Climate Constrains Photosynthetic Strategies in Darwin's Daisies: A Test of the Climatic Variability and Jack-of-All-Trades Hypotheses.

AbstractEmpirical evidence for the climate variability and performance trade-off hypotheses is limited to animals, and it is unclear whether climate constrains the photosynthetic strategies of plants. The plant genus Scalesia Arn. ex Lindl (family Asteraceae), endemic to the Galápagos archipelago, provides an ideal study system to test these hypotheses because of its species with markedly different leaf morphologies that occupy distinct climatic zones. In this study we tested the classic hypotheses that (1) climate constrains leaf size, (2) high climatic temperature variability selects for thermal generalists (i.e., the climate variability hypothesis), and (3) there is a trade-off between the breadth and rate of photosynthetic performance (i.e., jack-of-all-trades but master of none hypothesis). To do this we measured the leaf morphologies and photosynthetic temperature response curves of 11 Scalesia species. In support of a priori predictions, we found that small-leaved Scalesia species were more likely to occupy hotter and drier climates than large-leaved species, there was a positive relationship between climatic temperature variability and the breadth of photosynthetic performance, and photosynthetic performance was negatively correlated with photosynthetic breadth. Our study is among the first to provide evidence for the performance-breadth trade-off hypothesis in photosynthesis, suggesting that climate change may select for photosynthetic thermal generalists.

Photosystem II heat tolerances characterize thermal generalists and the upper limit of carbon assimilation.

The heat tolerance of photosystem II (PSII) may promote carbon assimilation at higher temperatures and help explain plant responses to climate change. Higher PSII heat tolerance could lead to (a) increases in the high-temperature compensation point (Tmax ); (b) increases in the thermal breadth of photosynthesis (i.e. the photosynthetic parameter Ω) to promote a thermal generalist strategy of carbon assimilation; (c) increases in the optimum rate of carbon assimilation Popt and faster carbon assimilation and/or (d) increases in the optimum temperature for photosynthesis (Topt ). To address these hypotheses, we tested if the Tcrit , T50 and T95 PSII heat tolerances were correlated with carbon assimilation parameters for 21 plant species. Our results did not support Hypothesis 1, but we observed that T50 may be used to estimate the upper thermal limit for Tmax at the species level, and that community mean Tcrit may be useful for approximating Tmax . The T50 and T95 heat tolerance metrics were positively correlated with Ω in support of Hypothesis 2. We found no support for Hypotheses 3 or 4. Our study shows that high PSII heat tolerance is unlikely to improve carbon assimilation at higher temperatures but may characterize thermal generalists with slow resource acquisition strategies.

Herbarium-based measurements reliably estimate three functional traits.

PREMISE: The use of functional traits has surged in recent decades, providing new insights ranging from individual plant fitness to ecosystem processes. Global plant trait databases have advanced our understanding of plant functional diversity, but they remain incomplete because of geographic and taxonomic biases. Herbarium specimens may help fill these gaps by providing trait information across space and time. We tested whether herbarium specimen-derived measurements are reliable estimates of three important, commonly measured functional traits-specific leaf area (SLA), branch wood specific gravity, and leaf thickness. METHODS: Leaves and branches were collected from species cultivated at Fairchild Tropical Botanic Garden and Florida International University in Miami, FL, USA. Fresh components of SLA (area), branch wood specific gravity (volume), and leaf thickness were measured following standard trait measurement protocols. We compared these trait values to corresponding measurements using plant tissues dried in a plant press following standard herbarium plant collecting protocols. RESULTS: Herbarium-derived trait measurements (dried tissues) were highly correlated with those measured using fresh tissues following standard protocols (SLA: R2 = 0.72-0.97, p < 0.01; wood specific gravity: R2 = 0.74-0.75, p < 0.01; leaf thickness: R2 = 0.96, p < 0.01). However, except for leaf thickness, linear model slope or intercept coefficients differed from 1, indicating herbarium-derived trait measurements may provide biased estimates of fresh traits without the use of correction factors. CONCLUSIONS: Herbarium-derived traits cannot always be used interchangeably with those measured from fresh tissues because of tissue shrinkage. However, herbarium-derived trait data still have the potential to drastically expand the temporal, geographic, and taxonomic scope of global trait databases.

Publisher Correction: Open Science principles for accelerating trait-based science across the Tree of Life.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Open Science principles for accelerating trait-based science across the Tree of Life.

Synthesizing trait observations and knowledge across the Tree of Life remains a grand challenge for biodiversity science. Species traits are widely used in ecological and evolutionary science, and new data and methods have proliferated rapidly. Yet accessing and integrating disparate data sources remains a considerable challenge, slowing progress toward a global synthesis to integrate trait data across organisms. Trait science needs a vision for achieving global integration across all organisms. Here, we outline how the adoption of key Open Science principles-open data, open source and open methods-is transforming trait science, increasing transparency, democratizing access and accelerating global synthesis. To enhance widespread adoption of these principles, we introduce the Open Traits Network (OTN), a global, decentralized community welcoming all researchers and institutions pursuing the collaborative goal of standardizing and integrating trait data across organisms. We demonstrate how adherence to Open Science principles is key to the OTN community and outline five activities that can accelerate the synthesis of trait data across the Tree of Life, thereby facilitating rapid advances to address scientific inquiries and environmental issues. Lessons learned along the path to a global synthesis of trait data will provide a framework for addressing similarly complex data science and informatics challenges.

Botanic gardens are an untapped resource for studying the functional ecology of tropical plants.

Functional traits are increasingly used to understand the ecology of plants and to predict their responses to global changes. Unfortunately, trait data are unavailable for the majority of plant species. The lack of trait data is especially prevalent for hard-to-measure traits and for tropical plant species, potentially owing to the many inherent difficulties of working with species in remote, hyperdiverse rainforest systems. The living collections of botanic gardens provide convenient access to large numbers of tropical plant species and can potentially be used to quickly augment trait databases and advance our understanding of species' responses to climate change. In this review, we quantitatively assess the availability of trait data for tropical versus temperate species, the diversity of species available for sampling in several exemplar tropical botanic gardens and the validity of garden-based leaf and root trait measurements. Our analyses support the contention that the living collections of botanic gardens are a valuable scientific resource that can contribute significantly to research on plant functional ecology and conservation.This article is part of the theme issue 'Biological collections for understanding biodiversity in the Anthropocene'.