Leaf carbon and nitrogen constituents of some actinorhizal tree species

Six actinorhizal tree species suitable for use in mixed plantations were studied to determine the chemical composition of fresh leaf litter. Carbon and nitrogen content of leaves, water soluble extract and skeletal residue after chloroform and hot water extraction were determined on leaves from Alnus species ( A. incana, A. cordata, A. subcordata and a hybrid A. incana-cordata) and on leaves from Hippophae rhamnoides and Elaeagnus angustifolia. Temperature Programmed Pyrolysis associated with elemental analysis of C and H (TPPy-C,H) was used to estimate cellulose, hemicellulose and lignin content of the unextractable residue. C:N ratios of leaves were low (16:1 to 20:1) and contrasted with high C:N ratios of hot water-extractable substances (26:1 in E. angustifolia to 95:1 in A. subcordata). Amounts of water-soluble substances ranged 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-extractable substances and of structural insoluble components differed among species. Load litter characteristics need to be considered for estimating the relative decomposition and nutrient release rates from litter when actinorhizal species are planted to increase associated tree growth.