Seeking Spatial Patterns of Photosynthesis:
Innovative technology and the UC Botanical Garden Collections
Paul Seibert
How does photosynthesis change across the surface of a leaf? This was the driving question that led to my involvement with the UC Botanical Garden at Berkeley. My name is Paul Seibert, and I am an environmental engineering PhD student at UC Berkeley interested in characterizing photosynthesis across spatial scales.
In summer 2023, I toured the Garden in search of the right plant to study. The taro plant in the Crops of the World Garden stood out as the perfect plant, as the leaves can reach up to a meter in length.
Historically, it was difficult to quantify spatial patterns of photosynthesis, with most research using leaf-level tools to get a single value for an entire leaf. Hyperspectral imagery is an innovative technology that captures images of radiation beyond the visible spectrum. Highly specialized hyperspectral imagers can quantify solar-induced chlorophyll fluorescence (SIF), an indicator of photosynthesis occurring within the cells of a plant.
By using a SIF imager at the Garden, I hoped to see the spatial patterns of photosynthesis within a single leaf.
Foreground: SIF imager at the Crops of the World Garden. Background: The large-leaved taro plant of interest.
On August 30, 2023, I deployed the SIF imager with the help of Curator Holly Forbes and Horticulturist Catherine Callaway. The SIF images I captured (shown below) provide an opportunity to look at the taro leaves in detail, as the anatomy of the surface of the leaf is resolved well by the SIF imager. On the left side is an image (SIF) taken in the morning when photosynthesis for the taro plant peaked. In the middle is an image taken in the afternoon when the plant had begun to slow down photosynthesis in response to the highest temperatures of the day. The plots on the right show the pattern of SIF across a cross section of the largest taro leaf, where the X-axis is the length along the leaf and the Y-axis is SIF.
Left: SIF images of the taro plant at two times in the day. Right: Line plots of SIF across a section of the largest leaf, shown in the left SIF images.
With these images we can see that photosynthesis is concentrated within the right side of the taro leaves in the morning and transitions to the left as the sun moves across the sky. Importantly, SIF is not homogeneous across the surface of the leaf! We see that the veins and midrib of the leaf have lower SIF values, with SIF being higher in the lamina where most of the chloroplasts and stomata are found.
This experiment is unique because photosynthesis was observed within a leaf without ever touching the plant, and I hope to publish the results to a scientific journal soon.
Paul Seibert on the Lost Coast Trail.