In vitro model to study the biological properties of humic fractions from landfill leachate and leonardite during root elongation of Alnus glutinosa L. Gaertn and Betula pendula Roth

Abstract

Humic substances (HS) are organic compounds resulting from the physical, chemical and microbiological transformations of organic residues. Our study aims to determine the main biological properties of HS comparing landfill leachate (LHS) source to a stable formulation extracted from leonardite (HHS) and using an in vitro system of root development from shoot and leaf explants of silver birch (Betula pendula Roth) and black alder (Alnus glutinosa L. Gaertn). Results showed that both explants of both species rooted closely to 100 % when cultivated in absence of HS. The incorporation of HS or their fractions into the culture medium affect root growth, mainly lateral roots formation and primary root length. Applied at low concentration (10 ppm), HS stimulated especially primary root growth. But at high concentration (100 ppm), LHS inhibited root formation of alder, while birch was more tolerant. The application of 100 ppm of HHS did not affect alder root growth but increased root growth in birch. Humic acids (HA) fractions were favorable and improved root growth while, fulvic acids (FA) and other molecules (OM) decreased significantly root growth, especially those extracted from LHS. The root inhibition expressed at high LHS concentration may be due to the presence of different toxic molecules and root growth inhibitors in OM and FA fractions and that some of them remained in the OM fraction from leonardite.