|1. Plant chemical and structural defence compounds are well known to impact upon herbivory
of fresh leaves and in?uence decomposition rates after leaf senescence. A number of theories
predict that alleviat ing nutrient limitation and reducing other environmental stressors will
result in decreased production of plant chemical defences.
2. In this study, we measured plant defence properties [total polyphenols (TP), condensed tan-
nins (CT) and lignin concentrations, and protein complexation capacity (PCC)] in both fresh
and senesced plant leaves in a fully factorial N and P fertilization experiment set-up at each of
three elevations along an elevational gradient in Swedish subarctic tundra heath vegetation.
Further, we performed a decomposition of variance analysis on community-weighted averages
(CWAs) of plant defence prop erties to determine the relative contributions of interspeci?c and
intraspec i?c variation to the total variation observed in response to elevation and nutrient
3. We hypothesized that N fertilization would reduce plant defence properties and that this
reduction would be greater at higher elevat ions, while the e?ects of P fertilization would have
no e?ect at any elevation.
4. At the community level, N addition reduced CT and PCC in both fresh and senesced leaves
and TP in senesced leaves, while P addition had few e?ects, broadly in line with our hypo -
thesis. The e?ects of N addition frequently varied with elevation, but in contrast to our
hypothesis, the said e?ects were strongest at the lowest elevations. The e?ects of N addition
and the interactive e?e ct of N with elevation were primarily driven by intraspeci?c, rather than
interspec i?c, variation.
5. Our ?ndings suggest that as temperatures warm and N availability increases due to global
climate change, secondary metabolites in subarctic heath vegetation will decline particularly
within species. Our results highlight the need to consider the e?ects of both nutrient availabil-
ity and temperature, and their interaction, in driving subarctic plant defence.|