No abstract

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).

No abstract

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 stomatal density, 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 water use efficiency, photosynthesis-related parameters and plant growth under water deficit conditions.

MATEUS, N. S. Integrated effects of K and Na application on initial growth of eucalyptus seedlings submitted to water stress: water use efficiency, leaf gas exchange and δ 13 C isotopic variation. 2019. 76 p. Dissertação (Mestrado em Ciências) -

No abstract

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 (Ψ 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.