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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 (WUEL). 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, WUEL, and δ13C, besides higher Na accumulation, δ15N, H2O2 and MDA content.

The Eucalyptus grandis L. plantations for industrial purposes (e.g., wood charcoal and pulp) are largely adopted worldwide, mainly in acidic and poorly fertile soils. The application of lime to soil is recommended for eucalyptus plantation, but lime reduces the availability of metallic micronutrients to plants. Therefore, the aim of this study was to investigate the performance of field-grown Eucalyptus grandis in Ferralsol amended with lime at different rates (0.0 and 1.6 and 3.7 Mg ha-1) and Cu plus Zn [0.0 and 0.0 kg ha-1 (-CuZn) and 0.5 and 1.5 kg ha-1 (+CuZn)]. The soil chemical attributes, shoot biomass, and nutrient accumulation were evaluated, while nutrient use efficiency, chlorophyll (Chl) and flavonoid (Flav) contents, and enzymatic antioxidant performance [superoxide dismutase (SOD), catalase (CAT), glutathione reductase (GR), ascorbate peroxidase (APX), guaiacol peroxidase (GPOX), and glutathione peroxidase (GPX)] were assayed to assess the nutritional status of the plants. Despite the lime application rate increasing Ca and Mg soil availabilities, effective cation exchange capacity (eCEC), base saturation (BS), and pH values, the available Cu, Fe, and Zn concentrations decreased at 6 and 30 months after planting. Conversely, Mn soil availability increased with lime application rates. Liming augmented Cu-, Fe-, Mn-, and Zn-use efficiency, while +CuZn supply increased enzymatic antioxidant performance in 30-month-old plant. Overall, the combined application of lime and +CuZn enhanced shoot biomass relative to that of non-treated plants. However, there was no observed difference in shoot biomass in 30-month-old limed and non-limed eucalyptus trees that were supplied with +CuZn. This result can be partially explained by the improvement in soil chemical attributes, such as soil pH, eCEC, and BS. In conclusion, the use of integrative approaches and temporal evaluations provided new insights into wood yield, biochemical traits, antioxidant metabolism, and the nutritional status of field-grown eucalyptus under lime and +CuZn application rates.

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 (Ψw), 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, Ψw, 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.

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 (UEK), 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).

Eucalyptus are widely planted in regions with low rainfall, occasioning frequent drought stresses. To alleviate the stress-induced effects on plants growing in these environments, soil fertilization with potassium (K) may affect drought-adaptive plant mechanisms, notably on tropical soils with low K availability. This work aimed to evaluate the K dynamic nutrition in eucalyptus in response to soil-K and -water availabilities, correlating the K-nutritional status with the physiological responses of contrasting eucalyptus clones to drought tolerance. A complete randomized design was used to investigate the effects of three water regimes (well-watered, moderate water deficit, and severe water deficit) and two K soil supplies (sufficient and low K) on growth and physiological responses of two elite eucalyptus clones: "VM01" (Eucalyptus urophylla × camaldulensis) and "AEC 0144" (E. urophylla). Results depicted that the K-well-nourished E. urophylla × camaldulensis clone under severe water deficit maintained shoot biomass accumulation by upregulating the K-content in leaves and stems, gas exchange, water-use efficiency (WUEI ), leaf water potential (Ψw), and chlorophyll a fluorescence parameters, compared to E. urophylla clone. Meanwhile, E. urophylla with a severe water deficit showed a decreased of K content in leaves and stem, as well as a reduction in the accumulation of dry mass. Therefore, the K-use efficiency and the apparent electron transport rate through photosystem II were positively correlated in plants grown in low K, indicating the importance of K in maintaining leaf photochemical processes. In conclusion, management strategy should seek to enhance K-nutrition to optimize water-use efficiencies and photosynthesis.

Made available in DSpace on 2020-12-10T17:27:30Z (GMT). No. of bitstreams: 0 Previous issue date: 2020-02-26 Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) Jatropha is an excellent plant model to evaluate physiological responses involving species tolerance to abiotic stresses, such as low calcium (Ca), magnesium (Mg) and sulfur (S) availability. Moreover, Ca, Mg and S are essential for the establishment of this plant in large areas. Better acknowledgment of appropriate nutrient levels can help with proper fertilization. This study aimed to gain insight during initial growth in Jatropha plants deficient in Ca, Mg and S by measuring leaf gas exchange, nutrient uptake efficiency (UpE), nutrient use efficiency (UtE) and biomass partitioning at plant harvest. Chlorophyll, carotenoid concentration, net photosynthesis rate (A), stomatal conductance (g(S)), transpiration (E), leaf-scale intrinsic water use efficiency (IWUE) and instantaneous carboxylation efficiency (k) in leaves of Ca-, Mg- and S-deficient plants revealed imbalances prior to visual symptom appearance. Nutrient deficiencies decreased A, which in turn hindered plant growth and biomass partitioning among leaves, stem and roots. However, S-deficient plants maintained values of UtE (at 120 days after S withdrawal), as well as of A, g(S), E, k and biomass allocation similar to those of control plants, during all evaluation periods. Jatropha was highly and very sensitive to Ca and Mg deficiency, respectively, with all results were dramatically decreased in contrast to the control. In conclusion, early physiological evaluation of Ca and Mg status in starved young plants with contrasting UtE values may be a reliable tool with which to predict early nutritional deficiencies before visual symptom appearance. Univ Sao Paulo, Ctr Nucl Energy Agr, Ave Centenario 303 CP 96, BR-13416000 Piracicaba, Brazil Univ Sao Paulo, Luiz de Queiroz Coll Agr, Piracicaba, Brazil Sao Paulo State Univ, Fac Ciencias Agr & Vet, Jaboticabal, Brazil Sao Paulo State Univ, Fac Ciencias Agr & Vet, Jaboticabal, Brazil FAPESP: 2011/15208-0 CNPq: 310572/2017-7

