Associations between leaf structure, orientation, and sunlight exposure in five Western Australian communities

Tight coupling between leaf δ13 C and N content along leaf ageing in the N2 -fixing legume tree black locust (Robinia pseudoacacia L.)

N2 -fixing legumes can strongly affect ecosystem functions by supplying nitrogen (N) and improving the carbon-fixing capacity of vegetation. Still, the question of how their leaf-level N status and carbon metabolism are coordinated along leaf ageing remains unexplored. Leaf tissue carbon isotopic composition (δ13 C) provides a useful indicator of time-integrated intrinsic water use efficiency (WUEi). Here, we quantified the seasonal changes of leaf δ13 C, N content on a mass and area basis (Nmass , Narea , respectively), Δ18 O (leaf 18 O enrichment above source water, a proxy of time-integrated stomatal conductance) and morphological traits in an emblematic N2 -fixing legume tree, the black locust (Robinia pseudoacacia L.), at a subtropical site in Southwest China. We also measured xylem, soil and rainwater isotopes (δ18 O, δ2 H) to characterize tree water uptake patterns. Xylem water isotopic data reveal that black locust primarily used shallow soil water in this humid habitat. Black locust exhibited a decreasing δ13 C along leaf ageing, which was largely driven by decreasing leaf Nmass , despite roughly constant Narea . In contrast, the decreasing δ13 C along leaf ageing was largely uncoupled from parallel increases in Δ18 O and leaf thickness. Leaf N content is used as a proxy of leaf photosynthetic capacity; thus, it plays a key role in determining the seasonality in δ13 C, whereas the roles of stomatal conductance and leaf morphology are minor. Black locust leaves can effectively adjust to changing environmental conditions along leaf ageing through LMA increases and moderate stomatal conductance reduction while maintaining constant Narea to optimize photosynthesis and carbon assimilation, despite declining leaf Nmass and δ13 C.

Leaf water potential-dependent leaflet closure contributes to legume leaves cool down and drought avoidance under diurnal drought stress

Efficient thermoregulation under diurnal drought stress protects leaves from photosystem damage and water supply-demand imbalance, yet the cool effect and drought avoidance by leaflet closure have not been well understood. We investigated the cool effect and the drought avoidance of leaflet closure in legume species that survived in the semi-arid region facing seasonal and diurnal drought stress. The results showed that leaflet closure effectively cooled down legume leaves through a reduction of projected leaflet area and the cosine of the angle of incidence (cos i). The leaflet closure was strongly dependent on leaf water potential (Ψleaf). In addition, by characterizing the sequence of key leaf drought response traits, we found leaflet closure occurred after stomatal closure and reduced transpiration rate but before hydraulic failure and turgor loss point (Ψtlp). The meta-analysis also showed that the leaflet closure and cos i decreased after the stomatal conductance declined but before midday. These results imply that Ψleaf-dependent leaflet closure as an alternative to transpiration for leaflet cooling down and as a protective drought avoidance strategy assisting sessile legume plants survival under drought stress.

Leaf thickness of barley: genetic dissection, candidate genes prediction and its relationship with yield-related traits

In this first genetic study on assessing leaf thickness directly in cereals, major and environmentally stable QTL were detected in barley and candidate genes underlying a major locus were identified. Leaf thickness (LT) is an important characteristic affecting leaf functions which have been intensively studied. However, as LT has a small dimension in many plant species and technically difficult to measure, previous studies on this characteristic are often based on indirect estimations. In the first study of detecting QTL controlling LT by directly measuring the characteristic in barley, large and stable loci were detected from both field and glasshouse trials conducted in different cropping seasons by assessing a population of 201 recombinant inbred lines. Four loci (locating on chromosome arms 2H, 3H, 5H and 6H, respectively) were consistently detected for flag leaf thickness (FLT) in each of these trials. The one on 6H had the largest effect, with a maximum LOD 9.8 explaining up to 20.9% of phenotypic variance. FLT does not only show strong interactions with flag leaf width and flag leaf area but has also strong correlations with fertile tiller number, spike row types, kernel number per spike and heading date. Though with reduced efficiency, these loci were also detectable from assessing second last leaf of fully grown plants or even from assessing the third leaves of seedlings. Taking advantage of the high-quality genome assemblies for both parents of the mapping population used in this study, three candidate genes underlying the 6H QTL were predicted based on orthologous analysis. These results do not only broaden our understanding on genetic basis of LT and its relationship with other traits in cereal crops but also form the bases for cloning and functional analysis of genes regulating LT in barley.

