Skip to main content
Doctoral thesis, 2014

Plant-microbe-soil interactions and soil nitrogen dynamics in boreal forests

Blasko, Robert


Widespread nitrogen (N) limitation of plant growth in boreal forests is a well recognized phenomenon. Yet, the mechanisms responsible for the development of N limitation are unknown. By exploring the linkage between N cycling and microbial community structure, this thesis examines the role of soil microorganisms in N limitation development. The first part of the thesis addresses effects of long-term N additions on microbial communities and N cycling in Norway spruce (Picea abies (L.) Karst.) and Scots pine (Pinus sylvestris L.) forests and if the effects are reversible after termination of N addition. The second part of the thesis explores the role soil microbes play in the development of N limitation in primary forest ecosystems. The general structure and biomass of soil microbial communities was assessed by phospholipid fatty acid analyses. Soil and ecosystem N cycling were inferred from gross N mineralisation measurements and 15N natural abundance in soil and foliage. Retention of the 15N label by soil microorganisms was used to infer N retention capacity of the ecosystems. Despite unique responses in microbial communities and gross N mineralisation to long-term N additions between the two studies, some common patterns emerged. Gross N mineralisation, microbial community structure, and N retention were strongly linked. Microbial biomass decreased but gross N mineralisation increased after N addition. The increased biotic N retention after termination of N addition coincided with increased functional role ectomycorrhizal fungi play in ecosystem N cycle as inferred from changes in 15N natural abundance. In the land uplift chronosequence, large inputs of N through N2-fixation resulted in soil N accumulation but a decline in N supply rates. This coincided with increasing microbial N-immobilisation and increasing abundance of ectomycorrhizal fungi suggesting their importance in N retention. I suggest that the strong N limitation typical of boreal forests can develop in about 150 years. This thesis provides strong evidence that ectomycorrhizal fungi played an important role both in the return of N limitation two decades after termination of N addition and in the development of N limitation in a primary boreal forest.


gross nitrogen mineralisation; phospholipid fatty acids; ectomycorrhizal fungi; N limitation; boreal forest; land uplift; long-term N addition; N retention

Published in

Acta Universitatis Agriculturae Sueciae
2014, number: 2014:103
ISBN: 978-91-576-8154-6, eISBN: 978-91-576-8155-3
Publisher: Department of Forest Ecology and Management, Swedish University of Agricultural Sciences

Authors' information

Blasko, Robert
Swedish University of Agricultural Sciences, Department of Forest Ecology and Management

UKÄ Subject classification

Forest Science
Other Earth and Related Environmental Sciences

URI (permanent link to this page)