Linking Functional Leaf Traits to Ecophysiology in South African Pelargoniums

Plant responses to drought impact the distribution and persistence of species yet are usually assessed over time frames that may not reflect dynamic stomatal responses, i.e. isohydry and anisohydry. Iso-/anisohydry is a well-known continuum across species from many lineages and communities, but few studies associate iso-/anisohydry with functional trait variation or evolutionary history. We investigated phylogenetic effects on iso-/anisohydry in species from the two major clades with the specific intent of determining whether functional leaf traits link to differences in stomatal behavior. We compared the extent of isohydry/anisohydry in a total of 23 Pelargonium species at two different sites across a seasonal dry-down in the field and a total of 12 species in a dry-down experiment in a greenhouse by measuring functional leaf traits, photosynthetic rates, stomatal conductance and predawn water potentials during the dry-down period on the same individuals. In the greenhouse and the field, species range in expression of iso-/anisohydry but clades differ significantly; we show that linkages between functional leaf traits and stomatal responses are largely clade-specific. We propose that differences in stomatal behavior reflect adaptations to contrasting climates during clade diversification and/or current species distributions across a climatically diverse region. While interactions between functional leaf traits reflect contrasting strategies of resource acquisition across diverse plant lineages, seasonal variation in traits among co-occurring congeners and the extent to which traits predict changes in physiology during a single growing season is relatively unexplored. In field species of Pelargonium, we investigate seasonal shifts in functional leaf traits and photosynthesis, and ask if photosynthetic shifts are predicted by leaf longevity, functional traits and climate. Amazingly, we find that variation in leaf longevity for 23 Pelargonium species parallels the global range of leaf longevities for deciduous species, and variation in functional traits and their interactions are strongly affected by season of measurement. Compared to global datasets in which leaf longevity links strongly to climate, we find no association, and show that seasonal shifts in photosynthetic rates are also not strongly dictated by climate but instead predicted by individual species’ leaf longevities and traits reflecting access to resources (light and water)

Contrasting Leaf Shapes Vary in Extent of Solar Tracking: Revisiting Darwin\u27s Service to the Plant

Solar tracking affects leaf temperature through the amount of direct light intercepting the lamina. However, leaf shape also affects leaf temperature due to heat transfer across boundary layers, and no studies have addressed the effect of leaf shape on solar tracking and leaf temperatures in the field. We compare solar tracking, leaf temperatures, photosynthetic rates and leaf longevity in two co-occurring species with contrasting leaf morphologies: Pelargonium lobatum has a large, shallowly lobed leaf and P. triste has a highly dissected leaf composed of many small leaflets. Pelargonium triste tracked the sun more closely than P. lobatum, although P. lobatum intercepted more direct light at midday despite less solar tracking. Leaf temperatures for the two species were more similar than predicted based on leaf energy budgets. Photosynthetic rates declined more in P. lobatum than P. triste at the end of the growing season and P. triste leaves were estimated to live 20% longer. Leaf three-dimensionality has thermal effects beyond that predicted from a traditional energy budget equation. By moving, P. triste leaves heat up quickly in the morning yet experience little direct light at midday from self-shading leaflets. Pelargonium lobatum leaves warm more slowly but reach the same maximum temperature as P. triste. We hypothesize that the one-month longer life span of P. triste leaves is in part due to the avoidance of lethal leaf temperatures as summer approaches. The combination of leaf shape and solar tracking may be directly linked to differences in leaf longevity in these exposed geophytes through their modulation of direct light absorption and the downstream effects on leaf thermodynamics and photosynthetic rate. Leaf shape may predict leaf function better than many commonly measured functional traits, and the full extent of Darwin’s “service to the plant” results from the synergistic effects of leaf movement and morphology

Extent of solar tracking differs between two co-occurring congeneric geophytes that differ in leaf shape

