most widely planted tree genus worldwide, is frequently cultivated in soils with low water and nutrient availability. Sodium (Na) can substitute some physiological functions of potassium (K), directly influencing plants’ water status. However, the extent to which K can be replaced by Na in drought conditions remains poorly understood. A greenhouse experiment was conducted with three Eucalyptus genotypes under two water conditions (well-watered and water-stressed) and five combination rates of K and Na, representing substitutions of 0/100, 25/75, 50/50, 75/25, and 100/0 (percentage of Na/percentage of K), to investigate growth and photosynthesis-related parameters. This study focused on the positive effects of Na supply since, depending on the levels applied, the Na supply may induce plants to salinity stress (>100 mM of NaCl). Plants supplied with low to intermediate K replacement by Na reduced the critical level of K without showing symptoms of K deficiency and provided higher total dry matter (TDM) than those Eucalyptus seedlings supplied only with K in both water conditions. Those plants supplied with low to intermediate K replacement by Na had improved CO₂ assimilation (A), stomatal density (Std), K use efficiency (UE_K), and water use efficiency (WUE), in addition to reduced leaf water potential (Ψw) and maintenance of leaf turgidity, with the stomata partially closed, indicated by the higher values of leaf carbon isotope composition (δ¹³C‰). Meanwhile, combination rates higher than 50% of K replacement by Na led to K-deficient plants, characterized by the lower values of TDM, δ¹³C‰, WUE, and leaf K concentration and higher leaf Na concentration. There was positive evidence of partial replacement of K by Na in Eucalyptus seedlings; meanwhile, the ideal percentage of substitution increased according to the drought tolerance of the species (Eucalyptus saligna < Eucalyptus urophylla < Eucalyptus camaldulensis).

The objective of this study was to quantify the effect of potassium (K) supply on osmotic adjustment and drought avoidance mechanisms of Eucalyptus seedlings growing under short-term water stress. The effects of K supply on plant growth, nutritional status, leaf gas exchange parameters, leaf water potential (Ψ_w), leaf area (LA), stomatal density (SD), leaf carbon (C) and nitrogen (N) isotopic compositions (δ¹³C and δ¹⁵N ‰) and leaf C/N ratio under polyethylene glycol (PEG)-induced water deficit were measured. Under both control (non-PEG) and osmotic stress (+PEG) conditions, K supply increased plant growth, boosting dry matter yield with decreased C/N leaf ratio and δ¹⁵N ‰ values. The +PEG significantly reduced LA, plant growth, dry matter yield, Ψ_w, number of stomata per plant and leaf gas exchange, relative to non-PEG condition. Potassium supply alleviated osmotic-induced alterations in Eucalyptus seedlings by better regulating leaf development as well as SD, thus improving the rate of leaf gas exchange parameters, mesophyll conductance to CO₂ (lower δ¹³C ‰ values) and water use efficiency (WUE). Consequently, K-supplied plants under drought better acclimated to osmotic stress than K-deficient plants, which in turn induced lower CO₂ assimilation and dry matter yield, as well as higher leaf δ¹³C ‰ and δ¹⁵N ‰ values. In conclusion, management practices should seek to optimize K-nutrition to improve WUE, photosynthesis-related parameters and plant growth under water deficit conditions.

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.

Cassava (Manihot esculenta Crantz) is a crucial staple food in South America, providing starchy storage roots that contribute to the sustenance of millions. To address deficiencies in iron (Fe), zinc (Zn), and selenium (Se), a global initiative is underway to identify plant species and genotypes that naturally accumulate these nutrients for human consumption, such as cassava. In this way, this study aims to identify potential cassava genotypes for biofortification in Fe, Zn, and Se, while also improving the overall cassava yield. We evaluated the accumulation potential of Fe, Zn, and Se in 20 South American cassava genotypes under traditional growing conditions, concurrently examining their photosynthetic and growth characteristics. Cassava roots exhibited Zn content ranging from 3.20 to 8.56 mg kg⁻¹, Fe content from 2.20 to 10.73 mg kg⁻¹, and Se content from 1.20 to 9.43 µg kg⁻¹ (expressed on a dry basis). Genotypes MS018, DG014, and DG839 emerged as promising candidates for biofortification programs, displaying elevated levels of Fe, Zn, and Se, coupled with superior photosynthetic capacity. These genotypes, recommended for biofortification programs, also demonstrated increased yield potential. The findings from this study contribute to the development of cassava genotypes with enhanced agronomic biofortification and elevated yield potential.