Disentangling the effect of heritability and plasticity on Populus fremontii leaf reflectance across a temperature gradient

We quantified the relative effect of plasticity and heritability on Populus fremontii (Fremont cottonwood) leaf reflectance using clonal replicates propagated from 16 populations and grown across three common gardens spanning a mean annual temperature gradient of 10.7–22.3°C.

We used variance partitioning to decompose phenotypic variation expressed in the leaf spectra into genotypic versus environmental components and estimate broad-sense heritability and found that heritability was most strongly expressed in the red-edge (∼680-750nm) and SWIR (∼1400-3000nm).

Support vector machine models predicted P. fremontii source population and garden location at 78% and 93% accuracy, respectively, demonstrating that genotypic and environmental variation can be differentiated from the same leaf spectra. However, model accuracy declined by ∼49% when using leaf reflectance from any two common gardens to predict the source population at the third site. Prediction accuracies were lowest for the hottest site, which was linked to leaf stress responses in the visible and red-edge wavelengths (400-750nm).

We conclude that leaf spectra display heritability and plasticity across different parts of the spectrum. When mapping in regions/seasons with extreme climates, spectral plasticity linked to heat stress can decrease spectral heritability but may offer opportunities to understand phenological responses to extreme temperatures at large scales.