Research into the optimisation of spectral quality to improve plant growth and development
Research into the optimisation of spectral quality to improve plant growth and development
Summary
Plants respond to spectral quality (i.e. colour of the incident light) by altering their morphology (eg. Leaf area and stem length). This creates canopies that permit the plant to intercept light at high efficiency and drive photosynthesis to produce adequate yield (dry weight of the harvestable product). A key goal of all plant production is to maximize yield per unit energy input (radiation use efficiency). Only around 50% of wavelengths within the solar radiation spectrum drive photosynthesis. Of these photosynthetically active regions (PAR) of the spectrum, red and blue are the most important, with red being the energetically most efficient since both drive photosynthesis with equal efficiency. In addition to driving photosynthesis other wavelengths, via photoreceptors that include phytochrome and cryptochrome, activate discrete developmental pathways to change leaf area, thickness and stem length.
LEDs now offer relatively cheap, cool, controllable sources of light that can selectively and quantitatively provide different wavelengths. This provides us an opportunity to investigate the manipulation (by natural means) of the quality and quantity of produce for markets to meet the demands of retailers. The combination of possibilities is large, for example Far Red (FR) light drives phytochrome activity which regulates leaf area and stem internode length while blue light can drive photosynthesis but is also required for efficient stomatal opening and regulation of leaf features such as thickness.
This provides an opportunity to raise the resource use efficiency (light, water and nutrients) above the theoretical maximum seen for plants growing in natural environments (Murchie et al 2009, New Phytologist 181(3) 532-552). For example we could provide a FR enriched environment that will stimulate leaf area expansion more rapidly. Once the canopy can absorb all of the light available we can increase fluence rate (photons per unit area) to stimulate photosynthesis and critical features such as leaf thickness (blue light) to enhance photosynthetic capacity at a key stage. One opportunity not yet realized is the possibility of sensing photosynthetic capacity of the canopy in real time (see below)
Our aim is therefore to undertake research into the optimised set of wavelengths needed to maximise yield with suitable trade-offs on energy input. We expect to be able to create an LED lighting system that can be programmed to generate an optimised wavelength recipe unique for each plant species.
Each variety or plant species responds in different ways and so we need to consider this variation when designing the hardware and software to do this. Ideally we need an interaction between plant and LED control system whereby the growing environment responds to, and anticipates, the plants requirement for radiation. Additionally it gives the ability to slow down or accelerate plant growth and development to meet the demands of retailers. This cannot be easily achieved in the natural environment which has a financial cost for the industry (e.g. http://www.bbc.co.uk/news/uk-scotland-tayside-central-17413495).
There are other opportunities waiting to be exploited, including the potential for sensing both growth stage and physiological status and adjusting spectral quality and fluence rate to optimize the radiation use efficiency of plants. We can use chlorophyll fluorescence imaging, an established technique and in use at Nottingham to measure photosynthetic capacity and provide just enough light to saturate photosynthesis but not so much that it is in excess for the crop. The technology to produce such intelligent plant growth systems, that only provides the appropriate quality and intensity required, already exists but requires a synthesis of engineering and biological knowledge to define how the technical and biological processes should interact, via software and hardware design. A recent workshop at Nottingham on ‘vertical farming’ showed clearly that light recipes were required to optimize yield and quality, in addition to design of the appropriate hardware and software combinations to achieve it.
In summary this Engineering PhD will focus on the necessary research into the optimisation of the optics, LED spectral control and associated electronic instrumentation in partnership with the analysis of plant growth by the plant Science based PhD.
