Chemical and biochemical properties of humic substances isolated from forest soils and plant growth

To investigate the relationships among litter composition and C-13-nuclear magnetic resonance spectra (C-13-NMR), we studied delta(13)C values and bio chemical activities of the humic constituents extracted from the Ah horizon s of two undisturbed forest soils, located in a unique climatic area under different vegetative covers, Pinus mugo T, and Pinus sylvestris L. The two litters differed greatly in composition, while the C-13-NMR spectra of the humic substances extracted from the two Ah horizons were similar. The C-13- NMR spectra of the low molecular humic size (LMS) 1-2 revealed high aromati c and carboxylic contents and low aliphatic and carbohydratic ones, The tot al humic extracts (TQ) 1-2 and the high molecular humic size (HMS) 1-2 exhi bited an opposite trend. The delta(13)C values of the humic fractions range d from -24.36 to -25,84 parts per thousand, indicating an advanced stage of humification. The biochemical activities of the humic fractions were studi ed by evaluating the invertase, peroxidase, and eaterase activities in Pinu s mugo and Pinus sylvestris seedling roots grown in the presence of their h umic matter. These forest species were differently affected by their humic substances. In particular, the Pinus sylvestris humic matter, endowed with a higher indoleacetic acid (IAA) content, positively influenced all the enz ymes tested in Finns sylvestris seedlings, while the Pinus mugo humic matte r only increased the peroxidase activity in its seedlings. The plant specie s differ in their capacity to respond to biological humus activity, which i s reflected in their natural distribution.