The aim of this study was to determine the effects of new Micro Carbon Technology (MCT®) fertilizers based on humic acids biologically digested on the growth and development of pepper plants. In this work, the biostimulant effect of MCT® fertilizers was compared to conventional mineral fertilizers. In order to evaluate MCT® fertilizers, a previous chemical characterization (infrared spectroscopy, liquid chromatography and mass spectrometry) of seven MCT® fertilizers was performed. Two fertilization tests of pepper plants were carried out in hydroponic conditions, where the fertilization and the age of the plants were studied in order to evaluate the specific effects on roots and leaves. Plant weight and foliar analysis (chlorophyll indices and nutrients) have been determined. Transmission electron microscopy was used to visualize the morphological differences in the root and leaf cells. Comparison between conventional and MCT® based fertilizers showed that, with the MCT® fertilizers, the plant is exposed to the presence of free amino acids (Glycine and Alanine), polyphenols and humic substances. Although no significant differences were found in plant mass production, the plants fertilized with MCT® products presented better nutritional status than plants treated with conventional fertilization in terms of nutrient content in leaves. Important morphological differences in root cells were found. A large central vacuole that represented the 68–83% of the total root cell area was shown if the MCT® products were used, suggesting significant changes of membrane permeability in terms of water adsorption and consequently nutrient storage. The morphological differences observed in the root cells were more noticeable in adult plants.
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