Premise of research. By adjusting leaf angles to orient toward or away from the sun, solar tracking modifies direct light interception, which consequently modifies leaf temperature. Leaf temperature is also influenced by leaf shape, due to its effect on heat transfer across boundary layers. Two co-occurring, closely related geophytic species of Pelargonium that differ dramatically in leaf shape were observed to exhibit differences in diurnal leaf movements. We asked whether leaf movements were consistent with solar tracking, whether they differed between the two species, and whether leaf shape and movement interacted to influence leaf temperature. Methodology. We measured solar tracking, leaf temperatures, stomatal conductance, and light interception across a diurnal time course in midwinter in the field at De Hoop Nature Reserve in South Africa. Pivotal results. Highly dissected leaves of P. triste moved to track the sun more closely than shallowly lobed leaves of P. lobatum. In contrast to predictions based on leaf energy budget calculations, average diurnal temperatures for both leaf shapes remained close to ambient, with the only significant deviation occurring early in the morning in P. triste. The best model predicting the extent of leaf temperature difference from ambient included leaf shape, leaf movement, and the proportion of the leaf surface receiving direct light, and, notably, the interaction between leaf shape and movement. Conclusions. Leaf three-dimensionality interacts with movement to dictate direct light absorption, and all are critical to fully understanding leaf thermal profiles of nonflat leaves under field conditions

Phylogenetic influences on leaf trait integration in Pelargonium (geraniaceae): Convergence, divergence, and historical adaptation to a rapidly changing climate

Premise of the study: Trait integration may improve prediction of species and lineage responses to future climate change more than individual traits alone, particularly when analyses incorporate effects of phylogenetic relationships. The South African ge

Data from: Divergent trait and environment relationships among parallel radiations in Pelargonium (Geraniaceae): a role for evolutionary legacy?

Functional traits in closely related lineages are expected to vary similarly along common environmental gradients due to shared evolutionary and biogeographic history, or legacy effects, and due to biophysical tradeoffs in construction. We test these predictions in Pelargonium, a relatively recent evolutionary radiation. Bayesian phylogenetic mixed effects models assessed, at the subclade level, associations between plant height, leaf area, leaf nitrogen content and leaf mass per area (LMA), and five environmental variables capturing temperature and rainfall gradients across the Greater Cape Floristic Region of South Africa. Trait-trait integration was assessed via pairwise-correlations within subclades. Of 20 trait-environment associations, 17 differed among subclades. Signs of regression coefficients diverged for height, leaf area and leaf nitrogen content, but not for LMA. Subclades also differed in trait-trait relationships and these differences were modulated by rainfall seasonality. Leave-one-out cross-validation revealed that whether trait variation was better predicted by environmental predictors or trait-trait integration depended on the clade and trait in question. Legacy signals in trait-environment and trait-trait relationships were apparently lost during the earliest diversification of Pelargonium, but then retained during subsequent subclade evolution. Overall, we demonstrate that global-scale patterns are poor predictors of patterns of trait variation at finer geographic and taxonomic scales

results-2014-03-06-09-01-02

Ultrametricized tree used in Pelargonium analysis

posterior-comparisons.tex

Posterior comparison results in tex format

Pel_CFR_2011_2012

Site and trait data for Pelargonium individuals used in this study

Data from: Functional traits in parallel evolutionary radiations and trait-environment associations in the Cape Floristic region of South Africa

Evolutionary radiations with extreme levels of diversity present a unique opportunity to study the role of the environment in plant evolution. If environmental adaptation played an important role in such radiations, we expect to find associations between functional traits and key climatic variables. Similar trait-environment associations across clades may reflect common responses, while contradictory associations may suggest lineage-specific adaptations. Here, we explore trait-environment relationships in two evolutionary radiations in the fynbos biome of the highly biodiverse Cape Floristic Region (CFR) of South Africa. Protea and Pelargonium are morphologically and evolutionarily diverse genera that typify the CFR yet are substantially different in growth form and morphology. Our analytical approach employs a Bayesian multiple-response generalized linear mixed-effects model, taking into account covariation among traits and controlling for phylogenetic relationships. Of the pairwise trait-environment associations tested, 6 out of 24 were in the same direction and 2 out of 24 were in opposite directions, with the latter apparently reflecting alternative life-history strategies. These findings demonstrate that trait diversity within two plant lineages may reflect both parallel and idiosyncratic responses to the environment, rather than all taxa conforming to a global-scale pattern. Such insights are essential for understanding how trait-environment associations arise and how they influence species diversification