Initial rates and limit values for decomposition of Scots pine and Norway spruce needle litter: a synthesis for N-fertilized forest stands

Nitrogen fertilization increased concentrations of N, P, S, and K in Scots pine (Pinus sylvestris L.) needle litter, and in those of N, S, and Ca in Norway spruce (Picea abies (L.) Karst.). Lignin concentrations increased for both species. Initial rates and limit values for decomposition were estimated using a simple equation. For Scots pine litter, initial rates ranged between 0.0618 and 0.2986%/day with P, K, N, and Mg being positively related, but lignin and Ca negatively related. For Norway spruce, initial rates were low (0.0455-0.1007%/day) and positively related with initial concentrations of water solubles, K, and P but negatively with N, Ca, and lignin. Limit values for Scots pine litter ranged from 53.1 to 94.3% decomposition in fertilized plots and from 71.5 to 93.2% in controls. They were negatively related to N concentrations and positively to Mn and Ca. Limit values for Norway spruce litter ranged from 53.8 to 74.3% in controls and from 48 to 71.3% in fertilized plots and were positively correlated to Mn and Ca but not to N. The paper concludes that N fertilization will increase the fraction of Scots pine litter that accumulates as humus but not for Norway spruce.