LEAF CARBON AND NITROGEN CONSTITUENTS OF SOME ACTINORHIZAL TREE SPECIES

Six actinorhizal tree species suitable for use in mixed plantations we re studied to determine the chemical composition of fresh leaf litter. Carbon and nitrogen content of leaves, water soluble extract and skel etal residue after chloroform and hot water extraction were determined on leaves from Alnus species (A. incana, A. cordata, A. subcordata an d a hybrid A. incana-cordata) and on leaves from Hippophae rhamnoides and Elaeagnus angustifolia. Temperature Programmed Pyrolysis associate d with elemental analysis of C and H (TPPy-C,H) was used to estimate c ellulose, hemicellulose and lignin content of the unextractable residu e. C:N ratios of leaves were low (16:1 to 20: 1) and contrasted with h igh C:N ratios of hot water-extractable substances (26:1 in E. angusti folia to 95:1 in A. subcordata). Amounts of water-soluble substances r anged from 25 to 38% of leaf weight, 18 to 34% of leaf C, 5 to 25% of leaf N. Lignin content varied consistenly between species: 8% of leaf was in the form of lignin in A. incana contrasting with 26% in leaves of E. angustifolia. Amounts and elemental characteristics of water-ext ractable substances and of structural insoluble components differed am ong species. Load litter characteristics need to be considered for est imating the relative decomposition and nutrient release rates from lit ter when actinorhizal species are planted to increase associated tree growth.