Some like it hot: the physiological ecology of C plant evolution.

The evolution of C photosynthesis requires an intermediate phase where photorespiratory glycine produced in the mesophyll cells must flow to the vascular sheath cells for metabolism by glycine decarboxylase. This glycine flux concentrates photorespired CO within the sheath cells, allowing it to be efficiently refixed by sheath Rubisco. A modest C biochemical cycle is then upregulated, possibly to support the refixation of photorespired ammonia in sheath cells, with subsequent increases in C metabolism providing incremental benefits until an optimized C pathway is established.

Sunflecks in trees and forests: from photosynthetic physiology to global change biology.

Sunflecks are brief, intermittent periods of high photon flux density (PFD) that can significantly improve carbon gain in shaded forest understories and lower canopies of trees. In this review, we discuss the physiological basis of leaf-level responses to sunflecks and the mechanisms plants use to tolerate sudden changes in PFD and leaf temperature induced by sunflecks. We also examine the potential effects of climate change stresses (including elevated temperatures, rising CO(2) concentrations and drought) on the ability of tree species to use sunflecks, and advocate more research to improve our predictions of seedling and tree carbon gain in future climates.

The taxonomic distribution of C4 photosynthesis in Amaranthaceae sensu stricto.

C(4) photosynthesis evolved multiple times in the Amaranthaceae s.s., but the C(4) evolutionary lineages are unclear because the photosynthetic pathway is unknown for most species of the family.

Leaf display and photosynthesis of tree seedlings in a cool-temperate deciduous broadleaf forest understorey.

To examine a possible convergence in leaf photosynthetic characteristics and leaf display responses to light environment in seedlings of three canopy and two shrub tree species in understorey of cool-temperate deciduous broadleaf forest, relationships between light environment, leaf orientation and leaf light-photosynthetic response were measured. Light capture of the seedlings (17-24 individuals with 2-12 leaves for each species) was assessed with a three dimensional geometric modeling program Y-plant. Leaf photosynthetic characteristics of the five species were found to have acclimated to the understorey light environment, i.

Crown architecture in sun and shade environments: assessing function and trade-offs with a three-dimensional simulation model.

Sun and shade environments place markedly different constraints on the photosynthetic performance of plants. Leaf-level photosynthetic responses to sun and shade have been extensively investigated, whereas there has been much less research on the functional role of crown architecture in these environments. This paper focuses on the role of architecture in maximizing light capture and photosynthesis in shaded understories and in minimizing exposure to excess radiation in open high light environments.

Photoinhibition and drought in Mediterranean woody saplings: scaling effects and interactions in sun and shade phenotypes.

Interacting effects of high light and drought on the performance of sun and shade phenotypes were experimentally undertaken following survival, chlorophyll fluorescence and gas exchange in 2-year-old saplings of four Mediterranean trees (Quercus ilex and Q. coccifera as water-saving species, and Pistacia lentiscus and P. terebinthus as water-spending species).

A functional analysis of the crown architecture of tropical forest Psychotria species: do species vary in light capture efficiency and consequently in carbon gain and growth?

The crown architectures of 11 Psychotria species native to Barro Colorado Island, Panama were reconstructed from field measurements of leaf and branch geometry with the three-dimensional simulation model Y-plant. The objective was to assess the role of species differences in architecture in light capture and carbon gain in their natural understory environment. When species were grouped according to their putative light environment preference, the shade tolerant species were found to have a small but significantly higher efficiency of light capture for both diffuse and direct light as compared to the light demanding species.

Functional correlates of leaf demographic response to gap release in saplings of a shade-tolerant tree, Elateriospermum tapos.

For a shade-tolerant SE Asian tropical tree, Elateriospermum tapos (Euphorbiaceae), we studied field-established saplings in gaps and the shaded understory to test the hypothesis that differences in leaf demography and leaf life span under contrasting light regimes should be functionally correlated with architecture, self-shading and nitrogen distribution within the sapling crown. Rates of leaf production and net leaf gain were greater for saplings in gaps than those in the understory. Median leaf life span was approximately 26 months in the gap saplings, while it was estimated to be greater than 38 months in the understory saplings.

