Abstract
Longstanding ecological theory states that plants integrate their structure – the three-dimensional (3D) orientation, density, and vertical distribution of stems and leaves – with function to maximize carbon gain. However, most studies that examine plant performance focus on physiological traits, and slight structural ones, at the leaf level. Additionally, studies focusing on plant responses to environmental change also focus on physiological changes, and tend to ignore changes in canopy structure. My dissertation is focused on addressing this longstanding knowledge gap, and examines the relationships between canopy structure and function. Specifically, I focused on understanding the connection between the leaf angle distribution (LAD) – a critical and long-overlooked canopy trait – and foliar traits. I explored how the connection between LAD and foliar traits affects remotely-sensed canopy reflectance and solar-induced chlorophyll fluorescence (SIF), both of which are used to understand plant functioning. Finally, I studied how canopy structure, canopy reflectance, and SIF, all respond to a multi-year drought. I found that LAD is tightly coupled with leaf chlorophyll content (LCC) within and across species. Canopies with more vertical leaves have a lower LCC, while canopies that have a greater variability in leaf angle have a higher LCC. Remote sensing observations of canopy function, including SIF, are also positively related to variability in leaf angle, which is attributed to the relationship with LCC. Lastly, in response to a multi-year drought of mild intensity, I observed adjustments in LAD towards more vertical leaves, and changes in the vertical distribution of foliage. These changes caused SIF to decline in canopies exposed to drought. Together, these results are the first to definitively show that whole-canopy LAD is intrinsically connected to light acquisition and foliar pigments, which in turn, affects remote sensing observations of canopy SIF and reflectance.
