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Remote sensing methods enable detection of solar-induced chlorophyll a fluorescence. However, to unleash the full potential of this signal, intensive cross-disciplinary work is required to harmonize biophysical and ecophysiological studies. For decades, the dynamic nature of chlorophyll a fluorescence (ChlaF) has provided insight into the biophysics and ecophysiology of the light reactions of photosynthesis from the subcellular to leaf scales. Recent advances in remote sensing methods enable detection of ChlaF induced by sunlight across a range of larger scales, from using instruments mounted on towers above plant canopies to Earth-orbiting satellites. This signal is referred to as solar-induced fluorescence (SIF) and its application promises to overcome spatial constraints on studies of photosynthesis, opening new research directions and opportunities in ecology, ecophysiology, biogeochemistry, agriculture and forestry. However, to unleash the full potential of SIF, intensive cross-disciplinary work is required to harmonize these new advances with the rich history of biophysical and ecophysiological studies of ChlaF, fostering the development of next-generation plant physiological and Earth-system models. Here, we introduce the scale-dependent link between SIF and photosynthesis, with an emphasis on seven remaining scientific challenges, and present a roadmap to facilitate future collaborative research towards new applications of SIF.

Understanding the pronounced seasonal and spatial variation in leaf carboxylation capacity (Vc,max ) is critical for determining terrestrial carbon cycling in tropical forests. However, an efficient and scalable approach for predicting Vc,max is still lacking. Here the ability of leaf spectroscopy for rapid estimation of Vc,max was tested. Vc,max was estimated using traditional gas exchange methods, and measured reflectance spectra and leaf age in leaves sampled from tropical forests in Panama and Brazil. These data were used to build a model to predict Vc,max from leaf spectra. The results demonstrated that leaf spectroscopy accurately predicts Vc,max of mature leaves in Panamanian tropical forests (R2 = 0.90). However, this single-age model required recalibration when applied to broader leaf demographic classes (i.e. immature leaves). Combined use of spectroscopy models for Vc,max and leaf age enabled construction of the Vc,max -age relationship solely from leaf spectra, which agreed with field observations. This suggests that the spectroscopy technique can capture the seasonal variability in Vc,max , assuming sufficient sampling across diverse species, leaf ages and canopy environments. This finding will aid development of remote sensing approaches that can be used to characterize Vc,max in moist tropical forests and enable an efficient means to parameterize and evaluate terrestrial biosphere models.

The association between increased lineage diversification rates and the evolution of latex and resin canals is widely cited as a paradigmatic example of Ehrlich and Raven’s ‘escape‐and‐radiate’ hypothesis of co‐evolution. However, it has been over a quarter‐century since the original study, and updates to phylogenetic comparative methods, plant molecular systematics, and phenotypic data warrant a reassessment of this classic finding. We gathered data on latex and resin canals across 345 families and 986 genera of vascular plants and conducted a multi‐scale test of the association between these traits and lineage diversification rates. At a broad scale (across clades), we used sister‐clade comparisons to test whether 28 canal‐bearing clades had higher net diversification rates than their canal‐lacking sister clades. At a finer scale (within clades), we used ancestral state reconstructions and phylogenetic models of lineage diversification rates to examine the relationship between trait evolution and the timing of diversification rate shifts in two better‐characterized clades – Araceae and Papaveraceae. At both scales of our analyses we found poor support for the predicted relationship between diversification and the evolution of latex and resin canals. Follow‐up analyses clarified that the qualitative change between our results and those of the Farrell et al.’s classic study is not the result of different phylogenetic comparative methods. Instead, the differences are attributable to updates to plant systematic hypotheses and new data on laticifers and resin canal presence/absence. Synthesis. Our updated study reveals that there is no longer strong evidence for latex or resin canals as general, consistently replicable drivers of species diversity across plants. However, we cannot rule out a relationship in all groups. We therefore argue that theoretical and empirical work aimed at understanding ecological factors that condition ‘escape‐and‐radiate’ dynamics will allow for more nuanced tests of the hypothesis in the future.

Background: Global climate change has the potential to shape evolutionary trajectories of invasive species via many routes, including through changes in mating systems. Many cleistogamous (CL) plants adjust investment in CL (selfed) vs. chasmogamous (CH, potentially outcrossed) progeny across environmental gradients. However, the details of such adjustments are lacking for highly invasive plant species.Aims: We used a highly invasive grass, Microstegium vimineum, as a model for understanding how changes in water-induced stress (including potential associated changes in soil nutrient availability) might affect mating systems and thus evolutionary change in invasive species. We predicted that plants would respond to increased water-induced stress through a relative reduction in investment in CL vs. CH reproduction (i.e., a decrease in the CL:CH ratio).Methods: Under greenhouse conditions, we measured fecundity (number of inflorescences and florets per plant) as well as relative investment in CL vs. CH flore...

