Effect of inner canopy irradiation on plant productivity in a sealed environment

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Authors

Stasiak, Michael Andrew

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University of Guelph

Abstract

It is clear that future human exploration of space will be based on advanced life support (ALS) systems which utilize plants and microorganisms. As the primary basis of life on Earth, plants are uniquely able to provide food, potable water and oxygen, while removing carbon dioxide. The high cost of space travel necessitates the development of plant growth systems with high volumetric efficiencies, and in dense plant canopies, shaded leaves represent considerable unused photosynthetic capacity which can be exploited to improve productivity in closed, space limited environments. Inner canopy lighting was used as a means to modify and enhance the distribution of photosynthetically active radiation (PAR) in a dense canopy of soybean ('Glycine max' L. Merr. cv. Secord). This resulted in an overall increase in canopy energy supply of 12 percent compared to overhead microwave powered lighting systems alone. Using specialized growth chambers, a series of short and long term experiments were performed. In short term studies, soybean canopies supplemented with inner canopy irradiation (ICI) had net carbon exchange rates (NCER) that were 30 percent greater that of control canopies which had received only overhead irradiation. Further productivity enhancement, as high as 270 percent over control, was obtained with the addition of higher carbon dioxide levels. In long-term studies, ICI enhanced plant growth and primary gas exchanges, and altered biomass partitioning within the canopy. Carbon uptake and oxygen and water production were increased by 27, 59 and 180 percent respectively. Relative growth rates (RGR) were unaffected by the addition of ICI, however water use efficiency (WUE) was decreased. Dry mass partitioning between the upper and lower canopy was significantly altered, with leaf area and mass, as well as pod number and mass higher in the lower canopy of ICI crops. Ethylene, a potent plant growth regulator with numerous biological effects, was higher in crops receiving supplemental ICI, with levels reaching 60 and 85 ppb in control and ICI crops respectively. When ethylene concentrations were normalized for estimated stand biomass accumulation obtained from daily NCER, no difference between ICI and control canopies was observed. There is clearly a benefit from the use of inner canopy irradiation, with increases in the production of biomass, oxygen, potable water, and carbon dioxide removal.

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Keywords

inner canopy irradiation, plant productivity, sealed environment, photosynthetically active radiation, soybean, Glycine max L. Merr. cv. Secord

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