Structure and chlorophyll fluorescence of heteroblastic foliage affect first-year growth in Pinus massoniana Lamb. seedlings

Pine seedlings exhibit heteroblastic foliage (primary and secondary needles) during seedling development. However, few trials have studied how heteroblastic foliage influences pine seedling growth by seasonal variation. This study first investigated the anatomical differences between the primary and secondary needles of one-year-old Pinus massoniana seedlings. We measured chlorophyll fluorescence (ChlF) and evaluated the photoprotective mechanisms and light energy partitioning of these heteroblastic leaves from September to November. The results showed that the primary needles, as juvenile foliage, had a greater fraction of mesophyll tissue and stomata. In addition, the primary needles had two vascular bundles, and shorter distance from xylem and phloem to mesophyll cells, exhibiting a luxury growth strategy of rapidly obtaining high returns. The ChlF parameters indicated that the primary needles maintained a relatively high level of photoprotection by thermal dissipation (nonphotochemical quenching (NPQ)) and nonregulated energy dissipation (Y(NO)). The secondary needles, representing mature foliage, had greater area of xylem and phloem tissues. The contents of Chl b and carotenoids (Car) significantly increased in November, promoting φPo and photoprotection, which suggested that the secondary needles were more resistant to low temperatures. During the whole light response process of secondary needles, the increases in the electron transfer rate (ETR) and light energy utilization efficiency (α) helped to increase the actual photosynthetic quantum yield (Y(II)) by reducing energy dissipation by decreasing the proportion of regulated energy dissipation (Y(NPQ)) and Y(NO). Given the sensitivity of this heteroblastic foliage to environmental changes, the practical use and extension of P. massoniana for afforestation purposes should be carried out with caution.

Functional Traits of a Rainforest Vascular Epiphyte Community: Trait Covariation and Indications for Host Specificity

Trait matching between interacting species may foster diversity. Thus, high epiphyte diversity in tropical forests may be partly due to the high diversity of trees and some degree of host specificity. However, possible trait matching between epiphyte and host is basically unexplored. Since the epiphytic habitat poses particular challenges to plants, their trait correlations should differ from terrestrial plants, but to what extent is unclear as epiphytes are underrepresented or missing in the large trait databases. We quantified 28 traits of 99 species of vascular epiphytes in a lowland forest in Panama that were related to plant size, leaf, stem, and root morphology; photosynthetic mode; and nutrient concentrations. We analyzed trait covariation, community weighted means, and functional diversity for assemblages on stems and in crowns of four tree species. We found intriguing differences between epiphytes and terrestrial plants regarding trait covariation in trait relations between plant maximal height, stem specific density, specific root length, and root tissue den-sity, i.e., stem and root economic spectra. Regarding host specificity, we found strong evidence for environmental filtering of epiphyte traits, but only in tree crowns. On stems, community weighted means differed in only one case, whereas > 2/3 of all traits differed in tree crowns. Although we were only partly able to interpret these differences in the light of tree trait differences, these findings mark an important step towards a functional understanding of epiphyte host specificity.

From one side to two sides: the effects of stomatal distribution on photosynthesis

The functions of stomata have been studied for a long time; however, a clear understanding of the influences of stomatal distribution on photosynthesis, especially the CO₂ diffusion, is still unclear. Here, we investigated the stomatal morphology, distribution on leaf surfaces, vein traits and gas exchange parameters of 61 species, of which 29 were amphistomatous, spanning 32 families. Photosynthesis (A) was tightly coupled with operational stomatal conductance (g_s ) and mesophyll conductance (g_m ) regardless of whether phylogenetic relationships were accounted for. Although the enhancement of g_s from ferns and gymnosperms to angiosperms could largely be explained by the increase in leaf vein density (VLA) and stomatal density (SD), the g_s was decoupled from VLA and SD across angiosperm species. Instead, A in angiosperms was further influenced by the allocation of stomatal pores on leaf surfaces, which dramatically increased g_s and g_m . Moreover, the ratio of g_s to anatomically based maximum g_s was, on average, 0.12 across species. Our results show that the shift of stomatal pores from one leaf side to both sides played an important role in regulating CO₂ diffusion via both stomata and mesophyll tissues. Modifications of stomata distribution have potential as a functional trait for photosynthesis improvement.

