Into the Field
How advances in instrumentation technology has allowed agronomic research to move out of the laboratory and into the f ield.
Roy Newman,
G.I.Biol., MSB, CBiol, Sales and Marketing Manager, ADC BioScientific Ltd. 1st Floor, Charles House, Furlong Way, Great Amwell, Hertfordshire, SG12 9TA Tel: +44 (0)1920 487901 • Email:
sales@adc.co.uk • Web:
www.adc.co.uk
Being able to feed the world’s increasing population is one of the fundamental priorities of the global community. Understanding crop production, plant biochemical activity and the plant’s
interaction with its changing environment, therefore, is a high priority with both national and multi-national administrations. Prior to the 1950s, the only way that many researchers were able to assess plant growth was to dig the plant up and weigh it on returning to the laboratory; a rather crude, unreliable and impractical technique.
Back in the 1970s
A significant step forward in plant science research was the development of the infrared gas analyser, often affectionately known by researchers as an “IRGA”. First produced in the UK in the 1940s, IRGAs measure energy absorbed by heteroatomic gases and vapours at very precise wavelengths within the infrared region. Two such heteroatomic gases of significant interest to plant
scientists are carbon dioxide (CO2) and water vapour (H2O). By measuring these gases, it is possible to monitor photosynthesis and transpiration, the two key biophysiological processes of a plant. During photosynthesis, carbon dioxide is taken up by the leaf and during transpiration, water vapour passes out of the leaf. The result is a change in the gas concentrations in the ambient air in close proximity to the leaf. If the rate of these changes is accurately measured then it can be used to provide an accurate indication of biochemical activity and growth efficiency of the plant. This type of measurement is often referred to as gas exchange. The first IRGA specifically designed for plant science research was the ADC225 laboratory analyser introduced in 1971. Researchers throughout the world were now able to accurately measure photosynthesis and transpiration without damaging the plant material. The availability of these highly accurate and reliable laboratory instruments greatly enhanced our understanding of the fundamentals of plant physiology and plant growth.
However these single gas instruments were mains powered and were sensitive to vibration. Bulky and weighing over 27kg, these early analysers were very much confined to the laboratory. To be able to apply our increased knowledge of plant physiology to improving our understanding of crop growth, research must be carried out in the field, in normal growth conditions. To do this required the development of a new generation of portable gas exchange equipment.
Going portable
The most critical stride in providing researchers with field portable instrumentation was the development of smaller, vibration insensitive optical technology for the infrared gas analysers. This involved utilising a single optical cell, which is primed with carbon dioxide free gas as a zero against which reference and analysis air can be sequentially measured. The “reference” being the air measured prior to the leaf, while the “analysis” is the air being measured after the leaf. The “differential” (reference-analysis) is the effect of the leaf on
Figure 1. " Early portability, the ADC225 and bearers".
the close proximity ambient air. This single optical cell technique provides very accurate measurements in a highly portable and power efficient format. The first portable IRGA of this type was the ADC LCA-2 Portable Photosynthesis system, introduced in 1984. To allow a single instrument to measure both carbon dioxide and water vapour exchange these instruments were fitted with humidity sensors to complement the carbon dioxide IRGA. The complete system consisted of several other components as well as a battery operated IRGA. A separate data logger was provided not only to store data, but also to automatically calculate photosynthesis rate, transpiration rate and other related parameters. A flow control unit maintained a continuous supply of ambient air to the system. A selection of specially designed leaf chambers allowed physiological measurements to be made on a variety of plant species.
In addition to gas exchange data, the LCA-2 also incorporated
sensors to measure air and leaf temperature and light concentration in the photosynthetically active radiation region (400nm – 700nm). Not only was equipment now field portable it was also providing researchers with more information to interpret. The result was that the physiology of a plant could now be directly equated to the ambient environmental conditions.
Global climatic change
Over the past 20 years the nature of agronomic research has evolved to reflect the growing international concern in global climatic change and how increasing atmospheric carbon dioxide concentrations could affect global crop production. Instrumentation has therefore been developed to allow scientists to directly address these issues. Fundamentally, equipment has become yet more field portable, more sophisticated and easier to use.
AET October / November 2011
www.envirotech-online.com
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