Abstract Detail


Smith, Duncan [1], Adams, Mark [2], Salvi, Amanda [3], Buckley, Thomas N [4], Ané, Cécile [1], McCulloh, Katherine [1], Givnish, Thomas [5].

Integrated adaptations to moisture supply and cross-over in whole-plant growth among Eucalyptus species along an Australian rainfall gradient.

Terrestrial plants face a fundamental trade-off: any variation in leaf structure that increases the inward diffusion of CO2 to enhance photosynthesis also increases the outward diffusion outward of water vapor, raising the risk of tissue desiccation, lower photosynthetic performance, and even death. To maximize competitive ability, plants should maximize the difference between photosynthetic benefits and transpirational costs, and adjust their leaf form and physiology, hydraulic traits, and resource allocation among leaves, stems, and roots to maximize their realized rates of whole-plant carbon gain and/or height growth. Eucalyptus species that dominate different portions of a macroclimatic moisture gradient in Victoria, Australia provide an excellent system for testing the predictions of economic theory for trait-environment and trait-trait relationships, and for assessing the core prediction that species with the highest growth rate relative to others under a particular set of conditions will be those that dominate those conditions. Here we report on a five-year study aimed at testing these ideas, based on quantifying whole-plant growth and photosynthetic, hydraulic, and allocational traits in ten Eucalyptus species stratified by subgenus and by parts of the large-scale moisture gradient they dominate in Victoria. Relative moisture supply was quantified as P/Ep, where P is annual precipitation and Ep is pan evaporation, averaged over each species’ distribution. We studied trait expression, growth, and survival as a function of species and site P/Ep, scoring 49 traits in transplants to common gardens in mallee, eucalypt woodland, eucalypt forest, and tall wet sclerophyll forest. Most trait-environment relationships – evaluated using phylogenetically structured analyses – accord qualitatively with economic theory, with weaker relationships within species (plasticity) than across species. Stomatal conductance was a conspicuous exception, decreasing with species P/Ep. However, this reflects a decline in g with species P/Ep in the two driest gardens; this might reflect lower root allocation in species from moister habitats, as well as their greater mesophyll photosynthetic sensitivity. The first two axes of a pPCA accounted for 60% of trait variation within and among species and gardens, with a strong relationship to site and garden P/Ep. The relationship of PCA axis 1 scores to species P/Ep becomes stronger at moister gardens, with species showing less divergence in more strongly xeromorphic traits in dry gardens. Trait-trait relationships and correlation structures varied with garden P/Ep. We tested for true trait-trait coadaptation (vs. both traits simply tracking P/Ep) by regressing residuals of each trait vs. species P/Ep against each other. Finally, we largely found support – as predicted – for adaptive cross-over, with the realized height growth of most species being higher than that of other species in gardens with P/Ep like the climates dominated by the focal species.

1 - University of Wisconsin-Madison, Botany, Madison, WI, 53706, USA
2 - Swinburne University, Biosciences and Innovation, Hawthorn, Victoria, 3122, Australia
3 - University Of Wisconsin-Madison, Department Of Botany, 322 Birge Hall 430 Lincoln Drive, Madison, WI, 53706, United States
4 - University of California at Davis
5 - University Of Wisconsin-Madison, Department Of Botany, 315 Birge Hall, 430 Lincoln Drive, Madison, WI, 53706, United States

adaptive crossover
trait-environment relationship
trait-trait relationship
trait evolution
Phenotypic plasticity
species distributions
relative moisture supply

Presentation Type: Oral Paper
Number: EPH3005
Abstract ID:584
Candidate for Awards:None

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