Effects of Crop Leaf Angle on LAI-Sensitive Narrow-Band Vegetation Indices Derived from Imaging Spectroscopy

Leaf area index (LAI) is an important biophysical variable for understanding the radiation use efficiency of field crops and their potential yield. On a large scale, LAI can be estimated with the help of imaging spectroscopy. However, recent studies have revealed that the leaf angle greatly affects the spectral reflectance of the canopy and hence imaging spectroscopy data. To investigate the effects of the leaf angle on LAI-sensitive narrowband vegetation indices, we used both empirical measurements from field crops and model-simulated data generated by the PROSAIL canopy reflectance model. We found the relationship between vegetation indices and LAI to be notably affected, especially when the leaf mean tilt angle (MTA) exceeded 70 degrees. Of the indices used in the study, the modified soil-adjusted vegetation index (MSAVI) was most strongly affected by leaf angles, while the blue normalized difference vegetation index (BNDVI), the green normalized difference vegetation index (GNDVI), the modified simple ratio using the wavelength of 705 nm (MSR705), the normalized difference vegetation index (NDVI), and the soil-adjusted vegetation index (SAVI) were only affected for sparse canopies (LAI < 3) and MTA exceeding 60°. Generally, the effect of MTA on the vegetation indices increased as a function of decreasing LAI. The leaf chlorophyll content did not affect the relationship between BNDVI, MSAVI, NDVI, and LAI, while the green atmospherically resistant index (GARI), GNDVI, and MSR705 were the most strongly affected indices. While the relationship between SR and LAI was somewhat affected by both MTA and the leaf chlorophyll content, the simple ratio (SR) displayed only slight saturation with LAI, regardless of MTA and the chlorophyll content. The best index found in the study for LAI estimation was BNDVI, although it performed robustly only for LAI > 3 and showed considerable nonlinearity. Thus, none of the studied indices were well suited for across-species LAI estimation: information on the leaf angle would be required for remote LAI measurement, especially at low LAI values. Nevertheless, narrowband indices can be used to monitor the LAI of crops with a constant leaf angle distribution.

Leaf surface traits and water storage retention affect photosynthetic responses to leaf surface wetness among wet tropical forest and semiarid savanna plants

While it is reasonable to predict that photosynthetic rates are inhibited while leaves are wet, leaf gas exchange measurements during wet conditions are challenging to obtain due to equipment limitations and the complexity of canopy-atmosphere interactions in forested environments. Thus, the objective of this study was to evaluate responses of seven tropical and three semiarid savanna plant species to simulated leaf wetness and test the hypotheses that (i) leaf wetness reduces photosynthetic rates (Anet), (ii) leaf traits explain different responses among species and (iii) leaves from wet environments are better adapted for wet leaf conditions than those from drier environments. The two sites were a tropical rainforest in northern Costa Rica with ~4200 mm annual rainfall and a savanna in central Texas with ~1100 mm. Gas exchange measurements were collected under dry and wet conditions on five sun-exposed leaf replicates from each species. Additional measurements included leaf wetness duration and stomatal density. We found that Anet responses varied greatly among species, but all plants maintained a baseline of activity under wet leaf conditions, suggesting that abaxial leaf Anet was a significant percentage of total leaf Anet for amphistomatous species. Among tropical species, Anet responses immediately after wetting ranged from -31% (Senna alata (L.) Roxb.) to +21% (Zamia skinneri Warsz. Ex. A. Dietr.), while all savanna species declined (up to -48%). After 10 min of drying, most species recovered Anet towards the observed status prior to wetting or surpassed it, with the exception of Quercus stellata Wangenh., a savanna species, which remained 13% below Anet dry. The combination of leaf wetness duration and leaf traits, such as stomatal density, trichomes or wax, most likely influenced Anet responses positively or negatively. There was also overlap between leaf traits and Anet responses of savanna and tropical plants. It is possible that these species converge on a relatively conservative response to wetness, each for divergent purposes (cooling, avoiding stomatal occlusion, or by several unique means of rapid drying). A better understanding of leaf wetness inhibiting photosynthesis is vital for accurate modeling of growth in forested environments; however, species adapted for wet environments may possess compensatory traits that mitigate these effects.

