Nitrogen Isotope Patterns in Alaskan Black Spruce Reflect Organic Nitrogen Sources and the Activity of Ectomycorrhizal Fungi
Author
Summary, in English
Global patterns in soil, plant, and fungal stable isotopes of N (delta N-15) show promise as integrated metrics of N cycling, particularly the activity of ectomycorrhizal (ECM) fungi. At small spatial scales, however, it remains difficult to differentiate the underlying causes of plant delta N-15 variability and this limits the application of such measurements to better understand N cycling. We conducted a landscape-scale analysis of delta N-15 values from 31 putatively N-limited monospecific black spruce (Picea mariana) stands in central Alaska to assess the two main hypothesized sources of plant delta N-15 variation: differing sources and ECM fractionation. We found roughly 20% of the variability in black spruce foliar N and delta N-15 values to be correlated with the concentration and delta N-15 values of soil NH4 (+) and dissolved organic N (DON) pools, respectively. However, N-15-based mixing models from 24 of the stands suggested that fractionation by ECM fungi obscures the N-15 signature of soil N pools. Models, regressions, and N abundance data all suggested that increasing dependence on soil DON to meet black spruce growth demands predicates increasing reliance on ECM-derived N and that black spruce, on average, received 53% of its N from ECM fungi. Future research should partition the delta N-15 values within the soil DON pool to determine how choice of soil delta N-15 values influence modeled ECM activity. The C balance of boreal forests is tightly linked to N cycling and delta N-15 values may be useful metrics of changes to these connections.
Publishing year
2012
Language
English
Pages
819-831
Publication/Series
Ecosystems
Volume
15
Issue
5
Document type
Journal article
Publisher
Springer
Topic
- Biological Sciences
Keywords
- 15N
- black spruce
- denitrifier method
- dissolved organic nitrogen
- ectomycorrhiza
- isotope fractionation
- mixing models
Status
Published
Research group
- Microbial Ecology
ISBN/ISSN/Other
- ISSN: 1432-9840