Explaining trajectories of chemical changes during decomposition of tropical litter by 13C-CPMAS NMR, proximate and nutrients analysis

Background and aim: Litter decomposition is of great concern as it plays a key role in regulating global carbon cycle and nutrient budgets, especially in tropical forests where it is very fast. Therefore, we studied the decomposition and subsequent changes in element concentrations and amounts of 11 tropical leaf litter. Methods: Fresh litters were characterized in terms of elemental, proximate features, as well as organic carbon compositions by 13C-NMR spectroscopy. Controlled litterbag decomposition was carried out for 180 days in the laboratory, bags were retrieved at three dates and analyzed for mass loss and concentration of nitrogen (N), potassium (K), sodium (Na), carbon (C), magnesium (Mg), manganese (Mn), iron (Fe), phosphorus (P), zinc (Zn), and percentage of ash, extractives, cellulose and lignin. Results: Terminalia arjuna showed highest mass loss, while the lowest was observed in Shorea robusta showing significant positive correlation with litter initial K, Mg, Fe and di-O-alkyl C, O-alkyl C, while significant negative correlation with Mn, lignin and Methoxyl C, Alkyl C. Trajectories shows that Fe, Mg, K, Mn, Zn and Na concentrations increased in most of the litter types, except Terminalia arjuna and Toona ciliata, where Fe, Mg, K concentrations decreased during decomposition. Surprisingly, in most of the species with the exception of Terminalia arjuna, N concentrations decreased at a faster rate than C concentrations, resulting in an increase in C/N ratios. Expectedly, lignin progressively increased, while cellulose decreased. Conclusions: Observed differences in decomposition rate and dynamics of chemical changes among litters were strongly affected by the litter type, decomposition time and their interactions.