Three Key Sub-leaf Modules and the Diversity of Leaf Designs

Earth harbors a highly diverse array of plant leaf forms. A well-known pattern linking diverse leaf forms with their photosynthetic function across species is the global leaf economics spectrum (LES). However, within homogeneous plant functional groups such as tropical woody angiosperms or temperate deciduous woody angiosperms, many species can share a similar position in the LES but differ in other vital leaf traits, and thus function differently under the given suite of environmental drivers. How diverse leaves differentiate from each other has yet to be fully explained. Here, we propose a new perspective for linking leaf structure and function by arguing that a leaf may be divided into three key sub-modules, the light capture module, the water-nutrient flow module and the gas exchange module. Each module consists of a set of leaf tissues corresponding to a certain resource acquisition function, and the combination and configuration of different modules may differ depending on overall leaf functioning in a given environment. This modularized-leaf perspective differs from the whole-leaf perspective used in leaf economics theory and may serve as a valuable tool for tracing the evolution of leaf form and function. This perspective also implies that the evolutionary direction of various leaf designs is not to optimize a single critical trait, but to optimize the combination of different traits to better adapt to the historical and current environments. Future studies examining how different modules are synchronized for overall leaf functioning should offer critical insights into the diversity of leaf designs worldwide.

Limited acclimation in leaf anatomy to experimental drought in tropical rainforest trees

Dry periods are predicted to become more frequent and severe in the future in some parts of the tropics, including Amazonia, potentially causing reduced productivity, higher tree mortality and increased emissions of stored carbon. Using a long-term (12 year) through-fall exclusion (TFE) experiment in the tropics, we test the hypothesis that trees produce leaves adapted to cope with higher levels of water stress, by examining the following leaf characteristics: area, thickness, leaf mass per area, vein density, stomatal density, the thickness of palisade mesophyll, spongy mesophyll and both of the epidermal layers, internal cavity volume and the average cell sizes of the palisade and spongy mesophyll. We also test whether differences in leaf anatomy are consistent with observed differential drought-induced mortality responses among taxa, and look for relationships between leaf anatomy, and leaf water relations and gas exchange parameters. Our data show that trees do not produce leaves that are more xeromorphic in response to 12 years of soil moisture deficit. However, the drought treatment did result in increases in the thickness of the adaxial epidermis (TFE: 20.5 ± 1.5 µm, control: 16.7 ± 1.0 µm) and the internal cavity volume (TFE: 2.43 ± 0.50 mm³ cm^-2, control: 1.77 ± 0.30 mm³ cm^-2). No consistent differences were detected between drought-resistant and drought-sensitive taxa, although interactions occurred between drought-sensitivity status and drought treatment for the palisade mesophyll thickness (P = 0.034) and the cavity volume of the leaves (P = 0.025). The limited response to water deficit probably reflects a tight co-ordination between leaf morphology, water relations and photosynthetic properties. This suggests that there is little plasticity in these aspects of plant anatomy in these taxa, and that phenotypic plasticity in leaf traits may not facilitate the acclimation of Amazonian trees to the predicted future reductions in dry season water availability.

