Vergara - 1976 - Physiological and morphological adaptability of ri

PHYTUPRONS IN aciucruutiaia RESEARCH 23
should not, however, blind us to the many differences in energy-balance rc—
Iations between plants under most artificially controlled conditions and those
in the field. These are discussed for wheat by King and Evans (l96?), and only
one example need be given. Taking field and phy-"totron crops with the same rate
of photosynthesis. it ivas found that they could also display similar rates of
evapotranspiration although the radiation load on the field crop was about four
times that in the cabinet. In the field. evapotranspiration accounted for only
one-third of the incident radiation and one-half of the net radiation. In the
phytotron. the energy required for evapotranspiratioii exceeded the radiant
energy absorbed by the crop, and was made up for by the adveetion of air warmer
than the leaves.
These and many other differences between plants in the field and in the phytotron
urge caution in extrapolation from the responses of single plants in controlled
environments to the responses of crops.
PROBLEMS OF EXTRAPOLATION
The major complications in relating phyrtotron and field results have been
discussed previously (Evans, 1963), and in the face of these one may wonder
what hope there is of agreement between the two kinds of experiments. The fact
is, many examples have now accumulated indicating that meaningful extrapolation
from phyttotron to field can be made.
Probably the easiest responses to extrapolate are those to day length and
vemalization, for which the artificialities under controlled conditions are of
least account. Certainly; the flowering behavior of many plants in the field can
now be understood in terms of their response, in phyitotrons.
As for light intensity’. while there are problems in relating natural radiation
to artificial illumination, results like those in Fig, 5 indicate that significant
agreement can be obtained for short-term measurements, and even over periods
of several days. as in Fig. l. Difference. in spectral composition of natural
and artificial light may be ttery’ important in come cases. however; for example,
the extent of branching and of tillering is extremely sensitive to the balance of
red and far-red radiation. and great care must be exercised where branching is
an important component of the response under study.
In spite of the complexities of responses to temperature, excellent agreement
can be found between the responses of plants in the field and in the phytotrtwn.
A good example is that provided by Warren Wilson (1972) for the effect of leniperature
on the relatibe growth rate of sunflower plants in the Canberra phytotron
and in arctic. alpine, and arid localities in the field. Likewise, Hesketh and
Loe (1968) have shtiwn that the effects of controlled temperatures on the fibre
characteristics of cotton agree ivell Wllh those deduced from field experiments.
In his extensive work on tobacco in the Raleigh pl'l_\-'l.tJl.l'L5Il. Raper aimed to
“fascimilate” nonnal field patterns of development and leaf characteristics under
controlled conditions. The objective required a combination of sequences in