Absorption and distribution of root, fruit, and foliar-applied 45 Ca in 'Clemenules' mandarin trees

Mineral Particles in Foliar Fertilizer Formulations Can Improve the Rate of Foliar Uptake

The application of foliar sprays of suspensions of relatively insoluble essential element salts is gradually becoming common, chiefly with the introduction of nano-technology approaches in agriculture. However, there is controversy about the effectiveness of such sparingly soluble nutrient sources as foliar fertilizers. In this work, we focussed on analysing the effect of adding Ca-carbonate (calcite, CaCO3) micro- and nano-particles as model sparingly soluble mineral compounds to foliar fertilizer formulations in terms of increasing the rate of foliar absorption. For these purposes, we carried out short-term foliar application experiments by treating leaves of species with variable surface features and wettability rates. The leaf absorption efficacy of foliar formulations containing a surfactant and model soluble nutrient sources, namely Ca-chloride (CaCl2), magnesium sulphate (MgSO4), potassium nitrate (KNO3), or zinc sulphate (ZnSO4), was evaluated alone or after addition of calcite particles. In general, the combination of the Ca-carbonate particles with an essential element salt had a synergistic effect and improved the absorption of Ca and the nutrient element provided. In light of the positive effects of using calcite particles as foliar formulation adjuvants, dolomite nano- and micro-particles were also tested as foliar formulation additives, and the results were also positive in terms of increasing foliar uptake. The observed nutrient element foliar absorption efficacy can be partially explained by geochemical modelling, which enabled us to predict how these formulations will perform at least in chemical terms. Our results show the major potential of adding mineral particles as foliar formulation additives, but the associated mechanisms of action and possible additional benefits to plants should be characterised in future investigations.

Regulation of magnesium and calcium homeostasis in citrus seedlings under varying magnesium supply

Magnesium (Mg) and calcium (Ca) are two essential macronutrients in plants; however, the characteristics of Mg and Ca concentrations in organ, subcellular and chemical forms and their relationships in citrus plants, especially under varying Mg supply, are not well understood. In this study, Citrus sinensis seedlings (cv. Xuegan) were cultivated in conditions of Mg deficiency (0 mmol Mg2+ L-1) and Mg sufficiency (2 mmol Mg2+ L-1) to investigate the responses of Mg and Ca homeostasis in different organs and fractions. Compared with Mg sufficiency, Mg deficiency significantly decreased root and shoot growth, with the shoot biomass reduction of branch organs was greater than that of parent organs. In addition to increasing the Ca concentration in the parent stem and lateral root organs, Mg deficiency significantly decreased the concentrations and accumulations of Mg and Ca in citrus seedlings, further altering their distribution in different organs. More than 50% of Ca and Mg were sequestrated in the cell wall and soluble fractions, respectively, with Mg concentration decreasing by 15.4% in roots and 46.9% in leaves under Mg deficiency, while Ca concentration decreased by 27.6% in roots and increased by 23.6% in parent leaves. Approximately 90% of Mg exists in inorganic, water-soluble, and pectate and protein-bound forms, and nearly 90% of Ca exists in water-soluble, pectate and protein-bound, phosphate and oxalate acid forms. Except for the decreased inorganic Mg in roots and water-soluble Mg and Ca in leaves, Mg deficiency increased the proportions of Mg and Ca in all chemical forms. However, Mg deficiency generally increased the Ca/Mg ratio in various organs, subcellular and chemical forms, with negative relationships between Mg concentration and Ca/Mg ratio, and the variations of Mg and Ca were highly separated between Mg supply and organs. In conclusion, our results provide insights into the effects of Mg supply on Mg and Ca homeostasis in citrus plants.

Foliar Calcium Absorption by Tomato Plants: Comparing the Effects of Calcium Sources and Adjuvant Usage

The deficiency of calcium (Ca) reduces the quality and shelf life of fruits. In this scenario, although foliar spraying of Ca²⁺ has been used, altogether with soil fertilization, as an alternative to prevent deficiencies, little is known regarding its absorption dynamics by plant leaves. Herein, in vivo microprobe X-ray fluorescence was employed aiming to monitor the foliar absorption of CaCl₂, Ca-citrate complex, and Ca₃(PO₄)₂ nanoparticles with and without using adjuvant. We also investigated whether Sr²⁺ can be employed as Ca²⁺ proxy in foliar absorption studies. Moreover, the impact of treatments on the cuticle structure was evaluated by scanning electron microscopy. For this study, 45-day-old tomato (Solanum lycopersicum L., cv. Micro-Tom) plants were used as a model species. After 100 h, the leaves absorbed 90, 18, and 4% of aqueous CaCl₂, Ca-citrate, and Ca₃(PO₄)₂ nanoparticles, respectively. The addition of adjuvant increased the absorption of Ca-citrate to 28%, decreased that of CaCl₂ to 77%, and did not affect Ca₃(PO₄)₂. CaCl₂ displayed an exponential decay absorption profile with half-lives of 15 h and 5 h without and with adjuvant, respectively. Ca-citrate and Ca₃(PO₄)₂ exhibited absorption profiles that were closer to a linear behavior. Sr²⁺ was a suitable Ca²⁺ tracer because of its similar absorption profiles. Furthermore, the use of adjuvant affected the epicuticular crystal structure. Our findings reveal that CaCl₂ was the most efficient Ca²⁺ source. The effects caused by adjuvant suggest that CaCl₂ and Ca-citrate were absorbed mostly through hydrophilic and lipophilic pathways.

Metabolomic profiling of brassinolide and abscisic acid in response to high-temperature stress

Hormone treatment enhanced the content of osmotic substances under high-temperature conditions. The effect of ABA and BR treated separately is better than treated together. To determine the effect of abscisic acid (ABA), brassinolide (BR) and ABA + BR on grape quality under high-temperature stress, various metabolites were analyzed. Compared with the control (CK), DL-tryptophan, D-raffinose, geniposidic acid, dodecanedioic acid and polyphenols were found to be higher after ABA treatment. After BR treatment, amino acids and poricoic acid B were higher than in CK. And carbohydrates and amino acids were up-regulated after ABA + BR treatment. BR and ABA + BR treatment also induced higher endogenous ABA and epibrassinolide contents. In addition, treated grape had higher soluble solid concentrations and soluble sugar content, and delayed the degradation of middle lamella and microfibrils. Antioxidant and heat shock-related genes were examined, which significantly increased in treated grape. The finding of this study suggested that ABA, BR and ABA + BR are very useful for alleviating high-temperature damage by increasing the accumulation of osmotic adjustment substances, and endogenous hormones content.