Hyperspectral phenotyping of the reaction of grapevine genotypes to Plasmopara viticola

A major aim in grapevine breeding is the provision of cultivars resistant to downy mildew. As Plasmopara viticola produces sporangia on the abaxial surface of susceptible cultivars, disease symptoms on both leaf sides may be detected and quantified by technical sensors. The response of cultivars 'Mueller-Thurgau', 'Regent', and 'Solaris', which differ in resistance to P. viticola, was characterized under controlled conditions by using hyperspectral sensors. Spectral reflectance was suitable to differentiate between non-infected cultivars and leaf sides of the bicolored grapevine. Brown discoloration of tissue became visible on both leaf sides of resistant cultivars 2 days before downy mildew symptoms appeared on the susceptible 'Mueller-Thurgau' cultivar. Infection of this cultivar resulted in significant (P<0.05) reflectance changes 1-2 days prior to abaxial sporulation induced by high relative humidity, or the formation of adaxial oil spots. Hyperspectral imaging was more sensitive in disease detection than non-imaging and provided spatial information on the leaf level. Spectral indices provided information on the variability of chlorophyll content, photosynthetic activity, and relative water content of leaf tissue in time and space. On 'Mueller-Thurgau' downy mildew translated reflectance to higher values as detectable by the index DMI_3=(R₄₇₀+R₆₈₂+R₈₀₀)/(R₈₀₀/R₆₈₂) and affected reflectance at 1450nm. Tissue discoloration on 'Regent' and 'Solaris' cultivars was associated with lower reflectance between 750 and 900nm; blue and red reflectance demonstrated differences from leaf necroses. With high inoculum densities, P. viticola sporulated on even resistant cultivars. Hyperspectral characterization at the tissue level proved suitable for phenotyping plant resistance to pathogens and provided information on resistance mechanisms.

Making pore choices: repeated regime shifts in stomatal ratio

Ecologically important traits do not evolve without limits. Instead, evolution is constrained by the set of available and viable phenotypes. In particular, natural selection may only favour a narrow range of adaptive optima constrained within selective regimes. Here, I integrate data with theory to test whether selection explains phenotypic constraint. A global database of 599 plant species from 94 families shows that stomatal ratio, a trait affecting photosynthesis and defence against pathogens, is highly constrained. Most plants have their stomata on the lower leaf surface (hypostomy), but species with half their stomata on each surface (amphistomy) form a distinct mode in the trait distribution. A model based on a trade-off between maximizing photosynthesis and a fitness cost of upper stomata predicts a limited number of adaptive solutions, leading to a multimodal trait distribution. Phylogenetic comparisons show that amphistomy is the most common among fast-growing species, supporting the view that CO2 diffusion is under strong selection. These results indicate that selective optima stay within a relatively stable set of selective regimes over macroevolutionary time.

Low levels of ribosomal RNA partly account for the very high photosynthetic phosphorus-use efficiency of Proteaceae species

Proteaceae species in south-western Australia occur on phosphorus- (P) impoverished soils. Their leaves contain very low P levels, but have relatively high rates of photosynthesis. We measured ribosomal RNA (rRNA) abundance, soluble protein, activities of several enzymes and glucose 6-phosphate (Glc6P) levels in expanding and mature leaves of six Proteaceae species in their natural habitat. The results were compared with those for Arabidopsis thaliana. Compared with A. thaliana, immature leaves of Proteaceae species contained very low levels of rRNA, especially plastidic rRNA. Proteaceae species showed slow development of the photosynthetic apparatus (‘delayed greening’), with young leaves having very low levels of chlorophyll and Calvin-Benson cycle enzymes. In mature leaves, soluble protein and Calvin-Benson cycle enzyme activities were low, but Glc6P levels were similar to those in A. thaliana. We propose that low ribosome abundance contributes to the high P efficiency of these Proteaceae species in three ways: (1) less P is invested in ribosomes; (2) the rate of growth and, hence, demand for P is low; and (3) the especially low plastidic ribosome abundance in young leaves delays formation of the photosynthetic machinery, spreading investment of P in rRNA. Although Calvin-Benson cycle enzyme activities are low, Glc6P levels are maintained, allowing their effective use.

Effects of experimental warming on stomatal traits in leaves of maize (Zea may L.)

