Plants engineered for the perfect compromise
Image credit: salk
Nature and engineering appear to be on the same wavelength according to scientists at the Salk Centre for Integrative Biology, who have used 3D laser scans to monitor growing plants. It has revealed that plant branching architectures resemble the cost/performance trade-offs that engineers make when designing networks such as underground systems
“The idea for this work really started with an engineering question,” said Saket Navlakha, assistant professor and senior author of the paper. “How do transportation networks like a subway system or an electric grid resolve the tension between two competing objectives, such as cost and performance? And do plants resolve similar competing objectives in the same way?”
The findings could result in breeding plants that are better suited to environments that are experiencing climate change, or increasing crop yields
Scientists compared nature’s strategy to designing an underground system. For maximum convenience every suburb would have a direct link to a city centre, but that would be prohibitively expensive. Fewer lines would reduce cost but decrease its usefulness, so compromises need to be reached. The parallel with a plant is in regarding the base of the plant as the city centre, leaves as suburbs and finding the optimal configuration of branches to connect the two.
Scientists grew plants of three common agricultural crops (sorghum, tomato and tobacco) and used 3D scanning to regularly monitor the plants’ growth over a period of 20 days with the goal of trying to find out how plants managed the balance of energy required for growth against the necessity of transporting water and nutrients from roots to leaves. Around 500 scans were taken in total.
“Scanning plants in three dimensions can be fairly time consuming,” said research assistant Adam Conn. “But it’s non-invasive, and once you’ve done it you can discover things from the data that you couldn’t learn by just looking at the plants.”
With these digital impressions, the team extracted coordinates corresponding to each plant’s base and leaves in 3D space. They used the coordinates to create and graph theoretical plant shapes that prioritise either efficient routes for nutrients (performance), minimal branch length (cost), and the various trade-offs between the two objectives – a Pareto analysis to establish optimal growth strategy. Placing real plant co-ordinates on this graph revealed nature had come up with almost perfect balance for their particular environment.
“Our hypothesis was that if total length and travel distance were important evolutionary criteria for plants, there would be evolutionary pressure to minimise the criteria together, and that’s actually what we found,” said Ullas Pedmale, who was a postdoctoral researcher on the project.
Interestingly, the plants clustered by species, but within each species, plants made different trade-offs based on their growth environment. In other words, all tomatoes were in generally the same region of the curve, but ones grown in high light found a different balance between cost and performance from those grown in low light.
“This means the way plants grow their architectures also optimises a very common network design trade-off. Based on the environment and the species, the plant is selecting different ways to make trade-offs for those particular environmental conditions,” said Navlakha. “By understanding these trade-offs we may be able to dynamically tune our crop varieties to a changing climate.”