Leaf size and venation show remarkable diversity across dicotyledons, and are key determinants of plant adaptation in ecosystems past and present. Here we present global scaling relationships of venation traits with leaf size. Across a new database for 485 globally distributed species, larger leaves had major veins of larger diameter, but lower length per leaf area, whereas minor vein traits were independent of leaf size. These scaling relationships allow estimation of intact leaf size from fragments, to improve hindcasting of past climate and biodiversity from fossil remains. The vein scaling relationships can be explained by a uniquely synthetic model for leaf anatomy and development derived from published data for numerous species. Vein scaling relationships can explain the global biogeographical trend for smaller leaves in drier areas, the greater construction cost of larger leaves and the ability of angiosperms to develop larger and more densely vascularised lamina to outcompete earlier-evolved plant lineages.

Across plant species, leaves vary enormously in their size and their venation architecture, of which one major function is to replace water lost to transpiration. The leaf hydraulic conductance (K leaf ) represents the capacity of the transport system to deliver water, allowing stomata to remain open for photosynthesis. Previous studies showed that K leaf relates to vein density (vein length per area). Additionally, venation architecture determines the sensitivity of K leaf to damage; severing the midrib caused K leaf and gas exchange to decline, with lesser impacts in leaves with higher major vein density that provided more numerous water flow pathways around the damaged vein. Because xylem embolism during dehydration also reduces K leaf , we hypothesized that higher major vein density would also reduce hydraulic vulnerability. Smaller leaves, which generally have higher major vein density, would thus have lower hydraulic vulnerability. Tests using simulations with a spatially explicit model confirmed that smaller leaves with higher major vein density were more tolerant of major vein embolism. Additionally, for 10 species ranging strongly in drought tolerance, hydraulic vulnerability, determined as the leaf water potential at 50% and 80% loss of K leaf , was lower with greater major vein density and smaller leaf size (|r| = 0.85-0.90; P , 0.01). These relationships were independent of other aspects of physiological and morphological drought tolerance. These findings point to a new functional role of venation architecture and small leaf size in drought tolerance, potentially contributing to well-known biogeographic trends in leaf size.

Clarifying the evolution and mechanisms for photosynthetic productivity is a key to both improving crops and understanding plant evolution and habitat distributions. Current theory recognizes a role for the hydraulics of water transport as a potential determinant of photosynthetic productivity based on comparative data across disparate species. However, there has never been rigorous support for the maintenance of this relationship during an evolutionary radiation. We tested this theory for 30 species of Viburnum, diverse in leaf shape and photosynthetic anatomy, grown in a common garden. We found strong support for a fundamental requirement for leaf hydraulic capacity (Kleaf) in determining photosynthetic capacity (Amax), as these traits diversified across this lineage in tight coordination, with their proportionality modulated by the climate experienced in the species' range. Variation in Kleaf arose from differences in venation architecture that influenced xylem and especially outside-xylem flow pathways. These findings substantiate an evolutionary basis for the coordination of hydraulic and photosynthetic physiology across species, and their co-dependence on climate, establishing a fundamental role for water transport in the evolution of the photosynthetic rate.

Leaf hydraulic conductance (Kleaf) is a major determinant of photosynthetic rate in well-watered and drought-stressed plants. Previous work assessed the decline of Kleaf with decreasing leaf water potential (Ψleaf), most typically using rehydration kinetics methods, and found that species varied in the shape of their vulnerability curve, and that hydraulic vulnerability correlated with other leaf functional traits and with drought sensitivity. These findings were tested and extended, using a new steady-state evaporative flux method under high irradiance, and the function for the vulnerability curve of each species was determined individually using maximum likelihood for 10 species varying strongly in drought tolerance. Additionally, the ability of excised leaves to recover in Kleaf with rehydration was assessed, and a new theoretical framework was developed to estimate how rehydration of measured leaves may affect estimation of hydraulic parameters. As hypothesized, species differed in their vulnerability function. Drought-tolerant species showed shallow linear declines and more negative Ψleaf at 80% loss of Kleaf (P80), whereas drought-sensitive species showed steeper, non-linear declines, and less negative P80. Across species, the maximum Kleaf was independent of hydraulic vulnerability. Recovery of Kleaf after 1 h rehydration of leaves dehydrated below their turgor loss point occurred only for four of 10 species. Across species without recovery, a more negative P80 correlated with the ability to maintain Kleaf through both dehydration and rehydration. These findings indicate that resistance to Kleaf decline is important not only in maintaining open stomata during the onset of drought, but also in enabling sustained function during drought recovery.

