Plant traits-the morphological, anatomical, physiological, biochemical and phenological characteristics of plants-determine how plants respond to environmental factors, affect other trophic levels, and influence ecosystem properties and their benefits and detriments to people. Plant trait data thus represent the basis for a vast area of research spanning from evolutionary biology, community and functional ecology, to biodiversity conservation, ecosystem and landscape management, restoration, biogeography and earth system modelling. Since its foundation in 2007, the TRY database of plant traits has grown continuously. It now provides unprecedented data coverage under an open access data policy and is the main plant trait database used by the research community worldwide. Increasingly, the TRY database also supports new frontiers of trait-based plant research, including the identification of data gaps and the subsequent mobilization or measurement of new data. To support this development, in this article we evaluate the extent of the trait data compiled in TRY and analyse emerging patterns of data coverage and representativeness. Best species coverage is achieved for categorical traits-almost complete coverage for 'plant growth form'. However, most traits relevant for ecology and vegetation modelling are characterized by continuous intraspecific variation and trait-environmental relationships. These traits have to be measured on individual plants in their respective environment. Despite unprecedented data coverage, we observe a humbling lack of completeness and representativeness of these continuous traits in many aspects.We, therefore, conclude that reducing data gaps and biases in the TRY database remains a key challenge and requires a coordinated approach to data mobilization and trait measurements. This can only be achieved in collaboration with other initiatives. Geosphere-Biosphere Program (IGBP) and DIVERSITAS, the TRY database (TRY-not an acronym, rather a statement of sentiment; https ://www.try-db.org; Kattge et al., 2011) was proposed with the explicit assignment to improve the availability and accessibility of plant trait data for ecology and earth system sciences. The Max Planck Institute for Biogeochemistry (MPI-BGC) offered to host the database and the different groups joined forces for this community-driven program. Two factors were key to the success of TRY: the support and trust of leaders in the field of functional plant ecology submitting large databases and the long-term funding by the Max Planck Society, the MPI-BGC and the German Centre for Integrative Biodiversity Research (iDiv) Halle-Jena-Leipzig, which has enabled the continuous development of the TRY database.

Whether rising atmospheric carbon dioxide (CO2) concentrations will cause forests to grow faster and store more carbon is an open question. Using free air CO2 release in combination with a canopy crane, we found an immediate and sustained enhancement of carbon flux through 35-meter-tall temperate forest trees when exposed to elevated CO2. However, there was no overall stimulation in stem growth and leaf litter production after 4 years. Photosynthetic capacity was not reduced, leaf chemistry changes were minor, and tree species differed in their responses. Although growing vigorously, these trees did not accrete more biomass carbon in stems in response to elevated CO2, thus challenging projections of growth responses derived from tests with smaller trees.

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Vascular epiphyte species exclusively, or at least primarily, germinate and grow on other plants without contact with the soil and, in contrast to mistletoes, without parasitizing their hosts. The last review of the systematic distribution of this diverse group of plants dates back more than two decades. The present study pursues three major goals: (1) it critically discusses conceptual problems arising from the distinction of epiphytes from non‐epiphytes; (2) it presents a compilation of epiphytic diversity derived from a vast number of sources; and (3) it arranges epiphyte diversity in an up‐to‐date taxonomic framework. The resulting compilation, which identifies 27 614 species of vascular epiphytes (including primary hemiepiphytes) representing 913 genera in 73 families, or approximately 9% of extant vascular plant diversity, is meant to be an important tool for studies on the ecology and evolution of epiphytes, but also for comparative studies with a focus on other life forms. © 2013 The Linnean Society of London

The current knowledge of the physiological ecology of vascular epiphytes is reviewed here with an emphasis on the most recent literature. It is argued that by far the most relevant abiotic constraint for growth and vegetative function of vascular epiphytes is water shortage, while other factors such as nutrient availability or irradiation, are generally of inferior importance. However, it is shown that the present understanding of epiphyte biology is still highly biased, both taxonomically and ecologically, and it is concluded that any generalizations are still preliminary. Future studies should include a much wider range of taxa and growing sites within the canopy to reach a better understanding how abiotic factors are limiting epiphyte growth and survival which, in turn, should affect epiphyte community composition. Finally, a more integrative approach to epiphyte biology is encouraged: physiological investigations should be balanced by studies of other possible constraints, for example, substrate instability, dispersal limitation, competition or herbivory.

