Evaluation of Complex Phenotypes Using Digital Image Analysis: Leaf Area Traits in a Polymorphic forb Species With Highly Dissected Foliage — 60p — Sage Robinson, Maddy Reichert, April Dunn, Tara Ramsey, Justin Ramsey

Plant leaves have a critical role in carbon fixation and gas exchange, and vary widely in size, shape and anatomy. Leaf traits are strongly influenced by phylogeny yet often differ among related species and sometimes among populations of a single taxonomic species; such variation may reflect adaptation to contrasting climate features (temperature, sun vs. shade exposure, etc.). Functional leaf traits can be challenging to measure, especially for plants with needle-like, lobed or dissected foliage. Here we report on use of digital image analysis to quantify leaf area and shape in wild yarrow, a widespread species with finely dissected leaves. Our prior studies revealed differences in plant size and architecture among yarrow populations of the Black Hills and Great Plains:  short plants with small leaves are found in low elevation prairies and mountain summits, while tall plants with large leaves occur in shady forests and wet meadows. Beyond their variable footprint, however, it is unclear how the leaves differ in traits like surface area, blade thickness, dividedness, and transpiration.

As a pilot study, we compared leaves of two yarrow populations (low elevation shortgrass prairie, “Bentonite” vs. high elevation open deciduous forest, “Cement Low”) grown in a recent garden experiment. Mature leaves were collected, pressed flat on herbarium paper, and dried.  High resolution photographs were generated using a dSLR camera mounted in a lightbox that provided uniform illumination; a color reference and ruler were included with each specimen. Resulting .tiff files were imported to ImageJ software and converted to black/white; manual and automatic exposure thresholds were tested for several area and perimeter calculations, which produced similar values. On average, forest yarrows had ~5-fold greater leaf surface area and ~20 fold greater perimeters. These results highlight the utility of digital image analysis for measuring of complex phenotypes in plants and other organisms.

Black Hills State University
Justin and Tara Ramsey