We examined the warming effects on the stomatal frequency, stomatal aperture size and shape, and their spatial distribution pattern of maize (Zea may L.) leaves using a light microscope, an electron scanning microscope, and geostatistic techniques. A field manipulative experiment was conducted to elevate canopy temperature by 2.08°C, on average. We found that experimental warming had little effect on stomatal density, but significantly increased stomatal index due to the reduction in the number of epidermal cells under the warming treatment. Warming also significantly decreased stomatal aperture length and increased stomatal aperture width. As a result, warming significantly increased the average stomatal aperture area and stomatal aperture circumference. In addition, warming dramatically changed the stomatal spatial distribution pattern with a substantial increase in the average nearest neighbor distance between stomata on both adaxial and abaxial surfaces. The spatial distribution pattern of stomata was scale dependent with regular patterns at small scales and random patterns at larger scales on both leaf surfaces. Warming caused the stomatal distribution to become more regular on both leaf surfaces with smaller L(t) values (Ripley's K-function, L(t) is an expectation of zero for any value of t) in the warming plots than the control plots.

Unified changes in cell size permit coordinated leaf evolution

The processes by which the functions of interdependent tissues are coordinated as lineages diversify are poorly understood. Here, we examine evolutionary coordination of vascular, epidermal and cortical leaf tissues in the anatomically, ecologically and morphologically diverse woody plant family Proteaceae. We found that, across the phylogenetic range of Proteaceae, the sizes of guard, epidermal, palisade and xylem cells were positively correlated with each other but negatively associated with vein and stomatal densities. The link between venation and stomata resulted in a highly efficient match between potential maximum water loss (determined by stomatal conductance) and the leaf vascular system's capacity to replace that water. This important linkage is likely to be driven by stomatal size, because spatial limits in the packing of stomata onto the leaf surface apparently constrain the maximum size and density of stomata. We conclude that unified evolutionary changes in cell sizes of independent tissues, possibly mediated by changes in genome size, provide a means of substantially modifying leaf function while maintaining important functional links between leaf tissues. Our data also imply the presence of alternative evolutionary strategies involving cellular miniaturization during radiation into closed forest, and cell size increase in open habitats.

Leaf mesophyll diffusion conductance in 35 Australian sclerophylls covering a broad range of foliage structural and physiological variation

Foliage structure, chemistry, photosynthetic potentials (V(cmax) and J(max)), and mesophyll diffusion conductance (g(m)) were quantified for 35 broad-leaved species from four sites with contrasting rainfall and soil fertility in eastern Australia. The aim of the study was to estimate the extent to which g(m) and related leaf properties limited photosynthesis (A), focusing on highly sclerophyllous species typical of the 'slow-return' end of the leaf economics spectrum. Leaf dry mass per unit area (M(A)) varied approximately 5-fold, leaf life span (L(L)) and N (N(M)) and P (P(M)) contents per dry mass approximately 8-fold, and various characteristics of foliage photosynthetic machinery 6- to 12-fold across the data set. As is characteristic of the 'leaf economics spectrum', more robust leaves with greater M(A) and longevity were associated with lower nutrient contents and lower foliage photosynthetic potentials. g(m) was positively correlated with V(cmax) and J(max), and these correlations were stronger on a mass basis. Only g(m)/mass was negatively associated with M(A). CO(2) drawdown from substomatal cavities to chloroplasts (C(i)-C(C)) characterizing mesophyll CO(2) diffusion limitations was larger in leaves with greater M(A), lower g(m)/mass, and lower photosynthetic potentials. Relative limitation of A due to finite mesophyll diffusion conductance, i.e. 1-A(infinite g(m))/A(actual g(m)), was always >0.2 and up to 0.5 in leaves with most robust leaf structure, demonstrating the profound effect of finite g(m) on realized photosynthesis rates. Data from different sites were overlapping in bivariate relationships, and the variability of average values between the sites was less than among the species within the sites. Nevertheless, photosynthesis was more strongly limited by g(m) in low rain/high nutrient and high rain/low nutrient sites that supported vegetation with more sclerophyllous foliage. These data collectively highlight a strong relationship between leaf structure and g(m), and demonstrate that realized photosynthesis rates are strongly limited by g(m) in this highly sclerophyllous flora.

