Rethinking the Plant Economics Spectrum for Annuals: A Multi-Species Study.

Susanne Kurze,Leonor Álvarez-Cansino,Bettina M J Engelbrecht,Mark C Bilton,Katja Tielbörger

doi:10.3389/fpls.2021.640862

Abstract

The plant economics spectrum hypothesizes a correlation among resource-use related traits along one single axis, which determines species’ growth rates and their ecological filtering along resource gradients. This concept has been mostly investigated and shown in perennial species, but has rarely been tested in annual species. Annuals evade unfavorable seasons as seeds and thus may underlie different constraints, with consequences for interspecific trait-trait, trait-growth, and trait-environment relations. To test the hypotheses of the plant economics spectrum in annual species, we measured twelve resource-use related leaf and root traits in 30 winter annuals from Israel under controlled conditions. Traits and their coordinations were related to species’ growth rates (for 19 species) and their distribution along a steep rainfall gradient. Contrary to the hypotheses of the plant economics spectrum, in the investigated annuals traits were correlated along two independent axes, one of structural traits and one of carbon gain traits. Consequently, species’ growth rates were related to carbon gain traits, but independent from structural traits. Species’ distribution along the rainfall gradient was unexpectedly neither associated with species’ scores along the axes of carbon gain or structural traits nor with growth rate. Nevertheless, root traits were related with species’ distribution, indicating that they are relevant for species’ filtering along rainfall gradients in winter annuals. Overall, our results showed that the functional constraints hypothesized by the plant economics spectrum do not apply to winter annuals, leading to unexpected trait-growth and trait-rainfall relations. Our study thus cautions to generalize trait-based concepts and findings between life-history strategies. To predict responses to global change, trait-based concepts should be explicitly tested for different species groups.

Highlights

Trait-based schemes, such as the plant economics spectrum, characterize general combinations and trade-offs among functional traits and their relations to environmental conditions (e.g., Grime, 1977; Westoby et al, 2002; Wright et al, 2004; Reich, 2014)
The attribute range of several leaf traits in the studied annuals almost corresponded to 60–80% of the globally documented trait ranges in plant species from different ecosystems and life forms worldwide (Kattge et al, 2020, see details in Supplementary Table S2)
PC 2 was highly negatively correlated with Amass, Nmass, Cmass, and SLA, four traits associated with carbon gain

Summary

Introduction

Trait-based schemes, such as the plant economics spectrum, characterize general combinations and trade-offs among functional traits and their relations to environmental conditions (e.g., Grime, 1977; Westoby et al, 2002; Wright et al, 2004; Reich, 2014). Annual species substantially contribute to species diversity, primary production, and ecosystem services in many dryland ecosystems worldwide (Noy-Meir, 1973; Tielbörger et al, 2014; Ruppert et al, 2015). These ecosystems have been characterized as vulnerable to global change (Sala et al, 2000; Schröter et al, 2005), underscoring the relevance of assessing and predicting species’ responses to climate and land-use change. Understanding interspecific trait-trait relations and the ecological filtering of annuals is timely and of practical relevance

Methods

Results

Discussion

Conclusion