Removing the inefficiencies of 3-dimensional canopy photosynthesis by the alteration of leaf light-response dynamics and plant architecture

Photosynthesis in plants is the uptake of CO2 by leaves and its assimilation into carbohydrates within specialized organs (chloroplasts), a process that requires the absorption of light by chlorophyll. However the rate of photosynthesis over a given period of time varies according to environmental changes such as light intensity, leaf age, temperature and other factors.
This has consequences for productivity of crops which depend on high rates of photosynthesis for high yields. Productivity is the sum total of a large number of leaves in a canopy, many of which shade (or partly shading each other) and are usually 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. The reasons are unclear but a large part is thought to be due to the way leaves respond when re-constructed into a large 3D 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 very sensitive to light intensity. The difference in light intensities that exist within the canopy (an exponential decline from top to bottom) is significant and is affected by the precise architecture of the canopy i.e. the amount of leaf area per unit ground area, 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 e.g with frequent and transient appearance of 'light-flecks'. The movement of the canopy plays a major part in how fast or slow light flecks are generated, and where in the canopy they appear. Photosynthesis should be optimized to these rapidly changing conditions, but there are indications that it is not. The environment can cause a 'down-regulation' of photosynthesis in the field and this can be measured by comparing actual leaf photosynthesis against the maximum. It is not clear how this down-regulation interacts with canopy architecture and the responses of leaves.
One problem is that we do not have detailed images of crop canopies in 3 dimensions and we do not have sophisticated models that allow us to map the complex changes in light intensity to photosynthesis. Crop canopies perform a number of important agronomic roles, some photosynthetic , others not. Therefore we need to understand the problem 'in reverse' - i.e. to take good 3D images of crop canopies, both still and moving, calculate the typical changes in light intensity that occur in that canopy and then change photosynthetic dynamics so that it matches those changes.
We will grow canopies of productive crop plants, rice and wheat in a special glasshouse that will enable us to image crop canopies, when still, and produce 3D high resolution images using laser scanning and camera techniques. Novel techniques will be tested for detecting plant movement in wind and we will then distort these images to examine the effect of wind induced leaf 'flutter' and stem bending on light distribution. We will use these images in a mathematical ray-tracing program to finely map the changes in light that occur within the canopy. These changes will be used to predict which processes dominate the canopy-productivity process.
This is essentially a modelling and imaging project of plant canopies: we will begin the following phase by ordering rice mutants altered in key reactions identified from these models and grow these to test whole canopy productivity. If successful we can achieve a step change in productivity by eliminating any wasteful processes that occur within the canopy.

Photosynthetic rate within plant canopies frequently fluctuates. However much of our understanding arises from steady state photosynthesis measurements. Solar movement and wind result in the formation of complex 3-dimensional plant canopy structures which induces large fluctuations in photosynthetic rate. In order to understand and improve the contribution of dynamic photosynthesis to plant productivity we must understand the relationship between canopy architecture, spatio-temporal kinetics in irradiance and biochemical regulation.
This project will utilize new glasshouses in which crop canopies of key species (rice and wheat) will be grown in which plants have full root and canopy interaction. The destructive and non - destructive imaging of these canopies in high resolution will be made using stereo cameras and laser scanners. In this environment plants will be kept motionless. Plant movement will be induced by fans and the frequency of movement assessed by novel techniques using newly available sensors.
Existing software packages will recreate full high resolution images of contrasting canopy structure that can be used in ray tracing analyses to generate complex spatio-temporal maps of light fluctuations according to solar position. Canopy movement data will be used to distort these images to investigate the impact of movement on the distribution of light..
Dynamic photosynthesis models will be used to predict the dominant processes that are likely to prevent photosynthesis from accurately tracking the changes in light. A model will be developed based on existing models of dynamic photosynthesis and parameterized using physiological data collected during this project.
The processes identified as likely to dominate for a given canopy structure will be tested using rice mutants ordered from existing collections. Canopies grown will be measured for key photosynthetic parameters and biomass production rate.

Who will benefit from this research?

In addition to the academic beneficiaries described elsewhere :
1. Crop improvement. Those attempting to genetically improve crop plants for higher yields and resource use efficiency (such as commercial and government plant breeders) will be provided with a source of traits and gene combinations.
2. Food production. Rising global population and pressures upon land use caused by urbanization and erosion mean that higher productivity is essential to meet food security needs by 2050. If the gap between theoretical and actual production rates are closed then beneficiaries are universal because this would represent a sustainable improvement via inherent improvement in resource use efficiency. Most notable are those in poor areas and marginal environments.
3. Energy production. Sustainable (not competing with food) production of energy crops and secondary fuels which use the by products of food crops would increase production.
4. Agricultural businesses would benefit from increased productivity and resource use efficiency and may invest more in the area of modeling of basic plant processes.
5. The tools (software, hardware and techniques) produced by this project would be made available to the public and scientists and may provide those in technological research and development with the knowledge to innovate further.
6. These data may be used for prediction of vegetative productivity. They may be incorporated into predictive models of crop yield that are utilized by policy advice bodies such as the IPCC. The PI collaborates with individuals, applied consortia and institutes such as the Wheat Yield Consortium and the International Rice Research Institute which have programmes that could directly use the results in predictive models of crop yield.
7. Public sector may benefit if the tools prove useful for imaging of processes relevant to the quality of life and society in general, e.g. in the imaging of plant canopies to aid in the realistic recreation of landscapes for the construction amenity areas and recreation.
8. An improvement in crop yield or crop resource use efficiency results in the potential to reduce impact on the natural environment by reducing land cultivated and inputs of water and nitrogen (via the inherent improvement in photosynthesis).

How will they benefit ?

If successful it will result in a step change in resource use efficiency and yield for many scenarios. Almost a billion people in the world are defined by the FAO as 'hungry'. A step change in yield would instantly alleviate this whilst for poor farmers it would help them to generate extra cash to lift them out of poverty and improve health and wellbeing. For the rest of the world it may result in a lowering of food prices which would benefit economies and prevent surplus depletion allowing security. It would also reduce risky speculation on food prices.
The time taken would be restricted by the ability to introduce genes into crop plants by breeding, introgression and transformation. Possibly prototype plants could be available 3-5 years after the lifetime of this grant (allowing time to breed for stable mutant lines).
For plant breeders the improvement in productivity would allow a focus on areas that may be critical to specific crops such as diseases and pests.

Activities that will enhance impact of this project

A website dedicated to the project, updated regularly will be hosted and created by Nottingham.
A techniques workshop will take place in Nottingham in 2011 as part of the EU Harvest network of photosynthesis researchers, co-organized by the PI. The project will be exposed to about 60 academics, post-doctoral workers and Phd students by holding a special session on canopy imaging and measurement. The techniques used and the project objectives will be presented.