The effect of leaf-level spatial variability in photosynthetic capacity on biochemical parameter estimates using the Farquhar model: a theoretical analysis

Application of the widely used Farquhar model of photosynthesis in interpretation of gas exchange data assumes that photosynthetic properties are homogeneous throughout the leaf. Previous studies showed that heterogeneity in stomatal conductance (g(s)) across a leaf could affect the shape of the measured leaf photosynthetic CO(2) uptake rate (A) versus intercellular CO(2) concentration (C(i)) response curve and, in turn, estimation of the critical biochemical parameters of this model. These are the maximum rates of carboxylation (V(c,max)), whole-chain electron transport (J(max)), and triose-P utilization (V(TPU)). The effects of spatial variation in V(c,max,) J(max), and V(TPU) on estimation of leaf averages of these parameters from A-C(i) curves measured on a whole leaf have not been investigated. A mathematical model incorporating defined degrees of spatial variability in V(c,max) and J(max) was constructed. One hundred and ten theoretical leaves were simulated, each with the same average V(c,max) and J(max), but different coefficients of variation of the mean (CV(VJ)) and varying correlation between V(c,max) and J(max) (Omega). Additionally, the interaction of variation in V(c,max) and J(max) with heterogeneity in V(TPU), g(s), and light gradients within the leaf was also investigated. Transition from V(c,max)- to J(max)-limited photosynthesis in the A-C(i) curve was smooth in the most heterogeneous leaves, in contrast to a distinct inflection in the absence of heterogeneity. Spatial variability had little effect on the accuracy of estimation of V(c,max) and J(max) from A-C(i) curves when the two varied in concert (Omega = 1.0), but resulted in underestimation of both parameters when they varied independently (up to 12.5% in V(c,max) and 17.7% in J(max) at CV(VJ) = 50%; Omega = 0.3). Heterogeneity in V(TPU) also significantly affected parameter estimates, but effects of heterogeneity in g(s) or light gradients were comparatively small. If V(c,max) and J(max) derived from such heterogeneous leaves are used in models to project leaf photosynthesis, actual A is overestimated by up to 12% at the transition between V(c,max)- and J(max)-limited photosynthesis. This could have implications for both crop production and Earth system models, including projections of the effects of atmospheric change.

A latitudinal cline and response to vernalization in leaf angle and morphology in Arabidopsis thaliana (Brassicaceae)

Adaptation to latitudinal patterns of environmental variation is predicted to result in clinal variation in leaf traits. Therefore, this study tested for geographic differentiation and plastic responses to vernalization in leaf angle and leaf morphology in Arabidopsis thaliana. Twenty-one European ecotypes were grown in a common growth chamber environment. Replicates of each ecotype were exposed to one of four treatments: 0, 10, 20 or 30 d of vernalization. Ecotypes from lower latitudes had more erect leaves, as predicted from functional arguments about selection to maximize photosynthesis. Lower-latitude ecotypes also had more elongated petioles as predicted by a biomechanical constraint hypothesis. In addition, extended vernalization resulted in shorter and more erect leaves. As predicted by functional and adaptive hypotheses, our results show genetically based clinal variation as well as environmentally induced variation in leaf traits.

Leaf size and angle vary widely across species: what consequences for light interception?

•  Architecture can vary widely across species. Both steeper leaf angles and increased self-shading are thought to reduce potential carbon gain by decreasing total light interception. An alternative hypothesis is that steeper leaf angles have evolved to improve day-long carbon gain by emphasising light interception from low angles. •  Here we relate variation in architectural properties (leaf angle and leaf size) to cross-species patterns of leaf display, light capture and simulated carbon gain in branching-units of 38 perennial species occurring at two sites in Australian forest. Architectural comparison was made possible by combining 3D-digitising with the architecture model YPLANT. •  Species with shallow angled leaves had greater daily light interception and potentially greater carbon gain. Self-shading, rather than leaf angle, explained most variance between species in light capture and potential carbon gain. Species average leaf size was the most important determinant of self-shading. •  Our results provide the first cross-species evidence that steeper leaf angles function to reduce exposure to excess light levels during the middle of the day, more than to maximise carbon gain.