Leaf vein length per unit leaf area (VLA; also known as vein density) is an important determinant of water and sugar transport, photosynthetic function, and biomechanical support. A range of software methods are in use to visualize and measure vein systems in cleared leaf images; typically, users locate veins by digital tracing, but recent articles introduced software by which users can locate veins using thresholding (i.e. based on the contrasting of veins in the image). Based on the use of this method, a recent study argued against the existence of a fixed VLA value for a given leaf, proposing instead that VLA increases with the magnification of the image due to intrinsic properties of the vein system, and recommended that future measurements use a common, low image magnification for measurements. We tested these claims with new measurements using the software LEAFGUI in comparison with digital tracing using ImageJ software. We found that the apparent increase of VLA with magnification was an artifact of (1) using low-quality and low-magnification images and (2) errors in the algorithms of LEAFGUI. Given the use of images of sufficient magnification and quality, and analysis with error-free software, the VLA can be measured precisely and accurately. These findings point to important principles for improving the quantity and quality of important information gathered from leaf vein systems.The leaf vein system delivers water, nutrients, and signals throughout the leaf, and sugars and signal molecules back to the rest of the plant, and supports the lamina mechanically (Roth-Nebelsick et al., 2001; Sack and Scoffoni, 2013). The leaf vein length per unit leaf area (VLA; also known as venation density) has key implications for leaf development, physiology, and ecology. In typical angiosperm leaves, the venation system is constructed of three orders of major veins (i.e., one or more first-order [1°] veins entering the lamina from the petiole, second-order [2°] veins branching off along the 1°vein length, and third-order veins forming a mesh in between) along with one to several additional orders of smaller, minor veins that complete the mesh throughout the leaf, typically bounding loops known as areoles (Ellis et al., 2009). The total VLA including both systems is positively related to physiological performance (e.g. hydraulic conductance and photosynthetic rate per leaf area; for review, see Brodribb et al

the terms of the Creative Commons-AttributionNoncommercial-Share Alike License 4.0 International (http://creativecommons.org/licenses/by-nc-sa/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly attributed, not used for commercial purposes, and, if transformed, the resulting work is redistributed under the same or similar license to this one. AbstractObjective -This paper summarizes two studies that share the same research question: do universities produce more scholarly research when they invest more in their libraries? Research libraries spend a great deal of effort reporting their expenditures, collections statistics, and other measures that serve as a basis for interlibrary comparison and even rankings. The straightforward assumption implied by this activity is that libraries better serve their student and research communities when they are well-funded and well-resourced. The studies examined here both ask if that notion can be validated empirically, not because research libraries require some sort of justification, but because in an environment of tough budget decisions and shifting opinions about the changing role of libraries, it may be useful to demonstrate that sustained investment in libraries offers tangible returns or that the failure to do so can result in tangible costs.Methods -A cross-sectional design featuring ordinary least squares regression analysis was used in both studies to estimate the relationship between scholarly research productivity at U.S. doctoral institutions and an array of institutional characteristics presumed to influence that productivity. The concept of research productivity is operationalized as the total number of scholarly journal articles produced by each institution over a five year period -as journal articles represent the most common form of scholarly expression across the greatest number of academic fields. Serving as the dependent variable, this data was regressed against a variety of institutional Evidence Based Library and Information Practice 2015, 10.2 35 characteristics including faculty size, research expenditures, and grant awards, and several library variables centered mostly on expenditures. The concept behind this design is that to realistically explore the relationship between levels of library investment and research productivity, all other institutional drivers of research productivity must also be represented in the dataset. While the design was similar for both studies, they each drew on different data sources and marginally different populations.Results -Both studies found that an institution's research productivity is positively and significantly correlated with the level of investment it makes in its libraries. Furthermore, both studies found electronic library material expenditures to be particularly associated with increased productivity. This relationship was so strong that an institution's level of research productivity appears to be sensitive to how its library's collec...

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