Changes in organic compounds during leaf litter leaching: laboratory experiment on eight plant species of the Sudano-guinea Savannas of Ngaoundere, Cameroon

A laboratory experiment was carried out on the leaf litter of 8 agroforestry plant species of the Sudano-guinea Savannas of Ngaoundere in order to compare patterns of their water absorption and dynamics of four important energetic organic compounds (soluble sugars, cellulose, phenol and lignin) among these plant species during the leaching phase and to determine the influence of initial litter properties on these processes. To this end, 168 samples of leaf litter (5.00 ± 0.01 g) of Annona senegalensis, Lophira lanceolata, Syzygium guineense var. guineense, Syzygium guineense var. macrocarpum, Vitellaria paradoxa, Vitex doniana, Vitex madiensis and Ximenia americana were immersed for 15 days in distilled water at a temperature of 23 °C and relative humidity of 65 ± 1%. Three samples of each plant species were taken at 1, 6, 24, 72, 168, 240 and 360 hours. Depending on the species, water absorption capacity after 360 h of leaching varied from 162.77 (S. g. var. macrocarpum) to 264.00% (V. madiensis) of dry litter mass. The release of water-soluble substances varied between 9.61 (L. lanceolata) and 34.12% (X. americana). Water absorption and release of water-soluble substances rate constants were the highest in V. madiensis (0.32 h-1 and 0.25 h-1) and the lowest one respectively in S. g. guineense (0.03 h-1) and S. g. var. macrocarpum (0.006 h-1). Organic compound of original litter also varied significantly among species and decreased with leaching time for water-soluble sugars and phenols, while increased for cellulose and lignin. Water absorption by litter was significantly correlated with initial water-soluble sugars and phenol content, leaf litter area and thickness. The release of water-soluble substances by litters was also correlated with initial water-soluble sugars, water content and leaf litter area. The leaching rate constant was correlated with that of water absorption. These preliminary results lead to a better understanding of the litter decomposition processes of agroforestry plant species of Ngaoundere and thus help in making the most appropriate choice of indigenous plant species for domestication that could help to improve soil fertility and eventually to protect the biodiversity.