Mammalian herbivory shapes intraspecific trait responses to warmer climate and nutrient enrichment.

Maria‐Theresa Jessen,Johan Olofsson,Elina Kaarlejärvi,Anu Eskelinen

doi:10.1111/gcb.15378

Abstract

Variation in intraspecific traits is one important mechanism that can allow plant species to respond to global changes. Understanding plant trait responses to environmental changes such as grazing patterns, nutrient enrichment and climate warming is, thus, essential for predicting the composition of future plant communities. We measured traits of eight common tundra species in a fully factorial field experiment with mammalian herbivore exclusion, fertilization, and passive warming, and assessed how trait responsiveness to the treatments was associated with abundance changes in those treatments. Herbivory exhibited the strongest impact on traits. Exclusion of herbivores increased vegetative plant height by 50% and specific leaf area (SLA) by 19%, and decreased foliar C:N by 11%; fertilization and warming also increased height and SLA but to a smaller extent. Herbivory also modulated intraspecific height, SLA and foliar C:N responses to fertilization and warming, and these interactions were species-specific. Furthermore, herbivory affected how trait change translated into relative abundance change: increased height under warming and fertilization was more positively related to abundance change inside fences than in grazed plots. Our findings highlight the key role of mammalian herbivory when assessing intraspecific trait change in tundra and its consequences for plant performance under global changes.

Highlights

Around the globe, high latitude and altitude systems face shifts in grazing regimes concurrently with increasing temperatures and accelerated nutrient cycling (Aerts, 2006; Uboni et al, 2016; Wookey et al, 2009)
Recent studies suggest that climate warming and nutrient enrichment can lead to pronounced intraspecific trait shifts (Bjorkman et al, 2018; Firn, McGree, et al, 2019) and highlight the need to assess trait responses to multiple global changes that mimic future novel conditions (Donelson et al, 2018; Matesanz et al, 2010)
We found that while increased temperature and nutrients modified intraspecific traits, grazing was a key factor affecting intraspecific trait change in a tundra plant community

Summary

| INTRODUCTION

High latitude and altitude systems face shifts in grazing regimes concurrently with increasing temperatures and accelerated nutrient cycling (Aerts, 2006; Uboni et al, 2016; Wookey et al, 2009). Nutrient addition has been shown to modify intraspecific traits, for example, to enhance plant height, SLA, foliar N content and leaf greenness (Mudrák et al, 2019; Tatarko & Knops, 2018) These are traits related to rapid growth in resource-rich conditions (Reich, 2014; Wright et al, 2004) and they are likely to confer greater performance and competitive ability under nutrient-rich conditions (Carmona et al, 2019; Suding et al, 2005). We predicted: (a) Herbivory would decrease intraspecific height and SLA (but not leaf greenness), and increase foliar C:N. (b) Fertilization and warming would increase intraspecific height, SLA and leaf greenness and decrease foliar C:N. (c) These shifts, induced by warming and fertilization, would be more pronounced in the absence of herbivores and smaller in the presence of herbivores. (d) Intraspecific trait change in response to fertilization and warming measured at the individual level would correlate with increased abundance at the community level in the absence of herbivores, but with smaller or decreased abundance in the presence of herbivores

| MATERIALS AND METHODS

Findings

| DISCUSSION