Foliar spectra accurately distinguish most temperate tree species and show strong phylogenetic signal

PREMISE

Spectroscopy is a powerful remote sensing tool for monitoring plant biodiversity over broad geographic areas. Increasing evidence suggests that foliar spectral reflectance can be used to identify trees at the species level. However, most studies have focused on only a limited number of species at a time, and few studies have explored the underlying phylogenetic structure of leaf spectra. Accurate species identifications are important for reliable estimations of biodiversity from spectral data.

METHODS

Using over 3500 leaf-level spectral measurements, we evaluated whether foliar reflectance spectra (400-2400 nm) can accurately differentiate most tree species from a regional species pool in eastern North America. We explored relationships between spectral, phylogenetic, and leaf functional trait variation as well as their influence on species classification using a hurdle regression model.

RESULTS

Spectral reflectance accurately differentiated tree species (κ = 0.736, ±0.005). Foliar spectra showed strong phylogenetic signal, and classification errors from foliar spectra, although present at higher taxonomic levels, were found predominantly between closely related species, often of the same genus. In addition, we find functional and phylogenetic distance broadly control the occurrence and frequency of spectral classification mistakes among species.

CONCLUSIONS

Our results further support the link between leaf spectral diversity, taxonomic hierarchy, and phylogenetic and functional diversity, and highlight the potential of spectroscopy to remotely sense plant biodiversity and vegetation response to global change.

Finding common ground: Toward comparable indicators of adaptive capacity of tree species to a changing climate

Adaptive capacity, one of the three determinants of vulnerability to climate change, is defined as the capacity of species to persist in their current location by coping with novel environmental conditions through acclimation and/or evolution. Although studies have identified indicators of adaptive capacity, few have assessed this capacity in a quantitative way that is comparable across tree species. Yet, such multispecies assessments are needed by forest management and conservation programs to refine vulnerability assessments and to guide the choice of adaptation measures. In this paper, we propose a framework to quantitatively evaluate five key components of tree adaptive capacity to climate change: individual adaptation through phenotypic plasticity, population phenotypic diversity as influenced by genetic diversity, genetic exchange within populations, genetic exchange between populations, and genetic exchange between species. For each component, we define the main mechanisms that underlie adaptive capacity and present associated metrics that can be used as indices. To illustrate the use of this framework, we evaluate the relative adaptive capacity of 26 northeastern North American tree species using values reported in the literature. Our results show adaptive capacity to be highly variable among species and between components of adaptive capacity, such that no one species ranks consistently across all components. On average, the conifer Picea glauca and the broadleaves Acer rubrum and A. saccharinum show the greatest adaptive capacity among the 26 species we documented, whereas the conifers Picea rubens and Thuja occidentalis, and the broadleaf Ostrya virginiana possess the lowest. We discuss limitations that arise when comparing adaptive capacity among species, including poor data availability and comparability issues in metrics derived from different methods or studies. The breadth of data required for such an assessment exemplifies the multidisciplinary nature of adaptive capacity and the necessity of continued cross-collaboration to better anticipate the impacts of a changing climate.

Gas Exchange, Water Use Efficiency, and Biomass Partitioning among Geographic Sources of Acer saccharum Subsp. saccharum and Subsp. nigrum Seedlings in Response to Water Stress

Responses to water stress were measured for sugar maple (Acer saccharum subsp. saccharum Marshall) sources from Oklahoma (Caddo sugar maple), Missouri, Tennessee, Ontario, and a black maple (Acer saccharum subsp. nigrum F. Michx.) source from Iowa. Seedling sources were selected for differences in temperature and precipitation of their geographic origins. Seedlings were preconditioned through moist (watered daily) or dry (watered every 4-7 days) cycles and then exposed to prolonged water stress. As water stress increased, dry preconditioned 17-week-old sugar maple seedlings from Oklahoma, Missouri, and Tennessee, sources from warmer, and/or drier climates with greater restrained photosynthesis, stomatal conductance, and water use efficiency than those from cooler and moister climates. Under imposed water stress, the Ontario and Iowa sourced seedlings increased their root to shoot ratios and decreased their specific leaf area, mechanisms for drought avoidance. However, no corresponding changes in these values occurred for Oklahoma, Missouri, and Tennessee sources and for the variable of leaf wilting across all sources. Results from this study suggest greater tolerance of water stress in the Oklahoma, Missouri, and Tennessee ecotypes from the western and southern range of sugar maple resulted primarily with water use efficiency (WUE) rather than other water stress coping mechanisms. Findings from this study provide evidence to support selection of sugar maples sources for forestation.

Development and characterization of species-diagnostic ISSR and SCAR DNA markers for differentiating red maple (Acer rubrum) and silver maple (A. saccharinum)

Red maple (Acer rubrum) and silver maple (A. saccharinum) are sister species that readily hybridize in nature. No genetic or barcoding markers have been tested in these species. The main objective of the present study is to develop and characterize molecular markers for distinguishing A. rubrum and A. saccharinum and to validate the hybridity of A. freemanii derived from their crossings using the ISSR marker system. Thirteen A. rubrum and seven A. saccharinum populations were used. Four ISSR primers including ISSR 5, ISSR 8, ISSR 10, and ISSR UBC 825 were selected to amplify genomic DNA from the two species and their hybrids. Each primer generated at least one species-diagnostic ISSR marker for a total of six. Analysis of A. freemanii collected from North Dakota (USA) confirmed that the genotypes screened were true hybrids between A. rubrum and A. saccharinum. These markers were cloned and sequenced. Successful sequences were converted to SCAR markers using specifically designed primers. Overall, the developed diagnostic and specific ISSR and SCAR markers are useful in the certification of these two maple species and their hybrids. They can be used in tracking the introgression of A. rubrum and A. saccharinum DNA in other hybrid trees or populations.

Morphological and molecular data to determine the origin and taxonomic status of Prosopis chilensis var. riojana (Fabaceae, Mimosoideae)

This study analyzes the morphological and genetic characteristics of three sympatric populations of Prosopis from Argentina. Although morphological and geographical data suggest that Prosopis chilensis var. riojana is an interspecific hybrid of Prosopis chilensis var. chilensis and Prosopis flexuosa var. flexuosa, no correlation was found between morphological traits and genetic distances generated by random amplified polymorphic DNA - polymerase chain reaction (RAPD-PCR). Genetic similarity is greater among P. chilensis var. chilensis and P. flexuosa var. flexuosa than between either of these two taxa with P. chilensis var. riojana. Also, P. chilensis var. riojana has unique genetic markers that are absent from its putative parents. Additionally, dendrograms generated by unweighted pair group method with arithmetic means (UPGMA) and Neighbor-Joining clustering criteria group P. chilensis var. chilensis and P. flexuosa var. flexuosa apart from P. chilensis var. riojana. Possibilities for the lack of congruence between morphology and RAPD markers are discussed. The results obtained are insufficient to conclusively establish the origin of P. chilensis var. riojana; however, the morphological and genetic traits observed suggest this taxon is well differentiated from P. chilensis var. chilensis and P. flexuosa var. flexuosa.Key words: genetic distances, hybridization, morphology, Prosopis, RAPD, rare taxon.