Abstract. Plant traits reflect growth strategies and trade-offs in response to environmental conditions. Because of climate warming, plant traits might
change, altering ecosystem functions and vegetation–climate interactions. Despite important feedbacks of plant trait changes in tundra ecosystems
with regional climate, with a key role for shrubs, information on responses of shrub functional traits is limited. Here, we investigate the effects of experimentally increased permafrost thaw depth and (possibly thaw-associated) soil nutrient availability on
plant functional traits and strategies of Arctic shrubs in northeastern Siberia. We hypothesize that shrubs will generally shift their strategy from
efficient conservation to faster acquisition of resources through adaptation of leaf and stem traits in a coordinated whole-plant fashion. To test this hypothesis,
we ran a 4 year permafrost thaw and nutrient fertilization experiment with a fully factorial block design and six treatment combinations –
permafrost thaw (control, unheated cable, heated cable) × fertilization (no nutrient addition, nutrient addition). We measured 10 leaf and
stem traits related to growth, defence and the resource economics spectrum in four shrub species (Betula nana, Salix pulchra,
Ledum palustre and Vaccinium vitis-idaea), which were sampled in the experimental plots. The plant trait data were statistically
analysed using linear mixed-effect models and principal component analysis (PCA). The response to increased permafrost thaw was not significant for most shrub traits. However, all shrubs responded to the fertilization treatment,
despite decreased thaw depth and soil temperature in fertilized plots. Shrubs tended to grow taller but did not increase their stem density or bark
thickness. We found a similar coordinated trait response for all four species at leaf and plant level; i.e. they shifted from a conservative towards
a more acquisitive resource economy strategy upon fertilization. In accordance, results point towards a lower investment into defence mechanisms,
and hence increased shrub vulnerability to herbivory and climate extremes. Compared to biomass and height only, detailed data involving individual plant organ traits such as leaf area and nutrient contents or stem water
content can contribute to a better mechanistic understanding of feedbacks between shrub growth strategies, permafrost thaw and carbon and energy
fluxes. In combination with observational data, these experimental tundra trait data allow for a more realistic representation of tundra shrubs in
dynamic vegetation models and robust prediction of ecosystem functions and related climate–vegetation–permafrost feedbacks.
The legacy of Southern American extinct megafauna on plants and biomes biomes
