Decomposition rate and chemical changes of Scots pine needle litter. II. Influence of chemical composition.

Decomposition of Scots pine needle litters with initially differing levels of the nutrients N, P, K, Ca, S, and Mg, as well as lignin, was studied. The initial levels of N, P, K, and S in the litter were positively correlated. The positive correlation noted between nutrient level and weight loss was restricted to weight losses less than 30%, up to which mainly solubles and some cellulose and hemicellulose were degraded. When the decomposition of lignin started, the weight-loss enhancing effect by nutrients was overrun by the slow decomposition of lignin. Lignin appeared to retard the weight loss of the components cellulose and hemicellulose. The decomposition rate of the lignin fraction was unaffected by the plant nutrient concentrations and its decomposition started sooner in litters with much lignin than in those with little. No lignin appeared to be degraded until it had reached a concentration of about 30%. Additional keywords: Cellulose, lignin, litter-bag, mineralization, plant nutrient.