Title: Nitrogen isotope patterns in Alaskan black spruce reflect organic nitrogen sources and the activity of ectomycorrihizal fungi
Author: Mayor, Jordan R.; Schuur, Edward A.G.; Mack, Michelle C.; Hollingsworth, Teresa N.; Bääth, Erland.
Source: Ecosystems. 15: 819-831
Description: Global patterns in soil, plant, and fungal stable isotopes of N (15N) 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 15N variability and this limits the application of such measurements to better understand N cycling. We conducted a landscape-scale analysis of 15N values from 31 putatively N -limited monospecific black spruce (Picea mariana) stands in central Alaska to assess the two main hypothesized sources of plant 15N variation: differing sources and ECM fractionation. We found roughly 20% of the variability in black spruce foliar N and 15N values to be correlated with the concentration and 15N values of soil NH4 + and dissolved organic N (DON) pools, respectively. However, 15N-based mixing models from 24 of the stands suggested that fractionation by ECM fungi obscures the 15N 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 15N values within the soil DON pool to determine how choice of soil 15N values influence modeled ECM activity. The C balance of boreal forests is tightly linked to N cycling and 15N values may be useful metrics of changes to these connections.
Keywords: 15N, black spruce, denitrifier method, dissolved organic nitrogen, ectomycorrhiza, isotope fractionation, mixing models
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Mayor, Jordan R.; Schuur, Edward A.G.; Mack, Michelle C.; Hollingsworth, Terresa N.; Bääth, Erland. 2012. Nitrogen isotope patterns in Alaskan black spruce reflect organic nitrogen sources and the activity of ectomycorrhizal fungi. Ecosystems.15: 819-831.
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