Fungal Effects on Tree Growth in a Primary Succession

Abstract: In the Boreal zone, ectomycorrhiza is the most common mycorrhiza found among trees and helps with nitrogen and nutrient uptake. Most research on mycorrhiza, its effect, and community development are done on secondary succession (succession in an ecosystem after a disturbance) such as after a clearcut. This case study focuses on primary succession (succession in a previous lifeless ecosystem with no organic matter) of 15- and 30-year-old Scots pine (Pinus sylvestris) in an old gravel pit outside Uppsala, Sweden. The aim of the study is to find a connection between tree growth and its associated soil fungal community, especially with the ectomycorrhizal community. To do this, two hypotheses are proposed: (i) Difference in tree growth depends on which fungal guild dominates around that tree; trees with lower growth are dominated by free-living saprotrophs, and trees with higher growth are dominated by symbiotic ectomycorrhizal fungi. (ii) Species diversity of ectomycorrhizal fungi increases with higher tree growth, and there is a gradient from pioneer species to N-immobilizers, to N-miners as tree height increases. The categorization relies on how the genus obtains nitrogen and when they first colonize a habitat. A few selected genera of ectomycorrhiza were categorized as either pioneers (first colonizers), N-immobilizers (later colonizers), or N-miners (late colonizers). Overall, the results support the two hypotheses. What was found regarding the first hypothesis was that as tree height increased, the abundance of saprotrophs decreased while ectomycorrhiza or other root associated fungi increased. For the second hypothesis, the number of observed ectomycorrhiza increased with tree height, and the hypothesized gradient was observed.