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Abstract

Plant growth chambers are commonly used to minimize environmental
variation but the light sources used vary considerably from natural light and
from each other. Incandescent globes are often used to add more far-red light,
with the aim of producing a more natural red to far-red ratio (R:FR), but also add
to thermal load. High-intensity discharge lamps are often used to produce
higher irradiances, more akin to natural light, but the thermal implications are
rarely considered because air temperature is controlled. This paper examines
the spectral properties and thermal implications of growth chamber light
sources and takes a whole-plant physiology approach, by examining growth
responses of a photoperiodic pea line (Pisum sativum L. cv. Torsdag) in the
same growth chamber type under different light sources – in essence using
plants to study the controlled environments rather than vice-versa. High R:FR
delayed flowering and inhibited internode extension in pea. However, the
addition of far-red-rich incandescent globes in the proportions provided in the
growth chambers (400–500 W) did little to reduce R:FR, did not induce earlier
flowering and actually further inhibited internode length. Leaflet size and yield
were significantly reduced. While air temperature was maintained at 20C in
all experiments, radiant temperature was significantly higher under high
irradiance and/or with incandescent added, and soil temperatures were
elevated. Growth responses under these lights were similar to the effect caused
by elevating the air temperature. An alternative method of controlling R:FR,
without thermal load implications, using light-emitting diodes is described.

Item Type:	Article
Authors/Creators:	Cummings, IG and Reid, JB and Koutoulis, A
Journal or Publication Title:	Physiologia Plantarum
ISSN:	0031-9317
DOI / ID Number:	https://doi.org/10.1111/j.1399-3054.2007.00958.x
Additional Information:	The definitive published version is available online at: http://onlinelibrary.wiley.com/ Sherpa = author cannot archive publisher's version/PDF Publisher = http://olabout.wiley.com/WileyCDA/Section/id-406074.html Wiley-Blackwell restricts posting of the final published version in order to ensure the integrity of the version of record and as a result of our considerable investment in the journal and the article.
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