Brazil is a global reference in forest management for wood production (e.g., pulp and solid wood products), and large areas are planted mainly in acidic and poorly fertile soils, with a predominance of Eucalyptus species. Liming is widely adopted in acidic soils in humid tropical regions planted with Eucalyptus to increase the availability of some nutrients and supply Ca and Mg. However, liming decreases the availability of some micronutrients, such as Cu and Zn, depending on the lime content. Copper and Zn fertilization for Eucalyptus is usually intended to replace the amount of micronutrients extracted after wood harvesting. However, few studies have been carried out to investigate the combined effects of lime and Cu plus Zn application on forest plantations in tropical soils. Here, the effects of these factors on soil chemical-attributes, as well as nutrition, and growth performance of Eucalyptus grandis plantations were evaluated on a medium-textured Ferralsol. The stem volume yield improved after liming, regardless of the rate of application, and after Cu plus Zn fertilization. Liming increased soil pH and Ca and Mg availability and reduced Cu and Zn availability. Overall, liming reduced soil Cu and Zn contents in the residual-fraction, while increasing the fraction bound to organic-matter. High contents of Cu and Zn were linked to the organic-matter fraction in the soil under the Eucalyptus plantation. Eucalyptus trees grown in soils amended with lime had higher values for leaf area index and leaf Ca and Mg concentrations but showed reduced Cu and Zn concentrations. The combined application of lime and Cu plus Zn improved Eucalyptus growth, with the higher contribution of lime compared to Cu and Zn. In conclusion, the combined application of lime and Cu plus Zn is a useful strategy to provide balanced nutrition and optimize stem volume yields.

In Brazil, Eucalyptus plantations are found, generally in soils with naturally low chemical fertility. Silicon (Si) can improve photosynthesis, decrease plant transpiration and increase water use efficiency (WUE). This study aimed to evaluate the effect of Si supply at five rates (0, 0.25, 0.50, 0.75 and 1.00 mmol L-1) for growing Eucalyptus clone IPB8 seedlings (E. urophylla E. grandis) in Clark's nutrient solution in a greenhouse. Plant growth, nutritional status, gas exchange, leaf water potential (?w), leaf area (LA), inclination angle of leaves and stomatal density (SD) were measured. There was no significant response in Eucalyptus seedling growth due to Si application, which was related to the absence of benefits provided by Si in plant nutritional status and physiology. The efficiency of assimilation (EA), efficiency of translocation (ET) and efficiency of utilization (EU) did not show significant results either. The low ET indicates that Si was highly accumulated in the root (75.4 % in relation to total Si absorbed by plants), which may also have contributed to the lack of the benefits expected. Despite that, Si application promoted higher rates of photosynthesis when compared to plants with 0 mmol Si L-1, increasing the total dry matter production by up to 28 % at an Si rate 0.50 mmol L-1, which also provided a trend of higher growth, EU, LA and SLA, showing it to be the best rate for this Eucalyptus species.

International audience; Potassium (K) is the most required macronutrient by Eucalyptus, while sodium (Na) can partially substitute some physiological functions of K and have a positive response on plant growth in K-depleted tropical soils. However, the right percentage of K substitution by Na is not yet known for Eucalyptus seedlings, since a few experiments have only compared treatments receiving K or Na. This study evaluated five levels of Na supply (0, 0.45, 0.90, 1.35 and 1.80 mM) as substitution for K in Eucalyptus seedlings grown in nutrient solution. Plants growth, biomass, K-nutritional status, leaf gas exchange, leaf carbon isotopic composition (δ13C ‰), leaf water potential (Ψw), leaf area (LA), stomatal density (SD) and water use efficiency (WUE) were measured. The highest total biomass yield was achieved by the Na estimated rate of 0.25 mM, corresponding to a leaf K: Na ratio of 3.41, and having the lowest δ13C values. Conversely, the highest Na rate (1.8 mM) induced K deficiency symptoms, lower growth, reduced total dry matter yield, leaf gas exchange, LA, SD and a higher δ13C, which presented a trend to an inverse correlation with CO2 assimilation rate (A), WUE and shoot dry matter. Collectively, our results conclude that substitution of 25% of K by Na (0.45 mM of Na) provided significant gains in nutritional status and positive plant physiological responses by increasing WUE, stomatal diffusion, and by augmenting CO2 uptake efficiency. This nutritional management can therefore be an alternative option to optimize yields and resource use efficiencies in Eucalyptus cultivation.