In 2003, Central Europe experienced the warmest summer on record combined with unusually low precipitation. We studied plant water relations and phenology in a 100-year- old mixed deciduous forest on a slope (no ground water table) near Basel using the Swiss Canopy Crane (SCC). The drought lasted from early June to mid September. We studied five deciduous tree species; half of the individuals were exposed to elevated CO(2) concentration ([CO(2)]) (530 ppm) using a free-air, atmospheric CO(2)-enrichment system. In late July, after the first eight weeks of drought, mean predawn leaf water potential about 30 m above ground was -0.9 MPa across all trees, dropping to a mean of -1.5 MPa in mid-August when the top 1 m of the soil profile had no plant accessible moisture. Mean stomatal conductance and rates of maximum net photosynthesis decreased considerably in mid-August across all species. However, daily peak values of sap flow remained surprisingly constant over the whole period in Quercus petraea (Matt.) Liebl., and decreased to only about half of the early summer maxima in Fagus sylvatica L. and Carpinus betulus L. (stomatal down- regulation of flux). Although we detected no differences in most parameters between CO(2)-treated and control trees, predawn leaf water potential tended to be less negative in trees exposed to elevated [CO(2)]. Leaf longevity was greater in 2003 compared with the previous years, but the seasonal increase in stem basal area reached only about 75% of that in previous years. Our data suggest that the investigated tree species, particularly Q. petraea, did not experience severe water stress. However, an increased frequency of such exceptionally dry summers may have a more serious impact than a single event and would give Q. petraea a competitive advantage in the long run.

Grape (Vitis vinifera cv Silvaner) vine plants were cultivated under shaded conditions in the absence of ultraviolet (UV) radiation in a greenhouse, and subsequently placed outdoors under three different light regimes for 7 d. Different light regimes were produced by filters transmitting natural radiation, or screening out the UV-B (280-315 nm), or screening out the UV-A (315-400 nm) and the UV-B spectral range. During exposure, synthesis of UV-screening phenolics in leaves was quantified using HPLC: All treatments increased concentrations of hydroxycinnamic acids but the rise was highest, reaching 230% of the initial value, when UV radiation was absent. In contrast, UV-B radiation specifically increased flavonoid concentrations resulting in more than a 10-fold increase. Transmittance in the UV of all extracted phenolics was lower than epidermal UV transmittance determined fluorimetrically, and the two parameters were curvilinearly related. It is suggested that curvilinearity results from different absorption properties of the homogeneously dissolved phenolics in extracts and of the non-homogeneous distribution of phenolics in the epidermis. UV-B-dependent inhibition of maximum photochemical yield of photosystem II (PSII), measured as variable fluorescence of dark-adapted leaves, recovered in parallel to the buildup of epidermal screening for UV-B radiation, suggesting that PSII is protected against UV-B damage by epidermal screening. However, UV-B inhibition of CO 2 assimilation rates was not diminished by efficient UV-B screening. We propose that protection of UV-B inactivation of PSII is observed because preceding damage is efficiently repaired while those factors determining UV-B inhibition of CO 2 assimilation recover more slowly.Photosynthetic organisms form energy-rich compounds using the energy of the sun's visible radiation. When harvesting light, photosynthetic organs are inevitably exposed to the UV region of natural radiation. In general, UV radiation damages lipids, nucleic acids, and proteins in leaves of higher plants, and specifically targets the photosystem II (PSII) reaction center, Rubisco, chloroplast ATPase, and violaxanthin deepoxidase (Jordan, 1996;Vass, 1997).To cope with UV radiation damage, plants have evolved a variety of mechanisms including: screening out UV radiation by accumulating UV-absorbing phenolic compounds in the leaf epidermis, repairing UV-induced DNA damage, and formation of antioxidants to scavenge peroxides and oxygen radicals (Bornman and Teramura, 1993; Jordan 1996). Increases in natural UV radiation due to decreased stratospheric ozone concentrations have stimulated research on mechanisms and maximum capacities for protection against UV exposure (Caldwell et al., 1998).Studies with Arabidopsis mutants deficient in synthesis of phenolic sunscreens have demonstrated the essential role of epidermal screening in UV protection (Li et al., 1993; Lois and Buchanan, 1994; Landry et al., 1995; Booij-James et al., 2000; Mazza et al., 2000). In many higher plants, two classes...

A considerable number of plants depend on structural support of other plants. To understand their diversity and ecology, it is essential to know how strongly potential host species differ in their suitability as hosts. This review focuses on vascular epiphytes, i.e. structurally dependent plants that do not parasitize their hosts. Despite a longstanding interest in the topic, our knowledge on the strength of their host specificity is still scanty. This is arguably due to conceptual confusion, but also because of the large complexity of the study system, which turns quantifying host specificity in the field into a challenge.