The role of terpenes in carbon and nitrogen cycling in boreal forest soils

Cycling of carbon (C) and nutrients plays pivotal role for functioning of every ecosystem. Biogeochemical cycles of carbon and nitrogen (N) are balanced by a network of interactions between plants, litter and soil chemistry, microbial communities, enzyme machinery and climate conditions. This thesis focuses on the role of terpenes in C and N transformations in boreal forest soils. Terpenes are abundant plant secondary compounds. The focus was on certain mono-, di-, and triterpenes. Soil incubation experiments revealed that terpenes increased the mineralization of carbon but decreased net nitrogen mineralization and net nitrification. Additionally they increased the amounts of carbon and nitrogen in the microbial biomass through enhancement of bacterial growth; however, they inhibited fungal growth. This study suggests that terpenes can act as a C source for some microbial communities. Moreover, terpenes showed inhibitory potential against enzymes, which are involved in C, N, P, S cycling. The mechanism of inhibition seems to be based at least partially on ability of terpenes to bind enzymes. The field experiment presented the effect of logging residues and wood ash on composition of terpenes and C and N cycling in soil five years after clear-cutting a Norway spruce stand. Logging residue treatment increased the concentrations of certain terpenes in the organic layer. Both, logging residue and wood ash treatments increased net N mineralization and net nitrification. Some changes in terpene concentrations correlated with C and N cycling processes, but the relationship between terpene concentration and C and N cycling processes remained still unclear in the field conditions. In conclusion, terpenes can affect C and N transformations in boreal forest soil. It is probable that terpenes change N cycling retaining more N in organic forms and potentially decrease nitrogen losses from forest ecosystem.