On 28. August 2019 Kaie Kriiska will defend her doctoral thesis „Variation in annual carbon fluxes affecting the soil organic carbon pool and the dynamics of decomposition in hemiboreal coniferous forests“.
senior researcher Ivika Ostonen-Märtin, UT,
senior researcher Jane Frey, UT
professor Lars Vesterdal, University of Copenhagen, Denmark
Globally, soils store more carbon (C) than combined in the atmosphere and terrestrial biomass, while forest soils contain one of the world’s largest organic carbon stocks. Hence, minor changes in the balance between the forest soil organic carbon (SOC) stocks and associated C fluxes could have a significant effect on the C cycle at regional as well as global level, thereby affecting the climate. The overall aim of this thesis was to estimate the variability of annual soil C fluxes and the dynamics of the associated processes, such as above- and belowground (fine root, <2mm) litter production of trees and understory; soil respiration; decomposition of site-specific Norway spruce and Scots pine fine roots, needle litter and standardised materials (α-cellulose, green and rooibos tea); the release of macronutrients (nitrogen, phosphorus, potassium) from fine root and needle litter in hemiboreal coniferous forests in Estonia over the course of three years; and the factors controlling decomposition of standardised substrates from local to global scale. In addition, the applicability of the Yasso07 soil model in carbon balance accounting was evaluated. One of the key findings was that fine root production and turnover could be one of the most important factors that determine the size and the C dynamics of forest SOC pool. Litter decomposition was mainly controlled by the substrate type and soil macronutrients, while the effect of temperature and precipitation was only important under less favourable (e.g. xeric) climatic conditions. The estimates of the measured and modelled soil C stocks and fluxes presented in this thesis would considerably improve the accuracy of the forestry sector data in the Estonian greenhouse gas inventory, and hence support implementation of science-based climate change policy.