Data from: Integrated metabolic strategy: a framework for predicting the evolution of carbon-water tradeoffs within plant clades

1. The fundamental tradeoff between carbon gain and water loss has long
been predicted as an evolutionary driver of plant strategies across
environments. Nonetheless, challenges in measuring carbon gain and water
loss in ways that integrate over leaf lifetime have limited our
understanding of the variation in and mechanistic bases of this tradeoff.
Furthermore, the microevolution of plant traits within species versus the
macroevolution of strategies among closely related species may not be
same, and accordingly, the latter must be addressed using comparative
phylogenetic analyses. 2. Here we introduce the concept of ‘integrated
metabolic strategy’ (IMS) to describe the ratio between carbon isotope
composition (δ13C) and oxygen isotope composition above source water
(Δ18O) of leaf cellulose. IMS is a measure of a leaf-level conditions that
integrate several mechanisms contributing to carbon gain (δ13C) and water
loss (Δ18O) over leaf lifespan, with larger values reflecting higher
metabolic efficiency and hence less of a trade-off. We tested how IMS
evolves among closely related yet ecologically diverse milkweed species,
and subsequently addressed phenotypic plasticity in response to water
availability in species with divergent IMS. 3. IMS varied strongly among
20 Asclepias species when grown under controlled conditions, and
phylogenetic analyses demonstrate species-specific tradeoffs between
carbon gain and water loss. Larger IMS values were associated with species
from dry habitats, with larger carboxylation capacity, smaller stomatal
conductance and smaller leaves; smaller IMS was associated with wet
habitats, smaller carboxylation capacity, larger stomatal conductance and
larger leaves. The evolution of IMS was dominated by changes in species’
demand for carbon (δ13C) more so than water conservation (Δ18O). Although
some individual physiological traits showed phylogenetic signal, IMS did
not. 4. In response to experimental decreases in soil moisture, three
species maintained similar IMS across levels of water availability because
of proportional increases in δ13C and Δ18O (or little change in either),
while one species increased IMS due to disproportional changes in δ13C
relative to Δ18O. 5. Synthesis: IMS is a broadly applicable mechanistic
tool; IMS variation among and within species may shed light on unresolved
questions relating to evolution and ecology of plant ecophysiological
strategies.