The most expensive option for investments and running
costs is to grow plants in climate-controlled growth chambers.
They offer the most sophisticated possibilities for environmental
control and thereby allow (at least theoretically) for an orthogonal
dissection of environmental factors and good replicability of
experiments. Consequently, they are widely used by plant
biologists. However, their application has some drawbacks as
well. First, conditions in growth chambers are generally the
furthest away from those in the field, not only because
environmental values are often programmed within a relatively
small diurnal range, but also with regard to the absolute values
of, for example, light and temperature, at which they operate
(Garnier and Freijsen 1994). Second, although growth chambers
enable a strong temporal control over conditions, spatial
variability is often larger than anticipated and higher than
those measured in experimental gardens. For example, light
intensity may vary from place to place in the growth chamber
(Granier et al. 2006) and can be especially lower close to the
walls (Fig. 2a). Another often ignored gradient relates to
the vertical light profile: the closer the plants grow to the
lamps, the higher the light intensity. For rosette species like
Arabidopsis this is not a point of concern, but erect species
may experience substantial gradients, especially when they
grow over 40 cm tall (Fig. 2b). As growing taller is inevitably
connected to development, plants that are older or in later stages
of development often experience significantly higher light
regimes than younger ones; despite this, differences in plant
characteristics are then often associated with development and
not with changed light conditions. Adjusting lamp height to a
fixed distance relative to the top of the shoot may partly mitigate
the fact that plants that grow faster because of, for example, a
higher nutrient supply, will by consequence also grow faster
because they experience higher light levels and higher
temperatures. These examples illustrate that even in controlled
environments it is not easy to separate different environmental/
developmental responses from each other