Professor Susanne von Caemmerer: the mathematical elegance of plants

by Natalia Bateman, January 2017

As a child, Professor Susanne von Caemmerer’s grandmother told her: “just follow your nose” and that is exactly what she did. It was her nose that took her from Germany to Australia and through an unexpected and thrilling career in plant science.

Nineteen year old von Caemmerer arrived in Canberra from Europe to study a mathematics arts degree at The Australian National University. Initially, she was going to stay just for a year, but then she was trapped in this far away land by a fascination for plant physiology.

Now, Susanne von Caemmerer is a worldwide recognised expert for using mathematics to represent the process by which plants convert sunlight, gases and water into sugars and oxygen: photosynthesis.

“I am interested in the way carbon dioxide (CO₂) moves inside plants and to follow this, I put numbers to the different variables that affect this path. In other words, I design mathematical models to quantify CO₂ uptake in plants, which is the substrate for photosynthesis to happen.”

 

 

 

Connecting maths, plants and musical notes

von Caemmerer remembers that as a child she always wanted to do mathematics, so as an undergraduate at ANU, she focused on pure maths and philosophy. “My uncle, Professor Bernhard Neumann, who lived in Australia, was also a mathematician, and he was very supportive at the beginning of my career, and from there I was not going back to Europe.”

“I grew up assuming that I could study and work in anything I wanted to. I had lots of relatives who were professionals.  My aunt, Hanna Neumann, for whom a building at ANU is named, was a professor in mathematics. My father was a university professor in international law and my mother’s sister set up the first female law firm in my home town in Germany.”

“It is often what you are exposed to that defines your decisions in life. When I was young, we weren’t pushed towards engineering or something like that, which I could have enjoyed as a career.  Later on, when I took a short course in electronics I thought I could have been good at designing circuits, I liked it a lot as it was very logical. ”

While she doesn’t connect electric circuits, her work is still all about connections, flows and logic. The elegant equations that she has designed to represent photosynthesis have been extensively tested and utilised all around the world. Those models are still used today in a range of scales from crop canopies to leaves, explaining biochemical processes and atmospheric gas exchanges.

Music has been another constant in von Caemmerer’s life. “I have been taking flute classes for several years now. I used to play the violin but I gave it up when I had kids as it was very tricky to play with them around. I have also sung in the choirs of the Canberra opera; my husband and I sang in Aida, and learnt all the Italian by heart. It was lots of fun, we even had an elephant and a camel on stage!”

 

When a model is born

Soon after finishing her undergraduate degree, von Caemmerer looked around for options to stay in Australia and took a job as a technical officer. “I began working on stomata – the pores that plants cells have to interchange gases and water with the atmosphere – and after a while I was offered a PhD scholarship, so I took the challenge, she says.”

At that time, Graham Farquhar and Ian Cowan were looking at optimisation of stomata conductance, but to achieve that they needed an underlying model of photosynthesis, the fundamental biological process by which plants capture sunlight and convert this energy into sugars. This became von Caemmerer’s PhD project.

The combination of mathematical and plant physiology minds working together resulted in a successful model for plants like wheat and rice, which use the C₃ photosynthesis pathway. Farquhar, Berry and von Caemmerer created what is now considered the most widely used biochemical model in plant biology.

She recalls that at the time they started the project, there was already a large body of literature on photosynthesis models, which had their pluses and minuses. “Graham suggested a slightly different formulation; I think the main reason why our model turned out to be very successful was that we set up the right structure and parameters, based on our knowledge of plant physiology and there was a special emphasis on experimental verification.”

“When I first started, I tried to look for the experimental verification inside plant physiology literature, but I found that experimental biologists did not always measure things the way you want, so I began to measure them myself.”

After finishing her PhD, Susanne decided to focus on plants that use the C₄ photosynthesis pathway and produced a photosynthesis model for plants such as maize and sorghum.

The models she has helped to construct are very specifically designed to explain how leaves exchange gases, take and lose water from the atmosphere, and how CO₂ intake changes with variations in temperature and other environmental parameters. They are needed in ecology, climate studies, physiology and biochemistry.

“The models have been incredibly useful. They permit people around the world to measure photosynthesis and use the models to compare how different plants function under different environments. The applications extend from the biochemistry of individual cells to a global atmospheric scale, which is very nice to see.”