Leaf shape linked to photosynthetic rates and temperature optima in South African Pelargonium species

Abstract

The thermal response of gas exchange varies among plant species and with growth conditions. Plants from hot dry climates generally reach maximal photosynthetic rates at higher temperatures than species from temperate climates. Likewise, species in these environments are predicted to have small leaves with more-dissected shapes. We compared eight species of Pelargonium (Geraniaceae) selected as phylogenetically independent contrasts on leaf shape to determine whether: (1) the species showed plasticity in thermal response of gas exchange when grown under different water and temperature regimes, (2) there were differences among more- and less-dissected leafed species in trait means or plasticity, and (3) whether climatic variables were correlated with the responses. We found that a higher growth temperature led to higher optimal photosynthetic temperatures, at a cost to photosynthetic capacity. Optimal temperatures for photosynthesis were greater than the highest growth temperature regime. Stomatal conductance responded to growth water regime but not growth temperature, whereas transpiration increased and water use efficiency (WUE) decreased at the higher growth temperature. Strikingly, species with more-dissected leaves had higher rates of carbon gain and water loss for a given growth condition than those with less-dissected leaves. Species from lower latitudes and lower rainfall tended to have higher photosynthetic maxima and conductance, but leaf dissection did not correlate with climatic variables. Our results suggest that the combination of dissected leaves, higher photosynthetic rates, and relatively low WUE may have evolved as a strategy to optimize water delivery and carbon gain during short-lived periods of high soil moisture. Higher thermal optima, in conjunction with leaf dissection, may reflect selection pressure to protect photosynthetic machinery against excessive leaf temperatures when stomata close in response to water stress.

On the reconstruction of plant photosynthetic and stress physiology across the Triassic–Jurassic boundary

“…Modeling of decreased convective heat loss caused by reduced stomatal frequencies at the TJB (from approximately 50 stomata per mm 2 at the start of the Astartekløft section, reaching a low of approximately 13 per mm 2 in the Late Triassic before rising to approximately 90 stomata per mm 2 in the Early Jurassic), in conjunction with regional warming, shows that leaf temperatures would have exceeded lethal levels (McElwain et al, 1999). This is supported by fossil leaf evidence showing that leaves decrease in size and increase in dissection at the TJB, indicative of selection pressures to increase heat loss (McElwain et al, 1999;Nicotra et al, 2008). One of the most widely observed environmentally influenced features in plants is the occurrence of sun and shade leaves, whereby the amount of energy in the form of solar radiation determines specific characteristics of leaf morphology.…”

“…These data suggest that Ginkgoites may have begun to exhibit the effects of thermal stress due to larger leaf size before any significant environmental perturbation. Moving up-section from Bed 1, leaves become more dissected, indicative of selection pressures favoring enhanced heat loss (Gauslaa, 1984;McElwain et al, 1999;Nicotra et al, 2008). This is followed by a concomitant improvement in plant performance (as indicated by an increase in F v / F m ) and reduction in heat stress (decreased NPQ) into Bed 2.…”

Variations in Leaf Morphological Traits of Quercus guyavifolia (Fagaceae) were Mainly Influenced by Water and Ultraviolet Irradiation at High Elevations on the Qinghai-Tibet Plateau, China

“…Smaller leaves have thinner vapor boundary layers, which then support more rapid cooling and restrict evaporation and corresponding water losses (Nicotra et al, 2008). Although leaf length, width, ratio of leaf length to width, shape factor, petiole length, and petiole width may change allometrically with leaf area, their decreases in parallel with lower MAP may also alleviate the effects of a water deficit (Dunbar-Co et al, 2009;Tošković and Veličković, 2013).…”

“…Meanwhile, water availability is another important factor that influences leaf morphology (Givnish, 1987;Mahmood et al, 2015). Under drought conditions, plants commonly produce smaller leaves and have a thinner vapor boundary layer so that evaporative water losses are decreased (Nicotra et al, 2008). Although the effects of environment and elevation on leaf traits have already been examined, most of the research has focused on regions at lower elevations, i.e.…”

The ecological adaptability of four typical plants during the early successional stage of a tropical rainforest

“…With increase in light intensity, air temperature increases whereas humidity decreases. Plants can improve transpiration rate by regulating stomatal conductance to maintain leaf temperature to an appropriate physiological extent (Larcher 1995;Nicotra et al 2008). Excessive light, often occurring with high-leaf temperature or water deficit, is a major environmental stress leading to midday depression of photosynthesis (Valladares & Pearcy 1997).…”