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Background and Aims Ferns are the second largest group of vascular plants and are distributed nearly worldwide. Although ferns have been integrated into some comparative ecological studies focusing on hydathodes, there is a considerable gap in our understanding of the functional anatomy of these secretory tissues that are found on the vein endings of many fern leaves. In this study, we aimed to investigate the phylogenetic distribution, structure and function of fern hydathodes. Methods We performed a global review on fern hydathodes and their phylogenetic distribution, carried out an ancestral character state reconstruction, and studied the structure, guttation and elemental composition of salt residues of eight species, and the diurnal patterns of xylem pressure of two species. Key Results Hydathodes are known from 1189 fern species, 92 genera and 19 families of 2 orders, Equisetales and Polypodiales. Stochastic character mapping indicated multiple gains and losses of hydathodes at the genus level, occurring especially during the last 50 million years of fern evolution. Hydathodes were located on the adaxial leaf surface and characterized by a cytoplasm-rich, pore-free epidermis, and became functional for several weeks after nearly complete leaf expansion. In two species, positive xylem pressure built up at night, potentially facilitating guttation. Guttation fluid was rich in Ca and often Si, but also contained P, Mg, Na and Al. Conclusions Stochastic character mapping and the structural and functional diversity of hydathodes indicate multiple origins, and their presence/absence in closely related taxa implies secondary losses during fern evolution. Positive xylem pressure and high air humidity play an important role as drivers of guttation. Hydathodes may contribute to the regulation of leaf nutrient stoichiometry by the release of excessive compounds and minerals other than waste products, but the presence of essential chemical elements in salt residues also indicates possible leakage. [ABSTRACT FROM AUTHOR]

* Background and Aims The structural properties of leaf venation and xylem anatomy strongly influence leaf hydraulics, including the ability of leaves to maintain hydraulic function during drought. Here we examined the strength of the links between different leaf venation traits and leaf hydraulic vulnerability to drought (expressed as P50leaf by rehydration kinetics) in a diverse group of 26 woody angiosperm species, representing a wide range of leaf vulnerabilities, from four low-nutrient sites with contrasting rainfall across eastern Australia. v Methods For each species we measured key aspects of leaf venation design, xylem anatomy and leaf morphology. We also assessed for the first time the scaling relationships between hydraulically weighted vessel wall thickness (th) and lumen breadth (bh) across vein orders and habitats. * Key Results Across species, variation in P50leaf was strongly correlated with the ratio of vessel wall thickness (th) to lumen breadth (bh) [(t/b)h; an index of conduit reinforcement] at each leaf vein order. Concomitantly, the scaling relationship between th and bh was similar across vein orders, with a log-log slope less than 1 indicating greater xylem reinforcement in smaller vessels. In contrast, P50leaf was not related to th and bh individually, to major vein density (Dvmajor) or to leaf size. Principal components analysis revealed two largely orthogonal trait groupings linked to variation in leaf size and drought tolerance. * Conclusions Our results indicate that xylem conduit reinforcement occurs throughout leaf venation, and remains closely linked to leaf drought tolerance irrespective of leaf size. [ABSTRACT FROM AUTHOR]

Background and Aims The influence of leaf mechanical properties on local ecosystem processes, such as trophic transfer, decomposition and nutrient cycling, has resulted in a growing interest in including leaf mechanical resistance in large-scale databases of plant functional traits. 'Specific work to shear' and 'force to tear' are two properties commonly used to describe mechanical resistance (toughness or strength) of leaves. Two methodologies have been widely used to measure them across large datasets. This study aimed to assess correlations and standardization between the two methods, as measured by two widely used apparatuses, in order to inter-convert existing data in those global datasets. Methods Specific work to shear (WSS) and force to tear (FT) were measured in leaves of 72 species from southeastern Australia. The measurements were made including and excluding midribs. Relationships between the variables were tested by Spearman correlations and ordinary least square regressions. Key Results A positive and significant correlation was found between the methods, but coefficients varied according to the inclusion or exclusion of the midrib in the measurements. Equations for prediction varied according to leaf venation pattern. A positive and significant (r=0.90, P<0.0001) correlation was also found between WSS values for fresh and rehydrated leaves, which is considered to be of practical relevance. Conclusions In the context of broad-scale ecological hypotheses and used within the constraints recommended here, leaf mechanical resistance data obtained with both methodologies could be pooled together into a single coarser variable, using the equations provided in this paper. However, more detailed datasets of FT cannot be safely filled inwith estimations based on WSS, or vice versa. In addition, WSS values of green leaves can be predicted with good accuracy from WSS of rehydrated leaves of the same species. [ABSTRACT FROM AUTHOR]

Background and Aims The large distance between peripheral leaf regions and the petiole in large leaves is expected to cause stronger negative water potentials at the leaf apex and marginal zones compared with more central or basal leaf regions. Leaf zone-specific differences in water supply and/or gas exchange may therefore be anticipated. In this study, an investigation was made to see whether zonal differences in gas exchange regulation can be detected in large leaves. Methods The diurnal course of stomatal conductance, gs, was monitored at defined lamina zones during two consecutive vegetation periods in the liana Aristolochia macrophylla that has large leaves. Local climate and stem water potential were also monitored to include parameters involved in stomatal response. Additionally, leaf zonal vein densities were measured to assess possible trends in local hydraulic supply. Key Results It was found that the diurnal pattern of gs depends on the position within a leaf in A. macrophylla. The highest values during the early morning were shown by the apical region, with subsequent decline later in the morning and a further gradual decline towards the evening. The diurnal pattern of gs at the marginal regions was similar to that of the leaf tip but showed a time lag of about 1 h. At the leaf base, the diurnal pattern of gs was similar to that of the margins but with lower maximum gs. At the the leaf centre regions, gs tended to show quite constant moderate values during most of the day. Densities of minor veins were lower at the margin and tip compared with the centre and base. Conclusions Gas exchange regulation appears to be zone specific in A. macrophylla leaves. It is suggested that the spatial–diurnal pattern of gs expressed by A. macrophylla leaves represents a strategy to prevent leaf zonal water stress and subsequent vein embolism. [ABSTRACT FROM PUBLISHER]