MSc Janne F.J. Korhonen will defend his doctoral dissertation

2.6.2020
MSc Janne Korhonen will defend his doctoral dissertation entitled 'Nitrogen cycling from the perspective of boreal Scots pine trees' on Tuesday, June 9.

The opponent is Associate Professor Tobias Rütting from University of Gothenburg, Sweden, and the custos professor Jaana Bäck, Institute for Atmospheric and Earth System Research and Faculty of Agriculture and Forestry, University of Helsinki.
An electronic version of the dissertation is found here: https://dissertationesforestales.fi/article/10378

The defence, Tuesday June 9 at 12:15, can be followed remotely using the following link: https://helsinki.zoom.us/j/65577985364?pwd=ZDJ6dkVBUktiQTN0SmdNdjU2N1paQT09

Meeting ID: 65 577 985 364
Password: 194234

It will also be possible to attend the defence in Metsätalo, lecture hall 1 (Unioninkatu 40).
NOTE: The audience is limited to 40 persons who are allowed to enter the room in the order of presence. Doors will be closed when 40 people are in.

Dissertation summary:

Nitrogen (N) and associated carbon (C) cycling were studied in an N-limited boreal Scots pine (Pinus sylvestris L.) forest in Hyytiälä, southern Finland and were compared to two N-rich temperate forests, the Speulderbos Douglas fir (Pseudotsuga menziesii (Mirb.) Franco) forest in the Netherlands and the Sorø European beech (Fagus sylvatica L.) forest in Denmark. Nitrogen and carbon cycling in the Scots pine forest were modelled. These results were compared to continuous year-round observations to obtain an overall understanding of nutrient cycling in the forest. The N balance of the Scots pine forest was calculated based on direct measurements, measurement-based estimations and model results. Nitrogen uptake and resorption by trees were estimated based on continuous measurements. Litter fall dynamics of the Scots pine and Douglas fir forest were compared. Scots pine needle N dynamics were compared between the three forests. Soil was the main N storage in the boreal Scots pine forest and most of this N was in recalcitrant form. Scots pine trees were very efficient at saving and recycling N. This together with atmospheric N deposition, potential N uptake by the canopy and organic N uptake mean that the importance of mineralization as the process driving N cycling may have been overestimated. Most of the N was allocated simply to replace dead tissue in the Scots pine forest. This means that the additional N received via N deposition may significantly increase the N pool size that trees have for extending their biomass N (net growth). Because Scots pine trees were found to be dependent on efficient N use and recycling, this adversely also means that even slight snow and storm damages may cause foliar biomass to decrease due to reduced relocation on top of the direct effect of losing the foliage due to damage, affecting forest carbon sink strength.