Prediction of mass loss in different organic materials under field Mediterranean conditions: influence of the initial chemical quality

The influence of chemical quality on decomposition was studied under Mediterranean conditions using the litter bag methodology.Litter of twenty-seven organic materials of different origins was enclosed in litter bags, buried, and periodically sampled during a 14-month period.The mass loss of each material was calculated, different empirical models of one and two pools were adjusted, and the respective constants were estimated.Linear regressions were established between the labile (M L ) and recalcitrant (M R ) mass loss pools and initial material characteristics to determine the best predictor of decomposition.The M L and M R pools were related to the presence of soluble or recalcitrant compounds, with values varying between 66.7-685 and 316-934 g kg -1 , respectively.Materials with higher soluble compounds, such as PMM or LL, showed significantly higher M L values than CSS or OWM materials, with higher M R values where recalcitrant fractions were predominant.Various quality parameters were correlated with mass loss with best predictability of M L and M R presented by labile indicators as TAPPI soluble elements that explained 79% and 77% of variation results, respectively.For structural parameters, the best result was presented by total condensed tannins followed by lignin content that explained between 40% and 51% variation of M L and M R .Improved predictability was observed by integrating other labile indicators, like water soluble C and N and the respective ratio, or recalcitrant total condensed tannins and holocellulose, in M L (r 2 adj = 0.890***) and M R (r 2 adj = 0.866***) pool estimation, respectively.