The global spectrum of plant form and function

Abstract

Vascular plants are the main entry point for energy and matter into the Earth's terrestrial ecosystems. Their Darwinian struggle for growth, survival and reproduction in very different arenas has resulted in an extremely wide variety of form and function, both across and within habitats. Yet it has long been thought 1-8 that there is a pattern to be found in this remarkable evolutionary radiation-that some trait constellations are viable and successful whereas others are not.Empirical support for a strongly limited set of viable trait combinations has accumulated for traits associated with single plant organs, such as leaves 7,9-12 , stems 13,14 and seeds [15][16][17] . Evidence across plant organs has been rarer, restricted geographically or taxonomically, and often contradictory [18][19][20][21][22][23][24][25][26][27][28][29] . How tightly whole-plant form and function are restricted at the global scale remains unresolved.Here we present the first global quantitative picture of essential functional diversity of extant vascular plants. We quantify the volume, shape and boundaries of this functional space via joint consideration of six traits that together capture the essence of plant form and function: adult plant height, stem specific density, leaf size expressed as leaf area, leaf mass per area, leaf nitrogen content per unit mass, and diaspore mass. Our dataset, based on a recently updated communal plant trait database 30 , covers 46,085 vascular plant species from 423 families and to our knowledge spans the widest range of growth-forms and geographical locations to date in published trait analyses, including some of the most extreme plant trait values ever measured in the field (Table 1, Extended Data Fig. 1). On this basis we reveal that the trait space actually occupied is strongly restricted as compared to four alternative null hypotheses. We demonstrate that plant species largely occupy a plane in the six-dimensional trait space. Two key trait dimensions within this plane are the size of whole plants and organs on the one hand, and the construction costs for photosynthetic leaf area, on the other. We subsequently show which sections of the plane are occupied, and how densely, by different growth-forms and major taxonomic groups. The design opportunities and limits indicated by today's global spectrum of plant form and function provide a foundation to achieve a better understanding of the evolutionary trajectory of vascular plants and help frame and test hypotheses as to where and Earth is home to a remarkable diversity of plant forms and life histories, yet comparatively few essential trait combinations have proved evolutionarily viable in today's terrestrial biosphere. By analysing worldwide variation in six major traits critical to growth, survival and reproduction within the largest sample of vascular plant species ever compiled, we found that occupancy of six-dimensional trait space is strongly concentrated, indicating coordination and trade-offs. Threequarters of trait variation is captured in a t...

Intraspecific trait variation can weaken interspecific trait correlations when assessing the whole‐plant economic spectrum

“…Identifying general principles and trade‐offs that underlie the diversity of organism form and function is a central goal of functional ecology because trade‐offs constrain demographic rates and their linkages to ecosystem processes (Díaz et al., 2016; Shipley et al., 2016). An important step toward this goal, in relation to plants, was the recognition of close coordination among a suite of leaf functional traits: All vascular plant species align around a global spectrum from those with expensive, long‐lived leaves that process resources slowly, to those with low‐cost short‐lived leaves that process resources quickly (Reich, Walters, & Ellsworth, 1997; Wright et al., 2004).…”

Examining variation in the leaf mass per area of dominant species across two contrasting tropical gradients in light of community assembly

“…2004; Díaz et al. 2016). Nutrient‐ or water‐depleted environments select for nutrient and water savings via long‐lived, thick, robust leaves with a high LMA (slow end of the leaf economic spectrum, LES), while nutrient‐rich environments favor more tender, faster‐growing (and often low‐LMA) leaves that are better able to outcompete potential neighbors (Wright et al.…”

Functional trade‐offs and the phylogenetic dispersion of seed traits in a biodiversity hotspot of the Mountains of Southwest China

“…Similar trends have been found at both local (Mexican desert; Flores & Briones, 2001) and global (Díaz et al., 2016; Moles et al., 2007) scales. In the present study, differences in overall seed mass and time to germination represent different modes of resource investment (such as energy and time), confirming that global distribution patterns of woody and nonwoody species are uneven in both form and function (Díaz et al., 2016). …”

“…Regardless of these sources of variation, overall the proportion of resources allocated to reproduction does not vary greatly among species, and plant mass and seed mass can explain most seed production variation in plant species (Shipley & Dion, 1992). That our results show the same but weaker trends compared to those of previous studies at different scales indicates that the negative relation between seed mass and seed number is likely scale‐independent (Díaz et al., 2016; Donoso, Schleuning, García, & Fründ, 2017), but the strength of this relation may be affected by the environment heterogeneity and the composition of highly diverse taxa. It is worth noting that the method to quantify seed number may be limited in our study.…”