Satellite and tower-based metrics of forest-scale photosynthesis generally increase with dry season progression across central Amazônia, but the underlying mechanisms lack consensus. We conducted demographic surveys of leaf age composition, and measured the age dependence of leaf physiology in broadleaf canopy trees of abundant species at a central eastern Amazon site. Using a novel leaf-to-branch scaling approach, we used these data to independently test the much-debated hypothesis – arising from satellite and tower-based observations – that leaf phenology could explain the forest-scale pattern of dry season photosynthesis. Stomatal conductance and biochemical parameters of photosynthesis were higher for recently mature leaves than for old leaves. Most branches had multiple leaf age categories simultaneously present, and the number of recently mature leaves increased as the dry season progressed because old leaves were exchanged for new leaves. These findings provide the first direct field evidence that branch-scale photosynthetic capacity increases during the dry season, with a magnitude consistent with increases in ecosystem-scale photosynthetic capacity derived from flux towers. Interactions between leaf age-dependent physiology and shifting leaf age-demographic composition are sufficient to explain the dry season photosynthetic capacity pattern at this site, and should be considered in vegetation models of tropical evergreen forests. © 2018 The Authors. New Phytologist © 2018 New Phytologist Trust

© 2016 The Authors. New Phytologist © 2016 New Phytologist Trust Leaf age structures the phenology and development of plants, as well as the evolution of leaf traits over life histories. However, a general method for efficiently estimating leaf age across forests and canopy environments is lacking. Here, we explored the potential for a statistical model, previously developed for Peruvian sunlit leaves, to consistently predict leaf ages from leaf reflectance spectra across two contrasting forests in Peru and Brazil and across diverse canopy environments. The model performed well for independent Brazilian sunlit and shade canopy leaves (R2 = 0.75–0.78), suggesting that canopy leaves (and their associated spectra) follow constrained developmental trajectories even in contrasting forests. The model did not perform as well for mid-canopy and understory leaves (R2 = 0.27–0.29), because leaves in different environments have distinct traits and trait developmental trajectories. When we accounted for distinct environment–trait linkages – either by explicitly including traits and environments in the model, or, even better, by re-parameterizing the spectra-only model to implicitly capture distinct trait-trajectories in different environments – we achieved a more general model that well-predicted leaf age across forests and environments (R2 = 0.79). Fundamental rules, linked to leaf environments, constrain the development of leaf traits and allow for general prediction of leaf age from spectra across species, sites and canopy environments.

Historically, the persistence of mixed mating (reproduction via both self- and cross-fertilization) has presented a puzzle because classic theory predicts that mixed mating should be evolutionarily unstable. One mechanism that could contribute to the maintenance of mixed mating in cleistogamous species is the ability to invest in the appropriate type of reproduction (outcrossing vs. selfing) for a given pollination environment. We tested whether Collomia grandiflora plants responded to pollen limitation by plastically shifting relative investment in cleistogamous (obligately self-fertilizing) versus chasmogamous (potentially outcrossing) reproduction. We estimated reproductive effort (seed production) for chasmogamous and cleistogamous reproductive modes in hand-pollinated and unpollinated plants. We also investigated whether plastic responses to pollen limitation could be constrained by water availability or early nutrient fertilization. Pollen limitation significantly increased cleistogamous rep...

Hybridization plays an important role in the evolution of many taxonomic groups, but large-scale phylogenetic patterns of hybridization are poorly known. Here, we investigate patterns of hybridization in vascular plants. Our dataset included 282 families, 3212 genera and ≈37,000 species accounts from eight regional floras covering continental Europe, two island regions, and parts of North America and Australia. Interspecific hybrids were common in the wild, occurring in 40% of families and 16% of genera, with an overall frequency of 0.09 hybrids per nonhybrid species. Taxon species richness explained a large amount of variation in the number of hybrids, but taxon bias (study effort) did not. We accounted for species richness in calculating hybridization propensities, and found that both families and genera differed in hybridization propensity. Hybridization propensity of a given group was generally consistent across regions (with the exception of Hawaii), suggesting that hybridization behavior may be determined more by intrinsic properties of a group than by environmental conditions. We found evidence of a strong phylogenetic signal ( λ =0.93) in hybridization propensity as hybrids were not uniformly distributed across orders of vascular plants. Characterization of the hybridization behavior of groups should lead to increased predictive power regarding their traits and evolutionary trajectories, and will allow comparative tests of the traits driving differences in hybridization propensity.