Carboxyl and phenolic humic fractions affect pinus nigra callus growth and metabolism
A humic substance was separated into carboxyl and phenolic fractions by affinity chromatography using a weak-base amine resin. The humic extract and its fractions were analyzed for physical and chemical characteristics. Their biological effects were compared, at concentrations of 1 and 5 mg C L–1, on the growth of callus of Pinus nigra J.F. Arnold. A higher molecular weight and a greater degree of aromaticity were observed for the unfractionated humus and carboxyl fraction than for the phenolic fraction. Spectra from 13C nuclear magnetic resonance and diffuse reflectance infrared Fourier-transform spectroscopy showed a low content of lignin-derived, aromatic compounds and a high amount of carboxyl C and total sugars in the carboxyl fraction. The phenolic fraction was found to contain high amounts of fatty acids as well as phenolic acids. The unfractionated humus amended only at the lower concentration (1 mg C L–1) increased the callus growth and enzyme activities. The carboxyl fraction improved the growth of calluses and increased the levels of enzymatic activities. The phenolic fraction had an inhibitory effect. Thus, the positive biological effects of the humic fractions utilized might be attributed to the relative content of specific classes of humic components, such as a high amount of peptidic, carbohydratic, and carboxylic groups, and low content of phenolic acids and fatty acids. The heterogeneity of humic substances is strongly influenced by the origin, age, and decomposition processes of parent organic materials. Therefore, the diverse amounts of chemical compounds in humus may influence the function of ecosystems in similarly diverse ways.