Convergence in light capture efficiencies among tropical forest understory plants with contrasting crown architectures: a case of morphological compensation.

Leaf and crown characteristics were examined for 24 tree and herbaceous species of contrasting architectures from the understory of a lowland rainforest. Light-capture efficiency was estimated for the crowns of the different species with a three-dimensional geometric modeling program. Causal relationships among traits affecting light absorption at two hierarchical levels (leaf and whole crown) were quantified using path analysis.

The functional ecology of shoot architecture in sun and shade plants of Heteromeles arbutifolia M. Roem., a Californian chaparral shrub.

The functional roles of the contrasting morphologies of sun and shade shoots of the evergreen shrub Heteromeles arbutifolia were investigated in chaparral and understory habitats by applying a three-dimensional plant architecture simulation model, YPLANT. The simulations were shown to accurately predict the measured frequency distribution of photosynthetic photon flux density (PFD) on both the leaves and a horizontal surface in the open, and gave reasonably good agreement for the more complex light environment in the shade. The sun shoot architecture was orthotropic and characterized by steeply inclined (mean = 71) leaves in a spiral phyllotaxy with short internodes.

Photosynthetic responses to dynamic light under field conditions in six tropical rainforest shrubs occuring along a light gradient.

 We examined in the field the photosynthetic utilization of fluctuating light by six neotropical rainforest shrubs of the family Rubiaceae. They were growing in three different light environments: forest understory, small gaps, and clearings. Gas exchange techniques were used to analyse photosynthetic induction response, induction maintenance during low-light periods, and lightfleck (simulated sunfleck) use efficiency (LUE).

A three-dimensional crown architecture model for assessment of light capture and carbon gain by understory plants.

A model simulating the three-demensional crown architecture of a plant was developed with the objective of assessing the light capture and whole-plant carbon gain consequences of leaf display in understory plants. This model uses geometrical measurements taken in the field to reconstruct the projected image of a plant so that light absorption from any direction can be assessed. The photon flux density (PFD) from a given direction was estimated from the canopy openness derived from hemispherical canopy photographs and equations simulating the daily course of direct and diffuse PFD.

Stomatal dynamics and its importance to carbon gain in two rainforest Piper species : II. Stomatal versus biochemical limitations during photosynthetic induction.

The relative importance of biochemical and stomatal limitations on assimilation (A) during photosynthetic induction were compared in sun and shade plants of Piper auritum, a pioneer tree, and shade plants of Piper aequale, a shade tolerant shrub native to a Mexican tropical rainforest. For non-induced leaves, increases in A during induction depended on the dynamics of stomatal conductance (g) and ribulose-1,5-bisphosphate carboxylase (RuBisCO) activation. At high leaf-air vapor pressure deficit (VPD), more of the limitation during induction was stomatal.

Stomatal dynamics and its importance to carbon gain in two rainforest Piper species : I. VPD effects on the transient stomatal response to lightflecks.

The effects of leaf-air vapor pressure deficit (VPD) on the transient and steady-state stomatal responses to photon flux density (PFD) were evaluated in Piper auritum, a pioneer tree, and Piper aequale, a shade tolerant shrub, that are both native to tropical forests at Los Tuxtlas, Veracruz, México. Under constant high-PFD conditions, the stomata of shade-acclimated plants of both species were sensitive to VPD, exhibiting a nearly uniform decrease in g as VPD increased. Acclimation of P.

Photosynthetic gas exchange response of poplars to steady-state and dynamic light environments.

The steady-state and dynamic photosynthetic response of two poplar species (Populus tremuloides and P. fremontii) to variations in photon flux density (PFD) were observed with a field portable gas exchange system. These poplars were shown to be very shade intolerant with high light saturation (800 to 1300 μmol photons m s) and light compensation (70 to 100 μmol m s) points.

