Chemical Similarity of Co-occurring Trees Decreases With Precipitation and Temperature in North American Forests

Brian E Sedio ,Jack H Dwenger,Hamssika Chandrasekaran,Christian A López,Jordan G Kueneman ,Nicola J Day ,Jennifer L Baltzer ,Christopher W Dick ,Maria D Person ,Emily A Dewald-Wang ,John D Parker ,Norman A Bourg ,Ian R Mcgregor ,Kristina J Anderson‐Teixeira ,Buck T Castillo ,Geoffrey G Parker ,Jonathan A Myers ,David Allen ,Marko J Spasojevic ,María Laura Prechi ,Sean M Mcmahon ,James A Lutz ,S Joseph Wright ,Timothy Y James ,Joseph C Lamanna ,John Vandermeer

doi:10.26686/wgtn.14752590.v1

Abstract

Plant diversity varies immensely over large-scale gradients in temperature, precipitation, and seasonality at global and regional scales. This relationship may be driven in part by climatic variation in the relative importance of abiotic and biotic interactions to the diversity and composition of plant communities. In particular, biotic interactions may become stronger and more host specific with increasing precipitation and temperature, resulting in greater plant species richness in wetter and warmer environments. This hypothesis predicts that the many defensive compounds found in plants’ metabolomes should increase in richness and decrease in interspecific similarity with precipitation, temperature, and plant diversity. To test this prediction, we compared patterns of chemical and morphological trait diversity of 140 woody plant species among seven temperate forests in North America representing 16.2°C variation in mean annual temperature (MAT), 2,115 mm variation in mean annual precipitation (MAP), and from 10 to 68 co-occurring species. We used untargeted metabolomics methods based on data generated with liquid chromatography-tandem mass spectrometry to identify, classify, and compare 13,480 unique foliar metabolites and to quantify the metabolomic similarity of species in each community with respect to the whole metabolome and each of five broad classes of metabolites. In addition, we compiled morphological trait data from existing databases and field surveys for three commonly measured traits (specific leaf area [SLA], wood density, and seed mass) for comparison with foliar metabolomes. We found that chemical defense strategies and growth and allocation strategies reflected by these traits largely represented orthogonal axes of variation. In addition, functional dispersion of SLA increased with MAP, whereas functional richness of wood density and seed mass increased with MAT. In contrast, chemical similarity of co-occurring species decreased with both MAT and MAP, and metabolite richness increased with MAT. Variation in metabolite richness among communities was positively correlated with species richness, but variation in mean chemical similarity was not. Our results are consistent with the hypothesis that plant metabolomes play a more important role in community assembly in wetter and warmer climates, even at temperate latitudes, and suggest that metabolomic traits can provide unique insight to studies of trait-based community assembly.

Highlights

Plant diversity varies immensely over large-scale climatic gradients at regional and global scales
We found that the five metabolomic superclasses and the three morphological traits we considered represented largely orthogonal axes of variation in the principal components analysis (PCA) (Figure 2 and Supplementary Table 6), but there was some covariation among metabolomic and morphological traits
The functional strategies of species present at each of these seven sites varied along these major gradients. This was reflected in variation in both the morphological traits, and in quantitative investment in broad chemical superclasses, which represent largely orthogonal axes of variation (Figure 2)

Summary

Introduction

Plant diversity varies immensely over large-scale climatic gradients at regional and global scales. Woody plant diversity increases with precipitation and temperature (Gentry, 1988; Hawkins et al, 2003; Kreft and Jetz, 2007; Esquivel-Muelbert et al, 2017). Prominent hypotheses for these large-scale diversity gradients propose that environmental filtering reduces community membership, and diversity, in abiotically stressful climates and that increased specialization of biotic interactions increases species richness in less stressful climates (Schemske et al, 2009; Lamanna et al, 2014; Chu et al, 2019). These hypotheses make testable predictions regarding relationships between climatic gradients and the traits that mediate plant interactions with the abiotic and biotic environment

Methods

Results

Conclusion