Elucidating Root Functional Traits in Dryland Grasses: An Exploration of Modeling Methods, Root Growth Strategies and Decomposition

Plant functional traits, characteristics that describe plant roles beyond species identity, offer a powerful tool for assessing restoration success in ecological projects. These traits are categorized as being associated with aboveground structures (leaf, stem, seeds and flowers) or roots. While aboveground traits are frequently measured due to their accessibility, root traits are also important as they impact plant growth, stability, survival and the soil carbon cycles. Specifically, root functional traits reveal the plant’s capacity to absorb and transport water and nutrients, allocate carbon and contribute to longevity. In my dissertation I investigate root traits through my three chapters: 1) evaluating the accuracy of methods to measure root traits, 2) understanding factors influencing root trait development and 3) examining how these traits affect decomposition processes. First, I examined the precision and accuracy of root trait measurements using three dimensional (3D) SfM-derivated models. By modeling 32 fine roots of two plant species and ten copper wires of known size as controls, I measured total length, diameter, area and volume and compared these with manual and two-dimensional (2D) methods. The results showed that 3D models were more accurate than 2D models for length and diameter, while 2D models were better for area and volume. Next, I examined how species and soil type impacted early root trait development by growing three Sonoran grasses used for restoration in a glasshouse with three soil types varying in water-holding capacity. I found that species identity primarily impacted root diameter and tissue density, with some species growing rapidly to acquire resources while others grow slowly to increase longevity. Furthermore, roots in soils with low and medium water-holding capacity grew longer to access resources rapidly. Finally, I studied root decomposition through laboratory incubations, assessing if diameter and species affected mass remaining and CO2 efflux rates. Results showed both species and diameter significantly affect decomposition. Species with finer diameters, greater specific root length (i.e., ratio of length and mass) and lower carbon:nitrogen ratio decomposed faster than thicker roots, highlighting the importance of root traits in decomposition. My dissertation shows the potential of 3D modeling techniques and root trait analysis to enhance understanding of root ecology, improve ecological restoration practices, and elucidate the complex dynamics of root decomposition in soil carbon cycling.