Carbon functional groups of leaf litter in cacao and rubber agroforestry systems in southern Bahia, Brazil

Agroforestry systems (AFS) promote a continuous deposition of organic material in the soil via litter and roots. Litter has a diversity of organic compounds with different chemical complexities, and which act as raw materials in forming and maintaining soil organic carbon. The objective of this study was to characterize the chemical composition of litter provided in soils under natural forest, rubber tree and cacao AFSs of different ages (old and young AFS) and a pure rubber plantation. Litter samples were collected in each of the AFSs in both cacao and rubber lines. The determination of functional groups was performed by Diffuse Reflectance Fourier Transform Infrared Spectroscopy. The results showed that the old AFS (cacao line) mainly presented bands associated with aromatic compounds (1600−1500 cm−1), while the highest absorbance intensity observed in the old AFS (rubber line) was in the range of 1097−1040 cm−1, attributed to the presence of cellulose. The main difference observed between cacao line and rubber line in the young AFS was the presence of polysaccharide functional groups (1380−1240 cm−1) in the rubber line. The similarity between the young AFS cacao line and rubber line, old AFS (rubber line) and the pure rubber plantation can be explained by the presence of phenolic (3690, 3620, 3290 cm−1) and aliphatic (2922 cm−1) compounds. The natural forest was dissimilar to the other systems mainly in the bands around 1051−1040 cm−1 and 918 cm−1, suggesting a forest litter with a predominance of less complex chemical structures.