Fulvic acid-like substance-Ca(II) complexes improved the utilization of calcium in rice: Chelating and absorption mechanism

Abstract

Water-soluble chelated calcium has been widely used in agriculture as a fertilizer to improve the absorption and utilization of calcium by plants. This paper prepared a new organic mineral fertilizer, based on fulvic acid-like substance chelated calcium (PFA-Ca2+ complex), using optimal parameters (i.e., pH, time, temperature, and Ca2+ concentration) to achieve a high chelation efficiency. The absorption, utilization, and distribution of the PFA-Ca2+ complex in rice roots were analyzed using laser scanning confocal microscopy (LSCM). Our results demonstrated that the optimal PFA-Ca2+ complex chelating efficiency (87%) was achieved at an initial Ca2+ concentration of 0.1 mol L−1, an equilibration time of 120 min, a pH of 5.0, and a temperature of 40 °C. The chelating reaction of a fulvic acid-like substance with Ca2+ primarily occurred on phenol hydroxyl, alcohol hydroxyl, and carboxyl groups. The PFA-Ca2+ complex was primarily enriched in the roots' pericycle, cortical, and epidermis cells, in both chelating and non-chelating forms. To our knowledge, this is the first report investigating how the PFA-Ca2+complex affects transformation in plants, which has significant implications for research on plant nutrition and nutrient distribution.

Keywords

• Fulvic acid fertilizer
• Essential element
• Chelated calcium fertilizer
• Chelating mechanisms
• Calcium enrichment and distribution