The 4-dimensional plant: enhanced mechanical canopy excitation for improved crop performance

Lead Research Organisation: University of Manchester
Department Name: Mathematics

Abstract

There is an urgent need to improve crop yield (tonnes per per hectare) in order to meet the needs of a growing global population and declining fertile agricultural land base. One of the current important targets for crop improvement is photosynthesis, a neglected trait in previous plant breeding efforts.

Photosynthesis requires the uptake of carbon dioxide by leaves and its 'conversion' into carbohydrates using water and absorbed solar energy. However high rates of photosynthesis, on which yield depends, are sensitive to environmental changes such as light intensity, temperature and other factors. Crop productivity is the sum total of photosynthesis in leaves in a canopy, many of which shade each other and have different ages. We can calculate the potential productivity of whole canopies based on leaf photosynthetic attributes and other physical and physiological factors. When we do this the theoretical productivity tends to be much higher than the measured productivity which is partly due to the way leaves respond when re-constructed into a large three dimensional canopy. In this state, plants exist as a community which has emergent properties that we cannot necessarily predict from plants grown individually. If we can eliminate the gap between the theoretical and measured productivity we can achieve a step change in productivity.

Photosynthetic rate is sensitive to light intensity. The difference in light intensities that exist within the canopy is significant and is affected by the architecture of the canopy i.e. the angle, shape and size of leaves and their position within 3 dimensional space. This means that the light intensity has great variability in space and time within canopies. Photosynthesis is not perfectly adapted to instantaneously match the fluctuations in light intensity - its lag results in substantial reductions in productivity and even water use efficiency.

This proposal tackles a much ignored factor. Plants 'move' in light to moderate wind and this occurs on a daily basis, sometimes continually during growth which shifts the light patterns within the canopy. In recent work we found that movement has a strong effect on the rate at which light levels change in the canopy with strong implications for canopy photosynthesis. Such movement of the canopy plays a major part in how fast or slow light flecks are generated, and where in the canopy they appear. It seems that movement may enable the production of more rapid 'lightflecks', enhancing photosynthesis at the canopy level. We don't consider high speeds that result in damage, but we do incorporate lodging in our assessments of canopy viability.

In a recent paper (Burgess et al (2016) Frontiers in Plant Science 7, 1392) showed that canopy movement has the means to alter photosynthetic responses at the canopy level. We also developed the techniques to generate high resolution 3D images of field grown wheat and rice canopies and for 'tracking' moving canopies. In this proposal we will bring these techniques together to produce models of canopies of rice and wheat and make these models move realistically in response to physical factors. At the same time we will use wheat and rice populations and panels with varied physical characteristics and responsiveness to wind and create data driven tracking movies of these canopies , making the 3D reconstruction move realistically. We will create methods for predicting light distribution in these canopies combining ray tracing techniques with field measurements of light distribution. We predict that the most productive property is for leaves to be highly responsive to wind at the top of the canopy but retaining a strong stiff stem.
At the same time we will measure photosynthesis and biomass production in wheat lines which are amenable to genetic analysis so that we can discover the hereditary basis for the movement. Therefore the results will be used in plant breeding.

Technical Summary

Crop canopy architecture is hard to capture and quantify in the field in high resolution despite it being fundamental in determining both radiation use efficiency and final yield. One of the most important reasons is occlusion within dense canopies. At the University of Nottingham we developed, released and published accessible methods for full automated high resolution 3D canopy reconstruction using a RGB stereo approach, removing entire plants from the canopy and rapidly scanning. This was used to study key canopy light-driven processes.

The general architectural ideotype for enhanced photosynthetic performance in crops is relatively well understood, largely associated with upright leaves, but there is an understanding that dynamic photosynthetic responses are suboptimal.
Here we analyse an overlooked (but ubiquitous) event in nature - the movement of canopies in light to moderate wind. Our recent work (Burgess et al 2016, Frontiers in Plant Science, doi:10.3389/FPLS.2016.01392) used high resolution 3D reconstruction to show that gentle, non-tropic, non-fatal movement in canopies has a substantial impact on canopy photosynthesis (up to 17 %) and hence crop yield via alterations in canopy light dynamics.

In this proposal we will use new image tracking technology and high resolution 3D reconstruction (developed at Nottingham) to produce the world's first ideotype for optimised movement for enhanced photosynthesis in wheat and rice canopies. We will use tracking of plant motion to develop data-driven dynamic models of mechanically excited plants and altered canopy light distribution. In parallel we develop a mechanical model informed by plant physical and biomechanical properties. We will apply these new technologies to wheat populations growing in the field to uncover new mechanical traits that will be investigated by genome wide association studies (GWAS) and sequencing within the lifetime of the project.

Planned Impact

Please see the Impact Summary in the Nottingham application form

Publications

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Description This is a sub-project associated with grant BB/R004633/1. Theoretical studies have addressed the role of leaf motion on the impact of light on plants, specifically considering how the mechanical properties of leaves affect the manner in which they move when forced by wind. The dynamical features of this motion may impact on the manner in which plants achieve photosynthesis. Research findings, which integrate mechanical models with statistical fitting procedures, are currently being prepared for publication.
Exploitation Route The results address motion of individual leaves under environmental forcing. There is significant potential to extend the approaches developed in the proposal by others to consider motions of full plants, to gain a deeper understanding of the impact of plant mechanical properties on light dynamics in crops.
Sectors Agriculture, Food and Drink