Effect of leaf flutter on the light environment of poplars.

The dynamics of the canopy light environment for two poplar species (Populus tremuloides Michx., and P. fremontii Wats.

Dynamic stomatal behavior and its role in carbon gain during lightflecks of a gap phase and an understory Piper species acclimated to high and low light.

Steady-state and dynamic stomatal and assimilation responses to light transients were characterized in sun- and shade-acclimated plants of Piper auritum, a pioneer tree, and Piper aequale a shade-tolerant shrub from a tropical forest at Los Tuxtlas, Veracruz, México. Despite essentially identical steady-state responses of stomatal conductance to PFD of P. aequale and P.

Influence of sunflecks on the δ C of Adenocaulon bicolor plants occurring in contrasting forest understory microsites.

Leaf characteristics and carbon isotope ratios (δC) of Adenocaulon bicolor were examined in the understory of a redwood forest along a gradient of microsites that differed in the amount of direct (sunfleck) photon flux density. Comparisons were made between plants that had been shaded from sunflecks with shadow bands but still received diffuse light, and adjacent plants that received both sunflecks and diffuse light. The δC of the shaded plants were 1.

Photosynthesis and respiration in Alocasia macrorrhiza following transfers to high and low light.

Photosynthetic capacities and respiration rates of Alocasia macrorrhiza leaves were measured for 4 weeks following reciprocal transfers between high (20% of full sun) and low (1% of full sun) light environments. Photosynthetic capacities and respiration rates of mature, high-light leaves were 1.7 and 4.

Steady-state and dynamic photosynthetic response of Adenocaulon bicolor (Asteraceae) in its redwood forest habitat.

The gas exchange characteristics under steadystate and transient light conditions were determined for a redwood forest understory herb Adenocaulon bicolor, that depends on use of sunflecks for a large fraction of its daily carbon gain. Measurements under steady-state conditions indicated that this species has photosynthetic characteristics that are typical for understory plants. The mean light-saturated assimilation rate was 5.

Daily carbon gain by Adenocaulon bicolor (Asteraceae), a redwood forest understory herb, in relation to its light environment.

The relationships between carbon gain and availability of sunfleck- and diffuse-light were determined for Adenocaulon bicolor by following the daily courses of assimilation and incident PFD on different days and locations in a redwood forest understory. Total PFD for the days sampled ranged from 1 to 4% of full sun values. Sunflecks accounted for 50 to 90% of the total PFD and were responsible for the majority of variation among days and locations.

Photosynthetic characteristics of a tropical forest understory herb, Alocasia macrorrhiza, and a related crop species, Colocasia esculenta grown in contrasting light environments.

Photosynthetic acclimation to 5 light environments ranging from 2 to 60% full sun was determined in Alocasia macrorrhiza, a shade tolerant species from tropical forest understories, and Colocasia esculenta, a cultivated species which occurs naturally in open marshy areas. Photosynthetic capacities of both species increased nearly 3 fold with increased photon flux density (PFD). In a given environment, however, photosynthetic capacities of C.

Photosynthetic responses to light variation in rainforest species : II. Carbon gain and photosynthetic efficiency during lightflecks.

The dependence of net carbon gain during lightflecks (artificial sunflecks) on leaf induction state, lightfleck duration, lightfleck photosynthetic photon flux density (PFD), and the previous light environment were investigated in A. macrorrhiza and T. australis, two Australian rainforest species.

Photosynthetic responses to light variation in rainforest species : I. Induction under constant and fluctuating light conditions.

Photosynthetic induction under constant and fluctuating light conditions was investigated in intact leaves of Alocasia macrorrhiza and Toona australis, two species native to Australian rainforests. When leaves were exposed to saturating light following a long period at low light intensity, an induction period of 25-40 min was required before steady-state photosynthesis was achieved. A long induction period was required regardless of plant growth conditions (high vs.