The Effects of Temperature and Mineral Nitrogen and Phosphorus on the Decay Processes and Composition of Soil–Bark Substrates

Abstract

The bark of coniferous trees (BCT) is an essential component of the litter in boreal forests. The effects of temperature and mineral additives (N and P) on the rate of BCT decomposition (DecR), its constant (k), total loss of C–CO2, and the changes in BCT chemical composition are assessed in a long-term (12 months) laboratory experiment with soil–bark substrates (SBSs) using three contrasting temperatures (2, 12, and 22°C) and sufficient moisture. The temperature coefficient (Q10) for the mean DecR during the experiment varies from 1.1 to 2.5 depending on temperature range and SBS composition. The effect of temperature was the most pronounced during the first and second months of the experiment, explaining 47% of the DecR variation. At later stages of the experiment, the SBS composition affected by the addition of mineral N and P compounds is the key factor influencing the BCT decomposition; it explains 18–63% of the DecR variance. The maximum losses of C–CO2 (158–187 g С/(kg bark), or 34–41% of the initial С content) are observed at 22°C. Irrespectively of the temperature, the most significant loss of ethanol-soluble compounds (56–64%) is recorded in the variant with the mineral N additive, whereas the cellulose content most significantly decreases (by 64–69%) in the variant with combined application of N and P and is almost independent of temperature. The loss of lignin was insignificant, amounting to only 3–12% of its initial content. The addition of mineral N and P is a key factor stimulating the BCT decomposition, considerably shortening the decomposition time and improving the quality of the resulting substrates.